Capacity of Wireless Mesh Networks: Comparing Single- Radio, Dual-Radio, and Multi- Radio Networks By: Alan Applegate

Capacity of Wireless Mesh Capacity of Wireless Mesh Networks: Comparing Single-Networks: Comparing Single-Radio, Dual-Radio, and Multi-Radio, Dual-Radio, and Multi-

Radio NetworksRadio Networks

By: Alan ApplegateBy: Alan Applegate

IntroductionIntroduction

Common Topologies:Common Topologies: Bus NetworkBus Network

BackboneBackbone All nodes hear all transmissionsAll nodes hear all transmissions

Star NetworkStar Network Central switch/routerCentral switch/router Nodes only hear transmissions intended for themNodes only hear transmissions intended for them

MeshMesh All nodes logically connected to each otherAll nodes logically connected to each other Connection to only one node requiredConnection to only one node required Packets forwarded through nodes to reach destinationPackets forwarded through nodes to reach destination

Introduction Cont’dIntroduction Cont’d

Types of Mesh Networks:Types of Mesh Networks: WiredWired

Physical connection of every node to every other nodePhysical connection of every node to every other node WirelessWireless

Ad-hocAd-hoc Permanent infrastructurePermanent infrastructure SharedShared SwitchedSwitched Single-RadioSingle-Radio Dual-RadioDual-Radio Multi-RadioMulti-Radio

History of Mesh NetworksHistory of Mesh Networks

11stst wireless mesh networks were mobile ad-hoc wireless mesh networks were mobile ad-hoc Wireless stations dynamically participated in a peer-Wireless stations dynamically participated in a peer-

to-peer network (i.e. mobile p2p)to-peer network (i.e. mobile p2p)

Mesh used because it allowed a node to Mesh used because it allowed a node to participate in a network without needing to participate in a network without needing to communicate with every other nodecommunicate with every other node Also very flexibleAlso very flexible

Why We Need Wireless Why We Need Wireless Mesh NetworksMesh Networks

Traditional approach of a collection of Traditional approach of a collection of WiFi access point’s connected to a WiFi access point’s connected to a backhaul network is extremely expensivebackhaul network is extremely expensive

Wireless mesh ad-hoc networks are Wireless mesh ad-hoc networks are much more flexiblemuch more flexible Lower costLower cost Wider coverageWider coverage More reliableMore reliable

Why Wireless Mesh Why Wireless Mesh WorksWorks

Wireless works best with LoSWireless works best with LoS Permanent wireless infrastructure mesh systems Permanent wireless infrastructure mesh systems

can utilize forwarding capabilities of the mesh can utilize forwarding capabilities of the mesh architecture to maneuver around physical obstaclesarchitecture to maneuver around physical obstacles Less expensive than using high-power signals to blast Less expensive than using high-power signals to blast

through obstructions as used with traditional point to through obstructions as used with traditional point to multipoint systemsmultipoint systems

Maintains LoS for best quality signalMaintains LoS for best quality signal Redundancy = ReliabilityRedundancy = Reliability High levels of frequency re-use between mesh linksHigh levels of frequency re-use between mesh links

Increases overall system capacityIncreases overall system capacity Works well in dense urban areasWorks well in dense urban areas

TerminologyTerminology

Single-Radio (Shared Mesh Network)Single-Radio (Shared Mesh Network) A wireless mesh network that uses a single-A wireless mesh network that uses a single-

radio to communicate to all neighboring radio to communicate to all neighboring nodesnodes

Total B/W between all nodesTotal B/W between all nodes

Mesh Access Points (MAPs)Mesh Access Points (MAPs) Include both mesh interconnection links and Include both mesh interconnection links and

client accessclient access


Mesh Points (MPs)Mesh Points (MPs) Mesh nodes used exclusively for forwardingMesh nodes used exclusively for forwarding

Dual-Radio Shared MAPDual-Radio Shared MAP Uses separate access and mesh link radiosUses separate access and mesh link radios Only the mesh link radio is sharedOnly the mesh link radio is shared B/W shared between mesh links and client B/W shared between mesh links and client

accessaccess


Multi-Radio (Switched Mesh Network)Multi-Radio (Switched Mesh Network) Uses multiple radios to communicate via Uses multiple radios to communicate via

dedicated mesh links to each neighboring dedicated mesh links to each neighboring node in the meshnode in the mesh

All B/W of radio channel dedicated to All B/W of radio channel dedicated to neighboring node’s linkneighboring node’s link

Uses separate access and multiple mesh Uses separate access and multiple mesh link radioslink radios


Mesh ClusterMesh Cluster The collection of mesh APs that “home” to a The collection of mesh APs that “home” to a

particular wired egress connectionparticular wired egress connection

Mesh PortalMesh Portal The mesh point located at the egress The mesh point located at the egress

connectionconnection

Single-Radio Shared Single-Radio Shared Wireless MeshWireless Mesh

DescriptionDescription Each AP node acts as a regular AP that Each AP node acts as a regular AP that

supports WiFi client access as well as supports WiFi client access as well as forwarding traffic wirelessly to other mesh forwarding traffic wirelessly to other mesh pointspoints

Same radio used for access and wireless Same radio used for access and wireless mesh linksmesh links

