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Introducing Cisco Small Business Analog Telephone Adapters
ATA Soft ware Features
ATA Administration Guide 27
1
SIP Proxy Redundancy
In typical commercial IP Telephony deployments, all calls are established through
a SIP proxy server. An average SIP proxy server may 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 device supports
the use of backup SIP proxy servers (via DNS SRV) so that service disruption
should be nearly eliminated.
A relatively simple way to support proxy redundancy is to configure your DNS
server with a list of SIP proxy addresses. The ATA device can be instructed to
contact a SIP proxy server in a domain named in the SIP message. The ATA device
consults the DNS server to get a list of hosts in the given domain that provides 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 device tries to contact the list of hosts in the order of
their stated priority.
If the ATA device is currently using a lower priority proxy server, it periodically
probes the higher priority proxy to see whether it is back on line, and switches
back to the higher priority proxy when possible. SIP Proxy Redundancy is
configured in the Line and PSTN Line tabs in the Administration Web Server. See
“ATA Routing Field Reference,” on page111.
Other ATA Software Features
The following table summarizes other features provided by ATA devices.
Feature Description
Streaming Audio
Server
See “Configuring a Streaming Audio Server,” on page 90.
T.38 Fax Relay See “Using a FAX Machine (SPA2102, SPA3102 or
SPA8000),” on page 55.
Silence
Suppression
See “Silence Suppression and Comfort Noise
Generation,” on page 60.