Paper Title: A Quantitative Survey of Mobile Ad hoc Multicast Routing Protocols

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International Journal of Emerging Technology and Advanced Engineering

Website: www.ijetae.com (ISSN 2250-2459, ISO 9001:2008 Certified Journal, Volume 3, Issue 1, January 2013)

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Paper Title: A Quantitative Survey of Mobile Ad hoc Multicast

Routing Protocols

First Author

1

, Second Author

2

, Third Author

3

1

Lecturer,

3

Associate Professor, Department Of Computer Applications, Lovely Professional University

2

Project Officer, Division Of Lovely InfoTech, Lovely Professional University

Abstract - A mobile ad hoc network is a set of mobile nodes which constructs the network dynamically without any centralized coordinators and without any existing infrastructure. In wired networks changes in network topology are not feasible which led to the invention of wireless ad hoc network. Here in ad hoc network mobile nodes establish wireless connections among themselves without any central coordinator. The connections made among them can be direct connections if the communicating nodes are within the range of each other, otherwise multihop connections are used where each node will have to forward the packet until the destination node has been reached which led to the invention of different routing protocols for both unicast and multicast communication. In this paper we are going to present the comparative analysis of different routing protocols available.

Keywords - Communication, AODV, CBT, DVMRP, CAMP, Multicast, Manet, ODMRP, SBT

I. INTRODUCTION

In ad hoc network portable devices establish communications without any central infrastructure. While moving mobile nodes which are without central infrastructure, raises various problems like security, routing and link break etc. There are different multicast routing protocols available which are summed up in Fig 1, these protocols further fall into two types table driven and on demand (reactive) protocols. Table driven protocols will maintain tables based on the routing information available and on demand protocols cannot prepare any table in advance but react according to the situation.

The use of wireless networks has become more and more familiar these days. A Mobile Ad-hoc Wireless Network (MANET) which is also known as collection of various autonomous mobile nodes and other nodes that can communicate with each other by forming a multi-hop

network, and by maintaining connectivity in a

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II. RELATED WORK

A quantitative analysis and comparison of protocol performance is not provided in this paper. Each protocol performs differently when coupled with different MAC and physical layer technologies. Consequently, an analysis and comparison of protocol performance is only valid within the context of a single implementation, and different protocols may be optimal for different implementations. Furthermore, few quantitative performance comparisons have been reported in the literature, and the ones that have been reported are far from comprehensive.[16]

III. MOTIVATION AND CONTRIBUTION

Although there are so many existing surveys available on ad hoc mulicast routing protocols and each of them basically deals with the same technical trend [4] and are not up-to-date in one way or the other. There are many research papers that we have referenced to carry out this research and we came to know how to compare all the protocols based upon some research examples. But firstly we are going to provide the taxonomy of the protocols available which will help us to analyze the difference among all that are already existing and also tells us about the parameters where they are lacking.

IV.

C

ATEGORIES

O

F

M

ULTICAST

R

OUTING

P

ROTOCOLS

There are three basic categories of multicast methods

[4]:

1.Flooding: A basic method is to simply flood the network. Every node receiving a message floods it to a list of neighbors. Flooding a network acts like a chain reaction that can result in exponential growth. 2.The proactive approach pre-computes paths to all

possible destinations and stores this information in the routing table. To maintain an up-todate database, routing information is periodically distributed through the network.

3.The final method is to create paths to other nodes on demand. The idea is based on a query response mechanism or reactive multicast. In the query phase, a node explores the environment.

A.

Source Based Multicast Tree (SBT)

Here we establish a multicast tree and the purpose is to maintain the tree for each multicast source node in every group [16]. For example, in an environment consisting of „m‟ multicast groups which further consists of „n‟ multicast source nodes, it results in (m*n) multicast trees.

The advantage of this scheme is each multicast packet is forwarded along the most efficient path from the source node.

