The Journal of Systems and Software 83 (2010) 1318–1326
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GLBM: A new QoS aware multicast scheme for wireless mesh networks Liang Zhao a,*, Ahmed Y. Al-Dubai a, Geyong Min b a b
School of Computing, Edinburgh Napier University, Edinburgh EH10 5DT, UK Department of Computing, University of Bradford, Bradford BD7 1DP, UK
a r t i c l e
i n f o
Article history: Received 14 September 2009 Received in revised form 20 January 2010 Accepted 21 January 2010 Available online 2 February 2010 Keywords: Multicast routing algorithms Wireless mesh network Gateway
a b s t r a c t Wireless mesh networks (WMNs) have been attracting significant attention due to their promising technology. The WMN technology is becoming a major avenue for the fourth generation of wireless mobility. Communication in large-scale wireless networks can create bottlenecks for scalable implementations of computationally intensive applications. A class of crucially important communication patterns that have already received considerable attention in this regard are group communication operations, since these inevitably place a high demand on network bandwidth and have a consequent impact on algorithm execution times. Multicast communication has been among the most primitive group capabilities of any message passing in networks. It is central to many important distributed applications in science and engineering and fundamental to the implementation of higher-level communication operations such as gossip, gather, and barrier synchronisation. Existing solutions offered for providing multicast communications in WMN have severe restriction in terms of almost all performance characteristics. Consequently, there is a need for the design and analysis of new efficient multicast communication schemes for this promising network technology. Hence, the aim of this study is to tackle the challenges posed by the continuously growing need for delivering efficient multicast communication over WMN. In particular, this study presents a new load balancing aware multicast algorithm with the aim of enhancing the QoS in the multicast communication over WMNs. Our simulations experiments show that our proposed multicast algorithm exhibits superior performance in terms of delay, jitter and throughput, compared to the most well known multicast algorithms. Ó 2010 Elsevier Inc. All rights reserved.
1. Introduction Recently, internet access has been used by more than a billion of people worldwide and the number of internet users has been increasing, especially in the developing countries (Attwood, 2007). In this context, new users plan to bypass traditional internet access providers, opening access to the net in a more direct and affordable way. As a new cost effective technology, the wireless mesh network (WMN) is a natural candidate for constructing a resilient, locally networked access to communication infrastructure. This is due to its desirable characteristics, including, but not limited to, multi-hop routing, auto-configuration, bandwidth fairness, low cost, easy deployment, self-healing and self-organized, etc. A WMN combines the fixed network (backbone) and mobile network (backhaul). In contrast to the traditional fixed network and Mobile Ad-hoc Network, WMN stands in the middle of them and combines wireless network with fixed characteristics. For each WMN, there are internet gateways, mesh routers and mesh clients. Every node in WMNs acts as a router, forwards the packet to other nodes. A node without access to the backbone network can require * Corresponding author. E-mail address:
[email protected] (L. Zhao). 0164-1212/$ - see front matter Ó 2010 Elsevier Inc. All rights reserved. doi:10.1016/j.jss.2010.01.044
