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rfc:rfc1861

Network Working Group A. Gwinn Request for Comments: 1861 Southern Methodist University Obsoletes: 1645 October 1995 Category: Informational

   Simple Network Paging Protocol - Version 3 - Two-Way Enhanced

Status of this Memo

 This memo provides information for the Internet community.  This memo
 does not specify an Internet standard of any kind.  Distribution of
 this memo is unlimited.

Abstract

 This RFC suggests a simple way for delivering wireless messages, both
 one and two-way, to appropriate receiving devices.  In its simplest
 form, SNPP provides a simple way to implement a "shim" between the
 Internet and a TAP/IXO paging terminal. In its level 3 form, it
 provides an easy-to-use (and build) method for communicating and
 receiving end-to-end acknowledgments and replies from two-way
 messaging devices (such as ReFLEX units).
 Gateways supporting this protocol, as well as SMTP, have been in use
 for well over a year at several commercial paging companies, and
 private businesses.  Client software supporting this protocol has
 become widespread, and is being integrated into many of the new
 paging and messaging products being built.  In addition to commercial
 software, email filters and SNPP client software for Unix and Windows
 (WikiPage) are available at no cost.  Please contact the author for
 more information.
 Earlier versions of this specification were reviewed by IESG members
 and the "822 Extensions" Working Group.  They preferred an alternate
 strategy, as discussed under "Relationship to Other IETF Work",
 below.

1. Introduction

 With all due apologies to the Glenayre engineers (who take offense at
 the term "nerd") beepers are as much a part of computer nerdom as X-
 terminals--perhaps, unfortunately, more. The intent of Simple Network
 Paging Protocol is to provide a standard whereby pages can be
 delivered to individual paging terminals.  The most obvious benefit
 is the elimination of the need for modems and phone lines to produce
 alphanumeric pages, and the added ease of delivery of pages to
 terminals in other cities or countries. The benefits of the Internet

Gwinn Informational [Page 1] RFC 1861 SNPP - Version 3 October 1995

 become even more realized when growing towards acknowledgment-based
 messaging such as ReFLEX paging--where it may be impossible to
 accurately predict costs associated with telco services such as 1-800
 numbers.

2. System Philosophy

 Radio paging is somewhat taken for granted, because of the wide
 availability and wide use of paging products.  However, the actual
 delivery of the page, and the process used (especially in wider area
 paging) is somewhat complicated.  When a user initiates a page, by
 dialing a number on a telephone, or entering an alphanumeric page
 through some input device, the page must ultimately be delivered to
 some paging terminal, somewhere.  In most cases, this delivery is
 made using TAP (Telocator Alphanumeric input Protocol, also known as
 IXO).  This protocol can be a somewhat convoluted, and complicated
 protocol using older style ASCII control characters and a non-
 standard checksumming routine to assist in validating the data.
 Even though TAP is widely used throughout the industry, there are
 plans on the table to move to a more flexible "standard" protocol
 referred to as TME (Telocator Message Entry Protocol).  The level two
 enhancements to SNPP (as described below) are intended for use with
 this forthcoming standard.
 The recently-added level three enhancements have been engineered for
 use, specifically, with acknowledgment-based paging.  With the recent
 advances in wireless technology, two-way paging is fast approaching
 reality--therefore creating a need for a workable end-to-end
 acknowledged protocol.  Two-way messaging, however, opens up several
 new areas of unpredictability.  The most pronounced is the subscriber
 response time.  Although deliveries from host to subscriber, and
 subsequent receipt-acknowledgments happen in a rather predictable
 manner, it is impossible to know when the subscriber will physically
 pull the unit out, read the message and respond to it.  Therefore, it
 could well be cost prohibitive to conduct such transactions online
 using a phone line as medium--especially an 800-number. This makes
 the Internet an extremely attractive alternative because of its
 (generally) usage insensitive nature.
 However, acknowledging the complexity of task, and flexibility of the
 current protocols (or the lack thereof), the final user function is
 quite simple: to deliver a page from point-of-origin to someone's
 beeper.  That is the simple, real-time function that the base
 protocol attempts to address.

