The document discusses the data link layer of the OSI model. It has two sublayers: the Media Access Control (MAC) sublayer and the Logical Link Control (LLC) sublayer. The data link layer is responsible for error-free transmission over the physical layer through functions like framing, error control using techniques like parity checking and cyclic redundancy checks, flow control using methods like stop-and-wait and sliding windows, and physical addressing using protocols like Ethernet, HDLC, Frame Relay, and devices like bridges and switches.

1. PRESENTED BY:-> SHASHANK TIWARI
1238210034
CS 3RD YEAR

2. CONTENT
 OSI model
 Data Link Layer
 Sub-layers
 Functions of data link layer
 Devices and protocols

3. OSI MODEL

4. DATA LINK LAYER
“Manages the flow of data over the physical media”
Working-
 Responsible for error-free transmission
over the physical layer
 Assures error-free data submission to
the Network Layer

6. SUB LAYERS OF DATA LINK LAYER

7. 1> MEDIA ACCESS CONTROL
It is lower layer
Addresses the frame
Marks the beginning and ending of the frame
Access control

8. 1-> LOGICAL LINK CONTROL
 It is upper layer
 Frames the network layer packet
 Identifies the network layer protocol
 Error detection
 It prepares data for transmission

9. FUNCTIONS OF DATA LINK LAYER
Framing
Error control
Access control
Flow control
Physical add.

10. FRAMING
 IT USES FOR RECEIVING ERROR FREE MASSAGES
 LARGE MASSAGES MAY BE CORRUPTED BY NOISE OR OTHER
“BREAKDOWN A STREAM OF BIT
INTO SMALLER DIGESTIBLE CHUNKS
CALLED FRAMES”
WHY IT COMES INTO EXISTENCE

11.  FORMAT

12. METHODS
1) Character count
2) Byte stuffing
3) Bit stuffing

13. 1-> CHARACTER COUNT METHOD
 FIRST BIT DEFINES THE FRAME SIZE
 IT COULD NOT DEFINES STARTING OF FRAME WHEN NOISE OCCURS

14. 2-> BYTE STUFFING

15. 3-> BIT STUFFING
 ADD ‘0’ AFTER 5 CONSECUTIVE 1’S AT SENDER SIDE AND
REMOVAL OF IT AT RECEIVER SIDE
 NOT GOOD EFFICIENT FOR LONG MASSAGES

16. ERROR DETECTION
 errors caused by signal attenuation, noise.
 receiver detects presence of errors
 signals sender for retransmission or drops
frame
 Error correction
 receiver identifies and corrects bit error(s) without
resorting to retransmission

17. METHODS USING IN ERROR CONTROL
 PARITY CHECKING
 CYCLE REDUNDANCY CHECK

18.  PARITY CHECKING (USING HAMMING CODE)

19.  CYCLE REDUNDANCY CHECK
a. It is based on binary
division
b. Obtained remainder
is CRC
c. Code word =data +
CRC code

20.  FLOW CONTROL
“FLOW CONTROL REFERS TO A SET OF PROCEDURES USED TO
RESTRICT THE AMOUNT OF DATA THAT THE SENDER CAN SEND
BEFORE WAITING FOR ACKNOWLEDGMENT”
 Manages data flow rate over slow receiver device than sender
 Receiving device has a limited speed at which it can process incoming
data
 Receiver has a block of memory , called a BUFFER
 Buffer stores incoming data until they processed
 Incoming data must be checked before used

22. 1) STOP-AND-WAIT FLOW CONTROL
Timeout
Timeout
Frame lost A
retransmits
ACK lost A
retransmits
A B
B discards
duplicate
frame

23. 2) SLIDING-WINDOW
 In sliding window method multiple
frames are sent by sender at a time
before needing an
acknowledgment
 Multiple frames sent by source are
acknowledged by receiver using a
single ack frame
 Acknowledge by receiver at any
point even when window is not full
on receiver side

24. ACCESS CONTROL

26. PHYSICAL ADDRESSING

27.  PROTOCOLS
PPP(POINT –TO-POINT PROTOCOL)
FRAME RELAY
ETHERNET
HDLC(HIGH LEVEL DATA LINK CONTROL)

28. FRAME RELAY
ETHERNET

30.  DEVICES
Bridge

31. SWITCH

32. ETHERNET