Good Discussion of Merits of Gigabit Ethernet v ATM in the enterprise market and how Bay is working to make Gigabit Ethernet more like ATM
ATM stays strong, Gbit Ethernet grows
June 08, 1998, TechWeb News
By Ann R. Thryft
Although some predictions last year aggressively forecast Gigabit Ethernet's
rise in corporate enterprise networks seeking more bandwidth, the reality is
that Asynchronous Transfer Mode (ATM) remains firmly entrenched. Both
Gigabit Ethernet and 622-Mbit/second ATM are switched technologies, and a
greater proportion of the network is becoming switched as bandwidth, lower
cost and ease-of-management concerns rise along with LAN traffic and its
variety and complexity.
Last year, 10,000 Gigabit Ethernet LAN-switch ports were shipped, vs. a
combined 437,000 ports of 100/155/622-Mbit ATM, according to
market-watcher Dell'Oro Group (Portola Valley, Calif.). In 1998, combined
100-plus ATM ports will out-ship Gigabit Ethernet ports by about four to
one. However, Dell'Oro forecasts nearly even numbers by 2001 for both
types of LAN switches.
"ATM is still strong in the corporate network," said a Dell'Oro spokeswoman.
"With Gigabit Ethernet, the standard has not yet been set and few products
are available. We believe that, for voice and video, the perception is that
ATM is the more robust solution." Because of that perception, it was
100-Mbit/s or 155-Mbit/s ATM, and not Fast Ethernet, that was deployed in
the backbone before Gigabit Ethernet technology became available.
Problems with the Gigabit Ethernet standard are largely to blame for its slow
progress. Gigabit Ethernet is the first Ethernet technology to radically depart
from previous forms-it is switched, not shared-and in its physical layer
interface. "The PHY is totally different, and even at the protocol level there is
some difference," said. Santanu Das, president and CEO of TranSwitch Corp.
(Shelton, Conn.). "Those differences mean that it is not easy to migrate from
Ethernet or Fast Ethernet to Gigabit Ethernet systems or chips." The standard
is expected to become final this month.
In the meantime, some switch vendors such as Bay Networks Inc. (Santa
Clara, Calif.) are working to make Gigabit Ethernet more like ATM. "We
want to take out the feature differences of ATM and bring them into the frame
world, plus drive down the cost of ATM so it's more in line with frame
solutions," said senior product marketing manager Rick Lougee. Bay is adding
the reliability of ATM and services it calls "application intelligence" to
frame-based solutions. Application intelligence includes application
prioritization-otherwise known as quality of service (QoS)-and access
security. Access security service has traditionally been centralized within a
router, and is therefore subject to delays. The switched version, however,
distributes access-list information to switches in the wiring closet, thereby
speeding up and simplifying the process.
Whether enterprise networks are using ATM or Gigabit Ethernet in the
backbones depends to some extent on how large the network is and whether
it is the core or the edge being discussed. Some smaller sites decide on one or
the other technology depending on their biases, said Bob Schiff, senior
planning manager for FORE Systems Inc. (Warrendale, Pa.). But in larger
environments, such as those with 1,000 or more users, ATM is being
identified as the core infrastructure, providing switched connections in the
backbone to ATM-attached servers and ATM-attached LAN switches in the
wiring closet. "We are seeing a desire for switched solutions, whether
switched ATM, switched frame-relay or both," he said. "Switched frame in
the wiring closet is predominant, but there's some switched ATM there for
high-performance users." In addition, some networks are running ATM to the
desktop for multimedia voice and video.
The 622-Mbit/s ATM is hot in corporate backbones, especially for those that
own their own fiber and have multimedia or image-intensive needs, such as
hospitals with filmless imaging requirements, said Mohammad Raza, senior
ATM marketing manager for General DataComm (Middlebury, Conn.). Most
small companies that aren't early adopters of new technology are using
100BASE-T to the desktop, possibly with a link to a router and a server, said
Subhash Roy, principal engineer for system engineering at TranSwitch. "They'll
add gigabit ports if needed, but they don't really need them at this point. So
we see tremendous growth in the 100-Mbit market and slower growth in the
gigabit market."