Gwinn Informational [Page 2] RFC 1861 SNPP - Version 3 October 1995

3. Why not just use Email and SMTP for paging?

 Email, while quite reliable, is not always timely.  A good example of
 this is deferred messaging when a gateway is down. Suppose Mary Ghoti
 (fish@hugecompany.org) sends a message to Zaphod Beeblebrox's beeper
 (5551212@pager.pagingcompany.com). Hugecompany's gateway to the
 Internet is down causing Mary's message to be deferred.  Mary,
 however, is not notified of this delay because her message has not
 actually failed to reach its destination.  Three hours later, the
 link is restored, and (as soon as sendmail wakes up) the message is
 sent.  Obviously, if Mary's page concerned a meeting that was
 supposed to happen 2 hours ago, there will be some minor
 administrative details to work out between Mary and Zaphod!
 On the other hand, if Mary had used her SNPP client (or simply
 telnetted to the SNPP gateway), she would have immediately discovered
 the network problem.  She would have decided to invoke plan "B" and
 call Zaphod's pager on the telephone, ringing him that way.
 The obvious difference here is not page delivery, but the immediate
 notification of a problem that affects your message. Standard email
 and SMTP, while quite reliable in most cases, cannot be positively
 guaranteed between all nodes at all times, making it less desirable
 for emergency or urgent paging.  This inability to guarantee delivery
 could, whether rightly or wrongly, place the service provider in an
 uncomfortable position with a client who has just received his or her
 emergency page, six hours too late.
 Another advantage of using a separate protocol for paging delivery is
 that it gives the sender absolute flexibility over what is sent to
 the pager.  For instance, in the paging arena, where messages are
 sent to alphanumeric pagers, it is less desirable to send the
 recipient general header lines from a standard SMTP message.  Much of
 the information is useless, possibly redundant, and a waste of
 precious RF bandwidth.
 Therefore, when implementing an SMTP gateway, the service provider
 should elect to parse out needed information (such as the sender, and
 possibly subject) such to maximize the utility of the transmission.
 Parsing generally means less control over content and format by the
 message originator.  SNPP provides a clean, effective way to send a
 message, as written, to the recipient's pager.
 The other consideration is the relative simplicity of the SNPP
 protocol for manual telnet sessions versus someone trying to manually
 hack a mail message into a gateway.

Gwinn Informational [Page 3] RFC 1861 SNPP - Version 3 October 1995

4. The SNPP Protocol

 The SNPP protocol is a sequence of commands and replies, and is based
 on the philosophy of many other Internet protocols currently in use.
 SNPP has several input commands (the first 4 characters of each are
 significant) that solicit various server responses falling into the
 following categories:
  2xx - Successful, continue
  3xx - Begin DATA input (see "DATA" command)
  4xx - Failed with connection terminated
  5xx - Failed, but continue session
 SNPP version 3 (two-way) adds the following categories:
  7xx - UNsuccessful two-way specific transaction, but continue
        session
  8xx - Successful two-way specific transaction, continue
  9xx - Successful QUEUED two-way transaction, continue
 The first character of every server response code is a digit
 indicating the category of response.  The text portion of the
 response following the code may be altered to suit individual
 applications.
 The session interaction, especially at SNPP level one, is actually
 quite simple (hence the name).  The client initiates the connection
 with the listening server.  Upon opening the connection, the server
 issues a "220" level message (indicating the willingness of the
 server to accept SNPP commands).  The client passes pager ID
 information, and a message, then issues a "SEND" command.  The server
 then feeds the information to the paging terminal, gathers a
 response, and reports the success or failure to the client.

4.1 Examples of "simple" SNPP Transactions

 The following illustrate examples of client-server communication
 using SNPP.

Gwinn Informational [Page 4] RFC 1861 SNPP - Version 3 October 1995

4.1.1 A Typical Level One Connection

          Client                         Server
  Open Connection               -->
                                <--  220 SNPP Gateway Ready
  PAGE 5551212                  -->
                                <--  250 Pager ID Accepted
  MESS Your network is hosed    -->
                                <--  250 Message OK
  SEND                          -->
                                <--  250 Message Sent OK
  QUIT                          -->
                                <--  221 OK, Goodbye

4.1.2 A Typical Level Two, Multiple Transaction

 The following example illustrates a single message sent to two
 pagers.  Using this level protocol, pager-specific options may be
 selected for each receiver by specifying the option prior to issuing
 the "PAGEr" command.  In this example, an alternate coverage area is
 selected for the first pager, while delayed messaging is specified
 for the second.
          Client                         Server
  Open Connection               -->
                                <--  220 SNPP Server Ready
  COVE 2                        -->
                                <--  250 Alternate Area Selected
  PAGE 5551212 FOOBAR           -->
                                <--  250 Pager ID Accepted
  HOLD 9401152300 -0600         -->
                                <--  250 Delayed Message OK
  PAGE 5552323 XYZZY            -->
                                <--  250 Pager ID Accepted
  SUBJ Seattle Meeting          -->
                                <--  250 Message Subject OK
  DATA                          -->
                                <--  354 Begin Input, End With '.'
  Please meet me tomorrow at    -->
  the Seattle office            -->
                                <--  250 DATA Accepted
  SEND                          -->
                                <--  250 Message Sent OK
  QUIT                          -->
                                <--  221 OK, Goodbye

Gwinn Informational [Page 5] RFC 1861 SNPP - Version 3 October 1995

4.1.3 A Typical Level Three (two-way) Transaction

 Level three transactions are inherently single-unit oriented because
 of the one-to-one issues surrounding responses.  Each transaction
 begins with the "2WAY" command and terminates with a "SEND" command.
      Client                         Server

Open Connection –>

                            <--  220 SNPP (V3) Gateway Ready

2WAY –>

                            <--  250 Two-Way Mode Enabled

NOQUEUE –>

                            <--  250 Msg will either be Sent or Rejected

PAGER SHIRLEY –>

                            <--  850 Unit online; Don't call me Shirley!

