GENWiki

Premier IT Outsourcing and Support Services within the UK

User Tools

Site Tools


rfc:rfc929

Network Working Group Joel Lilienkamp (SDC) Request for Comments: 929 Richard Mandell (SDC)

                                       Michael Padlipsky (Mitre Corp.)
                                                         December 1984
                  PROPOSED HOST-FRONT END PROTOCOL

Status Of This Memo

 The reader should be aware of several things in regard to what the
 present document is up to.  First and foremost, IT IS A PROPOSAL FOR
 A STANDARD, NOT A STANDARD ITSELF.  Next, it assumes that the
 separate document, RFC 928, which is an introduction to the present
 document, has been read before it is. Next, it should be understood
 that "final cut" over this version of the document has been exercised
 by the author of RFC 928, not by the primary author of the present
 document, so any readers bothered by style considerations should feel
 free to blame the former, who's used to it, rather than the latter,
 who may well be guiltless.  (Editing at a distance finally become too
 hard to manage, so if I'm typing it myself I'm going to fiddle with
 it myself too, including, but not limited to, sticking my own section
 on the Conceptual Model in before Joel's words start, rather than
 leaving it in the Introduction.  MAP)
 Finally, it should be noted that this is not a finished document.
 That is, the intent is eventually to supply appendices for all of the
 protocol offloadings, describing their uses of protocol idiosyncratic
 parameters and even their interpretations of the standard per-command
 parameters, but in order to get what we've got into circulation we
 haven't waited until all such appendices have been written up.  (We
 do have notes on how to handle FTP, e.g., and UDP will be pretty
 straightforward, but getting them ready would have delayed things
 into still another calendar year, which would have been very annoying
 ... not to say embarrassing.) For that matter, it's not even a
 finished document with respect to what is here. Not only is it our
 stated intention to revise the protocol based upon implementation
 experience gained from volunteer test implementations, but it's also
 the case that it hasn't proven feasible to iron out all known
 wrinkles in what is being presented.  For example, the response codes
 almost certainly need clarification and expansion, and at least one
 of us doesn't think mandatory initial parameters need control flags.
 However, to try too hard for polish would be to stay in subcommittee
 for the better part of forever, so what you see is what we've got,
 but certainly isn't meant to be what you or we are stuck with.
 This RFC suggests a proposed protocol for the ARPA-Internet
 community, and requests discussion and suggestions for improvements.
 Distribution of this memo is unlimited.

Lilienkamp & Mandell & Padlipsky [Page 1]

RFC 929 December 1984 Proposed Host-Front End Protocol

Conceptual Model

 There are two fundamental motivations for doing outboard processing.
 One is to conserve the Hosts' resources (CPU cycles and memory) in a
 resource sharing intercomputer network, by offloading as much of the
 required networking software from the Hosts to Outboard Processing
 Environments (or "Network Front-Ends") as possible. The other is to
 facilitate procurement of implementations of the various
 intercomputer networking protocols for the several types of Host in
 play in a typical heterogeneous intercomputer network, by employing
 common implementations in the OPE.  A third motivation, of basing a
 network security approach on trusted mandatory OPEs, will not be
 dealt with here, but is at least worthy of mention.
 Neither motivation should be allowed to detract from the underlying,
 assumed desire to perform true intercomputer networking, however.
 Therefore, it is further assumed that OPEs will be attached to Hosts
 via a flexible attachment strategy, as described in [1]. That is, at
 the software level an explicit Host-Front End Protocol (H-FP) will be
 employed between Hosts and OPEs, rather than having OPEs emulate
 devices or device controllers already "known" to Host operating
 systems (in order to avoid introducing new code into the Host).
 For reasons discussed in the Introduction, an H-FP resolves into
 three layers.  The Link layer enables the exchange of bits between
 Host and OPE.  The Channel layer enables the bit streams to be
 demultiplexed and flow controlled  (both the Channel and Link layers
 may use preexisting per-Host mechanizations, it should be recalled).
 The Command (or "Service Access") layer is our primary concern at
 present. It serves as the distributed processing mechanism which
 allows processes on Hosts to manipulate protocol interpreters (PIs)
 in OPEs on their behalf; for convenience, it will be referred to as
 "the H-FP" here.  (It should be noted that the Link and Channel
 layers may be viewed as roughly equivalent to the inboard processing
 investment for a Host-comm subnet processor PI and device driver, so
 in practical terms the savings of resources achieved by outboard
 processing come from making the H-FP "smaller" than the inboard
 implementations of the protocols it allows to be offloaded.)
 The crucial property of the H-FP conceptually is that it stands as
 the interface between a (Host) process and a PI (which is actually
 outboard).  Usually, the model is that of a closed subroutine
 interface, although in some cases an interprocess communication
 mechanism model must be appealed to.  That is, the interactions
 between cooperating H-FP PIs in some sense mimic subroutine or IPC
 calls, from the perspective of Host processes calling upon their own
 H-FP PIs, which in turn are of course interfacing via just such

Lilienkamp & Mandell & Padlipsky [Page 2]

RFC 929 December 1984 Proposed Host-Front End Protocol

 mechanisms themselves. Another way of putting it is that "if the
 protocols were inboard," the processes invoking H-FP wouldn't know
 the difference.  H-FP, then, may be viewed as a roundabout way of
 letting Host processes "get at" various PIs.
 Naturally, the mechanization of the desired concept cannot be
 particularly literal.  After all, the Hosts and the OPEs are
 different processors, so we're not envisioning a passing through of
 parameters in an exact fashion.  However, in broad terms the model is
 just that of a somewhat funny interface between a process and a PI.
 (This should not be construed as ruling out the occurrence of events
 which prompt the OPE to initiate an exchange of commands with the
 Host, though; see the Introduction for more on the topic of
 "Symmetric Begins.")

Interaction Discipline

 The interaction between the Host and the OPE must be capable of
 providing a suitable interface between processes (or protocol
 interpreters) in the Host and the off-loaded protocol interpreters in
 the OPE.  This interaction must not, however, burden the Host more
 heavily than would have resulted from supporting the protocols
 inboard, lest the advantage of using an OPE be overridden.
 Channel Level Interaction
 As stated elsewhere, the Channel level protocol (implicitly in
 conjunction with the Link level) provides two major functions. These
 are demultiplexing the traffic from the Link level into distinct data
 streams, and providing flow control between the Host and the OPE on a
 per stream basis.  These hold even if the Host-OPE attachment is DMA.
 The data streams between the Host and the OPE are bidirectional. In
 this document, the basic unit of data transferred by the Channel
 level is referred to as a "chunk".  The primary motivation for this
 terminology is that the H-FP permits the Channel level to be one of
 several possible protocols, each with its own terminology.  For
 example, a chunk on an X.25 Channel would be a packet, while a chunk
 on the DTI H-FP channel would be a message.  While the Command level
 is, in a sense, "more efficient" when the chunk size is permitted to
 be large, the flexibility permitted in the choice of protocols at the
 Channel level precludes any assumptions about the chunk size.
 Each data stream is fully asynchronous.  A Channel protocol user can
 send data at any time, once the channel has been properly opened.
 (The Command level's logic may render some actions meaningless,
 however.) The data transfer service provided by the Channel protocol

Lilienkamp & Mandell & Padlipsky [Page 3]

RFC 929 December 1984 Proposed Host-Front End Protocol

 is reliable;  this entails delivery in the correct order, without
 duplication, and checked for bit errors.  All retransmission, error
 checking, and duplicate detection is provided by this protocol in a
 way that is transparent to the user.  (If the attachment is DMA,
 stream identification and chunk length must still be provided for.)
 The flow control at the Channel level is provided to prevent the OPE
 and the Host from overloading each other's resources by excessive
 transmissions.  In general, this flow control should not directly
 affect the outboard protocol interpreters' operation.  On the other
 had, this flow control has the same effect as explicit interface
 events that provide flow control between the user and the protocol
 interpreter (e.g., the Allocate event of the interface specification
 for TCP found in MIL-STD 1778).  Hence, such events do not need to be
 communicated explicitly at the Command level.  (If the attachment is
 DMA, flow control must still be provided for.)
 Should Hosts require an OPE to be attached via a Link Level that
 furnishes physical demultiplexing (e.g., a group of RS232 ports), any
 attempt to avoid furnishing reliability and explicit flow control, is
 done at their peril;  we have not chosen to assist such an
 enterprise, but neither have we precluded it.  (It would certainly
 violate the spirit of the thing, however.)
 Command Level Interaction
 The approach chosen for this H-FP is to base the interaction on a
 small set of commands, separately applicable to a given Channel Level
 channel. The commands are simple, but sufficiently flexible to permit
 the off-loading of the interpreters of the large number of protocols
 at various levels in the hierarchy.  This flexibility is made
 possible in part by the similar nature of the interfaces to most
 protocols, combined with the provision of "protocol idiosyncratic
 parameters". These parameters are defined for each offloaded protocol
 interpreter in the OPE.  The use of such parameters does not
 complicate the basic design of the OPE, since it must be customized
 for each off-loaded protocol anyway, and all that is required of the
 OPE for those parameters is to pass them to the off-loaded protocol
 interpreter.  Hence, an interface tailored to a particular protocol
 can be created in a straightforward and cost-effective way.
 The command dialog is more or less asynchronous.  Commands can be
 issued at any particular time (except when there is a pending
 command, which will be discussed below), and there is no need for
 dummy traffic on a channel when no commands are issued.
 Associated with each command is a response.  The purpose of this

Lilienkamp & Mandell & Padlipsky [Page 4]

RFC 929 December 1984 Proposed Host-Front End Protocol

 response is to indicate, at some level that depends in part on the
 particular protocol interpreter that is offloaded to the OPE, whether
 the command was successfully executed, and if unsuccessful, the
 reason.  Often, generating the response involves interaction with the
 protocol interpreter before a response can be generated.
 When a command is issued, the issuer must wait for a response before
 another command is issued.  The nature of the communication between
 the Host and the OPE is thus a lock step command/response dialog.
 There are two major exceptions to this principle, however. One
 exception is the abrupt form of the End command, which can be issued
 at any time to cancel any previously issued commands, and indicate
 that services are no longer desired.  The other exception is the
 Signal command.  Since a Signal is out-of-band and usually of high
 importance, forcing it to wait on a response would be undesirable.
 Hence, a Signal command can be issued while commands (other than
 Signal) are pending.  However, a Signal command should not be issued
 before a successful response to the Begin command has been received.
 Since it is possible for more than one command of different types to
 be pending at one time, a mechanism to distinguish responses is
 needed.  Since there are never two commands of the same type pending,
 including the command name in the response is sufficient to make this
 distinction.
 A special case command is the Transmit command.  Details of the
 Transmit command are provided in the next section. Essentially, the
 Transmit command is used to invoke the data transfer services of the
 off-loaded protocol (when issued by the Host) or to indicate the
 arrival of new data from the network (when issued by the OPE).  The
 nature of specific protocol interfaces for these events varies widely
 between protocols.  Some may block until the data is accepted by the
 remote counterpart (or "peer") protocol interpreter, while others may
 not.  Hence, there is a special parameter which indicates the nature
 of the Transmit command interface.  It can either require that the
 response should be generated immediately after determining the
 Transmit command is complete and formed properly, or can indicate
 that the response should not be generated until the appropriate
 interface event is given by the remote protocol interpreter.  The
 default action for all Transmit commands can be initialized using the
 Begin command and changed using the Condition command.  Also, the
 default action can be temporarily overridden by specifying a
 parameter with the Transmit command. The net result of this mechanism
 is to allow the Host to determine within reason just how lock-stepped
 transmissions are to be.  (It is assumed that the usual case will be
 to transfer the burden of buffering to the OPE by taking immediate
 responses, provided that doing so "makes sense" with the particular
 offloaded protocol in play.)

