In network terminology, you will often hear the term protocol when describing communications, signaling and services. A protocol is a special set of rules that end-points in a telecommunication connection use when they setup connections and ultimately communicate. Protocols specify interactions between the communicating entities. A protocol may amongst other function stipulate type of error checking, data compression or encryption options that can be used during the communication session.
Protocols are not just sets of rules and options they function as a language by having their own methods for data formatting, signaling and flow control so they can manage the polite flow of information over the communication channel.
The protocols used most commonly in VoIP that you are likely to encounter are:
- SIP – session initiation protocol
- SDP – session description protocol
- MIME – formats messages for email extensions
- Megaco H.248 – gateway control protocol
- MGCP – media gateway control protocol
SIP is the most commonly encountered protocol as it is the foundation of VoIP session initiation between SIP enabled devices. SIP devices have their own SIP address, or an address can be embedded into a website, for example when using click-to-talk. By using a simple protocol structure, it provides the market with fast operation, flexibility and scalability with multiservice support.
Another common VoIP protocol is RTP or real-time transport protocol as this is another foundation of VoIP. RTP is the protocol of choice for delivering voice and video as it has several key advantages over TCP/IP. RTP is designed for end-to-end real time transfer of streaming media. The protocol provides facilities for jitter compensation and the detection of out-of-sequence packets, which are common on IP networks. RTP is typically used in conjunction with other protocols such as RTCP, which sends control and QoS parameters.