RFC 1568 - Simple Network Paging Protocol, Version 1(b)
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 in one nationwide paging firm. One other paging firm
is in the process of adopting it.
Earlier versions of this specification were reviewed by IESG members
and the IETF's "822 Extensions" Working Group. They preferred an
alternate strategy, as discussed under "Relationship to Other IETF
Beepers are as much a part of computer nerdom as X-terminals
(perhaps, unfortunately, more). The intent of Simple Network Paging
Protocol (SNPP) 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 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 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. One
note: even though the TAP protocol allows for a password for sending
simple pages, they are rarely used (especially in commercial
markets), and therefore support for them has not been implemented in
this version of the protocol.
Even though TAP is widely used throughout the industry, there are
plans on the table to move to a more flexible "standard" protocol
(the proposal for which is actually more convoluted than most
Internet RFC's). 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
this protocol attempts to address. Validation of the paging
information is left completely up to the TAP/IXO paging terminal,
making an SNPP gateway a direct "shim" between a paging terminal and
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
(email@example.com) sends a message to Zaphod Beeblebrox's beeper
(firstname.lastname@example.org). 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. 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 Future of SNPP
While the current form of the SNPP protocol is designed for use with
TAP/IXO, it is intended to provide a porting base for use with the
newer TME (TDP) protocol. In addition, future releases of SNPP will
allow for multiple recipient messages with individual "envelope"
options and specifications as allowed by TME. For example, the
protocol should allow the user to specify delivery of an urgent
message to Zaphod in Denver, while carbon-copying Mary in Des Moines
at a lower priority.
5. The 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 six input commands (the first 4 characters of each are
significant) that solicit various server responses falling into three
categories: (1) successful, (2) failed-but-continue, and (3) failed-
with-connection-terminated. The first character of every server
response code is a digit indicating the category of response: '2xx',
'5xx', and '4xx' respectfully. 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 greeting followed by "250
READY" (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 TAP paging terminal, gathers a response, and reports the
success or failure to the client.
6.1 A Typical Successful Connection
Open Connection -->
<-- 220 SNPP Gateway Ready
PAGE 5551212 -->
<-- 250 OK
MESS Your network is hosed -->
<-- 250 OK
<-- 250 Page Sent
<-- 221 OK, Goodbye
The PAGEr command sets the pager ID (PID) number, for the
transaction, into the gateway. The PID used must reside in the TAP
terminal (and there is where it should be validated). Limited
validation may optionally be done on the server (such as all numeric,
and ID length), or it can all be done by the TAP terminal at the time
the page is sent. Duplicating the PAGEr command before SENDing the
message should produce an "503 ERROR, Already Entered" message, and
allow the user to continue.
In the future, a series of PAGEr commands may be specified to allow
for multiple recipients of the same message. Right now, however,
TAP/IXO only validates the PID at the time the message is accepted by
the paging terminal. This makes "pre" validation of PID's currently
The MESSage command sets the numeric or alphanumeric message for the
transaction, 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 TAP/IXO paging terminal.
Duplicating the MESSage command before SENDing the message should
produce an "503 ERROR, Already Entered" message, and allow the user
The RESEt command clears the PAGEr and MESSage fields, and allows the
client to start over. This is provided, primarily, as a means to
reset accidentally entered information during a manual session. Upon
a successful reset, the server should respond "250 RESET OK".
The SEND command processes the page to the TAP terminal. Prior to
processing, the PAGEr and MESSage fields 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 all of the
fields are filled in, the SNPP server should format and send the page
to the TAP terminal, and await a response. Upon receiving a reply,
the server should respond as follows:
250 Page Sent - successful delivery
554 Failed, - unsuccessful, and gives a 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
550 Failed, Illegal Pager ID (or other explanation)
After processing a SEND command, the server should remain online to
allow the client to enter another page.
The QUIT command terminates the current session. The server should
respond "221 OK, Goodbye" and close the connection.
The HELP command (optional) 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 OK" is issued.
6.3 Illegal Commands
Should the client issue an illegal command, the server should respond
"421 ERROR, Goodbye" and close the connection immediately.
Optionally, the server may respond "502 Command Error, try again"
should it be desirable to leave the connection open.
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.
6.5 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 should one
desire. The following is a hunk of C code that is used currently in
an SNPP gateway. The only response that has not been discussed is
"421 SERVER DOWN, Goodbye" and is used when the gateway is
administratively down, or when there are communication problems with
the TAP/IXO paging terminal.
/* SNPP Client Commands */
#define PAGER "PAGE"
#define MESSAGE "MESS"
#define SEND "SEND"
#define QUIT "QUIT"
#define RESET "RESE"
#define HELP "HELP"
/* Responses from SNPP server to client */
#define SNPP_OK "250 OK"
#define SNPP_RESET "250 Reset OK"
#define SNPP_SENT "250 Page Sent"
#define SNPP_BADPIN "550 Failed,"
#define SNPP_NOTSENT "554 Failed,"
#define SNPP_ENTERR "503 Error, Already Entered"
#define SNPP_ERRINC "503 Error, Incomplete Info"
#define SNPP_OKCLOS "221 OK, Goodbye"
#define SNPP_TIMEOUT "421 Timeout, Goodbye"
#define SNPP_ERRCLOS "421 ERROR, Goodbye"
#define SNPP_DOWN "421 SERVER DOWN, Goodbye"
7. 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
When a bad pager ID message (IXO/TAP administrative failure was
received from the paging terminal, a 554 series (general failure) was
returned. This has been changed to a 550 failure code allowing a
distinction to be made.
8. 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  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 
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.