Cisco SPA1001 Administration Guide - Page 17

Chapter 1 Introducing Linksys Analog Telephone Adapters Ensuring Voice Quality Each Linksys ATA is an intelligent low-density Voice over IP (VoIP) gateway that enables carrier-class residential and business IP Telephony services delivered over broadband or high-speed Internet connections. Linksys ATAs maintain the states of all the calls it terminates and makes the proper reaction to user input events (such as on/off hook or hook flash). Because the ATAs use the SIP standard, there is little or no involvement by a "middle-man" server or media gateway controller. The response of a Linksys ATA includes playing a dial tone, collecting DTMF digits and comparing them against a dial plan, or terminating the call. Note The information contained in this guide is not a warranty from Linksys, a division of Cisco Systems, Inc. Customers planning to use Linksys ATAs in a VoIP service deployment are advised to test all functionality they plan to support before putting the ATA in service. By implementing Linksys ATAs with the SIP protocol, intelligent endpoints at the edges of a network perform the bulk of the call processing. This allows the deployment of a large network with thousands of subscribers without complicated, expensive servers. The ATA is a key element in the end-to-end IP Telephony solution. It provides one or more standard telephone RJ-11 phone ports (identical to the telephone phone wall jacks) to which the subscriber connects standard analog telephone equipment to access phone services. The ATA connects to a wide area IP network, such as the Internet, through a broadband (DSL or cable) modem or router. Ensuring Voice Quality Voice quality, as perceived by the subscribers of the IP Telephony service, should be equivalent (or better) compared to the PSTN. Voice quality can be measured with such methods as Perceptual Speech Quality Measurement (PSQM), with a scale of 1-5, in which lower is better; and Mean Opinion Score (MOS), with a scale of 1-5, in which higher is better. Table 1-2 displays speech quality metrics associated with various audio compression algorithms. Table 1-2 Speech Quality Metrics Algorithm G.711 G.726 G.729a G.729 G.723.1 Bandwidth 64 kbps 16, 24, 32, 40 kbps 8 kbps 8 kbps 6.3, 5.3 kbps Complexity Very low Low Low-medium Medium High MOS Score 4.5 4.1 (32 kbps) 4 4 3.8 Note The Linksys ATA supports all the above voice coding algorithms. The following sections describe the factors that contribute to voice quality. Document Version 3.1 Linksys ATA Administrator Guide 1-3