Wireless Mesh Networks For Broadband Internet Access Computer Science Essay

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ABSTRACT

The next generation wireless networks experienced a great development with emergence of wireless mesh networks (WMNs), a wireless technology that is conceptually similar to mobile ad hoc networks with capability of self-configuration and self-healing. With great potentials in wireless mesh networks, this type of wireless networks can be seen as a feasible solution to provide ubiquitous wireless broadband access and be used in many applications.

Wireless mesh networks technology has drawn significant attention as a promising broadband access technology despite the explosive growth in the number of internet accesses technologies. In this thesis the performance issues of wireless mesh networks such as throughput capacity will be studied and analysed. The effect of increasing number of nodes and network load on throughput capacity of wireless mesh networks with a fixed number of gateways will be investigated and throughput capacity improvement with increasing number of gateways will be investigated and analysed.

The load balancing among the internet gateway nodes in wireless mesh networks will be necessary for efficient utilisation of the network capacity. The effect of load balancing in wireless mesh networks will be studied and analysed in this thesis. The throughput capacity of wireless mesh networks will not be analysed without considering the flows unfairness behaviour in multihop networks. The unfairness behaviour of the flows in wireless mesh networks will be investigated and method to improve end-to-end fairness of the traffic flows will be proposed.

AIMS AND OBJECTIVES

The main aim of this research is use OPNET to study and analyse the performance of wireless mesh networks for broadband internet access as promising wireless architecture for the next generation wireless technology.

OBJECTIVES

-To investigate and analyse the end-to-end throughput unfairness behaviour of flows in multihop wireless networks based on the position of the source in the network relative to the gateway position and propose method to improve end-to-end fairness of the traffic flows.

-To investigate and analyse the capacity of wireless mesh networks as a function of number nodes and traffic loads in a wireless mesh network with a fixed number of getaways.

- To investigate and analyse the effect of increasing numbers of gateways in wireless mesh networks capacity.

- To investigate and analyse the effect of load balancing on the capacity of wireless mesh networks deployed to provide broadband internet access.

CHANGES IN THE PROPOSED THESIS OBJECTIVES

In the submitted proposal, to compare and evaluate the performance of some routing protocols proposed to be use in wireless mesh networks was among the thesis objectives. This is now removed and replaced with another objective, investigation and addressing unfairness problem of traffic flows in wireless mesh network as this is very important when analyzing the performance of wireless mesh networks for broadband access.

INTRODUCTION

Wireless mesh networking (WMN) is an alternative option of scaling wireless network, is a type of ad hoc network that form mesh of wirelessly interconnected nodes and. It defers from ad hoc network in the nature of packets movement in the network which is mostly from the clients to the gateway of vice versa, while the packets movement in ad hoc network is between pair of the network nodes. [NOMINAL] In wireless mesh networks the host nodes can also act as routers (typically stationary) to forward the clients packets in a multi-hop fashion to the destination which is normally gateway connected to the internet when the network is deployed to provide internet access. Wireless mesh networks offer advantages over other wireless networks; these include easy deployment, greater reliability, self-configuration, self-healing, and scalability.

Without needs of costly infrastructures broadband wireless access can be provided to very large areas using wireless mesh networks. Wireless mesh networks can be employed for wide variety of applications such as cellular radio access networks or WLAN hotspot multi-hopping, Wireless sensor networks (WSNs), broadband home and office indoor networking, intelligent transport system networks, community and neighbour networking, micro base station backhaul, citywide surveillance systems and many others [SECURITY AND 0521]

While the wireless mesh networks aims to offer broadband internet connectivity to enterprise and community users, the issues that limit the network capacity and improve the must be addressed to exploit the optimum network performance. The capacity of the wireless mesh network is affected by many factors such as network architecture, node mobility, node density, traffic pattern, number of channels used, and transmission range. A clear understanding of the effect of these factors on capacity of the wireless mesh networks provides insight to protocol design, architecture design, and deployment of the network.

