If we really aim for successful offloading when having time constraints, some QoS mechanisms should be incorporated to allow differentiation between traffic types and guarantee allocation of resources to the offloaded applications with real time requirements. These QoS mechanisms The QoS mechanisms can be performed within or outside traffics as
it is illustrated in Fig.16, called also ”Traffic handling mechanisms”
or ”bandwidth management mechanisms” respectively. In-traffic mechanisms
are designed to classify, handle, and monitor the traffic across the
network, while out-of traffic mechanisms manage the network resource
and coordinate the network devices. The main In-traffic mechanisms are:
classification, channel access and packet scheduling, whereas resources
reservation and admission control are the main mechanisms of out-of
traffic mechanisms.
The three major mechanismswhich are: Classification, admission control and scheduling.
First of all, packet classification is used to
categorize packets into flows and distinguish between different
kinds of traffics. Once packets are classified, an admission control
mechanism is performed to take a decision of accepting
or not the incoming flow according to its QoS requirements
and the available network resources. Afterwards, packets are
scheduled and queued into memory buffers.
Basically, admission
control mechanism can be classified into three categories:
measurement, model, and hybrid based admission control.
In measurement-based schemes [45][46][47][48], admission
control decisions are made based on the continuously measured
network conditions such as throughput and delay. The
model-based schemes [49][50][51][52] are based on analytical
models and metrics to evaluate the status of the network. Both
these two categories are used for Hybrid [53][54][55] based
admission control.
In
IEEE 802.11ac wireless local area networks, enhanced distributed
channel access (EDCA) is the primarily adopted access control
mechanism for multimedia traffic transmission. However, the
performance is degraded due to the unpredictable delay caused
by its inefficient backoff procedure.