Distance Vector Multicast routing protocol (DVMRP)

DVMRP [3] is an interior gateway protocol that is completely based upon Routing Information Protocol (RIP) which is used to support connectionless multicast data transmission to a group of hosts over a network. DVMRP uses tunnels which can multicast transmission within unicast packets and which are again reassembled into multicast data when they will arrive at their destination.

DVMRP uses the Internet Group Management Protocol (IGMP) to exchange routing datagram [6].

DVMRP datagram is composed of two portions:

a. An IGMP Header

b.A stream of tagged data

Following depicts the IGMP header for DVMRP messages:

IGMP Header for DVMRP Messages

Version Type SubType Checksum

In this header, the components are as follows:

a. The ‘version’ of the DVMRP messages is 1.

b.The „type‟ for the DVMRP messages in 2.

c. The subtype is one of the following:

Response: In which the DVMRP message provides routes to some destination [7].

Request: In which the DVMRP message requests routes to some destination.

Non-membership report: In which the DVMRP message provides non-membership report.

d.The „checksum’ of the DVMRP header is the 16-bit one's complement of the one's complement sum of the entire message, excluding the IP header [7]. For computing the checksum, the checksum field is zeroed.

Protocol Overview

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[image:3.612.66.271.237.451.2]

Fig 2a: will depict how the packets flooded and how the leaf nodes are identified based on the concept that which node is not participating in that particular multicast group and is also falling under the concept of leaf nodes. Then as shown in Fig 2c, all the leaf nodes are “pruned off” which means they are not participating in this group for multicasting. Similarly this process continues to be carried off recursively.

Fig 2: Broadcast and Prune Method in DVMRP

In this protocol, firstly the multicast packets will be flooded in the network. Then upon receiving this multicast flooded traffic the leaf nodes are identified. The leaf nodes are those nodes which have no further links available and which are not interested in multicast grouping. These leaf nodes will send an uplink to the intermediate node available. Then the intermediate node will mark that link to be Pruned-off which reveals that no further multicasting will be made available on these links and these links will be considered as discarded.

Analysis and Discussion

As we know that SBT scheme suffers from scalability problems because a lot of overhead is incurred in establishing and maintaining several multicast trees as the number of groups and source nodes increases. Also some prior knowledge is required for topology information as in mobile and ad hoc networks frequent changes may occur in the topology also. Moreover we have also analyzed that DVMRP do not try actively to repair broken links. DVMRP is more passive when a link breakage occurs.

B.

Core Based Tree

This approach is more feasible than SBT [16] described above. Here we are going to maintain only a single shared tree which can be used to connect all the multicast group members together. The only need of this approach is to select the „Core‟ node which will act and that‟s why it is named as core based tree and for this we need a core selection algorithm which will help to select that which node will act as core node of the tree.

Ad hoc On Demand Distance Vector Routing Protocol AODV [3] is suitable for both unicast and multicast routing. This protocol on on-demand reactive protocol which is based on the concept of destination sequence number in DSDV. Sequence numbers are basically used to check the staleness and freshness of the routes.

The Ad hoc On Demand Distance Vector (AODV) routing algorithm is a routing protocol designed for ad hoc mobile networks [4]. It is an on demand algorithm, meaning that it builds routes between nodes only as desired by source nodes. It maintains these routes as long as they are needed by the sources. Additionally, AODV forms trees which connect multicast group members. The trees are composed of the group members and the nodes needed to connect the members.

We will assign one sequence number to each and every route that is coming. The route with the latest sequence number is the fresh one then route having previous sequence number.

According to our Literature survey, AODV protocol shows the overall best performance among other protocols based on the following factors:

a. Packet Delivery Fraction or Throughput: According to experiments made in literature AODV shows to have the best overall performance. On-demand protocol like AODV [2] drops a considerable number of packets during the route discovery phase, as route acquisition takes time proportional to the distance between the source and destination.

b. End-to-end Delay: the end to end delay factor

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Protocol Overview

AODV [4] uses RREQ and RREP messages as it used this concept in unicast routing also and now same is used in multicast also. We use the sequence number concept for every route in unicast routing but in multicast routing, a node is selected to generate and update the multicast group sequence number and this node will be termed as “multicast group leader”.

