Hardware Noise; End-To-End Delay; Feature Descriptions; Sip Proxy Redundancy - Linksys SPA1001 Administrator User Manual

Chapter 1 Introducing Linksys Analog Telephone Adapters

Hardware Noise

Certain levels of noise can be coupled into the conversational audio signals because of the hardware
design. The source can be ambient noise or 60 Hz noise from the power adaptor. The Linksys ATA
hardware design minimizes noise coupling.

End-to-End Delay

End-to-end delay does not affect voice quality directly but is an important factor in determining whether
subscribers can interact normally in a conversation taking place over an IP network. Reasonable delay
figure should be about 50–100 ms. End-to-end delay larger than 300 ms is unacceptable to most callers.
The Linksys ATA supports end-to-end delays well within acceptable thresholds.

Feature Descriptions

The Linksys ATA is a full featured, fully programmable phone adapter that can be custom provisioned
within a wide range of configuration parameters. This chapter contains a high-level overview of features
to provide a basic understanding of the feature breadth and capabilities of the Linksys ATA.
•
•
•
•
•
•
•

SIP Proxy Redundancy

In typical commercial IP Telephony deployments, all calls are established through a SIP proxy server.
An average SIP proxy server may handle tens of thousands of subscribers. It is important that a backup
server be available so that an active server can be temporarily switched out for maintenance. The Linksys
ATA supports the use of backup SIP proxy servers so that service disruption should be nearly eliminated.
A relatively simple way to support proxy redundancy is to configure a static list of SIP proxy servers to
the Linksys ATA in its configuration profile where the list is arranged in some order of priority. The
Linksys ATA attempts to contact the highest priority proxy server whenever possible. When the
currently selected proxy server is not responding, the Linksys ATA automatically retries the next proxy
server in the list.
The dynamic nature of SIP message routing makes the use of a static list of proxy servers inadequate in
some scenarios. In deployments where user agents are served by different domains it is not feasible to
configure a static list of proxy servers for each domain.
One solution in this situation is through the use of DNS SRV records. The Linksys ATA can be
instructed to contact a SIP proxy server in a domain named in the SIP message. The Linksys ATA
consults the DNS server to get a list of hosts in the given domain that provides SIP services. If an entry
Document Version 3.1
SIP Proxy Redundancy, page 1-5
Supported Codecs, page 1-6
Streaming Audio Server and Music on Hold, page 1-6
Silence Suppression and Comfort Noise Generation, page 1-7
Modem and Fax Pass-Through, page 1-7
Adaptive Jitter Buffer, page 1-7
Other Features, page 1-8
Feature Descriptions
Linksys ATA Administrator Guide
1-5