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Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless...

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Chapter 16 Wireless Mesh networks
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Page 1: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Chapter 16Wireless Mesh networks

Page 2: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Overview

IntroductionMesh network definedBenefits of wireless meshCurrent issues and solutionsMesh deployment issuesConclusion

Page 3: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Introduction

Used by Municipalities to enterprises Telecom providers Public safety Military

Popular do to Ease of deployment Increase in network capacity mobility

Page 4: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Network Defined

A set of fully interconnected network nodes that support traffic flows between any two nodes over one or more paths or routes

Wireless provides connectivity while in motion

Biggest example is the internet

Page 5: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Benefits of wireless mesh

Deployment Each node maintains multiple connectivity Allows for multiple paths

Cost Wired networks are more expensive Many nodes use the same access point

Continuity of services in case of device failure Users expect this because of the fee they pay

Scalability Easy and cost effective to add more capacity

Page 6: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Examples of Deployment

Small in home mesh networks T.v., audio systems

Public safety Police, fire, emergency

responseswiMAX or 3G access

links

Page 7: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Current issues and solutions

Netowork structureIntra-mesh channel re-useMedium access contentionMesh routing and forwardingMesh securityCongestion controlVoice over meshMesh network management

Page 8: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Network structure

Plays a big role in performance of voice services Determines delay encountered by voice packets

Parking lot effect Is a function of the number of hops in a mesh and the

peering ratio As seen the hop depth H is 3 and the peering ratio Rp is 2 The load on the portal link is equal to 7 peer links

Solutions for the parking lot effect include proper dimensioning of the links of mesh network and/or limiting access to the mesh so as to keep the offered load within the limits imposed by the capacity of the available RF links

Page 9: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Intra-mesh Channel Re-use

Links between mesh nodes may use one or more RF channels One RF channel for rapid peer acquisition and mesh

formation May cause interference between links

Re-use worsens parking lot effect The further from a portal, the more a packet has to

compete for the channel In some cases nodes may not see other node

transmissions This leads to interference and packet loss

Page 10: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Intra-mesh Channel Re-use

Due to exponential back off for MAC in IEEE 802.11 protocol, packet loss may lead to significant delays per packet per link

Solutions require increasing the isolation between links Three dimensions are available:

Space(directional antennas) Frequency(multiple RF channels) Coding(using orthogonal codes for mesh links)

Which is best depends on requirements and conditions of a given network deployment

Page 11: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Medium Access Contention

IEEE 802.11 MAC is designed for bursty data traffic in unpredictable RF environments Channel state is re-established for every packet

Done with listen-before-talk and collision avoidance through use of contention window

Medium access is subject to jitter

For voice and video services, QoS extensions have been added to the standard EDCA is an enhancement of the basic distributed

access control mechanism with a priority bias for certain types of traffic like voice, video, and best effort data

Page 12: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Routing and Forwarding

Routing of packets has an important role in the service level offered by a mesh network. Route set-up is based on finding the most efficient

path to the portal Once links are formed, path does not change except

for node or link failure

Mobile mesh networks do not have static links A lot of research efforts have been invested in finding

a solution to routing in fixed and mobile mesh networks

Page 13: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh routing and Forwarding

Spanning tree routing Networks consisting of wireless bridges naturally

form tree-like structures Rooted in a portal node May be set up using a combination of parameters

Such as hop count and link transit delay Monitor functions which detect link failure and/or

portal loss, may be used to trigger link or tree rebuilding

These structures can be simple and efficient

Page 14: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Routing and Forwarding

AODV: Ad-hoc, On-demand Distance Vector protocol Fairly simple, but not as efficient as spanning tree When route is needed or needs repair, its originator

floods the network with a request for a destination The latter replies with a unicast that is forwarded

back to the originator Loss of a link triggers a route error message up and

down the route The cost of flooding in AODV depends on the rate of

change of the environment

Page 15: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Routing and Forwarding

OLSR: Optimized Link State Routing protocol Is a pro-active routing protocol that uses the link state

as a driving factor and includes a multicast capability A subset of nodes called multi-point relays, provides

anchors for neighbor nodes Link state information distribution can remain local

and multicasting is supported naturally Although simple, the implementation of OLSR

requires many different control messages. More efficient than flooding based parents, overall

efficiency is not the best for this protocol

Page 16: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Routing and Forwarding