Lilienkamp & Mandell & Padlipsky [Page 5]

RFC 929 December 1984 Proposed Host-Front End Protocol

 Some protocols provide a block-oriented data transfer service rather
 than a stream-oriented one.  With such a service, the data associated
 with a transfer request is viewed as an integral unit.  For actual
 network transmission, the protocol may permit these units to be
 grouped or fragmented. However, the receiving end must deliver the
 data in the original, integral units. Protocols that conform to this
 model include some datagram protocols such as IP and UDP, and also
 some connection protocols such as NBS TP.
 To cater to these types of protocols, it is a convention that
 commands, their parameters, and any associated data be transferred
 between the Host and the OPE in a single chunk. Any data associated
 with an H-FP command is viewed as an integral unit which is used in
 the corresponding service request given to the outboard protocol
 interpreter or delivered as a complete unit to the process in the
 Host. Operation of stream-oriented protocols such as TCP will not be
 adversely affected by this convention.
 To accommodate Channel protocols that do not provide for arbitrarily
 large chunks, a mechanism at the Command level is required to permit
 the linking of multiple chunks into a single command, in order to
 transfer the burden of buffering as much as possible from the Host to
 the OPE.  The facility proposed here would consist of an indication
 at the beginning of each chunk which would distinguish integral
 commands, fragments of a command for which more fragments are yet to
 arrive, and the final fragment of a command.  The details of this
 mechanism are discussed in the section on the syntax of commands and
 responses.
 It is a convention for this H-FP that any data associated with a
 command must start on a word boundary (as defined by the local
 system).  Consequently, there is a need to provide padding within the
 commands.  Such padding is used only to fill to the next appropriate
 boundary, and has no semantic significance to the command interpreter
 (i.e., two commands that are identical except for the amount of
 padding should behave identically).  The details of this padding are
 discussed in the section on the syntax of commands and responses.

Lilienkamp & Mandell & Padlipsky [Page 6]

RFC 929 December 1984 Proposed Host-Front End Protocol

Syntax Rules

 At the Command Level, communication between the Host and the OPE
 takes the form of commands and responses.  A command is a request for
 some particular action, and the response indicates the success or
 failure of performing the requested action.
 All commands and responses are coded in ASCII characters. (Nothing
 precludes OPEs from accepting EBCDIC from Hosts that use it in native
 mode, but that is not required.) These characters are sent in some
 way convenient for the Host, and the OPE is sufficiently flexible to
 interpret them.  (i.e., OPEs are expected to accommodate Host
 idiosyncracies in regard to such things as use of 7-bit ASCII in a
 9-bit field.) This approach offers several advantages:
 Adaptabilities in most Hosts:  Most Hosts have the ability to
 generate and interpret ASCII character streams.  Hence, integrating
 H-FP into a Host will not require difficult software.
 Script generation:  Generation of test and operational command
 scripts will be simplified, since they will not need to contain
 special characters.
 Terminal Operation:  Using simple command streams simplifies the
 conversion of an OPE to a generic virtual terminal support machine.
 This is particularly useful during development and testing.
 Testing:  Testing will not require special hardware to interpret
 commands and responses.  A terminal or data line analyzer would be
 adequate.
 The specific format for the commands and responses will be discussed
 in the sections that follow. In those sections, the quote character
 is used to indicate strings.  The symbols "<" and ">" (referred to as
 angle brackets) are used as meta-characters.
 Syntax of Commands
 As alluded to in the section discussing the interaction discipline
 between the Host and the OPE, a function is provided by which a chunk
 can be used to carry either a complete command or a fragment of a
 command.  The mechanism chosen to provide this function entails use
 of the first character position in the chunk as a chunk usage
 identifier.  The character "C" in the first position indicates a
 chunk containing a single, complete command.  "F" in the first
 position indicates a chunk which is the first part of a multichunk
 command. "M" in the first position indicates the chunk is a middle

Lilienkamp & Mandell & Padlipsky [Page 7]

RFC 929 December 1984 Proposed Host-Front End Protocol

 part (neither the first nor the last chunk) of a command.  Finally,
 "L" indicates the chunk is the last chunk of a multi-chunk command.
 Hence, the following sequences of chunks (the letter corresponds to
 the chunk usage identifier in each chunk, and the angle brackets
 enclose a chunk) are legal:
    <C>
    <F><L>
    <F><M><M><L>
 while the following are not legal:
    <L>
    <M><L>
    <F><C>
 Tactics for handling multiple chunks with regard to OPE buffering
 limits are left to the ingenuity of OPE builders. The spirit is to
 take as much as you can, in order to relieve the Host of the
 necessity of buffering itself.
 A command always begins immediately following the indicator
 character, with possible intervening spaces.  This implies a chunk
 can contain at most one complete command.  The end of the command
 (not including the data) is signified by a newline (denoted as <nl>
 in this document) that does not appear inside a quoted string (see
 below).  The end of the data is designated by the end of the last
 chunk.
 Commands take the form of an ASCII string.  The command identifier is
 the first word of the chunk.  It consists of at least the first two
 letters of the command, in either upper or lower case (e.g., the
 sequences "BE", "Be", "bE", and "be" all identify the Begin command).
 Additional letters of the command name can be included if desired to
 aid readability of the command stream.
 Following the command identifier is a list of parameters. These
 parameters are also represented as ASCII strings, although the
 specific format will depend on the particular parameter.  The data to
 be transmitted is not considered a control parameter, however, and
 need not be ASCII data.
 Parameters are separated by one or more spaces.  Tabs, newlines, and
 other white space are not legal parameter separators.
 Parameter strings may be quoted, using the character <">. Any

Lilienkamp & Mandell & Padlipsky [Page 8]

RFC 929 December 1984 Proposed Host-Front End Protocol

 characters between the <"> characters are a part of the parameter,
 including spaces and newlines.  The character <"> that is part of the
 parameter is represented inside a quoted string as <"">.
 The order in which the parameters appear within the command is
 significant to their interpretation by the Host and by the OPE.
 Optional parameters may be skipped by using the characters ",," to
 indicate a NULL parameter.  Such a NULL parameter takes its default
 value.  Alternatively, each parameter has a MULTICS/UNIX style
 Control Argument/Flag associated with it that can be used to identify
 the parameter, without placing NULL parameters for each parameter
 skipped.  This flag consists of one or two ASCII characters, and
 either upper or lower case may be used.  For example, if the fourth
 parameter of a command had a flag of "-p" and the user wished the
 first three parameters to be null, he could use:
    command -p value
 or
    command -P value
 instead of
    command ,, ,, ,, value
 if it were more convenient for the Host to do so.  Flagged parameters
 must still appear in the correct sequence within the command,
 however.
 There may be data associated with some of the commands.  Any such
 data is placed into the chunk following all the parameters and the
 unquoted newline. Padding can be provided by placing spaces between
 the end of the final parameter string and the newline, so that data
 begins on a word boundary. The OPE will always pad to a host word
 boundary.  Padding by hosts is optional.
 Syntax of Responses
 Responses are actually just a special form of a command.  It is
 anticipated that all responses would fit into a single channel chunk,
 although the mechanisms described for multichunk commands can
 certainly be used in responses.  The ASCII string used to uniquely
 identify the response command is "RE" ("Re", "rE", and "re" are also
 permitted).
 After the response command identifier is the original command

Lilienkamp & Mandell & Padlipsky [Page 9]

RFC 929 December 1984 Proposed Host-Front End Protocol

 identifier, so the response can be associated with the proper
 command.  Following this identifier is a three ASCII digit response
 code, a set of protocol idiosyncratic parameters, and a textual
 message.  The protocol idiosyncratic parameters are used to transfer
 interface information between the Host and the OPE, and may not be
 needed when off-loading some protocol interpreters.  The textual
 message is intended for human interpretation of the response codes,
 and is not required by the protocol.  The three digits uniquely
 identify the semantics of the response, at least within the context
 of a particular command and particular outboarded protocol
 interpreter.
 Responses are numerically grouped by the type of information they
 convey.  The first digit identifies this group, and the last two
 digits further qualify the reply.  The following list illustrates
 this grouping.
    0XX Successful:  The command was executed successfully. The
        response code may contain further information.
    1XX Conditional Success:  The command was executed successfully,
        but not exactly according to the service and flow control
        suggestions.  If those suggestions were particularly important
        to the requester, he may wish to issue an End command.  The
        response code contains information on what suggestion or
        suggestions could not be followed.
    2XX Command Level Error:  An error at the command level has
        occurred.  This could include requesting services of a
        protocol not supported, or a problem in the way those services
        were requested.  This level does not include problems with the
        syntax of the command or its parameters.
    3XX Syntax and Parameter Errors:  An error in the syntax of the
        command or a problem with one of its parameters has occurred.
        A problem with a parameter may be other than syntactical, such
        as illegal address.
    4XX Off-loaded Protocol Interpreter Problems:  Some problem with
        the particular off-loaded protocol has occurred.
    5XX Local OPE Internal Problems:  Problems, such as insufficient
        OPE resources, or problems with OPE to subnet interface.
    6XX Security Problem:  Some problem with Host, network, or OPE
        security has occurred.  The response code indicates the
        problem.

Lilienkamp & Mandell & Padlipsky [Page 10]

RFC 929 December 1984 Proposed Host-Front End Protocol

    7XX Reserved for Future Expansion
    8XX Reserved for Future Expansion
    9XX Protocol Idiosyncratic Errors:  Some error occurred that is
        idiosyncratic to the particular off-loaded protocol being
        used.  The response code indicates the error.

Description of the Commands

 As stated above, communication between the Host and the OPE at the
 Command Level is accomplished using commands and responses.  Commands
 may be issued by either the Host or the OPE, and are used to
 stimulate activity in the other entity. Some commands may only have a
 meaningful interpretation in one direction, however.  A response
 indicates that the activity started by the command was completed, and
 a code indicates success or failure of the command, and perhaps other
 information related to the command as well.
 Associated with each command is a set of parameters.  The order in
 which the parameters appear is significant to the correct operation
 of the protocols.  More information on the syntax of command
 parameters can be found in the syntax descriptions.
 The commands are:
  1. Begin: initiate communication between a process in the Host and

an off-loaded protocol interpreter in the OPE. (A Channel level

    stream/connection will typically have been opened as a prior step.
    All other commands, except No-op, apply to a stream on which a
    successful Begin has been done.)
  1. Transmit: transmit data between a process in the Host and an

off-loaded protocol interpreter in the OPE.

  1. Signal: cause an out-of-band signal to be sent by the

off-loaded protocol interpreter to its peer, or indicate the

    arrival of such a signal from the remote side.
  1. Condition: alter the off-loaded protocol interpreter's

operational characteristics.

  1. Status: transfer status requests or information between a

process in the Host and an off-loaded protocol interpreter in the

    OPE.

Lilienkamp & Mandell & Padlipsky [Page 11]

RFC 929 December 1984 Proposed Host-Front End Protocol

  1. End: indicate that services from the off-loaded protocol

interpreter are no longer required, or will no longer be provided.

  1. No-op: performs no operation, but facilitates testing.
 These commands will be discussed in the following sections. Each of
 these sections includes a discussion of the purpose of the command, a
 description of each of the parameters used with the command, a list
 of responses for the command, an example of the command, and a set of
 notes for the implementor.  (An appendix will eventually be furnished
 for each protocol offloading, showing the use of its protocol
 idiosyncratic parameters as well as of the general parameters on a
 per-command basis.  Initially, only representative offloadings will
 be treated in appendices, with others to be added after the protocol
 gains acceptance.)
 Begin
    Purpose of the Begin Command
       The purpose of a Begin command is to initiate communication
       between the Host and the OPE on a particular stream or channel
       (the channel is opened as a separate step, of course). The
       interpretation of the command is somewhat dependent upon
       whether it was issued by the Host of the OPE.
  1. If the command was issued by the Host, it means some process

in the Host is requesting services of a protocol that was

       off-loaded to the OPE.  The user request results in the
       establishment of a channel connection between the Host and the
       OPE, and a Begin command to the Command interpreter in the OPE.
  1. If the command was issued by the OPE, it means some protocol

interpreter in the OPE has data for some process in the Host

       which is not currently known by the OPE.  An example would be
       an incoming UDP datagram on a new port, or if no Begin for UDP
       had been issued at all by the Host.  (An incoming TCP
       connection request could be handled by a response to the user's
       Passive Open request, which had previously caused a Begin
       request from the Host; an incoming TCP connection request to a
       port on which no Listen had been issued would cause an OPE
       generated Begin, however.)
       As indicated earlier, any particular Host is not required to
       support two-way Begins.

