## 2 Mechanisms Specific to QoS and Multicast in Ad Hoc Networks
### Mechanisms for Providing Multiple QoS Constraints
#### 2.2.2. Independent Metric Technique  
An alternative is to consider multiple metrics independently and only path segments that can satisfy all requirements are considered. Generally, all paths satisfying the QoS constraints are selected first. The next step is to apply an evaluation function, based on the other metrics, to select the best path, for building the multicast tree/mesh. The evaluation function is usually the function of some parameters such as cost of tree, tree stability. The protocols in [12, 13, 14, 26, 33, 35, 41, 43] use this type of technique.  
In CQMRP [12], the four parameters considered are bandwidth, delay, jitter, and buffer capacity. An intermediate node will forward a request packet (which is sent from source) if the following conditions are satisfied: its available bandwidth is greater than the required bandwidth, the transmission delay and delay variations is less than an allowed delay, and the buffer level is higher than a threshold. This protocol does not use an evaluation function.  
QMRPCAH [13] uses delay, bandwidth, jitter, and packet loss metrics. However, the authors mainly considered the delay and bandwidth QoS constraints. In this protocol, the links that violate the bandwidth constraint will first be deleted. Then routing process uses a cost function of link delay to decide the multicast routes.  
The protocol HQMGA [33] finds a multicast tree which satisfies the constraints (bandwidth and delay) and maximizes the value of an evaluation function. The evaluation function is a function of tree stability, latency, and the number of nodes that can receive the data stream.  
Protocol EGA [35] considers two QoS constraints: propagation delay and residual battery energy. The propagation delay is used for building the multicast tree. The maximum lifetime of the multicast tree is defined based on a function of the total residual battery energy in the multicast tree. The protocol MACO [41] uses a modified biology inspired algorithm for multicast routing. Multiple multicast trees, where the links satisfying bandwidth, delay, and jitter constraints, are found; then the best multicast tree is selected based on the value of cost function of these trees.  
In QoS-MAODV-2 Lqos [43], QoS constraints are delay, throughput, and cost. Metrics considered for selecting the paths are end-to-end delay, bandwidth, power level, buffer level, stability level, and hop count. The power level is acquired from MAC layer. It indicates the availability of current amount of battery. The buffer level is used to present the available unallocated buffer. Stability level is defined as the connectivity variance of a node with respect to its neighboring nodes over time. The protocol provides services for three classes of applications: the delay sensitive application, throughput constraint application, and best effort application. When receiving the request from source, the receiver selects the path based on QoS class and QoS state, which are included in the request, and sends a reply packet forward to the source. When the source receives the reply packet, the stability metric followed by power level is used to select the path.