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


Capacity of Wireless Mesh Networks: Comparing Single-Radio, Dual-Radio, and Multi-Radio Networks By: Alan Applegate Introduction Common Topologies: Bus Network ... – PowerPoint PPT presentation

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

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

  • Common Topologies
  • Bus Network
  • Backbone
  • All nodes hear all transmissions
  • Star Network
  • Central switch/router
  • Nodes only hear transmissions intended for them
  • Mesh
  • All nodes logically connected to each other
  • Connection to only one node required
  • Packets forwarded through nodes to reach

Introduction Contd
  • Types of Mesh Networks
  • Wired
  • Physical connection of every node to every other
  • Wireless
  • Ad-hoc
  • Permanent infrastructure
  • Shared
  • Switched
  • Single-Radio
  • Dual-Radio
  • Multi-Radio

History of Mesh Networks
  • 1st wireless mesh networks were mobile ad-hoc
  • Wireless stations dynamically participated in a
    peer-to-peer network (i.e. mobile p2p)
  • Mesh used because it allowed a node to
    participate in a network without needing to
    communicate with every other node
  • Also very flexible

Why We Need Wireless Mesh Networks
  • Traditional approach of a collection of WiFi
    access points connected to a backhaul network is
    extremely expensive
  • Wireless mesh ad-hoc networks are much more
  • Lower cost
  • Wider coverage
  • More reliable

Why Wireless Mesh Works
  • Wireless works best with LoS
  • Permanent wireless infrastructure mesh systems
    can utilize forwarding capabilities of the mesh
    architecture to maneuver around physical
  • Less expensive than using high-power signals to
    blast through obstructions as used with
    traditional point to multipoint systems
  • Maintains LoS for best quality signal
  • Redundancy Reliability
  • High levels of frequency re-use between mesh
  • Increases overall system capacity
  • Works well in dense urban areas

  • Single-Radio (Shared Mesh Network)
  • A wireless mesh network that uses a single-radio
    to communicate to all neighboring nodes
  • Total B/W between all nodes
  • Mesh Access Points (MAPs)
  • Include both mesh interconnection links and
    client access

  • Mesh Points (MPs)
  • Mesh nodes used exclusively for forwarding
  • Dual-Radio Shared MAP
  • Uses separate access and mesh link radios
  • Only the mesh link radio is shared
  • B/W shared between mesh links and client access

  • Multi-Radio (Switched Mesh Network)
  • Uses multiple radios to communicate via dedicated
    mesh links to each neighboring node in the mesh
  • All B/W of radio channel dedicated to neighboring
    nodes link
  • Uses separate access and multiple mesh link radios

  • Mesh Cluster
  • The collection of mesh APs that home to a
    particular wired egress connection
  • Mesh Portal
  • The mesh point located at the egress connection

Single-Radio Shared Wireless Mesh
  • Description
  • Each AP node acts as a regular AP that supports
    WiFi client access as well as forwarding traffic
    wirelessly to other mesh points
  • Same radio used for access and wireless mesh
  • Omni-directional antenna

Single-Radio Shared Wireless Mesh
  • Pros
  • Lowest cost deployment of a wireless mesh network
  • Simplest implementation

Single-Radio Shared Wireless Mesh
  • Cons
  • Every packet generated must be repeated on the
    same channel to send it to at least one
    neighboring AP until reaching the mesh portal
  • Creates excessive traffic
  • More APs More traffic dedicated to forwarding
  • Very little channel capacity available to support

Single-Radio Shared Wireless Mesh
  • Cons contd
  • Capacity reduction as a result of forwarding is
    between 1/N and (1/2)N where N is equal to the
    number of mesh link hops.
  • i.e. Capacity available to users decreases with
    each additional AP

Single-Radio Shared Wireless Mesh
  • Cons contd
  • Use of 1/N or (1/2)N depends on a number of
    factors including topology, location of the mesh
    portal and interference domain
  • Interference domain of nodes whose
    transmissions will be sensed by and hence block
    the transmission of other nodes.
  • 1/N is the most optimistic, which is achieved via
    routing protocols that optimize forwarding and
    eliminate unnecessary transmissions.

Single-Radio Shared Wireless Mesh
  • All clients and mesh APs must operate on the same
    channel and use the 802.11 MAC protocol to
    control contention for the physical medium.
  • Entire mesh acts like a single AP, all APs and
    clients must contend for a single channel

Dual-Radio Shared Wireless Mesh
  • Description
  • Separate radios for client access and mesh links
  • Operate _at_ different frequencies
  • Typical configuration
  • 2.4 Ghz client access
  • 5 Ghz mesh link
  • 802.11 MAC

Dual-Radio Shared Wireless Mesh
  • Pros
  • Improved capacity and scalability over
  • Client access not affected by mesh link

Dual-Radio Shared Wireless Mesh
  • Cons
  • Mesh link contention still limits capacity
  • Sometimes results in blocking other APs
  • Results in reduced system capacity as the network
  • Dual-radio systems are a significant improvement
    over single-radio mesh designs and provide for
    more potential growth of a mesh cluster

Multi-Radio Switched Wireless Mesh
  • Description
  • Separates access and mesh links
  • Multiple radios
  • Typically uses directional antennas
  • Creates a dedicated link between mesh points
  • aka multiple point to point
  • Based on 802.11a
  • Operates _at_ unlicensed 5 Ghz band

Multi-Radio Switched Wireless Mesh
  • Pros
  • Provides increased capacity by overcoming shared
    mesh limitations inherent to single and
    dual-radio mesh architectures
  • No longer a shared network
  • Individual mesh links have dedicated radio
  • Very rich mesh topologies possible

Multi-Radio Switched Wireless Mesh
  • Pros contd
  • Low contention
  • Much higher performance than dual- or
  • More capacity and scalability
  • More nodes more capacity
  • Capacity only limited by wired backhaul
  • Co-existence eliminated
  • Interference reduced
  • Backhaul latency low and predictable
  • Mesh link range increased (directional antennas)

  • The capacity of wireless mesh networks is
    directly affected by the shared network
    contention of the mesh links between mesh points
    used to forward packets
  • Single-radio best for small mesh clusters at the
    edge of the network
  • Dual-radio represents evolution in the growth of
    a mesh network

Conclusion Contd
  • Multi-radio separate wireless access and mesh
  • This eliminates in-channel mesh forwarding and
    shared mesh link contention
  • Results in high capacity system that can scale to
    support large networks with broadband service for
    many users.