Gateway nodes are provided in wireless mesh networks to connect the network to the internet. As many clients in the network generate traffic to the gateway if the number of nodes increases with a fixed number of gateways then the overall throughput of the network goes down. The more the number of gateway nodes used the higher the overall network throughput. [NOTE] Thus, the capacity of the network increases with increasing the number of the gateways provided load balancing procedure is employed to share the network load among the gateway nodes in the network. Load balancing across gateway nodes is obtained by distributing the traffic generated by the network to the backhaul network through all gateway nodes in the networks.

The wireless mesh network throughput capacity can be also increased when the issue of unfairness behaviour of the traffic flows in the network is addressed. The fair sharing of network bandwidth can be achieved by giving the flows from distance source crossing many network hops over the flows from hops close to the gateway.

2.0 WIRELESS NETWORKS OVERVIEW

Wireless LAN networking structure can be broadly categorised into two distinct groups namely infrastuctureless also called peer- to-peer e.g. wireless Ad- hoc networks and infrastructure wireless networks e.g. cellular networks. Usually the infrastructure wireless LAN networks requires a single-hop wireless link to reach a base station terminal from a mobile node, while peer-to-peer wireless network normally involves a multi-hop wireless path from source to destination LOCATION although it can also use a single-hop. Infrastructure wireless network environment uses access points to which all the traffic pass through, while in wireless network without infrastructure (peer to peer) involves direct communication between the nodes in the network.

DRAWING THESIS ACHIEVING PAIRNESS

Multi-hop wireless networks use multi-hop wireless relying for its communication. It can be further classified into major categories: wireless Ad-hoc networks, wireless mesh networks, wireless sensor networks and hybrid wireless networks.

Wireless mesh networks which is our interest in the multi-hop wireless networks is an ad-hoc networks in which most of the nodes are fixed ARCHIT and most of the traffic in wireless mesh network is either forward towards the gateway node provided for internet connection or from the gateway nodes. Meshing may simply be thought of as multi-hopping with active route diversity. To use metaphors, a multi-hop network may be thought of as nodes within a tree and branch structure, whereas a mesh is more like nodes within a spider's web. 052157680

dRAWING ARCHIT

Wireless mesh network (WMN) is an alternative option of scaling wireless network. It provides means of extending the sharing range of existing wireless networks with improved channel capacity. So we can define wireless mesh network as a series of peer-to-peer communication between the network nodes where each node functions as a router and repeater. Although wireless mesh networks can be based upon a variety of technologies, their practical commercial evolution is primarily occurring through the use of wireless LAN communications. GILBERT

The wireless mesh networks can be considered as the special type of Ad hoc wireless networks, so the deployment of wireless mesh networks will not be complicated since essentials components to be used in the network is before now in existing in wireless Ad hoc networks (e.g in the form of ad hoc network routing protocols, IEEE 802.11 MAC protocol, wired equivalent privacy (WEP) security, et). [1]

2.2 MEDIA ACCESS CONTROL (MAC) PROTOCOL

The design of MAC layer protocol assumes significance in wireless mesh networks (WMN) because the achievable capacity depends heavily on the performance of MAC protocol. [MESH] The MAC protocol in wireless mesh networks should be designed with main objective of providing the maximum network throughput capacity and scalability while providing required quality of service (QoS) performances. The major issues related to MAC protocol design in wireless mesh networks include controlling the sharing range of the wireless medium and increasing spatial reuse, exploiting availability of multiple channels, hidden and exposed terminal.

2.2.1 THE IEEE 802.11

Wireless mesh networks is implemented using existing wireless networking technologies such as IEEE 802.11, IEEE 802.15, IEEE 802.16, and IEEE 802.20. The IEEE 802.11 defined set of standards for WLAN and many aspects of wireless networking which covers the physical and data link layers. One such aspect is mesh networking, which is currently under development by the IEEE 802.11 Task Group. This task group called IEEE 802.11s has been formed recently to standardize the ESS for mesh networking. It defines architecture and protocols based on IEEE 802.11 MAC to create an 802.11-based Wireless Distribution System (WDS). This WDS supports the broadcast, multicast, and unicast delivery using radio-aware metrics over self-configuring multi-hop topologies. [SURVEY]

