What is Mesh wi-fi ?

Mesh WiFi or Whole Home WiFi systems consists of a main router that connects directly to your modem, and a series of satellite modules, or nodes, placed around your house for full WiFi coverage. They are all part of a single wireless network and share the same SSID and password, unlike traditional WiFi routers.

Traditional WIFI systems consists of a single WIFI broadcast module, which is enough but often leads to dead spots and weak signal in your house.

This reduces the user experience. Be it watching 4k Video or playing games online.

Simple things like various walls, doors and other obstructions leads to weak signal within your house.

There are various articles about comparison between single WiFi, range extenders and mesh WiFi.

While Mesh WiFi systems have multiple access points.

Example of mesh-wifi product.

In this article we are going to cover more from the technical perspective. also, what are the various alternatives.  Mesh WiFi specifications and Easy Mesh

Above diagram shows a Mesh WiFi system. Before we go any further, we need to understand -what is SSID & BSSID?

SSID: Service Set Identifier or SSID is simply the name of WiFi.

BSSID: Basic service set identifiers. BSSID is simply the MAC address of a wireless access point.

In the above diagram Multiple AP nodes have unique BSSID’s but a single SSID.

In order to form a mesh network A Controller Node should be able to form a wireless topology. They should be able to identify Mesh-AP nodes and establish a L2 Network among themselves.

MBSS: Mesh BSSA basic service set (BSS) that forms a self-contained network of mesh stations (STAs). An MBSS contains zero or more mesh gates

What stds it follows :ieee 802.11s and 802.11r.

Mesh formation is currently done at Layer 3(IP layer). The solution approach for adhoc networking has evolved mostly in last 1 year. Before 2018, wireless adhoc network/MANET were the research topics with nearly no open implementation.

AS of now most of the Mesh implementations, try to solve these problems at Layer3(IP), But this is more of an engineering patch than a proper solution.

For a wireless mesh network to operate successfully as Mesh nodes

  • Network discovery, (Read broadcast channel, read ARP, DHCP)
  • Loop detection and avoidance via spanning tree is required.

Though these solutions Already exist in wired domain, but for WiFi is not achieved.

IEEE 80211s group is trying to address this problem and tries to solve it at Layer-2/MAC which is the right place to solve the problem, Because  MAC layer  is radio aware, it is capable of reading the signal strength of the WiFi devices , hence it can read the radio and channel parameters of nearby wireless-AP’s, and can help in projecting correct link strength in the Network topology.

Assuming with the help of 80211s the Network topology is created along with proper link quality this gives a clear picture how and where the packet will be transmitted.

802.11r protocol is designed to reduce the time required for authentication when roaming. When the phone is roaming between two wireless AP, it enables the phone to quickly disconnect from one wireless AP and reconnect to the other wireless router. The process is very fast, and the delay time will not exceed 50 ms. 

How does a mesh AP discover the other access points?

When a mesh station boots up, it needs to discover and join a mesh network (that is, establish peer relationships with other mesh stations). The discovery process uses the standard active and passive scanning mechanisms.

  1. Mesh AP scans the WiFi beacons and discovers the nearby wifi-ssids.
  2. If the Mesh AP discovers the its own Pre-configured SSID. Then It decodes the new IEs Present in beacon (MeshID)
mesh packet format
  1. Mesh Points (MPs) discover candidate neighbours based on new IEs in beacons and probe response frames
    1. – WLAN Mesh Capability Element
      1. – Summary of active protocol/metric
      1. – Channel coalescence mode and Channel precedence indicators
    1. – Mesh ID
      1. – Name of the mesh
  2. Mesh Services are supported by new IEs (in action frames), exchanged between MP neighbours.
  3. Membership in a WLAN Mesh Network is determined by secure peer links with neighbours.

All the above Capabilities needs 802.11s implementation. This requires changes in the WiFi-kernel drivers, if not then open802.11s kernel implementation is required.

  • It should be noted that Mesh capability implementation doesn’t require PHY Changes.
  • It requires changes only at the MAC Layer.

