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rfc:std:std45

Network Working Group K. Hardwick Request for Comments: 1044 NSC

                                                          J. Lekashman
                                                          NASA-Ames GE
                                                         February 1988
         Internet Protocol on Network Systems HYPERchannel
                       Protocol Specification

STATUS OF THIS MEMO

 The intent of this document is to provide a complete discussion of
 the protocols and techniques used to embed DoD standard Internet
 Protocol datagrams (and its associated higher level protocols) on
 Network Systems Corporation's HYPERchannel [1] equipment.
 Distribution of this memo is unlimited.
 This document is intended for network planners and implementors who
 are already familiar with the TCP/IP protocol suite and the
 techniques used to carry TCP/IP traffic on common networks such as
 the DDN or Ethernet.  No great familiarity with NSC products is
 assumed; an appendix is devoted to a review of NSC technologies and
 protocols.
 At the time of this first RFC edition, the contents of this document
 has already been reviewed by about a dozen vendors and users active
 in the use of TCP/IP on HYPERchannel media.  Comments and suggestions
 are still welcome (and implementable,) however.
 Any comments or questions on this specification may be directed to:
    Ken Hardwick
    Director, Software Technology
    Network Systems Corporation MS029
    7600 Boone Avenue North
    Brooklyn Park, MN 55428
    Phone: (612) 424-1607
    John Lekashman
    Nasa Ames Research Center. NAS/GE
    MS 258-6
    Moffett Field, CA, 94035
    lekash@orville.nas.nasa.gov
    Phone: (415) 694-4359

Hardwick & Lekashman [Page 1] RFC 1044 IP on Network Systems HYPERchannel February 1988

TABLE OF CONTENTS

  Status of this memo  . . . . . . . . . .  . . . . . . . . . . . .  1
  Goals of this document   . . . . . . . .  . . . . . . . . . . . .  3
  Basic HYPERchannel network messages  . .  . . . . . . . . . . . .  4
    Basic (16-bit address) Message Proper header  . . . . . . . . .  5
    TO addresses and open driver architecture   . . . . . . . . . .  7
    Extended (32-bit address) Message Proper header . . . . . . . .  8
    Address Recognition and message forwarding .  . . . . . . . . . 10
    32-bit message fields   . . . . . . . . . . . . . . . . . . . . 12
  Broadcasting   . . . . . . . . . . . . . . . . . .  . . . . . . . 14
  PROTOCOL SPECIFICATION .  .  .  . . . . . . . . . . . . . . . . . 17
    Basic (16-bit) Message Encapsulation    . . . . . . . . . . . . 18
    Compatibility with existing implementations . . . . . . . . . . 21
    Extended (32-bit) Message Encapsulation   . . . . . . . . . . . 24
    Address Resolution Protocol   . . . . . . . . . . . . . . . . . 27
    Maximum Transmission Unit . . . . . . . . . . . . . . . . . . . 31
  ADDRESS RESOLUTION    . . . . . . . . . . . . . . . . . . . . . . 32
    Local Address Resolution  . . . . . . . . . . . . . . . . . . . 33
    Configuration file format   . . . . . . . . . . . . . . . . . . 34
    ARP servers   . . . . . . . . . . . . . . . . . . . . . . . . . 35
    Broadcast ARP   . . . . . . . . . . . . . . . . . . . . . . . . 36
  Appendix A.
  NSC Product Architecture and Addressing   . . . . . . . . . . . . 38
  Appendix B.
  Network Systems HYPERchannel protocols    . . . . . . . . . . . . 42

Hardwick & Lekashman [Page 2] RFC 1044 IP on Network Systems HYPERchannel February 1988

GOALS OF THIS DOCUMENT

 In this document, there are four major technical objectives:
 1.  To bless a "de facto" standard for IP on HYPERchannel that  has
     been implemented by Tektronix, Cray, NASA Ames, and others.
     We are attempting to resolve some interoperability problems with
     this standard so as to minimize the changes to existing IP on
     HYPERchannel software.  If any ambiguities remain in the de facto
     standard, we wish to assist in their resolution.
 2.  To address larger networks, NSC's newer network products are
     moving to a 32-bit address from the current 16-bit TO address.
     This document would introduce the addressing extension to the
     user community and specify how IP datagrams would work in the
     new addressing mode.
 3.  To define an Address Resolution Protocol for HYPERchannel and
     other NSC products.  It is probably well known that current NSC
     products do not support the broadcast modes that make ARP
     particularly useful.  However, many have expressed interest in
     "ARP  servers" at a known network address.  These servers could
     fade away as NSC products with broadcast capability come into
     existence.  Host drivers that can generate and recognize this
     ARP protocol would be prepared to take advantage of it as the
     pieces fall into place.
 4.  Part of this effort is to standardize the unofficial "message
     type" field that reserves byte 8 of the HYPERchannel network
     message.  To permit better interoperability, NSC will initiate a
     "network protocol registry" where any interested party may
     obtain a unique value in byte 8 (or bytes 8 and 9) for their own
     public, private, commercial or proprietary protocol.  Lists of
     assigned protocol type numbers and their "owners" will be
     periodically published by NSC and would be available to
     interested parties.

Hardwick & Lekashman [Page 3] RFC 1044 IP on Network Systems HYPERchannel February 1988

BASIC HYPERCHANNEL NETWORK MESSAGES

 Unlike most datagram delivery systems, the HYPERchannel network
 message consists of two parts:
           Message Proper
          +--------------------+
          |                    |
          |                    |
          |     10-64 bytes    |
          |                    |
          |                    |
          +--------------------+
           Associated Data
          +----------------------------------------------------+
          |                                                    |
          |                                                    |
          |                                                    |
          |                                                    |
          |           Unlimited length                         |
          |                                                    |
          |                                                    |
          |                                                    |
          |                                                    |
          +----------------------------------------------------+
 The first part is a message header that can be up to 64 bytes in
 length.  The first 10 bytes contain information required for the
 delivery of the entire message, and the remainder can be used by
 higher level protocols.  The second part of the message, the
 "Associated Data," can be optionally included with the message
 proper.  In most cases (transmission over HYPERchannel A trunks), the
 length of the associated data is literally unlimited.  Others (such
 as HYPERchannel B or transmission within a local HYPERchannel A A400
 adapter) limit the size of the Associated Data to 4K bytes.  If the
 information sent can be contained within the Message Proper, then the
 Associated Data need not be sent.
 HYPERchannel lower link protocols treat messages with and without
 Associated Data quite differently; "Message only" transmissions are
 sent using abbreviated protocols and can be queued in the receiving
 network adapter, thus minimizing the elapsed time needed to send and
 receive the messages.  When associated data is provided, the
 HYPERchannel A adapters free their logical resources towards driving
 the host interface and coaxial trunks.

Hardwick & Lekashman [Page 4] RFC 1044 IP on Network Systems HYPERchannel February 1988

BASIC (16-BIT ADDRESS) MESSAGE PROPER HEADER

 The first 10 bytes of the network Message Proper are examined by the
 network adapters to control delivery of the network message.  Its
 format is as follows:
  byte   Message Proper
       +------------------------------+-----------------------------+
    0  |      Trunks to Try           |        Message Flags        |
       |   TO trunks  |  FROM trunks  |                 |EXC|BST|A/D|
       +--------------+---------------+-----------------+---+---+---+
    2  |                        Access code                         |
       |                                                            |
       +------------------------------+-----------------------------+
    4  |       Physical addr of       |                   | TO Port |
       |     destination adapter (TO) |                   | number  |
       +------------------------------+-----------------------------+
    6  |  Physical addr of source     |                   |FROM port|
       |        adapter (FROM)        |                   |  number |
       +------------------------------+-----------------------------+
    8  |                        Message type                        |
       |                                                            |
       +------------------------------+-----------------------------+
   10  |                                                            |
       |            Available for higher level protocols            |
       |                                                            |
       |                                                            |
       +------------------------------+-----------------------------+

TRUNKS TO TRY

 Consists of two four bit masks indicating which of four possible
 HYPERchannel A coaxial data trunks are to be used to transmit the
 message and to return it.  If a bit in the mask is ON, then the
 adapter firmware will logically AND it with the mask of installed
 trunk interfaces and use the result as a candidate list of
 interfaces.  Whenever one of the internal "frames" are sent to
 communicate with the destination adapter, the transmission hardware
 electronically selects the first non-busy trunk out of the list of
 candidates.  Thus, selection of a data trunk is best performed by the
 adapter itself rather than by the host.  "Dedicating" trunks to
 specific applications only makes sense in very critical real time
 applications such as streaming data directly from high speed
 overrunnable peripherals.
 A second Trunk mask is provided for the receiving adapter when it
 sends frames back to the transmitter, as it is possible to build
 "asymmetric" configurations of data trunks where trunk 1 on one box

Hardwick & Lekashman [Page 5] RFC 1044 IP on Network Systems HYPERchannel February 1988

 is connected to the trunk 3 interface of a second.  Such
 configurations are strongly discouraged, but the addressing structure
 supports it if needed.
 The "trunks to try" field is only used by HYPERchannel A.  To assure
 maximum interoperability, a value of 0xFF should be placed in this
 field to assure delivery over any technology.  Other values should
 only be used if the particular site hardware is so configured to not
 be physically connected via those trunks.

