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Link Capacity Adjustment Scheme (LCAS)
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LCAS is a method of dynamically provisioning and reconfiguring TDM channels to suit customer needs or carrier bandwidth management requirements. While VCAT added flexibility to SDH/SONET, LCAS added Dynamism. Because of the dynamic nature of LCAS, it can be used to add two key values to a next-gen SDH/SONET network, namely dynamic protection management and dynamic bandwidth management.
- In failure scenarios, LCAS comes into play by allowing members of a VCG to continue to carry traffic. Throughput of a given connection is decreased, but the connection remains live. This will be important in IP-based networks, so that during failures IP routers will be able to maintain network topologies even though throughput along various links has decreased. This avoids IP routing protocols having to re-converge after a failure while supporting more flexible billing options for operators offering connectivity services.
- LCAS can also be contemplated in bandwidth management scenarios. An operator can use LCAS to modify bandwidth based on time-of-day demands or specific application requirements. The most common scenario described for this kind of "bandwidth on demand" service is a time-of-day discount, so business customers might add bandwidth to their service late at night, when network utilization is at its lowest, to perform backups. As this concept evolves and carriers become more comfortable with the technology, LCAS could be used on a much more dynamic basis, tightly integrated with the data network signaling layer so that data devices themselves can request bandwidth changes on specific links to adjust for traffic changes.
From an Ethernet services perspective, LCAS will most commonly be used to provide in-service adjustments of bandwidth associated with a particular customer and to provide flexible protection options for Ethernet over SDH/SONET services.
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