A new approach to delivering packetized voice services is
rapidly growing within the DSL community, adding new momentum to the development of
network components that are tightly integrated into the ATM framework.
Several competitive local-exchange carriers specializing in
digital-subscriber-line transport systems are working with suppliers of interface systems
that will support multiple-line voice services together with high-speed data using
asynchronous transfer mode at the operations layer 3 normally occupied by IP (Internet
protocol) in packet-voice communications.
Meanwhile, Sprint Corp. has opted to use the ATM format
rather than IP in the voice component of its ION (Integrated On-Demand Network) service
when the carrier moves to mass rollouts starting in the first quarter of 2000.
"Once IP picks up congestion control, dynamic
bandwidth allocation and the other attributes we need, there will be a paradigm shift
where we can truly benefit from the bandwidth efficiencies offered by IP," Sprint
senior vice president and chief technical officer Marty Kaplan said.
Sprint will rely on the "Adaption Layer 2"
segment of the ATM protocol stack to handle these tasks, directly packetizing voice into
ATM cells and bypassing the IP-formatting process altogether.
"The big item for us is being able to scale and offer
a predictable quality of service, and ATM does that," Kaplan said.
Widespread uncertainty over the scalability and reliability
of the IP-voice framework has significantly altered expectations about packet-based
telecommunications, in some cases delaying rollouts while players wait for new standards
to replace key components of the H.323 protocols that were designed to support the
transition from circuit- to packet-switched voice.
"We may see some entities moving to launch services
over the second-generation H.323 platform during the next year," said Joel Hughes,
director of network products for Natural MicroSystems Corp., which supplies processor
boards used in packet-voice gateways.
"But we probably won't see real volume in deployments
of non-H.323 systems based on things like MGCP [Multimedia Gateway Control Protocol] or
SIP [Session Initiation Protocol] until mid-2000," Hughes added.
The inability of H.323-based vendors to convince carriers
that they can proceed with a solid, standards-based approach to integrating voice and data
services at mass-market scales has triggered a search for other options among those who
are anxious to exploit the surging demand for multiple lines and high-speed data.
This is especially true for carriers that are providing DSL
services to the business market.
The obvious choice, these carriers said, is to tie their
packet-based voice streams into the public switched network using the QOS dimensions of
ATM in conjunction with the call-control and feature-provisioning power of the
central-office switch, as conveyed through the telephone industry's GR 303 interface.
GR 303 is the protocol used in traditional phone networks
to extend CO functionality to remote service areas over digital-loop carriers.
Rather than trying to immediately generate a new class of
boards that incorporate this new approach, NMS is working with the leading suppliers of
these interface capabilities to create single-box solutions that will tap into the AL2
functionalities already built into its boards, Hughes said.
"We haven't highlighted the ATM side of our board
architecture in our marketing because the right message has been our ability to supply
board-level IP functionalities, but we're in a good position to supply product into this
new sector," he added.
Other manufacturers are making adjustments, as well, in
many cases working with the same three leading start-ups in the voice-over-DSL (VoDSL)
interface domain that many CLECs have been working with.
Lucent Technologies, for example, has decided that it's
better off tapping into these suppliers' expertise than trying to compete with them
through an internally developed product, Lucent manager for DSL-product management Chris
Poer said.
The company has been testing the VoDSL techniques supported
by CopperCom, Jetstream Communications and TollBridge Technologies, Poer said. "We've
done a lot of work, and we are quite impressed with the progress of these companies,"
he added.
The surge in demand for VoDSL solutions is driving
development of customer-premises equipment among a wide range of manufacturers to
accommodate the new platform. Most suppliers predicted that the gear will be available to
support market rollouts by the beginning of next year.
"It's going to take time to get the flow-through of
the provisioning aspects of the GR 303 interface integrated into the CPE," Poer said.
DSL-based CLEC Covad Communications Group Inc. - which has
conducted tests with CopperCom and Jetstream for delivering VoDSL in an end-to-end ATM
environment - is developing an integrated-access device with DSL and Ethernet ports that
will support connection to four to 16 voice jacks.
Added Tom Hecht, senior product manager for voice services
at Covad, "You'll see us using multiple vendors over time."
The DSL connection, whether SDSL (symmetric) or ADSL
(asymmetric), typically has enough bandwidth to support high-speed-data access along with
the voice lines.
This means that for a little more than the average per-line
lease cost of $30 per month and the DSL-transport cost of $10, DSL CLECs can offer
multiple lines of service that could generate hundreds of dollars in revenue per month,
noted John Reister, director of product marketing at Copper Mountain Networks Inc.
Copper Mountain uses a frame-relay transport, rather than
the ATM mode of carrying traffic, regardless of whether it's IP or AL2 at layer 3, thereby
eliminating a lot of overhead, Reister said.
This allows the system to deliver five
64-kilobit-per-second voice circuits within a 384-kbps data stream, rather than the four
that would be carried using ATM transport, leaving more than 1 megabit per second worth of
bandwidth for other data traffic over the SDSL platform, he added.
By using adaptive differential pulse-code modulation, which
cuts the voice-rate requirement to 32 kbps, the system can support as many as 22 voice
circuits in a 784-kbps segment, leaving one-half of the bandwidth for high-speed data,
Reister said.
By the fourth quarter, he added, there will be many CPE
options available on the market that will work with the different interfaces - some with
24 or more voice ports - which will allow carriers to serve a wide range of customer needs
at very low costs.
"This is a revolution in the economics of providing
services using evolutionary technology," he said.
Copper Mountain - working with interface suppliers
Jetstream and CopperCom on the AL2 side of the fence and with TollBridge on the IP side -
sees advantages to both formats, Reister said.
Where IP is concerned, he added, claims that it extracts
too great a cost in efficiency are addressed by TollBridge's header-compression technique
and by Copper Mountain's ability to deliver a virtual circuit that gets around the QOS
issue associated with IP-based traffic.
But, as TollBridge vice president of marketing Jim Grady
made clear, this is not H.323 IP.
"We're not doing IP instead of ATM, but rather, we are
utilizing the underlying QOS and VBR [virtual bit rate] types of things that ATM offers,
while retaining the flexibility to use the QOS capabilities of other transport formats, as
well," Grady said.
A big question haunting the surge of support behind the
VoDSL architecture is how carriers will be able to migrate into the voice-over-IP domain
once the scalability and quality issues are resolved to permit mass rollouts of what
Kaplan called "anything over IP."
Sprint, like most entities, remains committed to the
long-term IP vision, so accomplishing some kind of migration strategy is important.
"That's something we're really focusing on right
now," Poer said, even as Lucent prepares to support the demand for VoDSL in the near
term. "We'll have some announcements about this in connection with our 7RE
switch," he added. -BW
