Gokul Blog — A conversation on VoIP, IMS, Cisco and Just about Anything

Deeper analysis of VoIP

Is SIP still an emerging technology?

Posted by tggokul on February 16, 2007

I recently came across a presentation where SIP was given due mention under the Emerging Technology category and that got me thinking. Is SIP still an emerging technology? It has been around for nearly 10/11 years and still people are referring to it as a emerging technology? You know what is the irony in all this? H323 is just a year older than that and it is taunted as the ‘pre-dinosaur’ technology. Weird!!!

I am not going to get into the whole H323 v/s SIP v/s MGCP argument. I somehow always compared H323 with the traditional PSTN network and SIP with VoIP. Here is my reasoning. Here was a network (PSTN) which has served its purpose faithfully yet gets browbeaten at every step by the ‘new’ comers. I had blogged before to let them retire in peace and I say the same thing to H323 bashers. Say whatever you want to, H323 has done more than 10 billion minutes ( which cannot be said about SIP as of today). Wholesale carriers still use H323. SIP is predominant in only in the enterprise setup.

So coming back to the original question, why is SIP still thought of as an emerging technology? Great marketing and the carrot-stick story of the great potential of SIP. Yes, IM and Presence are easily enabled through SIP ( though I think H323 coupled with T.120 could the same? Somebody correct me if I am wrong).

Do I think we can do a lot of SIP? Absolutely!! Do I think are we going to do anything meaningful with SIP? That is where I have my doubts. Yes, IMS is going to be driven on a SIP backbone, SIP Trunking enables SMBs, but question is , Is SIP really living up to its hype? You tell me.


4 Responses to “Is SIP still an emerging technology?”

  1. Vivek said

    Hi Gokul,

    Under the hood, H.323 is a devilish protocol suite. The ASN PER (Packed Encoding Rules) were designed for a time when 2.4 kbps was the norm. We had a fun time supporting it (225,235,245).

    SIP is more appropriate for today, although I think for personal phones IAX2 (asterisk) is better than both SIP or H.323 because of its ease of working with firewalls and NAT.

  2. tggokul said


    I totally agree that H323 is bloated and surely more difficult thatn SIP when it comes to scalability/redudancy etc. The point I am trying to make is, Is SIP really going to live up its expectations? Is SIP really the answer or is it being overly glorified without any merit?


  3. S said

    There are three distinct application areas for VOIP, carrier connections to replace overpriced T1 / SS7 links, office PBX replacement and local loop replacement.

    All of the VOIP protocols except IAX and perhaps Skype assume end-to-end addressability which was one of the fundemental principles of the first Internet. NAT breaks this assumption and so protocols designed such that IP address are embedded in the packets are therefore also broken. Witness the mind-numbing discussions of how to solve the problem.

    Case 1, carrier to carrier connection, works because typically carriers can afford to set up public IP addresses on both ends. Original end-to-end assumption holds and VOIP works as a T1 replacement.

    Case 2, PBX replacement within an office LAN, the network admin can control the allocation of IP addresses and therefore the original end-to-end assumption also holds within the office environment and VOIP works as a PBX replacement. Outside trunking is like case 1 and also can be made to work.

    Case 3, local loop replacement, is where things really get bad. A NAT firewall is the most common situation and at present, none of the popularly marketed (at Walmart, Compusa) items are SIP aware. Which is really what must be the case for things to work with SIP in the general case of multiple clients behind the firewall.

    But thinks about what is being attempted. The local loop phone is so simple that a primitive phone could reasonably be constructed from the junk in cluttered garage (compressed carbon, coils of wire, magnets, etc). The device does not even need to supply it’s own power.

    Contrast this with the complexity of SIP and the tricks that must be performed to get it to work in the local loop setting. Multiply out the number of things that must be working correctly for success and you can, I think, quite easily see that there are some serious issues with SIP as a local loop replacement.

    I recently at a party and spoke with a relative who is the head of customer service at an ISP offering Internet, Voice and Video. The first words out of his mouth were, “I hate VOIP”.

    IAX has a little better chance in the local loop setting because at least you don’t have to mess around with the firewall. But hey, SIP is the bomb…

  4. tggokul said

    Hi S,

    Thanks for an interesting comment. You hit the nail when you talked about your relative saying ‘I hate VoIP’. That feeling is across all ISPs.

    NAT is going to be an issue for the foreseeable future as far as SIP is concerned. Yes, you can use STUN/ICE and all that stuff, but first these have some limitations as well (symmetric/asymmetric network traversal) and secondly what would you do with the current set of endpoints that are not STUN/ICE compliant?

    We had built something called a Media Proxy just for these scenarios and it worked like a charm for all cases. Basically this is what it did. This media proxy was in a public domain and the SIP proxy modified the SDP to include the Media Proxy’s ip address in the attribute and this was done for both the caller/callee. So the call went through the Media Proxy. All the Media Proxy did was maintain a connection between the two RTP ports ( one for the caller and one for the callee) and switched traffic between the two ( if it comes to the first port, send it to the second and vice versa).

    I would think solutions like these would make more sense than complicating stuff with STUN/ICE/UPnP etc. And yes,IAX scores surely better than SIP when it comes to firewall/NAT related issues.


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