2.2.1 THE IEEE 802.11 ARCHITECTURE

To my knowledge, IEEE 802.11 is the most popular WLAN standard. It defines the specifications for the physical and MAC layer and has been adopted by many vendors of WLAN products. The MAC layer defined by IEEE 802.11 is also divided into the point coordination function (PCF) and distributed coordination function (DCF). The 802.11 distributed coordination function (DCF) is the most common MAC protocol used in wireless mesh networks. [NOTE]

2.2.3 DISTRIBUTED COORDINATION FUNCTION (DCF)

The distributed coordination function (DCF) MAC protocol provides access to the channel using carrier sense multiple access (CSMA) protocol with collision avoidance (CA). The CSMA with CA is used in wireless networks since the collision cannot be detected because of some issues due to the nature of wireless networks e.g. Hidden and exposed problems.

In the DCF, the basic access scheme is by using CSMA which is also called Physical Carrier Sensing. In this scheme the status (idle or busy) of the medium is first checked before a station with data ready for transmission begins to transmit. This is to ensure no any other station is using the medium at the time.

If the medium is observed by the station ready for transmission to be busy, the station defers the transmission until the end of the ongoing transmission. When the medium busy period ends the station can start to transmit if the medium is detected to be free for a period of distributed interframe period (DIFS) interval. This waiting for a DIFS interval prevent more than one station from accessing the medium after the previous transmission. The station initialises a counter called backoff timer by selecting a random interval called backoff interval for scheduling its transmission attempt, the backoff timer is decremented for as long as the medium is sensed idle. The backoff timer is stopped when transmission is detected on the medium after which it continued. The station transmits when the backoff period reaches zero. To determine the successful transmission the CSMA/CA protocol employs the use of positive acknowledgement in which the receiver returns the acknowledgement to indicate the valid reception. The transmitter will wait for acknowledgement, if it is not received then it will assumed that the collision occurred and arrange retransmission.

DIFS

CW

SISF

DATA

DIFS

Source

Destination

Other

Defer access

Backoff after defer

ACKK

Defer access

Source

DATA

SIFS

DIFS

RTS

Other

Backoff after defer

DIFS

CW

SIFS

Destination

ACK

SIFS

NAV (RTS)

NAV (CTS)

CTS

Virtual carrier access scheme is employed in IEEE 802.11 to extend the basic access mechanism to avoid the problem caused by hidden and exposed terminal in wireless networks. This virtual carrier access scheme uses short control packets called request to send (RTS) and clear to send (CTS) handshake.

In the virtual carrier access mechanism when the station is granted access to the channel it first sends RTS packet to receiver stating the duration of intended transmission prior to the beginning of data transmission. CTS packets will be broadcast by the receiver if it is ready to receive data. CTS packets also include the duration of intended transmission prior. All other systems within the range of the transmitter of receiver see this information and remain silent for the specified period and store the information by setting the Network Allocation Vector (NAV) in each station. The medium is reserved for the specified duration of transmission by this exchange of the control information.

The Station now begins to transmit the data frames and receiver returns acknowledgement (ACK) to indicate valid reception. The system is also called 4-way handshake and is partially slotted with RTS, CTS, & ACK specific slots as shown in the Fig [] below.

ROUTING IN WIRELESS MESH NEWORKS (WMNs)

Routing in a network is a means of finding a source to destination path to forward message through the network. Communication within a network or internetworks can be achieved using a routing protocol. Due to the unpredictable nature of wireless networks surroundings, the routing protocols must to be quick in adapting to the change in a path when there is path break due to mobility of the nodes. The main routing concern in wireless mesh networks is finding a reliable and high throughput path to the destination.

Wireless mesh networks are multi-hop networks with some characteristics common to ad hoc networks, this makes protocols designed for ad hoc networks to also work in wireless mesh networks. The Current deployments of WMNs make use of routing protocols proposed for ad hoc networks such as AODV, DSR, and OLSR. The ad hoc routing protocols can be broadly classified into three categories as shown in the table below. [NOTE]

Proactive or table-driven routing protocols, reactive or

on-demand routing protocols, and hybrid routing protocols

Proactive or table-driven routing, in this routing approach every node exchanges its routing information with other nodes in the network periodically and maintains a routing table, which contains routing information to reach every node in the network. While reactive or on-demand routing approach, a node requests routing information and maintains the path information only when it needs to communicate with another node.

