Chapter 8. IP Telephony Solutions

IP Telephony represents the convergence of two distinct and dominant communications technologies: circuit-switched telephony and packet-switched, IP-based data networks. The impact of this convergence has been staggering in terms of the proliferation and development of new protocols, products, and communications solutions.

In November 1996, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) approved the first version of H.323 recommendation, titled “Packet-Based Multimedia Communications Systems.” In March 1999, the Internet community followed with the publication of RFC 2543, which specifies the Session Initiation Protocol (SIP), considered by some a competitor to H.323. Since then, H.323 and SIP have been revised and updated multiple times. H.323 version 4 was approved in November 2000, and the SIP specification has been updated via RFCs 3261 and 3265. In addition, numerous SIP-related RFCs have been published, and increasingly, the use of packet-based networks for multimedia communications (voice included) has completely obliterated any of the traditional distinctions between circuit-switched voice and packet-switched data networks.

Given the worldwide installed base of the traditional circuit-switched telephony infrastructure at the SMB, enterprise, and carrier levels, legacy telephony will be around for quite a while. However, given the capabilities of IP Telephony and the many business drivers that make its deployment appealing, new telephony installations are likely to be dominated by IP Telephony in the SMB, enterprise, and carrier markets.

This chapter considers the design of IP Telephony solutions in the context of the following:

• IP Telephony deployment considerations

• IP Telephony components and protocols

• Cisco IP Telephony solutions for SMBs (or enterprise branches) and Internet service provider (ISP)/carrier environments