From: Edward Monk (emonk@xxxxxxx)
Date: Tue Aug 20 2002 - 10:57:16 GMT-3
Ted,
This is an interesting link on how to set your Be higher than your Bc.
This allows you to save up enough tokens for future bursts that exceed
your token savings during certain intervals. This only works when you
have enough excess bandwidth available. Which should work in most cases.
Excerpt from document below: This following paragraph is a key excerpt
from the document and should help you to understanding what they are
doing here and how they achieve the desired result.
The bucket itself has a specified capacity. If the bucket fills to
capacity, newly arriving tokens are discarded and are not available to
future packets. Thus, at any time, the largest burst a source can send
into the network is roughly proportional to the size of the bucket. A
token bucket permits burstiness, but bounds it.
Configuring the functionality of the token bucket with a Be greater than
Bc in this manner helps to avoid what is called tail loss. Tail loss is
when a sudden dropping of packets occurs because you have run out of
tokens saved up in the token bucket. This configuration actually allows
for a more gradual dropping of packets while the bandwidth is being
throttled back. It actually prevents Bc from depleting the Be (token
bucket) to rapidly because Be is a larger value than Bc.
Very interesting thanks for the link. Another good day learned something
new.
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Ted Richmond
Sent: Tuesday, August 20, 2002 2:15 AM
To: ccielab@groupstudy.com
Subject: Bc Be S.O.S.....
Hello group,
When I finally thought that I've got Qos under-control
(err...well say 80% undercontrol), I came across a doc
- Selecting Burst and Extended Burst Values for
Class-Based Policing
http://www.cisco.com/warp/public/105/carburstvalues.html
This one really threw me off. Here are some questions:
* Are Be,Bc definitions different for shaping and
policing?
* The above doc says, "When bc is equal to be, the
traffic regulator cannot borrow tokens and simply
drops the packet when insufficient tokens are
available". I though this is the case when be=0
* The doc gives an example with 'CIR= 1 bit/sec, Bc= 2
bytes/sec and Be=4 bytes/sec' (pkt size as 1 byte). Is
this possible? How can he send 4 packets with the
above constraints and still maintain 1bit/sec CIR?
I am totally lost now - I should've never read this
doc. Please help -S.O.S
TIA.
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