MESSAGE FLAGS

 Contains options in message delivery.  In the basic type of message,
 three bits are used:
 ASSOCIATED DATA PRESENT (A/D) is ON if an Associated Data block
 follows the Message Proper.  0 if only a message proper is present in
 the network message.  The value of this bit is enforced by the
 network adapter firmware.
 BURST MODE (BST) Enables a special mode for time critical transfers
 where a single HYPERchannel A coaxial trunk is dedicated during
 transmission of the network message.  Not recommended for anything
 that won't cause peripheral device overruns if data isn't delivered
 once message transmission starts.
 EXCEPTION (EXC) Indicates to some channel programmed host interfaces
 that the message is "out of band" in some way and requires special
 processing.

ACCESS CODE

 A feature to permit adapters to share use of a cable yet still permit
 an "access matrix" of which adapter boxes and physically talk to
 which others.  Not currently in use by anyone, support is being
 discontinued.

TO ADDRESS

 Consists of three parts.  The high order 8-bits contains the physical
 address of the network adapter box which is to receive the message.
 The low order 8-bits are interpreted in different ways depending on
 the nature of the receiving network adapter.  If the receiving
 adapter has different host "ports," then the low order bits of the TO
 field are used to designate which interface is to receive the
 message.  On IBM data channels, the entire "logical" TO field is
 interpreted as the subchannel on which the incoming data is to be
 presented.  Parts of the logical TO field that are not interpreted by

Hardwick & Lekashman [Page 6] RFC 1044 IP on Network Systems HYPERchannel February 1988

 the network adapter are passed to the host for further
 interpretation.

FROM ADDRESS

 The FROM address is not physically used during the process of
 transmitting a network message, but is passed through to the
 receiving host so that a response can be returned to the point of
 origin.  In general, reversing the TO and FROM 16-bit address fields
 and the TO and FROM trunk masks can reliably return a message to its
 destination.

MESSAGE TYPE

 The following two bytes are reserved for NSC.  Users have been
 encouraged to put a zero in byte 8 and anything at all in byte 9 so
 as to not conflict with internal processing of messages by NSC
 firmware.  In the past, this field has been loosely defined as
 carrying information of interest to NSC equipment carrying the
 message and not as a formal protocol type field.  For example, 0xFF00
 in bytes 8 and 9 of the message will cause the receiving adapter to
 "loop back" the message without delivering it to the attached host.
 Concurrent with this document, it is NSC's intent to use both bytes 8
 and 9 as a formal "protocol type" designator.  Major protocols will
 be assigned a unique value in byte 8 that will (among good citizens)
 not duplicate a value generated by a different protocol.  Minor
 protocols will have 16-bit values assigned to them so that we won't
 run out when 256 protocols turn up.  Any interested party could
 obtain a protocol number or numbers by application to NSC.  In this
 document, protocol types specific to IP protocols are assigned.

TO ADDRESSES AND OPEN DRIVER ARCHITECTURE

 Since not all 16-bits of the TO address are used for the physical
 delivery of the network message, the remainder are considered
 "logical" in that their meaning is physically determined by host
 computer software or (in cases such as the FIPS data channel) by
 hardware in the host interface.
 Since HYPERchannel is and will be used to support a large variety of
 general and special purpose protocols, it is desirable that several
 independent protocol servers be able to independently share the
 HYPERchannel network interface.  The implementation of many of NSC's
 device drivers as well as those of other parties (such as Cray
 Research) support this service.  Each protocol server that wishes to
 send or receive HYPERchannel network messages logically "connects" to
 a HYPERchannel device driver by specifying the complete 16-bit TO

Hardwick & Lekashman [Page 7] RFC 1044 IP on Network Systems HYPERchannel February 1988

 address it will "own" in the sense that any network message with that
 TO address will be delivered to that protocol server.
 The logical TO field serves a function similar to the TYPE byte in
 the Ethernet 802.2 message header, but differs from it in that the
 width of the logical TO field varies from host to host, and that no
 values of the logical TO address are reserved for particular
 protocols.  On the other hand, it is possible to have several
 "identical" protocols (such as two independent copies of IP with
 different HYPERchannel addresses) sharing the same physical
 HYPERchannel interface.  This makes NSC's addressing approach
 identical to the OSI concept that the protocol server to reach is
 embedded within the address, rather than the IP notion of addressing
 a "host" and identifying a server through a message type.
 Since the HYPERchannel header also has a "message type" field, there
 is some ambiguity concerning the respective roles of the message type
 and logical TO fields:
  o   The logical TO field is always used to identify the protocol
      server which will receive the message.  Once a server has
      specified the complete TO address for the messages it wishes to
      receive, the message will not be delivered to a different
      protocol server regardless of the contents of the message type
      field.
  o   Although the "type" field cannot change the protocol server at
      the final destination of the message, the type field can be used
      by intermediate processes on the network to process the message
      before it reaches the server destination.  An obvious example is
      the 0xFF00 message loopback type function, where network
      processing to loop back the message results in nondelivery to
      the TO address.  In the future, intermediate nodes may process
      "in transit" messages based on the message type only for
      purposes such as security validation, aging of certain
      datagrams, and network management.

EXTENDED (32-BIT ADDRESS) MESSAGE PROPER HEADER

 In the original days of HYPERchannel, the limitation of 256 adapter
 "boxes" that could be addressed in a network message was deemed
 sufficient as 40 or so adapters was considered a "large" network.  As
 with the Ethernet, more recent networks have resulted in a need to
 address larger networks.  Although a few ad hoc modes have existed to
 address larger HYPERchannel networks for some years, newer
 technologies of HYPERchannel equipment have logically extended the
 network message to support 32-bits of addressing, with 24 of those
 bits to designate a physical network adapter.

Hardwick & Lekashman [Page 8] RFC 1044 IP on Network Systems HYPERchannel February 1988

 This 32-bit header has been designed so that existing network
 adapters are capable of sending and receiving these messages.  Only
 the network bridges need the intelligence to select messages
 designated for them.

Hardwick & Lekashman [Page 9] RFC 1044 IP on Network Systems HYPERchannel February 1988

      +------------------------------+-----------------------------+
   0  |      Trunks to Try           |        Message Flags        |
      |   TO trunks  |  FROM trunks  |GNA|CRC|     |SRC|EXC|BST|A/D|
      +--------------+---------------+---+---+--+--+---+---+---+---+
   2  |         TO Domain #          |         TO Network #        |
      |                              |                             |
      +------------------------------+-----------------------------+
   4  |O|    Physical addr of        |                   | TO Port |
      |N|  destination adapter (TO)  |                   | number  |
      +------------------------------+-----------------------------+
   6  |O| Physical addr of source    |                   |FROM port|
      |N|     adapter (FROM)         |                   |  number |
      +------------------------------+-----------------------------+
   8  |                         Message type                       |
      |                                                            |
      +------------------------------+-----------------------------+
   10 |          FROM Domain #       |       FROM Network #        |
      |                              |                             |
      +------------------------------+-----------------------------+
   12 |          - reserved -        |         age count           |
      |                              |                             |
      +------------------------------+-----------------------------+
   14 |      Next Header Offset      |      Header End Offset      |
      |        (normally 16)         |        (normally 16)        |
      +------------------------------+-----------------------------+
   16 |                  Start of user protocol                    |
      |              bytes 16 - 64 of message proper               |
      |                                                            |
      +------------------------------+-----------------------------+
        Associated Data
 +-----------------------------------------------------------------+
 |                                                                 |
 |     As with basic format network messages                       |
 |                                                                 |
 +-----------------------------------------------------------------+

ADDRESS RECOGNITION AND MESSAGE FORWARDING

 With the 32-bit form of addressing, NSC is keeping with the premise
 that the native HYPERchannel address bears a direct relation to the
 position of the equipment in an extended HYPERchannel network.
 Each collection of "locally" attached NSC network adapters that are
 connected by coax or fiber optic cable (with the possible addition of
 nonselective repeaters such as the ATRn series) is considered a
 "network".  Each network can have up to 256 directly addressable
 adapters attached to it which can be reached by the basic format

Hardwick & Lekashman [Page 10] RFC 1044 IP on Network Systems HYPERchannel February 1988

 network message.
 Existing bridges or "link adapters" can be programmed to become
 "selective repeaters" in that they can receive network messages
 containing a subset of network addresses send them over the bridge
 medium (if present) and reintroduce them on the other network.  Such
 interconnected local area networks are considered a single network
 from an addressing point of view.
 A large NSC network can have up to 64K networks which can be
 complexly interconnected by network bridges and/or "backbone"
 networks which distribute data between other networks.  To simplify
 the mechanics of message forwarding, the 16-bit network field is
 divided into two eight quantities, a "network number" identifying
 which network is to receive the message and a "domain number" which
 specifies which network of networks is the recipient.
 The bridge technology adapters which move messages between networks
 have address recognition hardware which examines all the 24-bits in
 bytes 2-5 of the network message header to determine if the bridge
 should accept the message for forwarding.  At any given instant of
 time in the network, each bridge will have a list of networks and
 domains that it should accept for forwarding to a network at the
 other end of the bridge.  Each Adapter (Including Newer Technology
 host adapters) contains in address recognition hardware:
  o   domainmask -- a 256-bit mask of domain numbers that should  be
      accepted for forwarding (not local processing) by this adapter.
  o   MyDomain  --  the  value  of the domain on which this host
      adapter or bridge end is installed.
  o   NetworkMask -- a 256-bit mask of network numbers that should be
      accepted for forwarding by this adapter.
  o   MyNetwork  -  the  value of the network on which this host
      adapter or bridge end is installed.
  o   AddressMask -- A 256-bit mask of the local network addresses
      that should be accepted by the adapter.
  o   MyAddress -- the "base address" of the box, which must be
      supplied in any message that is directed to control processes
      within the adapter, such as a loopback message.
 Address recognition takes place using the algorithm:
         IF Domain IN DomainMask OR
            IF (Domain = MyDomain AND Network IN NetworkMask) OR
               IF (Domain = MyDomain AND Network = MyNetwork AND
                  Address IN AddressMask) THEN accept-message
                                          ELSE ignore-message.

