Also, various incompatible versions of the H.323 standard exist. Version 1, which is not forward-compatible with the most widely supported Version 2; and Versions 3 and 4. Version 3 is a ratified standard at this point but Version 4 was not as we went to press (see graphic, right). Clearly so many versions of the same standard have contributed to industry confusion.
Confusion or not, H.323's Version 2 is the most widely implemented today, present in 49 products out of the 84 we analyzed. However, when we looked at what vendors are planning to do in the standards arena, other standards are gaining some major ground.
These include MGCP, a protocol that addresses control of media gateways, but it does not -- as H.323 does -- specify a complete end-to-end communication. Vendors supporting or planning to support MGCP within the next six months include Alcatel, Avaya, Cisco, Clarent, Dialogic, ECI Telecom, Inter-Tel, Motorola, Netcentrex, Syndeo, Telecom Technologies, Telogy, Unisphere Networks, Vertical Networks and Vsys.
Two variants of MGCP exist: one, per RFC 2705, under control of the IETF, and another version under the auspices of the ISC. Among the 36 products supporting MGCP, 22 support the RFC 2705 specification, while nine specifically support the ISC version.
H.248/Megaco, a joint undertaking of the ITU-T and the IETF, combines elements of the IETF's MGCP with the ITU's H.323. The main thrust of Megaco is to permit greater scalability than allowed by H.323, and to address the technical requirements of multimedia conferencing. At present H.248/Megaco is not nearly as widely supported as H.323 or MGCP, but vendors say they plan to implement it on 30 products within the next six months. The vendors that support H.248/Megaco now or plan to within the next six months are Avaya, Alitgen Communications Inc., Alcatel, Cisco Systems Inc., Clarent, Dialogic Corp., Motorola Inc., Sonus Networks Inc., Unisphere Networks Inc., Vertical Networks and Vive Synergies.
Yet another standard gaining widespread acceptance is SIP. SIP is an application-layer signaling protocol that specifies call control for multiparty sessions, IP phone calls or multimedia distribution. Unlike H.323, which is based on binary-encoding, SIP is a text-based protocol that vendors tell us is much easier to implement.
The vendors that currently or plan to support SIP are Avaya, 3Com, Altigen, Alcatel, Cisco, Com2001, Ericsson, ECI Telecom, NEC, Nortel (on the Business Communications Manager), Nuera, Pingtel, Shoreline, Syndeo, Telecom Technologies, Telogy, VocalData and Vsys. SIP is supported on 24 products and is planned to be implemented on 39 more within the next six months. This will boost SIP's prominence significantly.