An Overview of QoS Routing
This section provides literature reviews on the Quality of Service (QoS) routing. The paper divides this section into two parts. The first part provides a review of literature that examine the general overview of QoS, and the second part of this section examines QoS routing strategies.
Quality of Service (QoS) for networks communication is a mechanism that ensures high-quality communication in the network application. Typically, traditional concepts of network quality in the network traffic are treated equally where there was no guarantee of best-effort service delivery, and bandwidth-intensive application can result in poor and unacceptable performance in all applications. [1]. QoS routing is a provision of routing algorithms capable of identifying the path to achieve maximum flows process. The protocols in achieving the routing implementation must achieve efficient utilisation of resources, and QoS routing must be able to support traffic using integrated service. The modification of QoS routing should be able to support alternative paths through different paths, and the goal of routing is to provide routing algorithms that satisfy maximum flows with end-to-end constraints. For an effective network path, QoS routing must support multiple paths, and best-effort routing should be able to shift from one path to another upon finding a better path. Typically, the dynamic finding of feasible choice and optimisation of resources are among the possible choices of the requirements of a routing mechanism. |2][73][74].
However, Masip-Bruin et al. point out that QoS routing has been a complex problem in the QoS based network, with the toughest problem hampering the implementation of internet connectivity in the QoS routing protocol. However, finding QoS Routing that requires frequent distribution of multiple and dynamic parameters need effectively choosing of metrics to base routing decision, routing strategy, and the complexity of path computation algorithm. To establish a common understanding of QoS, there is a need to determine the degree of satisfaction of a user of service from the collective effect of service performance.[3][75].
An Overview of QoS
Mobile ad hoc network performances are largely dependent on the efficiency of routing protocols adapted to changing network topology.[4]. Achieving quality of service has become an important factor in business applications. QoS has become an important factor to satisfy the end-users. For any business to achieve market shares and gain competitive advantages, there is a need to increase the quality of service for the satisfaction of end-users. [5]. Typically, the network industry needs to set the standard and ensure high-quality performances in achieving Quality of Service (QoS). Using mechanisms of QoS is for the implementation of resources efficiency. [1] Oliveira and Monteiro argue that quality of service routing is a fundamental tool that can have a direct impact on routing oscillations under heavy network traffic, and overall, QoS needs a quality routing strategy to avoid network problems. [6].
Quality of Service (QoS) is increasingly gaining wider attention because of its real-time impact on multimedia. Typically, communication is the backbone of any organisation. With the increase in demand for the application of the network in transmitting data and for the enhancement of business, QoS has become important for managing network resources.[7]. Sun defines QoS as the totality of features and characteristics of a product or service that provide the satisfaction needed by customers. The totality of qualities for a specific product is a metric to evaluate the satisfaction of a product. For example, in providing network service, evaluations of the totality of quality service are the efficiency, reliability, maintainability, portability, and functionality. Typically, Kumar, Ryu, and Jang argue that QoS is the ability of a product to offer integrity and accuracy to users. Typically, the essential attributes of QoS could be classified into four categories:
Time-related characteristics: This is the ability to offer quality service without delay.
Importance-related characteristics: QoS is characteristics on its level of importance to the users. In the network industry, the ability of a specific network to offer a specific need to a user is categorised as one of the most important attributes of QoS.
Capacity-related characteristics: The ability to offer the highest capacity is an essential attribute to QoS. The capacity of a product or service is an important feature to measure the quality of service.
Fault tolerance characteristics: A quality service should b able to be fault tolerance, whereas a network service should be able to identify fault, and if possible, correct itself. [8] [9].
Major building blocks of quality of service are serviceability, trafficability performance, and dependability. Allowing implementation of the high level of QoS in a network performance depend on the ability of the network to meet traffic demand and be able to provide a critical point of impacting network performance. [10][91].
