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发表于 2008-5-6 07:42 |只看该作者 |倒序浏览

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在network 中如何用token bucket to control packet transmission rate.
编程序后做图表分析
能做的高手请与我联系QQ 346719984

内容如下

The risk of congestion collapse on the Internet is becoming a reality' x- A" Z A2 l* ]$ M* H s given the increasing number

of audio/video applications that use UDP as their main transport7 |7 I# v. g% V: E; v protocol. Unlike TCP, these

traffic do not respond to congestion signal; i.e., a packet loss. As a 9 j: x' p+ Y% X; O- Jresult, audio/video

applications may take an unfair share of the network bandwidth and( D6 Q8 I5 r/ B2 b0 T5 q9 s also cause persistent

congestion. To avoid congestion collapse, the IETF has proposed that * T5 C8 C" ^ ?* _6 N2 maudio/video applications

use equation based congestion control (see Lecture‐7 and the reference 1 g% \% F& m. G# f) E3 g V' kgiven on the next

page).

In this assignment, you will simulate n 5 b, q* f! V4 Tsources that uses* K' k T* D' P) H, c equation based congestion control to

set their transmission rate. From your simulation, you will determine$ q. _. i3 t! E5 _, t whether equation based

congestion! q( Q" \; i% [7 ~6 y8 r' z* C control is effective in reducing packet loss, and hence congestion.

The above network can then be simulated as follows:

Initialization

Set the router’s queue size to N, meaning it can hold up to N packets.

For each sender, set an initial transmission rate, and determine the$ \3 l+ ]* J$ ` z7 s. x- N K time when the first packet is

to be generated.

Body

FOR t=1 to SIM_TIME DO

{

1. IF the router’s queue is not empty then dequeue a packet, and. F8 q' Z+ k6 c, D$ j+ {! V enqueue that packet in

the corresponding receiver’s queue.

2. IF a sender has a packet to send THEN

‐ Check if the router’s queue is full. If not, enqueue the sender’s9 `+ ~7 `& g, s5 d# c packet. Otherwise,

discard the packet.

3. Determine whether any packet loss rate messages are generated by; d# \& t$ y1 ?7 e8 k receivers. If yes,

then re‐compute the sender’s transmission rate. Determine the new time1 P; ]7 I3 N. Z3 x/ `( a. c% j when the

next packet will be generated. I.e, t+k, where k is the time interval " z8 n& f& ]; k/ [* K# Nuntil the next packet

arrives.

4. Collect all required statistics.

}

In your simulation, collect the (a) queue length over time, (b) 6 D/ I+ K* ~3 u) x( A- a4 Gaverage queue length, (c) average

end‐to‐end packet delay, and (d) Jain’s fairness index. Determine the0 j h m) d- }6 g9 l effect of the following

factors: (i) increasing source and receiver pairs, (ii) varying N * S5 E: ?6 m9 ivalues, (iii) different packet loss

reporting periods, (iv) loss calculation methods, (v) load p, (vi)6 I8 t1 |% c5 @& v9 y& l7 V( D router’s transmission rate;

instead of one packet per‐tic, try k packets, and (vii) z( o2 ?0 Q# S+ T4 _ number of new flows& o4 f+ b* j, w6 [7 D0 D. P9 `- z arriving at time t .

9 E: j+ x. w, N C

& \. j2 `+ ?5 y% m) ?' ]7 a; Y6 E Do with sources& q, R" V) a2 ?9 d* ]" q using a token/leaky bucket to control their transmission rate.

Another difference is that each source has an application that , V4 I( w( X- D0 J1 D& s3 W# E' |5 H: Jgenerates bursty traffic, where

multiple packets arrive in consecutive time intervals.

To generate bursty traffic, use the following method:

! ?$ `7 T- \9 X0 C6 C. V* v# H

In the diagram above, an application generates a packet when it is in . G* W2 k4 m; [9 w! ?the ON state. With

probability k, it will transition to the OFF state where it will remain idle. In & Z4 D; q6 o4 [4 l6 L/ ?this state, it has

probability z of moving back to the ON state.

The pseudo‐code is as follows:

1. Start at a random state: ON/OFF.

2. At every simulation tic, do

a. Select a random number R in 0<= R <=1.

b. If in state=ON9 X8 D V/ r- b. c [& } AND R>=k, set state=OFF.

c. If in state=OFF AND R>z, set state=ON.

d. If state equals ON, generate a packet.

Design an algorithm to control the token/leaky‐bucket rate of each 5 n% g' ^, q9 U# @: Asource (or all sources

simultaneously) such that congestion does not happen. Note, you must ) U5 p5 C+ j3 [1 L, c/ \experiment with

different k8 D" F. h5 |: q5 L5 Q; H$ K and z' }* A" `% y+ Y9 Z% L values and determine : N& X a$ L' f( J2 A/ K d- \their impact on congestion.

Reference

S. Floyd, M. Handley, J. Padhye, 2 b P# T( Y/ \; B+ h8 hand J. Widmer (2000) Equation-based Congestion Control for Unicast

Applications, ACM SIGCOMM, May,* Y! j# U- F5 S/ e) X' L) ~* Y! v7 M 2000.

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