The Ad hoc On-Demand Distance Vector (AODV) routing protocol [1] is an on demand (reactive) distance vector routing protocol in which the routing operation is done using hop-by-hop routing. The traditional routing table is used by AODV in maintaining routing information at each node, where there is only one entry in the table for each destination. Using AODV routing protocol a destination can be easily obtained by the nodes, and maintained only needed routes or the routes in used. As a reactive routing protocol routes are only set on demand. The use of destination sequence number is employed in AODV routing protocol to ensure up-to-date loop free routes, and the highest sequence number is selected by the sending node requesting the path when there is more than one path to a destination. [1]

The AODV routing protocol reduced the routing control overhead by not allowing the nodes that are not parts of any path in used to maintain any routing information or participate in any periodic information exchange. But this results in a higher route acquisition latency, which will also lead to a higher initial packet delay because all data packets are buffered before a path is acquired or set up. [BROADBAND]

The AODV uses a simple route discovery process to set up a new route using a two-way message exchange, request and reply messages. In the absence of communication route to a new destination in the source node's routing table, the source node begins the route discovery in order to set up a route with a destination. The route discovery starts by broadcasting a route request (RREQ) message by a sender to its neighbours, the neighbours further broadcast the RREQ message received to their own neighbours and the broadcast continues till it arrives at the destination.

Upon receiving the route request (RREQ) message the destination reply by sending a route reply (RREP) message. This message used the route taken by the route request (RREQ) message and is unicast to the source node. The RREP sets up the path by updating the routing table at the intermediate nodes with information regarding the path it has traversed. The source node can start transmitting its first packet after receiving the RREP.

Each node needs to periodically transmit a locally (one-hop) broadcast message, called HELLO message in order to maintain routes and neighbourhood information. The routing table of a node is updated with information associated with its neighbour when it receives a HELLO message from the given neighbour. It marks the route to the neighbour as broken in the event of failure to receive a consecutive number of HELLO messages. In case of any link breakage, the node upstream to the broken link checks whether any active route had used this link. If not, nothing will be done. Otherwise, the upstream node may attempt a local repair. It sends out a RREQ to establish a new second half of the path to the destination. The node performing the local repair buffers the data packets while waiting for any RREP in response to its RREQ. Where the local repair fails or has not been attempted, the upstream nodes involved will be alerted by AODV and use lost link to cancel the link. [BROADBAND][]ADHOC

WIRELESS MESH NETWORKS (WMNs) THROUGHPUT CAPACITY

In a network either wired or wireless we can define throughput as the number of bits that can be transmitted over the network in a certain period of time. It is the measure of how fast we can successfully send traffic in the network. But the system capacity can be the measure of the amount of traffic it can handle; this can also be equivalent to the system maximum throughput.

While the wireless mesh networks aims to offer broadband connectivity to enterprise and community users, in a wireless network using single channel the increase in the number of nodes in the network tend to degrade the network. Thus, the capacity of the network depends on the number of nodes in the network or the network diameter because of the increase in interference with increasing the network diameter.

The capacity of wireless multihop networks decrease as a function of number of nodes in the network is shown by [GUPTA]. They showed that the throughput capacity of the nodes reduces significantly when node density increases. The maximum achievable throughput of randomly placed n identical nodes each with a capacity of W bits/second is_( W √nâˆ-log(n)) bits/second. This result is true for the ad hoc type of networks which is peer-to -peer and data flows between hop pairs in the network. [NOMINAL].In wireless mesh networks the capacity of the networks degrades and the node capacity of each node drops to O( 1n) due to the presence of hot spots introduced by the gateways in the network which act as bottlenecks to the network performance. The throughput capacity of the network can be increased by increasing the number of gateways in the networks and balancing the traffic loads across the gateways.[NOMINAL]

The capacity of the network can be improved by reducing interference this can be using non overlapping channels on the nodes within the same transmission range. The presence of multi-channel and multi-radio in the network can significantly increase the network capacity. In which more than multiple radio is assigned to the network nodes with each radio interface assigned one of the available non overlapping channels. So if the number of radios equal to the number of orthogonal channel, the network capacity can be increased by n-fold where n is the number of orthogonal channels available. The recent development of high speed physical layer technique can also improve the wireless mesh networks capacity. These techniques include: OFDM, MIMO, UWB and using smart antenna.

