Assignment #1- Transport Layer

1. What is the one's complement of 01011011 00110001?

2. Is it possible for an application to have reliable data transfer while using UDP?
Explain your answer.

3. a) What service or function does the receive window help perform?
b) What are the dimensions (units) of the receive window? (NOT the size of the field, which is 16 bits; what units are the number in that field?)
c) Why do we need sequence numbers in TCP?
d) What has replaced the NAK in TCP?

4. a) In a finite state machine (FSM) diagram, each transition arc is labeled. In that label, what is the meaning of the text above the horizontal line?
b) What is the meaning of the text below the horizontal line?

5. In the lecture notes we considered a situation where we're sending data from NY to LA one packet at a time, and saw very low utilization efficiency. Using pipelining, how many packets (n) would have to be in the window in order to get an 80% utilization of the connection? Assume each packet is 1500 bytes, including headers and data. The RTT is exactly 20 ms, and the link operates at 1 Gbps.

6. Imagine sending a large file (L bytes) from Host A to Host B. Assume the MSS is 1460 B.
a) What is the maximum value of L so that TCP sequence numbers are not reused?
b) How long would it take to transfer the file, assuming a total of 66 bytes of transport, network, and link layer headers per frame, over a 3 Mbps link? Ignore flow and congestion control limits for this problem.

7. See the SampleRTT data below.
a) Calculate EstimatedRTT, DevRTT, and TimeoutInterval for each sample. Use α=0.125 for calculating EstimatedRTT, β=0.25 for DevRTT, and the initial EstimatedRTT and DevRTT given in the table below. Show the results. Estimated RTT(new) = 0.875*Estimated RTT(old) + 0.125*Sample RTT
DevRTT(new) = 0.75*DevRTT(old) + 0.25*abs(SampleRTT-EstimatedRTT)
Careful for the absolute value (abs)!
TimeoutInterval = EstimatedRTT + 4*DevRTT
b) Make & show one scatter plot of TimeoutInterval versus sample number, and SampleRTT versus sample number.
c) How does the magnitude of change (e.g. range) in TimeoutInterval compare to the magnitude of change in SampleRTT data? Why are they different or not?

8. a) What mode is being used when the congestion window drops to 1 packet (MSS), and start doubling after that?
b) What mode is being used when the congestion window increases by one packet each RTT?
c) What event causes the congestion window size to be cut in half? Be specific.
d) What is the name of the mode described in 8.c)?

9. Why is the change in the congestion window (CongWin) different for different types of loss events? (Not how is it different, but why.)

10. How many networked processes could theoretically be running on a host at once?

Assignment #4 - Network & Link Layers

1. What is the numeric value of the protocol field in IPv4 for an ICMP packet?

2. What router performance or design characteristic is needed to prevent packet loss from input port buffers? (Other than infinite buffer size!)

3. a) How many IP addresses does an 8-port router have?
b) How many IP addresses does an 8-port hub have?

4. If an IPv4 address prefix uses 23 bits, how many hosts could be behind that subnet?

5. Suppose a packet is going on the Internet from Host F to Host G, and there are four routers it must cross between them.
a) How many network interfaces will the packet travel through?
b) How many routing tables will be consulted?

6. Suppose your application generates 60 B messages every 30 milliseconds. The messages are packaged in a TCP segment and an IPv6 datagram. What percent of the resulting datagram will be the message contents? Assume minimum header sizes, and the percent overhead is 100*(message contents) / (message contents + headers).

7. a) How does the recipient of a datagram know which transport protocol gets it?
b) How does the recipient of a segment know which application gets it?

8. a) What is the loopback address in IPv6? (i.e. 127.0.0.1 was it for IPv4)
b) What are the reserved addresses in IPv6? (e.g. 10.0.0.0/8 was one in IPv4)

9. Compare and contrast the advertisements used by RIP and OSPF. What routers in the network (autonomous system) get them? How often are they sent?

10. Convert the binary IPv4 addresses in Table 1 (below) to CIDR notation. Each prefix is underlined. Give the completed forwarding table and don't forget the last entry.

11. Suppose datagrams are limited to 1500 B including an IPv4 header. Assume a TCP header is also used in each datagram. How many datagrams are needed to send a 12 GB movie? Assume minimum header sizes, and round off carefully.

12. How is forwarding different in MPLS from a datagram network?

13. How does TTL in an ARP table differ from TTL in IPv4?

14. When byte stuffing is done in PPP, what is being stuffed into the message that wasn't part of the original message? Be specific.

15. What is the maximum link length for 1000BaseT Ethernet, in order to have an efficiency of 80%? Use the formulas from earlier in the course for propagation and transmission delays. Use 3 x 108 m/s for propagation speed. Assume the frame size is 1500 B. Watch out for bit/byte conversions!

16. a) In an Ethernet frame (NOT an IP datagram), what value is the protocol field for an IPv6 datagram? Notice this is asking for the Ethernet type code, NOT the IP Protocol field value. Cite the source used.
b) What is the Ethernet frame protocol field value for a unicast MPLS packet?