RFC1861 - Simple Network Paging Protocol - Version 3 -Two-Way Enhanced

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　　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 RFCsuggests 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

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.

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.

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.

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

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

"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

"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.

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:

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.

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.

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

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)

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:

- 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)

4.5.6 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

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.

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)

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)

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

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)

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

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

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, RFC821,
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, RFC1425, 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", RFC1521, 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.

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

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