Image Processing Reference
In-Depth Information
Fig. 8.8 Per-flow QoS-aware communication path control
maintenance during the session lifetime and the path release when the session
terminates. Hence, the UE1 (see Fig.
8.1
) wants to use the 3D media service from
the remote media server. So, UE1 sends a service request to the QoS Broker located
in the Network Operations Centre. Note that the QoS Broker is responsible for the
overall control of the network. In this sense, the QoS Broker triggers the Edge
Router 3 (ER3) to check whether the available network resource is sufficient to
transport the requested 3D media with acceptable quality. For this purpose, ER3
sends a Probe message on a path, which may be provided by the underlying routing
protocol, Open Shortest Path First (OSPF) [
86
], to acquire the minimum unused
resource on the path. Assuming that there is sufficient available resource, the
receiving ER1 signals the path in the reverse direction, so the required resource is
reserved on each node on the path and the session is established afterward.
Otherwise, the request must be denied or admitted in best-effort CoS, depending
on the Service Level Agreement (SLA) between the provider and the user. Then, as
long as the 3D media session is active (running), the Refresh and Response
signaling messages are periodically (e.g., every 30 s) issued in such a way as to
maintain the reservation parameters on the path. When the 3D media session
terminates, the Release and Response messages are used to release the reserved
resources for future use.
It becomes clear that the per-flow QoS reservation control is not acceptable from
the scalability and the energy efficiency perspectives. This is even more critical in
cooperative communications scenarios where the UEs, seeking to maximize their
battery lifetime, may happen to dynamically change their access Edge Routers. For