FAIRNESS ISSUES IN WIRELESS MESH NETWORKS

Allocation of network resources equally between the traffic flows from the network nodes in a network is refers to as fairness. Throughput fairness in a network can be achieved when all the nodes in the network with same traffic load acquire equal network recourses.

In wireless mesh networks unfairness in sharing network bandwidth between the nodes in the network is an essential issue that must be consider when discussing the performance of wireless mesh networks. Wireless mesh networks implementing IEEE 802.11 standards use distributed coordinate function (DCF) MAC protocol as a medium access protocol. In wireless networks since the collision cannot be detected the MAC protocol uses CSMA/CA to avoid collision. But employing MAC protocol using CSMA/CA to resolve contention in the medium results in throughput unfairness between the traffic flows in the networks particularly when the network is heavily loaded. [MESH] This problem of poor throughput and unfairness mostly occur in multi hop wireless networks, because original the MAC protocol standard is based on the on-hop communications in infrastructured network.

In wireless mesh networks the unfairness problem can be either local which happens among the nodes within interference range or end to end unfairness occurred over multi-hop flows. The communication in wireless mesh networks designed for broadband access mostly is between the routers and the gateways in the networks. A router in a multihop wireless network performs the job of forwarding its clients generated traffic and relaying other routers traffic depend on its position relative to the position of the gateway in the network. The traffic flow from a source passing through multiple routers to the gateway receives low throughput compared to the flow from the router close to the gateway. This is because of the medium contention when using MAC protocol which result in increasing the inter arrival rates of the packets passing through large number of nodes to the destination. The packets forwarded on a longer path are more likely to be dropped and TCP congestion control mechanism. [NOTE]

LOAD BALANCING IN WMNs

Wireless mesh networks deployed to provide broadband internet access use gateway nodes in order to connect all network nodes to internet and capacity of the network improve with multiple gateways in the network. In providing internet connection through the gateway nodes, the gateway nodes may turn out to be a bottleneck due to inadequate wireless link capacity since the generated traffic of the networks nodes aggregate at the gateways if not load balancing scheme is employed. The load balancing scheme must be employed for efficient utilisation of the network capacity. Load imbalance will be created if there is unequal loading among the gateway nodes in the network, which leads to congestion, packet loss and results in degradation in network performance. Hence, load balancing across gateway nodes in WMNs improves bandwidth utilization and also increases network throughput since the available gateways nodes in the network will be utilized for optimum performance.

Another issue is the centre loading problem, since most of the routing protocols used in wireless mesh networks such as AODV and DSR use hop count as routing metric there shortest path routing leads to unbalanced loading where some nodes will experienced high traffic particularly the nodes located close to the network centre. The path from the source to the gateway node though the centre nodes are most often the shortest path than peripheral nodes further away. [NOTE] So to achieve optimum throughput and network scalability the use of load balancing scheme is important in wireless mesh networks.

Load balancing across gateway nodes is achieved by distributing the network generated traffic to the backbone network through all the available gateway nodes in the WMNs. The load balancing across multiple gateway nodes can be measured quantitatively by a metric called Index of Load Balance (ILB) [MESH FROM ] which is calculated as follows.

Load index (LI) of a gateway i is defined as

Where βk(i) is the fraction of node k's traffic that is sent through gateway i, Tk is the total traffic generated by node k, and C(i) is the capacity of the backhaul link connected to the gateway node i. The LI value ranges from 0 to 1, with 1 representing 100 percent loaded gateway. The ILB of the network is calculated as

Therefore a perfectly balanced network has ILB equal to zero and a highly imbalanced network has ILB equal to one. The objective of all load balancing techniques is to obtain ILB values as small as possible. [MESH]

LITERATURE INFLUENCING THE WORK

The wireless mesh networks field is now receiving a lot of researchers' attention and practical interest in various academia, companies and research laboratories. My work is influenced by numerous research contributions in the field of wireless mesh networks.