Hardwick & Lekashman [Page 11] RFC 1044 IP on Network Systems HYPERchannel February 1988

 This algorithm means that an adapter's hardware address recognition
 logic will accept any messages to the box itself, any secondary or
 aliased local addresses owned by the adapter, and any message
 directed to a remote network or domain that that particular adapter
 is prepared to forward.

32-BIT MESSAGE FIELDS

TRUNK MASK

 Is as in the basic network message.  Messages that are to be
 delivered outside the immediate network should have 0xFF in this byte
 so that all possible trunks in intermediate networks should be tried.
 Locally delivered 32-bit messages may still contain specially
 tailored trunk masks to satisfy local delivery needs.

MESSAGE FLAGS

 The currently defined bits remain as before.  Three new bits have
 been defined since that time.
 CRC (END-END MESSAGE INTEGRITY).  Newer technology host adapters are
 capable of generating a 32-bit CRC for the entire network message as
 soon as it is received over the channel or bus interface from the
 host.  This 32-bit CRC is appended to the end of the associated data
 block and is preserved through the entire delivery process until it
 is checked by the host adapter that is the ultimate recipient of the
 message, which removes it.  This end to end integrity checking is
 designed to provide a high degree of assurance that data has been
 correctly moved through all intermediate LAN's, geographic links, and
 internal adapter hardware and processes.
 SRC (SOURCE FROM ADDRESS CORRECT).  This bit is provided to take
 advantage of the physical nature of the network address to optionally
 verify that the 32-bit FROM address provided in the network message
 is in fact the location that the message originated.  If the bit is
 not set by the transmitting host, no particular processing occurs on
 the message.  If the bit is set, then all intermediate adapters
 involved in the delivery of the message have the privilege of turning
 the bit off if the received message FROM address is not a TO address
 that would be delivered to the originator if the message were going
 the opposite direction.
 If the message is received by a host computer with this bit still
 set, then the FROM address is guaranteed correct in the sense that
 returning a message with TO and FROM information reversed will result
 in delivery of the message to the process that actually originated

Hardwick & Lekashman [Page 12] RFC 1044 IP on Network Systems HYPERchannel February 1988

 it.  By careful attention to the physical security of adapters and
 intermediate links between networks, a high degree of security can be
 built into systems that simply examine the FROM address of a message
 to determine the legitimacy of its associated request.
 GNA (GLOBAL NETWORK ADDRESSING).  This bit ON indicates that 32-bit
 addressing is present in the message.  When this bit is on, bytes 2-3
 (Domain and Network numbers) should also be nonzero.

TO ADDRESS

 Four bytes contain the TO address, which is used to deliver the
 network message as described in "Address Recognition and Message
 Forwarding" on page 8.  The "logical" part of the TO address is used
 to designate a protocol server exactly as in the basic format network
 message header.
 The existing "address" field has its high order bit reserved as an
 outnet bit for compatibility with existing A-series network adapter
 equipment.  Were it not for this bit, the A-series adapters would
 attempt to accept messages that were "passing through" the local
 network on their way elsewhere simply because the address field
 matched while the the Domain and Network numbers (ignored by the A-
 series adapters) were quite different.
 This "outnet" bit is used in the following way:
  o   All network adapters (of  any type) in an extended set of
      networks containing A-Series adapters that will ever use 32-bit
      addressing must have their addresses in the range 00-7F (hex.)
  o   If a message is to be sent to a destination on a nonlocal
      network and domain on such an extended network, then the
      high order bit of the address field is turned on.
  o   When the last bridge in the chain realizes that it is about to
      forward the message to its final destination (the Domain and
      Network numbers are local), then it turns the Outnet bit off.
      This will result in local delivery to the destination adapter.

FROM ADDRESS

 The FROM address follows the same logic as the TO address in that any
 message can be returned to its source by reversing the FROM and TO
 fields of the message.  Since so many protocols examine byte 8 of the
 message to determine its type, the FROM field has been split so that
 the Domain and Network numbers extend into bytes 10-11.

Hardwick & Lekashman [Page 13] RFC 1044 IP on Network Systems HYPERchannel February 1988

MESSAGE TYPE

 This field (informally defined in the past) has been extended to 16-
 bits so that a unique value can be assigned to any present or future
 protocol which is layer on HYPERchannel messages for either private
 or public use.

AGE COUNT

 This field serves the same purpose as the IP "time to live" in that
 it prevents datagrams from endlessly circulating about in an
 improperly configured network.  Each time a 32-bit message passes
 through a bridge, the Age Count is decremented by one.  When the
 result is zero, the message is discarded by the bridge.

NEXT HEADER OFFSET AND HEADER END OFFSET

 These are used as fields to optionally provide "loose source
 routing", where a list of 32-bit TO addresses can be provided by the
 transmitter to explicitly determine the path of a message through the
 network.  If this feature is not used, both these fields would
 contain the value 16 (decimal) to both indicate extra TO addresses
 are absent and that the beginning of protocol data following the
 HYPERchannel header is in byte 16.
 Although it is conceivable that a HYPERchannel IP process could use
 this source routing capability to direct messages to hosts or
 gateways, this capability is not felt to be of sufficient value to IP
 to build it into a HYPERchannel IP protocol.
 In the future, all higher level protocols should be able to examine
 Header End Offset to determine the start of the higher level protocol
 information.

BROADCASTING

 NSC message forwarding protocols use low level link protocols to
 negotiate transmission of a message to its next destination on the
 network.  Furthermore, NSC network boxes often "fan out" so that
 several hosts share the same network transmission equipment as in the
 A400 adapter.  Both these characteristics mean that providing a
 genuine broadcast capability is not a trivial task, and in fact no
 current implementations of NSC technology support a broadcast
 capability.
 The last several years have seen broadcast applications mature to the
 point where they have virtually unquestioned utility on a local and
 sometimes campuswide basis.  Accordingly, new NSC technologies will

Hardwick & Lekashman [Page 14] RFC 1044 IP on Network Systems HYPERchannel February 1988

 support a broadcast capability.  Information on the use of this
 capability is included here as it is essential to the discussion of
 the Address Resolution Protocol later in this document.
 Broadcast capability will be supported only with the extended (32-bit
 address) message format.  A broadcast message will have the following
 general appearance:
  byte   Message Proper
       +------------------------------+-----------------------------+
    0  |      Trunks to Try           |        Message Flags        |
       |   TO trunks  |  FROM trunks  |GNA|CRC|     |SRC|EXC|BST|A/D|
       +--------------+---------------+---+---+--+--+---+---+---+---+
    2  |       TO Domain Number       |      TO Network Number      |
       |          or 0xFF             |          or 0xFF            |
       +------------------------------+-----------------------------+
    4  |           0xFF               |   Broadcast channel number  |
       |                              |                             |
       +------------------------------+-----------------------------+
    6  |O| Physical addr of source    |                   |FROM port|
       |N|     adapter (FROM)         |                   |  number |
       +------------------------------+-----------------------------+
    8  |                         Message type                       |
       |                                                            |
       +------------------------------+-----------------------------+
    10 |     FROM Domain Number       |    FROM Network Number      |
       |                              |                             |
       +------------------------------+-----------------------------+
    12 |          - reserved -        |         age count           |
       |                              |                             |
       +------------------------------+-----------------------------+
    14 |      Next Header Offset      |      Header End Offset      |
       |        (normally 16)         |        (normally 16)        |
       +------------------------------+-----------------------------+
    16 |                  Start of user protocol                    |
       |              bytes 16 - 64 of message proper               |
       |                                                            |
       +------------------------------+-----------------------------+
        Associated Data
  +-----------------------------------------------------------------+
  |                                                                 |
  |     As with basic format network messages                       |
  |     Maximum associated data size 1K bytes.                      |
  |                                                                 |
  +-----------------------------------------------------------------+

Hardwick & Lekashman [Page 15] RFC 1044 IP on Network Systems HYPERchannel February 1988

TRUNKS TO TRY AND MESSAGE FLAGS

 These fields are defined just as with a normal 32-bit message.  All
 bits in the Message Flags field are valid with broadcast modes.

BROADCAST ADDRESS

 For Domain, Network and Adapter Address fields, the value 0xFF is
 reserved for use by the broadcast mechanism.  A value of 0xFF in the
 adapter address field indicates to the local network hardware that
 this message is to be sent to all connected network equipment on the
 individual network.
 A value of 0xFF in the network or domain fields, respectively
 indicates a request that the scope of the broadcast exceed the local
 network.  The bridging link adapters will receive the broadcast
 message along with everyone else and will examine the "Broadcast
 Channel" field and their internal switches to determine if the
 message should be forwarded to other remote networks.
 If the Network and Domain fields contain the local network and
 domain, then the broadcast message will only be broadcast within the
 local network.  If a remote Network and Domain is specified, then the
 message will be delivered as a single message to the remote network
 and broadcast there.

