Cable interests pursuing Internet-protocol telephony are
looking at a new way to manage calls, developed by Cisco Systems Inc. and Bell
The new concept stems from an architecture where the
IP-telephony network, or large segments of it, functions as a "virtual switch."
In that scenario, a centralized "call-agent" controller interacts with
distributed gateways as if they were line cards. Those line cards then interface with the
external telephone network.
The structure, officials said, rests on the ability of the
call agent to conduct a "dialogue" with the line cards, using a new protocol:
SGCP, for single-gateway-control protocol.
"SGCP is intended to allow carriers to build
scaleable, very reliable telephone services on top of the voice-over-IP structure,"
Cisco software developer David Oran said.
Oran added that the initiative started when telco carriers
asked whether Cisco's current call-control solution, based on the H.323 standard,
could scale beyond tens of thousands of end-users.
"We couldn't look them straight back in the eye
and tell them that we felt confident that we could take an H.323-based solution and scale
it up to carrier-class operation over the long haul," Oran said.
At least one cable company is using the new Cisco/Bellcore
SGCP architecture in an end-to-end IP-telephone-network test, Oran added, declining to
name the operator.
The cable industry's PacketCable task force is also
weighing the protocol as part of the set of interface recommendations that it plans to
issue at year's end, according to participants in that process.
Cable is an especially strong early market for the
virtual-switch concept, Oran said. "Cable companies ... need to be able to deploy a
telephone service that has the properties that everyday people are familiar with for
telephone service," such as lifeline service, operator services, directory service
and 911 emergency calls, he added.
Bellcore -- which, along with Cisco, is a primary supplier
for Sprint Corp.'s IP-based ION (Interactive On-Demand Network) project -- appears to
also be moving toward the introduction of products based on SGCP.
Bellcore officials indicated earlier this year that they
would offer a call-management solution for the IP-telephony market by September. But as of
last week, they were unwilling to discuss the state of preparations.
"We can't comment on rumors or speculation with
respect to any relationships that may or may not be evolving between Bellcore and
Cisco," a Bellcore spokesman said.
In the larger IP-telephony picture, sources said last week
that SGCP will soon become a cornerstone in IP-telephony solutions from a number of
However, SGCP is one of several new protocols vying for
endorsement, as standards bodies look for ways to achieve interoperability across networks
owned by multiple carriers.
The goal: to achieve a uniform way to do call setup,
call-redirection "triggers" and other functions that are currently handled by
the Signaling System 7 (SS7) protocols of the public-switched telephone network.
Another new approach, which contrasts with SGCP, is known
as "SIP," for session-initiation protocol. SIP operates by distributing the
call-signaling process, along with the gateways, into geographically dispersed servers.
SIP already has momentum in the Internet world, and it is
reaching the final stages of standardization within the Internet Engineering Task Force,
officials said. Internet developers like SIP because it was designed to be more
IP-friendly by using more intelligence than what exists within the H.323 protocol stack.
Those smarts are helpful not only to enhance features for
voice services, but also to enhance any type of Internet session.
The goal of the SIP standard is to make the development of
features for IP applications, including voice, as simple and Web-centric as possible, said
Henning Schulzrinne, a researcher and professor at Columbia University.
"SIP is a signaling-type protocol that can be used for
any type of session on the Internet," whether or not telephony is involved,
SIP was designed for the all-IP environment, where gateway
interfaces for the translation of packets to circuit-type signals are not part of the
equation. If such interfaces are needed, SIP can be coordinated with H.323 gateways, just
as it can be used with other Internet protocols, such as RTSP (real-time streaming
protocol) and SMIL (synchronized multimedia-integration language), Schulzrinne said.
"SIP is a platform for developing additional services
in a Weblike telephone environment, where creating services has as much diversity and is
done by as many people as now create Web services of various types," he added.
The SIP protocol provides a fast, simple means of
connecting users via Web addresses. That includes confirmation of the connections,
establishing the type of communication or application to be undertaken and ascertaining
the capabilities of each user's connection and operating platform -- all in 80
milliseconds or less of setup time.
But no matter what is accomplished within the pure IP
domain, cable, like everyone else, will have to interface with the PSTN. Because of that,
PacketCable must focus on the gateways that link cable-originated or cable-terminated
calls to the PSTN, including the protocols used in connecting gateways with central
Thus, SIP might be used in connection with enhanced
features specific to the PacketCable IP domain, while SGCP could be used as the basic
format for managing traditional types of calls.
The widespread demand for scaleable IP-telephony
architecture is forcing people to rethink H.323, which was "initially developed with
a mind-set toward an end client that has it all -- does the media, does the signaling,
does everything," said Steven Thomas, cofounder and chief technical officer of
TransNexus Inc., a provider of Internet-settlement services, and chairman of the Voice
Over IP Forum.
"When you start parceling out some of these pieces,
you have to do one of two things," Thomas said. "You either pull apart H.323 and
define separate protocols to talk to those individual pieces, or you've got to think,
'Maybe I should be designing something fundamentally different.'"
Debate over the best way to go is pushing the
smooth-flowing IP-telephony world into turmoil. Carriers are reacting by choosing
proprietary options now, as they expand or build new networks.
While that happens, they are watching for resolution of the
issues at the standards level. Few entities appear willing to wait, but it's
anybody's guess as to which approaches will prevail in the marketplace.