1. Data Communications - Data Link Control Protocols Key Points

3. Model of Frame Transmission (mengelirukan)

6. Bit length of link B=R x d/V B = length of the link in bits , this is the number of bits present on the link at an instance in time when a stream of bits fully occupies the link R = data rate of the link, in bps d = length, or distance of the link in meter V = velocity of propagation, in m/s Propagation delay a = B/L L = number of bits in the frame (length of the frame in bits)

7. Stop and Wait Link Utilization length of link > length of frame (1 frame/time =Inefficient) length of link < length of frame

8. Example

10. Sliding Window Diagram- Sender Assume using 2 3 = 8,no. = 0,1,2,3,4,5,6,7,0… Each time a frame is sent  window shrink (# of frames may be transmitted) Each time ACK is received  window grows (to end side (total of 7 frames)) acknowledged Sent but not yet acknowledged

11. Sliding Window Diagram-receiver ACK must includes F0 (RR 0) “ Receiver has received all frames up to F7 and is ready to receive F0.” Each time a frame is received  window shrink (# of frames available) Each time ACK is sent  window grows (to end side (total of 7 frames)) *RR = Ready Receive

12. Example Sliding Window A may transmits 7 frames, beginning with F0 A transmits F0,F1,F2 (no ACK) A shrunk its window to 4 frames, maintains copy of F0,F1,F2 A may transmits 4 frames, beginning with F3 B transmits RR 3 frames (received frames up to F2, ready to receive 7 more frames starts from F3) B grows back to 7 frames, starts from F3 A discards copy of F0,F1,F2 A transmits F3,F4,F5,F6 B returns RR 4 (ACK F3, allows A transmits from F4 – F2) By the time RR 4 reaches A, A already transmitted F4,F5,F6,So A can only transmits 4 frames starts from F7. B may receives 7 frames, beginning with F0 B shrunk its window to 4 frames (available frames)

17. Stop and Wait - Diagram # of frame : Labeled alternately 0 and 1 ACK0 : Receiver received frame 1, Ready to receive frame 0. ACK1 : Receiver received frame 0, Ready to receive frame 1.

25. Go Back N - Diagram RR 2: REJ 4: RR(P bit=1)

27. Selective Reject - Diagram

35. Frame Structure HDLC uses synchronous transmission (frames) header trailer END!!

38. Sliding Window Diagram