Negotiated Connections; Negotiated Voice Compression - 3Com NBX 100 Administrator's Manual

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PPENDIX ONNE
Negotiated
Connections
Negotiated Voice
Compression
X H.323 G
TIONS ATEWAY
The H.323 protocol addresses these main areas:

Negotiated Connections

Negotiated Voice Compression

Standard Extensions
Remote Internet Device Connections
The H.323 protocol adds negotiated call setup and tear-down capabilities
to Internet Protocol (IP) connections. It exists because Internet protocols
were designed to deliver text messages and computer files in data
packets. IP networks were not originally concerned about involving a
person in a real-time conversation as a telephone does.
H.323 provides call setup capability to negotiate the readiness of two
parties to exchange information and how they do it. It then keeps the
connection alive until one of the parties ends the connection. A call
tear-down signal indicates to the network, and to the other party, when a
call ends. On standard telephone networks, the telephone company uses
this signal to determine when to start and stop charging for long distance
calls, but long distance charges do not normally apply to H.323 calls.
Other reasons for call setup and tear-down signals are to indicate when
an IP network can release bandwidth to support other calls, and to
inform other devices, such as voice mail systems, when to stop their
conversation-related activities.
IP networks can carry a lot of traffic, creating competition for the
available bandwidth. Devices have the best access, and the least delay,
when they communicate messages by using fewer and smaller packets.
This also means lower cost.
Voice compression offers a way to reduce the number and size of the
data packets needed to carry each second of a voice conversation.
However, voice compression needs high-speed processors to remove the
redundancies that are inherent in the way standard voice is represented.
The international standard for representing voice (G.711) requires 64 Kb
for each second of conversation. NBX Business and Basic Telephones
contain a digital signal processor (DSP) that transforms spoken voice into
this form. An Ethernet interface, also within each telephone, breaks up
the 64 Kbps stream into frames, adds addressing and error checking, and
dumps the voice-data frames (now 83 Kbps) onto a 10 Mbps LAN.