[ieee 2012 international conference on computer & information science (iccis) - kuala lumpur,...

2012 International Conference on Computer & Information Science (ICCIS)

A Comparative Survey of Multicast Routing

Protocol in MANETs

Abdulmalek AI-hemyari, Kasmiran Jumari, Mahamod Ismail, Sabri Saeed Faculty of Engineering & Built Environment

Universiti Kebangsaan Malaysia 43600 Bangi, Selangor, Malaysia

Alhmyari [email protected], [email protected], [email protected], [email protected]

Ahstract- The need for Mobil Ad-Hoc Network (MANET) in environments where there is a lack of communication infrastructure is so important. In some cases, existing infrastructure cannot work well to transfer the data between members, so MANET must be designed as a solution. MANETs are constructed by an independent group of mobile nodes that relate to each other without any base station or fixed infrastructure. Implementing multicast routing protocols to MANETs leads to improve the consumption of bandwidth, reducing the cost of communication in the network and improving the efficiency of communication links. MANETs have several mechanisms under several routing topologies. In this paper, we provide an overview of the most exiting multicast routing mechanisms especially in routing based on mesh and tree topology. In mobility environments the initialization and maintenance the multicast structure (tree or mesh) represents the main target of multicast routing protocols that lead to decrease the packet loss. The aim of this paper is to help the researchers in MANETs to develop the proper multicast routing protocols for their own environments.

Keywords: MANET, Multicast Routing Protocols, Mesh, Tree

I. INTRODUCTION

Mobile Ad Hoc Networks (MANETs) or Mobile multi-hop ad hoc networks are defined as the category of wireless information dynamically using their mobile devices, video con feren cing, civilian operations, e-education, classroom meetings and emergency search-and-rescue [I].

Multicast routing protocols play an important role in MANET to provide this communication. In MANETs environment where the bandwidth is the primary concerned, it is suitable to use multicast rather than multiple unicast. Multicasting is a technique to transmit the data packets to groups of users by single IP Address as a destination. Multicast protocol that used in wired network does not proceed well in MANETs because of its topology structure. There are two types of multicast routing protocol structure in MANETs include mesh and tree. Multicast tree structure always needs re-building in network topology because of the nodes dynamic nature, and it requires high control traffic in it maintaining routing mechanism. MAODV (Multicast AdHoc On-Demand Distance Vector Routing Protocol) [2] represent one of the most important protocols in this type of structure. Moreover, the second type of this protocol structure is a multicast mesh structure. It represents the most significant type of multicast protocols that connect between

978-1-4673-1938-6/12/$31.00 ©20 12 IEEE

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networks that utilize multi-hop radio relaying and are capable of operating without the support of any fixed infrastructure. Comparing to cellular networks, the absence of base station and central coordinator makes the routing in MANETs is the most challenging. Therefore, the resource management and routing done in a distributed method in which the communication between the node will coordinate by all nodes. Transmission of control and data packets are fulfilled by one hope if the position of target node is covered by source node transmission range, or by rebroadcasting through middle nodes if there is outside of source node covered area. However, the node must be more intelligent because it has additional tasks. Beside the network host function, it will work as a router for routing packets between nodes. MANETs have several characteristics like quick, dynamic topology, economically, easily by adding and removing devices and the ability to work anywhere where is no network infrastructure, that make many applications in several areas can be completed. Some of these applications where setting up and maintaining the infrastructure communication may be costly or difficult include, military battlefield, disaster recovery, conventions where users share

source and receiver pair with more than one exist path. It uses the periodic flooding mechanism to construct the paths. The most famous protocol in this area is ODMRP (OnDemand Multicast Routing Protocol) [3].

The rest of this paper organizes as: section IT, describes the parameters that be covered when implementing a multicast routing protocol in MANETs. Section TIT, covers the related work of classification of multicast routing protocols. Section IV, discusses tree mechanism and MAODV protocol as an

example of this mechanism. Section V, describes the mesh mechanism and ODMRP protocol as an example of this mechanism. Finally, in section VI the paper will be summarized.

IT. PARAMETERS OF MULTICAST ROUTING PROTOCOL

There are many properties and constraints must be considered when implementing and designing the multicast routing protocols in MANETs such as the limitation of available bandwidth, dynamic topology that make network structure changes frequently and unpredictably, limited


energy, arbitrarily moving of nodes, instability of multicasting paths and drawback of security and scalability [1] [4] [5] [6]. Therefore, a practical designing of multicast routing protocols should be treat some issues like reliability, robustness, efficiency, control overhead, scalability, quality of service (QoS), battery power control, dependency on the unicast routing protocol and security as discussed below:

Reliability: Tn some applications like real time and military applications it's not permitted to lose any data packets and it must all data packets to receives completely from the destinations, so multicast routing protocol should be guaranty this characteristic.