ACKRead 1 –>

                            <--  250 Read Acknowledgment Requested

DATA –>

                            <--  354 Begin Input, End With '.'

Little Bo Binary has lost –> her Sparcstation and doesn't –> know where to find it. Have –> you seen it recently? –>

                            <--  250 DATA Accepted

RTYPE MULTICHOICE –>

                            <--  250 Multichoice Responses Enabled

MCRESP 01 In the West Pasture –>

                            <--  250 MCR Code Accepted

MCRESP 02 GoldiFLOCKs has it –>

                            <--  250 MCR Code Accepted

MCRESP 03 Haven't a clue –>

                            <--  250 MCR Code Accepted

MCRESP 04 Haven't a life –>

                            <--  250 MCR Code Accepted

MCRESP 05 Oh, GO AWAY! –>

                            <--  250 MCR Code Accepted

SEND –>

                            <--  860 00321 1234 Message Delivered

QUIT –>

                            <--  221 OK, Goodbye

4.2 General Response Code Theory

 Before discussing specific SNPP transactions, it may be helpful to
 discuss some of the response codes.  As mentioned previously, every
 response from the SNPP server to the client contains a 3 digit code
 that categorizes the response. Several of these codes fall into the

Gwinn Informational [Page 6] RFC 1861 SNPP - Version 3 October 1995

 "general" category, and may occur more frequently throughout a given
 SNPP transaction. There are some lesser used (somewhat transaction
 specific) responses that will be discussed in conjunction with the
 format of a specific command.

4.2.1 Code 214 - Multi-line "help/info" message

 This code prefixes a line of response information (such as in
 response to the HELP command).  It should be terminated with a "250
 OK" message.  This code is used when the response will take more than
 one line to display.

4.2.2 Code 218 - Single-line "help/info" message

 This code prefixes a single line of response information (such as the
 request for a single database entry).  Unlike the 214 series, it has
 no "250" series terminator.

4.2.3 Code 250 - Successful Transaction

 This code is a general positive acknowledgment from the server
 indicating that a command was successfully processed. Additionally,
 code 250 can appear at the end of the response to a HELP command (214
 series commands--discussed below).

4.2.4 Code 421 - Fatal Error, Connection Terminated

 This code is displayed just prior to the SNPP server terminating a
 connection with a client for errors. Such a connection termination
 may occur at any time and for any reason (administrative or
 technical).

4.2.5 Code 500 - Command Not Implemented

 This code is a "fail but continue code" that appears when an illegal
 command is entered.

4.2.6 Code 503 - Duplicate Command Entry; Already Entered That

 This code indicates that the specified information has already been
 entered.  This code would appear, for instance, if the client
 attempted to enter a MESSage command after specifying a "DATA"
 sequence.

4.2.7 Codes 550 and 554 - Transaction Failed, but Continue

 These codes indicate a failed command, but the session is allowed to
 continue.  A 550 code should be used to indicate a more

Gwinn Informational [Page 7] RFC 1861 SNPP - Version 3 October 1995

 "administrative" failure (such as an invalid pager ID, or illegal
 parameter), while a 554 series indicates a more technical reason
 (such as a gateway down or equipment failure).  In addition to the
 specified failure codes, additional 550 and 554 failures may be
 specified as necessary to allow for greater flexibility.

4.2.8 Code 552 - Maximum Entries Exceeded

 This code is in response to the entry of the "n+1" item when the
 server only permits "n" items in a category.  As an example, the
 client would expect to see this message when trying to enter the 6th
 PAGEr command when the terminal only supported 5.

4.3 Level 1 Commands

 Level one commands are designed as a minimum implementation of the
 protocol.  This collection of commands may be used with either
 TAP/IXO or TME for message delivery to the paging terminal.

4.3.1 PAGEr <Pager ID>

 The PAGEr command submits a pager ID (PID) number, for inclusion in
 the next messaging transaction.  The PID used must reside in, and be
 validated by the paging terminal.  Limited validation may optionally
 be done on the server (such as all numeric, and ID length), or
 validation can be left up to the terminal at the time the page is
 sent.
 When implementing SNPP, the user may elect to support multiple
 recipients per message sent.  However, be wary that validation-
 prior-to-sending is not possible with TAP/IXO (and is not an official
 option of the current TME specification).  What this means is that in
 order to validate a PID, one must generate a message to the pager.
 The terminal responds favorably or negatively.  When reporting
 failure of a single PID in a sequence, delineating and reporting the
 failure in a "standard format" may prove to be a challenge.
 Possible responses from the SNPP server, with suggested text, in
 response to a PAGEr command are:
  250 Pager ID Accepted
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  550 Error, Invalid Pager ID
  554 Error, failed (technical reason)
 Both level 2 and level 3 enhancements affect the PAGEr command.
 Please refer to the appropriate section(s) for details.

