This chapter covered many details of the H.323 and SIP protocols. Choosing between the H.323 and SIP protocols depends on where you are starting from and what you are trying to do. In many cases, your choice is dictated by the nature of your existing voice network. This tends to favor H.323 simply because it is a more mature and well-established protocol. This is certainly the more conservative approach that you may favor if you're looking at immediate deployment of a large-scale VoIP network, and you don't want to get caught up in new technology issues.
If you are just getting started with VoIP trials, if you have no legacy network to worry about, and you are interested in exploring the latest new ideas in VoIP, SIP is a good choice.
In the end, your decision is best based on looking at solid business functions and economic factors. Your VoIP system end users are not likely to care what the underlying protocol is. You should be looking primarily to see which vendors have the best products and user features that are available within your deployment schedule.
In the end, the choice between H.323 and SIP is generally not an irrevocable decision. They are both very good protocols for implementing peer-to-peer voice networks. Cisco CME supports both protocols and will continue to evolve as they do. Many other vendors of VoIP systems are likely to follow a similar dual-track approach to this issue. It's unlikely that any radically new voice telephony features will be available using just one basic protocol. The key innovation is to use VoIP and embrace the concept of a converged voice and data network. You can do this with either H.323 or SIP.
Integrating Cisco CME with Cisco CallManager