Accessing Your Paging Server
with the Async Professional Paging Components
Async Professional 3.0 includes new paging components that
support the growing TAP and SNPP protocol standards for Alphanumeric paging.
For these to work, your paging company has to provide “servers” that support
these protocols. Having an available Paging Server is an absolute requirement,
but even giving that your company provides them is far from a guarantee that
their implementations are complete or conform to the standards.
TAP
The main awkwardness that is likely to arise is from poor
or incomplete TAP implementations, as the “standards” (if one may call them
that) for TAP are relatively new and don’t have the full force of Internet
standard making behind them (as is the case with SNPP and RFC-1861).
The TApdTAPPager component provides what should be a
reasonably generic approach to communicating with a wide range of TAP paging
servers; even so there may still arise some locations to which you find yourself
unable to successfully log into or send.
TApdTAPPager provides a few built in properties to let you
modify how it interacts with the Paging server. In particular the MessageLength
property lets you specify the maximum length that a message block will occupy,
some Paging Servers appear to have trouble dealing with message blocks greater
than about 80 characters (thus the default); even though the TAP specification
allows blocks up to 256 characters.
Similarly the TAP version 1.8 specification allows sending
“control” characters as part of messages via an escaping system. This may be
turned on and off via the TApdTAPPager UseEscapes property. But since many
Paging Servers are still apparently using software that supports lower versions,
the default for this is to have UseEscapes turned off.
Another possibility is that some servers may respond to
subtly different message structures, or may send subtly different response codes
than are expected by the TApdTAPPager component as-is. We anticipate this being
a rarity, but if you find yourself in this situation, you have access to the
codes that are being used in the
AdPager source
code.
const
{TAP server repsonse
sequences}
TAP_ID_PROMPT : string
= 'ID=';
TAP_LOGIN_ACK : string
= cAck + cCr;
TAP_LOGIN_NAK : string
= cNak + cCr;
TAP_LOGIN_FAIL : string
= cEsc + cEot + cCr;
TAP_MSG_OKTOSEND: string
= cEsc + '[p';
TAP_MSG_ACK : string
= cAck + cCr;
TAP_MSG_NAK : string
= cNak + cCr;
TAP_MSG_RS : string
= cRs + cCr;
TAP_DISCONNECT : string
= cEsc + cEot + cCr;
TAP_AUTO_LOGIN : string
= cEsc + 'PG1' + cCr;
TAP_LOGOUT : string
= cEot + cCr;
(Note, the various “cXxx” constants for the control
characters are to be found in the
OoMisc unit)
Since these are defined as “typed constants”, these may be
modified by run-time code. You should change these only after you’ve determined
for certain that the Paging Server is sending incompatible sequences. One good
way to examine in detail what you’re actually getting from the server is to
configure your TApdComPort component to generate a “Dispatcher Log” (set
TApdComPort.Logging = tlOn). This will show precisely what is being sent over
the port.
Explaining the precise functioning of all of these
sequences is really beyond the scope of this particular how-to, if you find you
need this you’ll also need to peruse the TAP specification (and determine how
your Server’s implementation varies from it).
SNPP
An SNPP communication consists of a series of
request/response transactions wherein the client sends some information and the
server responds with either an acknowledgement or an error. The formatting of
these requests and responses is defined in the SNPP specification (RFC-1861); it
remains possible, of course, for SNPP servers to do non-compliant things. This
will most likely arise in the form of non-standard response strings from the
SNPP server.
The TApdSNPPPager component provides run-time properties
that allow changing the strings used to send server requests and to detect
server responses:
·
ServerInitString
·
ServerSuccessString
·
ServerDataInput
·
ServerResponseFailContinue
·
ServerResponseFailTerminate
·
ServerDoneString
The functioning of each of these properties is described in
the Async Professional Reference Guide.
