Describe how packet loss can occur at input and outputs of a router.

Describe why an application developer might choose to run over TCP rather than UDP.
3.2 Suppose host A is sending host B a large file over a TCP connection. If the acknowledge number for a segment of this connection is y, then the acknowledge number for the subsequent segment will necessarily be y+ 1. Is this true or false? Why?
3.3 Suppose 5 TCP connections are present over some bottleneck link of rate X bps. All connections have a huge file to send (in the same direction over the bottleneck link). The transmissions of the files start at the same time. What is the transmission rate that TCP would like to give to each of the connections?
3.4 How to identify a UDP socket? How to identify a TCP socket? Are these data fields same? Why?
3.5 UDP and TCP use 1s complement for their checksums. Suppose you have the following three 8-bit words: 11010101, 01111000, 10001010. What is the 1s complement of the sum of these words? Show all work. Why UDP takes the 1s complement of the sum, that is, why not just use the sum?
3.6 Suppose Client A initiates a SMTP session with server S. Provide possible source and destination port numbers for:
a. The segment sent from S to A.
b. The segment sent from A to S.
3.7 Compare two pipelining protocols shown in the textbook go-back-N and selective repeat.
3.8 In our textbook, protocol rdt 3.0 shows a data transfer protocols that uses only acknowledges.
As an alternative, consider a reliable data transfer protocol that uses negative acknowledgements.
Suppose the sender sends data only infrequently. Will a NAK-only protocol be preferable to
protocol that uses ACKs? Why? Suppose the sender has a lot of data to send and the end-to-end
connection experiences few losses. In the second case, would a NAK-only protocol be preferable
to a protocol that uses ACKs? Why?
3.9 Let us assume that the roundtrip delay between sender and receiver is constant and known to
the sender. Would a timer still be necessary in protocol rdt 3.0, assuming that packets can be
lost? Please explain.
3.10 Briefly discuss the basic mechanisms adopted by TCP congestion control.
Chapter 4 40 points
4.1 Describe two major network-layer functions in a datagram network.
4.2 Describe how packet loss can occur at input and outputs of a router. Is it possible to eliminate
packet loss at these ports? If so, how? If not, please explain.
4.3 Suppose an application generates chunks of 960 bytes of data every 20 msec, and each chunk
gets encapsulated in a TCP segment and then an IP datagram. What percentage of each datagram
will be overhead, and what percentage will be application data?
4.4 Consider a datagram network using 8-bit host addresses. Suppose a router uses longest prefix
matching and has the following forwarding table:
Prefix Match Interface
00 0
001 1
otherwise 2
For each of the 3 interfaces, give the associated range of destination host addresses and the
number of addresses in the range.
4.5 Consider the following network. With the indicated link costs, use Dijkstras shortest-path
algorithm to compute the shortest path from x to all network nodes. Show how the algorithm
works by computing a table similar to the textbook example. In cases when several candidate
nodes have the same minimal costs, choose a node according to non-decreasing alphabetical
4 2
1 3
4.6 Consider the count-to-infinity problem in the distance vector routing. Will the problem occur
if we decrease the cost of a link? Why?
4.7 IPv6 adopts a fixed-length 40 byte IP header. What is the major advantage of this approach
compared to that in IPv4?
4.8 Suppose an ISP owns the block of addresses of the form Suppose it wants
to create four subnets from this block, with each block having the same number of IP addresses.
What are the prefixes (of form a.b.c.d/x) for the four subnets?
4.9 Why are different inter-AS and intra-AS protocols used in the Internet?
Part 3. Practical assignment 20 points
For this assignment, you can choose to use either Java or Python.
Please submit the following items in a ZIP file.
1) Source code;
2) Instructions on how to install and run your program;
3) A brief design document explaining your solution.
Note: I shall not provide remedial help concerning coding problems that you might have.
Students are responsible for the setup of their own coding environment. Each student is also
expected to debug their code. In addition most SMTP servers (e.g., NSUs email server at require authentication before sending messages. You can either hard-code the
email accounts authentication information into the source code, or create a dummy or a free
SMTP server (shown as follows) to test your program.