Smith On VoIP

[This is a guest post by Tsahi Levent-Levi. Tsahi is a Product Manager at RADVISION and writer at VoIP Survivor. Tsahi was formerly the IMTC 3G-324M Activity Group co-chairman up until recently, when he moved to chair the IMTC IMS Activity Group.]

Several years ago, when we took the decision at RADVISION to develop our 3G-324M stack, we assumed a five year window of opportunity, after which a VoIP-based technology (SIP/IMS) will replace it. Now, more than five years later, the end of 3G-324M is nowhere to be seen. The reasons for this stem from the differences between 3G-324M and SIP – between circuit switching and packet-based communication technologies.

3G-324M

3G-324M is a circuit switched-based protocol. It runs on a bidirectional 64kbps circuit switched connection, and on top of it, 3G-324M multiplexes different logical channels – audio, video and control.

The main aspects associated to 3G-324M as a protocol are:

• The bandwidth available is always the same – 64kbps.
• The latency will usually be around 800 milliseconds for a roundtrip, though it may fluctuate or change depending on the operator, the cell, time of day and the color of the sky.
• The protocol is a p2p protocol. You have two sides communicating with each other. There are no proxies or registrars along the way. No third parties.
• It is deployed… almost every 3G handset out there has it embedded into it.

SIP

SIP is an IP-based protocol. It is also used in IMS. It sends packets over a network that doesn’t guarantee quality of service or any bandwidth (you can argue that it does, but that is done using higher level protocols). SIP can be used for a myriad of communication purposes, one of which can be video telephony.

The main aspects associated to SIP when taken for mobile video telephony are:

• The bandwidth available may vary during the call and cannot be guaranteed, unless all-IP and full policy function (PCRF) will be in place.
• Latency is a real issue due to the use of an IP-based network. A round trip of less than 2 seconds will be viewed as an achievement.
• The protocol is distributed with different network entities – user agents, proxies, registrars, etc.
• Few commercial deployments by operators exist, and even these are not large ones. There are trials and there are “underground” solutions you can install independently on your handset, piggybacking the operator’s network.

SIP has its advantages and they are many – support for different resolutions, bandwidths and frame rates, support for non video telephony services like instant messaging, presence, voice only calls, mobility, nomadity and much more. This is also what causes the delay – more features = complexity.

3G-324M is a lot easier for an operator to digest in today’s networks. It can do simple billing, it can use existing UMTS networks, and it works – no need for upgrades, it can use existing handsets. SIP, however, is not that easy for an operator. It’s much more open, which leads to issues of billing, management and owning the network and its data. It doesn’t exist in handsets in a way that is easy to deploy and it is definitely not as interoperable as 3G-324M.

SIP has two ways to become important in mobile handsets:

1. Operators will take the decision to plunge head-on into the world of IMS, where SIP is used in the mobile handsets.
2. Internet companies will find a way to have enough handsets and utilize the mobile operators’ data networks to deploy a video telephony service.

I must admit I believe the first option is a lot more realistic, but it will take time. At least 2-3 more years if not more.

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