Lilienkamp & Mandell & Padlipsky [Page 12]

RFC 929 December 1984 Proposed Host-Front End Protocol

    Parameters of the Begin Command
       The Begin command has several parameters associated with it.
       These parameters contain information needed by the offloaded
       protocol to provide an adequate level of network service.  This
       information includes protocol, source and destination
       addresses, and also type of service and flow control advice.
       These parameters are discussed in detail below.
    Protocol
       The protocol parameter identifies that off-loaded protocol in
       the OPE to which Begin is directed, or which issued the Begin
       to the Host.  For example, if the user wished to utilize TCP
       services, and the TCP software was off-loaded into the OPE,
       then the Protocol parameter for the Begin command would be TCP.
       There are two categories of protocol parameters -- generic and
       specific.  A generic parameter identifies a type of protocol
       service required, but does not identify the actual protocol.
       Use of generic protocols allows a Host process to obtain
       network services without specific knowledge of what protocol is
       being used; this could be appropriate for use in situations
       where no specific aspect(s) of a specific protocol is/are
       required.  For example, the user may select a generic
       Host-to-Host connection protocol, and (at some point in the
       future) may actually receive services from either TCP or the
       NBS Transport Protocol, depending on the network (or even the
       foreign Host) in question.  A specific protocol parameter
       identifies some particular protocol, e.g., TCP, whose use is
       required for the given channel.
       The valid entries for the protocol field include:
          Generic   Specific  Comment
          GIP       IP        Datagram Internetwork Protocol
          HHP       TCP       Connection Transport/Host-Host Protocol
          GDP       UDP       Datagram Transport/Host-Host Protocol
          VTP       TEL       Virtual Terminal (Telnet) Protocol
          GFP       FTP       File Transfer Protocol
          MAIL      SMTP      Mail Transfer Protocol
          PROX      PROX      Proximate Net Interface Protocol
       (Note that the final line is meant to allow for a process in an
       OPE'd Host's getting at the PI of the Network Interface
       Protocol for whatever the proximate network is.  Of course, so

Lilienkamp & Mandell & Padlipsky [Page 13]

RFC 929 December 1984 Proposed Host-Front End Protocol

       doing only makes sense in specialized contexts.  We conceive of
       the desirability of "pumping bits at a peripheral" on a LAN,
       though, and don't want to preclude it, even if it would be
       impossible on many LAN's to deal with the problem of
       distinguishing traffic coming back on the LAN in this "raw"
       mode from normal, IP traffic.  Indeed, in some contexts it is
       likely that administrative considerations would preclude
       avoidance of IP even if technical considerations allowed it,
       but it's still the case that "the protocol" should provide a
       hook for going directly to the L I protocol in play.)
       There is no default value for this parameter.  If it is not
       present, the Begin command is in error.  The control flag for
       this parameter is -pr.
    Active/Passive
       The Active/Passive parameter indicates whether the issuer of
       the Begin command desires to be the Active or Passive user of
       the protocol.  This parameter is particularly relevant to
       connection-oriented protocols such as TCP, where the user may
       actively pursue connection establishment, or else may passively
       wait for the remote entity to actively establish the
       connection; it also allows some process to establish itself as
       the Host "fielder" of incoming traffic for a connectionless
       protocol such as IP.
       Active is requested using the single character "A".  Passive is
       indicated using the character "P".  The default value of this
       parameter is "A". Also, when the OPE issues the Begin command,
       the value must be "A".  The control flag for this parameter is
       -ap.
    Foreign Address Primary Component
       The addressing structure supported by H-FP is two level. Each
       address has two components, the primary and the secondary.  The
       exact interpretation of these two components is protocol
       specific, but some generalities do apply.  The primary
       component of the address identifies where the protocol is to
       deliver the information. The secondary component identifies
       which recipient at that location is to receive the information.
       For example, the TCP primary address component is the Host's
       Internet Address, while the secondary address component is the
       TCP port.  Similarly, IP's primary address component is the
       Host's Internet Address, and the secondary address component is
       the IP ULP field.  Some protocols provide only a single level

Lilienkamp & Mandell & Padlipsky [Page 14]

RFC 929 December 1984 Proposed Host-Front End Protocol

       of addressing, or the secondary level can be deduced from some
       other information (e.g., Telnet).  In these cases, only the
       primary component is used.  To cater to such cases, the
       secondary component parameter comes later in the parameter
       list.
       The Foreign Address Primary Component parameter contains the
       primary component of the destination address.  It may be in
       either a numeric or symbolic form.  (Note that this allows for
       the OPE to exercise a Name Server type of protocol if
       appropriate, as well as freeing the Host from the necessity of
       maintaining an in-board name to address table.) The default
       value for this parameter, although it only makes sense for
       Passive Begins, is "Any Host".  The control flag for this
       parameter is -fp.
    Mediation Level
       The mediation level parameter is an indication of the role the
       Host wishes the OPE to play in the operation of the protocol.
       The extreme ranges of this mediation would be the case where
       the Host wished to remain completely uninvolved, and the case
       where the Host wished to make every possible decision.  The
       specific interpretation of this parameter is dependent upon the
       particular off-loaded protocol.
       The concept of mediation level can best be clarified by means
       of example.  A full inboard implementation of the Telnet
       protocol places several responsibilities on the Host. These
       responsibilities include negotiation and provision of protocol
       options, translation between local and network character codes
       and formats, and monitoring the well-known socket for incoming
       connection requests.  The mediation level indicates whether
       these responsibilities are assigned to the Host or to the OPE
       when the Telnet implementation is outboard.  If no OPE
       mediation is selected, the Host is involved with all
       negotiation of the Telnet options, and all format conversions.
       With full OPE mediation, all option negotiation and all format
       conversions are performed by the OPE.  An intermediate level of
       mediation might have ordinary option negotiation, format
       conversion, and socket monitoring done in the OPE, while
       options not known to the OPE are handled by the Host.
       The parameter is represented with a single ASCII digit.  The
       value 9 represents full OPE mediation, and the value 0
       represents no OPE mediation.  Other values may be defined for

Lilienkamp & Mandell & Padlipsky [Page 15]

RFC 929 December 1984 Proposed Host-Front End Protocol

       some protocols (e.g., the intermediate mediation level
       discussed above for Telnet).  The default value for this
       parameter is 9.  The control flag for this parameter is -m.
    Transmit Response Discipline
       The Transmit Response Discipline parameter is used to set the
       desired action on the OPE's part for generating responses to
       Transmit commands.  Essentially the parameter determines when
       the OPE's response to the transmit command occurs (i.e.,
       immediately or delayed).
       The Transmit Response Discipline value is represented by a
       single ASCII character.  The character "N" is used for
       nonblocking Transmit commands, which implies that responses for
       Transmit commands should be generated as soon as the command
       has been examined for correctness (i.e., that the syntax is
       good and the parameters appear reasonable).  In other words,
       the outboard protocol interpreter has the data in its queue,
       but hasn't necessarily transmitted it to the net.  The
       character "B" is used for blocking Transmit commands, which
       requests that the response not be generated until the protocol
       interpreter has successfully transmitted the data (unless, of
       course, the Transmit command was badly formed). The default
       value for this parameter is "N", or a nonblocking Transmit
       command.  The control flag for this parameter is -tr.
       (Depending on the protocol in play, "successfully transmitted"
       might well imply that an acknowledgment of some sort has been
       received from the foreign Host, but for other protocols it
       might only mean that the given collection of bits has been
       passed from the OPE to the proximate net.)
    Foreign Address Secondary Component
       The addressing mechanisms supported by this level of H-FP are
       discussed above.  The Foreign Address Secondary Component
       parameter contains the value of the destination address's
       secondary component.  Some protocols do not require this
       parameter, or can obtain it from other information.  Therefore,
       the default value for this parameter is NULL.  A NULL secondary
       component might be an error for some protocols, however.  The
       secondary component can be expressed either numerically or
       symbolically.  The control flag for this parameter is -fs.
       (Note that it is intended to be "legal" to specify a Secondary
       Component other than the Well-Known Socket for the protocol in
       play; in such cases, the result should be that the virtualizing
       of the given protocol be applied to the stream, in the

Lilienkamp & Mandell & Padlipsky [Page 16]

RFC 929 December 1984 Proposed Host-Front End Protocol

       expectation that that's what the other side is expecting.  This
       is to cater to, for example, a Terminal-Terminal protocol that
       merely "does Telnet" to a socket other than the usual Logger.)
    Local Address Secondary Component
       The Local Address Secondary Component parameter contains the
       value of the local address's secondary component.  (The primary
       component is assumed to be the default for the Host, but can be
       altered as well; see below.) Some protocols do not require this
       parameter, or can obtain it from other information.  In some
       cases, the OPE may already know the value for this parameter
       and therefore not require it. The default value of this
       parameter is NULL.  The local address secondary component can
       be expressed either numerically or symbolically.  The control
       flag for this parameter is -ls.
    Begin Timeout Interval
       After a Begin command is issued, a timer can be started.  If
       the activity requested cannot be performed within some timed
       interval, then the Begin command may expire.  An expired Begin
       command returns a response code indicating a Begin timeout
       occurred.  The Begin Timeout Interval parameter contains the
       length of time the timer will run before the Begin timeout
       occurs.
       The parameter is represented as a string of ASCII digits
       indicating the time interval in seconds.  The default value of
       this parameter is infinity (i.e., the Begin command will never
       timeout).  The control flag for this parameter is -bt.
    Type of Service Advice
       The Type of Service Advice parameter contains information on
       the service characteristics the user desires from the offloaded
       protocol.  Included in this parameter is the precedence of the
       data transfer, and also indication of whether high throughput,
       fast response time, or low error rate is the primary goal.
       The format of this parameter is a letter immediately (i.e. no
       intervening spaces) followed by a digit.  The letter "T"
       indicates that high throughput is desired.  The letter "R"
       indicates minimal response time is the goal.  The letter "E"
       indicates that low error rates are the goal.  The letter "N"
       indicates there are no special service requirements to be
       conveyed.  The digit immediately following the character

Lilienkamp & Mandell & Padlipsky [Page 17]

RFC 929 December 1984 Proposed Host-Front End Protocol

       indicates the desired precedence level, with zero being the
       lowest, and nine being the highest.  The specific
       interpretation of this parameter is dependent on what service
       options are provided by the protocol.  The default value of
       this parameter is the lowest precedence (ROUTINE), and no
       special service requests.  The control flag for this parameter
       is -ts.
    Flow Control Advice
       The Flow Control Advice parameter contains information on the
       flow characteristics desired by the user.  Some applications
       such as file transfer operate more efficiently if the data is
       transferred in large pieces, while other, more interactive
       applications are more efficiently served if smaller pieces are
       used.  This parameter then indicates whether large or small
       data blocks should be used.  It is only relevant in stream or
       connection-oriented protocols, where the user sends more than a
       single piece of data.
       This parameter is represented by a single ASCII digit. A value
       0 means the data should be sent in relatively small blocks
       (e.g., character or line oriented applications), while a value
       9 means the data should be sent in relatively large blocks
       (e.g., block or file oriented applications). Other values
       represent sizes between those extremes.  The character "N"
       indicates that no special flow control advice is provided.  The
       actual interpretation of this parameter is dependent on the
       particular protocol in the OPE.  The default value of this
       parameter is no flow control advice. In this case, the protocol
       in the OPE will operate based only on information available in
       the OPE.  The control flag for this parameter is -fc.
    Local Address Primary Component
       This parameter contains the local address primary component. It
       is anticipated that under most circumstances, this component is
       known to both the Host and the OPE.  Consequently, this
       parameter is seldom required.  It would be useful if the Host
       desired to select one of several valid addresses, however.  The
       control flag for this parameter is -lp.
    Security
       The security parameters contain a set of security level,
       compartment, community of interest, and handling restriction
       information.  Currently, security is provided by performing all

Lilienkamp & Mandell & Padlipsky [Page 18]