connection by route packets from a neighbour node that has a backbone network connection. All the network capable devices can be used in WMNs. These devices include the traditional desktop PCs, laptop PCs and mobile devices such as mobile phones, and PDAs. In the last few years, the demand for group communication technology has significantly increased. More and more people prefer to watch football matches and TV drama from the internet rather than from traditional TV. As a technology of group communication, multicast aims to send information from the source sender to multiple receivers. For the same results, the source has to send the packet to multiple receivers for multiple transmissions using the unicast (one-to-one) approach. However, using multicast technology, the packet is copied in each link only once and the packet is copied in the replicator nodes. This can reduce the cost of communication compared to send unicast packets multiple times. In other words, multicast conserves bandwidth, reduces packet delay and network congestion. Thus, multicast is used by the service provider to deliver service to multiple subscribers. For example, it has been applied to online TV, video conference, distance learning and online multicast based games and the uses of multicast are manifold. As the increasing demand of these applications, the multicast technology becomes an even more important research topic in WMNs. Although, some research has already been studied for multicast in
L. Zhao et al. / The Journal of Systems and Software 83 (2010) 1318–1326
Mobile Ad-hoc Networks (Zeng et al., 2007; Yuan et al., 2007; Ruiz et al., 2006; Nguyen and Xu, 2007; Ke et al., 2007; Nguyen, 2008), these proposals cannot be used in WMN directly without modification as none of these research have considered the gateway involvement characteristic of WMN. The study of multicast for WMN is very limited. Ruiz et al. (2006) have studied efficient multicast routing in wireless mesh networks. Ruiz and Gomez-Skarmeta (2005) have also studied the problem of computing minimal cost multicast trees in multi-hop WMNs. Zeng et al. (2007) have proposed a Level Channel Assignment (LCA) algorithm and a Multi-Channel Multicast (MCM) algorithm to optimize throughput for multi-channel and multi-interface mesh networks. In Nguyen (2008), multicast routing between shortest path trees and minimum cost trees have been compared. However, none of the previous research covers the load balancing of multicast in WMNs. In Zeng et al. (2007), Yuan et al. (2007) and Ruiz et al. (2006), high-throughput and efficiency are the key issues they want to achieve. In WMNs, the client nodes connect to the internet via gateways. A gateway acts as a relay node in the multicast tree as well. The multicast traffic load of a gateway node can be extremely heavy during certain periods. This is due to the fact that when a gateway relays multicast messages, there are also unicast packets as background traffic. Thus, this can be resulted in disastrous consequences on the overall performance of the network. With controlling client-gateway registration, the load balancing can be improved dramatically. Although the gateway plays a key role in WMNs, the existing works on multicast communication in WMNs have not fully considered the gateways of WMNs (Zeng et al., 2007; Ruiz et al., 2006; Roy et al., 2006). Motivated by these observations, we proposed earlier in Zhao et al. (2009) a Gateway-cluster based Load Balancing Multicast algorithm (GLBM) to investigate the load balancing problem of multicast of WMNs. However, the performance of GLBM was not investigated thoroughly. Thus, in this extended paper, we investigate further the GLBM algorithm, considering additional issues such as gateway involvement, multicast source, multicast receiver and mesh client. Furthermore, GLBM is compared to ODMRP and MAODV to investigate the performance in all evaluation metrics. The multicast applications such as multicast conference and multicast TV require instant real time communication and large packet size. Due to these requirements, end-to-end delay and throughput are the priority performance metrics we concern. Our algorithm focuses on high throughput and low end-to-end delay multicast session through achieving load balancing. The rest of this paper is organized as follows. Section 2 depicts related work. In Section 3, we discuss the network architecture and technique requirements. Section 4 provides the description of the proposed algorithm. And Section 5 presents the simulation results of our algorithm; Section 6 concludes the paper with the indication of future research directions.
