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Overview of Voice over IP (VoIP)
Overview of Voice over IP
2-3
Voice Coding Standards 2
There are a number of voice coding standards. The Avaya 4600 Series IP Telephones offer the
options described below.
G.711, which describes the 64 kbps PCM voice coding technique. G.711-encoded voice is
already in the correct format for digital voice delivery in the public phone network or through
PBXs.
G.729A and G.729B, which describe adaptive code-excited linear-predictive (CELP)
compression that enables voice to be coded into 8 kbps streams.
Release 1.6 of the 4600 Series IP Telephones provides support for G.711 silence suppression and
custom packet loss concealment, which can improve audio quality significantly.
H.323 Standard 2
Internal signaling provides connection control and call progress (status) information. The H.323
standard is used for internal signaling for IP packet voice networks. H.323 defines more than
simply voice. It defines a complete multimedia network (voice, video, data), with everything from
devices to protocols. The H.245 standard links all the entities within H.323 by negotiating facilities
among participants and H.323 network elements.
The H.323 standard makes G.711 PCM compression the default form of compression. All other
compression formats are optional.
DHCP 2
Dynamic Host Configuration Protocol (DHCP) allows a server to assign IP addresses and other
parameters to devices such as the 4600 Series IP Telephones on an as-needed basis. This
eliminates the need to configure each end station with a static IP address. The DHCP application
also passes information to the 4600 Series IP Telephone, identifying the IP Addresses of the PBX
and the TFTP server and the path to the upgrade script and the application file on the TFTP server.
For further information, refer to DHCP and TFTP Servers
on page 2-7 and DHCP on page 4-6.
TFTP 2
During the installation and, if necessary, during the reset of the 4600 Series IP Telephones, the
upgrade script and potentially, the application file, are downloaded from the Trivial File Transfer
Protocol (TFTP) server to each IP Telephone, simplifying the software upgrade process. For
further information, refer to DHCP and TFTP Servers
on page 2-7 and TFTP on page 4-17.