Gwinn Informational [Page 8] RFC 1861 SNPP - Version 3 October 1995

4.3.2 MESSage <Alpha or Numeric Message>

 The MESSage command specifies a single-line message, into the
 gateway.  Limited validation of the message may be done on the SNPP
 server (such as length), but type-of-message validation should be
 done by the paging terminal.  Duplicating the MESSage command before
 SENDing the message should produce an "503 ERROR, Message Already
 Entered" message, and allow the user to continue.
 Possible responses from the SNPP server, with suggested text, in
 response to a MESSage command are:
  250 Message OK
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  503 ERROR, Message Already Entered
  550 ERROR, Invalid Message
  554 Error, failed (technical reason)

4.3.3 RESEt

 The RESEt command clears already entered information from the server
 session, resetting it to the state of a freshly opened connection.
 This is provided, primarily, as a means to reset accidentally entered
 information during a manual session.
 Possible responses from the SNPP server, with suggested text, in
 response to a RESEt command are:
  250 RESET OK
  421 Too Many Errors, Goodbye (terminate connection
  421 Gateway Service Unavailable (terminate connection)

4.3.4 SEND

 The SEND command finalizes the current message transaction, and
 processes the page to the paging terminal.  Prior to processing, the
 PAGEr and MESSage fields (or message DATA when using the level two
 option) should be checked for the existence of information.  Should
 one of these required fields be missing, the server should respond
 "503 Error, Incomplete Information" and allow the user to continue.
 Assuming that the information is complete, the SNPP server should
 format and send the page to the paging terminal, and await a
 response.
 Possible responses from the SNPP server, with suggested text, in
 response to a SEND command are:

Gwinn Informational [Page 9] RFC 1861 SNPP - Version 3 October 1995

  250 Message Sent Successfully
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  503 Error, Pager ID or Message Incomplete
  554 Message Failed [non-administrative reason]
 Or, in the case of an illegal or non-existent pager ID, or some other
 administrative reason for rejecting the page, the server should
 respond:
  550 Failed, Illegal Pager ID (or other explanation)
 After processing a SEND command, the server should remain online to
 allow the client to submit another transaction.
 Level 3 enhancements to this command allow for other responses.
 Please refer to the appropriate section for discussion.

4.3.5 QUIT

 The QUIT command terminates the current session.  The server should
 simply respond:
  221 OK, Goodbye"
 and close the connection.

4.3.6 HELP (optional)

 The optional HELP command displays a screen of information about
 commands that are valid on the SNPP server.  This is primarily to
 assist manual users of the gateway.  Each line of the HELP screen
 (responses) are preceded by a code "214".  At the end of the HELP
 sequence, a "250" series message is issued.
 Possible responses from the SNPP server, with suggested text, in
 response to a HELP command are:
  214 [Help Text]  (repeated for each line of information)
  250 End of Help Information
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented

4.4 Level 2 - Minimum Extensions

 This section specifies minimum enhancements to the SNPP protocol for
 added functionality.

Gwinn Informational [Page 10] RFC 1861 SNPP - Version 3 October 1995

4.4.1 DATA

 The DATA command is an alternate form of the MESSage command,
 allowing for multiple line delivery of a message to the paging
 terminal.  This command's function is similar to the DATA command
 implemented in SMTP (Internet STD10, RFC821).  The SNPP server should
 only allow one DATA or MESSage command to be issued prior to a SEND.
 Possible responses from the SNPP server, with suggested text, in
 response to a DATA command are:
  354 Begin Input; End with <CRLF>'.'<CRLF>
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  503 ERROR, Message Already Entered
  500 Command Not Implemented
  550 ERROR, failed (administrative reason)
  554 ERROR, failed (technical reason)
 Upon receiving a "354" response, the client begins line input of the
 message to send to the pager.  A single period ("."), in the first
 position of the line, terminates input.  After input, the server may
 respond:
  250 Message OK
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  550 ERROR, Invalid Message (or administrative reason)
  554 ERROR, Failed (technical reason)

4.5 Level 2 - Optional Extensions

 This section discusses enhancements to the SNPP protocol for more
 control over paging functions.  These are primarily designed to
 mirror the added functionality built into the Telocator Message Entry
 (TME) protocol as specified in the TDP protocol suite. These
 functions may, optionally (as is being done by the author), be
 integrated into a paging terminal.  There is no requirement to
 implement all of these functions.  Requests for invalid functions
 should return a "500 Function Not Implemented" error.
 It is important to note that, at the time of this publication, the
 TME standard is still not finalized.

4.5.1 LOGIn <loginid> [password]

 This command allows for a session login ID to be specified.  It is
 used to validate the person attempting to access the paging terminal.

