User guide

March 2005 Understanding Canopy Networks
Through Software Release 6.1
Page 62 of 425 Issue 1
Canopy System User Guide
Token Bucket Concept
The Canopy software uses a theoretical token bucket that
◦ stores credits (tokens) for the SM to spend on bandwidth for reception or
transmission.
◦ drains tokens during reception or transmission.
◦ refills with tokens at the sustained rate set by the network operator.
For each token, the SM can send toward the network (or receive from the network) an
equivalent number of kilobits. Each SM employs two buckets for the permitted
throughput: one in the SM for uplink and one in the AP for downlink.
The Uplink Burst Allocation and Downlink Burst Allocation parameters in the AP or
the BAM database establish the number of tokens that can fill each bucket. When the SM
transmits (or receives) a packet, the equivalent number of tokens is removed from the
uplink (or downlink) bucket.
◦ Except when full, the bucket is continuously being refilled with tokens at rates
that the Sustained Uplink Data Rate and Sustained Downlink Data Rate
parameters establish in the AP or the BAM database. The bucket often drains at
a rate that is much faster than the sustained data rate but can refill at only the
sustained data rate.
7.1.8 Maximum Information Rate (MIR)
A cap value specifies whether and how the aggregate (uplink plus downlink) throughput
should be capped at a Maximum Information Rate (MIR). The uplink and downlink data
rate caps are calculated as shown in Figure 24.

NOTE:
In these figures, entry refers to the setting in the data rate parameter,
not the burst allocation parameter.
uplink cap enforced =
uplink entry x aggregate cap for the
S
M
u
p
link entr
y
+ downlink entr
y
downlink cap enforced =
downlink entry x aggregate cap for the
SM
uplink entry + downlink entry
Figure 24: Uplink and downlink rate caps adjusted to apply aggregate cap