Robustness: Tn MANETs data packets that sent by sources may be dropped or lost by some reasons like the breakage of link, that will be present when the nodes moving away from the coverage area. As we can see, a low of packet delivery ratio (PDR) will be the result. Therefore, a multicast routing protocol must be robust enough to achieve high PDR in environments that have high mobility of nodes.

Scalability: It represents the ability of the multicast routing protocol to manage and control increasing of nodes like sources, destinations and intermediate node in the network. As we can see, the increasing of nodes in multicast session will produce more control packet in the network, so the multicast routing protocol must try to reduce the control packets.

Efficiency: The efficiency of multicast routing protocols is defined as the ratio of total number of all data packets that arrive to the destinations to the total number of data packets and control packets that transmitted in the network. The efficiency of multicast routing protocols in MANETs is a very significant issue especially in the networks where the bandwidth is scarce.

Battery power control: Tn MANETs, each mobile node has its own limited battery power, which determines the lifetime of node to still in connecting with others. The periodic messages in network will affect of the node lifetime so multicast routing protocol must have a good algorithm to improve the power capacity consumption.

Control overhead: MANETs faces many challenges for

managing available bandwidth. Whereas, needing of exchange control packets to save tracking of multicast group members will consumes an enormous amount of that bandwidth. Therefore, the designing of multicast routing protocols should keep simple to maintain low channel overhead by reducing the total number of control packets.

Security: Many multicast routing protocol not interest in security issues, although its represent one of the most important issues in communication between networks. Multicast routing protocol should be able to protect the multicast sessions from intruders or from any other illegal operations.

Quality of service: The guarantee of QoS in MANETs is very difficult comparing to other networks type because its available bandwidth is shared among nodes and the network structure will be changed as nodes moving away from network. "QoS multicast routing means that it selects routes with sufficient resources for the requested QoS parameters"

[4]. Multicast routing protocol should be provided by mechanism to control and management the total traffic that can flow in the network and achieve a globally efficient in resource utilization.

Dependency on the unicast routing protocol: Tn the real world, there are many networks with different operating system and protocols. These networks are called heterogeneous network and sometimes multicast routing protocol needs to work with. Therefore, it is more important for the multicast routing protocol to design as independent of any unicast routing protocol.

TTT. TAXONOMY OF MULTICAST ROUTING PROTOCOLS (RELATED WORK)

There are several exiting classifications of multicast routing protocols over MANETs. Murthy et al [1] and Sarkar et al [4] classifY the multicast routing protocols according to the dependency of the applications into application-independent multicast protocols and application-dependent multicast protocols. Application-dependent multicast protocols used for special applications, which designed for it. Tn the other

hand, most multicast routing protocol represents application-independent multicast protocols and its can classified to different dimensions as based on architecture, based on initialization of the multicast session and based on topology maintenance mechanism [1] [4]. Based on architecture the multicast routing protocols can be classified based on a topology architecture into two categories as tree based and mesh based. We will discuss these two categories in details later. Moreover, there is another way to classifY the multicast routing protocols based on the initialization of the multicast session, it is source-initiated multicast routing protocol which the source will initiate the multicast session such as ODMRP and receiver-initiated multicast routing protocol which receiver will initiate the multicast session like MAODV. Finally based on topology maintenance mechanism, according to flooding the control packets, topology maintenance mechanism can classifY the multicast routing protocol into the soft state approach and hard state approach. Soft state need to update the route periodically by flooding control packets at fixed time intervals so this leads to a high packet delivery ratio and increasing the control overhead. While in a hard state, the control packet needed when the link was broken, so it decreased the control overhead but will be producing low packet delivery ratio.

Cordeiro and Agrawal [7] classifY the multicast routing protocol into four type depending how to creating the route into the members of the group as tree approaches, mesh approaches, stateless approaches and hybrid approaches. Stateless multicast routing protocol use mechanism to

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reduce the overhead because there is no required the routing information to be maintained at forwarding nodes at all. Stateless approach concentrates on small group multicast like Differential Destination Multicast protocol (DDM) [8]. Hybrid approach combining the best characteristics of both tree and mesh approach to achieve better performance like An Optimized Polymorphic Hybrid Multicast Routing Protocol for MANET (OPHMR) [9].

The multicast routing protocol also classified based on topology and services within this topology by Rajashekhar and Sunilkumar [1], including tree, mesh, zone, hybrid, hierarchical and link stability topologies. Moreover, they concentrate to the services that provide by these mechanisms as reliability, bandwidth, delay and bandwidthdelay.

