Wireless Mesh

Mesh Overview

Dynamic Mesh  &  Static Mesh (Wireless Distribution System (WDS)) extends traditional networks without installing cable or fiber

Dynamic Mesh, a proprietary solution aligned with 802.11s Hybrid Wireless Mesh Protocol (HWMP) , non-register, proactive mode but is not fully 802.11s compliant,  is extension of the WDS capabilities.

Static Mesh or Wireless Distribution System (WDS) is part of the IEEE 802.11 specification that allows APs to use RF to provide both network access and data backhaul, making it possible to extend the traditional network to less traditional locations without installing additional cable or fiber.

The AP supports  links on either the 5 GHz or 2.5 GHz frequency bands. Therefore they can be leveraged, yielding better overall performance and creating a far more scalable network. The Mesh network is secure as it automatically negotiates pair-wise master keys to encrypt data using AES and to secure links between each node so that data is never transmitted in the clear. Lastly, it is completely integrated into Wireless framework (VNS, Availability, etc.)

Note: Dynamic Mesh is supported on all AP3xxx models only, excluding the AP3605.  WDS or Static Mesh is supported on all APs with the exception of the AP2605/AP3605.

AP roles in Mesh/WDS topology

A Simple Mesh configuration is used when a Wireless AP is installed in a remote location and can’t be wired to the distribution system (DS). A Root  or Mesh Portal Wireless AP is connected to the distribution system via an Ethernet link. This intermediate Wireless AP forwards and receives the user traffic from the remote Wireless AP, also called a Satellite or Mesh AP, over a radio link.

If there is a Wireless AP between the Root/Mesh Portal and Satellite/Mesh AP, it is used to relay the user traffic; this AP acting as a Repeater. A Repeater AP relays the user traffic between the Root/Mesh Portal and the destination Mesh AP/ Satellite AP is acting as both a child and a parent, thus increasing the WLAN range. When configuring WDS in a Wireless Repeater configuration, you should limit the number of repeaters to 3 for optimum performance.

In the Wireless Bridge configuration, the traffic between wireless APs that are connected to two separate wired LAN segments is bridged via a Mesh link; this is also referred to Workgroup Bridge.  To avoid loops, make sure that it the remote wired LAN is a truly isolated segment with no other connections to the wired network since the Mesh solution does not offer protection from loops.

Mesh AP is connected only to one parent/Root AP at a time, a Repeater and Satellite AP may connect an isolated Ethernet segment to the wired network, limiting the number of hops in the tree reduces the latency and provides better performance because packets are duplicated on each hop.

Mesh Tree

The Wireless APs in a Mesh Network configuration form a tree-like structure. The tree builds in a top down manner with the Root / Mesh Portal Wireless AP being the tree root, the Mesh AP / Satellite Wireless or Repeaters being the tree leaves. The Wireless AP that provides the Mesh service to the other Wireless APs in the downstream direction is called a parent. The Wireless APs that establish a link with the Wireless AP in the upstream direction for Mesh service are children.   The Controller can be set up with either a single WDS/Mesh VNS or multiple WDS/Mesh VNSs. If a VNS shares a single WDS/Mesh, it uses the same SSID and a single pre-shared key for the links. The tree can have multiple roots.  In a multi-Mesh environment two independent WDS/MESH trees will be created and each tree will operate on separate SSIDs and use separate pre-shared keys.

The Parent AP enables WDS IE in the beacon once it is connected to the Controller and announces its AP Name using a proprietary IE (SSID is not suppressed).  The child AP scans for the preferred parent and/or backup parent on the radio defined in the WLAN Service. When found it will connect to the parent AP using a proprietary protocol and establish a WDS/Mesh link.

When an AP starts the discovery process in a Mesh environment the AP will obtain its IP address using a DHCP Request that is broadcasted through the link until it reaches the controller. The DHCP response will be transmitted down through the Mesh link until it reaches the AP. The AP will register to the Controller over the Mesh link and then the Controller manages the Mesh AP as any other AP.  The Repeater AP tunnels traffic through the Mesh bridge, not through its own tunnel to the Controller.

Multiple/Backup Bridge Environment

Once the Mesh/WDS link has been established between the parent and client, the link is monitored.

In a WDS environment, heartbeat messages are exchanged in the form of Poll_Req messages are sent from the client AP to the parent AP. The parent is responsible for responding to the polls with a Poll_Resp. The parent AP will disconnect the WDS link if no traffic or no Poll_Requests are received for 20 seconds.  Once the link is broken between the parent and child the child will attempt to automatically discover its backup parent by performing a full scan of the (2.4 or 5GHz) band. In the Static Mesh configuration or WDS, if a backup parent is not defined, the child AP will be left stranded.

Mesh AP uses the Beacons from the parent to detect its presence. Mesh AP monitors other potential parents while connected to the current parent. Mesh AP changes to another parent either because parent is lost (Consecutive Beacon loss) or there is a parent with significantly better link quality (self-healing). In the both cases, the Mesh AP transfers to the new parent without a need for a full scan. The Mesh AP does a full scan if there is no other available parent or on the startup.

During the transition from parent to backup parent service to clients is lost.

Mesh can co-exist with WDS WLAN (used with statically defined).

Mesh Network and RF

Dynamic Frequency Selection (DFS) should be avoided when using Radio A

The Mesh tree operates on the channel determined by the Root/Mesh Portal  AP radio. Therefore, the Mesh/Satellite AP channel is determined by parent radio. A Wireless AP may connect to its parent Wireless AP and children Wireless APs on the same radio or on different radios. Similarly, a Wireless AP can have two children operating on two different radios.

Dynamic Frequency Selection (DFS) should be avoided when using radio A (region and country dependent) in a Mesh environment.  When DFS is enabled prior to establishing a Mesh link and transmitting over any channel, the child AP will perform a 60 second scan to check for the presence of radar signals on the channel. During operation, the WDS AP continues to monitor for radar and if radar is detected on an AP, the AP dissociates clients and signals radar to its parent and child APs.

Changes to the radio channel or power on the child AP may cause the AP to become inaccessible.  During deployment, if the child AP rejects changes to a channel or power for the radio used for the link connection to the parent AP, an alarm will be generated.

To reduce interference, radio hopping may be used where neighboring links are on different radio; however, channel planning is difficult. WDS (only) backhaul can co-exist with client VNSs on same radio.  However, the best performance is achieved when client VNSs are on a different radio than the WDS backhaul.  Radio A is sometimes the best choice for WDS backhaul because most clients operate on b/g.