BROADCAST CHANNEL

 Since individual hosts and protocol servers generally are not
 interested in all broadcast messages that float about the network, a
 filtering mechanism is provided in the header and network adapter
 equipment so that only proper classes of broadcast messages are
 delivered to the end point.
 Broadcast channel numbers in the range 00-0xFF will be assigned by
 NSC much like the "message type" field.  Host protocol servers
 specify a specific TO address containing a channel number (such as
 0xFF04) when they bind themselves to the HYPERchannel device driver.
 The driver and the underlying equipment will deliver only broadcast
 messages with the correct channel number to the protocol server.  If
 a protocol server wishes to receive several different broadcast
 messages, it must bind itself to the driver several times with the
 desired addresses.
 Link adapters that are prepared to handle multinetwork broadcast
 messages may be equipped with switches to determine which broadcast
 channels will be propagated into the next network.  Since
 multinetwork broadcast is an arrangement that must be configured with

Hardwick & Lekashman [Page 16] RFC 1044 IP on Network Systems HYPERchannel February 1988

 care, these switches are off by default.

FROM ADDRESS

 The FROM address is constructed just as with a normal 32-bit network
 message.  The Source Address Correct bit is processed just as with a
 normal message.

MESSAGE TYPE

 Message type is defined as with normal messages.  Presumably
 broadcast applications will have unique message types that are not
 generally found in normal messages.

AGE COUNT

 Age count is vitally important in a multinetwork broadcast as "loops"
 in the network can cause a great deal of activity until all the
 progeny of the original broadcast message die out.

PROTOCOL SPECIFICATION

 This section contains information on the technique used to
 encapsulate IP datagrams on the HYPERchannel network message.  It
 contains three sections to describe three protocol packagings:
  o   The technique used to encapsulate IP datagrams on the basic
      16-bit network message.  This is a de facto standard that has
      been in use for several years and is documented here to make it
      official.
  o   The encapsulation technique for IP datagrams on 32 bit network
      messages.
  o   The definition of an Address Resolution Protocol on
      HYPERchannel.

Hardwick & Lekashman [Page 17] RFC 1044 IP on Network Systems HYPERchannel February 1988

BASIC (16-BIT) MESSAGE ENCAPSULATION

         Message Proper
       +------------------------------+-----------------------------+
    0  |      Trunks to Try           |        Message Flags        |
       |   TO trunks  |  FROM trunks  |GNA|CRC|     |SRC|EXC|BST|A/D|
       +------------------------------+-----------------------------+
    2  |                      Access code 0000                      |
       |                   (no longer supported)                    |
       +------------------------------+-----------------------------+
    4  |       Physical addr of       |  Protocol server  |Dest Port|
       |     destination adapter      |  logical address  | number  |
       +------------------------------+-----------------------------+
    6  |       Physical addr of       |    Originating    | Src Port|
       |       source  adapter        |  server address   |  number |
       +------------------------------+-----------------------------+
    8  |    IP on HYPERchannel        |   Offset to start of IP     |
       |    type code  0x05           |  header from message start  |
       +------------------------------+-----------------------------+
   10  |      IP type designator      |   Offset to start of IP     |
       |           0x34               |    header from byte 12      |
       +------------------------------+-----------------------------+
   12  |          Padding (variable length incl. zero bytes)        |
       |                                                            |
       +------------------------------+-----------------------------+
   Off |          First (64-Offset) bytes of IP datagram            |
       |                                                            |
       |                                                            |
       |                                                            |
       +------------------------------+-----------------------------+
         Associated Data
       +------------------------------+-----------------------------+
       |                                                            |
       |                Remainder of IP datagram                    |
       |                                                            |
       |            No associated data is present if IP             |
       |            datagram fits in the Message Proper             |
       |                                                            |
       +------------------------------+-----------------------------+

TRUNK MASK

 From the vantage of an IP driver, any trunk mask is valid so long as
 it results in successful delivery of the HYPERchannel network message
 to its destination.  There is no reason to check this field for
 validity on reception of the message.  Specification of the Trunk
 Mask on output is a local affair that could be specified by the
 transmitting driver's address resolution tables.

Hardwick & Lekashman [Page 18] RFC 1044 IP on Network Systems HYPERchannel February 1988

MESSAGE FLAGS

 No use is made of the Flags field (byte 1) other than to
 appropriately set the Associated Data bit.  Burst Mode and the
 Exception bit should not be used with IP.

ACCESS CODE

 Although some current implementations of IP on HYPERchannel support
 the access code, no one appears to be using it at the current time.
 Since this field is currently reserved for the use of 32-bit
 addresses, no value other than 0000 should be placed in this field.

TO ADDRESS

 The TO field is generally obtained by a local IP driver through a
 table lookup algorithm where a 16-bit TO address is found that
 corresponds to the IP address of a local host or gateway.  The high
 order bits of the TO address of course refer to the adapter number
 the adapter attached to the destination host.
 The logical TO field should contain the protocol server address of
 the HYPERchannel IP driver for that host as determined by the host's
 system administrator.  Many HYPERchannel TCP/IP drivers in the field
 today are not "open" in that any network message delivered to that
 host will be presumed to be an IP datagram regardless of the logical
 TO field; however any transmitting IP process should be capable of
 generating the entire 16-bit TO field in order to generate a message
 capable of reaching a destination IP process.
 The process of determining which HYPERchannel address will receive an
 IP datagram based on its IP address is a major topic that is covered
 in "Address Resolution".

FROM ADDRESS

 The FROM address is filled in with the address that the local driver
 expects to receive from the network, but no particular use is make of
 the FROM address.

MESSAGE TYPE

 Network Systems requests that a value of 5 (decimal) be placed in
 this byte to uniquely indicate that the network message is being used
 to carry IP traffic.  No other well-behaved protocol using
 HYPERchannel should duplicate this value of 5.

Hardwick & Lekashman [Page 19] RFC 1044 IP on Network Systems HYPERchannel February 1988

 Many current implementations of IP on HYPERchannel place a zero or
 other values in this field simply because no value was reserved for
 IP usage.  Transmitting versions of IP should always place a 5 in
 this field; receiving IP's should presume a delivered message to be
 an IP datagram until proven otherwise regardless of the contents of
 the Message Type field.
 Developers should note that it is often convenient to permit
 reception of the value 0xFF00 in bytes 8 and 9 of the IP datagram.
 Transmitting a message with this value will cause it to be looped
 back at the destination adapter and returned to the protocol server
 designate in the FROM address.  This permits the developer have host
 applications talk to others on the same host for purposes of network
 interface or other protocol debugging.

IP HEADER OFFSET

 Byte 9 contains the offset to the start of the IP header within the
 message proper, such that the Message Proper address plus the IP
 header offset generates the address of the first byte of the IP
 header (at least on byte addressable machines.)
 This field is redundant with the offset field in byte 11, and is
 present for cosmetic compatibility with 32-bit implementations.  On
 reception, the value in byte 11 should take precedence.
 As part of the migration to larger HYPERchannel headers, this field
 will become significant with the 32-bit addressing format, as the
 length of the header is no longer 10 bytes and byte 11 is used for
 other purposes.

IP TYPE DESIGNATOR

 Early implementations of IP drivers on HYPERchannel wanted to leave
 bytes 8 and 9 alone for NSC use and place a "message type" field in
 later in the message.  A value of 0x34 had been selected by earlier
 developers for reasons that are now of only historical interest.
 Once again, implementations should generate this value on
 transmission, but not check it on input, assuming that an IP datagram
 is present in the message.

IP HEADER OFFSET

 This value is used by a number of commercial implementations of IP on
 HYPERchannel to align the start of the IP header within the network
 message.  This offset is relative to byte 12 of the network message
 so that a value of zero indicates that the IP header begins in byte
 12.  This value should be both correctly generated on transmission,
 and always respected on input processing.

Hardwick & Lekashman [Page 20] RFC 1044 IP on Network Systems HYPERchannel February 1988

 The maximum permissible offset in this field is 52 indicating that
 the IP header begins at the start of the associated data block.

IP DATAGRAM CONTENTS

 Beginning at the offset designated in byte 11, the IP datagram is
 treated as a contiguous block of data that flows from byte 63 of the
 message proper into the first byte of associated data, so that the
 entire message plus data is treated as a single contiguous block.
 If the IP header is small enough to fit within the entire network
 message, then only the message proper is transmitted.  The length of
 the message proper sent should always be 64 bytes, even if the IP
 datagram and HYPERchannel header do not occupy all 64 bytes of the
 message proper.
 If the datagram flows over into the associated data, then both
 message and data are sent.  Since a number of machines cannot send a
 length of data to the HYPERchannel that is an exact number of bytes
 (due to 16-64 bits on the channel bus,) the length of the associated
 data received should not be used as a guide to the length of the IP
 datagram -- this should be extracted from the IP header.  A driver
 should verify, of course, that the associated data received is at
 least as long as is needed to hold the entire IP datagram.

COMPATIBILITY WITH EXISTING IMPLEMENTATIONS

 The basic format described here is clearly a compromise between
 several implementations of IP on HYPERchannel.  Not all existing
 implementations are interoperable with the standard described above.
 Currently there are two known "families" of IP HYPERchannel drivers
 in existence:

THE "CRAY-NASA AMES" PROTOCOL

 This protocol is in the widest production use and has the largest
 number of supported drivers in existence.  It is interoperable and
 identical with the standard described above with the sole exception
 that bytes 8 and 9 are set to zero by these drivers.  As these bytes
 are ignored by most implementations of this driver, they have been
 assigned values to formalize the use of the message type field and to
 make it consistent with the 32-bit protocol.

