1、A Novel Cross-layer Quality-of-service Model For Mobile AD hoc Network Leichun Wang, Shihong Chen, Kun Xiao, Ruimin Hu National Engineering Resarch Center of Multimedia Software, WuhanUniversity Wuhan 430072, Hubei ,china Email: Abstract The divided-layer protocol architecture for Mobile ad hoc Netw
2、orks(simply MANETs)can only provide partial stack. This leads to treat difficulties in QoS guarantee of multimedia information transmission in MANETs, this paper proposes Across-layers QoS Model for MANETs, CQMM. In CQMM ,a core component was added network status repository(NSR), which was the cente
3、r of information exchange and share among different protocol layers in the stack. At the same time,CQMM carried out all kinds of unified QoS controls. It is advantageous that CQMM avoids redundancy functions among the different protocol layers in the stack and performs effective QoS controls and ove
4、rall improvements on the network performances. Keyword Cross-layers QoS Model, Mobile Ad hoc Networks(MANETs)；Network Status Repository(NSR) QoS Controls. 1 introduction With the rapid development of multimedia technologies and the great increase of he bandwidth for personal communication,video and
5、Video services begin to be deployed in MANETs. Different from static networks and Internet,multimedia communications in MANETs such as Voice and Video services require strict QoS guarantee, especially the delay guarantee. In addition, communication among different users can be integrated services wi
6、th different QoS requirements. These lead to great challenges in QoS guarantee of multimedia communication in MANETs. There are two main reasons in these: 1)MANETs runs in atypical wireless environment with time-varying and unreliable physical link, broadcast channel, and dynamic and limited bandwid
7、th and so forth. Therefore, it can only provide limited capability for differentiated services with strict QoS requirements 1.2) It is difficult that traditional flow project and access control mechanism are implemented because of mobility, multiple hops and self-organization of MANETs. At present,
8、most researches on QoS based on traditional divided-layer protocol architecture for MANETs focus on MAC protocol supporting QoS2,QoS routing protocol 3 and adaptive application layer protocol with QoS support4, and so on. It is avoidless that there will be some redundancies on functions among the di
9、fferent protocol layers in the stack. This will increase the complexity of QoS implementation and cause some difficulties in overall improvement on the network performances. Therefore, it is not suitable for MANETs with low processing ability In recent years, the cross-layers design based on the par
10、tial protocol layers in MANETs was put forward.1 proposed the mechanism with QoS guarantee for heterogeneous flow MAC layer.5,6,7,8 did some researches on implementing video communication with QoS guarantee by exchange and cooperation of information among a few layers in MANETs. These can improve Qo
11、S in MANETs communication to some extent. However, MANETs is much more complex than wired system and static network, and improvements on QoS guarantee depend on full cooperation among all layers in the protocol stack. Therefore, it is difficult for the design to provide efficient QoS guarantee for c
12、ommunication and overall improvements on the network performances in MANETs. To make good use of limited resources and optimize overall performances in MANETs, this paper proposes a novel cross-layer QoS model, CQMM, where different layers can exchange information fully and unified QoS managements a
13、nd controls can be performed. The rest of the paper is organized as follows. CQMM is described in section 2 in detail. In section 3,we analyze CQMM by the comparison with DQMM.The section 4 concludes the paper. 2. A CROSS-LAYER QOS MODEL FOR MANETS-CQMM 2.1 Architecture of CQMM In MANETs, present re
14、searches on QoS are mostly based on traditional divided-layer protocol architecture, where signals and algorithms supporting QsS are designed and implemented in different layers respectively, such as MAC protocol supporting QoS in data link layer 9, routing protocol with QoS support in network layer
15、10.11,and so forth. It can be summarized as A Divided-layer QoS Model for MANETs, DQMM (see fig.1). In DQMM, different layers in the protocol stack are designed and work independently； there are only static interfaces between different layers that are neighboring in logic； and each protocol layer ha
16、s some QoS controls such as error control in logic link layer, congestion control in network, etc. On the one hand, DQMM can simplify the design of MANETs greatly and gain the protocols with high reliability and extensibility. On the other one, DQMM also has some shortcomings: ) due to the independe
17、nt design among he different protocol layers, there are some redundancy functions among the different protocol layers in the stack, 2) it is difficult that information is exchanged among different layers that are not neighboring in logic, which leads to some problems in unified managements, QoS cont
18、rols and overall improvements on the network performances. Fig.1 Therefore, it is necessary that more attention are focused on the cooperation among physical Application Constraint Layer Status QoS controls (QoS requirements form Application layer) Transport Constraint Layer Status Network Constrain
19、t Layer Status Data Link Constraint Layer Status Physical Constraint Layer Status QoS controls (transport control and rate control) QoS controls （ queue and cache management, congestion control） QoS controls (error control and channel management) QoS controls (selection of media frequency and modula
20、tion) layer data link layer, network layer and higher when attempting to optimize performances of each of layer in MANETs. For this reason, we combine parameters dispersed in different layers and design a novel cross-layer QoS model, CQMM, to improve the QoS guarantee and the overall network perform
21、ances. The architecture of CQMM is provided in fig 2 Fig 2 From fig.2 ,it can be seen that CQMM keeps the core functions and relative independence of each protocol layer in the stack and allows direct information exchange between two neighboring layers in logics to maintain advantages of the modular
22、 architecture .On the basic of these , a core component is added in CQMM, Network Status Repository (simply NSR).NSR is the center, by which different layers can exchange and share information fully. On the one hand, each perotocol layer can read the status information of other protocol layers from
23、NSR to determine its functions and implementation mechanisms. On the other one , each protocol layer can write its status information to NSR that can be provided with other layers in the protocol stack. In CQMM, the protocol layers that are neighboring in logics can exchange information directly or
24、indirectly by NSR, and the protocol layers that are not neighboring in logics can exchange information using cross-layer ways via NSR. Therefore, information exchange is flexible in CQMM. All kinds of QoS controls in CQMM such as management and scheduling of network resources, network lifetime, erro
25、r control, and congestion control and performance optimization and so on, are not carried out independently. On the contrary, CQMM is in charge of the unified management and all QoS controls by the cooperation among different protocol layers in the stack. Each QoS control in MANETs is related to all
26、 layers in the protocol stack, and also constrained by all layers in the stack. The results of all QoS operations and managements are fed back to the different layers and written back to NSR, which will become the parameters of all kinds of QoS controls in MANETs. 2.2 protocol design in CQMM In CQMM
27、, the protocol designs aims at the full and free information exchange and cooperation among different protocol layers to avoid possible redundancy functions when maintaining the relative independence among different layers and the advantages of the modular architecture. Physical layer: Physical laye
28、r is responsible for modulation , transmission and receiving of data ,and also the key to the size, the cost and the energy consumption of each node in MANETs. In CQMM,the design of physical layer is to choose the transmission media, the frequency range and the modulation algorithm wit the low cost,
29、 power and complexity, big channel capability and so on, according to the cost of implementation, energy constraint, and capability and QoS requirements from high layer. Data link layer: The layer is low layer in the protocol stack and can be divided into two sub-layers: logic link sub-layer and MAC
30、 sub-layer. Compared with high layers, data link layer can sense network status in MANETs earlier such as the change of channel quality, the network congestion and so on. Therefore, on the one hand data link layer can perform the basic QoS controls such as error control and management of communication channel. On the other one, the layer can be combined with high layers to establish, choose and maintain the routing faster , prevent the congestion of the network earlier, and choose appropriate transport mechanisms and control strategies for transport layer.
