Traffic Engineering and Dumb Aggregation Pipes
February 4, 2009
Let’s talk about traffic engineering … I won’t start with Poisson tables–just some fundamental thoughts.
Any type of communications application, whether data, video, voice, or graphics, always originates and terminates in the local metropolitan and related access networks. You will not find origination or termination of such applications on an oceanic or long haul network. Those are dumb aggregation pipes that add little value.
Trying to keep things simple, optical fiber is lit with a laser. The distance a laser travels has much to do with the type of network, type of fiber, quality of fiber, and the number of service nodes. Lasers are expensive and regenerating their wave lengths after a certain distance is also an expensive proposition. It is much easier and cheaper to light an oceanic or long haul network, as they are strictly aggregation pipes of bits that get their signal regenerated every 60 to 100 miles. For oceanic or long-haul, the fiber is spliced over great distances–miles at a time–to create it’s physical footprint.
Splicing is an important concept to understand–it is taking two fiber strands, on two different cable sheaths, and uniting them as one. Every time you splice fiber (or cut copper as a matter of fact) you introduce a loss of carrying capacity to the signal (electrical or optical), as any splice will have a margin of error. Even the slightest margin of error adversely affects the signal amplitude. More splices in a given cable requires more regeneration over short distances, which is costly.
In industry terms, we call this a “loss budget”. When fiber is installed, the loss budget defines how much bandwidth you can reliably support over a pair of fiber strands as you splice or add nodes. Lots of buildings and homes means a more sensitive loss budget, as well as a need for additional available fiber inventory within the sheath as bandwidth demand grows.
What affects the loss budget of fiber? Location, uninterrupted signal distance and fiber count!
In comparison, for the thousands of buildings and homes in any market, the metropolitan fiber backbone and the access network are subject to hundreds–if not thousands–of splice points or nodes to interconnect users. Unlike an oceanic or long-haul network, it’s loss budget sensitivity is much higher. The physical costs associated with installing a metropolitan network are 10x higher than an oceanic or long-haul network. The add/drops of signals and multiple nodes in a metropolitan access network are complex and costly when compared to oceanic and long-haul networks.
From a traffic engineering perspective, for every mile of aggregated traffic in an oceanic or long-haul network, 10 miles of local metropolitan fiber backbone is required to feed it. For every mile of local metropolitan fiber optic backbone, you need 100 miles of access network to feed it.
The signal engineering in metropolitan settings is monumental and complex. In simple terms, long-haul/oceanic networks require less fiber than local networks to operate–they are simpler and cheaper to build and run. This is why an OC-X or GigaBit Ethernet circuit are cheaper on long-haul routes than metropolitan routes, which are complex and costly. OC-X or GigaBit circuits offer more redundancy and diversity than just two fiber strands between New York City and the beltway serving as a dumb aggregation pipe.
On Wednesday–coaching for Harry Homemaker, the Enterprise CIO, and Financiers…
Written by Dave Rusin - Telecom Executive
Posted by wbrache | Filed Under Long-Haul Networks, OCx, Telecommunications industry
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