RFC 929 December 1984 Proposed Host-Front End Protocol

       processing at system high level or at a single level.
       Consequently, these parameters are probably redundant, since
       the security information is known.  In the future, however,
       these parameters may be required.  Therefore a field is
       provided. The control flag for this parameter is -s.
    Protcol Idiosyncratic Parameters
       The remaining parameters are protocol idiosyncratic.  That is,
       each protocol that is off-loaded may have a set of these
       parameters, which are documented with a description of the
       off-loaded protocol.  The default value for these parameters is
       NULL, unless otherwise specified by a particular offloaded
       protocol.  The control flag for this set of parameters is -pi,
       which identifies the first protocol idiosyncratic parameters.
       Control flags for other protocol idiosyncratic parameters must
       be defined for each off-loaded protocol.
    Data
       After the Protocol Idiosyncratic Parameters, if any, and the
       required <nl>, if the protocol in play allows for it at this
       juncture the rest of the chunk will be interpreted as data to
       be transmitted.  That is, in connection oriented protocols data
       may or may not be permitted at connection initiation time, but
       in connectionless protocols it certainly makes sense to allow
       the H-FP Begin command to convey data. (This will also be
       useful when we get to the Condition command.)
    Responses
       The following responses have been identified for the Begin
       command:
          000    Command completed successfully
          101    Throughput not available; using maximum
          102    Reliability not available; using maximum
          103    Delay not available; using minimum
          110    Flow Control advice not followed; smaller blocks used
          111    Flow Control advice not followed; larger blocks used
          201    Failed; Begin not implemented in this direction
          202    Failed; timeout
          203    Failed; Begin command on already active channel
          300    Problem with multiple chunks
          301    Syntax problem with Begin command
          302    Protocol not supported in OPE/Host
          303    Active service not available

Lilienkamp & Mandell & Padlipsky [Page 19]

RFC 929 December 1984 Proposed Host-Front End Protocol

          304    Passive service not available
          305    Invalid Foreign Address Primary Component
          306    Invalid Transmit Discipline
          307    Invalid Foreign Address Secondary Component
          308    Invalid Local Address Secondary Component
          309    Invalid Timeout Interval
          310    Invalid Type of Service Advice
          311    Invalid Flow control Advice
          312    Invalid Local Address Primary Component
          401    Protocol Interpreter in OPE not responding
          402    Remote Protocol Interpreter not available
          403    Failed; insufficient protocol interpreter resources
          501    Failed; insufficient OPE resources
          601    Request violates security policy
          602    Security parameter problem
       Additionally, protocol idiosyncratic responses will be defined
       for each off-loaded protocol.
    Example of Begin Command
       The Begin command is the most complex of the H-FP Command
       Level. When the off-loaded protocol is TCP, the Begin command
       is used to open TCP connections.  One possible example of a
       Begin command issued by an inboard Telnet interpreter to open a
       TCP connection to ISIA, with no begin timeout interval, is:
          C BE TCP A ISIA 9 N 23 ,, ,, N0 S <nl>
       Where:
          TCP    The code for the protocol TCP
          A      Indicates Active Begin
          ISIA   The name of a Host at USC-ISI
          9      Mediation Level 9:  Full OPE mediation
          N      Non-blocking transmit
          23     Destination Telnet Port
          ,,     skip  over parameters  (Local Address Secondary,
                 Begin Timeout Interval)
          N0     Type of Service Advice:  No special Advice,
                 Normal Precedence
          S      Flow Control Advice: use small blocks
       This command will cause the OPE to invoke the TCP interpreter
       to generate the initial SYN packet to the well-known Telnet
       socket on Host ISIA.  It also informs the OPE to do all TCP
       related processing via the Mediation Level, accepts default

Lilienkamp & Mandell & Padlipsky [Page 20]

RFC 929 December 1984 Proposed Host-Front End Protocol

       Local Address parameters, and sets the Begin Timeout Interval
       to infinity.  The precedence of the TCP connection is Normal,
       and the TCP interpreter is informed that the data stream will
       consist of primarily small blocks.
    Notes to the Implementor
       Response 203 might seem silly to some readers, but it's there
       in case somebody goofed in using the Channel Layer.
 Transmit
    Purpose of the Transmit Command
       The purpose of the Transmit command is to permit the process in
       the Host to send data using an off-loaded protocol interpreter
       in the OPE, and also to permit the OPE to deliver data received
       from the network destined for the process in the Host.  The
       Transmit command is particularly relevant to connection and
       stream type protocols, although it has applications for
       connectionless protocols as well.  After the Begin command is
       issued successfully and the proper Response received, Transmit
       commands can be issued on the given channel.  The semantics of
       the Transmit command depend on whether it was issued by the
       Host or the OPE.
  1. If the Host issues the Transmit command, a process in the

Host wishes to send the data to the destination specified to

       the off-loaded protocol interpreter that was established
       (typically) by a previous Begin command on the given H-FP
       channel.
  1. If the OPE issues the command, the OPE has received data

destined for a process in the Host from a connection or stream

       supported by the off-loaded protocol that was established by a
       previous Begin command on the given H-FP channel.
    Parameters of the Transmit Command
       The Transmit command has one parameter associated with it. It
       is an optional parameter, to temporarily override the response
       discipline for this particular transmit command. Some protocols
       may have protocol-idiosyncratic parameters as well.  The
       transmit command also has data associated with it.  All
       parameters must precede the data to be transmitted.

Lilienkamp & Mandell & Padlipsky [Page 21]

RFC 929 December 1984 Proposed Host-Front End Protocol

    Response Discipline Override
       The Response Discipline Override parameter indicates the
       desired response discipline for that individual Transmit
       Command, overriding the default response discipline.  A single
       ASCII character is used to indicate the desired discipline.
       The character "N" indicates that this Transmit command should
       not block, and should return a response as soon as the data is
       given to the protocol interpreter in the OPE. The character "B"
       indicates that this Transmit command should block, meaning that
       a response should not be generated until the data has been sent
       to the destination.  The default value of this parameter is the
       currently defined Transmit Command response discipline.  The
       use of this parameter does not alter the currently defined
       Transmit command response discipline; the default is changed
       with the Condition command.  The control flag for this
       parameter is -rd.
    Protocol-Idiosyncratic Parameters
       Any other parameters to the Transmit command are
       protocol-idiosyncratic. That is, each protocol that is
       off-loaded has a set of these parameters, which are documented
       with a description of the off-loaded protocol.  The default
       value for these parameters is NULL, unless otherwise specified
       by a particular off-loaded protocol.  The control flag for this
       set of parameters is -pi, which identifies the first
       protocol-idiosyncratic parameters.  Control flags for other
       protocol-idiosyncratic parameters must be defined for each
       off-loaded protocol.
    Responses
       The following responses for the Transmit command have been
       identified:
          000    Transmit Command completed successfully
          201    Transmit Command not appropriate
          300    Problem with multiple chunks
          301    Syntax problem with Transmit Command
          302    Invalid Transmit Command Response Discipline
          401    Protocol Interpreter in OPE not responding
          402    Failure in remote protocol interpreter
          403    Failed; insufficient protocol interpreter resources
          501    Failed; insufficient OPE resources
          601    Request violates security policy

Lilienkamp & Mandell & Padlipsky [Page 22]

RFC 929 December 1984 Proposed Host-Front End Protocol

       Additionally, protocol-idiosyncratic responses will be defined
       for each off-loaded protocol.
    Example of Transmit Command
       The transmit command is used in TCP to provide the TCP write
       call.  An example of such a transmit command would be:
          C TR N <nl> <DATA>
       Where N indicates non-blocking transmission discipline, <nl> is
       the required command-ending newline, and <DATA> is presumed to
       be the user's data that is to be transmitted.
    Notes to the Implementor
       If you get a 403 or a 501 response and have sent a multiple
       chunk it probably makes sense to try a single chunk; if you've
       sent a single chunk, it makes sense to wait a while and try
       again a few times before giving up on the stream/channel.
 Condition
    Purpose of the Condition Command
       The primary purpose of the Condition command is to permit a
       process to alter the characteristics that were originally set
       up with the Begin command. (That is, "condition" is a verb.)
       These characteristics include the addresses, the mediation
       level, the type of service, and the flow control parameters
       from Begin. They may also include protocol-idiosyncratic
       characteristics. (Although Condition is usually thought of as a
       Host->OPE command, it may also be used OPE->Host in some
       contexts.)
       Condition is a generic command that may find little use in some
       off-loaded protocols.  In others, only some of the parameters
       identified may make sense.  For example, changing the
       destination address of a TCP connection involves closing one
       connection and opening another.  Consequently, in may make more
       sense to first issue an End command, and then a Begin with the
       new address.  In other protocols, such as IP or UDP, changing
       the address on each datagram would be a perfectly reasonable
       thing to do.

Lilienkamp & Mandell & Padlipsky [Page 23]

RFC 929 December 1984 Proposed Host-Front End Protocol

    Parameters of the Condition Command
       The Condition command has the same parameters as the Begin
       command.  Any parameters expressed in a Condition command
       indicate the new values of the characteristics to be altered;
       all parameters not expressed retain the current value.
       Although it is possible to express the change of any of the
       characteristics originally set up in the Begin command using
       the Condition command, there are some characteristics that do
       not make sense to alter, at least for some protocols. For
       example, once a connection is opened, it does not make much
       sense to change the Foreign Address Primary or Secondary
       Components.  Doing so is inconsistent with current versions of
       TCP, and would require the closing of the existing connection
       and opening a new one to another address.  Earlier versions of
       TCP did permit connections to be moved.  If a protocol that
       provided such a feature was implemented in the OPE, the
       changing the Secondary Address Components would be a reasonable
       thing to do.
    Responses
       The responses to the Condition command are the same as those to
       the Begin command.
    Example of Condition Command
       The Condition Command can be quite complex, and can be used for
       many purposes.  One conceived use of the condition command
       would be to change the type of service advice associated with
       the channel. An example of this (which also demonstrates the
       ability to skip parameters) is:
          C -ts T <nl>
       which causes the offloaded PI associated with the current
       channel to attempt to achieve high throughput (in its use of
       the comm subnet(s) in play).
    Notes to the Implementor

Lilienkamp & Mandell & Padlipsky [Page 24]

RFC 929 December 1984 Proposed Host-Front End Protocol

 Signal
    Purpose of Signal Command
       The purpose of the Signal Command (implicitly at least) is to
       permit the transfer of out-of-band signals or information
       between the Host and the OPE, in order to utilize (explicitly)
       out-of-band signaling services of the off-loaded protocol. The
       semantics of the Signal command depend upon whether it was
       issued by the Host or the OPE.
  1. If the Signal command was issued by the Host, it means a

process in the Host desires to send out-of-band data or an

       out-of-band signal.
  1. If the Signal command was issued by the OPE, it means

out-of-band data or an out-of-band signal arrived for the

       process associated with the channel in the Host.
    Parameters of the Signal Command
       The basic usage of the Signal command is with no parameters,
       which sends or reports the receipt of an out-of-band signal.
       Some protocols, such as the NBS Transport Protocol, permit the
       user to send data with the out-of-band signal.  Hence, data is
       permitted to accompany the Signal command.  There may also be
       protocol-idiosyncratic parameters for the Signal command.  If
       this is the case, these parameters would come before the data.
    Protocol-Idiosyncratic Parameters
       The parameters for the Signal command are protocol
       idiosyncratic.  That is, each protocol off-loaded has a set of
       these parameters.  The default value for these parameters is
       their previous values. Control flags for multiple
       protocol-idiosyncratic parameters must be defined for each
       off-loaded protocol.
    Responses
       The following responses have been identified for the Signal
       command:
          000    Command completed successfully
          201    Command not appropriate
          300    Problem with multiple chunks
          301    Syntax problem with Command

Lilienkamp & Mandell & Padlipsky [Page 25]

RFC 929 December 1984 Proposed Host-Front End Protocol

          401    Protocol Interpreter in OPE not responding
          402    Failure in remote protocol interpreter
          403    Failed; insufficient protocol interpreter resources
          501    Failed; insufficient OPE resources
          601    Request violates security policy
       Additionally, protocol-idiosyncratic responses will be defined
       for each off-loaded protocol.
    Example of Signal Command
       The major perceived use for the Signal command when offloading
       a connection protocol is sending an out-of-band signal with no
       data.  In such a case, the appropriate signal command would be:
          C SI <nl>
    Notes to the Implementor
       Some protocols may allow only only one outstanding signal at a
       time.  For these protocols, it is an implementation issue
       whether the OPE will buffer several signals, but a good case
       could be made for the position that a scrupulous OPE would
       reflect a 202 response back to the Host in such cases.
       There is some question as to the proper handling of the
       "expedited data" notion of some (particularly ISO) protocols.
       It might be more appropriate to deal with such a thing as a
       protocol idiosyncratic parameter on the Transmit command
       instead of using the Signal command (even if it's the closest
       approximation to an out-of-band signal in the given protocol).
       If it's provided using the Signal command, the expedited data
       should not be passed as ASCII, and should appear after the
       command-terminating newline character (and appropriate padding
       with space characters).
 Status
    Purpose of Status Command
       The purpose of the Status command is to permit the Host to
       request and obtain status information from the OPE, and vice
       versa. This includes status request of a conventional protocol
       interface (e.g., in TCP, there is a request to determine the
       state of a particular connection).

