Overview of Mesh Links

The mesh link is the data link between a mesh point and its parent. A mesh point uses the parameters defined in the mesh cluster profile, to establish a mesh link with a neighboring mesh point. The mesh link uses a series of metrics to establish the best path to the mesh portal.

The term uplink is used to distinguish the active association between a mesh point and its parent through this chapter.

The following list describes how mesh links are created:

  • Creating the initial mesh link
  • When creating the initial mesh link, mesh points look for others advertising the same MSSID Mesh Service Set Identifier. MSSID is the SSID used by the client to access a wireless mesh network. as the one contained in its mesh cluster profile. The mesh point scans the channels in its provisioned band Band refers to a specified range of frequencies of electromagnetic radiation. of operation to identify a list of neighbors that match its mesh cluster profile. The mesh point then selects the MSSID Mesh Service Set Identifier. MSSID is the SSID used by the client to access a wireless mesh network. from highest priority neighbors based on the least expected path cost.
  • If no provisioned mesh cluster profile is available, mesh points use the recovery profile to establish an uplink. If multiple cluster profiles are configured, mesh points search, in order of priority, their list of provisioned backup mesh cluster profiles to establish an uplink. If the configured profiles are unavailable after searching for 5 minutes, the recovery profile is used.
  • Moving to a better mesh link
  • If the existing uplink quality degrades below the configured threshold, and a lower cost or more preferable uplink is available on the same channel and cluster, the mesh point reselects that link without re-scanning. In some cases, this invalidates all of the entries that have this mesh point as a next hop to the destination and triggers new learning of the bridge tables.
  • Using a new mesh link if the current mesh link goes down
  • If an uplink goes down, the affected mesh nodes re-establish a connection with the mesh portal by re-scanning to choose a new path to the mesh portal. If a mesh portal goes down, and a redundant mesh portal is available, the affected mesh nodes update their forwarding tables to reflect the path to the new mesh portal.

The following sections provide information on link metrics and optimizing link metric algorithm:

About Link Metrics

Mesh points use the configured algorithm to compute a metric value, or path cost, for each potential uplink and select the one with the lowest value as the optimal path to the mesh portal. Table 1 describes the components that make up the metric value: node cost, hop count, link cost and 802.11 802.11 is an evolving family of specifications for wireless LANs developed by a working group of the Institute of Electrical and Electronics Engineers (IEEE). 802.11 standards use the Ethernet protocol and Carrier Sense Multiple Access with collision avoidance (CSMA/CA) for path sharing. capacity.

The link metrics indicate the relative cost of a path to the mesh portal. The best path (lowest metric value) is used to create the uplink.

Table 1: Mesh Link Metric Computation

Component

Description

Node cost

Indicates the amount of traffic expected to traverse the mesh node. The more traffic, the higher the node cost. When establishing a mesh link, nodes with less traffic take precedence. The node cost is dependent on the number of children a mesh node supports. It can change as the mesh network topology changes, for example if new children are added to the network or old children disconnect from the network.

Hop count

Indicates the number of hops it takes the mesh node to get to the mesh portal. The mesh portal advertises a hop count of 0, while all other mesh nodes advertise a cumulative count based on the parent mesh node.

Link cost

Represents the quality of the link to an active neighbor. The higher the RSSI Received Signal Strength Indicator. RSSI is a mechanism by which RF energy is measured by the circuitry on a wireless NIC (0-255). The RSSI is not standard across vendors. Each vendor determines its own RSSI scale/values., the better the path to the neighbor and the mesh portal. If the RSSI Received Signal Strength Indicator. RSSI is a mechanism by which RF energy is measured by the circuitry on a wireless NIC (0-255). The RSSI is not standard across vendors. Each vendor determines its own RSSI scale/values. value is below the configured threshold, the link cost is penalized to filter marginal links. A less direct, higher quality link may be preferred over the marginal link.

The following factors also affect mesh link metrics:

High-throughput APs add a high cost penalty for links to non-high-throughput APs.

Multi-stream high-through APs add proportional cost penalties for links to high-throughput APs that support fewer streams.

802.11 capacity

High-throughput APs can send 802.11 802.11 is an evolving family of specifications for wireless LANs developed by a working group of the Institute of Electrical and Electronics Engineers (IEEE). 802.11 standards use the Ethernet protocol and Carrier Sense Multiple Access with collision avoidance (CSMA/CA) for path sharing. information elements in their management frames, allowing high-throughput mesh nodes to identify other mesh nodes with a high-throughput capacity. High-throughput mesh points prefer to select other 802.11 802.11 is an evolving family of specifications for wireless LANs developed by a working group of the Institute of Electrical and Electronics Engineers (IEEE). 802.11 standards use the Ethernet protocol and Carrier Sense Multiple Access with collision avoidance (CSMA/CA) for path sharing.-capable mesh points in their path to the mesh portal, but can use a legacy path if no high-throughput path is available.

Path Cost

Path cost is calculated by analyzing the other components in this table, and adding the link cost, the mesh parent's path cost, and the parent's node cost.

Mesh portals typically advertise a path-cost of zero, but high-throughput portals add an offset penalty if they are connected to a 10/100 mbps port that is too slow for the high-throughput link capacity.

About Optimizing Links

You can configure and optimize operation of the link metric algorithm through the mesh radio profile. These configurable mesh link trigger thresholds can determine when the uplink or mesh path is dropped and another is chosen, provide enhanced network reliability, and contain flapping links. Although you can modify the behavior of the link metric algorithm, It is recommended to follow the default values for most deployments.