Omni-directional antennaOmni-directional antenna


Pros:Pros: Lowest cost deployment of a wireless mesh Lowest cost deployment of a wireless mesh

networknetwork Simplest implementationSimplest implementation


Cons:Cons: Every packet generated must be repeated Every packet generated must be repeated

on the same channel to send it to at least on the same channel to send it to at least one neighboring AP until reaching the mesh one neighboring AP until reaching the mesh portalportal Creates excessive trafficCreates excessive traffic More APs = More traffic dedicated to forwardingMore APs = More traffic dedicated to forwarding Very little channel capacity available to support Very little channel capacity available to support

usersusers


Cons cont’d:Cons cont’d: Capacity reduction as a result of forwarding Capacity reduction as a result of forwarding

is between 1/N and (1/2)^N where N is equal is between 1/N and (1/2)^N where N is equal to the number of mesh link hops.to the number of mesh link hops. i.e. Capacity available to users decreases with i.e. Capacity available to users decreases with

each additional APeach additional AP


Cons cont’d:Cons cont’d: Use of 1/N or (1/2)^N depends on a number Use of 1/N or (1/2)^N depends on a number

of factors including topology, location of the of factors including topology, location of the mesh portal and interference domainmesh portal and interference domain Interference domain = # of nodes whose Interference domain = # of nodes whose

transmissions will be sensed by and hence block transmissions will be sensed by and hence block the transmission of other nodes.the transmission of other nodes.

1/N is the most optimistic, which is achieved via 1/N is the most optimistic, which is achieved via routing protocols that optimize forwarding and routing protocols that optimize forwarding and eliminate unnecessary transmissions.eliminate unnecessary transmissions.


All clients and mesh APs must operate All clients and mesh APs must operate on the same channel and use the 802.11 on the same channel and use the 802.11 MAC protocol to control contention for MAC protocol to control contention for the physical medium.the physical medium.

Entire mesh acts like a single AP, all APs Entire mesh acts like a single AP, all APs and clients must contend for a single and clients must contend for a single channelchannel

Dual-Radio Shared Dual-Radio Shared Wireless MeshWireless Mesh

Description:Description: Separate radios for client access and mesh Separate radios for client access and mesh

linkslinks Operate @ different frequenciesOperate @ different frequencies

Typical configuration:Typical configuration: 2.4 Ghz client access2.4 Ghz client access 5 Ghz mesh link5 Ghz mesh link

802.11 MAC802.11 MAC


Pros:Pros: Improved capacity and scalability over Improved capacity and scalability over

single-radiosingle-radio Client access not affected by mesh link Client access not affected by mesh link

forwardingforwarding


Cons:Cons: Mesh link contention still limits capacityMesh link contention still limits capacity

Sometimes results in blocking other APsSometimes results in blocking other APs Results in reduced system capacity as the network growsResults in reduced system capacity as the network grows

Dual-radio systems are a significant Dual-radio systems are a significant improvement over single-radio mesh designs improvement over single-radio mesh designs and provide for more potential growth of a and provide for more potential growth of a mesh clustermesh cluster

Multi-Radio Switched Multi-Radio Switched Wireless MeshWireless Mesh

Description:Description: Separates access and mesh linksSeparates access and mesh links Multiple radios Multiple radios Typically uses directional antennasTypically uses directional antennas

Creates a dedicated link between mesh pointsCreates a dedicated link between mesh points aka multiple point to pointaka multiple point to point

Based on 802.11aBased on 802.11a Operates @ unlicensed 5 Ghz bandOperates @ unlicensed 5 Ghz band


Pros:Pros: Provides increased capacity by overcoming Provides increased capacity by overcoming

shared mesh limitations inherent to single shared mesh limitations inherent to single and dual-radio mesh architecturesand dual-radio mesh architectures

No longer a shared networkNo longer a shared network Individual mesh links have dedicated radio Individual mesh links have dedicated radio

channelchannel Very rich mesh topologies possibleVery rich mesh topologies possible


Pros cont’d:Pros cont’d: Low contentionLow contention Much higher performance than dual- or single-radioMuch higher performance than dual- or single-radio More capacity and scalabilityMore capacity and scalability

More nodes = more capacityMore nodes = more capacity Capacity only limited by wired backhaulCapacity only limited by wired backhaul

Co-existence eliminatedCo-existence eliminated Interference reducedInterference reduced Backhaul latency low and predictableBackhaul latency low and predictable Mesh link range increased (directional antennas)Mesh link range increased (directional antennas)

ConclusionConclusion

The capacity of wireless mesh networks The capacity of wireless mesh networks is directly affected by the shared network is directly affected by the shared network contention of the mesh links between contention of the mesh links between mesh points used to forward packetsmesh points used to forward packets

Single-radio best for small mesh clusters Single-radio best for small mesh clusters at the edge of the networkat the edge of the network

Dual-radio represents evolution in the Dual-radio represents evolution in the growth of a mesh network growth of a mesh network

Conclusion Cont’dConclusion Cont’d

Multi-radio separate wireless access and Multi-radio separate wireless access and mesh linksmesh links This eliminates in-channel mesh forwarding This eliminates in-channel mesh forwarding

and shared mesh link contentionand shared mesh link contention Results in high capacity system that can Results in high capacity system that can

scale to support large networks with scale to support large networks with broadband service for many users.broadband service for many users.

Documents

Capacity of Wireless Mesh Networks: Comparing Single- Radio, Dual-Radio, and Multi- Radio Networks By: Alan Applegate