In the network multimedia industry, the application of QoS needs a high-quality guarantee for smooth video service in order to satisfy end users. Due to the precautions that need to be taken for the proper implementation of smooth video playing, QoS has become the parameter for multimedia applications. As being argued by Braumandi, Kemper, and Kossmann, provision of quality of service in multimedia requires adequate precaution in the network infrastructure, where parameters in multimedia application involve distributed query processing. Typically, the motivation behind integrating good service quality is to concentrate on providing quality service because the provision of service quality in query processing is rare, and there is a need for concentration on improving response time. [11]. However, Mavromoustakis provide an explanation of the importance of QoS application wireless communication. The author asserts there is increasing awareness on the importance of wireless communication based on the application of multimedia that is gaining importance in the telecommunication industry. Thus, improper management of the network in the Information Technology environment can lead to delay of sensitive application and implementation of quality service delivery of an organisation. This can degrade the overall corporate image. Thus, to allow for an effective communication system for the enhancement of service management, QoS is essential to provide adequate satisfaction for end-users. Typically, applications of network devices have created the need for QoS for end-users, especially for data transfer across the network. [5]|92]. However, Vadde and Syrotiuk argument on QoS is a little bit different from the previous works of literature reviewed. Authors argue that in mobile ad hoc networks (MANETs), there is a need for the support of voice communication, and this makes QoS be challenging to the application of a wireless network. In addition, there are frequent changes in the nodes of wireless network dynamic, which makes QoS be applicable in a wireless network.[12].
However, there are still problems associated with QoS in network devices where the survival of networks depends on the level of energy consumed, and network problems can result in unacceptable QoS for end-users.[93]. Thus, effective energy conservation techniques are essential to sustain energy performances. Moreover, the requirements of some applications are more critical than others, which shows that some network traffic should need preferential treatment than others. With an effort to achieve the best delivery system, the QoS concept needs to provide preferential delivery application service.[1]
QoS concept
The need to set the standard in the network industry is to ensure high-quality performances. The concept of QoS is to ensure that the functionality of networking achieves accurate latency and reduction of data loss. [1]. The growing attention to the concept of QoS in the network industry leads to an increase in traffic volume in the internet industry.[13]. To ensure proper operations of application of communication, there is a need to ensure QoS mechanisms that determine the applications of network resources and regulation of data flows where classifications, scheduling, and traffic control mechanisms ensure the delivery of traffic flow to the network. [1]. Some groups of researchers have correlated the concept of service quality to the difference between what is expected and what is delivered in the network service. The expectation of where the QoS is delivered matches what is expected. The customer finds service acceptable. [14]. For example, in the qualitative latency of network functions, the percentage of packets discarded by a router and the rate at which traffic is carried by the network have the greatest impacts on performances coordination. [15]. Typically, the ability to guarantee a level of service quality is very important. The drawback between network service and QoS parameters can have an impact on overall service delivery. [16].
Kajackas, Anskaitis, Guršnys argue that in the present telecommunication network, QoS depends on the level the applications are able to send data, and the level networks are able to deliver data. While products with the higher class will require more services network than products with lower classes, and it is obvious that in some network aspects, some parameters are needed for network resource management. [17]
Ensuring QoS, it is essential to determine the components of Quality of Service.
Components of QoS
Service Composition in the network service is based on the QoS-satisfied service-based, where the critical applications to achieve system reconfiguration in order to adapt to changing environment, and achieving network viability require the adoption of parameterised components of QoS in the networking parameter.[18][19]. Saxena argues that components of QoS can be classified in two standpoints. Technical and functional quality. Technical quality involves deliverable quality and process that meet customers’ detailed requirements. This approach is to ensure that there is a need for an understanding of detailed requirements and detailed designed documentation in order to mitigate risks. A functional quality involves conformity with technical quality, and this involves responsiveness, reliability, accuracy, and dependability. [20]
However, Jin and Nahrstedt offer a different argument from the previous works of literature reviewed. From the authors’ perspectives, a component of QoS in the network bandwidth is based on the adaptivity where the service component is able to satisfy the existing path of QoS. Typically, network service should be able to satisfy some requirements such as physical infrastructure with abundant resources and usage optimisation. It should be noted that network service should be able to provide robustness, whereas the quality of service should be able to provide a protocol to recover from failure.[19]. With the increase in the need for the broadband network, many modern applications require better service for internet connectivity, and consensus has been focused on QoS support for better internet service. Typically, the QoS framework requires a QoS routing mechanism. Many QoS routing algorithms require sufficient QoS requirements for network application |21]
QoS routing is an important feature in the wireless network infrastructure, especially the support of real-time communication. The next section provides QoS routing in the communication network.