Gwinn Informational [Page 11] RFC 1861 SNPP - Version 3 October 1995

 If no LOGIn command is issued, "anonymous" user status is assumed.
 Possible responses from the SNPP server, with suggested text, in
 response to a LOGIn command are:
  250 Login Accepted
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  421 Illegal Access Attempt
  550 Error, Invalid LoginID or Password
  554 Error, failed (technical reason)

4.5.2 PAGEr <PagerID> [Password/PIN]

 This PAGEr command is an enhancement to the level one specification.
 The primary difference is the ability to specify a password or PIN
 for validation or feature access.
 Before proceeding, it is important to understand the logical function
 of the PAGEr command with respect to the LEVEl, COVErage, HOLDtime,
 and ALERt commands (option parameters as described below).  Each time
 a PAGEr command is issued, it should be thought of as the last step
 in a multiple step transaction.
 When the PAGEr command is processed, the pager ID (and password) is
 submitted to the paging terminal with LEVEl, COVErage, HOLDtime, and
 ALERt.  If these parameters have not been altered, then their
 defaults are assumed for the transaction.  After the next PAGEr
 command has been processed, these option parameters are reset their
 defaults.  Using this type of "option-option-option-go" scheme, it is
 possible to specify a different priority level for "Jeff," and an
 alternate coverage area for "Kathy," while sending the same message
 to each.
 Possible responses from the SNPP server, with suggested text, in
 response to a PAGEr command are:
  250 Pager ID Accepted
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  550 Error, Invalid Pager ID or Password
  552 Max Recipients Exceeded
  554 Error, failed (technical reason)

4.5.3 LEVEl <ServiceLevel>

 The LEVEl function is used to specify an optional alternate level of
 service for the next PAGEr command.  Ideally, "ServiceLevel" should

Gwinn Informational [Page 12] RFC 1861 SNPP - Version 3 October 1995

 be an integer between 0 and 11 inclusive.  The TME protocol specifies
 ServiceLevel as follows:
  0 - Priority
  1 - Normal (default)
  2 - Five minutes
  3 - Fifteen minutes
  4 - One hour
  5 - Four hours
  6 - Twelve hours
  7 - Twenty Four hours
  8 - Carrier specific '1'
  9 - Carrier specific '2'
 10 - Carrier specific '3'
 11 - Carrier specific '4'
 The choice on how to implement this feature, or to what level it
 should be implemented, should be optional and up to the discretion of
 the carrier.
 Possible responses from the SNPP server, with suggested text, in
 response to a LEVEl command are:
  250 OK, Alternate Service Level Accepted
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  550 Error, Invalid Service Level Specified
  554 Error, failed (technical reason)

4.5.4 ALERt <AlertOverride>

 The optional ALERt command may be used to override the default
 setting and specify whether or not to alert the subscriber upon
 receipt of a message.  This option, like the previous command, alters
 the parameters submitted to the paging terminal using the PAGEr
 command.  The TME protocol specifies AlertOverride as either 0-
 DoNotAlert, or 1-Alert.
 Possible responses from the SNPP server, with suggested text, in
 response to a ALERt command are:
  250 OK, Alert Override Accepted
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  550 Error, Invalid Alert Parameter
  554 Error, failed (technical reason)

Gwinn Informational [Page 13] RFC 1861 SNPP - Version 3 October 1995

4.5.5 COVErage <AlternateArea>

 The optional COVErage command is used to override the subscriber's
 default coverage area, and allow for the selection of an alternate
 region.  This option, like the previous command, alters the
 parameters submitted to the paging terminal using the PAGEr command.
 AlternateArea is a designator for one of the following:
  1. A subscriber-specific alternate coverage area
  2. A carrier-defined region available to subscribers
 As an example, Mary Ghoti is a subscriber having local service in
 Chicago, Illinois (Mary's region '1').  Her account has been set up
 in such a manner as to allow Mary's pager to be paged nationwide upon
 demand (Mary's region '2').  Specifying "COVErage 2" prior to issuing
 the appropriate "PAGEr" command allows the default Chicago area to be
 overridden, and Mary's pager to be messaged nationally for that
 transaction.  It is assumed that the carrier providing Mary's service
 will keep track of how many pages have been sent to her pager in this
 manner, and will bill her accordingly.
 Possible responses from the SNPP server, with suggested text, in
 response to a COVErage command are:
  250 Alternate Coverage Selected
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  550 Error, Invalid Alternate Region
  554 Error, failed (technical reason)

4.5.6 HOLDuntil <YYMMDDHHMMSS> [+/-GMTdifference]

 The HOLDuntil command allows for the delayed delivery of a message,
 to a particular subscriber, until after the time specified.  The time
 may be specified in local time (e.g. local to the paging terminal),
 or with an added parameter specifying offset from GMT (in other
 words, "-0600" specifies Eastern Standard Time).  This option, like
 the previous command, alters the parameters submitted to the paging
 terminal using the PAGEr command.
 Possible responses from the SNPP server, with suggested text, in
 response to a HOLDuntil command are:
  250 Delayed Messaging Selected
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented

Gwinn Informational [Page 14] RFC 1861 SNPP - Version 3 October 1995

  550 Error, Invalid Delivery Date/Time
  554 Error, failed (technical reason)

4.5.7 CALLerid <CallerID>

 The CALLerid function is a message-oriented function (as opposed to
 the subscriber-oriented functions just described).  This allows for
 the specification of the CallerIdentifier function as described in
 TME.  This parameter is optional, and is at the discretion of the
 carrier as to how it should be implemented or used.
 Possible responses from the SNPP server, with suggested text, in
 response to a CALLerid command are:
  250 Caller ID Accepted
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  550 Error, Invalid Caller ID
  554 Error, failed (technical reason)

4.5.8 SUBJect <MessageSubject>

 The SUBJect function allows is a message-oriented function that
 allows the sender to specify a subject for the next message to be
 sent.  This parameter is optional and is at the discretion of the
 carrier as to how it should be implemented or used.
 Possible responses from the SNPP server, with suggested text, in
 response to a SUBJect command are:
  250 Message Subject Accepted
  421 Too Many Errors, Goodbye (terminate connection)
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  550 Error, Invalid Subject Option
  554 Error, failed (technical reason)

4.6 Level 3 - Two-Way Extensions

 This section specifies enhancements to the SNPP protocol to support
 acknowledgment-based paging (2-way).  One of the more powerful
 features of ReFLEX-style paging, in addition to confirmed message
 delivery, is the ability to "seed" a message with multiple-choice
 type responses.  After the recipient views the message, she can reply
 with one of the seeded messages.  In addition to the multiple-choice
 responses (MCR's), the sender may elect to receive confirmation when
 the message is first viewed by the recipient.

Gwinn Informational [Page 15] RFC 1861 SNPP - Version 3 October 1995

4.6.1 2WAY

 The 2WAY command prefaces each two-way transaction (see previous
 example).  This places the server in the mode to receive and process
 a single 2-way transaction. The server returns to "non-2WAY" mode
 upon the completion of a SEND command or a RESEt command.  In 2WAY
 mode, it is, however, possible to do multiple MSTAtus commands (to
 check responses from field message units).  Possible responses are:
  250 OK, Beginning 2-Way Transaction
  550 Error, Standard Transaction Already Underway, use RESEt
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  554 Error, failed (technical reason)
 4.6.2 PING <PagerID | Alias>
 This command localizes (finds) the field message unit on the system
 and returns its location and/or status.  Because of the sensitive
 nature of location information, the subscriber may elect to have a
 generic "pager located" message (ACLU mode) rather than to return her
 actual location. Possible responses are:
  820 <Locus_Code> Unit On System, This Area
  821 Unit On System, No Location Information Available (ACLU mode)
  750 Unit Valid But Not Online At This Time
  920 Unit Not Online, But Can Queue Message for Later Delivery
  550 Can't PING; Unit NOT 2-way capable
  550 Unknown or Illegal ID
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  554 Error, failed (technical reason)

4.6.3 EXPTag <hours>

 Changes the default expiry time for a queued message delivery.  If
 the message is not delivered in the specified number of hours, then
 it is deleted and the MSTAtus tag is updated to reflect the inability
 to deliver (code 760).  Possible responses are:
  250 Message Expiry Time Changed to 'nnn' Hours
  550 Cannot Change Expiry Time
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  554 Error, failed (technical reason)

Gwinn Informational [Page 16] RFC 1861 SNPP - Version 3 October 1995

4.6.4 NOQUEUEing

 Specifies that the server should not allow message queuing for this
 2WAY transaction.  In this mode, if a pager is not online, the client
 will receive a "750" series response to a PAGEr command.  This
 command must be specified prior to a PAGEr command.  Possible
 responses are:
  250 Queuing Disabled, This Transaction
  550 Can't Disable Queueing
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  554 Error, failed (technical reason)

4.6.5 ACKRead <0|1>

 Activates or deactivates message "read" acknowledgment.  When
 activated, instructs the field message unit to return a message when
 the subscriber actually views the received message.  This feature is
 independent of the actual reply.  Possible responses are:
  250 Read Acknowledgment <Enabled|Disabled>
  550 Cannot modify Read Acknowledgment
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  554 Error, failed (technical reason)

4.6.6 RTYPe <Reply_Type_Code>

 Changes the type of reply expected from the field message unit that
 is acceptable to the client program.  Initial appropriate reply type
 codes are:
  NONE        - (default) No Reply Permitted
  YESNO       - Seeds a simple "Yes" or "No reply
  SIMREPLY    - Only pre-coded replies from providers's reply base
  MULTICHOICE - Allows full multiple choice replies
  TEXT        - Allows full text replies (generated by field unit)
 Possible responses to an RTYPe command are:
  250 Reply Type Accepted
  550 Illegal Reply Type
  503 Already Entered That
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  554 Error, failed (technical reason)

