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Network Working Group                                           A. GwinnRequest for Comments: 1645                 Southern Methodist UniversityObsoletes:1568                                                July 1994Category: InformationalSimple Network Paging Protocol - Version 2Status 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 both alphanumeric and   numeric pages (one-way) to radio paging terminals.  Gateways   supporting this protocol, as well as SMTP, have been in use for   several months for nationwide paging and messaging.  In addition,   email filters and SNPP client software for Unix and Windows 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   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.  Additionally, automatic page   delivery should be somewhat more simplified.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 toGwinn                                                           [Page 1]

RFC 1645                    SNPP - Version 2                   July 1994   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.   However, acknowledging the complexity 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.  Validation of the paging information is left   completely up to the paging terminal, making an SNPP gateway a direct   "shim" between a paging terminal and the Internet.3. Why not just use Email and SMTP?   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.Gwinn                                                           [Page 2]

RFC 1645                    SNPP - Version 2                   July 1994   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.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 four   categories:    2xx - Successful, continue    3xx - Begin DATA input (see "DATA" command)    4xx - Failed with connection terminated    5xx - Failed, but continue session   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 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.Gwinn                                                           [Page 3]

RFC 1645                    SNPP - Version 2                   July 19944.1 Examples of SNPP Transactions   The following illustrate examples of client-server communication   using SNPP.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, Goodbye4.1.2 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 AcceptedGwinn                                                           [Page 4]

RFC 1645                    SNPP - Version 2                   July 1994    SEND                          -->                                  <--  250 Message Sent OK    QUIT                          -->                                  <--  221 OK, Goodbye4.2 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.4.2.1 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)   The level 2 enhancements affect the PAGEr command.  Please refer to   the appropriate section for details.4.2.2 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 AlreadyGwinn                                                           [Page 5]

RFC 1645                    SNPP - Version 2                   July 1994   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)4.2.3 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)4.2.4 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:    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]Gwinn                                                           [Page 6]

RFC 1645                    SNPP - Version 2                   July 1994   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.4.2.5 QUIT   The QUIT command terminates the current session.  The server should   simply respond:    221 OK, Goodbye"   and close the connection.4.2.6 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 Implemented4.3 Level 2 - Minimum Extensions   This section specifies minimum enhancements to the SNPP protocol for   added functionality.4.3.1 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.Gwinn                                                           [Page 7]

RFC 1645                    SNPP - Version 2                   July 1994   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)4.4 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.4.4.1 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.   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)Gwinn                                                           [Page 8]

RFC 1645                    SNPP - Version 2                   July 1994    421 Illegal Access Attempt    550 Error, Invalid LoginID or Password    554 Error, failed (technical reason)4.4.2 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    554 Error, failed (technical reason)4.4.3 LEVEl <ServiceLevel>   The LEVEl function is used to specify an optional alternate level of   service for the next PAGEr command.  Ideally, "ServiceLevel" should   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 hoursGwinn                                                           [Page 9]

RFC 1645                    SNPP - Version 2                   July 1994    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)4.4.4 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)4.4.5 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:Gwinn                                                          [Page 10]

RFC 1645                    SNPP - Version 2                   July 1994    - A subscriber-specific alternate coverage area    - 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)4.4.6 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    550 Error, Invalid Delivery Date/Time    554 Error, failed (technical reason)4.4.7 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 inGwinn                                                          [Page 11]

RFC 1645                    SNPP - Version 2                   July 1994   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)4.4.8 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)4.5 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   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.Gwinn                                                          [Page 12]

RFC 1645                    SNPP - Version 2                   July 19944.6 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.4.7 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.   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   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 newGwinn                                                          [Page 13]

RFC 1645                    SNPP - Version 2                   July 1994   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",RFC1486, Dover Beach Consulting, Inc., Internet Multicasting       Service, July 1993.Gwinn                                                          [Page 14]

RFC 1645                    SNPP - Version 2                   July 19948.  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@sulaco.lonestar.orgGwinn                                                          [Page 15]