What’s mesh?

Mesh overview

• IEEE published the 802.11 amendment for mesh networking, 802.11s, primary goal is targeted to provide more stable better performance for the whole network using more ‘connected nodes’.
• The entire wireless mesh could be treated as a single (giant) Ethernet switch.

• Mesh advantages: simple, fast installation, more suitable for the application:
  • Where wires are not desired (e.g., hotels, airports)
  • Where wires are impossible (e.g., historic buildings)

Mesh vs. Repeater

• Auto connect: A mesh node can automatically scan nearby mesh nodes and join the mesh network without further configuration.
• More available paths: each nodes in the network can communicate with each other.

• Path recovery: Mesh can resume network traffic if any node breaks down, repeater will have network breakdown if node in between breaks.

Terminology

• Mesh Point (MP)

A station (STA) that implements the mesh facility. A mesh STA that operates in the mesh BSS (MBSS) may provide the distribution services for other mesh STAs.

• Mesh Access Point (MAP)

A mesh station that is collocated with one or more access point(s).

• Proxy Mesh Station (Portal, MPP)

A mesh STA that represents 802 entities outside the mesh basic service set (MBSS).

• Peering

A logical relationship from one mesh STA to another mesh STA that has been established with the mesh peering management (MPM) protocol

• Mesh Gate

A mesh station that has access to external STAs (STAs outside MBSS) called a Mesh Gate. Both MAP and MPP are Mesh Gates

Mesh protocol introduction

Discovering & Peering

• Mesh nodes discover its one-hop neighbors through passive or active scan, that is listening Beacon or transmit Probe Req.

• Compare mesh profile (Mesh ID), data rate, mesh capability, etc in Beacon or Probe Rsp to find candidate peer mesh STA.

• Mesh nodes become “peer” (or “neighbor”) to each other through mutual association.

• Each mesh nodes maintains a neighbor table

• Mesh nodes can only transmit data through “neighbor”

HWMP

• Mesh path selection protocol - Hybrid Wireless Mesh Protocol (HWMP).

  • Proactive tree building mode

    • Gate announcement (GANN)

  • On demand mode (AODV)

    • Path request (PREQ)

    • Path reply (PREP)

    • Path error (PERR)

• Each mesh node maintains a routing table, in which contains forwarding information: {destination MAC, next-hop MAC, metrics, …}

• Gate Announcement frame (GANN)

  • Used to announce the presence of the mesh gate.
  • Mesh gate broadcast GANN for every 3 second.

• Ad hoc on-demand routing protocol (AODV) steps

  1. Source node broadcast a PREQ frame flooding to all mesh nodes

  2. Ever PREQ received, mesh node(s) create a reverse path to source

  3. When some mesh node knows destination, reply unicast PREP to source mesh node

Interworking with the DS

• When two STAs behind mesh gates (external STA ) need to communicate with each other.

• Each mesh gate maintains a proxy table, in which contains proxy information { external STA’s address, proxy mesh gate’s address, …}

• If the proxy information does not exist, do AODV first.

• These proxy information is carried by PREP, or PUX (proxy update) packet.

Data forwarding - address transform