Cisco SPA1001 Administration Guide - Page 20
Supported Codecs, Streaming Audio Server and Music on Hold
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Feature Descriptions Chapter 1 Introducing Linksys Analog Telephone Adapters 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 Linksys ATA tries to contact the list of hosts in the order of their stated priority. If the Linksys ATA 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. Supported Codecs Negotiation of the optimal voice codec sometimes depends on the ability of the Linksys ATA device to match a codec name with the codec used by the far-end device. The Linksys ATA allows the network administrator to individually name the various codecs that are supported so that the Linksys ATA can successfully negotiate the codec with the far-end equipment. The administrator can select which low-bit-rate codec is to be used for each line. G.711a and G.711u are always enabled. Table 1-3 Codecs Supported by Linksys ATAs Codec (Voice Compression Algorithm) G.711 (A-law and mμ-law) G.726 G.729A G.723.1 Description This very low complexity codec supports uncompressed 64 kbps digitized voice transmission at one through ten 5 ms voice frames per packet. This codec provides the highest voice quality and uses the most bandwidth of any of the available codecs. This low complexity codec supports compressed 16, 24, 32, and 40 kbps digitized voice transmission at one through ten 10 ms voice frames per packet. This codec provides high voice quality. The ITU G.729 voice coding algorithm is used to compress digitized speech. Linksys supports G.729. G.729A is a reduced complexity version of G.729. It requires about half the processing power to code G.729. The G.729 and G.729A bit streams are compatible and interoperable, but not identical. The Linksys ATA supports the use of ITU G.723.1 audio codec at 6.4 kbps. Up to two channels of G.723.1 can be used simultaneously. For example, Line 1 and Line 2 can be using G.723.1 simultaneously, or Line 1 or Line 2 can initiate a three-way conference with both call legs using G.723.1. Note When no static payload value is assigned per RFC 1890, the Linksys ATA can support dynamic payloads for G.726. Streaming Audio Server and Music on Hold This feature allows you to attach an audio source to one of the Linksys ATA FXS ports and use it as a streaming audio source device. The corresponding Line (1 or 2) can be configured as a streaming audio server (SAS) such that when the Line is called, the Linksys ATA answers the call automatically and Linksys ATA Administrator Guide 1-6 Document Version 3.1