The quality of a radio link has a direct impact on the throughput that can be achieved by device-to-device traffic. The PPP
over Ethernet (PPPoE) provides a process by which a device can request, or a radio can report, link-quality metric information.
With the Cisco Open Shortest Path First version 3 (OSPFv3) implementation, the route cost to a neighbor is dynamically updated
based on metrics reported by the radio, thus allowing the best route to be chosen within a given set of radio links and reducing
the effect of frequent routing changes.
The routing protocols receive raw radio-link data and compute a composite quality metric for each link In computing these
metrics, you should consider these factors:
-
Maximum data rate—the theoretical maximum data rate of the radio link, in scaled bits per second
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Current data rate—the current data rate achieved on the link, in scaled bits per second
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Resources—a percentage (0 to 100) that can represent the remaining amount of a resource (such as battery power)
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Latency—the transmission delay packets encounter, in milliseconds
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Relative link quality—a numeric value (0 to 100) representing relative quality, with 100 being the highest quality
Each Layer 2 feedback can contribute a cost in the range of 0 to 65535. To tune down this cost range, use the optional
weight keyword with the
throughput ,
resources ,
latency , or
L2-factor keyword. Each of these weights has a default value of 100 percent and can be configured in the range from 0 to 100. When
0 is configured for a specific weight, that weight does not contribute to the OSPF cost.
You can weight metrics during the configuration process to emphasize or deemphasize particular characteristics. For example,
if throughput is a particular concern, you can weight the
throughput metric so that it is factored more heavily into the composite route cost. Similarly, a metric of no concern can be omitted
from the composite calculation.
Because cost components can change rapidly, you might need to dampen the number of changes to reduce network-wide churn.
Use the optional
hysteresis keyword with the
threshold
threshold-value keyword and argument to set a cost change threshold. Any cost change below this threshold is ignored.
Link metrics can change rapidly, often by very small degrees, which can result in a flood of meaningless routing updates.
In a worst-case scenario, the network could churn almost continuously as it struggles to react to minor variations in link
quality. To alleviate this concern, Cisco provides a tunable dampening mechanism that allows you to configure threshold values.
Any metric change that falls below the threshold is ignored. The quality of a connection to a neighbor varies, based on various
characteristics of the interface when OSPFv3 is used as the routing protocol. The routing protocol receives dynamic raw radio-link
characteristics and computes a composite metric that is used to reduce the effect of frequent routing changes.
By using the tunable hysteresis mechanism, you can adjust the threshold to the routing changes that occur when the device
receives a signal that a new peer has been discovered or that an existing peer is unreachable. The tunable metric is weighted
and is adjusted dynamically to account for these characteristics:
You can deconfigure individual weights, and you can clear all weights so that the cost returns to the default value for the
interface type. Based on the routing changes that occur, you can determine the cost by applying these metrics. For more information
about the
ipv6 ospf cost command, see the
Cisco IOS IPv6 Command Reference.
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