Wireless Network Design: Optimization Models and Solution ...

9 Routing in Mobile Ad Hoc Networks 215
width usage and sets the conditioner’s parameters accordingly to shape BE traffic to
the residual bandwidth so that packets queues are short to avoid delay increase.
When a node intends to open a QoS-constrained connection, it sends a probe to
measure bottleneck bandwidth and available delay. Here it seems that any routing
protocol may be used, one that is QoS aware comes in especially handy. While
traversing the network towards the destination, the probe is marked by the routing
nodes with the measurement of the actual link delay and its minimum bandwidth.
The destination copies this gathered information in the reply packet and sends it
back to the source which can then decide whether to admit the flow or not. Once the
flow is admitted, it has to be routed through the chosen path.
9.5.6 QOLSR (Quality of Service for OLSR)
QOLSR [9] is an extension of the OLSR protocol which is capable of providing
multiple-metric routing. This extension can be added to OLSR functioning. No additional
control traffic is generated (only augmented HELLO and TC messages).
QOLSR protocol uses standard multipoint relays (MPRs) to ensure that the overhead
is as low as possible for forwarding control traffic. Local QoS metrics on links
are used to elect the quality of service MPRs (QMPRS). This information is then
flooded in the network by TC messages to calculate routing tables. QOLSR can
find optimal paths on the known partial topology having the same bandwidth performances
as those on the whole network. These paths contain only QMPRs as
intermediate nodes between a source destination pair. QOLSR carries out different
functions which are required to perform the task of routing:
• Neighbor sensing allows, by means of hellos messages, each node to detect the
neighbor nodes with which it has a direct and bi-directional link.
• Neighbor QoS measurement is done by the node to estimate the QoS conditions
(available bandwidth, delay, loss probability, cost, security, power consumption,
etc.) on links to each neighbor having direct and symmetric links.
• Quality of service multipoint relay selection is made by the node to design its
own set of QMPRs. This set is calculated to contain a subset of the 1-hop neighbors
which provides maximum bandwidth and minimum delay from each 2-hop
neighbor to the given node. The QMPR set needs to be optimal, however it should
be small enough to minimize the number of generated TC messages in the network.
Topology Control extension messages are sent to all the nodes by each
QMPR node at regular intervals to declare its QMPR selector set and QoS conditions.
• Each node maintains a routing table which allows it to route packets for the other
destinations in the network with optimal metrics respecting QoS constraints.