QoS routing
QoS routing has generated much interest among scholars because of its features in the interconnection of a wired network, mobile network, its support to the connection of Automatic Teller Machine (ATM), and internet connectivity. [22]. Gudrin, Kamat, and Tripathi point out that QoS routing is the process of selecting paths used by the packets based on the requirement of a flow. The motivation of using path selection is to improve service received by users for all network efficiencies. Although computational cost and protocol overhead leads to an increase in computation complexity, and this can become a primary inhibitor to QoS deployment. Typically, efficient gains of QoS routing is by obtaining simpler routing protocol, and QoS routing can be more improved by network
topologies. [23]. (QoS) routing is a tool to improve the flows of networking and achieve sufficient resources to meet the flow’s requirement. Meeting flow requirements in the form of bandwidth and meeting some network resources for an efficient flow network path, QoS routing is an essential tool to guarantee network flow, which enables a network operator to identify a path for every new flow and meet network requirements. Typically, network requirements in the form of bandwidth are suitable to find a path to the destination. In identifying path selection, there is a need to find paths with sufficient resources to accommodate requirements for path flow. It should be noted that each criterion of QoS routing are capable of satisfying the path selection process if a path is capable of minimising the amount of cost of resources being consumed. Path capable of satisfying requirement flow depends on the accuracy of the information in the network resources.[24][101].
Hu and Johnson argue that QoS is very important in a wired network, where over-provisioning can reduce the need for OoS sophisticated techniques. Although, using a QoS routing protocol needs careful analysis of routing paths for wireless network applications. Typically, routing selection can enhance the performance of network traffic, and in ad hoc networks, capacity and connectivity are be quite dynamic. [25]. With the argument presented by Shaikh, QoS routing can satisfy requirements for application performances and optimise network usage if selecting paths based on connection traffic parameters. Typically, there is significant bandwidth and processing overhead that can be imposed by distributing the quality of routings parameters. Typically, the QoS routing mechanism can impose significant bandwidth and processing load on the network. [26].[98][100].
As being described by Ouferhat, and Mellouck, QoS routing algorithms is the process of selecting, discovering, and maintaining pathways from one node to the other, and by using these routing paths, their networks deliver a flow of packets. Performance of QoS routing largely depends on the traffic patterns and the network topology, and maintaining text nodes requires choosing the best optimal path for networking, and this generally affects network performances. In network communication, the effectiveness of routing protocol has an impact on the routing destination. Deriving the shortest network routing protocol is a primary concern to network analysts. Routing protocol generally consists of the task of capturing the state of the network and its available resources for the dissemination of information in the networking. However, a routing failure can occur if the source selects a path that can not support a new connection, and set failures can incur extra overhead resources along the routing path.[27] [28].[99]. Although QoS routing has become rapidly in emergence search rescue operation, and with an increase in popularity of real-time multimedia applications, there has been the evolution of complicated problems. With the emergence of mobile and ad hoc networks (MANETs), there are new challenges in supporting predictable and reliable communication performances. [29]
Moreover, evidence has revealed QoS routing can provide an increase in network utilisation and network utilisation. There is still an argument that QoS routing can be costly to maintain because of the increase in routing protocol overheads.[30].
Routing Process
Routing manifestation is to find the shortest routing, where the shortest path tree provides the entire destination to the autonomous system. Transmission of packets of shortest path routing algorithms can only be done with two nodes, and in multipath algorithms, the transmission is done between two nodes, and the routing system can only take the shortest path region of the pair. It should be noted that nodes always route along the same row or the same column towards their destination process. [28]. Studies reveal that identifying a feasible route in communication networking requires complexity that corresponds to the QoS mechanism. [31].
Kuipers and Mieghem argue that with ab increase in demand for real-time multimedia, there has been an increase in the demand for QoS. However, the QoS requirement needs a QoS framework to find the shortest path for Qos routing algorithms. Typically, QoS routing algorithms use the information to compute the shortest path. [32].
Typically, a QoS routing process is very important to the network component, and to provide a guaranteed service, CPU, bandwidth, and the buffer need to be reserved during connection. Failing to observe this condition, traffic will not be effective during traffic dynamics of connection sharing links. In addition, the QoS routing algorithm may fail if search space does not cover the existing feasible path. It should be noted that QoS routing can assist in finding an available path.[33]. A computational efficiency stems from finding the shortest path stem from efficient gain from the alternative path, which can remove a number of unnecessary nodes. [34]. Research conducted by Sobrinho reveals that another routing that is presently attracting attention is path-vector protocol because of its advantage to converge with all networks and its inter-domain routing on the internet. [34].
Basically, many multicast protocols are being proposed: Distance Vector Multicast Routing Protocol (DVMRP), Open Shortest Path First (MOSPF), Core Based Trees (CBT), and Protocol Independent Multicast (PIM) and so on. The major challenges of this routing system are that there may be processing overhead, packet collisions, and maintenance of routing. To minimise the challenges that might have occurred from the routing system, the major strategies are to find the shortest path between source nodes, which will diminish transmission packets. Works of literature have revealed that to provide efficient multicast transmission. There is a need for a maintenance mechanism, where the basic idea of an integrated routing layer is to offer reliable multicast transmission.[36].