Therefore and according to previous studies, this paper gives the overview of ideal multicast routing protocols with popular classification depending on topology structure such as tree-topology and mesh-topology.

TV. TREE-BASED MECHANISM

Wired networks and infrastructure mobile networks are used tree-based mechanism to establish tree link between their groups and group members. The idea of tree-based mechanism has extended by different researchers to support multicasting in MANETs. Multicast trees in this mechanism built with a root of tree that represents a source node and

branches of tree that represent the tree link between group members to destinations. Therefore, one path will be provided between any pair of nodes from the multicast tree. The major drawback in unique path is link failure that will lead to the rebuilding of the entire tree topology. Tree-based mechanism classified into two types according to the number of trees per multicast group as a source-based tree and share-based tree. Tn each multicast group, source-based tree is established and maintained for each source node like Ad Hoc Multicast Routing (AMRoute) [11]. Whereas sharebased tree is established and maintained a single shared tree for all multicast nodes as Multicast Ad hoc On-Demand Distance Vector protocol (MAODV) [2]. The scalability of share-based tree is higher comparing to the source-based tree because when the number of sources increases it will be affected in performance of source-based tree in memory requirement and bandwidth consumption. However, tree

based mechanism guaranty high-multicast efficiency and low overhead. Tn addition, it has an efficient bandwidth because the minimum number of copies per packet needed to send along the tree branches. Tn the high mobility environment it has low packet delivery ratio because link failure so the entire tree structure will be reconfigured. MAODV protocol will discuss in details in the next section as an example of this mechanism.

Multicast Ad hoc On-Demand Distance Vector protocol

(MAODV):

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MAODV [2] [12] is an extended version of Ad hoc OnDemand Distance Vector (AODV) [13] Protocol that's adds

multicast capability to AODV using broadcast route discovery mechanism. It uses share-based tree mechanism to initialization and maintenance share tree route in the network multicast group. Any nodes need to join the group or want to send data packet, it unicasts a route request (RREQ) to the leader of the group if it has the address of the leader. Group leader represents the first node that joins the multicast group. It is responsible for initialization and updating the sequence number of multicast groups. So, if the node does not have any information of the group leader address, it broadcasts the RREQ packet. Nodes that are not members in the multicast tree rebroadcast packet and establish the reverse path in their route table. Node that receives the RREQ packet updates its route information in its routing table by saving source sequence number and its next hop information. The multicast group member that keeps a sequence number greater than that in RREQ packet, unicast route reply (RREP) packet to the requesting node. The current multicast group sequence number and the distance between group leader and replying node included in the RREP. Requested node often receives more than one RREP replay so it saves the most fresh and the shortest route from all the routes replay it receives and unicasts a multicast activation (MACT) message to the next hope at selected route to enable this route. MACT guaranty that, there is no more than one path to any tree node in the multicast tree. Figure 1 shows the MAODV mechanism as

discussed previously when node 2 (N2) needs to join multicast tree.

R

o

o Multicast Group member

§ Multicast Tree Node

o Non-participating Node

---I�� MACT control packet - - - - � RREQ control packet - .. ---. RREP control packet

o

Figur.1 Node-joining mechanism to the multicast tree in MAODY.


One of the important goals of the multicast protocol in MANET is to decrease the control overhead. MAODV provides this characteristic by a combination of unicast and multicast into a single framework. Thus, information that can get it during discovery the unicast path can be used in discovering the multicast path. On the other hand, mobility and congestion environment that uses shared-based tree mechanism causes drawback in packet delivery along link in the multicast tree. Therefore, this mechanism has two major drawbacks; it is not effective when the numbers of multicast group members are increased and it is not robustness because it has single-point failure when the group leader is failing.

V. MESH-BASED MECHANISM

Tn mobility environment with high number of mobile nodes, tree-based mechanism may not perform will because the structure of tree-based multicast protocols are weak and every short period need to be reconfigured as the connectivity changes. Mesh-based is a technique in the MANET that overcomes the constraints in tree-based mechanism. It provides multiple paths between source and destination for maintaining connectivity between the members of the multicast group. When the main route is broken due to mobility of nodes the other routes are presently and instantly available to guarantee continuity of communication between group members. Thus, the control overhead will reduce and the structure of the network no needs to reconfigure. Mesh-based is robustness to the

mobility environment than tree-based, this leads to increase delivery of multicast packet to all destination nodes even if the link fail. There are some protocols work within this structure, such as On-Demand Multicast Routing Protocol (ODMRP) [3] and Core-Assisted Mesh Protocol (CAMP) [14].

The major drawback in mesh mechanism is broadcasting multiple copy of the same control packet in the same coverage area will consumes more bandwidth from the available bandwidth. Moreover, increasing group members that deliver a large number of packets will lead to increased probability of collisions. Therefore, under high node mobility conditions, the control overhead will increase and packet delivery will decrease.