THE "TEKTRONIX-BERKELEY" PROTOCOL

 This protocol was historically the first IP on HYPERchannel
 implementation developed (at Tektronix) and subsequently made its way
 to Berkeley and BSD UNIX.  This protocol is not interoperable with

Hardwick & Lekashman [Page 21] RFC 1044 IP on Network Systems HYPERchannel February 1988

 the standard described above due to several distinct differences.
 First, bytes 8 through 11 are always zero.  The IP header always
 starts on byte 12.  Comments in some of these drivers designate byte
 11 as an "IP header offset" field, but apparently this value is never
 processed.
 The major difference (and the incompatibility) concerns the packaging
 of the IP datagram into the network message.  Due to historical
 difficulties in the early 80's with the sending and receiving of very
 small blocks of associated data on VAXes, this protocol the takes a
 curious approach to the placement of the IP header and the headers of
 higher level protocols (such as TCP or UDP.)
  o   If the entire length of the IP datagram is 54 bytes or less,
      it is possible to fit the entire datagram and the HYPERchannel
      header in the 64 byte message proper.  In this case, no
      associated data is sent; only a message proper is used to carry
      the data.  The length of the message proper transmitted is the
      exact length needed to enclose the IP datagram; no padding bytes
      are sent at the end of the message.
  o   If the length of the IP header is greater than 54 bytes, then:
  1. All higher level protocol information (TCP/UDP header and

their associated data fields) are placed in the associated

          data block, with the TCP/UDP header beginning at the start
          of the associated data block.
  1. On transmission, the length of the message proper

transmitted is set to the length of the HYPERchannel header

          plus the IP header --  it is not padded out to 64 bytes.
          The length of the associated data sent should be sufficient
          to accommodate the TCP/UDP header and its data fields.

Hardwick & Lekashman [Page 22] RFC 1044 IP on Network Systems HYPERchannel February 1988

WHICH PROTOCOL IS BEST?

 In choosing which to follow, the "Cray-Ames" approach was taken for
 several reasons:
  1.  Cray Research has performed exemplary work in dealing with other
      vendors to provide IP on HYPERchannel from the Cray computers to
      other hosts.  As a result, there are 4 or 5 vendor supported
      implementations of IP on HYPERchannel that use this approach.
  2.  The two part structure of the message proper has its uses when a
      machine wishes to make protocol decisions before staging the
      transfer of an immense block of associated data into memory.
      Many network coprocessors and intelligent I/O subsystems find it
      simpler to read in the entire network message before deciding
      what to do with it.  Arbitrarily catenating the two components
      does this best and permits streaming of messages from future
      technology network adapters.
  3.  Some TCP users (mostly  secure  DoD  sites) intend to load up IP
      datagrams with optional fields in the future.  The
      Tektronix-Berkeley implementation has problems if the IP header
      length exceeds 54 bytes.

Hardwick & Lekashman [Page 23] RFC 1044 IP on Network Systems HYPERchannel February 1988

EXTENDED (32-BIT) MESSAGE ENCAPSULATION

         Message Proper
       +------------------------------+-----------------------------+
    0  |      Trunks to Try           |1|       Message Flags       |
       |   TO trunks  |  FROM trunks  |GNA|CRC|     |SRC|EXC|BST|A/D|
       +------------------------------+-----------------------------+
    2  |    Destination  Domain       |    Destination  Network     |
       |         Number               |           Number            |
       +------------------------------+-----------------------------+
    4  |O|     Physical addr of       |  Protocol server  |Dest Port|
       |N|  destination adapter       |  logical address  | number  |
       +------------------------------+-----------------------------+
    6  |O|     Physical addr of       |    Originating    | Src Port|
       |N|     source  adapter        |  server address   |  number |
       +------------------------------+-----------------------------+
    8  |    IP on HYPERchannel        |   Offset to start of IP     |
       |    type code  0x06           |      datagram header        |
       +------------------------------+-----------------------------+
    10 |    Source Domain Number      |   Source Network Number     |
       |                              |                             |
       +------------------------------+-----------------------------+
    12 |          - reserved -        |         Age Count           |
       +------------------------------+-----------------------------+
    14 |      Next Header Offset      |      Header End Offset      |
       |                              |       (usually 16)          |
       +------------------------------+-----------------------------+
    16 |         Padding to IP header start (usually 0 bytes)       |
       |                                                            |
       +------------------------------+-----------------------------+
    Off|     Entire IP datagram if datagram length <= (64-Offset)   |
       |                                                            |
       |        else first (64-Offset) bytes of IP datagram         |
       +------------------------------+-----------------------------+
         Associated Data
       +------------------------------+-----------------------------+
       |                                                            |
       |                   Remainder of IP datagram                 |
       |                                                            |
       |            No associated data is present if IP             |
       |            datagram fits in the Message Proper             |
       |                                                            |
       +------------------------------+-----------------------------+

TRUNK MASK

 From the vantage of an IP driver, any trunk mask is valid so long as

Hardwick & Lekashman [Page 24] RFC 1044 IP on Network Systems HYPERchannel February 1988

 it results in successful delivery of the HYPERchannel network message
 to its destination.  There is no reason to check this field for
 validity on reception of the message.  Specification of the Trunk
 Mask on output is a local affair that can be specified by the
 transmitting driver's address resolution tables.
 The use of 0xFF in this value is strongly encouraged for any message
 other than those using exotic trunk configurations on a single local
 network.

MESSAGE FLAGS

 Several new bits have been defined here.
 EXTENDED ADDRESSING.  This bit should be set ON whenever a 32-bit
 address (Network and/or Domain numbers nonzero) is present in the
 message.  It should always be OFF with the 16-bit message header.  If
 this bit is improperly set, delivery of the message to the (apparent)
 destination is unlikely.
 END-TO-END CRC.  Some newer technology adapters are equipped to place
 a 32-bit CRC of the associated data at the end of the associated data
 block when this bit is on.  Similarly equipped adapters will examine
 the trailing 32-bits of associated data (when the bit is on) to
 determine if the message contents have been corrupted at any stage of
 the transmission.
 Transmitting device drivers should include the ability to set this
 bit on transmission as a configuration option similar to the specific
 HYPERchannel device interface used.  The bit should be generated to
 be turned ON if the HYPERchannel IP driver is attached to an adapter
 equipped to generated CRC information -- it should be left OFF in all
 other circumstances.
 If a message arrives at the host with the CRC bit still on, this
 indicates that the CRC information was placed at the end of
 associated data by the transmitting adapter and not removed by the
 receiving adapter; thus the associated data will be four bytes longer
 than otherwise expected.  Since the IP datagram length is self
 contained in the network message, this should not impact IP drivers.
 It is possible for host computers to both generate and check this CRC
 information to match the hardware assisted generation and checking
 logic in newer network adapters.  Contact NSC if there are particular
 applications requiring exceptional data integrity that could benefit
 from host generation and checking.

Hardwick & Lekashman [Page 25] RFC 1044 IP on Network Systems HYPERchannel February 1988

 FROM ADDRESS CORRECT.  This bit should be set by all transmitting IP
 drivers who have endeavored to provide a completely correct FROM
 address that properly reflects the adapter interface used.  No action
 should be taken on this bit by the receiving IP driver at this time.
 Additional work needs to be done to determine the action an IP driver
 should take if it detects a real or imagined "security violation"
 should a message arrive with this bit absent.

TO ADDRESS

 The TO address logically constitutes bytes 2-5 of the network
 message.
 NETWORK AND DOMAIN NUMBERS.  The Network and Domain numbers should
 both be nonzero when 32-bit addressing is used.  If the message is
 local in nature, then the local Network and Domain numbers should be
 placed in this field.
 ADAPTER ADDRESS.  Contains the adapter address as in the basic
 message.  The high order bit of this eight bit field (the "outnet"
 bit) should be set to zero if the destination network and domain are
 the same as the transmitting host's.  The high order bit should be
 set to one if the destination host is not in the local network or
 domain.
 LOGICAL TO AND SUBADDRESS.  The logical TO field should contain the
 protocol server address of the HYPERchannel IP driver for that host
 as determined by the host's system administrator.

FROM ADDRESS

 The FROM address is filled in with the address that the local driver
 expects to receive from the network, but no particular use is made of
 the FROM address.

MESSAGE TYPE

 The value 6 must be placed in this byte to uniquely indicate that the
 network message is being used to carry IP traffic.  No other well-
 behaved protocol using HYPERchannel should duplicate this value of 6.
 Note that all IP drivers should be prepared to send and receive the
 basic format network messages using the 16-bit HYPERchannel
 addresses.  The driver can distinguish an incoming network message by
 the value of byte 8 -- 32-bit messages will always have a 6 in byte
 8, while 16-bit messages should have a 5 here.  For interoperability
 with older drivers, a value of 0 here should be treated as 16 address
 bit messages.

Hardwick & Lekashman [Page 26] RFC 1044 IP on Network Systems HYPERchannel February 1988

IP HEADER OFFSET

 Byte 9 contains the offset to the start of the IP header within the
 message proper, such that the Message Proper address plus the IP
 header offset generates the address of the first byte of the IP
 header (at least on byte addressable machines.)
 Unlike the 16-bit header, receiving IP drivers should assume that
 this field contains a correct offset to the IP header and examine the
 information at that offset for conformance to an IP datagram header.
 Valid offsets are in the range of 16 through 44 bytes, inclusive.
 The limitation of 44 bytes is imposed so that routing decisions on
 the vast majority of IP datagrams can be made by examining only the
 message proper, as the basic IP datagram will fit into the message
 proper if it begins at an offset of 44.

