Question: 1. Explain under what crecumstances:

(a) Packets can get lost

(b) Packets may be delivered out of order

(c) Duplicate copies of a packet may be delivered

(d) Packets can be delayed for a long timekjj

2. Explain The role of:

(a) Round Trip Time (RTT) in Time Out (TO) calculation. Why estimation of RTT is not trivial?

(b) Explain The role of Address Resolution Protocol (ARP). What is its vulnerability?

(c) Explain The role of Domain Name System (DNS). What is its vulnerability?

3. The OSI model is inefficient; each layer must take the work of higher layers, add some result, and pass the work to lower layers. This process ends with the equivalent of a gift inside seven nested boxes, each one wrapped and sealed. Surely this wrapping (and unwrapping) is inefficient. Cite a security advantage of the layered approach.

4. TCP is a robust protocol: Sequencing and error correction are ensured, but there is a penalty in overhead (for example, if no re-sequencing or error correction is needed). UDP does not provide these services but is correspondingly simpler. Cite specific situations in which the lightweight UDP protocol could be acceptable, that is, when error correction or sequencing is not needed.