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Metro DWDM: What's Ahead?

Dense wavelength-division multiplexing (DWDM), the technology that has revolutionized long-distance carrier networks, hasn't made it big in the metro space -- yet.

But Metro DWDM, the latest report in Light Reading's series on metro networking, describes a promising future for DWDM in city networks, perhaps not too long from now.

Interest in metro DWDM is being driven by economics that hinge on the technology's potential to do more than just extend the capacity of fiber. According to the report, written by free-lance technical analyst Tim Hills, carriers are attracted by the chance to offer big corporate customers new high-value, high-bandwidth services using wavelengths while saving operational costs.

DWDM makes this possible because it doesn't rely on the Sonet infrastructure, which has limitations in terms of changing and configuring bandwidth. With Sonet, for instance, upgrades to faster services call for reconfiguring multiple nodes on rings running at fixed rates. With wave services, one fiber filled with many channels can be deployed to upgrade data rates on the same service -- and speeds aren't written in stone.

Fulfilling the potential of DWDM (and its little brother, CWDM, or coarse WDM) in metro networks is a matter of ongoing development, even though today's products have come a long way. Metro wavelength capabilities have moved to more than 64 wavelengths in the past three years, for instance, with 32 wavelengths standard; wavelength speeds have increased to 10 Gbit/s; and systems can support rings, meshed rings, and fully meshed architectures.

But DWDM gear needs to feature an optical layer that can be controlled, monitored, switched, routed, and manipulated for the rollout and maintainance of new services.

The DWDM vendors are finding they can't do it all, so most are focusing on specific aspects of metro DWDM. Some are concentrating on DWDM purely for transparent, protocol-independent transport over clear wavelengths. Many of the traditional Sonet vendors are promoting DWDM as a basis for multiservice provisioning platforms (MSPPs) that feature the use of a managed optical wavelength layer, support of an ever-wider range of services and technologies, and a migration path to an all-optical architecture (something that continues to intrigue most carriers).

Other vendors are focused on the integration of DWDM and Ethernet in metro services. Still others have adopted the use of digital wrappers to facilitate the management of DWDM channels.

Each of these approaches has its own issues, pro and con. The report breaks these out, featuring a dynamic table that lets readers compare nine vendors according to 14 features and functions.

Bottom line? DWDM and CWDM products are evolving to reflect carriers' metro requirements. Gone are the days of the "dumb" DWDM box. Emerging is gear that uses DWDM to make metro optical networks dynamic and intelligent.

To read the full report, see Metro DWDM.— Mary Jander, Senior Editor, Light Reading
www.lightreading.com
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mordecai 12/4/2012 | 9:42:27 PM
re: Metro DWDM: What's Ahead? SONET can do everything DWDM (or CWDM) can do, and more.

DWDM should be returned to the place in the network it was originally used - fibre relief beneath the transport layer.

There is only one application that I am aware of that absolutely must use lambdas as the only transport. All the rest are better served via TDM today.

Marketing blew this thing way out of proportion. As always, in my humble opinion.


gea 12/4/2012 | 9:42:26 PM
re: Metro DWDM: What's Ahead? "SONET can do everything DWDM (or CWDM) can do, and more.

DWDM should be returned to the place in the network it was originally used - fibre relief beneath the transport layer."

This is a major misconception. DWDM proliferated in the backbone not primarily for reasons of fiber exhaust, but to leveraqge optical amplifier technology,which greatly reduced costs (ie, for every N lambdas of DWDM, NxM SONET Regens were eliminated). This was desirable totally independently of fiber exhaust.

Unfortunately, in the Metro area this is not useful, as EDFAs are rarely used. However, if the network goes to big fat MPLS or ethernet pipes (a la OC-48c/192c), SONET can not provide protection, so it will have to be done in the optical layer.

Until then, it's SONET all the way. Sorry folks.
edgecore 12/4/2012 | 9:42:25 PM
re: Metro DWDM: What's Ahead? ----------
Metro wavelength capabilities have moved to more than 64 wavelengths in the past three years, for instance, with 32 wavelengths standard
----------

64 unprotected
32 protected

Sounds like an OM5200 brochure
from 2 years ago :-)

EC
mordecai 12/4/2012 | 9:42:23 PM
re: Metro DWDM: What's Ahead? Gea-

Optical amplifiers and regen savings work without DWDM. (lots of single channel line amps, bi-di amps have been shipped).

