The risk of congestion collapse on the Internet is becoming a reality
given the increasing number
of audio/video applications that use UDP as their main transport% ?: K/ w7 K4 }& z
protocol. Unlike TCP, these
traffic do not respond to congestion signal; i.e., a packet loss. As a
result, audio/video
applications may take an unfair share of the network bandwidth and) B4 n8 D4 i; s6 A
also cause persistent
congestion. To avoid congestion collapse, the IETF has proposed that
audio/video applications
use equation based congestion control (see Lecture‐7 and the reference$ B' g2 O" X) N' \& E
given on the next
page).
In this assignment, you will simulate n
sources that uses3 e+ M3 \- R# ~1 `: P2 i
equation based congestion control to
set their transmission rate. From your simulation, you will determine
whether equation based
congestion9 }" R) T$ O; K
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
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
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’s2 t5 d8 o: g* L, E V. E5 y
packet. Otherwise,
discard the packet.
3. Determine whether any packet loss rate messages are generated by% E( f3 \5 z& y# S
receivers. If yes,
then re‐compute the sender’s transmission rate. Determine the new time& i5 d/ G9 ^. c& w8 X' C
when the
next packet will be generated. I.e, t+k, where k is the time interval
until the next packet
arrives.
4. Collect all required statistics.
}
In your simulation, collect the (a) queue length over time, (b)
average queue length, (c) average
end‐to‐end packet delay, and (d) Jain’s fairness index. Determine the# E o ^9 t! _" H: Z: d! k
effect of the following
factors: (i) increasing source and receiver pairs, (ii) varying N5 K4 W" q: J. a& W- x0 E# G( p
values, (iii) different packet loss
reporting periods, (iv) loss calculation methods, (v) load p, (vi)) w4 N0 j! b* o9 m) u
router’s transmission rate;
instead of one packet per‐tic, try k packets, and (vii) z
number of new flows9 E8 t% T/ R8 W
arriving at time t .
Do with sources# s7 h- Q: U" m* B- H- L- x
using a token/leaky bucket to control their transmission rate.
Another difference is that each source has an application that. w; b' A& @3 B) b4 y) h! j
generates bursty traffic, where
multiple packets arrive in consecutive time intervals.
To generate bursty traffic, use the following method:
In the diagram above, an application generates a packet when it is in) e8 \- ^" P1 H% e" E# W# A
the ON state. With
probability k, it will transition to the OFF state where it will remain idle. In
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=ON
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: F" u' C- O' _8 S
source (or all sources
simultaneously) such that congestion does not happen. Note, you must
experiment with
different k* ^' B! P5 g- R$ J
and z. o5 G' U* N$ s7 L! k1 X' \
values and determine) b4 B3 d- Y: E5 k$ g
their impact on congestion.
Reference
S. Floyd, M. Handley, J. Padhye,- \' U9 S# A& J& P3 y0 V4 }
and J. Widmer (2000) Equation-based Congestion Control for Unicast
Applications, ACM SIGCOMM, May,) F' I7 `' E+ j) E3 W
2000.
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