[Sharing] Wi-Fi Mesh Network & IEEE802.11s Protocol [2]

Previous Article: [Sharing] Wi-Fi Mesh Network & IEEE802.11s Protocol [1]


  • Wireless Personal Ad-hoc Network (WPAN)
  • Mobile Ad Hoc Network (MANET)


  1. Intro
  2. General Characteristics of WMN
  3. Application Scenario
    • Broadband Home Networking
    • Metropolitan Area Networking
    • Transportation systems
  4. IEEE802.11s
    • HWMP


In the previous article, we roughly understood the definition of Mesh networks, commonly used nodes in mesh networks, and some wireless mesh network categories. Today, we are going to discuss the real-life applications of WMNs and the new IEEE802.11s protocol specifically for WMNs. In IEEE802.11s, the discussion will focus on the Hybrid Wireless Mesh Protocol (HWMP).

General Characteristics of WMN

WMN does not require centralized AP to mediate wireless connections. The multi-hop feature extends the coverage with low transmission power. Providing non Line of Sight (NLOS) connectivity. Self-forming, self-healing, and self-organization capability ease the deployment of WMN and increase the network fault-tolerant capability.
To bear in mind that WMN is not an energy-efficient network since most of the Mesh Routers are usually AC-powered, therefore energy efficiency is not an issue in protocol design.


  1. WMN has no wiring needed, wiring is always expensive/labor-intensive, time-consuming, inflexible. Thus, it has a very low installation and maintenance cost
  2. Easy to provide coverage in outdoors and hard-to-wire areas
  3. Rapid deployment
  4. Self-healing, resilient, extensible, scalable

Application Scenario

1. Broadband Home Networking


Traditional home networking might be facing the following problems:
1. Homes have many dead zones without service coverage
2. Expensive to do the site survey
3. Expensive to deploy multiple APs
4. Communications between nodes under 2 different APs have to go all the way back to access the hub

Where all the problems will be fixed by Mesh networking.

2. Metropolitan Area Networking

Communication between nodes in WMNs does not rely on a wired backbone. Compared to wired networks, e.g., cable or optical networks, WMN-MAN is an economic alternative to broadband networking, especially in
underdeveloped regions. WMN-MAN covers a potentially much larger area than home, enterprise, building, or community networks. The requirement on the network scalability by WMN-MAN is much higher.

3. Transportation systems

Morden transportation system contains only one wireless gateway that is connected to the mesh gateway at one of the ends of the train that is able to access the Wireless Internet. Then, the Mesh gateway will communicate with all the other Mesh Routers/Mesh Clients on the train.

IEEE 802.11s

IEEE 802.11s is an IEEE 802.11 amendment for mesh networking, defining how wireless devices can interconnect to create a WLAN mesh network, which may be used for static topologies and ad hoc networks.
802.11s extends the IEEE 802.11 MAC standard by defining an architecture and protocol that support both:

  • broadcast/multicast and
  • unicast delivery

using “radio-aware metrics over self-configuring multi-hop topologies” named Hybrid Wireless Mesh Protocol (HWMP).

One active path selection protocol/metric in one mesh, but allow for alternative path selection protocols/metrics in different meshes; supports single or multi-channel mesh.


HWMP combines the flexibility of on-demand route discovery with efficient proactive routing to a mesh portal.

- On-demand routing

On-demand routing in layman terms means the route is only established while there is a need to do so, therefore it is usually reactive routing. One of the most famous IEEE802.11 protocols is AODV.
However, HWMP is based on more advanced Radio Metric AODV (RM-AODV): use the features of AODV (RFC 3561); extensions to identify best-metric path with arbitrary path metrics; Destinations may be discovered in the mesh on-demand.

To avoid all the tedious details, the graph here shows the procedure of the Forward Path & Reverse Path formation from S (source node) to D (destination node).

- Proactive routing

Proactive routing of HWMP is based on tree-based routing: If a Root portal (=MPP) is present, a distance
from a vector routing tree is built and maintained. It is efficient for hierarchical networks and avoids unnecessary discovery flooding during discovery and recovery.

The graph below indicates how the tree-based topology forms a network from the Root Node:


This article avoids all the mathematical details and metric analysis used for HWMP. And lower-level concepts such as AODV, on-demand routing, reactive and proactive routings are not explained in detail. This is for the readers to just focus on MWN and have a basic concept of it. In the future, I will write more about other protocols and topologies used in IEE802.11 and Wi-Fi