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Because there could be many nodes attempting to join or re-join the network after an expected or
unexpected event, a hold-off time of 16 minutes is implemented. This means that no nodes are
exclusion-listed during this period of time after system initialization.
This exponential backoff and advance algorithm is unique and has the following useful properties:
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•
•
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The node exclusion-listing algorithm is constructed to guard the mesh network against serious stranding,
which was observed in customers' networks. It integrates into AWPP in such a way that a node can
quickly (re-)converge and find the correct network under many kinds of adversities.
Throughput Analysis
Throughput depends on packet error rate and hop count.
Throughput is calculated as:
Two assumptions apply to this calculation:
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•
Generally, the throughput numbers per hop are as shown in
Table 23
Hops
One
Two
Three
Four
Capacity and throughput are orthogonal concepts. Throughput is one user's experience at node N and
total area capacity is calculated over the entire sector of N-nodes and is based on the number of ingress
and egress RAPs, assuming separate non-interfering channels.
For example, 4 RAPs at 10 Mb/s each deliver 40 Mb/s total capacity. So, one user at 2 hops out, logically
under each RAP, could get 5Mb/s each of TPUT, but consume 40 Mb/s of backhaul capacity.
Cisco Aironet 1520, 1130, 1240 Series Wireless Mesh Access Points, Design and Deployment Guide, Release 6.0
OL-20213-01
It allows a node to correctly identify the parent nodes whether it is a true honeypot or is just
experiencing temporary outage conditions.
It credits the good parent nodes according to the time it has enabled a node to stay connected with
the network and the crediting requires lesser and lesser time over period in order to bring the
exclusion-list conviction period to be very low for real transient conditions and not so low for
transient to moderate outages.
It has built-in hysteresis for encountering the initial condition issue where many nodes try to
discover each other only to find that those are not really meant to be in the same network.
It has built-in memory for nodes that can appear as neighbors sporadically so they are not
accidentally considered as parents if they were, or are supposed to be, on the exclusion-list database.
Throughput = BR * 0.5 * 1/n * PSR
BR = Raw backhaul rate, i.e. 18, 24 Mb/s
n = Backhaul hop count
PSR = Packet success rate = (1.0-PER) = (0.0 .. 1.0)
There is no other traffic on the mesh
1/n factor is based on all hops hearing each other.
Throughput Numbers Per Hop
Throughput
Approximately 14 Mb/s
Approximately 8 Mb/s
Approximately 3 Mb/s
Approximately up to 1 Mb/s
Table
23.
Troubleshooting
149
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