User manual

AP User Manual January 2004
Software Release 4.1
4.2.2 Recharging Buckets
The Burst Allocation variable field in the AP sets the size of each bucket. This limits the maximum
number of tokens that can fill a bucket.
If the SM transfers data at the Sustained Data Rate, then the bucket refills at the same rate, and
burst is impossible. If the SM transfers data at a rate less than the Sustained Data Rate, then the
bucket continues to fill with unused tokens. In this case, required bursting occurs at the rate
determined by the number of unused tokens.
After a burst is completed, the bucket is recharged at the Sustained Data Rate. Short bursts
recharge faster than large bursts.
4.2.3 Subscriber Module Perspective
Normal web browsing, e-mail, small file transfers, and short streaming video are rarely rate limited,
depending on the bandwidth management settings in the AP or the BAM server. When the SM
processes large downloads such as software upgrades and long streaming video, or a series of
medium-size downloads, these transfer at a bandwidth higher than the Sustained Date Rate
(unless no unused tokens remain in the bucket) until the burst limit is reached.
When the burst limit is reached, the data rate falls to the Sustained Data Rate setting. Then later,
when the SM is either idle or transferring data at a rate slower than Sustained Data Rate, the burst
limit recharges at the Sustained Data Rate.
4.2.4 Interaction of Burst Data and Sustained Data Settings
A Burst Allocation setting
• less than the Sustained Data Rate yields a Sustained Data Rate equal to the Burst
Allocation. (See Figure 5 and Figure 7.)
• equal to the Sustained Data Rate negates the burst capability. (See Figure 6.)
• at zero shuts off the data pipe. (See Figure 8.)
Input Rate
56 Kbps
Sustained Rate
128 Kbps
Burst Allocation
512 Kb
Effective Rate
56 Kbps plus Burst
Figure 5: Burst Allocation vs. Sustained Rate, Example 1
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