An overview of the whole wireless mesh networks architecture is provided in [1], they presented a comprehensive literature in wireless mesh networks ranging from the architecture of the mesh to the issues that need to be addressed by the researchers in the field. The paper highlights the applications of wireless mesh networks, the network theoretical capacity and the issues related to the protocols to be used in the network design. They described the wireless mesh networks as the network with dynamic structure which is capable to be self organised, self configured and self healed, these features make the network benefits from easy deployment and easy maintenance.

The analytical capacity of wireless ad hoc networks is studied in [GUPTA]. The paper provides the upper and lower bounds of the capacity of wireless ad hoc networks. They randomly spread wireless nodes scaled at some distance with each node communicating using a common wireless channel. They were able to show that the throughput capacity of the wireless ad hoc networks depends on the number of wireless nodes in the network and there is considerable reduction in the throughput capacity with increase in the number nodes.

They concluded the maximum achievable throughput of randomly placed n identical nodes each with a capacity of W bits/second to be O () under non interference protocol model. Which they found to be true irrespective of where the wireless nodes is placed whether surface of a three-dimensional sphere or on a planar disk. Even under optimal circumstances the maximum achievable throughput is only O ( ) bits/second. The capacity of the network can be increased by deploying relaying nodes and using a multi-hop path for transmission. [GUPTA]

Another paper is presented by [NOMINAL] addressing the issues in finding the accurate wireless mesh network capacity, in their research they have found the throughput capacity of the wireless mesh network to be significantly below the throughput capacity for wireless ad hoc networks concluded by [GUPTA]. The result is true for the ad hoc type of networks and in the asymptotic case when the number of nodes n is very large.[NOMINAL].

They used a wireless mesh network scenario with only one gateway, while varying the traffic load send by each node in the network. They tried to proof their theory using simulations that the throughput of each node decreases as O (), where n is the total number of nodes in the network. This is not the case in wireless ad hoc network throughput capacity found in [GUPTA] .The concluded the decrease in the throughput capacity of wireless mesh networks to be from hot spot formation at the gateway that throttles the throughput of each node in the network. The networks throughput increases with direct proportion to the number of gateways in the network and additional number of gateways also improves the networks reliability. [NOMINAL].

In the two papers above to address the capacity of issue, issues of unfairness in the multihop networks is not addressed. [FAIRNES] has addressed the end-to-end unfairness issue in multihop environment by using different queueing schemes. The different queueing schemes give different result in terms of fairness to the traffic flows. They have shown that the optimal fairness among the traffic flows from the various sources can be achieved by setting priority queues in MAC and/or network layer.

[DISSERTATION] employed method of modifying the contention window of a node in the MAC layer. They used the scheme to provide priority among the nodes based on the traffic flows they carry. The node with traffic flows from distance sources passing multiple routers was given priority over the node carrying flows from the router closed to the gateway. The minimum contention window of the node is changed and the contention window assumed by a node before retrying the transmission depends on the minimum contention window set in the node.

Increasing the number of gateways only does not improve the wireless mesh network throughput capacity unless load balancing scheme is employed in the network to balance the load across the various gateways nodes available in the network and avoid gateways nodes overloading which otherwise will become bottleneck to the network performance due to congestion and increasing processing delay. []1.1 loadbalancing. In [MESH] gateway load balancing in wireless mesh networks is a complete chapter. They discussed various techniques to achieve load balancing in wireless mesh networks. The divide the scheme in to three major categories: moving boundary-based, partitioned host-based and probabilistic striping-based load balancing.

[LOAD BAL] proposed a technique to balance the traffic load between the available gateways in the network. In their research average queue length in the gateway is used to estimate congestion over time period and an alert is raised, upon which selective active sources are sent notification messages to switch their internet attachment to a possible alternate less-congested gateway. The network simulator ns-2 was used to simulate the proposed algorism.

METHODOLODY

Wireless mesh networks consist of two types of node, mesh clients with one wireless interface and mesh routers with two wireless interfaces. A Mesh router can also function as gateway to provide internet connection on one of its interfaces. To achieve our listed objectives, OPNET modeller simulation software will be used. The simulations will be done on the wireless mesh network scenarios to be created in the OPNET modeller simulation environment.

