Bridging POTS and VoIP
SS7 to IP integration is one of the major items in any IP-ization of a traditional telecommunications system. Most of the traditional telecommunications equipment still use PSTN signalling. Most smaller equipment use Q.931 (ISDN Connection Part) and some implement an entire suite of SS7 protocols. It is quite a long list.
There are number of ways to get this done. The fastest is to use hardware (or fully-integrated commercial) SS7-to-IP converters. A good list can be found here. Another way is to use a PC-based solutions.
The most prominent of which is the Asterisk+SS7 Project and OpenSS7 Project. Being an Asterisk fan, I believe using Asterisk would be the fastest way to do this. Besides, OpenSS7 is new learning for me. I got quite used to the extensibility of the Asterisk platform. Asterisk has something called a SS7 Channel Driver (chan_ss7) sub-project. This allows the use of a Zaptel-compatible PRI card (Digium) and Asterisk software to do SS7 signalling.
This is the current list of supported major SS7 features by the current SS7 Channel Driver:
- MTP2 (Q.703) implementation
- MTP3 (Q.704) implementation (bare essentials)
- ISUP (Q.76x) implementation (large subset)
- Supports Digium E1 (T1 and other zap-compatible cards should be easy to add).
- Supports incoming and outgoing calls.
- Supports full ALAW audio (ULAW should be easy to add).
- Facilities for raw MTP2 packet dump, suitable for Ethereal debugging.
- Supports high call volumes; tested with 120 simultaneous calls.
- Supports multiple linksets with different DPCs
- Supports linksets with multiple links.
- Supports load sharing and MTP changeover.
- Supports multiple hosts (cluster) configuration with load sharing and failover.
- Flexible Dial command syntax for SS7 to allow use on linksets
I seem to have trouble getting to the Sipira site but active development is still being done in the Asterisk SS7 mailing list hosted by Digium. The Asterisk project itself is pretty active and a lot of new development is still being done on that front. The latest version of the chan_ss7 driver was released just last March 2006 making it a pretty active project. This makes Asterisk SS7 a worth while investment.
Even the OpenSS7 project does not seem very active at this point in terms of applications. They are more focused on the stack code and writing improvements to the operating system layer (which is also very important). So our hope for now is that the chan_ss7 mailing list community stays active.
I already built chan_ss7 and have a working Asterisk installation. Now, I just need to get my hands on some Zaptel E1 PRI cards (Digium or Sangoma) to complete by testbed.
