Midterm Solutions ECE358

Fall 2024

Question 1

Name and explain all the fields present in an Ethernet frame (11 points).

• Preamble/flag:
  1. to synchronize transmitter and receiver.
  2. to indicate beginning and end of frames.
• Destination/source MAC address : MAC address is 48 bytes. Those are the addresses of the local source and destination (i.e., in the local network).
• Type : to indicate the higher layer protocol, e.g., IP or ARP
• CRC: 4 bytes . If an error is detected, the frame is dropped. No retransmission:
• Payload: datagram

Notes:

• There is a minimum frame size, hence padding might be necessary
• There is a maximum transfer unit of 1500 Bytes, i.e., the datagram cannot be larger than 1500 bytes.

Question 2

What are the five layers in the Internet protocol stack? What are the principal responsibilities for each of these layers? Please give at least one example of a protocol at each layer (except the lowest one) (11 points)

• L5: application: supporting network applications, end to end, message is the data unit
  • HTTP, IMAP, SMTP, DNS