Based upon this group leader a tree will be generated per multicast group and each group has a group sequence number which is incremented and broadcasted periodically throughout the network by the group leader. The leader will start requesting a route to particular group and thereafter a multicast tree will be built dynamically.[15]

Now if a node wants to join a particular multicast group then firstly it will have to broadcast a join request packet with a destination address of that particular multicast group. And once a request packet is reaches on tree node a reply message will be sent back to the joining node through the backward route.

It can also be possible that the joining node may get reply packets from the multiple groups then it will select the best reply packet based on the metric and this process will continue until a route is formed.

CBT [3] is a more scalable approach than SBT but still there is one disadvantage that in this approach traffic is concentrated on the shared links which results in higher frequency of congestion at the shared links specifically. To overcome these limitations we need to employ some extra mechanisms which led to the increase in the overhead.

One more thing to notice is that DVMRP do not try actively to repair broken links like AODV.

AODV does not perform well in networks with few nodes and little mobility. In networks with more load, more nodes and higher mobility AODV outperformed DSR, at the expense of generating more routing load on the network.

C.

Multicast Mesh

In the previous two approaches we are building trees for multicast delivery structure. But in mobile ad hoc network the rate of link changes so frequently that frequent tree reconfiguration is not feasible which results in the development of a new structure which is totally mesh based.

As in a mesh each node in it can have more than one parent. Multiple paths exists and they can be used if a primary path is broken. The protocol which is using this structure is CAMP which is discussed below.

CAMP (Core Assisted Mesh Protocol)

[image:4.612.350.535.234.352.2]

This protocol works on the structure of multicast mesh where it can create a multicast mesh for each multicast group. A multicast mesh can be established by having both the sender and receiver nodes join the multicast group. Fig 2.1 will discuss the difference between Multicast mesh and Tee protocols available:

Fig 2.1: Difference Between Multicast Mesh and Tree

CAMP basically extends the basic receiver-initiated approach which was initially introduced in the core-based tree (CBT) protocol [10] for the creation of multicast trees to enable the creation of multicast meshes. Basically the Cores are used to limit the control traffic which was needed by receivers so that they can join multicast groups. In contrast to CBT, one or multiple cores can be defined for each mesh, cores need not be part of the mesh of their group, and routers can join a group even if all associated cores become unreachable [10].

Besides the unicast routing table, CAMP relies on the following data structures:

CAM: It is the mapping of table cores to multicast groups.

CORES (g): It is the set of routers acting as cores to multicast group (g).

CACHE (i): It is the cache of multicast data packet control information (i)..

MRT (i): It is the multicast routing table, containing the set of groups known to router (i).

AT (i): It is the table containing anchor information pertaining to router (i).

Protocol Overview [5]

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In the worst case if the core node is not reachable then a ring mechanism will be followed.

Similarly if a node wants to leave the group it can simply broadcast a quit notification packet.

CAMP [9] is a Multicast Mesh protocol which follows a table driven approach. It is a proactive protocol but is far less in use as compared to AODV. Since AODV is on demand reactive protocol and reactive protocols are better in performance then proactive as in case of reactive there is ability to find out the mechanism that they can react dynamically. As there is no need of static approach in this case. Moreover AODV is better In terms of communication overhead in these protocols.

D.

Group Based Forwarding

In this method a group of nodes is maintained instead of the links that constitutes the tree or mesh. This simplifies the processing required at each node. This group of nodes will act as forwarding nodes for each multicast group. The example of the protocol that uses this approach is ODMRP (On Demand Multicast Routing Protocol)

ODMRP (On Demand Multicast Routing Protocol)

ODMRP is an on-demand mesh based multicast Routing protocol, besides it is a multicast routing protocol, ODMRP protocol can make use of unicast technique to send multicast data packet form the sender nodes toward the receivers in the multicast group. The source, in ODMRP, establishes and maintains group membership.

