Implementing Service Changes
As Ethernet over SONET/SDH（EoS）, ESCON, FICON, DVB and other client specific interfaces have been introduced into the SONET/SDH infrastructure, the importance of Virtual Concatenation（VCAT）to provide the correct size paths, and Link Capacity Adjustment Scheme（LCAS）to dynamically manage path size dependent on user traffic needs, will dramatically affect new TDM fabric features and the way in which they are administered.
Traditional NE ports such as T1s, DS3s or ATM via OC-3s use a fixed amount of bandwidth to support their paths. These access ports require a physical modification to change a service from T1 to DS3, for example. Hence bandwidth changes are infrequent, planned events normally requiring significant human intervention over a period of weeks. When a Fast Ethernet port is deployed with over-subscription, bandwidth changes do not require any physical port changes. Thus, service changes for additional revenue can be made with key strokes rather than ‘truck rolls（field service calls）.
Plans for implementing GMPLS or ASON will allow automation for bandwidth changes using LCAS between end points to complete bandwidth changes once the paths are made available to the end points. It becomes necessary to monitor the performance of each path added at each NE to assure that service delivery of the extra bandwidth can be achieved. Thus auditing of unequipped paths and monitoring of path trace identifiers will gain importance. Services such as temporary network bandwidth increases for video conferences or utilizing extra bandwidth at night for site backups are just a few ways in which carriers can satisfy user demands. Web-based tools can permit subscriber IT personnel to order the changes and execute them without a carrier's manual intervention further reducing the carrier's OPEX. Since service is delivered much closer to when service is needed, this can generate carrier revenue much faster.
Another attribute of EoS is that a path can be composed of either multiple VT1.5/ VC-12（low order）or several STS-1 / VC-4（high order）. For example, a mapper card that supports eight Fast Ethernet（FE）ports for both high and low order VCAT would require a similar amount of board real estate and almost identical physical connectors to eight T1 ports. However, the eight FE ports could use up to 16 STS-1 or up to 512 VT1.5s; the quantity of paths may grow as customers order more bandwidth. The eight T1 ports would only require eight VT1.5s and is fixed forever. Many existing NEs use this lower physical density fact for low order path mappers to provide only a fraction of the capacity of VT1.5 switching versus STS-1 switching. EoS challenges this assumption. As the EoS deployments grow and as customers demand more capacity per port, the quantity of VT1.5s requiring switching in a NE will grow. In this example, replacing eight T1 ports with eight FE ports could require up to 64 times the VT1.5 capacity over a period of time.
