?– Broadcast/multicast polling Instead of periodically granting all SSs dedicated
bandwidth for the purpose of bandwidth requests (as done with unicast
polling), it may be more efficient to give such bandwidth to a set of SSs and allow
them to use this bandwidth on a contention basis. This may be desirable when
the set of SSs are only serving best-effort traffic or the SSs are sitting idle. The
broadcast/multicast polling mechanism allows a BS to do just that by making
transmission opportunities (e.g., a transmission timeslot) available to all SSs
(broadcast polling) or a group of SSs (multicast polling) on a periodic basis. If a
node belonging to the group has a bandwidth need, it sends a request for bandwidth
using the transmission opportunity. Once the BS receives the request, it
subsequently makes bandwidth available to the requesting SS. The bandwidth
request mechanism is contention based, and the MAC provides several mechanisms
to minimize the impact of such contentions.
476 Chapter 15
Scheduling of Services As was discussed in an earlier section, one of the QoS parameters
of a service flow is Service Flow Schedule Type.
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