g., a
physical port) that cannot simultaneously support all these services and also meet their
respective bandwidth profiles; in such a case, a relative priority between these services
becomes necessary. A CoS essentially provides this.
The CoS is also useful because it enables Service Providers to model service demands
realistically; customers are increasingly subscribing to services with very different performance
demands, for example, Internet access and VoIP require different treatments.
With CoS, Service Providers can offer the required level of service and also charge accordingly.
It also gives subscribers flexibility.
Each CoS has performance parameters associated with it, and typically the Service
Provider will enforce the specified performance. These parameters include bandwidth
profile and also jitter, delay, and so on, which will be in the next section.
A CoS is identified using a CoS ID. The various CoS IDs are described in the following
sections.
66 Chapter 2
Physical Port Here a single CoS is provided per physical port. All traffic ingressing
and egressing the port receives the same CoS. This is a very simple implementation
of CoS, but it also affords the least flexibility; if a customer requires multiple CoSs for
their traffic (VoIP and Internet access), then two separate ports would be required to
enforce the appropriate CoS.
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