DWDM came along to boost the economics further, and avoid fibre exhaust.

DWDM = capacity
OLA = cheap regens

PS - how does fat pipes and MPLS help? How does the carrier do that and still sell private line?

Carriers need to get more opinionated about what they need archtecturally, and they should stop letting themselves be lied to with technology.

generalcharlesdegaulle 12/4/2012 | 9:42:23 PM
re: Metro DWDM: What's Ahead? hello!? did anyone read the article? It said
that DWDM comes in many flavors and i being
used in many ways...e.g., to enhance SONET,
to combine with Ethernet, or for pure transparent
services.....in the end, the metro market is
so diverse, there is no one magic bullet. SONET
is a big piece, but is rapidly coming a
commodity, especially with GFP framers coming
out to effectively "front-end" DWDM with many
SONET capabilities. In the end, DWDM needs
SONET for PM and stats, and SONET needs DWDM
for scalabilty....it is that simple, that is
what any carrier will tell you.
Belzebutt 12/4/2012 | 9:42:21 PM
re: Metro DWDM: What's Ahead? 64 unprotected
32 protected

Sounds like an OM5200 brochure
from 2 years ago :-)


This is all bullshit anyway, I'd like to know of a single customer who uses 32 wavelengths at capacity, let alone 64...

The real differentiators are stability and support, and you can't quantify those on a brochure.
skeptic 12/4/2012 | 9:42:20 PM
re: Metro DWDM: What's Ahead?
Cutting through everything said in the article,
the basics of DWDM are unchanged. Its a
economical way to get more capacity out of
existing fiber and associated equipment.

And it will continue to be used that way,
in the metro or anywhere else. DWDM is DWDM.
There isn't much (in my opinion) different
about how/why its deployed in the metro vs.
elsewhere.
gea 12/4/2012 | 9:42:17 PM
re: Metro DWDM: What's Ahead? Mordecai wrote...

"Optical amplifiers and regen savings work without DWDM. (lots of single channel line amps, bi-di amps have been shipped).

DWDM came along to boost the economics further, and avoid fibre exhaust"

Yes, of course. Indeed, at Bellcore I audited the Pirelli T30, which was a stand-alone, single-wavelength EDFA designed to replace SONET Regens, and even before DWDM was commercial these things were slowly killing of the Regen.

But my piont was this: You don't need fiber exhaust to justify the cost of DWDM: It leverages your EDFA costs tremendously, even without fiber exhaust.

But some time during the bubble, it was believed that the reason DWDM was selling like hotcakes was because carriers were running out of fiber (which was certainly true in some areas). After this everyone went around yelling "fiber exhaust fiber exhaust--just look at the DWDM sales!"

Next came Metro where everyone heard the cries of fiber exhaust, and so carriers started laying tons of fiber. SO when DWDM was ready for the Metro space, it was a niche application at best, because without the need for EDFAs you don't want to deploy DWDM unless there's fiber exhaust.

kokoro 12/4/2012 | 9:42:13 PM
re: Metro DWDM: What's Ahead?
There's no REAL value in the bare offer of more wavelength in a REAL metro environment, especially if you take a medium term time scale.

WDM can make sense in the metro only if it is able to support network SERVICES.

Then you may say that you can offer 64 lamdbas instead of 32 but it's like saying that you offer cars with 8 wheels instead of 4.

Cheers
gea 12/4/2012 | 9:42:11 PM
re: Metro DWDM: What's Ahead? "GFP is more beneficial to SONET networks where none TDM based services (D1 video, Gige, FC) can be supported now. Subrate connections are possible with GFP not wave lengths."

I'm not sure, but it sounds like you may have GFP confused with G.709, the "digital wrapper". GFP--the Generic Framing Procedure--is basically a more flexible replacement for PPP/HDLC:in other words, a way to map data services into transport protocols such as SONET and G.709. I don't think it is aware of any connections per se. G.709, however, does support its own version of TDM so that connections are possible.
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