Comparison of the construction costs of DWDM networks versus SDH networks

by www.fiber-mart.com

The construction problem of multi-layer network design for a high-speed telecommunication network based on Synchronous Digital Hierarchy (SDH) and Wavelength Division Multiplex (WDM) technology, has to carry a certain set of demands with the objective of minimizing the investment in the equipment.

 

It all start with the design phase – where the effective costs of either optical SDH or DWDM networks has to be competitive.

 

Design processA network design method proceeds by generating cycles, evaluating the economics of building rings on those cycle, and building any economic rings. Generating a cycle involves picking two endpoints between which two disjoint link and node paths are desired — the two nodes selected are thus nodes on the candidate rings.

 

In a telecommunications network, a “ring” is a sequence of nodes arranged in a “cycle” so that no node is repeated. The “links” between nodes are places where fiber can be placed. Nodes are generally physical locations such as buildings where fiber bundles can be connected to each other and where equipment such as multiplexers, amplifiers, regenerators, transponders, etc., can be placed. Ring design entails in part the making of decisions as to ring placement, i.e., which nodes and which links are to be included. Ring design also concerns the selection of equipment, i.e., what types and rates of multiplexers, amplifiers, regenerators, transponders, etc., and where to place the equipment. Finally, ring design necessarily entails decisions as to what demand to place on the rings.

 

The models used for SONET/SDH provide for the following costs and parameters:

 

frame and installation,

regeneration loss thresholds,

maximum number of SONET ADMs on a ring, and

fiber material, sheath installation, and structure expansion cost.

Currently, Dense Wavelength Division Multiplexing (DWDM) is being installed largely on long-distance routes. The DWDM vintage normally used is point-to-point DWDM, or in other words, DWDM systems are utilized as fiber concentrators. The reason for this equipment being so prevalent for long-distance carriers is simple economics: DWDM can substantially reduce capital investment because of the ability to multiply the number of signals being carried by each fiber and thus avoid expensive cable or route upgrade and also save the cost of multiple regenerators.

 

DWDM is multiple signal transmit over a single fiber called DWDM or Different frequencies (colors/wavelengths/lambdas) for different connections over the single fiber. Full featured DWDM equipment can comprise the same range of cards as SDH. They can support fully configurable cross connect features. DWDM technology provides very high bandwidth long haul inter-connect links. DWDM is considered as one of the best technologies to increase bandwidth over an existing fiber plant. It enables one to create multiple “virtual fibers” over one physical fiber.

 

The DWDM layer is protocol and bit rate independent, which means that it can carry ATM (Asynchronous Transfer Mode), SONET, and/or IP packets simultaneously. WDM technology may also be used in Passive Optical Networks (PONs) which are access networks in which the entire transport, switching and routing happens in optical mode.

 

The differences between demand types mostly are caused by the design efficiency of these two technologies’ interface cards in terms of density and price.

 

Cost from IP – Internet Protocol – traffic approach

IP traffic is growing exponentially as customers migrate to IP-based applications. As these networks evolve to include bandwidth-intensive IP based voice, video, and data services, carriers must boost capacity in response to demand, knowing that the collected revenue will not scale at the same rate. Therefore, carriers must find ways to optimize the operating and cost efficiency of service networks and drastically reduce costs per bit.

 

Traditionally this was implemented using (IP) Internet Protocol over SDH approach which has the inconvenient of the optical to electrical to optical (OEO) conversion at the aggregate interfaces. The IP over DWDM is practically implemented as connection between DWDM router interfaces with an optically switched DWDM layer.