Cisco SPA112 Administration Manual page 37

Configuring Voice
Getting Started with Voice Services
Cisco SPA100 Series Phone Adapters Administration Guide
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. SIP Proxy Redundancy is configured in the Voice >
Line 1/Line 2 pages. See
page 90.
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. For more
information, see the Audio Configuration section in
Settings (PHONE1 and PHONE2), page
• Modem and Fax Pass-Through
- Modem pass-through mode can be triggered only by predialing the
Vertical Service Activation Code for the Modem Line Toggle Code. See
Modem Line Toggle Code, page
- FAX pass-through mode is triggered by the detection of a CED/CNG
tone or an NSE event.
- Echo canceller is automatically disabled for Modem passthrough mode.
- Echo canceller is disabled for FAX pass-through if the parameter FAX
Disable ECAN (Line 1 or 2 tab) is set to "yes" for that line (in that case
FAX pass-through is the same as Modem pass-through)
- Call waiting and silence suppression are automatically disabled for both
FAX and Modem pass-through. In addition, out-of-band DTMF
transmission is disabled during modem or fax passthrough.
Line 1 and Line 2 Settings (PHONE1 and PHONE2),
85.
Line 1 and Line 2
90.
4
37