Tue, 14 Mar 2006

Here a VoIP, there a VoIP, everywhere a VoIP.

I've been using VoIP for many years. Some thoughts.

Asterisk has never really appealed to me. I can't put a definite finger on why this is so but it feels like having email printed. A half-step along the way. It is a good halfway point but doesn't feel like a full solution.

What does is something which turns PSTN into SIP; then you can use a SIP router (SER, OpenSER, partysip, sipXrouter and many others) to do what you need.

That kind of device is something like a Sipura 3000. Very easy to setup to register to your own SIP router, where you can do the heavy lifting. Of course, you don't need to interface to the PSTN to take advantage of VoIP.

I have SIP accounts at bbpglobal, ekiga, fwd, iptel, openwengo, sipme, sipgate and voipuser. As well as few other, more private, networks.

NOTE: openwengo requires some work to retrieve the SIP id.

I've also been playing with gaim2 recently. It is the reason I'm only vaguely online – gaim2 breaks sound on my laptop – and that interferes with the VoIP stuff I do.

Anyway, one interesting feature of gaim2 is that it supports SIP IM extensions (presence basically). I was trying to debug why this wasn't working which meant I was doing some tcpdumping and noticed some SIP messages go past — I normally have twinkle (currently the best SIP softphone on Linux) running, so this wasn't unusual.

What was, is that the originating machine wasn't my own. It was my mothers computer. I decided to investigate.

It turns out that Yahoo Messenger (which my mother has signed up for so she could speak to her nephew) can actually speak SIP. This could also be part of the impending MSN / Yahoo IM networks interop. that is being completed.

I'm not sure how they will achieve that but from looking through the packet traces of Yahoo's "PC-to-PC" calling, some kind of negociation takes place of the YMessenger channel and a SIP channel is established between the client and a seperate set of (Akamai-sed) media servers. It also seems like they have some kind of SIP proxy which normal/old clients can speak to and which speaks back SIP.

From the network traces I've done, one side sends a cookie down the YMessenger protocol pipe, and the other side responds via the SIP pipe. From further traces no Linux client can (currently) interoperate with Yahoo's service until the client supports SIP over TCP, SIPS, RTP and RTCP, not to mention Yahoo's special cookie scheme.

Now both networks, Yahoo and MSN need to open themselves up so that they provide presence information externally (via SIP) and allow users to talk to anyone with a SIP address anywhere. You know, just like you can with email.

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ॐ (aum) - what was, what is and what will be, wildfire's musing

Anand Kumria
wildfire@progsoc.org

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