3 - D.L.L Protocols

Question 1

D.L.L Services (3)

Answer 1

• bundling groups of bits into frames for P.L
• throttling the flow of frames between sender and receiver
• detecting and correcting “higher-level” transmission errors

Question 2

The three levels of D.L.L Complexity

Answer 2

• Simplex Connectionless
• Half-Duplex Connectionless
• Full-Duplex Connection-orientated

Question 3

Used to detect frame corruption

Answer 3

Checksums

Question 4

Detecting Frame Loss

Answer 4

Use ACK

Question 5

Benefits of Network Simulations (3)

Answer 5

• different aspects can be controlled and examined on very dynamic networks
• need to test for errors
• centralised control of a network

Question 6

StopandWait Protocol

Answer 6

• Sends packet and waits for ACK to be received before sending the next one off

Question 7

Frame Pipelining

Answer 7

Sender transmits many frames until the medium is full and then wait for ACK indicating that frames have been received correctly,
“permit multiple outstanding frames

Question 8

Go-back-N Protocol

Answer 8

Requires receiver to simply discard all frames after bad one, corresponding to window size of 1

Question 9

Selective Repeat Protocol

Answer 9

Receiver buffers all frames and waits for the bad frame to be retransmitted

Question 10

Problem with selective repeat

Answer 10

Disaster when the ACK frame is sent from receiver but not received by transmitted
Soln - make window sizes half the size of the max seq number