Analysis of the multipath routing conducted by Cidon and Rom show that the selection of routing system must meet certain requirements to ensure the appropriate desired quality of service in communication. Routing set up in ATM networking reveals that there is a need for sufficient resources for route set up. Typically, multipath reservation algorithms can perform comparably to single-path algorithms. However, the connection for multipath algorithms may be lower. Due to common network failures in both ATM and internet, multipath routing is slightly better than single-path routing because multipath routing has a shorter expected delay in network connection than single path routing. For example, in the telephone network, analysis shows that routing in the telephone should assume a fully connected network. [37][86].
On the other hand, the comparison made by Badis between multicast routing compared to unicast routing reveals that multicasting can reduce overall network load, whereas multicasting can increase the total capacity of network and data delivery. However, the challenging factor that multicasting can face in mobile and ad hoc network make multicasting face some criticisms. [38][87][88].
Before examining problems of unicasting and multicasting, the next subsection provides the problem statement.
Problem Statement
This subsection examines the problems statement for the network routing process.
Numerous studies have revealed problems with QoS network traffic. Routing Algorithms discussed by Siachalou and Georgiadis reveal that multimedia traffic can present many challenges to communication networking. For example, there can be a delay, loss probability, and jitter in order to maintain QoS routing and reception quality. Maintaining quality reception can give rise to problems in routing multimedia, which the author refers to as the Constrained Shortest Path Routing Problem. [39][90].
Typically, there are fundamental questions on how to select a QoS path to minimise cost, minimise chances of flow being blocked and overall maximisation the utilisation of resources. Typically, the are complications of finding path selection from a load of networks, especially in multicasting and unicasting routing.[40].[76][89]
Lorenz, Orda, and Raz also support the argument that finding a good path is a fundamental challenge in unicasting and multicasting routing, where each link is associated with delay and cost difference, and this can pose practical networking problems. The complexity of the QoS mechanism and constraints imposed on the whole connection can create overall routing problems.[41]
The detailed practical networking problems in unicasting and multicasting are discussed below. This paper reviews works of literature that discuss several challenging problems of unicasting and multicasting routings in the next section.
Problems of unicasting and multicasting routing
Reliability is very important in network routing and problems that can arise from routing protocol, which can come from loss rates in the unicast and multicast connections. Recently, there has been increased interest in multiple path routing because of several advantages it provides. Multiple cast routing is capable of meeting multiple performance objectives. While the multiple cast routing is advantageous in minimising delay, it is also tolerant to network failures. However, combined problems of unicasting and multicasting routing show that these problems can delay network requirements. [28] [41].[77].
Uncertainty in the network parameter can serve as a complex problem in the routing process. For example, loss of accuracy in the routing connection can lead to some level of uncertainty, and some problems may come from the complexity of network devices where there is no aggregate information on node and link parameters. Problems of inaccurate parameters can lead to temporary problems such as congestion, and these can lead to the impracticability of the accurate parameter. [42]. Although, studies reveal that multicasting provides a significant saving for network bandwidth, where the operation of multicasting on the internet can provide applications that include multiple video and audio conferencing. [96].[97].Multicasting has also been known to provide dissemination of textual information such as weather reports, multi-person communication, and general-purpose multicast functions that can be email functions. However, the provision of multicasting has become challenging to mobile communication.[43][78].
The argument presented by some scholars reveals that multicasting routing can be set with some constraints, such as non-availability of accurate state of information, and this can lead to complexity due to changes in traffic. Typically, uncertainty can make QoS routing to be a complex problem. However, Guerin and Orda provide a similar argument that inaccurate information, such as link and node metrics used in computing multicast routing, can lead to a network problem. It is very important to realise that information inaccuracy may affect database topology and path selection.
Thus, bandwidth delay in routing algorithms and means to find the shortest and minimum cost may lead to certain constraints during computation. In addition, successful QoS routing must be ensured for the flow of communication, and the decision is based on correct information. Typically, feasible expensive information and changes in resources availability can induce substantial inaccuracy in information in the multicasting routing and path selection process.
For example, linking 10M/bs may be more desirable than 20M/bs. [44] [34].
Typically, researchers have only concentrated on multicast routing and unicast routing protocol. The benefits of unicasting are that it can be easily extended to multicast routing, and quality multipath routing can explore an unlimited number of paths.[79].
