Asterisk, SIP and VSP compatibility...

[colinjones]

Does Asterisk interface with pretty much any VSP as long as they support SIP? Or do they specifically have to support the Asterisk protocol, IAX - dunno the difference between what each do, but I assume that IAX supports the special "PABX/PBX" functions, whereas SIP is a lighter, VoIP only protocol??

Does my VSP have to know and configure for the Asterisk installation, or can I just leave them out of the loop (my preference!)

Rgds
Col.

[1audio]

SIP is an open standard and Asterisk supports it. Most VOIP suppliers use it, but some like Vonage and Skype try to run closed systems and won't work with foreign hardware. IAX is Asterisk specific but you can ignore that for the most part. Your VOIP supplier doesn't need to know what you are using but they can probably figure that out anyway.

[colinjones]

I'm comfortable with the SIP side of it, and I know that Asterisk supports that, I guess what I am asking is does the VSP also need to support IAX as well as SIP for Asterisk to work, or is SIP on its own sufficient? You seem to be saying that SIP alone is OK.

Subsequently, I read that IAX is used between Asterisk servers (so clearly not required for what we are trying to do) but also in some client-server models (http://en.wikipedia.org/wiki/Iax) - assuming this is from the handset to the LMCE box? And that again this is optional, and only possible if the handset (or softphone) supports IAX?

It also says that IAX provides extra functionality to your provider, like a more efficient trunking, etc. Is this something that I should think about talking to them about, or is SIP, again, enough for my purposes - just want to be able to run a couple of "lines"/numbers, voice mail, interface with the GPRS/EDGE/3G/HSDPA networks for mobile data/video calls, conferencing, call waiting, etc...

[1audio]

SIP is all you should need to work with most providers. Once the session is connected is just a data stream. I don't know much about the video calling capabilities. I do know that I can connect to the cell phone. The special LMCE stuff on the cell phone doesn't go through the voice network. The GPRS etc. stuff is all data networks, and that is handled via the ISP.

[Matthew]

Asterisk supports many telephony protocols, including SIP and IAX. SIP is the most popular open standard (Skype is by far the most popular VoIP protocol, but it's closed and proprietary), and does quite a lot more than "just" VoIP (it's a Session Initiation Protocol for more than just global addressing and realtime duplex audio). It's the most well supported by TSPs (Telephony Service Providers), including lots (probably most) voice switching equipment, including the really big stuff.

IAX, though, is an Asterisk-specific protocol. It's open and standardized (and nonproprietary: free in every way except maybe trademark), but it's really the Inter-Asterisk eXchange protocol, originally designed for server-to-server Asterisk networks. But it has an advantage over SIP in that it uses a single socket for a session, rather than 2+ for SIP, and has other characteristics that make it work better over NAT and some other hacky network configs (including just plain firewalls). It's supported by clients, not just Asterisk servers, and even some HW, like hardphones and ATAs. Plenty of TSPs support connecting by IAX, especially if they're exposing Asterisk servers as gateways to their services, but it's nowhere near as popular as is SIP.

Whichever one you use, you've got to config Asterisk to use it specifically, even if just in order of preference in a list with SIP. And the peer to which you connect has to support the protocol you specified.