In this
section, we will present an overview of the main QoS provisioning strategies proposed for
OBS networks.
???. Offset-Based.QoS.Scheme: Offset-based QoS (Fan, Feng, Wang, & Ge, 2002) scheme
adds an extra offset time to the basic offset between the BCP and its corresponding
DB. The additional offset time, called QoS offset, is to compensate for the processing
time of the BCP. The duration of such a QoS offset is varied, depending on the priority
of the service class. This scheme is proposed for JET, whereby higher priority classes
have larger offsets. With this scheme, if a low priority DB with no additional QoS
offset time and a higher priority DB with a QoS offset try to make network resources
reservation, the DB with the larger offset will be able to reserve resources in advance,
before the low priority DB. In general, this will result in a lower burst loss probability
of high priority classes compared to the lower priority classes.
Although the offset-based QoS scheme does provide an acceptable service differentiation,
it is faced with some challenges that cannot be ignored. For example, DBs of high priority
classes suffer longer waiting time (delay) than the data bursts of low priority classes.
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