The rush to the hybrid architectures>
Small army of comms startups set to storm hybrid-switch front
January 12, 1999
ELECTRONIC ENGINEERING TIMES: Washington -
Acknowledging that circuit switches won't be
leaving the network anytime soon, five
startups will roll into ComNet here this month
to pursue a new class of switching
architecture that mediates between circuit
and packet services.
Opening an instant battleground in hybrid
switches, Castle Networks Inc., TransMedia
Communications Inc., Dynarc AB, Salix
Technologies Inc. and Advanced Switching
Communications Inc. will unveil their wares in
Washington. Some of the hybrid-switch
startups anticipate working on common
interfaces with the backbone-router
community, though some router companies,
such as Argon Networks Inc., will compete
with the new players by offering an
expanded suite of router software that will
duplicate some of the functions of a hybrid
switch.
The rush to the hybrid architectures
represents a significant shift in
communications design. The common
message from asynchronous transfer mode
and Internet Protocol advocates as recently
as a year ago was that voice-oriented circuit
switches in the telephone network would die
out in a matter of months, so broadband
switches had to be prepared to handle
packetized voice. More recently, developers
have come around to the idea that the
network will continue to rely on
circuit-switched architectures to perform
crucial call-handling functions.
Part of the impetus for the new hardware
rollouts came from the October completion of
the media gateway control protocol (MGCP),
an enhancement of Level 3 Communications
Inc.'s IP Device Control protocol, used to
interface packet-oriented IP switches and
circuit-oriented Signaling System 7 networks.
Some companies, such as Nortel Networks
and the alliance of Hewlett-Packard Co. and
Cisco Systems Inc., want to make dedicated
server-oriented gateways to handle call
mediation. But the new hybrid switch
startups anticipate incorporating many MGCP
gateway functions in their hybrid switch
platforms.
"A lot of this activity came out of what the
current services were not providing," said
Randy Brumfield, director of product
marketing at TransMedia. "ATM's Continuous
Bit Rate services were just about transport
of isochronous voice, not about
call-processing itself. You couldn't just
assume SS7 voice circuits would transform
magically overnight to ATM."
Bus architectures
The most common design for handling
high-speed data alongside call control is a
multiple bus architecture. To handle circuit
and packet assignments, TransMedia (San
Jose), Castle (Westford, Mass.), and Salix
(Gaithersburg, Md.) combine time-division
multiplexed (TDM) buses alongside
packet-switching fabrics.
Dynarc (Kista, Sweden), a spinoff of L.M.
Ericsson, is taking the more heretical
approach of promoting a new TDM-friendly
transfer mode it calls "dynamic synchronous
transfer mode," or DTM.
Advanced Switching Communications
(Vienna, Va.) is using the tried and true ATM
infrastructure to launch a scalable "RBOX"
architecture, which starts as a replacement
for digital subscriber line multiplexers and
Inverse ATM multiplexers, but grows to
handle central-office switching duties for
both packet and voice.
Most of the newcomers are targeting
competitive local exchange carriers (CLECs),
the new generation of carriers that must
share space in the central office with
incumbent carriers, but which must mediate
circuit traffic from large, traditional AT&T
5ESS circuit switches with the data traffic
from similarly large packet-based IP or ATM
backbones. Some switch startups see
significant opportunities from incumbent
CLECs, interexchange carriers and Internet
Service Providers too, but as with last year's
DSL services, CLECs represent the carrier
market of choice.
"The CLECs will be the driving force for
innovation in 21st century networks," said
Michael Welts, vice president of marketing at
Castle Networks. Castle, like Salix and
TransMedia, expects competition among the
startups to be fierce, but the company
worries the most about the large
circuit-switch vendors, such as Lucent and
Nortel, offering hybrid mediation switches, as
well as the broadband packet-switch
vendors, including Cisco Systems and Ascend
Communications Inc. So far, however, the
new breed of switching startups seem to be
defining a legitimate sub-market the big
players have failed to pursue.
Dynarc, along with its Stockholm-based
competitor Net Insight, has licensed
technology from L.M. Ericsson for updating a
circuit-switched format for traffic mixes.
Since 1985, Ericsson had worked on a
concept of dividing data links into
125-microsecond cycles, which are then
subdivided into 64-bit time slots. This mix of
space and time-division multiplexing provides
the channelizing concept called dynamic
synchronous transfer mode (DTM). When
Ericsson halted the research to focus on
ATM, several researchers formed Dynarc, and
Net Insight was formed later by others
interested in DTM.
