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
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
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
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
21.
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