However, criticisms are levied on distributed multipath routing as being characterised by limited searching. Zappala argues that an objective of both unicast and multicast routing systems is to find the shortest-path route. Typically, QoS routing is to compute QoS-capable path in a scalable manner, and by using the shortest path, the network can be overloaded. [45].[80].
Williamson, Bunt, and Mackrell also point out that multicasting routing can face tunnel convergence problems, duplication problems and scoping problems. Typically, multicasting routing may experience unacceptable packet losses when affected by a foreign network.[43].
However, Chen and Nahrstedt argue that problems of QoS routing can be difficult to analyse due to distributed application of internet phones, multicast routing problems may be diverse due to delay in jitter and loss ratio, and finding a feasible path for two independent paths can be problems. It should be noted that with increasing difficulty in wireless communication, QoS routing algorithms can be seriously degraded, and there can be path constrained routing, which may delay finding the least-cost routing. [44]. However, some authors believe that an alternative path can be a substitute for multicasting routing because of the indication that an alternative path is now available on the internet and is providing superior quality to the default path. For example, alternative path routing can provide a wide range of adaptive installation and path computing, and alternative path routing can have the ability to scale to large networks as well as meet the shortest routes.[45].(see Fig 1).
Due to the problems of finding a path in the routing problem, it is essential to review works of literature that examine a note on the NP-completeness property of QoS routing.
Note on the NP-completeness Property of QoS Routing
Studies reveal that finding a path can be subject to multiple constraints path (MCP), and QoS routing finding paths problems is NP-complete. Typically, this can be considered an integral part of QoS routing, and the additive measures can be proven to be NP-complete. There is a common belief in the research community that QoS routing can be intractable in nature. Although Kuipers and Mieghem argue that MCP may not be a big NP-complete problem, however, Vijayalakshmi and Radhakrishnan point out that with multimedia applications that involve video conferencing, e-learning, multi-person communication require the transmission of a message from one end to the other, and the mode of message transmission involve multicasting routing and finding a multicasting tree for cost optimisation is a problem of N-complete. [46][47][48]. ][75].
While unicast routing can involve finding a mini-cost path to a destination, finding a cost-effective path can be subject to constraint, and the constraint can be NP-complete if the number of constraints is one or more than one. Wang, Ergun and Xu2 point out that without path constraints, the path problem can be N-complete. However, with the problem of NP-complete, there is a need for efficient search space techniques, and to reduce the size of search space, there is a need to implement non-dominance paths, and among one of the algorithms employed. Kuipers and Mieghem propose SAMCRA algorithm for concept of non-dominance. [47][49].
With problems associated with QoS routing multiple constraints, which can give rise to N-complete, there is a need for routing strategies for finding optimum costs effective for QoS routing.
Routing strategies
Determine routing strategy is inherently complex due to traffic workloads. Adaptive traffic load may delay the effective flow of networks. Essential routing involves collecting the state of information and keeping the information up-to-date. Routing may also involve searching for an optimal routing path that can minimise routing constraints. Typically, searching feasible paths depends on methods of collecting information and information storage systems. [46][50]
The argument provided by some researchers show that multimedia application requires optimisation of cost, and routing strategies for cost minimisation involves finding rooting tree from a single source to multiple destinations. For example, finding a multicast routing tree involves cost minimisation and end-to-end delay. Typically, finding a routing path that can meet these two conditions is very hard. Some groups of researchers have proposed two routing strategies as heuristics and dynamic algorithms, which can produce the least-cost multicast tree, and these two algorithms have been studied to produce good results. [51]. Although, evidence has revealed that these algorithms can only provide a solution to routing problems in the small-sized network. However, Ma and Steenkiste argue that finding a routing path in the multiservice network that can guarantee QoS is very difficult because of the increased capacity to support internet telephony, video conferencing, and distance learning may involve multiple network sharing. Typically, many researchers have not yet covered inter-class routing sharing strategies. The author argues that an isolated routing approach and static link sharing policy, where the routing capacity depends on each traffic class. Careful interclass resources distribution with a dynamic sharing approach can achieve dynamic interclass traffic.[52].
However, the main tasks of QoS routing are to collect information and keep information up-to-date, and maintaining information is essential. Searching for a feasible path can be achieved using source routing, distributed routing, and hierarchical routing.
