Ability to allocate bandwidth as requested by an SS in itself is not sufficient to serve
the QoS in a shared medium. Equally important is the mechanism and opportunities
for SSs to request bandwidth in a timely manner to serve the QoS needs of its service
flows. The MAC defines bandwidth request mechanisms that provide such opportunities
for SSs to request uplink bandwidth:
?– Unicast polling Unicast polling is a mechanism by which an SS is granted
(by the BS) bandwidth (meaning a TDMA slot) solely for the SS to make
bandwidth requests. The rate of such unsolicited polling depends on the QoS
requirement of the service associated with the SS. SS can use each instance
of the periodically available bandwidth for any purpose that fits its need. It
may use the bandwidth to send data traffic piggy-backed with requests for
more bandwidth or it may send just its bandwidth requests to the BS. Unicast
polling also serves the purpose that with each SS transmitting some data to
the BS periodically, it allows the BS to monitor the quality of the physical
channel. The frequency of unicast polling of an SS is determined by the type
QoS requirement of the services being associated with the SS, as well as by the
need to monitor the physical channel.
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