Cable engineers sizing up ways to move to a more
distributed data-network architecture will have an ever broader array of options to choose
from as a new generation of edge routers and other components comes to market over the
next few months.
The latest major telecommunications player to include cable
as a target for its multiprotocol edge-router switches is Siemens AG, which has put $1
billion behind a new subsidiary, Unisphere Solutions Inc., to bring new solutions to
market for data-based carriers.
"Regardless of whether you're operating a DSLAM
[digital-subscriber-line-access multiplexer], data over cable or a wireless hub, our
edge-router switch can terminate all access traffic and provide edge routing into the
network," Unisphere cable-product manager Jon Mischel said.
Terminating cable-data traffic, including packet telephony,
involves using the master modem-control system known in cable as the CMTS
Today, that system sits in headends and in the primary hubs
of large metro cable systems. But -- as recently made clear by Oleh Sniezko, vice
president of engineering at AT&T Broadband & Internet Services -- there are
advantages to putting at least some of the CMTS functionality into edge points of the
network. They include fiber nodes and even the "mini-fiber nodes" of AT&T
Broadband's new "LightWire" hybrid fiber-coaxial architecture.
Speaking at last month's 2000 Conference on Emerging
Technologies in Anaheim, Calif., Sniezko predicted that within five years, distributed
CMTS gear would be used in 80 percent of the company's systems.
So far, Mischel noted, options available to cable operators
for remote positioning of CMTS gear invariably involve full replication of the headend
CTMS, but on smaller scales.
He added that what an edge device like Unisphere's allows
is a partitioning of the CMTS functions, where those that can be more efficiently
performed are left in the headend, while the remaining functions can be incorporated into
system processing at the company's "ERX" edge router.
"It makes more sense to centralize the layer-3 aspects
of DOCSIS [Data Over Cable Service Interface Specification], while applying lower-cost
layer-2 processes at the edges," Mischel said.
The layer-3 data-network operational-control elements are
complex and costly compared with the physical-layer functions that govern
quality-of-service parameters in the transmission stream, he added.
"You also eliminate multiple layer-3 routing hops by
using virtual ATM [asynchronous transfer mode] circuits to connect from the point of
physical-layer CMTS termination at the edge back to the layer-3 control at the
headend," Mischel said.
This approach could contribute greatly to reducing network
latency in packet-voice applications, he added.
Unisphere's first phase of cable-product release combines
the basic capabilities of the ERX with a server-based "Service Selection
Center," which supports automated subscriber sign-ups and service provisioning on an
on-demand basis across all ERX access points.
"This combination provides operators with the support
for dynamic configuration of network resources, which you need to deliver advanced
services," Mischel said, noting that CMTS processing and, eventually, full
PacketCable support will be added to the company's edge system in future product phases.
As Unisphere makes clear, cable's needs for managing
multiple layers of transport, service-class and media-access controls beyond the headend
dovetail with other demands for edge devices that can handle multiple transport protocols
while allowing network operators to distribute various layers of intelligence to different
points in the network.
Operating from a single advanced multiprotocol
router-switching platform that can be adapted to different industry-sector needs, Cisco
Systems Inc., Lucent Technologies, Nortel Networks and Newbridge Networks Corp. have been
able to tweak their systems to accommodate cable's data-services standards, including
packet telephony and high-speed Internet access.
Start-ups like General Bandwidth Inc., Dynarc and Aplion
Networks Inc. are devoted strictly to edge systems, hoping to capitalize on cable's
interest in distributed architectures.
General Bandwidth -- formed last year after the people who
founded DSL supplier NetSpeed Inc. sold the firm to Cisco -- offers a new type of
packet-voice gateway. It is designed to allow operators to deliver voice services over
different types of broadband-access links, while leaving them to choose the types and
locations of switches and routers.
General Bandwidth uses a wide array of DSPs (digital-signal
processors) that are managed across a very high-speed proprietary back plane. The various
functions of these DSPs are orchestrated so that they contribute whatever tasks are
required for the framing, compressing, modulating and other processes that are intrinsic
to any given access platform.
Austin-based General Bandwidth plans to begin demonstrating
its technology in customer labs during the second quarter of the year, hoping to begin
delivering product for market trials during the second half. "We expect that there
will be more massive deployments throughout 2001," director for product management
Sean Parham said.
Engineers will have their hands full sorting through the
options at the edge of their networks as even more exotic gear than the components offered
by Unisphere and General Bandwidth enter the field.
In many cases, they'll have to choose between the
interoperability afforded by using standardized optical-transport systems in the backbone
and the cost-effectiveness of using proprietary approaches to managing the optical layer.
For example, Palo Alto, Calif.-based Dynarc, the U.S. unit
of the Swedish start-up, is bringing to market an edge router that uses the company's
proprietary Internet protocol-over-fiber technology to provide a low-cost end-to-end IP
solution that avoids the inefficiencies of SONET (synchronous optical network) and ATM.
While this means the operator must use the same routing
system throughout the regional network, it opens the opportunity to create customized
service-level agreements based on dynamic bandwidth allocation and traffic-pattern
management, which is more efficient than standardized approaches, Dynarc president Olov
Even more exotic is a new line of gear being developed by
Aplion, another start-up based in Piscataway, N.J.
The company plans to supply intelligent machines that
interact with routers and switches to set up a means of streaming hosted applications from
various service providers that might be operating over a given network. This ensures that
the precise QoS and other parameters required for given applications are assigned by the
network as customers use the applications.
Aplion CEO John Holobinko said his company will introduce
hardware components through the remainder of the year.