Source Routing
Routing strategies can be classified according to how the state information is maintained and how methods of finding feasible paths. Source routing maintains network topology where each node maintains the global state and all state information. Maintenance of routing is carried out by sending a control message to the selected path by linking intermediate nodes and successive nodes. Meanwhile, every state information is kept, and collectively searching for the feasible path is to maintain the image of the global network state. Source routing can achieve simplicity by guaranteeing loop-free, evaluating, upgrading, and transforming a distributed problem into a centralised state. In a dynamic source routing protocol, a node in a packet can transmit to another node, where the source node chooses the route with the shortest hop count. In the sourcing routing, the source node will include traversing nodes in the packet headers to the ad hoc network. Each route may discover multiple routes and initiate route discovery. [53][95]. Flich et al. argue that with an increase in searching for a cost-effective network station that can provide wiring flexibility, scalability, and increment expansion, source routing is noted to improve the performance of the irregular network for improvement of overall throughput.
However, source routing can have a setback of having excessive-high communication overhead for large-scale networks, and there can be QoS routing failure as a result of inaccuracy in the global state.
Distributed Routing
Distributed routing algorithms provides path computation among intermediary nodes between source and destination. In the distant vector-protocol form, distant vector at link-state protocol require algorithms of each node to base on routing decision. [54][55][56].
As being pointed out by Lee et al., distributed routing strategy has increased in recent years due to an increase in demand for transaction processing rates and the development of multiprocessors or locally distributed systems. Typically, the data-sharing approach in the network process and hybrid data sharing database systems have contributed to the increase in the demand for distributed sharing routing. [58][102].
The problem associated with distributed routing involves inconsistency in the global states of each node, which may lead to the occurrence of loops.
Hierarchical routing
Complex routing problems in a large network where the interconnection leads to congestion require simplified methods of reducing network sizes into a hierarchical network where each level of the network is responsible for its own routing. |83]. On the other hand, a hierarchical routing system is noted to consist of several distributed routing where each routing is responsible for each network. Typically, where there is network clustering, hierarchical routing techniques are commonly used in the wired network for scalability.[59][94].. Although, there can be problems with implementation. Meanwhile, the calculation for finding the shortest path require topology that can overload small loads in a large network, and a routing scheme to reduce the size of the network give rise to a general hierarchical routing scheme, which allows nodes to partake in distributed routing network with a mission to find an optimal path.[71][72][81].[82][84].
The typical problem of locating users in mobile networks is becoming significant, which may lead to network congestion. Pei and et al. point out that Hierarchical Routing Protocol can be used to attack these problems. [61][62].
Lauder, Kummerfeld, and Fekete illustrate hierarchical routing as a network of the machine where each machine is given a unique name to distinguish from another machine, and the approach is to assign a name in an organised manner, and the entire names of all in the networks are represented like tree-based [63]. To optimise network performances in a hierarchical routing system, there is a need for the arrangement of network routing systems into a hierarchy routing nodes that are distributed to minimise the processing cost.[64].
Nodes are clustered into groups, and nodes are further clustered to create a multi-level hierarchy that makes each node maintain an aggregate global state. Meanwhile, each node in a group contains aggregate information about other groups. To find the feasible path, nodes are sent to control messages to establish a connection. Scalability is the most practical advantage of hierarchical routing, where each node maintains global states of accurate routing computation. [53][65][66].
Summary
The paper reviews works of literature that examine QoS routing in the communication network and its algorithms. Evidence from the literature reviewed reveals that QoS routing protocol in network infrastructure supports wireless network communication, which supports real-time communication. QoS routing also supports wired communication with ATM, internet, and stand-alone on mobile networks. [67].
Typically, QoS routing can be proved to be very difficult since there can be changes in network conditions, and a more general approach to QoS routing is to find the shortest path. [45]. Works of literature also establish that QoS routing protocols can be classified according to the techniques they use to in enhancing the qualities of service. Routing protocol manages their destination network using the period route update process. Typically, a communication network can support the application of QoS, where several network mechanisms need to support QoS routing mechanisms. The topology that supports both unicast and multicast trees can optimise the allocation of resources, which can provide efficient QoS requirements. [68][69]. Evidence also reveals that multicasting routings establish multi trees shortest path, where each node in multicasting provides an efficient method in multimedia applications. Although, there may be challenges in implementing scalable Mobile Ad Hoc Network because of the difficulties in managing multicasting packets.[70]. In general, works of literature reveal that choosing a routing path can be complex due to congestion in the networks, and this can affect choosing QoS routing for end users. However, choosing QoS routing requires effective routing strategies and analysis of available paths in order to achieve an efficient allocation of resources and cost minimisation.
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