Protocol Overview

If a source wishes to send packet to a multicast group but it has no route available to that group, then it simply broadcasts JOIN [4] control packet to all the nodes in the entire network. When an intermediate node receives the JOIN packet it stores its source address and its sequence number in its cache memory to detect whether it is a duplicate member or not. Then it performs necessary routing table updates for reverse path back to the source.

After this a multicast receiver constructs a JOINTABLE upon getting JOIN packet and broadcasts it to its neighbors. When a node receives a JOINTABLE, it resolves whether it is on the way to the source by consulting earlier cached data. Considering the matched entry this node builds new join table and broadcasts it.

[image:5.612.363.539.211.338.2]

In this way JOINTABLE is buit with the help of forwarding group members and ultimately it reaches to the multicast source. A multicast table is built on each node to carry multicast data. This process either constructs or revises the routes from sources to receivers and forms a mesh. Fig 3. Will depict join data propagation,

Fig 3: Join Data Propagation

[image:5.612.402.521.451.576.2]

As depicted in the Fig 4, this protocol initiates its work by detecting that whether the packets from Source node are coming through shortest path or not. If the packets are not coming from the shortest path then „R1‟ will send a “Push join” message through the shortest path that is available and to request to put that path into the mesh also. After receiving these push join messages at the source node the node will come to know about the path available.

Fig 4: R1 Detected packets not coming from shortest path

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Fig 5: Shortest Path is included in the Mesh

Here there is need to maintain group of nodes instead of the links that constitutes the tree or mesh. This simplifies the processing at each node.

It also uses on demand reactive scheme which is far better that table driven proactive scheme in terms of performance. It stores the information in the form of one set per multicast group which is better from DVMRP which stores the information of each and every node and each and every stage.

Basically the comparison between all the multicast routing protocols is completely dependent on the following factors:

a) Characteristics of the routing protocol

b) Overhead incurred in each and every protocol

c) Communication Performance

d) Multicast Operations

V. COMPARISON BASED UPON CHARACTERISTICS OF

MULTICAST ROUTING PROTOCOLS

If we will talk about delivery structure of the protocols then DVMRP is the only protocol which is using SBT approach whereas AODV is CBT based protocol, CAMP uses mesh based structure and ODMRP uses group based structure.

In the next comparison, AODV and CAMP are the only two protocols that are using core nodes as the use of core nodes introduces robustness problems when the core node is not available. Moreover these two are the only ones which are using the concept of centralized nodes. In terms of unicast routing protocol, all protocols except CAMP provide their own mechanism. All these comparisons are summed up in the Table 1 given below:

Table 1:

Comparison of Characteristics of Protocols

VI. COMPARISON BASED UPON PERFORMANCE AND

OPERATIONS OF MULTICAST ROUTING PROTOCOLS

The very first comparison basically deals with the session initiation which tells us about the procedure executed by the source node so as to enable it to transmit multicast packets.

VII. COMPARISON BASED UPON OVERHEAD IN

MULTICAST ROUTING PROTOCOLS

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Whereas AODV and CAMP keep track of all the links in the shared tree and mesh respectively, but ODMRP is good because a single forwarding flag needs to be maintained in this case. In terms of communication overhead, DVMRP [8] is still very poor because lot of bandwidth is wasted is flooding multicast data during its operation. ODMRP also uses the same approach of periodic flooding. All these comparisons are summed up in the Table 3 given below:

A.Application of different Protocols

Criteria For Evaluation Of Protocols

There are different kinds of ad hoc routing protocols which are suitable for several different kinds of network structures. When there is need for evaluating protocols one needs some appropriate classification for the performance metrics. The various features [6] of ad hoc networks are discussed below:

Setting Time Of Network: This feature tells about the time by which the source submits its first query up to the time it gets the first response.

