"Andrea Viscovich" <[EMAIL PROTECTED]> provided me a patch for
implementing a ring service for the at2 devices. Basical idea is to
use the GSM AT commands to get notice of incoming calls to the GSM
modem device -- yes! you can call them, but don't wonder if they don't
reply :)) -- and activate some kind of logic behind that.

Andrea did this very hard-coded in gw/smsc_at2.c for a very special
purpose and the way it is done there we will not be able to include it
to cvs. I'll have to break things up a bit and make it more cleanly.

Main intension is to introduce a new group called 'ring-service'. This
is a single-group, due to the fact that you don't have keywords like
in the 'sms-service' type to distinguish the logic, but -- yes, ofter
you have the famous but -- you may distinguish by another criterial
that is unique, like the caller's phonenumber itself.

So here are the considerations that I would like to have some comments
and discussion on:

(i) group ring-service should be a single-group type. Hence any
incoming call will be routed to the same URL/file, whatever, at least
the same logic. The logic behind the HTTP request, i.e. Servlet or PHP
script may distinguish by caller id and reply on a personalized basis.

Such a single-group would look like this:

  smskannel.conf:

  [...]
  group = ring-service
  url = "http://host/uri?<param>"
  [...]

with almost all fields that are used for the sms-service group.

(ii) group ring-service should be a multi-group type, like
sms-service. The keyword in sms-service group may be mapped to the
caller's phonenumber here, using again routine facilities that are
already available, like the unified-prefix things etc. The first group
would be the default group if the caller id does not match with the
other groups.

Such a multi-group would look like this:

  smskannel.conf:

  [...]
  group = ring-service
  pattern = "4917;+49173;"
  url = "http://host/uri?<param>"
  [...]

where pattern specifies search-patterns for the caller's phonenumber
that are routed to this service.

Pros and cons for ring-services IMHO:

pro: pull-operation without "investment", which means you "call" the
device and hence you don't need to pay for a SMS that initiates a
service.

pro: higher realtime closure, even while you "reply" by SMS you do
initiate the service with a realtime mechanism, the call itself.
(Think of the latency time an inbound SMS may take if the network is
busy or blocked for SMS).

con: we can not multiplex the incoming calls, so when user A calls the
device an other user B may get a busy line signal. (This depends of
course on the load of the system and the spread of request over time)

con: are we still safe with incoming SMS messages when a ring-service
is handled?! I don't know exactly, this should be investigated. At
least it should work, since it works in real human usage environment
too I guess?!


Any comments welcome.

Stipe

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