ECE6609: BROADBAND NETWORKING
SPRING 2005
HOMEWORK II
GIVEN: FEBRUARY 25, 2005
DUE: MARCH 13 (SUNDAY), 2005 (11:59 pm)
Video Students --> Add + 2 WEEKS
SUBMISSION INSTRUCTIONS:
(SUBMIT ONLY ON-LINE FILE (as a .DOC FILE OR TEXT FILE) to
"" BEFORE MIDNIGHT. PLEASE PUT THE COURSE NUMBER IN THE SUBJECT LINE. Also, please include your name inside the email.)
(NO HARD COPY WILL BE ACCEPTED!!)
Dr. Ian F. Akyildiz,
Ken Byers Distinguished Chair Professor
Broadband and Wireless Networking Laboratory
School of Electrical and Computer Engineering
Georgia Institute of Technology
Atlanta, GA 30332
Tel.: 404-894-5141; Fax: 404-894-7883; E_Mail:
QUESTION 1:
A 1500-byte user-PDU is transported over AAL3/4 in a single CPS-PDU.
a) How many additional bytes are introduced by CPS?
b) How many SAR-PDUs are required to carry the resulting CPS-PDU?
c) How many additional bytes are introduced by the SAR in each SAR-PDU?
d) What is the maximum and minimum useful payload in each ATM cell that carries the resulting SAR-PDUs (i.e., the maximum and minimum of the number of bytes belonging to the original user-PDU)?
QUESTION 2:
A 1500 byte user-PDU is transported over AAL5.
a) How many bytes of padding will be added?
b) How many cells are required to carry the resulting CPS-PDU?
c) What is the total overhead (i.e., additional bytes) associated with this user-PDU?
QUESTION 3:
Consider an on/off source whose off period is constant and equals to 5 ms. During the on period, the source transmits at the rate of 1Mbps. The maximum length of the on period is 6 ms. Calculate the following:
i. What is the PCR of the source?
ii. Assuming a 10 ms period, calculate its SCR.
iii. What is the MBS (maximum burst size) of the source?
iv. Consider that the source starts its transmission at t=0 sec and remains on for the maximum on period. i.e., 6 ms. Determine the time when the first 10 packets are generated by each source (assume that each packet consists of 48 bytes of data and 5 bytes of ATM header). Assume that the time required to create a packet is equal to the time the source require to generate data required to fill one packet, i.e., the time required to add the header is negligible.
v. Consider that GCRA (I, L) algorithm, where I = 600 µ sec and L = 1000 µ sec is used for traffic policing for the above scenario (part (iv)). Create a table as in lecture notes and show which of the cells will be confirmed/non-conformed and their transmission time (if confirmed) from the sources. Show your calculation till the first six confirmed cells the source.
QUESTION 4:
Suppose that an ATM traffic stream contains cells of two priorities, that is, high priority cells with CLP=0 in the headers and low priority cells with CLP=1. Suppose we wish to police the PCR and SCR of the combined CLP=0+1 traffic. Give an arrangement of two leaky buckets to do this policing. Nonconforming cells are dropped.
QUESTION 5:
Consider the ATM network of Figure 1 with two switches SW1 and SW2 interconnected by a link of capacity 1 million cells/sec and delay 2 µsec, and two senders A and B. The link from SW2 to the rest of the network also has capacity of 1 million cells/sec. Assume that the link from the sources (A and B) and the switch to which they are connected do not introduce any delay. Also consider that the allocation of A and B at SW2 is 50 % each. Consider that at time t=0, a large bursts of cells are generated by A such that the arrival time of its ith cell at SW1 is i-1 µ sec, i.e., the arrival time of the first, second, third, fourth etc cells are t=0, t=1 µ sec, t= 2 µ sec, t= 3 µ sec respectively. After 5 µ sec, B becomes active and generates a large burst of cells such that the arrival time of its jth cell at SW2 is 5+ j-1 µ sec, i.e., the arrival time of the first, second, third, fourth etc cells are t=5, t=6 µ sec, t= 7 µ sec, t= 8 µ sec respectively.
i. Determine the time when the 5th cell of A and 4th cell of B will leave the switch SW2 assuming that the Virtual Clock algorithm is used to schedule transmissions at SW1 and SW2 (HINT: take into account the delay in the link from SW1 and SW2 to calculate the arrival time of cells from A at SW2).
ii. Now assume that Weighted Fair Queuing is used instead at SW1 and SW2. Determine the time at which the 5th cell of A and 4th cell of B will leave SW2 (HINT: take into account the delay in the link from SW1 and SW2 to calculate the arrival time of cells from A at SW2).
------OPTIONAL (BONUS QUESTION ------
QUESTION 6 (Leaky Bucket (LB) Simulation)
Simulate LB policer for the traffic sources described in lecture note for the following two cases:
i) Fixed bucket size at 1000. Calculate the mean cell rate of a single ON-OFF source. Call this rate as nominal rate. Find the drop rate in the policer and the mean rate of the traffic allowed into the network while changing the source mean rate from 0.8 to 1.5 times the nominal rate.
(HINT: You can change the traffic rate of an ON-OFF source by changing the mean ON duration while keeping the OFF duration constant.)
Repeat this for Poisson traffic source. (Use the same nominal rate as above).
ii)) Assume the mean service rate equal to the nominal rate. Modify the bucket size from 1000 to 10000, and find the cell loss rate for two types of input traffic sources.
(In this problem, token generation (policed cell) rate is equal to the nominal cell rate of the sources)
------
THE FOLLOWING PROCEDURE WILL HELP YOU FOR RANDOM NUMBER GENERATION DUE TO CERTAIN DISTRIBUTIONS.
#include <stdio.h>
#include <math.h>
extern double drand48();
extern void exit();
/* -- Geometric Random Variate Generation ------*/
long Geom(x)
double x;
{
int y;
if (x<=0) {printf("Geom. error"); exit(-1);}
y=floor(log(drand48())/log(x/(1+x)));
if (y==0) y++;
return(y);
}
/* -- Exponential Random Variate Generation ------*/
double
Exponential(x)
double x;
{
return(-x*log(drand48()));
}