IP DATAGRAM CONTENTS

 The message and data are treated as logically contiguous entities
 where the first byte of associated data immediately follows the 64th
 byte of the message proper.
 If the entire IP datagram is less than or equal to (64-offset) bytes
 in length it will fit into the Message Proper.  If so, only a message
 proper containing the HYPERchannel header and IP datagram is sent on
 the network.
 If the IP datagram is greater than this length, the IP datagram
 spills over into the associated data.  On transmission, a 64 byte
 message proper is sent followed by as many bytes of associated data
 as are needed to send the entire datagram.
 On reception, the message proper can be read into the start of an IP
 input buffer and the associated data read into memory 64 bytes from
 the start of the message.  If the received message is in fact a 32-
 bit address message, no "shuffling" of the message will be required
 to build a contiguous IP datagram -- it's right there at buffer+16.

ADDRESS RESOLUTION PROTOCOL

 Address Resolution Protocol has achieved a great deal of success on
 the Ethernet as it permits a local IP network to configure itself
 simply by having each node know its own IP address.  Those unfamiliar
 with the intent, protocol, and logic of the Address Resolution
 Protocol should refer to RFC-826, "An Ethernet Address Resolution
 Protocol" [2].

Hardwick & Lekashman [Page 27] RFC 1044 IP on Network Systems HYPERchannel February 1988

 A later section of this document describes four techniques where a
 target HYPERchannel address is to obtained given the destination's IP
 address.  The protocol is defined in this section for completeness.
         Message Proper
       +------------------------------+-----------------------------+
    0  |      Trunks to Try           |1|       Message Flags       |
       |   TO trunks  |  FROM trunks  |GNA|CRC|     |SRC|EXC|BST|A/D|
       +------------------------------+-----------------------------+
    2  |      Server Domain or        |      Server Network or      |
       |          0xFF                |           0xFF              |
       +------------------------------+-----------------------------+
    4  |   Server Adapter Address or  | Server logical addr/port or |
       |           0xFF               |             07              |
       +------------------------------+-----------------------------+
    6  |O|     Physical addr of       |    Originating    | Src Port|
       |N|     source  adapter        |  server address   |  number |
       +------------------------------+-----------------------------+
    8  |                      NSC ARP type code                     |
       |             07               |             00              |
       +------------------------------+-----------------------------+
    10 |         Source Domain        |       Source Network        |
       +------------------------------+-----------------------------+
    12 |          - reserved -        |         Age Count           |
       +------------------------------+-----------------------------+
    14 |      Next Header Offset      |      Header End Offset      |
       |        (usually 16)          |       (usually 16)          |
       +------------------------------+-----------------------------+
    16 |        Padding to start of IP info (usually 0 bytes)       |
       +------------------------------+-----------------------------+

Hardwick & Lekashman [Page 28] RFC 1044 IP on Network Systems HYPERchannel February 1988

       +------------------------------+-----------------------------+
   Off |          ARP hardware address type for HYPERchannel        |
       |                              8                             |
       +------------------------------+-----------------------------+
    +2 |                 HYPERchannel protocol type                 |
       |             06                           00                |
       +------------------------------+-----------------------------+
    +4 | HYPERchannel address length  |     IP address length       |
       |             6                |           4                 |
       +------------------------------+-----------------------------+
    +6 |               ARP opcode (request or reply)                |
       +------------------------------+-----------------------------+
    +8 |          Domain              |           Network           |
       +-           Sender's 32-bit HYPERchannel address           -+
   +10 |       Adapter address        |     Logical addr/port       |
       +------------------------------+-----------------------------+
   +12 |                      Source's MTU size                     |
       +------------------------------+-----------------------------+
   +14 |                              |                             |
       +-                Sender's 32-bit IP address                -+
   +16 |                                                            |
       +------------------------------+-----------------------------+
   +18 |          Domain              |           Network           |
       +-        Destination's 32-bit HYPERchannel address         -+
   +20 |                (to be determined on request)               |
       |       Adapter address        |     Logical addr/port       |
       +------------------------------+-----------------------------+
   +22 |                  Destination's MTU size                    |
       |               (to be determined on request)                |
       +------------------------------+-----------------------------+
   +24 |                              |                             |
       +-             Destination's 32-bit IP address              -+
   +26 |                                                            |
       +------------------------------+-----------------------------+
 Layout of the fields of this ARP message is a fairly straightforward
 exercise given the standards of ARP and the 32-bit message header.  A
 few fields are worth remarking upon:

TO ADDRESS

 The TO address of an ARP message will be one of two classes of
 address.  A "normal" address indicates that the message is an ARP
 response, or that it is an ARP request directed at an ARP server at a
 well known address on the local network.  For those HYPERchannel
 networks which are equipped to broadcast, a value of 0xFFFFFF07 in
 the TO address will (by convention) be picked up only by those
 protocol servers prepared to interpret and respond to ARP messages.

Hardwick & Lekashman [Page 29] RFC 1044 IP on Network Systems HYPERchannel February 1988

 The issue of which address to use in an ARP request is discussed in
 the Address Resolution section.

FROM ADDRESS

 Must be the correct FROM address of the user protocol server issuing
 an ARP request.  The Source Correct bit in the Message Flags byte
 should be set by this requesting server, as some ARP servers may
 someday choose to issue ARP information on an "need to know" basis in
 secure environments.  With an ARP response, the FROM address will
 contain the "normal" HYPERchannel address of the protocol server
 responding to the ARP address, even if that server was reached via
 broadcast mechanisms.
 ARP responses are returned to the party specified in the FROM address
 specified in the message header, rather than the address in the
 "Source HYPERchannel Address" field within the body of the ARP
 message.

MESSAGE TYPE

 The 16-bit value 0x0700 is reserved for the exclusive use of ARP.
 Unlike IP messages, no provision is made for the ARP message to begin
 at an arbitrary offset within the message proper, so the value in
 byte 9 is an extension of the message type.

HEADER END OFFSET

 ARP uses the 32-bit addressing convention that byte 15 contains the
 offset to the start of user protocol (and hence the end of user
 protocol information).  Note that this is not a substitute for the IP
 offset fields, as this field also serves as the end of HYPERchannel
 header information -- future NSC message processing code may well
 take exception to "garbage" between the actual header end and the
 start of user data.

HYPERCHANNEL HARDWARE TYPE CODE

 This 16-bit number is assigned a formal ARP hardware type of 8.

HYPERCHANNEL PROTOCOL TYPE

 On the Ethernet, this field is used to distinguish IP from all other
 protocols that may require address resolution.  To be logically
 consistent, this field is identical to bytes 8 and 9 0x0600 in a 32-
 bit address HYPERchannel message carrying an IP datagram.

Hardwick & Lekashman [Page 30] RFC 1044 IP on Network Systems HYPERchannel February 1988

HYPERCHANNEL ADDRESS LENGTH

 This contains the value 6, a sufficient number of bytes to
 accommodate the four byte HYPERchannel address and 2 bytes to
 indicate the largest IP datagram size that source and destination can
 handle.

SOURCE AND DESTINATION HYPERCHANNEL ADDRESS

 This field contains the Domain, Network, and Adapter/port address of
 source and destination, respectively.  A value of 0000 in the Domain
 and Network fields has special significance as this is interpreted as
 a request to send and receive 16-bit HYPERchannel headers rather than
 32-bit headers.  If 32-bit headers are to be used within a single
 HYPERchannel network, then the local domain and network numbers may
 be specified.

MAXIMUM TRANSMISSION UNIT

 HYPERchannel LAN technology is such that messages of unlimited length
 may be sent between hosts.  Since host throughput on a network is
 generally limited by the rate the network equipment can be
 functioned, larger transmission sizes result in higher bulk transfer
 performance.  Since not every host will be able to handle the maximum
 size IP datagram, a more flexible means of MTU (maximum transmission
 unit) size negotiation than simply wiring the same value into every
 network host is needed.  With this field, each host declares the
 maximum IP datagram size (not the associated data block size) it is
 prepared to receive.  Transmitting IP drivers should be prepared to
 send the minimum of the source and destination IP sizes negotiated at
 ARP time.
 The MTU size sent refers to the maximum size of IP header + data.  It
 does not include the length of the HYPERchannel Hardware header or
 any offset between the header and the start of the IP datagram.
 Since it is the option of the transmitting hosts to use an offset of
 up to 44 bytes a receiving host must in any event be prepared to
 receive a 64 byte Message Proper and an Associated Data block of
 MTU-20 (that is 64 - 44, or the length of the basic IP header).
      An example of a typical 16-bit packet is:
          12 bytes hardware header.
          12 bytes offset.
          40 bytes IP/TCP header.
        4096 bytes of data.
     This gives an MTU of 4136.

Hardwick & Lekashman [Page 31] RFC 1044 IP on Network Systems HYPERchannel February 1988

     An example of a typical 32-bit packet is:
          16 bytes hardware header.
           8 bytes offset.
          40 bytes  IP/TCP header.
        4096 bytes of associated data,
     This also gives an MTU of 4136.
 The offset values are chosen so that the typical packet causes user
 data to be page aligned at the start of the associated data area.
 This is an implementation decision, which can certainly be modified
 as required.
 The maximum maximum transmission unit is 65536, the current largest
 size IP datagram.  In order to allow this value to fit into a 16-bit
 field, the offset length is not included in the MTU.  This MTU size
 is not a requirement that a local host be equipped to send or receive
 datagrams of that size; it simply indicates the maximum capacity of
 the receiving host.
 A note on trunk masks:
 There is no field for specifying trunk masks.  This is intentional,
 as new NSC hardware will contain trunk reachability information,
 eliminating the need for the host to maintain hardware configuration
 layouts.  All HYPERchannel messages generated as a result of an ARP
 response should use 0xFF in the trunk mask.