To illustrate this mechanism, ODMRP will discuss In

details in the next sections.

On-Demand Multicast Routing Protocol (ODMRP):

ODMRP is on demand protocol that has mesh-based structure. The main designing goal for on-demand protocols in a MANET to reduce the high loading in multicast routes, which affect the performance through the consumption of bandwidth. ODMRP is a very important protocol in MANET with high efficiency and more effective. It creates a multicast mesh topology and applies the concept of forwarding group that define by Lee et al [3] [15] as "only a

subset of nodes forwards the multicast packets via scoped flooding". Clearly, responsibility of forwarding group is

forwarding data packets between source-destination pair and keeps copies of source id and sequence number in its messages cash to detect the duplicate for any data packets or control packets. The forwarding group concept illustrates in figure 2.

Forwarding Group

o Multicast Members Node

@ Forwarding Group Nodes

Figure.2. The Forwarding Group Concept.

ODMRP uses it source-on-demand technique to initialize

and maintenance the multicast paths and group membership. It consists of two phases, request phase and replay phase like in unicast routing protocol as shown in figure 3.

----I�� Join Request

- - - - - ..... Join Table

Figure.3. On-Demand procedures for membership setup and maintenance

in ODMRP.

When any source nodes in multicast group want to send packets of data, but it does not have any information about the paths to the membership of the multicast group. It periodically and regularly broadcasts a Join Query packet to the network to update the paths and membership information. Mobile nodes that receive the Join Query packet scans its packet header based on source id and

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sequence number, as we explained before to guaranty no message duplicated. Tf not duplicate and TTL still not equal zero the routing table will update and the processes continue until reach to the target.

When the multicast receiver receives the Join Query, it updates the entries of the source in its member table. After that, it generates a Join Replay packet and rebroadcast it to all neighbor nodes. When the mobile node receives a Join Replay packet and the entries matches of its own TD contains the TD of the next mobile node, it represents part of forwarding group and thus become on the route to the multicast source. The Join Reply still rebroadcasted by the membership of forwarding group through the shortest route until reaching to the source. The previous process builds the paths between the source and receivers and constructs mesh topology of the mobile node as shown in figure 4.

Multicast Receiver

o Mobile Node

---- . �

Control Message

Figure.4. Creating a Mesh mechanism in ODMRP.

Explicitly in ODMRP, any mobile node wants to join or leave the multicast group; it does not need any control

packets. So, the multicast source stops broadcasting the Join Query packet, if it wants to leave the multicast group. Also, the receiver deals aren't transmitting any Join Replay packet, if it does not need to receive from the specific multicast group. This approach in ODMRP called soft state.

The efficiency of ODMRP can be affected by the values of timer like period of route refresh and the timeout period of forwarding group. So to choose the best value of this parameter in the timer, it must be adaptively to the network environment, such as degree of mobility, traffic load, capacity of channel, etc. For example, if the traffic load is heavy in the network, forwarding group timeout period

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adjusted as small value to prevent the excessive redundancy by the non-forwarding nodes. Tn the high mobility environment, larger value should be used to offer many of the routes.

ODMRP has some advantages that make it one of the most important multicast routing protocols in MANET. It is independent for any unicast routing protocol so it does not need any specific detached unicast protocol. Therefore, it can work with any unicast routing protocol in any network topology. Tn addition, although the performance of this protocol reduces the reliability of the group and packet delivery ratio in environments with high mobility of nodes and increasing of traffic load, ODMRP still has better performance than tree-based protocol like MAODV.

VI. SUMMARY

The review of mechanisms for multicast routing in this paper tries to illustrate the wide range of multicast routing in MANETs. So, it attempts to detect the design and the main principles behind the implementation of the routing mechanisms. There are many of the characteristics and limitations that must be considered when designing and implementing multicast routing protocols in MANETs including mobility, available bandwidth, instability of multicasting paths, dynamic topology that makes network structure changes frequently and unpredictably, limited energy and limitations related to security and scalability.

Therefore, multicast routing protocols researchers should treat some issues like reliability, robustness, efficiency, control overhead, scalability, QoS, battery power control, dependency on the unicast routing protocol and security. Moreover, this paper gives an overview of ideal multicast routing protocols with popular classifications depending on topology structure such as tree-topology like MAODV and mesh-topology like ODMRP.

ACKNOWLEDGMENT

This research has been conducted in the computer &

network security laboratory Universiti Kebangsaan Malaysia (UKM) , The authors would like to thank the university for sponsoring this research through Research University Grant -UKM-OUP-20 12-179.

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