view README @ 85:70c3c8ebee33

sip-in: handle MNCC RTP bogons from OsmoMSC
author Mychaela Falconia <falcon@freecalypso.org>
date Tue, 20 Sep 2022 22:47:53 -0800
parents dffcae9bc8a3
children 97317ede320a
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This Hg repository contains a work-in-progress named Themyscira Wireless system
software.  Themyscira Wireless (ThemWi) is an experimental GSM network operated
by Mother Mychaela of FreeCalypso at a semi-urban/semi-rural location in
Southern California, USA; this GSM network is operated with Osmocom CNI software
components, all running on a single Slackware Linux server.  ThemWi system sw
is going to be a suite of daemon processes and command line tools that run on
the same machine as all those Osmocom sw components and provide some additional
functionality that is not provided "out of the box" by Osmocom, most important
of which is outside connectivity to USA PSTN.

Right now we have a themwi-mncc daemon process that connects to OsmoMSC via the
MNCC socket interface provided by the latter and takes the place of OsmoMSC's
mncc_builtin.  themwi-mncc switches local calls (from one GSM subscriber to
another) just like mncc_builtin, but it also provides a hook (mtcall_socket)
for routing externally originated calls to GSM (which then become MT calls),
and it will later have a similar interface for routing MO calls to the outside
world.  Additional daemon processes that will interface with USA PSTN via SIP
(one process accepting SIP INVITEs from bulkvs.com servers, turning them into
MNCC and sending the calls toward GSM, and another process going the other way)
remain to be implemented.

We are currently experimenting with using bulkvs.com as our USA PSTN
connectivity provider.  Like most low-cost PSTN connectivity providers, they
provide the interface to PSTN in the form of a SIP trunk - while I would
absolutely love to get a traditional TDM trunk instead, with SS7 signaling,
such a toy would be far beyond my budget, hence I have to settle for SIP.
Our current status is:

* We have already obtained a block of USA phone numbers (NANP, chosen numbers
  from an exchange area local to us) from bulkvs.com;

* These bulkvs-sourced real NANP numbers have been entered as MSISDNs into
  OsmoHLR records for our test SIMs operating on ThemWi GSM;

* We can successfully dial calls from one ThemWi GSM phone to another, with
  themwi-mncc understanding all dialing formats that are considered standard
  for cellular phone networks in USA (full international, or 11 digits starting
  with '1' but no '+', or 10 digits only), as well as our own non-standard
  shorthand dialing method with only 4 digits;

* Whenever someone dials one of our NANP numbers from the outside world, bulkvs
  servers send UDP SIP INVITE packets to our server, and by dumping them with
  our sip-udp-dump utility, we can see exactly what we have to work with;

* The rest remains to be implemented.