2. Related work Recently, there are many proposals of multicast for MANET such as MAODV (Royer and Perkins, 1999), ODMRP (Jun and Sichitiu, 2008), ADMR (Jetcheva and Johnson, 2001), CAMP (Garcia-LunaAceves and Madruga, 1999) and ADAM (Toh et al., 2000). Most of these routing algorithms are demand driven routing due to the mobility and power nature of MANET. MAODV has been proposed in Royer and Perkins (1999) and it is a typical on demand multicast algorithm. MAODV uses a shared bidirectional multicast tree and the group leader maintains the tree by sending group hello periodically. A RREQ request is broadcasted by a node which tends to join the multicast group or send multicast data to this group. Group members receive RREQ, response RREP to the source node to build
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the multicast tree. ODMRP is proposed by Gerla et al. Compared to MAODV, a mesh topology with a source node root is maintained by ODMRP. In mesh topology, the source node has multiple routing paths towards a single receiver. This mechanism allows fast repair of failure links. The gateway loading is not considered in the existing MANET multicast algorithm such as MAODV and ODMRP. In these algorithms, most multicast data flows are directly hopping between the sources and receivers. However, in WMN, a gateway handles all the traffic flows between mesh clients and internet. None of the existing MANET protocols works well in WMNs as they do not have the mechanism to route through the gateways. There are also a limited number of multicast proposals devised for WMN environments. For instance, Zeng et al. (2007), Ruiz et al. (2006) and Ke et al. (2007) have discussed the multicast algorithm in WMNs. A gateway discovery scheme is introduced by Jelger and Noel (2005) and it uses prefix continuity to attach nodes with a gateway that has the same prefix. On the basis of this scheme, Ruiz et al. (2006) have proposed a multicast routing algorithm for WMNs. It builds a Steiner tree and multicast data packet via the prefix continuity gateways. However, the prefix continuity scheme only works when the ISPs set the prefix for all the gateways and mobile network subscribers. A mesh client node without a prefix will not have the authority to register with the gateway. The authors have proposed two algorithms, namely, Level Channel Assignment algorithm (LCA) and Multi-channel Multicast algorithm (MCM) to improve the throughput of WMNs (Zeng et al., 2007). They have considered the multi-channel characteristic of WMN and have enabled every node acts with two network interfaces. In addition, the goal of the MCM is to minimize the number of relay nodes and hop numbers in the multicast tree. In the multicast session, one interface is used to receive packets (RI) and another one is used to send packets (SI). Therefore, RI works with the upper level data flow and SI to transmit the replicated packets to the down level nodes. This mechanism can reduce the interference and improve the multicast throughput. However, this paper does not mention how the channel assignment algorithms work with the gateways. In Rong et al. (2008), authors have proposed a novel network graph pre-processing approach to enable traffic engineering and enhance the performance of QoS multicast routing algorithms. A prioritized admission control scheme and a utility-constrained optimal priority gain policy employ are employed to control the bandwidth usage of different connections in a multicast session. Then, Zhao et al. (2007) have proposed Probabilistically Reliable Multicast Routing (PRMR) which is a multicast routing algorithm based on link quality based metric (Link Cost). Furthermore, Han and Guo (2009) have studied the problem of collision-free multicast in multi-interface multi-channel wireless mesh networks, and present two heuristic-based algorithms with the aim of reducing both the interface redundancy and the multicast latency. In fact, the above works have not clearly considered the importance of either the key role of gateway in WMN or load balancing during the communication phase in multicast for WMNs. In an attempt to address this issue, we propose here a multicast algorithm, in which gateways maintain the traffic loading every time a mesh node made a registration request. The gateways are also responsible for recording and forwarding all the multicast information. This mechanism makes the multicast more efficient in WMNs and also enhances the load balancing and Quality of Service (QoS) awareness of the network.
3. Network architecture and requirements WMN is a particular type of mobile ad hoc network (MANET) (Sichitiu, 2005). However, the existing multicast routing protocols
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L. Zhao et al. / The Journal of Systems and Software 83 (2010) 1318–1326 Table 1 Notation used in our analysis. Internet Wired Link
IGW
MR
Wireless Link
MR MR MR
MR
Layer 2 MR
Description
LBi
the traffic load of node i the average load of the network
LB
Layer 1 IGW
Notation
MR
IGW Internet Gateway MR
LBðNÞ LBt@before j i LB(G)before LB(M)before
MR MC MR Mesh Router
LBG-hop LBM-hop
MC
MC
Layer 3
MC Mesh Client
LBG-load MC
Fig. 1. The architecture of a typical WMN.
