Four types of scheduling services
are defined by the standard and dictate how the services are scheduled:
?– Unsolicited Grant Service (UGS) This is equivalent to CBR in ATM and is
intended for applications that have real-time data streams consisting of fixed-size
data packets generated at periodic intervals. Examples include T1/E1 services. For
this type of service, BS grants fixed-size bandwidths periodically to SSs associated
with the service flows without being solicited for the bandwidth by the SSs. The
size of the bandwidth grants at periodic intervals is sufficient to transport the
fixed-size data needed by the service flow.
?– Real-time Polling Service (rtPS) rtPS is designed for real-time traffic with
variable size packets generated at periodic intervals. Examples of such traffic are
MPEG video stream, VoIP with silence compression, and so on. For this type of
service, SSs are given opportunities to specify their bandwidth needs by means of
periodic unicast polling. If the bandwidth requests are within the realm of what
can be granted, the bandwidth is granted to the SS.
?– Non-real-time Polling Service (nrtPS) nrtPS is designed to support delaytolerant
data traffic for which a minimum data rate is required.
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