Cisco Systems Linksys PAP2, RT31P2 1. Introduction

1. Introduction

This guide describes basic administration and use of the Linksys Technology PHONE ADAPTER

phone adapter – an intelligent low-density Voice over IP (VoIP) gateway. The PHONE ADAPTER

enables carrier class residential and business IP Telephony services delivered over broadband or

high-speed Internet connections. By intelligent, we mean the PHONE ADAPTER maintains the states

of all the calls it terminates. It is capable of making proper decisions in reaction to user input events

(such as on/off hook or hook flash) with little or no involvement by a ‘middle-man’ server or media

gateway controller.

Examples of proper reactions are: playing dial tone, collecting DTMF digits, comparing them against a

dial plan and terminating a call. With intelligent endpoints at the edges of a network, performing the

bulk of the call processing duties, the deployment of a large network with thousands of subscribers

can scale quickly without the introduction of complicated, expensive servers. As described later in

this section, the Session Initiation Protocol (SIP) is a good choice of call signaling protocol for the

implementation of such a device in this type of network.

The phenomenal growth of broadband Internet access (DSL, Cable, FTTH, etc.), has brought the

realization of reliable packet switched IP Telephony Services with circuit switched toll-quality and

subscriber feature transparency with that of the PSTN’s CLASS feature-set. In addition to basic

offerings comparable to traditional PSTN services, many service providers have integrated their IP

Telephony offering with a large number of web-based productivity applications like unified messaging

and call management features such as, remote call forward configuration via the web. Such advances

over traditional phone services, with equal or better voice quality and lower per-minute prices, have

made IP Telephony service a viable business. In fact, IP Telephony service providers in the US and

abroad have seen their subscriber base growing at a rapid pace.

The technical challenges in deploying and operating a residential IP Telephony service, however, are

not small. One of the main challenges is to make the service transparent to subscribers: The

subscribers shall expect to use their existing phones to make or receive calls in the same way as with

the existing PSTN service. To enable this level of transparency, the IP Telephony solution has to be

tightly integrated. A key element in this end-to-end IP Telephony solution is the provision of an

endpoint device that sits at a subscriber’s premises that serves as an IP Telephony gateway or

telephone adapter. This phone adapter offers one or more standard telephone RJ-11 phone ports –

identical to the phone wall jacks at home – where the subscriber can plug in their existing telephone

equipment to access phone services. The IP Telephony gateway may connect to the IP network, like

the Internet, through an uplink Ethernet connection.

Important!! Please note: The information contained herein is not a warranty from Linksys

Customers planning to use the PHONE ADAPTER in a VoIP service deployment are warned to test

all functionality they plan to support in conjunction with the PHONE ADAPTER before putting the

PHONE ADAPTER in service. Some information in Section 1 of this guide is written for educational

purposes and describes functionality not yet implemented in the PHONE ADAPTER.

There are many excellent articles and books that discuss the advantages of SIP.i Here are some of

the more popular details:

• SIP message constructs are very similar to those of HTTP which is well-known to be IP

Network (Internet) friendly.

• SIP is transport agnostic – meaning it can be used over TCP/IP or UDP/IP, with or without

security.

• SIP has a better chance of traversing NATs than other control protocols.