ADDRESS RESOLUTION

 This section describes techniques used by an IP driver to determine
 the HYPERchannel address and header that a message should contain
 given an IP datagram containing an IP address.  It describes
 techniques that are local to specific hosts (and hence can be
 modified without regard to the activities or techniques of other
 hosts) as well as techniques to use the Address Resolution Protocol
 on existing HYPERchannel equipment to better manage IP addresses.
 It also discusses the migration of name resolution on one of four
 steps.
  1.  Truncation of the IP address to form a HYPERchannel address.
  2.  Local resolution of HYPERchannel addresses through configuration
      files.
  3.  Centralized resolution of HYPERchannel addresses through an "ARP
      server" driven by a configuration file.

Hardwick & Lekashman [Page 32] RFC 1044 IP on Network Systems HYPERchannel February 1988

  4.  Distributed resolution of HYPERchannel addresses using a "real"
      address Resolution Protocol on future HYPERchannel media
      supporting a broadcast mode.

IP ADDRESS TRUNCATION

 A number of IP on HYPERchannel implementations support modes where
 the HYPERchannel address is generated by placing the low order 16-
 bits of the IP address in the TO address of the message proper.  This
 more or less treats a set of HYPERchannel boxes addressable through
 16-bit HYPERchannel addresses as a Class B IP network.
 This approach certainly offers simplicity:  IP addresses are simply
 chosen to match HYPERchannel addresses and no IP address
 "configuration files" need be kept.  Although this approach works in
 an environment where the HYPERchannel completely constitutes a Class
 B network, or where connection to a larger IP network is not a
 concern, its long term use is discouraged for several reasons:
  o   It simply will not work with any Class C address (the physical
      TO address is not controllable) or a Class A address (where host
      addresses are generally carefully administered.)  In addition,
      it will not support subnetworks.  It is quite incompatible with
      32-bit HYPERchannel addresses.
  o   By decoupling the IP and HYPERchannel addresses through more
      complex address resolution, the characters of the two addresses
      allow greater site flexibility:  the IP address becomes
      "logical" in character so that an address can move about a site
      with the user or host; the HYPERchannel address maintains its
      physical character so that a HYPERchannel address carefully
      identifies the physical location of the source and destination
      within the extended HYPERchannel network.

LOCAL ADDRESS RESOLUTION

 The current state of address resolution art with IP on HYPERchannel
 works as follows:  given an arbitrary IP address, the IP HYPERchannel
 driver looks up an entry with that address in a (generally hashed)
 table.  If found, the table entry contains the first 6 bytes of the
 HYPERchannel header that is used to send the IP datagram to the next
 IP node on the internet.  Since implementations such as the 4.3BSD
 UNIX IP are clever enough to provide its lower level drivers with the
 IP address of the next gateway as well as the destination address on
 the internet (assuming the message is not delivered locally on the
 HYPERchannel,) the number of entries in this table is more or less
 manageable, as it must only contain the IP hosts and gateway
 addresses that are directly accessible on the HYPERchannel.

Hardwick & Lekashman [Page 33] RFC 1044 IP on Network Systems HYPERchannel February 1988

CONFIGURATION FILE FORMAT

 So long as this technique of address resolution is used, the
 techniques used are exclusively local to the host in the sense that
 the techniques used to generate and store the information in the
 table are irrelevant to other hosts.
 Shown here is a typical file format.  This file should probably be
 program generated from a database, as asymmetric trunk configurations
 and multiply homed hosts can cause differences in physical routing
 and trunk usage.  This format is documented here to illustrate what
 sort of information must be kept at the link layer.
 The file consists of source lines each with the form:
    <type> <hostname> <trunks/flags> <domain/net> <addr> <MTU>
    an example:
         <type>  <hostname>             <t/f> <dom/net> <addr>  <MTU>
         # Random front end
         host    hyper.nsco.com          FF88    0103    3702    4148
         # because we want to show the 4 byte format
         host    192.12.102.1            FF00    0000    2203    1024
         # Small packets, interactive traffic.
         host    cray-b.nas.nasa.gov     FF88    0103    4401    4148
         # The other interface, for big packets.
         ahost   cray-b.nas.nasa.gov     FF88    0103    4501    32768
         # A loopback interface, (What else)
         loop    loop37.nsco.com         FF00    0000    3700    4148
         # And of course an example of arp service.
         arpserver hcgate.nsco.com       FF88    0103    7F07
  Comments may begin with  either # or ;.
  Case is not significant in any field.
  <type> indicates the type of entity to be defined.
    Currently defined types are "host," "ahost", "loop," "address,"
    and "arpserver".
    host    This token indicates an IP  host.  The following field  is
            expected to be a name that can be resolved to an IP
            address.
    ahost   This field indicates an additional network interface to
            the same host.  This may be used for performance
            enhancements.

Hardwick & Lekashman [Page 34] RFC 1044 IP on Network Systems HYPERchannel February 1988

    loop    Sets a flag in the entry for that host so that  0xFF00 is
            placed in bytes 8 and 9 of the message.  This will cause
            the IP datagram  to be directed towards the specified host
            (which must still be a valid host name) and looped back
            within the remote adapter.  This facility serves both as a
            debugging aid and as a crude probe of the availability of
            the remote network adapter.
    arpserver This indicates an address to use for directing ARP
            requests to the network.  If several arpserver addresses
            are specified, they will be tried in turn until a response
            is received (or we run out of servers.)  An arpserver with
            the  appropriate  broadcast address of FFFF FF07 would
            cause an ARP broadcast to take place when broadcasting
            becomes available.  Broadcast and specific addresses may
            be used in combination.
 <hostname> This field is the logical name of the destination.  For a
 host it is the logical name to be given to the local naming service
 to determine the associated IP address.  This field may contain four
 decimal numbers separated by dots, in which case it is assumed to be
 the explicit IP address.
 <trunks/flags> This field is the value to be placed in bytes 0 and 1
 of the message header when sending to this host.  The associated data
 bit need not be supplied as the driver must control it.  All other
 bits are sent as provided.  This field is a hexidecimal number.
 <domain/net> This field is the value to be placed in the Domain and
 Network number field of the message.  A value of 0000 in this field
 indicates that the destination should be reached by constructing a
 16-bit HYPERchannel header, rather than a 32-bit header.
 <address> This field is the value to be placed in the 16-bit TO field
 to reach <hostname>.  This field is a hexidecimal number.
 <MTU> This field contains the largest size IP datagram that the
 destination host is prepared to receive.  This field is a decimal
 number.  This field is optional.  If not present, a value of 4148 is
 assumed.  See the earlier discussion on Maximum Transmission Unit for
 more detail.

ARP SERVERS

 The primary problem with local host address resolution is that
 changes or additions to hosts on the local net must be replicated to
 every HYPERchannel host in that network.  While this is manageable
 for up to half a dozen hosts, it becomes quite unmanageable for

Hardwick & Lekashman [Page 35] RFC 1044 IP on Network Systems HYPERchannel February 1988

 larger networks.  An approach that can be implemented using existing
 HYPERchannel technology is to have a server on the HYPERchannel
 network provide the HYPERchannel destination address that is
 associated with an IP address.
 Although this is strictly a point-to-point request/response dialogue
 between two network nodes, the Address Resolution Protocol which was
 originally designed for Ethernet (but thoughtfully constructed to
 work with any pair of link and network addresses) performs an
 excellent job.
 ARP servers can be reached simply by placing the address of the
 server in the 32-bit TO address of the network message.  ARP servers
 only "listen" to messages that arrive on their well known normal
 address; they do not respond to ARP broadcast messages.  Properly
 equipped IP drivers should respond to the broadcast messages when
 they appear.
 If an ARP server receives a message containing an IP address it does
 not know how to resolve, it ignores the message so that another ARP
 server might be addressed at the source's next attempt.
 If the address is resolvable, it places the known HYPERchannel
 address and MTU size in the response and returns it to the location
 in the HYPERchannel header FROM address.
 Unlike a broadcast ARP, the ARP server will be required to service
 two requests when two hosts that are initially unknown to one another
 attempt to get in touch.  Since the destination did not receive the
 ARP request, it must contact the ARP server when its higher level
 protocols first generate a datagram to respond to the the source's
 first IP datagram to go through to the destination.
 The source configuration file described in the previous section was
 explicitly designed so that it could be sufficient as a data base for
 an ARP server as well as an individual host.

BROADCAST ARP

 When a local HYPERchannel network contains a broadcast capability,
 any IP driver wishing to perform HYPERchannel address resolution may
 be configured to emit the ARP message on a broadcast instead of a
 well known address.  IP drivers on other hosts are presumed to know
 if their local HYPERchannel interface can send broadcast messages; if
 so, they arrange to "listen" on the FF07 broadcast TO address for
 ARP.
 Processing of a received ARP broadcast message is otherwise identical

Hardwick & Lekashman [Page 36] RFC 1044 IP on Network Systems HYPERchannel February 1988

 to RFC-826:
  o   Messages are responded to if and only if the destination IP
      driver is authoritative for the designated IP address.
  o   Whenever an ARP message is processed, the IP driver takes the
      source HYPERchannel address and MTU size and adds it to its
      address resolution tables.  Thus the driver is equipped to
      turn around the IP datagram that arrives from the destination
      host when contact is made.
 Each IP driver may have address resolutions that are set through a
 static routing table (the configuration file specified above).  If
 ARP information arrives that contradicts a static entry (as opposed
 to previously set dynamic ARP information) then the ARP information
 should be ignored.  This decision is made on the premise that the
 only useful purpose of static routing in a broadcast ARP environment
 is to add authentication, as it's easy to lie with ARP.

