Data Link Control

Data Link Layer ProtocolsCategories:– Noiseless channels– Noisy channels

Data Link Layer Protocols• Noiseless channels– No requirement for error control (no noise, no

errors)

• Noisy channels– Requires error control

Noiseless Channel Protocols• Simplest Protocol– No flow control

• Stop and wait

Noiseless Simplest Protocol• No noise, so no error control required

• No flow control is required

The design of the simplest protocol with no flow or error control

1.Data Link Layer sender•Get the data from the Network Layer•Make the Data Link Layer Frame•Send the Frame to the Physical Layer

2.Data Link Layer Receiver•Receive the frame from the Physical Layer•Extract the data from the Frame•Deliver the data to the Network Layer

11.9

Flow diagram

Noiseless Stop & Wait Protocol• This protocol includes flow control.• Includes an acknowledgement frame.• No error control.

11.11

Design of Stop-and-Wait Protocol

Stop & Wait: Sender Side•Get the data from the Network layer•Make the Frame•Send Frame to the Physical Layer•Wait for an acknowledgement before sending the next frame

Stop & Wait: Receiver•Receive Frame from the Physical Layer•Extract data from the frame.•Deliver data to the Network Layer•Send an acknowledgement frame back to the sender.

11.13

Flow diagram

Noisy Channel Protocols• Stop & Wait ARQ <- start here• Go Back N ARQ• Selective Repeat ARQ

Stop & Wait ARQ Protocol• Stop & Wait ARQ– ARQ = automatic repeat request

• This protocol has flow control and error control.

Frame Sequence Numbers• The frames are numbered as the current

frame and the next frame. • Only one bit is required to number the frames.

Zero and one are the only frame numbers.

Design of the Stop-and-Wait ARQ Protocol

Flow diagram for Example

PipeliningWhat is the efficiency if fifteen 1000 bit frames

can be sent before waiting for an acknowledgement?

The efficiency is 75%.

THANK YOU