University of Kansas

Electrical Engineering & Computer Science

EECS 563 - Homework Assignment

Homework 7

1. A voice over IP system uses the following parameters:

Voice sample rate = 8000 samples/sec.
3 bits/sample
20 ms/voice packet
3 Overhead bytes/packet

a) What is the data rate for this VoIP packet stream?

b) The network delay varies between 25 ms and 125 ms. How many packets does the jitter buffer have to store to insure no packet loss due to network delay variation?

2. A sequence of fixed-length packets carrying digital audio signal is transmitted over a packet network. A packet
is produced every 10 ms. The transfer delays incurred by the first 5 packets are 45 ms, 50 ms, 53 ms, 46 ms, 30 ms.

a) Sketch the sequence of packet transmission times and packet arrival times.

b) Find the delay that is inserted at the receiver (by the jitter buffer) to produce a fixed end-to-end delay of 75 ms.

3. Consider an application in which information that is generated at a constant rate is transferred over a packet
network so timing recovery is required at the receiver.

a) As the maximum acceptable delay increases and the size of the jitter buffer in Bytes increases or decreases?

b) What happens if the jitter buffer is too small?

4. There are 200 cell phones in range of a base station, the cell phones are busy 5% of the time. How much traffic in Erlangs does the base station have to handle?

5. A smart phone is connected to network with a peak download speed of 10 Mb/s. The user is connected to a video service site for 3 min. While browsing, the site send the user 200 KB of information; using that information the user selects and downloads a 10 MB video file.

a) What is the average download rate during this session?

b) What is the peak down load rate?

c) What is the burstyness of this session?

6. What parameters can the designer trade-off to meet a delay constraint for aVoIP system?

7. A set of 50 users generate traffic with the following characterstices:

Average packet length = 1500B Arrival rate = 20 packets/sec. This traffic is input to a statistical multiplexer with a link capacity of C=24 Mb/s

a) What is the input rate in b/s to the statistical multiplexer?

b) What is the load on the statistical multiplexer?



Victor S. Frost, frost@eecs.ku.edu and some problems from Main Text: Communication Networks: Fundamentals Concepts and
Key Architectures, A. Leon-Garcia and I. Widjaja (Second edition)