2(a)

RTT: 

(i) Estimated RTT = alpha * EstRTT + (1 - alpha) * SampleRTT

SampleRTT = ACKTime - SendTime

(ii) Timeout = EstRTT + DevRTT 

(iii) SampleRTT can be wrong, an outlier (hence, we have the exp weight learning)

(iv) Drop packets which deviate too much

Congestion Window Size:

(i) Actively change according to whether we are at slow start, fast retransmitting, timeout.

Increase congestion window by 1 every RTT (for AIMD) 

Increase congestion window by 1 every ACK (for Slow Start)

(ii) Used to determine how many packet can be sent

(iii) ?

(iv) ? 

2(b) 

L3 = Network (IP)

L4 = Transport (TCP)

Drop earlier packets (forcing retransmissions of later packets)

Drop DNS packets

Drop initial SYN packets

Any other ideas?

4(a) [Doubt!] When does "Ethernet spanning tree loop" happen? Is it when the protocol fails? Or when some router misbehaves? Or is some non-trivial interesting reason as to when this happens?