Sizing Up SONET’s New Service
By Fred Dawson
FOR THE PRICE-CONSCIOUS PURCHASER of
wholesale transport services the process of choosing a supplier suddenly has
become a lot more complicated, thanks to an extraordinary range of options
taking shape around next-generation SONET platforms and their alternatives.
Traditional SONET rings remain the
obvious choice for delivering carrier-grade TDM-based services over metro and
long-haul backbones. However, SONET also has become a cost-effective means of
delivering packet-based services, not only at the "five 9s" level of
protection but also at somewhat less protected levels where only some of the
SONET capabilities are put to use. And, there are new packet transport
techniques being implemented that approach SONET-like protection without
incurring its costs as this flexibility to accommodate Ethernet and IP transport
requirements emerges with next-generation SONET systems.
Metro Optical Network Equipment Forecast
Source: Cahners In-Stat/MDR, January 2002
One example of how all this is
coming into play can be seen in a new unprotected Layer 2 Ethernet service XO
Communications Inc. offers. A provider of wholesale and retail services in the
metro market, XO continues to provide its traditional high-end Ethernet-over-SONET
service, but it believes it can put its SONET and wavelength division
multiplexed (WDM) rings to use in delivering a high performing service that
doesn’t make use of the SONET protection mechanisms.
"With some competitors now
offering unprotected service at lower costs, it hurts us when the buyer’s
decision is made on the basis of price alone in instances where they don’t need
five 9s protection or guaranteed bandwidth," says Garrett Hess, senior
product manager for XO’s Ethernet services. "So it makes sense for us to
take this step in order to meet the low-price competition."
The service, offered at speeds of
100mbps and 1gbps, entails use of an Ethernet switch at each customer’s premises
and makes use of the company’s existing ring infrastructure, operating over
SONET frames at 100mbps and in pure gigabit Ethernet format over WDM rings at
1gbps. Hess says the Layer 2 "four 9s" quality of performance meets or
beats that of unprotected private line services offered over ATM or frame relay
and allows customers to save 30 percent to 50 percent.
Such capabilities are causing the
Bell companies to consider using legacy SONET infrastructures in conjunction
with offering Ethernet. Until now Ethernet almost exclusively has been provided
as a private point-to-point transparent LAN service. "We’re seeing a real
pushback from the enterprise sector where more and more companies with
transparent LANs are looking for carrier support for turning those into managed
LANs and threatening to do it themselves or go elsewhere if their traditional
providers won’t cooperate," says Moshiko Levhar, director of IP product
line management at Telco Systems.
That’s why his and many other
companies have chosen to bring out products that, until recently, would not have
gotten the time of day from the RBOCs. In Telco Systems’ case, the latest move
in that direction involves adding a gigabit Ethernet converter and gigE copper
uplink to its edge routing switches. The company’s T5 routing switch supports up
to 64 Fast Ethernet (100mbps) or 8 gigE ports with a switching backplane that
operates at 30gbps, Levhar says, noting the module can operate as a Layer 3
router as well as a Layer 2 switch.
The presence of Layer 3
functionality has important implications for service evolution insofar as the
ability to read packet headers will give the switch the power to control traffic
in accord with QoS priorities. "We can go in with a Layer 2 configuration
supporting LAN services at very competitive price points and, through use of
software, turn on the system to support very granular levels of service as
carriers introduce voice over IP, video and other things," says David
Boulos, Telco Systems’ vice president of product marketing.
The other thing carriers want is to
have interfaces into legacy ATM, frame relay and SONET links that support
transmission of Ethernet without sacrificing bandwidth efficiency. "A year
ago packet over SONET or ATM was frowned upon because of the overhead costs you
incurred through incompatibilities between the formats," Boulos notes.
"But now with chipsets on the market that are fast enough to concatenate
Ethernet packets into small time slots, you get 100mbps of real throughput for
100mbps of bandwidth usage, and that’s a big reason carriers are looking
seriously at Ethernet."