Lilienkamp & Mandell & Padlipsky [Page 26]

RFC 929 December 1984 Proposed Host-Front End Protocol

    Parameters of the Status Command
       The parameters for the Status command indicate whether it is a
       request or a response, and contain the status information.
       Request/Report
          This parameter indicates whether the command is a Status
          request or a Status report.  It consists of a single ASCII
          character.  Q indicates a request (query), and R indicates a
          report.  It should be noted that a report may be generated
          as the result of a query, or may be generated as the result
          of specific protocol mechanisms.
    Protocol-Idiosyncratic Parameters
       The parameters to the status command are
       protocol-idiosyncratic. That is, each protocol off-loaded has a
       set of these parameters.  The default value for these
       parameters is their previous values.  Among these parameters is
       an identifier of the type of status information contained or
       requested, and a value or set of values that contain the
       particular status information. The status information itself
       should be the last item in the command. The control flag for
       this set of parameters is -pi, which identifies the first
       protocol-idiosyncratic parameters.  Control flags for other
       protocol-idiosyncratic parameters must be defined for each
       off-loaded protocol.
    Responses
       The following responses have been identified for the Status
       command:
          000    Command completed successfully
          201    Command not appropriate
          300    Problem with multiple chunks
          301    Syntax problem with Command
          302    Inappropriate status request
          303    Inappropriate status response
          401    Protocol Interpreter in OPE not responding
          402    Failure in remote protocol interpreter
          403    Failed; insufficient protocol interpreter resources
          501    Failed; insufficient OPE resources
          601    Request violates security policy
          9xx    Protocol Idiosyncratic status responses

Lilienkamp & Mandell & Padlipsky [Page 27]

RFC 929 December 1984 Proposed Host-Front End Protocol

    Example of Status Command
       The status command can be particularly complex, depending on
       the protocol and particular type of status information.  One
       possible use of the status command when off-loading TCP is to
       communicate the status service request.  For performing this
       operation the status command would be:
          C ST Q <nl>
    Notes to the Implementor
 End
    Purpose of the End Command
       The purpose of the End command is to communicate that services
       of the off-loaded protocol are not required.  The semantics of
       the End command depends upon whether it was issued by the Host
       or the OPE.
  1. If the Host issues the End command, it means the process in

the Host no longer requires the services of the offloaded

       protocol.
  1. If the OPE issues the End command, it means the remote entity

has no more data to send (e.g., the off-loaded protocol is TCP

       and the remote user has issued a TCP close).
    Parameters of the End Command
       One parameter is associated with the End Command.  It indicates
       whether the termination should be "graceful" or "abrupt" (see
       below).
       Graceful/Abrupt
          The Graceful/Abrupt parameter indicates whether the End
          should be handled gracefully or abruptly.  If it is handled
          gracefully, then data in transit is allowed to reach its
          destination before service is actually terminated.  An
          abrupt End occurs immediately; all data transmitted from the
          Host but still pending in the OPE is discarded, and no new
          incoming data is sent to the Host from the OPE.

Lilienkamp & Mandell & Padlipsky [Page 28]

RFC 929 December 1984 Proposed Host-Front End Protocol

          The parameter is indicated by a single ASCII character.  The
          character "G" denotes graceful, and "A" denotes abrupt.  The
          default value for this parameter is graceful.
    Responses
       The following responses have been identified for the End
       command:
          000    Command completed successfully
          201    Command not appropriate
          300    Problem with multiple chunks
          301    Syntax problem with Command
          302    Illegal Type of End Command
          401    Protocol Interpreter in OPE not responding
          402    Failure in remote protocol interpreter
          403    Failed; insufficient protocol interpreter resources
          501    Failed; insufficient OPE resources
          601    Request violates security policy
       Additionally, protocol idiosyncratic responses will be defined
       for each off-loaded protocol.
    Example of End Command
       The syntax of the End command is relatively straightforward. It
       consists of a chunk that contains only a chunk usage
       identifier, the end command string, and the parameter
       indicating whether the end should be graceful or abrupt.  A
       possible valid (abrupt) End command would be:
          C EN A <nl>
    Notes to the Implementor
       Once an End has been issued in a given direction any other
       commands on the channel in the same direction are in error and
       should be responded to appropriately.

Lilienkamp & Mandell & Padlipsky [Page 29]

RFC 929 December 1984 Proposed Host-Front End Protocol

 No-op
    Purpose of the No-op Command
       The No-op command performs no operation.  Its purpose is to
       permit the Host and OPE to participate in a dialog which does
       not alter the state of communication activities, both for
       debugging purposes and to support features of certain protocols
       (e.g., Telnet's Are You There command).
    Parameters of the No-op Command
       There are no parameters associated with the No-op command.
    Responses
       There are only two possible legal responses to the No-op
       command.  They are:
          000    No-op Command Completed Correctly
          300    Problem with multiple chunks
    Example of No-op Command
       Syntactically the No-op command is quite simple.  It consists
       of a chunk that contains only the chunk usage identifier and
       the string for the command, and the newline.  One possible
       valid No-op command is:
          C NO <nl>
    Notes to the Implementor
       No-ops are included for use in testing and initial
       synchronization.  (The latter use is not mandatory, however.
       That is, no exchange of No-ops is required at start-up time,
       but it is conceivable that some implementations might want to
       do it just for exercise.) They are also traditional.

Lilienkamp & Mandell & Padlipsky [Page 30]

RFC 929 December 1984 Proposed Host-Front End Protocol

References

 (References [1]-[3] will be available in M. A. Padlipsky's "The
 Elements of Networking Style", Prentice Hall, 1985.)
 [1] Padlipsky, M. A., "The Host-Front End Protocol Approach",
 MTR-3996, Vol. III, MITRE Corp., 1980.
 [2] Padlipsky, M. A., "The Elements of Networking Style", M81-41,
 MITRE Corp., 1981.
 [3] Padlipsky, M. A., "A Perspective on the ARPANET Reference Model",
 M82-47, MITRE Corp., 1982.
 [4] Bailey, G., "Network Access Protocol", S-216,718, National
 Security Agency Central Security Service, 1982.
 [5] Day, J. D., G. R. Grossman, and R. H. Howe, "WWMCCS Host to Front
 End Protocol", 78012.C-INFE.14, Digital Technology Incorporated,
 1979.

Lilienkamp & Mandell & Padlipsky [Page 31]

RFC 929 December 1984 Proposed Host-Front End Protocol

APPENDIX

 Per-Protocol Offloading Descriptions
 1.  Command Level Interface to an Off-loaded TCP
    This appendix discusses the use of the commands described in the
    body of this document to provide an interface between a Host
    process and an off-loaded interpreter of the DoD's Transmission
    Control Protocol (TCP).  The interface described here is
    functionally equivalent to the interface found in the MIL-STD 1778
    specification of TCP.  It is not, however, identical, in that some
    features of the interface are particularly relevant only in an
    inboard implementation.
    The first section describes the mapping between the interface
    events of MIL-STD 1778 and the commands and responses of this
    H-FP, and highlights the unique features of the interface.  The
    next sections discuss the details of each command.  These details
    include the specialized usages of the command and the
    protocol-idiosyncratic parameters for that command.
    1.1.  Relation to MIL-STD 1778 Interface
       Most of the requests and responses of the TCP interface
       specified in MIL-STD 1778 are mapped directly to H-FP Commands
       and responses.  The exceptions are noted in the following
       descriptions.
       1.1.1. Requests
          Unspecified Passive Open, Fully Specified Passive Open,
          Active Open, and Active Open with Data requests are all
          implemented using variations of the Begin command.  The
          distinction between Passive and Active Open is made using
          the Active/Passive parameter of Begin.  The distinction
          between unspecified and fully specified lies in the presence
          or absence of the destination address fields.  An active
          open with data is identical to a normal active open, except
          for the presence of data following the command.
          The Send Service Request is implemented using the Transmit
          command.  Special protocol idiosyncratic parameters are
          provided for Urgent, Push, and changing the ULP timeout
          action and values.  The response to the Transmit command
          indicates that the appropriate Send call has been made.

Lilienkamp & Mandell & Padlipsky [Page 32]

RFC 929 December 1984 Proposed Host-Front End Protocol

          There is no corresponding response in the specified TCP
          interface; its only significance is that the Host can issue
          another Transmit command.
          The Allocate event is a specification feature of MIL-STD
          1778 to indicate the willingness of the user to accept
          incoming data across the interface.  However, because this
          is precisely the type of flow control provided by the
          Channel level, the Allocate event would be a superfluous
          mechanism.  Thus, there is no direct analogy to that event
          in the H-FP interface. A Host process indicates its
          willingness to accept new data by informing the channel via
          its flow control interface (if it has an explicit one).
          Close and Abort are provided by the End command.  Close uses
          the graceful version of the End command, while Abort uses
          the abrupt version.  The response indicates that the End
          command has been received and the corresponding Close or
          Abort was issued.  There is no corresponding response in the
          specified TCP interface.
          Status is provided by using the query form of the Status
          command.  The response to the Status command contains the
          information (see below).
       1.1.2. Responses
          The Open Id response is provided so that the user has a
          shorthand name by which to refer to the connection.  With an
          outboarded TCP interpreter, there is a one-to-one mapping
          between TCP connections and H-FP channels.  Hence, the Open
          Id event is not needed, since the channel ID is sufficient
          to indicate the desired connection.
          The Open Failure and Open Success responses are provided
          using OPE-generated responses to Begin commands (which
          provide the Active and Passive Service response primitives)
          issued by the Host.  The value of the response code
          indicates whether the Begin command succeeded or failed, and
          can be mapped to the appropriate Open Failure or Open
          Success indication by the Host.
          Deliver is provided by having the OPE issue a Transmit
          command.  As mentioned above, the "flow control" between the
          TCP interpreter and the Host is provided by the Channel
          layer, so no explicit interface events are needed.  The

Lilienkamp & Mandell & Padlipsky [Page 33]

RFC 929 December 1984 Proposed Host-Front End Protocol

          response to the Transmit command indicates the data was
          received by the Host process.  There is no corresponding
          response in the specified TCP interface.
          The Closing and Terminate service responses are provided
          using the End command. Closing is indicated using the
          graceful version of the command, while terminate is provided
          using the abrupt version.  The response indicates the End
          command was received by the Host process.  There is no
          corresponding response in the specified TCP interface.
          Status Response is provided by a response to the query
          version of the Status command.  The status information is
          communicated via protocol-idiosyncratic parameters following
          the Response code.
          Error messages are reported using the spontaneously
          generated version of the Status command issued by the OPE.
          The error message is provided in a parameter.  The response
          indicates the error message was received by the Host
          process.  There is no corresponding event in the specified
          TCP interface.
    1.2.  The Begin Command
       The Begin command is used in TCP in three major ways:
          1. To inform the OPE that a process in the Host wishes to
          open a connection to a particular port on a internet
          address.
          2. To inform the OPE that a process in the Host wishes to be
          informed when a connection attempt is made to any or to a
          specific port at this Host's internet address.
          3. To inform the Host that a connection attempt to the OPE
          has arrived, and there was no Begin of the second type
          (passive open) issued by the Host relevant to that
          particular port.
       1.2.1. Specialized Usage
          There are four major aspects to the specialized usage of the
          Begin command and its parameters.  These parameters are:
             1. The meaning of the Mediation Level parameter

