Question 1

a)      TCP uses a host-centric, feedback-based, window-based resource allocation model. How might TCP have been designed to use instead the following models?

(i) Host-centric, feedback-based, and rate-based.

(ii) Router-centric and feedback-based.

b)      Frequency on a copper cable range from 300Hz to 3300Hz. If the signal to noise ratio (S/N) is 40 db, find the capacity of the link in bits per second. If the capacity of the link is 60 kbs, what will be the S/N ratio in db? Show all the steps.

Question 2

a)     IP Packet Sniffing and IP Spoofing are two techniques used in denial of service attack. Clearly distinguish between these and suggest ways to alert managers to combat such potentially harmful techniques.

b)     Suppose most of the Internet used some form of geographical addressing, but that a large international organization has a single IP network address and routes its internal traffic over its own links.

        i.   Explain the routing inefficiency for the organization's inbound traffic inherent in this situation.

       ii.   Explain how the organization might solve this problem for outbound traffic.

     iii.   For your method above to work for inbound traffic, what would have to happen?

c)      Having ARP table entries time out after 10 to 15 minutes is an attempt at a reasonable compromise. Describe the problems that can occur if the timeout value is too small or too large.

Question 3

a)      Suppose we want to transmit the message, D=1010001101 and protect it from errors using the CRC polynomial, P=x⁵ + x⁴ + x² + 1.

(i)     How many bits should be used for the remainder, R?

(ii)    Use division method to determine the message that should be transmitted.

Show all the details.

(iii) Suppose the leftmost bit (MSB) of the message is inverted due to noise on the transmission link. What is the result of the receiver's CRC calculation? How does the receiver know that an error has occurred? Show all the details.

b)     Why is collision detection more complex in wireless networks than in wired networks such as Ethernet? How can hidden terminals be detected in 802.11 networks?

c)     Suppose a bridge has two of its ports on the same network. How might the bridge detect and correct this?