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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.
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 paths to the upgrade script and the application file on the TFTP
server. For further information, refer to DHCP and TFTP Servers
, on page 2-8 and DHCP, on page
4-6.
TFTP 2
The Avaya 4600 IP Telephones get useful application information from the TFTP server. The
telephones also upgrade themselves using files stored on the TFTP server. While the Avaya 4600
Series IP Telephones can operate without a TFTP server once software has been downloaded,
some functionality can be lost if the TFTP server is not available when they are reset. For further
information, refer to DHCP and TFTP Servers
, on page 2-8 and TFTP, on page 4-17.
DNS 2
The Domain Name System (DNS) is a distributed Internet directory service. DNS is used mostly to
translate between domain names and IP Addresses. Release1.5 and later Avaya IP Telephones
can use DNS to resolve names into IP Addresses. In DHCP and TFTP files, DNS names can be
used wherever IP addresses were available as long as a valid DNS server is identified first (see
DNS Addressing
, on page 4-31).