CS 414 Assignment 5 Solutions
3 points per answer for 3a-g, 10 points per answer for 4a-c, 5a-b, 12 points for 2 and 14
points for 1 (100 max). Due Wednesday April 05.
1. In TCP slow start, at ﬁrst the sending host will double the number of packets it sends every time
it receives all acknowledgements for the previous packets it sent. In other words, the sending host
will send one packet, receive the ACK for that packet, send two packets, receive the ACKs for those
packets, send four packets, and so on. This exponential growth continues until there is a packet loss.
(Subsequent to this loss, the sending host will increase the number of packets linearly, not exponen-
tially.) Consider the scenario where a host H1 has two connections, one to a host HL on the same LAN,
and one to a host HW thousands of miles away. The one-way latency to host HL is 1 micro-second,
the one-way latency to host HW is 50 milli-seconds and the round-trip latency is twice the one-way
latency. Assuming no packet losses, and assuming near-inﬁnite bandwidth and processing speeds at
all hosts, how long does it take to send the ﬁrst 1023 packets to each host?
Since there is no packet loss, the number of packets sent in a window grows exponentially.
So it takes 10 send-ACK cycles to send the 1023 packets (1,ACK,2,ACK,4,ACK,.
..,512,ACK and TCP
send is not complete unless ACK is received). This comes to 20 micro-seconds for HL and 1 second for
2. The operating system uses segmentation with paging. The virtual address is 32-bits long. Consider
the scenario where a process has 6 segments with bases and limits given below:
Limit (base 16)