Dynarc president Olov Schagerlund said the
methodology can be used in both local
IP-based networks between routers and
hosts, or as a carrier backbone for
multiservice switching. Dynarc may see some
interest in the former field, because the DTM
service can be mapped on existing physical
networks like FDDI rings, but the enterprise
network is the tougher sale, because new
network interface cards and drivers are
required.
"The lesson from ATM is that it is easier to
add new transport methods into the public
backbone," he said. Hence, the DynaSwitch
is being promoted to a variety of carriers and
service providers, as well as OEMs for whom
Dynarc is willing to look at a variety of
subsystem development or chip-licensing
options. Dynarc has established a
hardware-development group in Mountain
View, Calif., to work on derivatives and
subsets of its first-generation DynaSwitch
100. Dynarc already has a model for licensing
chip-level implementations of DTM.
In late November, Net Insight reached an
agreement with Toshiba Electronics to
implement DTM features in a chip-level
switch core, to be marketed as " Twintin."
Schagerlund said that, despite the tough
competition between Dynarc and Net Insight,
his company is supporting Net Insight's
contributions to the European
Telecommunication Standards Institute for
native DTM structures. Dynarc also will
propose IP-over-DTM mappings to the
Internet Engineering Task Force, and
DTM-over-wave division multiplexing
mappings to the Optical Interoperability
Forum.
Key to the bifurcation of the Dynarc/Net
Insight group out of Sweden, and the
U.S.-based troika of Castle, Salix and
TransMedia, is the protocol layer at which
services come together. DTM advocates
insist that a true melding of services must
take place at the data-link layer, and that a
transport infrastructure must incorporate an
inherent TDM time-slot. ATM's failure to do
so made the creation of virtual circuits too
complex for many to implement, DTM
advocates claim.
Castle, Salix and TransMedia all are believers
in time-division multiplexing hardware, but
the service-mediation vendors claim that
there is little support for new data-link
technologies. Consequently, circuit and
packet services must be mediated at
network or transport layers, with some
encapsulation functions virtually required.
Even the giga-router companies, who are
supposedly too IP-centric to care about
aggregating packet and circuit services, are
finding that service aggregation is the buzz
terminology for this year's ComNet. For
instance, this week, Argon Networks Inc.
(Littleton, Mass.), developer of the
GigaPacket Node, will be launching a
software suite in which multiple routing
protocols, including Multi-Protocol Label
Switching and Border Gateway Protocol-4,
are implemented in a hardware architecture
that supports both IP and ATM.
Chris Baldwin, vice president of marketing at
Argon, said that even systems with hybrid
voice-switching capabilities will need to offer
very fast MPLS and BGP4 support for complex
service mixes. "TDM does not go away in the
network, and that's driving this new
mediation-switching architecture," Baldwin
said. "But we continue to believe that packet
division multiplexing ultimately displaces TDM
in the WAN backbone, and that service mixes
get driven by appropriate routing software."
Comparing architectures
The Castle 2100 switch, moving into trials
this month, incorporates a universal signaling
matrix capable of handling ATM and IP
packets, SS7 circuits and MGCP gateway
mappings. The first generation of the Castle
switch can handle up to 10,000 channelized
DS-0 (64-kbit) circuits.
For its part, TransMedia's control
architecture incorporates heavy pipelining to
achieve a multipath control stream in which
voice and data channels can be assigned
individual quality-of-service parameters,
protocol processing, TDM termination, and
signaling. The company developed a
three-bus design utilizing a control plane,
TDM plane and cell plane, and used a mix of
embedded RISC architectures for system
control, and DSP architectures for
channelizing circuits.
Salix, which debuted its ETX5000 in late
December, is calling its switch architecture
"class-independent," since it can interface to
Class 4 or 5 circuit switches in the public
backbone. The company developed an
independent service bus, and new
applications are added to the switch by
writing to a service provisioning interface, a
carrier's equivalent to an API. Packet and
circuit switching is carried out over a generic
topology Salix calls the FleXchange Unified
Switch Fabric.
As for ASC, its low-end RBOX 1000 can serve
as a feeder to a larger switch, but the
company's intent to move to a chassis-sized
system with a 5-Gbits/second switching
fabric indicates that the service-aggregator
RBOX switch could soon take over a smaller
central office. Ron Westernik, chief operating
officer for ASC, said the RBOX 1000 and 2000
aggregator systems actually allow CLECs and
ISPs to avoid purchasing their own central
office switch. As the smaller carriers grow,
they can insert the smaller RBOX 1000 and
2000 units into the shelves of the
yet-unnamed giga-switch, building their way
to a multi-service switch through modular
steps. |