SECTION 1 INVESTIGATION OF UNFIRENESS BEHAVIOUR

To achieve our first objective, investigation of end-to- end throughput unfairness behaviour of flows in multihop wireless mesh networks based on the position of the traffic source in the network relative to the gateway. A wireless multihop network scenario will be developed as shown in figure 1 below. The network will consist of eight wireless mesh nodes, each node with generated traffic from the connected clients (not shown) and the relayed traffic from other mesh nodes. All the mesh nodes will forward the traffic to only one gateway as shown in the figure 1 below. The simulation will be conducted with the simulation parameters below:

-Under the condition of RTS-CTS handshake disabled,

- IEEE 802.11b DCF

- UDP transport protocol

- CBR application protocol.

-The transmission range will be sent to 250m.

-constant packet size of 1500 bytes for all the UDP flows

- AODV routing protocol

Figure 1

SECTION 2 ADDRESSING THE UNFAIRNESS PROBLEM

The unfairness issue will be address by method of creating multiple queues (as shown in figure 2 below) in each mesh node to give the forward traffic priority based on its required bandwidth over locally originated traffic this will avoid dominating the channel by locally generated traffic when sharing a common queue with traffic to be forwarded. This scheme will enable flow fairness to be achieved in wireless mesh networks even though the scheme does not bring ideal fairness. For the ideal fairness to be achieved each flow supposed to have its own queue, that is provision of multiple queue at each node depend on the number of flows passing through it which will be very expensive to put in to practice. [10]

Scheduler

Lower Priority

Higher Priority

Packets flows

Processor

Figure 2 PRIORITY QUEUE

In this scheme packets will be first indentify using their source address and number of hops they passed to the destination (gateway) and put in the queue locally originated traffic queue or forwarded traffic queue that will be given priority by reducing their queueing delay.

The network scenario will be the same as above but the number of nodes will be increased to increase the number of nodes the flows will pass from a source to destination.

SECTION 3 INVESTIGATION OF THROUGHPUT CAPACITY

To achieve our second objective, investigation and analysis of the throughput capacity of wireless mesh networks as a function of number nodes and traffic loads in a wireless mesh network with a fixed number of getaways. A Wireless mesh network scenario will be created as shown in figure 3 below. The number of nodes in the network will be increased by making some nodes active while deactivating the other nodes and the traffic of send by the nodes will be varied. The analysis will be done based on the average node throughput of our nodes. The simulation parameters that will be set are:

- AODV routing protocol

-The transmission range will be sent to 250m.

- RTS-CTS handshake in MAC protocol

- IEEE 802.11b

- UDP flows to avoid effect TCP error reporting and acknowledgement on traffic behaviour.

-The transmission range will be sent to 250m.

- Constant bit rate CBR application protocol.

-constant packet size of 1500 bytes for all the UDP flows

- Varied aggregate offered load on each router

Figure 3

SECTION 4 EFFECTS OF GATEWAY ADDITION AND LAOD BALANCING

With wireless mesh network scenario in figure 3 and the same simulation parameters above the number of nodes will be 80 and the number of gateways in the network will be increased from 1 to 2, 4, 8 and 10 to investigate the effect of the number of gateways in the network.

Using the same network scenario and simulations parameters the effect of gateway load balancing will be investigated by using host partitioning technique. The network will be deployed in the simulation environment and the gateways will be shared among the mesh routers. A group of nodes will be assigned to a particular gateway node in the scheme and they only forward their traffic flows to that gateway node only.

LIMITATIONS AND CONSTRAINS

-Scheme that will be employed in this thesis to solve unfairness flow problem enable flow fairness to be achieved in wireless mesh networks but it does not bring ideal fairness. For the ideal fairness to be achieved each flow supposed to have its own queue, that is provision of multiple queue at each node depend on the number of flows passing through it which will be very expensive to put in to practice because of the hardware complexity. [10]

-UDP flows will be used in all the simulations to avoid complexity of TCP connection oriented protocols because of flow control and acknowledgement.

-The host partitioning load balancing scheme to be used a group of nodes will be assigned to a particular gateway node in the scheme and they only forward their traffic flows to that gateway node only. The scheme need manual configuration of the nodes instead for the nodes to dynamically obtained a gateway node with low network load.

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