Lilienkamp & Mandell & Padlipsky [Page 34]

RFC 929 December 1984 Proposed Host-Front End Protocol

             2. The selection of blocking treatment of Transmit
                command
             3. The meaning of the address components
             4. The selection of the TCP Active Open with Data
                primitive.
          The Mediation Level parameter has only two possible values
          when offloading TCP.  These are "9" and "0".  The normal
          usage of an off-loaded TCP uses the value "9", which means
          the Host is in no way involved in the operation of TCP.  The
          value "0" indicates the Host wishes to negotiate with the
          TCP options.
          The normal TCP Send event is non-blocking.  That is, when a
          user issues the send command, it counts on the reliability
          services of TCP, and is not explicitly notified when the
          data has reached the other end of the connection and been
          properly acknowledged. Hence, the default value for this
          parameter with TCP is "N".  There are some applications
          where the user may not wish to receive a response to a
          Transmit command until the data has been acknowledged by the
          other end of the connection.  In these cases, the value "B"
          should be used for this parameter.  If such a feature is not
          supported by the offloaded TCP interpreter, then it is
          acceptable to issue a 100 level Conditional acceptance
          indicating that blocking is not supported, but the Begin
          command will proceed using non-blocking Transmits.
          The primary address components of the local and remote
          addresses refer to the internet addresses of (or a symbolic
          Host name for) the respective Hosts.  The secondary
          components refer to the particular sockets at those internet
          addresses.  Normally, the secondary components (ports) are
          specified numerically. They may, however, be specified by
          name if the port is a well-known service port. In an Active
          Begin command, the remote addresses primary and secondary
          components must be specified.  The local address components
          need not be specified, unless the user wishes to indicate
          that the connection should be from a particular port or a
          particular internet address of a multi-homed Host.  In a
          Passive Begin command, the remote addresses are specified
          only if connection attempts from one particular Host are of
          interest.  The local address secondary component must be
          used to indicate on which port to perform the Listen.

Lilienkamp & Mandell & Padlipsky [Page 35]

RFC 929 December 1984 Proposed Host-Front End Protocol

          The way the TCP Active Open with data is provided is by
          including the data with the Begin Command.  This data is
          included in the same Channel level chunk, immediately
          following the newline.  If the data is more than a single
          chunk can hold, then the multi-chunk command feature of the
          H-FP must be used.
       1.2.2. Protocol-Idiosyncratic Parameters
          The protocol-idiosyncratic parameter identified for the TCP
          interface is the "ULP timeout" information.  This
          information includes whether the offloaded interpreter
          should abort the connection on a ULP timeout or report it to
          the inboard user, and also the numerical value of the
          timeout interval. The format chosen for this parameter is a
          single letter followed immediately (with no spaces) by an
          ASCII number. The letter can be either "R" or "A", and
          indicates that the ULP timeout should cause a report or an
          abort, respectively. The number is interpreted to be the
          timeout interval in seconds.
       1.2.3. Examples of the Command
          An example of an Active Begin command that might be issued
          by an inboard user Telnet is:
             C BE TCP A ISIA 9 N 23 ,, 60 R 0 -pi R120 <nl>
          ISIA is the destination Host, 23 is the well-known port
          number for Telnet connections, a Begin timeout of 60 seconds
          was chosen.  The desired type of service is to strive for
          good response time, the transmissions are expected to be in
          small units, and protocol-idiosyncratic parameter R120
          implies that a ULP timeout of 120 seconds should be
          reported.
          An example of a Passive Begin Command that might be issued
          by an inboard server Telnet is:
             C BE TCP P ,, 9 N ,, 23 ,, R 0 -pi R120 <nl>
          The major differences are that no remote address components
          are specified, and the local secondary address component is
          identified as the socket on which the Listen is being
          performed.  Also, the default ("infinite") timeout is taken.

Lilienkamp & Mandell & Padlipsky [Page 36]

RFC 929 December 1984 Proposed Host-Front End Protocol

    1.3.  The Transmit Command
       The Transmit command is used by the Host process to instruct
       the off-loaded TCP interpreter to send data to a remote site
       via the TCP connection associated with the command's channel.
       It is used by the OPE to deliver incoming data from the
       connection to the process in the Host.
       1.3.1. Specialized Usage
          The Transmit command must be capable of providing all the
          specialized features of the Send and Deliver Event.  These
          special features are Urgent, Push, and modification of the
          ULP Timeout action and/or interval.
          Urgent is a means to communicate that some point upcoming in
          the data stream has been marked as URGENT by the sender.
          While the actual Urgent bit travels through the connection
          out-of-band, it carries a pointer that is related to the
          sequence numbers of the in-band communication. Hence, the
          urgency must be indicated in the Transmit command rather
          than the Signal command.
          Push is a feature of the TCP Send Event that is used to
          indicate that the data in the Transmit command should be
          sent immediately (within the flow control constraints),
          rather than waiting for additional send commands or a
          timeout.  Push is indicated in the Transmit Command. The
          push feature has the same meaning when sent from the OPE to
          the Host.  If the Host implementation does no internal
          queuing, the flag has no meaning.
          The TCP Send event permits the user to modify the "ULP
          timeout action" and/or the "ULP timeout interval" associated
          with that connection.  When changed, the new values take
          effect for the remainder of the connection, unless changed
          later with another Send.  This feature is provided in this
          H-FP using the Transmit Command.
       1.3.2. Protocol-Idiosyncratic Parameters
          The three features identified above are provided using
          protocol-idiosyncratic parameters.
          The first such parameter is the Urgent parameter.  From the
          point of view of the interface, it is just a flag that
          indicates the data is urgent (the actual Urgent pointer is a

Lilienkamp & Mandell & Padlipsky [Page 37]

RFC 929 December 1984 Proposed Host-Front End Protocol

          concern of the off-loaded TCP interpreter, which is keeping
          track of the sequence numbers).  When issued by the Host
          process, the Urgent flag means the stream should be marked.
          When issued by the OPE, it means the receiver should go to
          (or remain in) the Urgent receive mode.  If the flag is not
          set in the Transmit issued by the OPE, then the receiver
          should remain in (or return to) the non-urgent receive mode.
          The value of this protocol-idiosyncratic parameter is "U" if
          the Urgent is set, or "N" if it is not set.  The default
          value for this parameter is "N".  Since this parameter is
          the first protocol-idiosyncratic parameter for the Transmit
          command, it requires no special flag, and can be indicated
          using the flag -pi.
          The second protocol-idiosyncratic parameter is the Push
          flag.  This parameter is only issued by the Host, since
          there is no Push in the TCP Deliver event.  Its value is "P"
          for push, or "N" for normal.  The default value of this
          parameter is "N".  Its control flag is -pu.
          The third protocol-idiosyncratic parameter is the ULP
          timeout action and value parameter.  The action part
          indicates whether the offloaded interpreter should abort the
          connection on a timeout or report it to the inboard user.
          The value part is the numerical value of the timeout
          interval.  The format used for this parameter is the same as
          in the Begin command, which is a single letter followed
          immediately (with no spaces) by an ASCII number.  The letter
          can be either "R" or "A", and indicates that the ULP timeout
          should cause a report or an abort, respectively.  The number
          is interpreted to be the timeout interval in seconds.  The
          default interpretation for this parameter is its previous
          value. The control flag for this parameter is -ul.
       1.3.3. Examples of the Command
          An example of a Transmit command issued by a Host process is
             C TR -pi N P R160 <nl> <DATA>
          where <DATA> is the data contained within the chunk.  This
          command is for a non-urgent but pushed TCP Send event, that
          also resets the timeout action and interval to Report with a
          value of 160 seconds. The response mode (i.e., nonblocking)
          is derived from the Begin command and not effected by
          transmit.

Lilienkamp & Mandell & Padlipsky [Page 38]

RFC 929 December 1984 Proposed Host-Front End Protocol

          An example of a Transmit command issued by the OPE is
             C TR -pi N <nl> <DATA>
          where <DATA> is the data contained within the chunk.  This
          command is for a non-urgent delivery (presumably, after a
          previous Urgent delivery).
    1.4.  The Condition Command
       The Condition command is used to modify the transmission
       characteristics of the connection.  The parameters that make
       sense to modify with TCP are the Transmit Response discipline,
       the Type of Service, and the Flow Control Advice.
       1.4.1. Specialized Usage
          There is no usage of the Condition command with an offloaded
          TCP interpreter that is particularly specialized.
       1.4.2. Protocol-Idiosyncratic Parameters
          There are no protocol-idiosyncratic parameters for the
          condition command for the off-loaded TCP. It would be
          possible for the ULP timeout action values to be changed
          with a condition command.  However, this is accomplished
          with the Transmit command, which more closely models the
          interface specified in MIL-STD 1778.  We propose that the
          condition command not provide this capability.
       1.4.3. Examples of the Command
          An example of the Condition command to change the flow
          control advice for a connection is
             C CO -fc 1 <nl>
          which indicates that relatively small transmission units are
          now expected.

Lilienkamp & Mandell & Padlipsky [Page 39]

RFC 929 December 1984 Proposed Host-Front End Protocol

    1.5.  The Signal Command
       As we currently understand it, TCP's URGENT feature provides an
       INband signal rather than a true out-of-band signal (and at
       least one of us deeply regrets this).  The actual URGENT bit is
       sent out-of-band, but it contains an URGENT pointer which
       relates the URGENT to its position in the data stream.  The
       actual semantics of the URGENT is left to the higher level
       protocol (e.g., Telnet says to discard all data up to the
       URGENT pointer).  Since the Signal command is allowed to cross
       a pending Transmit in the H-FP channel, it would be potentially
       dangerous to implement the interface to TCP URGENT using the
       Signal command since the wrong sequence number could be used as
       the urgent pointer.  Barring persuasive arguments to the
       contrary, it is proposed that Signal should not be used with
       TCP.
    1.6.  The Status Command
       The Status command maps directly into the TCP Status event when
       issued by a Host process. It is also used for the TCP error
       event when issued by the OPE.  There is currently some question
       as to how information from lower protocol levels (e.g., ICMP
       error messages) should be reported to TCP users. When these
       issues are resolved, there may be other uses for the Status
       command.  We solicit other ideas for the Status command with
       this report.
       1.6.1. Specialized Usage
          The major specialized usage of the Status command is to
          provide the error reporting service.  This usage is a form
          of the Status generated by the OPE.
       1.6.2. Protocol-Idiosyncratic Parameters
          When used as a TCP Status request (command issued by the
          Host process), there are no protocol-idiosyncratic
          parameters associated with the Status command.  The OPE
          response codes the TCP status.
          When used as a TCP error report (command issued by the OPE),
          there is one protocol-idiosyncratic parameter associated
          with the Status command.  It is an error description in the
          form of a text string. It requires no special control flag
          since the flag -pi is unambiguous and there are no other
          protocol-idiosyncratic parameters.

Lilienkamp & Mandell & Padlipsky [Page 40]

RFC 929 December 1984 Proposed Host-Front End Protocol

       1.6.3. Examples of the Command
          An example of the Status command issued by the Host process
          to request status information is
             C ST Q <nl>
          The status information is returned in the response to the
          status command.
          An example of the Status command issued by the OPE to report
          an error from the TCP interpreter is
             C ST R -pi "Connection already exists" <nl>
          which is issued when a TCP open (HFP Begin) is issued to an
          already opened (foreign) connection.
    1.7.  The End Command
       The End command is used to indicate that TCP services are no
       longer required.  Thus, it can be mapped into either the TCP
       Graceful Close or the TCP Abort events.  It is also used as the
       TCP Closing response (as contrasted with the response by the
       OPE to the close command), when issued by the OPE.
       1.7.1. Specialized Usage
          Because of the nature of the two-way close provided by TCP,
          there is a possibility that the Host and the OPE wish to
          gracefully terminate the connection at the same instant.  If
          this happens, then both the Host and the OPE would issue End
          commands at the same time.  To be prepared for this, it is
          necessary to make this the normal graceful closing sequence.
          In other words, both the Graceful Close request and the
          Closing response are mapped to End commands, and the
          response to one of those commands only indicates that the
          command has been received and executed, but not that the
          connection is actually fully closed.  The connection is
          gracefully closed when both End commands have been issued,
          and both successful responses have been received.
          With an abrupt end, a two-way exchange is not necessary.
          Only the Host or the OPE need issue it, for the connection
          to be aborted.