Hardwick & Lekashman [Page 37] RFC 1044 IP on Network Systems HYPERchannel February 1988

APPENDIX A. NSC PRODUCT ARCHITECTURE AND ADDRESSING

 This section is intended to be a concise review of the state of the
 art in NSC networks and the techniques they provide for the delivery
 of messages.  Those who are thoroughly familiar with HYPERchannel may
 wish to only skim this section; however, there is material on new
 technologies and addressing formats that are not yet generally known
 to most of NSC's customers.

NETWORK SYSTEMS HYPERCHANNEL TECHNOLOGIES

 Network Systems manufactures several different network technologies
 that use very different media and link controls, but still provide a
 common host interface in both the protocol and hardware sense of the
 term.  These four technologies are:
  o   HYPERchannel A -- A 50-megabit, baseband, CSMA with collision
      avoidance  network using a coaxial cable bus.  Individual
      HYPERchannel "network adapters" can control up to 4 of these
      coaxial cable "trunks,"  providing up to 200 megabits of
      capacity on a fully interconnected network.  HYPERchannel A
      is NSC's earliest product and has been in production since
      1977.  It is principally used to interconnect larger
      mainframe computers and high speed mainframe peripherals such
      as tape drives and laser printers.
  o   HYPERchannel  B -- a 10-megabit, baseband, CSMA with collision
      avoidance network using a single coaxial cable bus.  This
      technology is used for direct host to host communications under
      the name HYPERchannel B, and for terminal connections under the
      name HYPERbus.  It is currently used for three major
      applications -- local networks of ASCII terminals, networks
      of IBM 3270 terminals, and host to host communications of
      smaller computers.
  o   DATAPIPE[3]  --  a 275-megabit fiber optic "backbone" network
      that interconnects lower speed local area networks within a 20
      mile range, and to provide an ultra-high-performance network for
      the next generation of supercomputers and optical storage
      systems.  A prototype version of DATApipe is currently under
      development at a customer site.
  o   Bridges and Network Distance Extensions -- NSC quickly
      discovered that its customers wanted very high speeds over
      geographic areas, not just within the range of several miles
      that is conceivable with a coaxial cable network.  Starting
      in 1978, NSC began to build a series of "link adapters" that
      are integral bridges between local area networks.  These link

Hardwick & Lekashman [Page 38] RFC 1044 IP on Network Systems HYPERchannel February 1988

      adapters support common high speed communications media such
      as Telco T1 circuits, private microwave, high speed
      satellite links, and fiber optic point to point connections.

ATTACHMENT TO HOST COMPUTERS

 Network Systems' high speed interfaces use the attachment techniques
 of the manufacturer's highest speed peripheral controllers in order
 to achieve burst transfer rates of tens of megabits per second.
 These attachment techniques fall into three categories:

"MAINFRAME" DATA CHANNEL ATTACHMENT

    +-----------+-------+                   +------------+  | | | |
    |           |       |                   |HYPERchannel+--+ | | |
    |           |       +-------------------+  Network   +--|-+ | |
    | Host      |  I/O  +-------------------+  Adapter   +--|-|-+ |
    |           |       |   Standard host   |            +--|-|-|-+
    | Computer  |Control|    data channel   +------------+  | | | |
    |           |       |
    |           |       |
    |           |       |
    |           |       |
    +-----------+-------+
 The network adapter contains interface boards and firmware to be
 cabled to the manufacturer's data channel, such as would be done with
 a disk or tape controller.  Mainframe network adapters do not emulate
 an existing manufacturer's device (such as a tape drive) but are
 supported by software which functions the channel and adapter to send
 and receive network messages.
 Models of HYPERchannel adapters are available for essentially all
 large scale computers worldwide.

Hardwick & Lekashman [Page 39] RFC 1044 IP on Network Systems HYPERchannel February 1988

MINICOMPUTER AND WORKSTATION ATTACHMENT

 Since the network adapter contains lots of expensive, high speed
 logic, a different technique is used to provide attachment to
 minicomputers and workstations.
    +-------------+        +---------------+       +--------------+
    |             |        |               |       |              |
    | Minicomputer|        |  Supermini    |       | Workstation  |
    |             |        |               |       |              |
    +-----+-------+        +-------+-------+       +-------+------+
    |     |  DMA  |        |       |  DMA  |       |  DMA  |      |
    |     |control|        |       |control|       |control|      |
    +-----+---++--+        +-------+--++---+       +--++---+------+
              ||                      ||              ||
              ||                      ||              ||
              |+----------+           ||    +---------+|
              +----------+|           ||    |+---------+
                         ||           ||    ||
                       +-++--+-----+--++-+--++-+
                       |     |     |     |     |
                       +-----+-----+-----+-----+
                       |         x400          |
                       |    Network Adapter    |
                       |                       |
                       +-------+-+-+-+---------+
                               | | | |
             ------------------|-|-|-+----------------
             ------------------|-|-+------------------
             ------------------|-+--------------------
             ------------------+----------------------
 In this case, NSC provides a DMA controller designed for direct
 connection to that minicomputer's backplane bus.  These DMA
 controllers accept functions and burst blocks of data from host
 memory to a channel cable that is connected to one of four ports on a
 "general purpose computer adapter."  This adapter multiplexes
 transmissions to and from the HYPERchannel trunks from up to four
 attached processors.

Hardwick & Lekashman [Page 40] RFC 1044 IP on Network Systems HYPERchannel February 1988

NETWORK COPROCESSORS

 For about 10 different bus systems, Network systems provides a
 "smart" DMA controller containing onboard memory and a Motorola 68010
 protocol processor.
     +------------+-----+---------------+-------+
     |            |     |   Coprocessor |       |        +--------+
     |            |Host |    MC 68010   |Adapter+--------+  x400  |
     |    HOST    |DMA  |   256K memory |  DMA  +--------+ Adapter|
     |            |     |               |       |        +--------+
     |    Memory  +-----+---------------+-------+
     |            |
     +------------+
 This class of interface works through the network coprocessor's
 direct access to host memory.  Network transmit and receive request
 packets are placed in a common "mailbox" area and extracted by the
 coprocessor.  The coprocessor reads and writes system memory as
 required to service network requests in the proper order.  The
 coprocessors currently provide a service to read or write network
 messages (called Driver service as it is more or less identical to
 HYPERchannel dumb DMA drivers) and a service for NETEX, which is
 NSC's OSI-like communications protocol.

Hardwick & Lekashman [Page 41] RFC 1044 IP on Network Systems HYPERchannel February 1988

APPENDIX B. NETWORK SYSTEMS HYPERCHANNEL PROTOCOLS

 The protocols implemented by NSC within its own boxes are designed
 for the needs of the different technologies.  A compact summation of
 these protocols is:
    HYPERchannel B         HYPERchannel A            DATApipe
   10 Mbits/second       50-200 Mbits/second     275 Mbits/second

+———————-+———————-+———————+ | | | HYPERchannel network message | | connectionless datagram protocol | | | +———————-+———————-+———————+ | "HYPERchannel | | | | compatibility mode" | HYPERchannel A | DATApipe | | Virtual circuit | reservation and | acknowledgment | | estab. & control | flow control | & flow control | +———————-+ protocol | protocol | | | | | | Virtual Circuits | | | | Flow Control | | | +———————-+———————-+———————+ | CSMA / VT | CSMA / CA | | | frame (datagram) | frame (datagram) | TDMA packet delivery| | delivery and | delivery and | | | acknowledgment | acknowledgment | | +———————-+———————-+———————+ | | | Fiber optics | | 75 ohm coax | 1-4 75 ohm coax | (various cable sizes| | cable | cables | and xmission modes)| +———————-+———————-+———————+

 Without getting into great detail on these internal protocols, a few
 points are particularly interesting to system designers:
  o   All three technologies supply the same interface to the host
      computer or network coprocessor, a service to send and receive
      network messages that are datagrams from the host's vantage in
      that each contains sufficient information to deliver the message
      in and of itself.  Since this datagram and its header fields are
      of paramount interest to the host implementor, it is discussed
      in detail below.
  o   All technologies use acknowledgments at a very low level to
      determine if packets  have been successfully delivered.  In
      addition to permitting  a highly tuned contention mechanism for
      the coax medium, it also permits HYPERchannel A to balance the

Hardwick & Lekashman [Page 42] RFC 1044 IP on Network Systems HYPERchannel February 1988

      load over several coax cables -- a feat that has proven very
      difficult on, for example, Ethernet.
  o   All boxes go to some lengths to assure that resources exist
      in the receiving box before actual transmission takes place.
      HYPERchannel B uses a virtual circuit that endures for several
      seconds of inactivity after one host first attempts to send a
      message to the other.  Traffic over this "working virtual
      circuit" is flow controlled from source to destination and
      buffer resources are reserved for the path.
 HYPERchannel A exchanges frames at very high rates to determine that
 the receiver is ready to receive data and to control its flow as data
 moves through the network.
 DATApipe propagation time is relatively long compared to the time
 needed to send an internal packet of 2K-4K bytes.  As a result,
 DATApipe controllers use a streamlined TP4-like transport protocol to
 assure delivery of frames between DATApipe boxes.

REFERENCES

    [1]   HYPERchannel is a trademark of Network Systems Corporation.
    [2]   Plummer, D., "An Ethernet Address Resolution Protocol",
          RFC-826, Symbolics, September 1982.
    [3]   DATApipe is a registered trademark of Network Systems
          Corporation.

Hardwick & Lekashman [Page 43]

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