[SWLUG] SIP questions

[Steve Hill]

On Thu, 20 Aug 2009, Dave Cridland wrote:

> And of course there's Jingle, the XMPP stuff that was bootstrapped by Google 
> Talk. This, too, uses SDP, ICE, RTP, and many of the same codecs as SIP, so 
> you can argue it as being very closely related.

Indeed.  SIP stands for "session initiation protocol" - it doesn't 
actually carry the voice traffic, it just negotiates the RTP sessions 
which do.  Jingle is pretty much the same thing - it does all the session 
setup and the voice traffic is then carried in separate RTP streams.

> Asterisk can, I believe, route calls about through all the various flavours 
> of open-standard VOIP, too, so you can terminate your calls onto SIP around 
> your home LAN, but route out to the internet via Jingle as well.

Yes, that's right.  As I mentioned, I use CallWeaver, but Asterisk is 
another option.  In fact, CallWeaver is a fork of Asterisk as an attempt 
to make it more Free - the Asterisk project is run by Digium primarilly to 
support the telephony cards they make.  Their licensing policies basically 
make it impossible to link with other GPLed libraries and they have a 
habit of rejecting features that take the focus away from their own 
current hardware.  So the CallWeaver project was forked to get around both 
of these issues (and thus was able to add things like software fax 
support using existing GPLed code).

It has been a few years since I've used Asterisk, but it certainly used 
to be that a few features, such as conferencing, depended on Asterisk 
having access to timer hardware found on Digium's ZapTel cards.  There 
was a kludge so you could use these features without the extra hardware by 
loading a kernel module that emulated the timers, but it was a bit messy. 
One of the first things CallWeaver threw out after the fork was the 
requirement for these timers.

-- 

  - Steve
    xmpp:steve at nexusuk.org   sip:steve at nexusuk.org   http://www.nexusuk.org/

      Servatis a periculum, servatis a maleficum - Whisper, Evanescence