do not satisfy all the requirements of WMN. In this section, we describe the requirements and technical issues in detail. According to Akyildiz et al. (2005), there are three types of WMN, which are Infrastructure/backbone WMN, Client WMN, and Hybrid WMN. An Infrastructure/backbone WMN is constructed with 802.11 radio devices where some devices also have ability to connect to the backbone and others connect to these by one-hop distance, e.g. the Cloud Wi-Fi in Europe. Compared to Infrastructure WMN, a Client WMN is as same as MANET. In this paper, we refer WMN as Hybrid WMN. A Hybrid WMN combines both Infrastructure/backbone WMN and Client WMN, and consists of mesh clients and gateways. Mesh clients connect to gateway by either single hop or multi-hop as in Client WMNs. In another hand, these mesh clients connect to a backbone network via gateways and gateways relay the messages from internet to the mesh clients. Compared to MANET, most of the traffic is expected to flow between the mesh clients and the backbone network via gateways (Jun and Sichitiu, 2008). Furthermore, in MANET, all the nodes are assumed as mobile nodes moving in the network. Compared to MANET, most of nodes are stationary in a WMN. Only a limited number of nodes such as mobile phone and other portable devices are mobile. There are three layers in a typical wireless mesh network: Internet Gateway Layer (IGW Layer), Mesh Router Layer (MR Layer) and Mesh Client Layer (MC Layer) Akyildiz et al. (2005) as depicted in Fig. 1. To simplify the description of the routing algorithms, we combine the IGW Layer and MR Layer as gateway node in this paper. Both gateway nodes and mesh router nodes are routing devices to connect the mesh clients to the internet. For the load balancing of a typical WMN, mesh routers maintain traffic load of mesh client clusters and a gateway maintains the load of all the traffic from/to mesh routers to/from internet. In this paper, a gateway node works as the administrator of accessing backbone internet. It takes care of all the traffics in WMN and maintains the optimal load balancing. WMN is also known as Wireless Community Network (WCN) which is used to connect home networks together in the neighbourhood. For instance, when there is a sufficient cooperation among neighbours to forward packets for each other, they do not need to individually install an internet ‘‘tap” (gateway) but instead can share faster, cost-effective internet access via gateways that are distributed in their neighbourhood. Packets dynamically find a route, hopping from one neighbour to another to reach the internet through one of these gateways. Another advantage is that neighbours can cooperatively deploy backup technology and never have to worry about losing information due to a catastrophic disk failure. The third advantage is that this technology allows bits created locally to be used locally without
LBM-load o n h l v
the average load of a group of node N after multicast is started the total load of node t before multicast starts the number of nodes are involved in the packet transmissions the number of nodes in the network the total load of a network before multicast is started the total load of all the multicast nodes before multicast is started the average load of network after the multicast (if multicast best hop count algorithm is used) is started the average load of multicast tree after the multicast (if multicast best hop count algorithm is used) is started the average load of network after the multicast tree (if multicast best load count algorithm is used) is built the average load of multicast tree after the multicast (if multicast best load count algorithm is used) is started the load caused on each tree node by multicast packet transmission the total number of nodes in network the number of total nodes on the multicast tree for best hop count multicast the number of total nodes on the multicast tree for best load count multicast the number of multicast packet transmission in a node
having to go through a service provider and the internet. In addition, neighbourhood community networks allow faster and easier dissemination of cached information that is relevant to the local community. Moreover, these networks typically have low maintenance overhead, high data rates, and are not energy constrained. As described in Manoj and Rao (2006) and Tao et al. (2005), a load balancing network is defined as a network with no uneven traffic in any nodes. The unbalanced network can have problems such as high packet delay, and high packet loss. Therefore, a load balanced network can provide a better QoS constrains, such as jitter, delay, packet loss are all improved. In the rest of this section, we present the problem of load balancing multicast as a weighted directed graph. According to the definition, a typical WMN is a network with mesh nodes and these nodes connect to each other by wireless links. A WMN is presented as G = (V, E), where V denotes a set of nodes in the network and E is a set of links between each pair of nodes. The multicast routing is from one single source node to multiple receiver nodes. Then, let M = {m0, m1, m2, . . . , mn1} be a set of multicast receivers in a network where m0 denotes the source node, m0 e M. We present the following three definitions for load balancing and multicast communication. Our algorithm is designed in line with these definitions. Table 1 lists notations used in the proof of Definitions 1, 2, 3, Lemma 1, 2 and Theorem 1. Definition 1. The load balancing in a network G = (V, E) is achieved, if and only if, LBi ! LBði 2 VÞ. Definition 2. Given a WMN network, G = (V, E), the total load of a P network G is: LBðGÞ ¼ i2V LBi and the total load of a multicast P group M is: LBðMÞ ¼ i2M LBi . Definition 3. Given a multicast session M = {m0, m1, m2, . . . , mn1} in a network, G = (V, E), if the multicast session is load balancing, we have:
LBðMÞ ! LBðGÞ; where based on Definition 1 and 2, each node has traffic load which approximate to the average traffic load of the network. In a load bal-
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ancing network, the average load of multicast session, LBðMÞ therefore approaches to the average load of the whole network, LBðGÞ.
