Cisco SPA122 Administration Guide - Page 37
Line 1 and Line 2 Settings PHONE1 and PHONE2, Other ATA Voice Features - fax
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Configuring Voice Getting Started with Voice Services 4 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 Line 1 and Line 2 Settings (PHONE1 and PHONE2), 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 Line 1 and Line 2 Settings (PHONE1 and PHONE2), page 90. • 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 85. - 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. Cisco SPA100 Series Phone Adapters Administration Guide 37