Some manufactures implement MAC completely in the firmware also known as Hard-MAC.

Others implement MAC in the software (part of WiFi-kernel driver) known as Soft-MAC.

Those WiFi modules which run either Linux or openwrt and has soft mac can be upgraded to Mesh-WiFi with just software upgrade. How to upgrade old home routers as mesh-AP.

Open80211s is only suitable hardware’s supporting Soft-MAC.

open80211.s architecture

How does a mesh AP determine the “best path in the network”?

Routing function takes following things into consideration

  • Link Cost (Link strength)
  • Number of Hops
  • TTL

 Mesh Protocols

The protocols in general do not require a specific routing strategy be implemented at each node. However, each protocol does define what message formats are used and what information is available for computing route metrics. Protocols are classed as proactive, reactive, or hybrid, depending on whether routes are established on-demand or monitored and maintained.

  1. OLSR

Optimized Link State Routing (OLSR) gained tremendous early momentum. OLSR is one of the oldest mesh routing protocols in existence. It is defined by the Internet Engineering Task Force (IETF) Request for Comment (RFC) 3626 and was once the leading candidate routing protocol for IEEE 802. 11s.Performance studies show that newer protocols are more scalable and agile with lower overhead.7 Versions now exist with link quality sensing. OLSR is a proactive layer 3 protocol, which offers portability to more systems and enables the protocol to span link layers. OLSR has one of the bigger mesh networking communities to help promote its development and provide support.

  • HWMP

Hybrid Wireless Mesh Protocol (HWMP) is the standard in IEEE 802.11-2012 (which supersedes 802.11s). Today it is compiled into most versions of the Linux kernel. Curiously, we did not find a satisfactory performance comparison explaining the selection of HWMP over competitors for 802.11s. Secure HWMP (SHWMP) and Privacy Aware SHWMP (PA-SHWMP) propose a method for nodes to authenticate each other to prevent outside mischief, but this appears to be a research area and we did not find implementations10. HWMP also has an open source implementation open802.11s that provides a relatively weak supporting community for development and use.

HWMP specification can be downloaded here.

  • BATMAN and BATMAN-Advanced

BATMAN once attracted widespread support and is today compiled into most versions of the Linux kernel. It is defined in an expired IETF draft working document. BATMAN is a proactive layer 3 protocol, routing on IP addresses, and BATMAN-Advanced is a layer 2 protocol, self-assembling using MAC addresses. Distributed knowledge of topology makes BATMAN efficient and scalable, but the routing cost metric is simply the number of hops, weighted by a hop penalty advertised by the nodes. BATMAN-Advanced has an active open source community that promotes its development and provides support.

How should mesh APs form the mesh cloud?

A mechanism should be devised to allow various Mesh Access Points to borrow wireless link to transmit data elsewhere.

Mesh AP forming a mesh cloud should act both as a Station (STN) and as Access Point (AP).

Why Mesh-WiFi is needed?

Traditional routers come with a limited range. While adding a range extender can help with this issue, range extenders sacrifice speed for connectivity. Mesh WiFi gives you the best of both worlds – so you can experience both powerful speeds and long-range connectivity.

·       One Network for Your Entire Home

With a Mesh WiFi router, you can skip signing into a new network every time you go upstairs and stay connected to a single sturdy network no matter where you are. Mesh technology is smart and intuitive, letting you stay online even if one of your mesh nodes fails

·       Stable Long-Range Connectivity

With a mesh router, you can get a powerful and stable connection no matter where you are in your home. Because each mesh node piggybacks off the other nodes signal, you can get powerful WiFi whether you’re at the top of the stairs or the bottom of the basement.

·       Easy Setup and Management

Most mesh routers on the market today come with easy network setup and management, allowing you to toggle network settings, check speeds, and enact parental controls.

·       Designed for Your Smart Home

Some mesh routers are advanced that they function as a WiFi router and a smart hub, connecting your Zigbee, Bluetooth and WiFi devices and enabling you to manage all your smart devices through the app.

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