Assignment 3
B.Tech. (CS/IT)-V Semester
Computer Network (TCS-502/TIT-502)
Last Date for Submission: 26/11/2015
1. Give three examples of protocol parameters that might be negotiated when a connection
is set up.
2. If an application layer packet size is 5 Bytes long, how big is the corresponding Ethernet
frame? Assume that the application uses TCP at Transport layer and IP v4 at Network
layer.
3. A computer on a 6-Mbps network is regulated by a token bucket. The token bucket is
filled at a rate of 1 Mbps. It is initially filled to capacity with 8 megabits. How long can
the computer, transmit at the full 6 Mbps?
4. Is TCP checksum necessary or could TCP allow IP to checksum the data.
5. Describe four different scenarios when an IP router would drop packets that arrive on one
of its interfaces.
6. Datagram subnets route each packet as a separate unit, independent of all others. Virtualcircuit subnets do not have to do this, since each data packet follows a predetermined
route. Does this observation mean that virtual-circuit subnets do not need the capability to
route isolated packets from an arbitrary source to an arbitrary destination? Explain your
answer.
7. Suppose two TCP connections are present over some bottleneck link of rate R bps. Both
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 the
TCP would like to give to each of the connections?
8. Consider the following design problem concerning implementation of virtual-circuit
service. If virtual circuits are used internally to the subnet, each data packet must have a
3-byte header and each router must tie up 8 bytes of storage for circuit identification. If
datagrams are used internally, 15-byte headers are needed, but no router table space is
required. Transmission capacity costs 1 cent per 106 bytes, per hop. Very fast router
memory can be purchased for 1 cent per byte and is depreciated over two years, assuming
a 40-hour business week. The statistically average session runs for 1000 sec, in which
time 200 packets are transmitted. The mean packet requires four hops. Which
implementation is cheaper, and by how much?
9. “A datagram cannot be larger than the MTU of a network over which it is sent.” Is the
statement true or false? Explain with the help of a suitable example.
10. Explain Three-Way Handshake Mechanism used by TCP to terminate a Session reliably.
11. The byte-counting variant of the leaky bucket algorithm is used in a particular system.
The rule is that one 1024-byte packet, or two 512-byte packets, etc., may be sent on each
tick. Give a serious restriction of this system that was not mentioned in the text.
12. Suppose nodes A, B, and C each attach to the same broadcast LAN (through their
adapters). If A sends thousands of frames to B with each frame addressed to the LAN
address of B, will C's adapter process these frames? If so, will C's adapter pass the IP
datagram’s in these frames to C (i.e., the adapter's parent node)? How will your answers
change if A sends frames with the LAN broadcast address?
13. A large number of consecutive IP address are available starting at 192.16.0.0. Suppose
that four organizations, A, B, C, and D, request 4000, 2000, 500, 1000 and 7000
addresses, respectively, and in that order. For each of these, give the first IP address
assigned, the last IP address assigned, and the mask in the w.x.y.z/s notation.
14. Suppose there are three routers between a source host and destination host. Ignore
fragmentation. An IP datagram sent from the source host to the destination host will
travel over how many interfaces? How many forwarding table will be indexed to move
the datagram from the source to destination?
15. A router has just received the following new IP addresses: 57.6.96.0/21, 57.6.104.0/21,
57.6.112.0/21, and 57.6.120.0/21. If all of them use the same outgoing line, can they be
aggregated? If so, to what? If not, why not?
16. How could you change the IP datagram format to support high-speed packet switching at
router? Considering the fact that a router must recompute a header checksum after
decrementing the time-to-live field.
17. Consider sending a 2400-byte datagram into a link that has an MTU of 700 bytes.
Suppose the original datagram is stamped with the identification number 422. How many
fragments are generated? What are the values in the various fields in the IP datagram(s)
generated related to fragmentation?
18. Most IP datagram reassembly algorithms have a timer to avoid having a lost fragment tie
up reassembly buffers forever. Suppose that a datagram is fragmented into four
fragments. The first three fragments arrive, but the last one is delayed. Eventually, the
timer goes off and the three fragments in the receiver's memory are discarded. A little
later, the last fragment stumbles in. What should be done with it?
19. What is the fastest line speed at which a host can blast out 1500-byte TCP payloads with
a 120-sec maximum packet lifetime without having the sequence numbers wrap around?
Take TCP, IP, and Ethernet overhead into consideration. Assume that Ethernet frames
may be sent continuously.
20. When the IPv6 protocol is introduced, does the ARP protocol have to be changed? If so,
are the changes conceptual or technical?
21. Suppose Host A sends two TCP segments back to back to Host B over a TCP connection.
The first segment has sequence 100; the second segment has sequence number 1025.
a. How much data is there in the first segment?
b. Suppose that the first segment is lost but the second segment arrives at B. In the
acknowledgement that Host B send to Host A, what will be the acknowledgement
number?
22. Consider the effect of using slow start on a line with a 10-msec round-trip time and no
congestion. The receive window is 24 KB and the maximum segment size is 2 KB. How
long does it take before the first full window can be sent?
23. Explain with the help of diagram the TCP connection management and Window
management policy using proper flags.
24. Consider a TCP connection between Host A and Host B. Suppose that the TCP segments
traveling from Host A to Host B have source port number x and destination port number
y. What are the source and destination port numbers for the segments traveling from Host
B to Host A?
25. Describe why an application developer might choose to run an application over UDP
rather than TCP.