Jitter is the variation of interpacket arrival time, or the difference between when a packet is supposed to be received and when it is actually received.

One of the main benefits of IP is the fact that properly built IP networks are self-healing . This means that because dynamic routing protocols are used and multiple possible destinations exist, a network can reconverge based upon the best route. It also means that it is possible for your voice (packetized in IP) to take multiple paths to the same destination. Currently you cannot nail up a single path between two destinations. Each individual packet takes the best path between sender and receiver.

The fact that the packet layer is based upon open standards enables multiple vendors to provide solutions that are interoperable. These open standards enable increased competition at this packet layer. The ITU-T, Internet Engineering Task Force (IETF), European Telecommunication Standards Institute (ETSI), and EIA-TIA are only a few of the standards bodies you might be familiar with.

One key component of having a standards-based packet infrastructure is the ability to have open standards to layers at the call-control layer. Referring to Figure 1-12, these open standards are provided by protocols such as H.323, SGCP, MGCP, SIP, and so on, which have open defined interfaces and are widely deployed into the packet infrastructure. One of the jobs of the call-control protocol is to tell the RTP streams where to terminate and where to begin. Call-control accomplishes this task by translating between IP addresses and phone numbering plans.

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