Ensuring Voice Quality - Linksys SPA1001 Administrator User Manual

Chapter 1 Introducing Linksys Analog Telephone Adapters
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
Table 1-2
Algorithm
G.711
G.726
G.729a
G.729
G.723.1
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
displays speech quality metrics associated with various audio compression algorithms.
Speech Quality Metrics
Bandwidth
64 kbps
16, 24, 32, 40 kbps
8 kbps
8 kbps
6.3, 5.3 kbps
Complexity MOS Score
Very low 4.5
Low 4.1 (32 kbps)
Low–medium 4
Medium 4
High 3.8
Linksys ATA Administrator Guide
Ensuring Voice Quality
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