Lilienkamp & Mandell & Padlipsky [Page 41]

RFC 929 December 1984 Proposed Host-Front End Protocol

       1.7.2. Protocol-Idiosyncratic Parameters
          There are no protocol-idiosyncratic parameters for the End
          command used with TCP.
       1.7.3. Examples of the Command
          An example of the End command used to indicate either a TCP
          Close request (from the Host process) or TCP Closing
          response (from the OPE) is
             C EN G <nl>
          An example of the End command used as an Abort request (from
          the Host process) or as a Terminate response is
             C EN A <nl>
 2.  Command Level Interface to an Off-loaded Telnet
    This appendix is provided to discuss the use of the commands
    described in the body of this document to provide an interface
    between a Host process and an off-loaded interpreter of the Telnet
    protocol.
    The interface described here is not based on a formal interface.
    There are several reasons for this, including the lack of a widely
    accepted standard interface to Telnet, and its headerless nature.
    Consequently, the interface described here is very similar to the
    actual Telnet data stream.
    2.1.  The Begin Command
       The Begin command is used with Telnet to initiate Telnet
       connections.
       2.1.1. Specialized Usage
          There are three major specialized usages to the Begin
          command.  They are the meaning of the Mediation Level
          parameter, the way the number of incoming Telnet connections
          are supported, and the meaning of the secondary address
          components.
          The mediation level is used in Telnet to control which of
          the various Telnet activities are performed by the OPE, and
          which are controlled by the Host.  It has been determined

Lilienkamp & Mandell & Padlipsky [Page 42]

RFC 929 December 1984 Proposed Host-Front End Protocol

          that all monitoring of the Telnet Socket should be performed
          by the OPE.  Mediation level 9, which is the default,
          indicates the Host desires to play no role in Telnet
          operation. Level 5 means that protocol-idiosyncratic
          parameters to this Begin command indicate which incoming
          options the Host wishes to handle; all other options, and
          all NVT translations, are to be performed by the OPE. Level
          0 indicates that the Host will handle all options, while all
          NVT translations are to be performed in the OPE (see Section
          B.1.3).
          The Host can either accept the connections by fielding OPE
          generated Begins, or by issuing passive Begins to the OPE.
          The Host may wish to restrict the number of incoming Telnet
          connections that it will handle at any particular time.  It
          can do this by rejecting OPE-generated Begins above a
          certain number, or by limiting the number of Host-issued
          passive Begins.  However, precedence constraints dictate
          that the Host actually issue additional passive Begins or
          accept additional Begins from the OPE beyond the maximum
          number it is normally willing to support, so that
          high-priority service requests can be accommodated, possibly
          by preempting lower priority activities.
          The secondary address component is used to refer to specific
          ports. Normally, they are used only when the standard or
          default ports are not used, such as special purpose
          applications or testing.
       2.1.2. Protocol-Idiosyncratic Parameters
          The protocol-idiosyncratic parameters to the Telnet Begin
          command are the identifiers for the options which the host
          wishes to negotiate when using mediation level 5.  On other
          mediation levels, these parameters are not used.
       2.1.3. Examples of the Command
          An example of a passive Begin for an outboard Telnet
          protocol is:
             C BE TEL P ,, 5 N -fc 0 -pi 9 <nl>
          Where the parameters are:
             TEL   Code for the Telnet Protocol
             P     Passive Begin

Lilienkamp & Mandell & Padlipsky [Page 43]

RFC 929 December 1984 Proposed Host-Front End Protocol

             ,,    Skip the Foreign Address Primary Component
             5     Mediation Level is 5
             N     Non Blocking Transmits
             -fc   Skips over parameters up to Flow Control Advice
             S     Small Blocks are appropriate for Telnet
             -pi   Skips over parameters to the Protocol Idiosyncratic
                   List of Options to be Handled by the Host.
             9     Option Code for Line Length Option
          Here, no remote address component was specified, since the
          Host will accept connections from any Host.  Similarly, no
          local addresses are specified, since the default well-known
          socket for this Host is to be used.  In this example, the
          Host specifies it will handle the line length option (number
          9).  Other options are handled in the OPE.
          An example of an active Begin for an outboard Telnet
          protocol is:
             C BE TEL A ISIA 5 N -fc 0 -pi 9 <nl>
          This command is identical to the passive command, except
          that a remote primary address component is specified to
          identify the intended Host.  No remote secondary component
          is specified, since the well-known socket at that Host is to
          be used.  No local secondary address components are
          specified, since the connection can originate from any
          available socket of the appropriate type selected by the
          OPE.
    2.2.  The Transmit Command
       The Transmit Command is used to send data across a Telnet
       connection.
       2.2.1. Specialized Usage
          The Transmit command is used to transmit data over the
          Telnet connection.  There is one specialized aspect of the
          Transmit command used with an outboard Telnet interpreter.
          This is the provision of the Go Ahead feature of Telnet that
          supports half-duplex devices.
          Go Ahead is provided as a protocol idiosyncratic parameter
          to the Transmit.  It is only used if the Host will support
          it, however.  It is our opinion that Go Ahead is probably
          not a proper thing for the default case.

Lilienkamp & Mandell & Padlipsky [Page 44]

RFC 929 December 1984 Proposed Host-Front End Protocol

          Go Aheads are a matter between the Host and the terminal. It
          is difficult to offload the generation of Go Aheads to the
          OPE, since the OPE is not really cognizant of the semantics
          of the communication between the Host and the terminal.
          Hence, the OPE does not know when the Host is done
          transmitting and willing to pass "the turn" back to the
          terminal. Similarly when the remote site relinquishes
          control, the OPE includes Go Ahead in its TR.
          We don't believe this Go Ahead problem to be an indictment
          against outboard processing.  It merely illustrates that
          functionality not found in a Host cannot necessarily be
          provided by the OPE.  Hence, we provide this note to the
          implementor:  if the Host cannot generate the
          protocol-idiosyncratic Go Ahead parameter, then the DO
          Suppress Go Ahead must be issued immediately after the
          connection is established.
       2.2.2. Protocol Idiosyncratic Parameters
          The protocol idiosyncratic parameter is the Go Ahead
          indicator.  When present, the character "G" is used to mean
          the Go Ahead can be sent to the other end of the connection,
          but only after the data associated with that Transmit
          command is sent.  When the character is any other value, or
          is absent, the Go Ahead should not be sent.
       2.2.3. Examples of the Command
          An example of the Transmit command is:
             C TR -pi G <nl> <DATA>
          With this command, the Go Ahead is passed to the other side
          after the data is sent.
    2.3.  The Condition Command
       The Condition command is used with Telnet to modify the
       Transmission characteristics and to enable or disable Telnet
       options on a Telnet connection.
       2.3.1. Specialized Usage
          The Condition command takes on specialized usage with
          Telnet, in addition to its normal usage.  It is used to

Lilienkamp & Mandell & Padlipsky [Page 45]

RFC 929 December 1984 Proposed Host-Front End Protocol

          control the option selection and negotiation process, when
          such selection is performed by the Host (currently, this is
          done at mediation levels 5 and 1, but not at level 9).
          A set of protocol-idiosyncratic parameters has been defined
          for this purpose.  They are based heavily on the Telnet
          negotiation and subnegotiation mechanisms.  For simple
          negotiations there are two parameters, a negotiation type
          (from the set {DO, DONT, WILL, WONT}) followed by the code
          (numeric) or name (symbolic) for the desired option.  The
          codes for the options are identified below.  A basic
          difference between the H-FP interface to Telnet and the
          internal Telnet protocol is that additional parameters are
          included with the request (DO or WILL). The Telnet protocol
          subnegotiation is used internally to communicate that
          information in the Telnet data stream.  Option-specific,
          protocol-idiosyncratic parameters are used for these
          additional parameters.
          Both the Host and the OPE can issue these Condition
          commands. When issued by the Host, it means the user wishes
          to enable or disable a particular option. The OPE proceeds
          to issue the appropriate negotiation commands (i.e., IAC
          <DO> <code>) in the Telnet data stream.  When the results of
          the option negotiation are available, a response is
          generated by the OPE.  For the types DO and WILL, a 000
          Response indicates the appropriate acceptance (WILL or DO,
          respectively). A nonzero Response code may indicate
          negotiation failure or negotiation rejection (among other
          things).  For the types DONT and WONT, a 000 Response
          indicates the option will be disabled.  A negotiation
          rejection should not be expected in those cases.
          When the Condition command is issued by the OPE, it means
          the other end of the connection is negotiating a change.
          Here the response from the Host indicates the Host's desired
          action for the option negotiation.  Again, valid requests to
          disable options (DONT and WONT requests) should always get a
          000 Response.
       2.3.2. Protocol-Idiosyncratic Parameters
          There are two protocol-idiosyncratic parameters for primary
          negotiation using the Condition command.  These are the
          negotiation type and the option code.  The negotiation type
          is one of the set of {DO, DONT, WILL, WONT}.  The option
          code is a numeric value used to identify the particular

Lilienkamp & Mandell & Padlipsky [Page 46]

RFC 929 December 1984 Proposed Host-Front End Protocol

          option being negotiated.  The values for these codes are
          indicated here, but are identical to the codes used in the
          actual Telnet negotiation.  The codes are:
             Option Name     Option Code       Short Name
             Transmit Binary           0       Binary
             Echo                      1       Echo
             Suppress Go-Ahead         3       SuppressGA
             Approximate Message Size  4       NAMS
             Status                    5       Status
             Timing Mark               6       TimingMark
             RCTE                      7       RCTE
             Line Length               8       LineLength
             Page Size                 9       PageSize
             Carriage Return Disp     10       CRDisp
             Horizontal Tabstops      11       HTabStops
             Horizontal Tab Disp      12       HTabDisp
             Formfeed Disposition     13       FFDisp
             Vertical Tabstops        14       VTabStops
             Vertical Tab Disposition 15       VTabDisp
             Linefeed Disposition     16       LFDisp
             Extended ASCII           17       ExASCII
             Logout                   18       Logout
             Data Entry Terminal      20       DET
             Terminal Type            24       TermType
             Extended options list   255       ExOptions
          Options not listed here may of course be used. The code
          number should be the same as the option code used in Telnet
          negotiation.
          2.3.2.1.  Simple Options
             Options that do not require additional parameters use the
             simple negotiation mechanisms described briefly above and
             in greater detail in the Telnet documentation.  No
             additional parameters are required.  These options
             include the Transmit Binary, Echo, Suppress Go Ahead,
             Status, Timing Mark, and Logout options.
          2.3.2.2.  Approximate Message Size Option
             The Approximate Message Size option requires two
             parameters. The first indicates whether the approximate
             message size being negotiated applies to the local or the
             remote end of the connection.  DS means the size applies

Lilienkamp & Mandell & Padlipsky [Page 47]

RFC 929 December 1984 Proposed Host-Front End Protocol

             to the sender of the command (i.e., if the Host issues
             the command, DS means the local end of the connection;
             if issued by the OPE, DS means the remote end of the
             connection).  DR means the size applies to the receiver
             of the command (i.e., if the Host issues the command, DR
             means the remote end;  if issued by the OPE, DR means the
             local end of the connection).  This convention is
             consistent with the Telnet subnegotiation mechanisms.
             The second character is an ASCII encoded numeric value,
             which is a character count of the message size.
       2.3.3. Line Width and Page Size Options
          The Line Width and Page Size Options require two additional
          parameters.  The first indicates whether the line width or
          page size being negotiated applies to the local or the
          remote end of the connection, and uses the DS and DR
          convention described above.  The second parameter is an
          ASCII encoded numeric value, which is interpreted as follows
          (assuming the Condition command was issued by the Host):
             0         The Host requests that it handle length or size
                       considerations for the direction indicated by
                       the first parameter.
             1 to 253  The Host requests that the remote end handle
                       the size or length considerations for the
                       direction indicated by the first parameter, but
                       suggests that the value indicated be used as
                       the size or length.
             254       The Host requests that the remote end handle
                       the size or length considerations for the
                       direction indicated by the first parameter, but
                       suggests that the size or length be considered
                       to be infinity.
             255       The Host requests that the remote end handle
                       the tabstop considerations, and suggests
                       nothing about what the value should be.
          If the Condition command is issued by the OPE, then the
          roles of the Host and the remote end are reversed.