Gwinn Informational [Page 17] RFC 1861 SNPP - Version 3 October 1995

4.6.7 MCREsponse <2-byte_Code> Response_Text

 This command is issued prior the the SEND command, and "seeds" the
 transaction with an acceptable multiple choice response. Each
 response is specific to the current message.  The number of
 acceptable responses may be limited by the SNPP server as desired by
 the provider.  Examples of MCREsponse(s) are:
  MCREsponse 1E2C Here is one response
  MCREsponse 0002 This is another response
 Responses from the SNPP server to the client are:
  250 Response Added to Transaction
  502 Error! Would Duplicate Previously Entered MCResponse
  550 Invalid MCResponse Code
  550 MCResponses Not Enabled
  552 Too Many MCResponses Entered
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  554 Error, failed (technical reason)

4.6.8 PAGEr

 In 2WAY mode, the following enhanced responses are available:
  850 Two-Way Unit Online and Available; Transaction Accepted
  950 Unit NOT Online; Message Will be Queued for Later Delivery
  750 Two-Way Unit NOT Online; Transaction Denied
  550 Error, Pager Not 2WAY Capable
  550 Error, RTYPe Mode Invalid for This Unit
  503 Already Selected PAGEr
  421 Gateway Service Unavailable (terminate connection)
  554 Error, failed (technical reason)

4.6.9 SEND

 Instructs the SNPP server to "launch" the message (plus attached
 response codes) to the field message unit.  A successful SEND command
 will return, to the client, a "Message_Tag" number and a "Pass_Code"
 for periodic status checking.  The client then uses the MSTAtus
 command to check the progression of the transaction. The
 "Message_Tag" functions as a "record locator," while the "Pass_Code"
 should be a randomly generated "PIN" code to authorize checking of
 the "Message_Tag."
 Response codes to a SEND command, as well as the MSTAtus command,
 indicate the degree of "finality" to the transaction.  Based on the

Gwinn Informational [Page 18] RFC 1861 SNPP - Version 3 October 1995

 delivery process, there are four categories.  Together with their
 response code prefixes, these are:
  86x - Initial message delivered, awaiting requested action(s)
  87x - Intermediate processing completed, awaiting closure
  88x - Transaction concluded (final)
  96x - Queued transaction
 These prefixes make a multi-tiered transaction relatively simple to
 follow to closure.  When an 88x series response code is received from
 the server, all requested portions of the transaction have been
 processed, and no further status changes will take place.
 The SEND command should reply with the first tier of message
 processing. Following this, the status of the message in the system
 is checked, periodically, using the MSTAtus command.
 Possible responses to a SEND command are:
  860 <Message_Tag> <Pass_Code> Delivered, Awaiting Read Ack
  861 <Message_Tag> <Pass_Code> Delivered, Awaiting Reply (MCR)
  880 <Message_Tag> <Pass_Code> Message Delivered
  960 <Message_Tag> <Pass_Code> OK, Message QUEUED for Delivery
  550 Delivery Failed!  Message destroyed.
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  554 Error, failed (technical reason)

4.6.10 MSTAtus <Message_Tag> <Pass_Code>

 This is used by a client program to periodically check the status of
 delivery and response of a given message.  The SEND command returns
 the "Message_Tag" and "Pass_Code" required to check the status. A
 "Message_Tag" may be (should be) expired by the SNPP server after an
 appropriate amount of time has passed.  Expiration of these tags is
 vendor dependent, and may accelerate after the first check after
 final disposition of the message (such as after a client program has
 successfully received the field unit's response code).
 The tag record contains a "Sequence" number which is an incremental
 counter that rises as the record's status changes (such as from a
 delivery acknowledgment to a reply).  In addition, date and time of
 the current transaction should be kept in the following format:
  YYMMDDHHMMSS+GMT   (example: 950925143501+7)

Gwinn Informational [Page 19] RFC 1861 SNPP - Version 3 October 1995

 Because of the tiered structure of replies, possible responses to an
 MSTAtus command are:
  860 <Sequence> <Date&Time> Delivered, Awaiting Read Confirmation
  861 <Sequence> <Date&Time> Delivered, Awaiting Reply (MCR)
  870 <Sequence> <Date&Time> Delivered, Read, Awaiting Reply (MCR)
  880 <Sequence> <Date&Time> Message Delivered (No Reply Pending)
  881 <Sequence> <Date&Time> Message Delivered and Read by Recipient
  888 <Sequence> <Date&Time> <Reply_Code> MCR Reply Received
  889 <Sequence> <Date&Time> <Full_Text_Response>
  960 <Sequence> <Date&Time> Message Queued; Awaiting Delivery
  780 <Sequence> <Date&Time> MESSAGE EXPIRED Before Delivery!
  550 Unknown or Illegal Message_Tag or Pass_Code
  421 Gateway Service Unavailable (terminate connection)
  500 Command Not Implemented
  554 Error, failed (technical reason)
 After a closure-series (88x) command has been returned to the client,
 acceleration of message tag deletion may be desired to maximize use
 of resources on the server.

