It's the frustrated cry of computer users everywhere: "You call this an information superhighway?"Why do graphics take so long to download? Where is the stutter-free and twitch-free videoconferencing on every desktop I've heard about for years? Why are there always traffic jams on the 'Net? Why am I always waiting for data? If this is the future, it doesn't seem to be worth the wait."
Paradoxically, the future is here and it does work, we just can't feel it yet. The information superhighways have been built and they do live up to their promise. Thanks to dense wave-division multiplexing (DWDM), which multiplies fiber capacity several fold, data zips between cities on virtual autobahns. It just can't be felt because the problem isn't on the superhighways, it's elsewhere.
The intercity networks are built for sports cars, but the metropolitan scene is still for horses and carriages. It takes just as long to get data from around the corner as from around the world. The slowdown is right outside your garage.
While we've created these rapid interstates for voice, video and data, we forgot to build new, proportionately speedy city streets. Data rushes into town on a superhighway, then stops dead as it skids onto the telecom equivalent of dirt roads and tumbleweeds. The traffic piles up fast. If data moves fast between cities, but slow once it arrives, you don't feel the speed. You just feel the wait. And the wait. Website found, waiting for reply. ...
For some time now, the challenge has been integrating into the metropolitan area networks (MAN) the same DWDM technology that made the intercity information superhighways possible. Somebody needed to bring the speed of the superhighway into town and right up to the office building, right up to the users' desktops. So far, no solution has worked, and with demand for bandwidth climbing exponentially, the disparity between intercity speed and intracity slowness is becoming too glaring to ignore.
Previous Near-Misses
Until recently, competitive local exchange carriers (CLECs) and other service providers in the metro area had two options for deploying DWDM. Neither were very appetizing: offering 2.5 gigabits-per-second (gbps) pipe (that is, one DWDM-wavelength channel, appropriate for interoffice applications) per customer, or trying to break it into user-size bandwidth chunks with synchronous optical network (SONET) and asynchronous transfer mode (ATM) aggregation equipment.
Offering a 2.5gbps pipe to customers provided much desired speed, but it was hardly cost-effective. To make money from a typical 32-channel DWDM system--which could service a maximum of only 32 customers--prices were off-putting and even could kill a new service at conception. This made sales to enterprise customers difficult for CLECs.
The Metro Network Using ATM and SONET
On the other hand, the current technology used to break the outsized pipe into right-sized chunks is messy and requires complicated protocol conversions into ATM and SONET. The result is, once again, more cost and, even for those willing to pay, more latency. So customers essentially have a lose-lose choice: the super-fast but overpriced outsized pipe; or the right-sized pipe with the irritation of latency. The tacit agreement between CLECs and customer was to settle for the lesser evil. Until DWDM could be made cost-effective in MANs, everyone was going to hobble along in a world of latency.
Everybody knew there had to be a better answer, and now increased demand for bandwidth is pushing the market to come up with a better solution. The Internet is only going to increase in popularity, with 200 million users predicted by the end of this year. Furthermore, as sophisticated users move to cable and digital subscriber line (DSL) services, increased demand for intracity bandwidth is a given. What's the point of owning a high-powered vehicle if there are miles of dirt road between you and the interstate?
Metro DWDM Using Subrate Channels
Subrate Multiplexing
But subrate multiplexing brings desired speed to the customer without any of the latency that comes from SONET and ATM protocol conversions. It allows CLECs, for the first time, to cost-effectively use DWDM systems in the MAN. A CLEC now can serve up to 512 customers from a 32-channel DWDM system at an affordable price.
Besides the obvious benefits to the CLECs and their customers, the CLECs now face an unsurpassed opportunity to expand their businesses, to reinvent the way they serve their markets. Voice services, such as long distance, will be moved onto Internet protocol (IP)-based data networks and likely will ride free on the data network. Instead, CLECs will make their money with the new services that have been promised for years, but which have never really been practical until now because the metro paths were chronically congested.
Videoconferencing, for example, no longer will be a toy, a hassle or something that requires operators. It will be a basic, indispensable and convenient business reality--no latency, no twitch, no worries. It will be as simple as turning on the personal computer (PC) and cruising. Even residential services, such as movies-on-demand, high-definition television (HDTV) or live-event netcasts, will be appealing to users and profitable for the CLECs.
For DWDM to be effective in the MAN, it must have protocol and bit-rate transparency, which means each subrate channel must retain that transparency as well. Just about any piece of customer premises equipment (CPE) now can be directly connected to a DWDM via subrate channel. And, by supporting any speed within specified limits, virtually all signals can be transported natively with essentially no delay.
For example, fast Ethernet switches and routers now can have a direct link to a DWDM-based MAN. And since the overwhelming majority of originating corporate traffic is Ethernet, which must be delivered to another corporate user as Ethernet, data now can zip across the MAN in its native mode. Without the conversion to and from SONET, there is no added latency, cost or complexity.
By extending the granularity of a DWDM system, subrate technology now can improve upon DWDM's "pay-as-you-grow" ability to provide the desired amount of bandwidth. "For operators, optical networking offers the ability to increase network capacity in a scaleable manner and relieve network congestion," says Barry Flanigan, consultant with Ovum Inc., London (see "The X-File,"). "They can now make more effective use of installed fiber."
As the future arrives and all the long-promised services become daily business reality, controlling network infrastructure costs will become paramount. Here again, subrates offer help. After all, in modern fiber-equipped optical office parks, there is a tangle of different CPE: ATM switches, routers, gigabit switches and more. Subrate's transparent connectivity provides direct optical connection to the DWDM network for all of this diverse CPE. This flexible connectivity is one way to keep costs in check and prices proportionately attractive.
Typical 32-Channel DWDM EPC Subrate Multiplexing
As more applications move to packet-switched networks, the primary device that terminates connections in the central office (CO) can be a high-performance IP router. Furthermore, router speeds from the leading vendors are increasing dramatically to keep up with the new applications. Gigabit Ethernet switching is in its infancy. With 1998's many new product introductions, gigabit switches soon may connect to a customer premises router, a CO router or ATM switch, or the customer may elect to use the optical network by connecting optical gigabit Ethernet interfaces directly to the DWDM network. Subrate multiplexing is an ideal solution because it reduces latency. In DWDM technology, delays are measured in nanoseconds. Because there are such low delays involved, DWDM is an optimum transport solution for most protocols. Instead of routers and SONET cross-connects, which have millisecond delays, subrates permit network devices to be connected directly to DWDM, cutting the delay to nanoseconds and improving transmission. Because the number of conversions is reduced, there is considerably less aggregation required. In other words, the overall network has been simplified. An example of a new service is voice over IP (VoIP). VoIP is an emerging technology that will move a significant percentage of voice traffic from the circuit-switched network to the packet-switched network and onto the IP router and DWDM network.
With subrate channel multiplexing, the entrance ramp to the superhighway is right outside the garage. Graphics download fast. Data moves fast. Every connection--voice, video or data--is latency-free. Subrate multiplexing and DWDM means the metro roads are proportionally fast enough to keep up with the traffic flowing on and off the interstates. So now, CLECs will have the chance to reinvent themselves and give users what they've been dreaming of for years: a chance to feel the wind in their hair every time they log on.
James Chitkowski is vice president of sales and marketing, transmission products, at Osicom Technologies Inc., Santa Monica, Calif. He can be reached at (800) 854-2831.
