## 2 Categorization and Classification of Quality of Service Routing Protocols
### Probabilistic Routing Protocols (Hard Real Time)  
Multimedia Geographic Routing (MGR) introduces a new architecture called Mobile Multimedia Sensor Network (MMSN) in [20], that is based on the Mobile Multimedia Geographic Routing (MGR) scheme. In this scheme, the mobile multimedia sensor node (MMN) is used to improve the sensor network ability for event description. The purpose of this protocol is to reduce energy consumption in order to satisfy limitations on an average end-to-end delay of specific applications in MMSNs. The main goal of this protocol is to handle the delay to guarantee the priority for QoS provisioning. The protocol continuously attempts to reduce the energy consumption in order to prolong the sensor life time. This helps to exploit the energy delay adjustments for design of this protocol. However, the key operation of this protocol is to choose the suitable location of the current node for the next hop. In order to complete this, MGR estimates the distance of the desired hop for the next hop selection that can be obtained by dividing the distance between current to the sink node. MGR ensures the QoS delay and reduces about 30% energy consumption and prolongs the network lifetime as compared to classical geographic routing. MGR is more scalable than other protocols because it has the capability to control the mobility as depicted in Figure 2.  
The QoS-based routing (QBR) protocol [21] is a real-hard probabilistic-based routing protocol introduced to support event and periodic-based data reporting. QBR is composed of the features of geographic routing with QoS provisioning. The data packets are forwarded in the network based on the type of the packet. QBR sets different priorities levels for each type of data packet. Thus, multiple transmission queues are introduced for handling the priorities of data packets. In addition, the node is picked based on residual energy, high link quality and the path with minimum load. The selection process of nodes consists of one-hop neighbor nodes that help reduce additional energy consumption. In handling the congestion within the network, the ring or barrier mechanism that aggregates and captures the data packets is introduced. The barrier operation involves the barrier formation, shrinkage, repair, enlargement and termination. Despite these significant features, QBR is unable to meet the required QoS parameters. The main concern with this protocol is the use of extra control messages, which affect the throughput and consume additional energy. Figure 2: The Strategic Location Selection in MRG [20]. Multiple Inputs and Multiple output (MIMO) is proposed in [22]. In MIMO, the data is collected in Multi-hop Virtual MIMO through multiple source nodes and transmitted to a distant sink using multiple hops. The clusters are used to organize the sensors as given in Figure 4. The cluster head transmits the data to cluster nodes that are related to a specific cluster. Additive White Gaussian Noise (WGN) is used in such a transmission with squared power path loss because of the short intracluster transmission range. Further, the cluster nodes translate and transmit data to a cluster head to the next hop due to orthogonal Space-Time Block Code (STBC). Multi-hop Virtual MIMO shows that an average reduction of the channel between each cluster head and cluster node is estimated during construction of the clusters, so that it employs an equal Signal-to-Noise Ratio (SNR) policy to distribute the transmitted energy due to its spectral performance efficiency and simplicity. The Multi-Constrained QoS Multi-Path routing (MCMP) protocol is proposed in [23] to handle the QoS requirements. The MCMP uses braided paths to forward the packets to the sink station, which helps maintain the QoS parameters such as end-to-end delay and reliability. The protocol structure is based on the linear integer programming, which formulates the end-to-end delay as an optimized problem.