# CSC640 Homework Set 6 - Fall 2001

### Due: Tuesday, November 13

In the following 2 questions, assume a 1 km cable with signal propagation speed 200 m/µsec.

1. What is the minimum frame size of a hypothetical 1000 Mbps CSMA/CD LAN?
Hint: make sure that competing frame sources both "see" the collision.

2. What is the efficiency of the link in the preceding question with just 2 stations operating. Each station transmits with probability 0.2 in a slot. Assume piggybacked acknowledgements, the minimum frame size from the previous question and neglect overhead due to frame control bits.

Hint:
Efficiency = DT/(DT + 2 × tau × (1/A - 1))
Where:
A - The probability of successful transmission
DT - Packet length in seconds
tau - Cable length in seconds

3. 2 network stations are separated by 4 hops (links between nodes). Data rate is 9600 bps, packets are 1024 bits, including 16 bits of overhead. Propagation delay is 0.001 seconds per hop. Find the Total Delay (including all 1-way propagation, transmission and forwarding delays) for a 3200-bit message using the network as a Packet Switched network.

4. For the network in question 3, find the total delay for the same message using the network as a Virtual Circuit network with call setup time of 0.2 seconds. Assume that bits are transferred individually among nodes (cut-through switching).