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Overview of Voice over IP (VoIP) and Network Protocols
28 4600 Series IP Telephone LAN Administrator Guide
● Addressing: a unique address that must identify each terminal on a network.
In a voice network, the unique address is a permanent attribute, based on any
combination of:
- international numbering plans,
- national numbering plans,
- local telephone company practices,
- internal customer-specific codes.
In IP communications, dial plans track extension numbers assigned to terminals. No
fixed connection path is needed.
● Routing: related to addressing and allows connections to be established between
endpoints.
Although these functions are common to data and voice networks, the implementations differ.
Delay and Jitter
Data traffic is usually short and comes in bursts. Data networks like the Internet are designed to
manage these bursts of traffic from many sources on a first-come, first-served basis. Data
packets are sent to multiple destinations, often without any attempt to keep them in a particular
order.
Voice networks are designed for continuous transmission during a call. The traffic is not bursty,
and the conversation uses a specific amount of bandwidth between the two ends during the call.
Several features of data networks are unsuitable for voice telephony:
● Data network design delivers data at the destination, but not necessarily within a certain
time, producing delay (latency). In data networks, delay tends to be variable. For voice
messages, variable delay results in jitter, an audible choppiness in conversations.
● Variable routing also can result in loss of timing synchronization, so packets are not
received at the destination in the proper order.
● Data networks have a strong emphasis on error correction, resulting in repeated
transmissions.
Data network concepts include prioritization of traffic types to provide some form of greater
traffic reliability, for example, for interactive transactions. However, data requirements tend to
not be as strict as most voice requirements.
The 4600 Series IP Telephones include a dynamic jitter buffer. This feature automatically
smooths jitter to improve audio quality.