declare that the best load count multicast achieves better load balancing according to Definition 3. h
Lemma 1. Given a network G = (V, E), we compare the hop number of two kinds of multicasts so that we can have h < l.
4. Proposed solution
Proof. The best hop count multicast finds the shortest path which is path with lowest hop number. Therefore, the total hop number of the best hop count multicast is less than that of the other multicast. h Lemma 2. Given a network G = (V, E), where a multicast algorithm is running, the average network load is given by
Algorithm: Gateway-cluster based Load Balancing Multicast algorithm
LBðNÞbefore þ @ j LBðNÞ ¼ i Proof. The load of a node t caused by multicast is: LBt ¼ LBt@before þ @ v while the total number of the packet transmission of all nodes in a network is:
j ¼ v 0 þ v 1 þ þ v i1 The total load of i nodes before multicast is started:
LBðNÞbefore ¼ LB0@before þ LB1@before þ þ LBi1@before And the total load of a network after multicast is started is:
LBðNÞ ¼ LB0 þ LB1 þ þ LBi1 Finally we have: i1 LBðNÞ ¼ LBðNÞ ¼ LB0 þLB1 þþLB i i LB0@before þ @ v 0 þ LB1@before þ @ v 1 þ þ LBi1@before þ @ v i1 ¼ i LB0@before þ LB1@before þ þ LBi1@before þ @ v 0 þ @ v 1 þ þ @ v i1 ¼ i LB0@before þ LB1@before þ þ LBi1@before þ @ ðv 0 þ v 1 þ þ v i1 Þ ¼ i LBðNÞbefore þ @ j ¼ i
h Theorem 1. To perform multicast communication in a given network G = (V, E), the best load count multicast algorithm outperforms the best hop count algorithm in terms of load balancing. Proof.
LBðGÞbefore þ @ h n LBðGÞbefore þ @ l LBG-load ¼ n LBðMÞbefore þ @ h LBM-hop ¼ h LBðMÞbefore þ @ l LBM-load ¼ l LBG-hop ¼
ð1Þ ð2Þ ð3Þ ð4Þ
We have the load difference for the best hop count multicast is (3) – (1) and the load difference for the multicast best load count algorithm is (4)–(2) by Definition 3. Then, we check whether the load difference for best load count algorithm is smaller than the load difference for the multicast best hop count algorithm and we have:
ð4Þ ð2Þ ðð3Þ ð1ÞÞ ¼
In Zhao et al. (2009), we proposed a new multicast algorithm, namely, Gateway-cluster based Load Balancing Multicast algorithm (GLBM). The load capture mechanism is implemented in each node to get the load status along each edge on the multicast tree. As mentioned in Section 3, the main challenge of this algorithm is to achieve QoS multicast by avoiding uneven traffic load.
LBðMÞbefore ðh lÞ @ ðh lÞ