HWMP: Hybrid Wireless Mesh Protocol In 2005, the IEEE 802.11 working group started

development of the wireless LAN standard with a layer 2 mesh protocol

Includes simple tree building protocol to handle static mesh, and AODV elements to support mobile mesh

This allows a mesh to use the most efficient routing protocol appropriate for a given deployment or application

Page 17: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Routing and Forwarding

Regardless of the network structure, there will be alternative routes to a given destination and each node has to decide which next hop to send an a given packet to Requires the use of a consistent set of metrics

All nodes involved must share the same meaning and measurement of the metrics of a given link or path

Path metrics can include Number of hops, airtime needed to reach destination,

complex values that bring together a variety of parameters such as hop count, link load, and SNR

Page 18: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Routing and Forwarding

The best metric to use depends on the type of mesh network and the operational conditions

Different types of service have different requirements Voice packets are short and must be delivered within

certain time constraints In this case link reliability and hop count are important

routing metrics Background data service packets may be large and

timing is not important In this case a high data rate is more important than link

reliability

Page 19: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Security

Security in wireless mesh is complicated because of absence of human users that can be used as trusted parties during network initialization Security functionality and the storage of

cryptographic data cannot be fully relied upon Mesh nodes perform a number of functions, each of

which has its own security concerns

Page 20: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Security

Discovery This function serves to detect other mesh nodes that

belong to the same owner or administrative domain Security is limited to authentication of the information

provided by other nodes Can be provided by means of public key ciphers that

allow the verification of digital signatures This is done depending on operational needs, the

tolerance for overhead and the available budget In commercial mesh, the discovery function is left

unprotected Exposes the network to spoofing and DOS attacks

Page 21: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Security

Peer link establishment This function creates secure links between mesh

nodes and in the process it validates the non-protected data that nodes obtain during discovery

Secure link establishment requires Nodes are able to identify themselves They can be authenticated They are able to set up a cryptographic session with each

other that protects the flow of data and management information between nodes

Various means are available to secure link set-up A combination of symmetric key ciphers and asymmetric

ciphers are used

Page 22: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Security

Peer link establishment…continued IEEE 802.11X protocol

Client requests a connection This is done with a security server Validates the ID of a node and generates keys

Page 23: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Security

Routing Form paths through a network that is used to forward

data and management information Interfering with route set-up causes loss of

connectivity among nodes as well as loss or hiding of data Attacks against routing functions tend to result in DOS

like effects Solutions

Expanding routing protocols Tesla approach Secure the link before routing is initiated

Page 24: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Security

Forwarding The forwarding function delivers packets to their

destination, either directly or via intermediate nodes that lie on a path known to include the destination

Confidentiality and integrity are most important Symmetric key cryptography is preferred for efficiency Can either be hop-by-hop or end-to-end between the

original node and the end destination If connected to other networks, end-to-end is impractical,

therefore higher layer security solutions like IPSEC must be used

Page 25: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Congestion Control

Congestion occurs when a source produces more than its sink can handle Each link is a sink and all links that feed it are

potential sources Consider each link as potential sink for traffic Each link carries traffic in both directions Must monitor each outgoing link, and using flow

control messages

Page 26: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Congestion Control

Other forms of congestion control Rate limiting the traffic sources Pro-active form of source flow control Downside isinefficiency

Page 27: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Voice over Mesh

Factors that can affect the quality of voice over mesh Choice of codec

Different requirements with respect to jitter Choosing a codec dynamically

Handover Client link and intra mesh links may change Time depends on a number of factors

Other causes of voice quality impairment Radio measurement traffic Location signaling Legacy 802.11 devices that share the channel Non-802.11 devices like microwave ovens and cordless

phones, bluetooth

Page 28: Chapter 16 Wireless Mesh networks. Overview Introduction Mesh network defined Benefits of wireless mesh Current issues and solutions Mesh deployment issues.

Mesh Deployment Issues

For fixed mesh networks, deployment can be a complex issue, even though the self organizing capability makes life a bit easier The main factors that drive a fixed mesh deployment

are: The service level to be offered in terms of bits per second

per user and on which basis, best effort or guaranteed The user density– people per area The available sites for mounting the access transceivers The available favorable sites for mounting intra-network

transceivers The available RF frequency band and the number of

channels, shared or otherwise


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