Telephony Protocols

There are two major protocols used for Voice over IP (VoIP) signaling - Session Initiation Protocol (SIP) and H.323. The two protocols provide connection control and call progress signaling, but in very different ways. These protocols can be used simultaneously over the same network, but in general, no endpoint supports both protocols at the same time. Neither protocol is necessarily superior, but each offers some unique advantages. SIP telephones, for example, do not require centralized call servers, and can route telephone calls when a URL identifies the destination. H.323 telephones leverage the call server’s presence into the potential availability of hundreds of telephone-related features that a standalone SIP telephone cannot provide.