Cisco SPA112 Administration Manual page 8

Getting Started
Feature Overview
Cisco SPA100Series Administration Guide
Codec
G.729a
SIP Proxy Redundancy
In typical commercial IP Telephony deployments, all calls are established through
a SIP proxy server. A typical SIP proxy server can handle thousands of
subscribers. It is important that a backup server be available so that an active
server can be temporarily switched out for maintenance. The ATA supports the
use of backup SIP proxy servers (through DNS SRV) so that service disruption is
minimized.
An easy way to support proxy redundancy is to configure your DNS server with a
list of SIP proxy addresses. The ATA can be instructed to contact a SIP proxy
server in a domain named in the SIP message. The ATA consults the DNS server to
get a list of hosts in the given domain that provide SIP services. If an entry exists,
the DNS server returns an SRV record that contains a list of SIP proxy servers for
the domain, with their host names, priority, listening ports, and so on. The ATA tries
to contact the list of hosts in the order of their stated priority.
If the ATA is currently using a lower priority proxy server, it periodically probes the
higher priority proxy to see whether it is online, and switches back to the higher
priority proxy when possible. You can use the default settings or configure the
Proxy Redundancy Method in the Proxy and Registration section of the
Settings (PHONE Port)
Other ATA Voice Features
• Silence Suppression and Comfort Noise Generation
Voice Activity Detection (VAD) with Silence Suppression is a means of
increasing the number of calls supported by the network by reducing the
average bandwidth required for a single call. VAD distinguishes between
speech and non-speech signals, and Silence Suppression removes the
natural silences that occur in a conversation. Therefore the IP bandwidth is
used only to transmit speech. Comfort Noise Generation provides
artificially-generated background white noise (sounds) to reassure callers
that their calls are still connected during the silent periods. You can enable
Description
ITU G.729 voice coding algorithm used to
compress digitized speech. G.729a is a reduced
complexity version of G.729 requiring about half
the processing power of G.729. The G.729 and
G.729a bit streams are compatible and
interoperable, but not identical.
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