Time required to join the network: This feature tells us about the time when a single node or a group of nodes enter into the network and gets integrated with the network.

Departing time (Nodes): This feature tells us about the time when a single node or a group of nodes leaves the network.

Time to recover: This feature tells us about the time when a particular network needs a recovery.

Updation Frequency: How many data packets send in a particular time will tell us about the frequency.

Scalability: This feature tells us about the extent to which the network can scale by extending the number of nodes.

According to RFC [6] quantitative metrics for performance of multicast routing protocols are as follows:

Time required to acquire a route: It depicts the amount of time the network needs to acquire a particular route.

Efficiency of a network: It is the measure which tells us about the performance of the protocol that how effectively the protocol works.

B.Evaluation based on Architecture

Most the multicast routing protocols assumes flat network architecture where the mobile nodes are homogeneous in nature which is not really possible as each and every node has its own mobility factors having different roles and capability. Usually Manets have a hierarchical architecture which is the result of different mobile nodes at each hierarchy. [11]

A practical example for this will be Hierarchical Quality of service Multicast Routing Protocol which is used to build a multicast structure at each hierarchy.

Another example for this will be Self Organizing Map which also follows the same approach.

Location based protocols may use Global Positioning system (GPS).

C.Evaluation Based upon Quality of Service (QoS)

QoS basically deals with the sending of data from source to destination by keeping in mind the factors related to bandwidth and delay. But we cannot deny this fact that QoS is very difficult to achieve in Manet because of the bandwidth available to adjacent nodes and also due to the topology change which is very frequent in Mobile Ad hoc environment. But still there is one protocol which will pass this evaluation criteria also. For Example: Multicast Core Extraction Distributed Ad-hoc Routing (MCEDAR) [9] is an example for QoS-based multicast routing protocols for MANETs.

D.Evaluation based on Energy efficiency

Energy efficiency is the biggest constraint in the Mobile Ad hoc Multicast Routing Protocols. Since all the nodes in this network make a temporary network and these nodes are powered by batteries and will be stop working when the battery life exhausted. So there is a great need to develop energy efficient protocols. Researches have shown that there are protocols available which are energy efficient and they are:

Minimum Weight Incremental Arborescence (MWIA) [8], RB-MIDP and D-MIDP [9] are examples for energy-efficient multicast routing.

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1.The very first factor is based upon user parameters and its configurations, such as the average multicast degree, the control overhead, the average delay, the throughput and the multicast service cost [5].

2.The second way is to compare different multicast routing update methods. Multicast routing update can be done in the following three ways:

(a) Store and update the information: store the information in a routing table and update it by listening to routing messages.

(b) Delete all the information and refresh it: here we can delete all the stale routes.

(c) Simulation support: We can evaluate the performance of multicast routing protocols with the help of various simulation tools such as NS-2, Opnet, Matlab, CASSAP and SPW [11, 12].

3.With the increase in the popularity of MANET

protocols and being considering the dynamic network features of MANETs, criteria for evaluating performance of MANETs multicast routing protocols should be proposed to meet the different mobile application requirements in different environments

[13-15].

VIII. CONCLUSION AND FUTURE WORK

As it has been stated above there are number of protocols available for multicasting in mobile and ad hoc networks and all of them are different from each other in one way or the other. [9] Besides gaining the performance reliability still there are many factors which needs to be included to get the best performance of these protocols. Based upon the comparative analysis of the protocols discussed above it has been concluded that on-demand (reactive) protocols are far better that table-driven (proactive) protocols in the taxonomy of different routing protocols available in manet. On-demand routing generates source when it is required and this route will become available until the process for destination is going on, when it comes to completion the route will automatically lost.

Based upon the analysis we have discovered that there are many security risks which can be applicable to these protocols. We will take AODV as an example and we will try to improve the performance of each and every protocol one by one. [5]

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