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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 ! v: W% c. h" q2 Q/ R) q* Bgiven the increasing number

of audio/video applications that use UDP as their main transport ( q# C" g* `, Q9 t) r* q) cprotocol. Unlike TCP, these

traffic do not respond to congestion signal; i.e., a packet loss. As a2 A- i ^2 G. I: l+ n' I7 q) C result, audio/video

applications may take an unfair share of the network bandwidth and- w! I+ S {" ]8 ]2 k/ l1 V also cause persistent

congestion. To avoid congestion collapse, the IETF has proposed that . R% k! ~" ^) H1 S! haudio/video applications

use equation based congestion control (see Lecture‐7 and the reference : U! {2 Y1 ?: O% P+ `- wgiven on the next

page).

In this assignment, you will simulate n5 E4 H$ r( d; ?; ~# L: z5 R sources that uses( U" B) H' P- e* X equation based congestion control to

set their transmission rate. From your simulation, you will determine% P. a/ u/ A/ E4 T/ U whether equation based

congestion4 ]$ r( G& \6 v# d5 g 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/ ?7 @7 p+ f" Q8 F7 z5 t 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 . Y, w ?* r/ n5 Qenqueue 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’s 9 w' c: ^4 E( j. dpacket. Otherwise,

discard the packet.

3. Determine whether any packet loss rate messages are generated by ; d" Z" @& A7 wreceivers. If yes,

then re‐compute the sender’s transmission rate. Determine the new time8 a4 |, n2 R; d when the

next packet will be generated. I.e, t+k, where k is the time interval $ ^+ `7 W% P( C0 ~) b4 muntil the next packet

arrives.

4. Collect all required statistics.

}

In your simulation, collect the (a) queue length over time, (b)2 y% o6 `4 H! F( Z5 U average queue length, (c) average

end‐to‐end packet delay, and (d) Jain’s fairness index. Determine the6 N" X( P: X' S! g, v2 w' F: O effect of the following

factors: (i) increasing source and receiver pairs, (ii) varying N- @4 O8 F) p0 Q, q& v) M& a# _5 I values, (iii) different packet loss

reporting periods, (iv) loss calculation methods, (v) load p, (vi)$ n1 M7 d1 X& t: Z+ s router’s transmission rate;

instead of one packet per‐tic, try k packets, and (vii) z, z: J' {: Y G$ Y/ i1 q. ~$ K/ w number of new flows ! O: m" R. S% Q: Darriving at time t .

! y) B Q, b" ^0 U

* R) L8 m) E, c. P; {8 I9 X; [ Do with sources 2 d) S' K$ q6 B: r6 i) \; E4 v5 Busing a token/leaky bucket to control their transmission rate.

Another difference is that each source has an application that( f; V6 j; V* q: P generates bursty traffic, where

multiple packets arrive in consecutive time intervals.

To generate bursty traffic, use the following method:

0 ?6 t: ~" E% Q# w- A

In the diagram above, an application generates a packet when it is in ; c3 S4 i" \" Ythe ON state. With

probability k, it will transition to the OFF state where it will remain idle. In % u+ S+ z: T- E& y- z- Mthis 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=ON ! |3 u$ L; I) ?/ }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 l; ~$ g9 r8 [; |5 osource (or all sources

simultaneously) such that congestion does not happen. Note, you must( O0 `) R4 Z% H: F6 A) m. i experiment with

different k: Y& d7 D3 I/ a- ^& V+ @9 J and z& C \+ v6 N6 m( X5 m4 B3 g values and determine6 G6 T, [2 ?3 R8 L3 X4 F their impact on congestion.

Reference

S. Floyd, M. Handley, J. Padhye, + I" C5 N' ^ S3 ?/ rand J. Widmer (2000) Equation-based Congestion Control for Unicast

Applications, ACM SIGCOMM, May, ( Y1 p* j6 {$ o8 r* e H2000.

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