AT&T Corp. is weighing a fast-track approach to
Internet-protocol telephony to avoid the delays it would encounter by waiting for its
preferred architectural strategy to become commercially viable.
"We want, ultimately, to be able to meet all of our
requirements for voice service over IP, but we see an opportunity to get started with
technology that would be adequate to handle early levels of penetration," an AT&T
executive said, asking not to be named.
AT&T is committed to getting voice services under way
this year in several of its own and Time Warner Inc.'s cable markets, using
proprietary cable-phone systems based on traditional circuit-switched technology.
But the cost assumptions underlying its aggressive
cable-acquisition strategy are largely based on the economies of using an IP platform,
which, on a per-customer basis, are expected to be about one-half the costs of the
Nonetheless, company engineers insisted on a new
architectural approach to IP-voice service that could take considerably longer to
implement than the approach that was endorsed by the PacketCable group at Cable Television
Laboratories Inc. before AT&T became involved in the standards-setting process.
Where cable operators previously focused on launching a
basic residential phone service over IP, AT&T wants to be able to offer a richer set
of features at lower costs than telcos currently charge, and to extend those features into
the business and residential sectors.
The engineers are ready to compromise in the interest of
meeting the strategic business needs of the company, the AT&T source said.
"We're not wavering on the need for scalability
and robustness that's addressed in our new architecture," he said, "but we
also have a need to move quickly to the IP platform."
The new thinking comes as the PacketCable group seeks to
incorporate AT&T's distributed open-signaling architecture (DOSA) into phase one
of its specifications, which it hopes to issue in August.
While the DOSA specs might be completed by that date, it
may take longer for the DOSA approach to be commercially viable than for the
call-signaling architecture in the original phase one of PacketCable, noted Dave
Bukovinsky, director of the PacketCable process at CableLabs.
"DOSA is definitely part of phase one,"
Bukovinsky said. "AT&T has had the effect of accelerating the inclusion of
solutions in the specifications that we otherwise would have addressed later."
One clue that AT&T wants to move faster into IP-voice
service than it could using the DOSA approach is its development work with Cisco Systems
Inc. and General Instrument Corp. on an end-to-end IP-voice system for testing by
GI recently announced an alliance with Telcordia
Technologies Inc. (formerly Bell Communications Research, or Bellcore) to use
Telcordia's signaling technology in its IP-telephony products.Officials refused to
say whether the AT&T trial would include Telcordia's call-signaling protocol,
SGCP (Single Gateway Control Protocol), which it developed with Cisco. The PacketCable
signaling protocol is a variation of an evolved form of SGCP known as MGCP, or Multimedia
Gateway Control Protocol.
MGCP uses a simple set of "primitives," or basic
instructions, to allow an IP-telephony network or large segments of it to function as a
virtual switch. A centralized call agent or controller interacts with distributed end-user
gateways as if they were line cards interfacing with the external networking environment.
MGCP supports the dialogue between the call agent and the
gateways, allowing IP calls to be originated from simple, relatively unintelligent
pulse-code-to-IP signal translators attached to standard touch-tone telephones.
It is not designed to exploit the richer functionality that
comes with a more distributed architecture, where features can be provisioned at the
premises using more intelligent end-user devices.
In contrast, DOSA ties together three key points within the
HFC (hybrid fiber-coaxial) voice-over-IP cloud.
They are: the end-user BTI (broadband-telephony-interface)
device, which connects telephones to the network; the CMTS (cable-modem-termination
system), which controls data distribution over the HFC plant; and the gateway controller,
or call agent, which interfaces with the BTI and the CMTS.
The two designs are incompatible, making it impossible to
evolve from an MGCP-based platform to DOSA without reconfiguring basic network components,
according to Chuck Kalmanek, an engineering executive at AT&T Labs.
"MGCP offers an easy path to getting started in IP
telephony, but it may not be the architecture that would allow us to evolve as our market
base expands and we add new services," he said.AT&T's concerns with MGCP
have to do with issues of scalability, security and flexibility in how service features
are provisioned, Kalmanek explained in a presentation at the Voice on the Net conference
in Las Vegas last month.
DOSA provides the means to deliver services to very thin
clients, such as what might be used in residential service, and also to very intelligent
devices, allowing businesses and others with highly computerized premises equipment the
option of adding features independently of the network provider, he said.
In addition, DOSA provides a means of end-user
authentication that protects against fraud in a more robust fashion than is possible with
MGCP, Kalmanek noted.
AT&T wants to make sure that when end-users take
advantage of special quality-of-service parameters, they can't bypass registration
with the network-management system
AT&T officials it made clear that no final decisions
have been made on how to proceed with rolling out IP telephony.
But the pressing need to move forward as soon as possible
seems likely to be the determining factor, even if it means taking a short-term approach
that is incompatible with its ideal platform.