Long Haul Optical Network Equipment Forecast
Source: Pioneer Consulting LLC, November 2001
Some good clues to what carriers are
thinking can be found in the technology provided by ADVA Optical Networking
Inc., which is supplying BellSouth Corp. and Verizon Communications Inc. with
point-to-point access systems for their Ethernet services. The vendor also has a
carrier class metro DWDM solution in distribution. Sprint Corp. and Dominion
Telecom are the first publicly named customers, each of which is deploying the
Alcatel 1690. Both ADVA products are designed to transport virtually any type of
telecom service either in native format or in SONET TDM mode, says Abdul Kasim,
vice president of marketing for ADVA.
"We’re seeing significant
movement in the marketplace, especially from the edge where there’s a big surge
in demand driven by the need for improved disaster recovery capabilities as well
as LAN interconnectivity," Kasim says. "The appeal lies in the
simplicity of use, which allows customers to deploy premises boxes to end users
on a plug-and-play basis, no matter what type of protocol they’re using."
If a carrier wants to map gigE into SONET as opposed to assigning it a
wavelength over the metro system, the ADVA platform strips redundant information
from the Ethernet packet headers, thereby making more efficient use of the
bandwidth, he adds.
Adding to the opportunities, and the
confusion, surrounding choices between SONET and non-SONET options for
transporting packet services at high levels of quality is the emergence of the
technology known as multiprotocol label switching (MPLS), which uses a method of
earmarking packet headers (the transport and routing instruction part of a
packet) so routers, ATM switches and other devices know where to send the
packets without having to "look up" all the information in the header
or duplicate it when the packet is transferred into another protocol transport
domain. MPLS and a host of refinements or extensions suited to making it
applicable for specific types of service are being implemented across the
transport industry in next-generation routers, ATM switches and multiprotocol
A case in point is the success of
recent vendor efforts to improve what is known as MPLS "fast reroute."
Fast reroute provides a means by which the label switched path (LSP)
configuration of an MPLS network is reconfigured quickly in the event of a link
or node failure. This amounts to an effort to emulate the restoration
effectiveness of SONET. There’s more to do, but the gap between carrier-class
restoration standards and what an MPLS-based Layer 3 infrastructure can do has
"If you can do Layer 3
protection comparable to SONET, you don’t need redundant circuits," notes
Azhar Sayeed, product line manager for the Internet Technologies Division at
Cisco Systems Inc. "This is a capability we can add (to MPLS equipped
routers) without any need for specialized hardware."
In field trials of the latest
version of fast reroute, Cisco demonstrated link protection at the sub-50
millisecond speeds of SONET, Sayeed says. "We’re also showing node
protection with rerouting after a timeout is detected at under 100ms."
Heretofore, observes Vinay Rathore,
director of marketing at the Broadband Networking Division of Alcatel, fast
reroute was limited in its applicability because it didn’t scale quickly enough
if there was more than one node failure in the network. Now, he says, draft
solutions submitted to the Internet Engineering Task Force are combining fast
reroute, which relies on communications transmitted in the LSPs. This uses the
"backup path," where one to four backup paths are preselected as
options that can kick in automatically if the primary path fails.
Sayeed expects the standardization
process to proceed smoothly as Cisco and two other proponents of fast reroute
are implementing a compromise version of their original drafts commercially.
"We’re already seeing some people deploying a form of fast reroute for link
failures," he says. "I’d guess that over the next nine to 12 months,
we’ll see many more providers actually taking this on."
One of the first carriers to make
use of fast reroute protection is Williams Communications Group Inc., which
launched in March IP VPN service over its OC48, MPLS-enabled core IP network. A
measure of the robustness that comes with these latest Layer 3 capabilities is
the fact two of Williams’ first customers for the IP VPN service are companies
that require high levels of performance for the applications involved. One of
those, Dancris Telecom LLC, a provider of prepaid calling cards, long-distance,
international operations and Internet services, will use the IP VPN service to
facilitate transmission of call data records for wholesale customers between
branch and switch locations.
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January 21 2020 @ 19:35:32 UTC