Lilienkamp & Mandell & Padlipsky [Page 48]

RFC 929 December 1984 Proposed Host-Front End Protocol

       2.3.4. Tabstop Options
          The Horizontal and Vertical Tabstops options require two
          option specific parameters.  The first is either DR or DS,
          as was described previously.  The second is a list of one or
          more ASCII encoded numeric values separated by spaces which,
          assuming the Condition command is issued by the Host, are
          individually interpreted as:
             0         The Host requests that it handle tabstops for
                       the direction indicated by the first parameter.
             1 to 250  The Host requests that the remote end handle
                       the tabstop considerations for the direction
                       indicated by the first parameter, but suggests
                       that the value(s) indicated should be used as
                       the tabstops.
             255       The Host requests that the remote end handle
                       the tabstop considerations for the direction
                       indicated by the first parameter, and suggests
                       nothing about what the value should be.
          If the Condition command is issued by the OPE, then the
          roles of the Host and the remote end are reversed.
       2.3.5. Character Disposition Options
          The Carriage Return Disposition option, the Horizontal Tab
          Disposition option, the  Formfeed Disposition option, the
          Vertical Tab Disposition option, and the Linefeed
          Disposition option are all considered character disposition
          options from the perspective of H-FP.  Two option-specific
          parameters are required for the character disposition
          options.  The first is the DR or DS code, which was
          described previously. The second is a single ASCII encoded
          numeric value, which is interpreted as (assuming that the
          Host issued the Condition command):
             0         The Host requests that it handle the character
                       disposition for this connection.
             1 to 250  The Host suggests that the remote end handle
                       the character disposition considerations, but
                       suggests that the value indicated should be
                       taken as the number of nulls which should be

Lilienkamp & Mandell & Padlipsky [Page 49]

RFC 929 December 1984 Proposed Host-Front End Protocol

                       inserted in the data stream following the
                       particular format character being
                       subnegotiated.
             251       The Host suggests that the remote end handle
                       the character disposition considerations, but
                       recommends that it replace the character with
                       some simplified character similar to but not
                       identical with it (e.g., replace a tab with a
                       space, or a formfeed with a newline).
             252       The Host suggests that the remote end handle
                       the character disposition considerations, but
                       recommends that it discard the character.
             253       The Host suggests that the remote end handle
                       the character disposition, but recommends that
                       the effect of the character be simulated using
                       other characters such as spaces or linefeeds.
             254       The Host suggests that the remote end handle
                       the character disposition considerations, but
                       recommends that it wait for additional data
                       before sending more data.
             255       The Host suggests that the remote end handle
                       the tabstop considerations, and suggests
                       nothing about what the value should be.
          Some of the codes between 251 and 254 are not used with some
          character disposition options. Refer to the ARPANET
          documentation for additional details.
          If the Condition command is issued by the OPE, then the
          roles of the Host and the remote end are reversed.
          2.3.5.1.  RCTE Option
             The Remote Controlled Transmission and Echoing option
             requires parameters to indicate the sets of break
             characters and transmit characters.  There are two
             option-idiosyncratic parameters for RCTE.  The first is a
             list of the character classes that make up the set of
             break characters, as defined in the RCTE documentation.
             The second is a list of character classes that make up
             the set of transmit characters, as defined in the RCTE
             documentation.  Since the two classes are optional and

Lilienkamp & Mandell & Padlipsky [Page 50]

RFC 929 December 1984 Proposed Host-Front End Protocol

             can be of arbitrary length, it is necessary to precede
             each list with a -bc (break characters) or -tc (transmit
             characters). The character classes are defined as
                1 Upper Case Letters   A through Z
                2 Lower Case Letters   a through z
                3 Digits  0 through 9
                4 Format effectors  <BS> <CR> <LF> <FF> <HT> <VT>
                5 Non-format control codes, plus <ESC> and <DEL>
                6 Punctuation  . , ; : ? !
                7 Grouping    { [ ( < > ) ] }
                8 Misc  ' ` " / \ % @ $ &   + - * = ^ _ | ~
                9 <space>
          2.3.5.2.  Extended Option List
             The Extended Option List option requires a parameter to
             carry the number of the option on the extended list.
             There is thus one option specific parameter to the
             Condition command when used for this purpose, which is
             the number of the option on the extended option list.  It
             can be expressed in ASCII using an octal, decimal, or
             hexadecimal format.
          2.3.5.3.  Terminal Extension Options
             The Extended ASCII, SUPDUP, and Data Entry Terminal
             options of Telnet were all attempts to extend the basic
             capabilities of the Telnet data stream beyond the simple,
             scroll mode terminal model that was the basis of the
             original Telnet design.
             All of these options have limitations to their
             effectiveness.  The Extended ASCII option lacks a
             standardized interpretation of the bit patterns into
             extended ASCII characters.  The SUPDUP effort was
             actually an independent mode where a different virtual
             terminal protocol was used, and the option was there
             merely to switch to and from this protocol. The Data
             Entry Terminal option requires the excessive overhead of
             subnegotiation for each use of extended features.  All of
             these options lack the more valuable asset of widespread
             implementation and use.
             The way these options should be handled is not detailed
             in this appendix. It is clear that the Condition command
             could be used for initiating and terminating the use of

Lilienkamp & Mandell & Padlipsky [Page 51]

RFC 929 December 1984 Proposed Host-Front End Protocol

             these options.  The actual transmission of characters
             related to the extended terminal features should be
             provided by the Transmit command, either as part of the
             normal Host-to-OPE data stream or by using
             protocol-idiosyncratic parameters.
             A more recent option, the Terminal Type option, should be
             mentioned here.  It permits one end of a connection to
             request information about the terminal at the other end
             or send information about the terminal at the local end.
             This is convenient for systems that provide a wide
             variety of terminal support, but it clearly does not
             follow the model of reducing the MxN problem by use of a
             virtual terminal. Its use is very straightforward in the
             H-FP context.  It only requires sending the terminal type
             to the other end, and activating the Binary Transmission
             Option.
          2.3.5.4.  Status Option
             The Status option is enabled using the negotiation
             mechanism of Telnet.  However, the means to transfer
             status information between OPE and the Host is provided
             via the Status command.  Therefore, details of status
             negotiation are irrelevant to the interface to the
             outboard Telnet.
       2.3.6. Examples of the Command
          The following example shows the command issued by a Host to
          the OPE, requesting that the OPE negotiate with the other
          side so that remote echo is performed.
             C CO -pi DO 1 <nl>
          The numeral 1 is the option code for ECHO from the table
          above. All of the simple options listed above use this same
          basic format.
          The options with additional parameters use straightforward
          extensions of this syntax.  For example, a possible usage of
          Condition by the Host to set the approximate message size
          is:
             C CO -pi DO 4 DS 1024

Lilienkamp & Mandell & Padlipsky [Page 52]

RFC 929 December 1984 Proposed Host-Front End Protocol

          The 4 is the Option Code for the Approximate Message Size
          option, the DS indicates that Host's message size should be
          set, and 1024 is the desired size.
    2.4.  The Signal Command
       The Signal command is used with Telnet to provide the Telnet
       Interrupt Process and Abort Output services.
       2.4.1. Specialized Usage
          The Signal command is used with an outboard Telnet
          interpreter to interface to the Telnet synch mechanism.
          This mechanism is used with a protocol-idiosyncratic
          parameter, which indicates what particular command is being
          "synched." It is expected that normally, this Signal
          mechanism will only be used with the Interrupt Process and
          Abort Output Telnet signals.  When the Signal command is
          issued by the Host, it goes through the Channel
          (out-of-band) to the OPE, where the Telnet interpreter
          issues the corresponding Telnet signal and synch sequence.
          When such a sequence is received by the OPE, it immediately
          issues a Signal to the Host.  It is expected that a Host or
          OPE would not, in general, reject the Signal command unless
          it is badly formed.
       2.4.2. Protocol-Idiosyncratic Parameters
          The Telnet protocol-idiosyncratic parameter used with the
          Signal command identifies which Telnet signal is begin
          issued.  Normally, it would have the value of either "IP" or
          "AO", for Interrupt Process or Abort Output.  If absent, the
          default value is "IP".
       2.4.3. Examples of the Command
          An example of a Telnet Signal Command (in this case, to send
          an Interrupt Process signal) is:
             C SI IP <nl>

Lilienkamp & Mandell & Padlipsky [Page 53]

RFC 929 December 1984 Proposed Host-Front End Protocol

    2.5.  The Status Command
       The Status command is used with Telnet to obtain information
       about the Telnet connection and the options in effect.
       2.5.1. Specialized Usage
          The Status command has one specialized aspect when used to
          interface to an outboard Telnet interpreter.  That is to
          send and receive the Telnet Protocol status request
          subnegotiation message to and from the data stream.  In
          order to invoke the status command for this purpose,
          however, the user must have previously issued the Condition
          Status command, which causes the ability to request status
          to be negotiated.  The OPE, when it receives a valid Status
          request command, immediately responds to the user indicating
          the status.  The OPE can issue a status to request the
          Host's negotiated positions.
       2.5.2. Protocol-Idiosyncratic Parameters
          There are no protocol-idiosyncratic parameters to the Status
          query command. The Status Response command has a single
          protocol-idiosyncratic parameter.  It is an ASCII string
          containing the status of the various options (not at their
          default values).
       2.5.3. Examples of the Command
          An example of a Status Query command is:
             C ST Q
          An example of a Status Response command is:
             F ST R "WILL ECHO  DO SUPPRESS-GO-AHEAD
             L WILL STATUS  DO STATUS" <nl>
          In the previous example, note the opening quote is in the
          first chunk, and the closing quote is in the last chunk.
          This technique permits parameters to span chunk boundaries.

Lilienkamp & Mandell & Padlipsky [Page 54]

RFC 929 December 1984 Proposed Host-Front End Protocol

    2.6.  The End Command
       The End command is used to terminate the Telnet connection,
       either gracefully or abruptly.
       2.6.1. Specialized Usage
          The graceful termination of a Telnet requires End commands
          to be issued by both the Host and the OPE.  This specialized
          usage is identical to that of the outboard TCP interface,
          however.
       2.6.2. Examples of the Command
          An example of the graceful End command is:
             C EN G <nl>
          The abrupt End command is similar.
    2.7.  The No-op Command
       The No-op command is used with Telnet so the Host can determine
       if the OPE is active, and vice versa.
       2.7.1. Specialized Usage
          The No-op command has one specialized usage when offloading
          Telnet.  This is to provide the Telnet Are You There (AYT)
          feature.  When an (AYT) message is received by the OPE, it
          issues a No-op command to the Host. Upon receiving the
          response from the Host, the appropriate response is sent
          back in the data stream.
       2.7.2. Protocol Idiosyncratic Parameters
          There are no protocol-idiosyncratic parameters to the No-op
          command.
       2.7.3. Examples of the Command
          An example of the No-op command is:
             C NO <nl>

Lilienkamp & Mandell & Padlipsky [Page 55]

RFC 929 December 1984 Proposed Host-Front End Protocol

 3. FTP Offloading
    TBS
 4. Mail Offloading
    TBS
 5. Whatever Offloading
    TBS
 Where TBS nominally = To Be Supplied, but really means: We'll argue
 through these once we get sufficiently positive feedback on the
 others (and on the H-FP as a whole).

Lilienkamp & Mandell & Padlipsky [Page 56]

/data/webs/external/dokuwiki/data/pages/rfc/rfc929.txt · Last modified: 1992/09/22 21:03 by 127.0.0.1

Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki