1. CSE 3231 – Computer Networks – Midterm Exam – Spring 2021
Submit your answers in Canvas before midnight on Friday,
March 5, 2021.
1. One of the methods used for framing in the Data Link layer
uses special ASCII codes called sentinel codes
to indicate the beginning and end of the data in a frame. Explain
why this can cause a problem when
transmitting binary data and describe one technique for
avoiding this problem when using sentinel codes.
2. Explain the hidden node problem for wireless links and
describe how IEEE 802.11 avoids it.
3. Explain how the Stop-and-Wait protocol in the Data Link
layer makes sure that each frame it transmits is
delivered before it sends the next frame and describe a
disadvantage of using that protocol.
4. Explain how Network Address Translation (NAT) allows
multiple nodes within a LAN to share one
Internet-facing IP address when interacting with computers
outside the LAN.
5. a) Explain how the Random Early Detection approach reduces
congestion in a network.
b) In your opinion, is Random Early Detection more fair or less

2. fair than the Traffic Throttling approach?
(To receive credit for this part, you must give a good reason to
back up your opinion.)
6. Explain the difference between virtual circuit switching and
the datagram, or connectionless, approach for
packet delivery in a network and include at least one advantage
and one disadvantage of each approach.
7. Describe how fragmentation is used to deal with differences
in size of the Maximum Transmission Unit
(MTU) as a packet travels from sender to receiver. Make sure
that you mention where a packet is
fragmented and where it is re-assembled.
8. Describe the purpose of the following fields in an IP packet
header. If the field has a default value make
sure that it is included in your description.
a. Version
b. Flags/Offset
c. Checksum
d. Protocol
9. a) Explain how one node uses the Address Resolution
Protocol (ARP) to get the MAC address of another
node in the same LAN.
b) Explain how a node uses the Dynamic Host Configuration
Protocol (DHCP) to get an IP address.
10. Using the network diagram below, produce the tables
described in part a) and part b).

3. a) Create distance tables for Node D using the distance vector
algorithm below:
b) Create routing tables for Node D a using the distance tables
from part a).
In your table, specify the next hop for the route and the total
cost along that path.