KTAG <Message_Tag> <Pass_Code>

 Used to "kill" the message tag after final reading (or when no
 further responses are desired).  This is more of a courtesy feature
 that allows the client to "clean up" rather than wait for the SNPP
 server to expire the tag.

4.7 Illegal Commands

 Should the client issue an illegal command, the server may respond in
 one of the two following ways:
  421 Too Many Errors, Goodbye (terminate connection)
  500 Command Not Implemented, Try Again
 The number of illegal commands allowed before terminating the
 connection should be at the discretion of the operator of the SNPP
 server.  The only response that has not been discussed is:
  421 SERVER DOWN, Goodbye

Gwinn Informational [Page 20] RFC 1861 SNPP - Version 3 October 1995

 This is used to refuse or terminate connections when the gateway is
 administratively down, or when there is some other technical or
 administrative problem with the paging terminal.

4.8 Timeouts

 The SNPP server can, optionally, have an inactivity timeout
 implemented.  At the expiration of the allotted time, the server
 responds "421 Timeout, Goodbye" and closes the connection.

4.9 Rigidity of Command Structure

 The commands from client to server should remain constant. However,
 since the first character of the response indicates success or
 failure, the text of the server responses could be altered to suit
 the tastes of the operator of the SNPP server. It is suggested that
 the response codes mirror SMTP response codes as closely as possible.

5. Revision History

 Originally, when proposed, the author employed POP2 style
 result/response codes.  The Internet community suggested that this
 '+' and '-' style theory be altered to provide numeric response codes
 -- similar to those used in other services such as SMTP.  The
 protocol has been altered to this specification from the first
 proposed draft.
 Administrative errors (Illegal Pager ID, for example) have been
 separated from technical errors (out-of-space on disk, for example).
 Administrative failures are generally preceded with a 550 series
 response, while technical failures bear a 554 series code.
 Level two enhancements to the protocol have been added in preparation
 for TME deployment.
 Level three enhancements to the protocol have been added in
 preparation for acknowledgment-based messaging.
 Error code "502 Command not implemented" was changed to a general
 "500 Command not recognized" failure result to closer follow SMTP.

6. Relationship to Other IETF Work

 The strategy of this specification, and many of its details, were
 reviewed by an IETF Working Group and three IESG members.  They
 concluded that an approach using the existing email infrastructure
 was preferable, due in large measure to the very high costs of
 deploying a new protocol and the advantages of using the Internet's

Gwinn Informational [Page 21] RFC 1861 SNPP - Version 3 October 1995

 most widely-distributed applications protocol infrastructure.  Most
 reviewers felt that no new protocol was needed at all because the
 special "deliver immediately or fail" requirements of SNPP could be
 accomplished by careful configuration of clients and servers.  The
 experimental network printing protocol [4] was identified as an
 example of an existing infrastructure approach to an existing
 problem. Other reviewers believed that a case could be made for new
 protocol details to identify paging clients and servers to each other
 and negotiate details of the transactions, but that it would be
 sensible to handle those details as extensions to SMTP [1, 2] rather
 than deploying a new protocol structure.
 The author, while recognizing these positions, believes that there is
 merit in a separate protocol to isolate details of TAP/IXO and its
 evolving successors from users and, indeed, from mail-based
 approaches that might reach systems that would act as SMTP/MIME [3]
 to SNPP gateways.  Such systems and gateways are, indeed, undergoing
 design and development concurrent with this work.  See the section
 "Why not just use Email and SMTP?" for additional discussion of the
 author's view of the classical electronic email approach.

7. References

 [1] Postel, J., "Simple Mail Transfer Protocol", STD 10, RFC 821,
     USC/Information Sciences Institute, August 1982.
 [2] Klensin, J., Freed, N., Rose, M., Stefferud, E., and D. Crocker,
     "SMTP Service Extensions", United Nations University, Innosoft,
     Dover Beach Consulting, Inc., Network Management Associates,
     Inc., The Branch Office, RFC 1425, February 1993.
 [3] Borenstein, N., and N. Freed, "MIME  (Multipurpose Internet Mail
     Extensions) Part One:  Mechanisms for Specifying and Describing
     the Format of Internet Message Bodies", RFC 1521, Bellcore,
     Innosoft, September 1993.
 [4] Rose, M., and C. Malamud, "An Experiment in Remote Printing", RFC
     1486, Dover Beach Consulting, Inc., Internet Multicasting
     Service, July 1993.

Gwinn Informational [Page 22] RFC 1861 SNPP - Version 3 October 1995

8. Security Considerations

 Security issues are not discussed in this memo.

9. Author's Address

 R. Allen Gwinn, Jr.
 Associate Director, Computing Services
 Business Information Center
 Southern Methodist University
 Dallas, TX  75275
 Phone:  214/768-3186
 EMail:  allen@mail.cox.smu.edu  or  allen@radio.net

Gwinn Informational [Page 23]

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