Gigabit Ethernet is a fairly good work-group-concentration methodology, said
Stu Aaron, assistant vice president of enterprise marketing for Newbridge
Networks Inc. (Herndon, Va.). "But somewhere there must be routing, not
switching." Multiprotocol over ATM (MPOA) for routing over an ATM
infrastructure is more germane for the backbone, he said, because it's not a
box-based connectionless solution like traditional routing, which is unreliable
and difficult to debug. MPOA keeps control mechanisms simple and
consolidated, and retains the reliability and scalability benefits of the telephony
model it is based on. "The higher-end the requirements and the more
future-proof the network must be, the more ATM is needed at the core, and
Gigabit Ethernet around the edges, if and where it makes sense."
The bandwidth burden
In response to ATM's challenge of MPOA Layer 3, switching and the move
to switched routing were born, said Vern Little, director of strategic marketing
for Ethernet products for PMC-Sierra Inc. (Vancouver, Canada). "ATM has
also forced Ethernet [equipment vendors] to add service-aware queuing for
voice, video and Web connections, or QoS." The discussion of whether the
network is becoming entirely switched often focuses on which desktops need
greater bandwidth. Switching is moving closer to the desktop for engineers
and a few other workgroup types with high-bandwidth needs, but most users
don't require even a switched 10-Mbit port, said many vendors. There are
other reasons as well for extending switching throughout the net, including
handling increased traffic volume and more sophisticated traffic-routing
patterns, as well as ease of management and of upgradability.
Drivers for an all-switched backbone are multiple services and
"future-proofing" the network, said Tony Ferrugia, senior product manager for
FORE Systems. The latter "is hard enough to do for data, let alone video and
voice." One-fifth of the ATM switches FORE sells have some kind of voice
traffic running over them. But Gigabit Ethernet proponents point out that the
corporate backbone is still predominantly carrying data.
"If you throw bandwidth at the QoS problem, it mostly goes away," said Jack
Basi, director of marketing for datacom and computer products at AMCC
(San Diego). "You can either implement QoS or put in another Gigabit
Ethernet pipe."
The edge of the LAN will continue to be serviced by routers because of their
firewall capability and their ability to deal with different speeds and protocols,
said Bay's Lougee. The first phase of routing-switch technology addressed
delivery of high performance at Layers 2 and 3 and elimination of the router
bottleneck, he said. The second phase seeks to add application intelligence
and distribute it throughout the network. Application requests for priority, such
as voice-over-Internet Protocol (IP) and desktop videoconferencing, may be
more newsworthy; but from the standpoint of usability in the corporate net,
they're not happening yet.
"The killer app for QoS won't be voice and video but the same one we've had
for the last five years: data," Lougee said.
Performance leap
Added George Prodan, vice president of marketing for Extreme Networks
(Cupertino, Calif.), "There's no question that when ATM was designed it was
designed for a strict QoS capability, but you'd be hard-pressed to find any
ATM adapters that can do that. No one has integrated the fundamental pieces
of ATM-like cell interleaving and ABR down to the NIC level. But if you
don't do it end-to-end, the ATM story breaks down." Prodan said QoS will
be used for exception management or for mission-critical applications.
The ability of routing switches to deliver their quantum leap in performance for
a far lower cost than traditional routers is attributable to developments in
ASIC integration, said Lougee. "Before, we couldn't afford to put router
technology or routing-switch technology into the wiring closet. Now ASICs
can take on more complex tasks than just simple MAC-layer switching." He
noted that the highest-end routers on the market can handle 1 million
packets/second at a cost of $5,000 for a 100-Mbit port but that a routing
switch can handle 7 million packets/s for a $700 100-Mbit port.
"Although ATM is still perceived by some as more expensive than Ethernet
technologies, the cost of 622-Mbit/s ATM has come down. [That's] because
the cost of PHY chips and associated electronics has fallen considerably due
to standardization," said TranSwitch's Das. The company believes that
CMOS can support ATM speeds of up to 622 Mbits/s. Up to 2.5 Gbits,
either GaAs or CMOS might apply; at 0.18-micron process technology,
CMOS should be able to achieve 2.5-Gbit/s speeds.
At the same time, 2.5-Gbit ATM is coming to private networks, and
transceivers are appearing from such vendors as Lucent Technologies'
Microelectronics Group (Breinigsville, Pa.). At 1 Gbit/s, some of the
traditional optical sources, such as LEDs, don't work anymore, and the trend
is toward lasers in private network applications, said Arlen Martin, transceiver
product manager for Lucent's optoelectronics group. |
