Ppt

2. ELEMENTARY DATA LINK
PROTOCOLS

3. Protocols in the data link layer are designed so that this
layer can perform its basic functions: framing, error
control and flow control. Framing is the process of
dividing bit - streams from physical layer into data
frames whose size ranges from a few hundred to a few
thousand bytes

4. UNRESTRICTED SIMPLEX PROTOCOL
Data transmission is only done in one direction.
Transmission (Tx) and reception (Rx) are always available;
processing time is irrelevant. This protocol has an infinite buffer
space and no faults, meaning no damaged or lost frames.
The graphic below depicts the Unrestricted Simplex

6. A SimplexStop-and-Wait Protocol
for an Error-FreeChannel

7. Stop – and – Wait protocol is data link layer protocol for
transmission of frames over noiseless channels. It provides
unidirectional data transmission with flow control facilities but
without error control facilities. This protocol takes into account the
fact that the receiver has a finite processing speed.

8. Working of Stop and Wait Protocol
The sender sends the packet, referred to as a data packet if
there is a sender and a receiver. After receiving a data
packet, the receiver sends an acknowledgement. Without
receiving acknowledgement for the first packet, the sender
won't send the second packet.

9. Primitives Of Stop-and-Wait Protocol
•Sender Side
Send one Data Packet at a
Time.
Send the next packet only after
receiving ACK from the
Previous.
• Receiver Side
 Receive and consume Data
Packet.
 After Consuming packets,
ACK need to be sent (Flow
Control)

10. SIMPLEX PROTOCOL
FOR NOISY CHANNEL

11. WHAT IS MEANT BY A
PROTOCOL?
• A protocol refers to a defined set of guidelines and regulations that
control the communication between different devices in a network.
These guidelines specify the way in which data is formatted, timed,
sequenced, and checked for errors during transmission.

13. NOISY CHANNEL
PROTOCOLS
• A Noisy Channel Protocol is a type of communication
protocol that is used in communication systems where
the transmission channel may introduce errors into
the transmitted data. This type of protocol is designed
to deal with errors in the communication channel and
ensure that the data being transmitted is received
accurately at the receiver end. The main objective of
Noisy Channel Protocols is to minimize the error rate
in the transmitted data by using techniques such as
error detection and correction, flow control, and
retransmission of lost or corrupted data frames.

14. DIF F E R E N T T Y P E S
• Stop & wait Automatic Repeat Request.
• Go-Back-N Automatic Repeat Request.
• Selective Repeat Automatic Repeat Request.

16.  Here K=1 at the senders side.
 Then the size of the senders window is,
2k -1
K=1
21 -1 = 2-1 =1
 This is same as the stop and wait protocol.

17. - A sliding window of size 1, with a 3-bit sequence number-
 Initially.
 After the first frame has been sent.
 After the first frame has been received.
 After the first acknowledgement has received.

18. One Bit Sliding Window Protocol
• The notation is (seq, ack, packet number).
Part (a): If B waits A’s first frame before sending one of its own. Each frame arrival
brings a new packet for the network layer; there are no duplicates.
Part (b): If A and B simultaneously initiate commication, their first frames cross, and
the data link layers gets into a situation. Half of the frames contain duplicates, even
though there are no transmission errors.

20. Sliding Protocol
Window

21. • Sliding Window Algorithms are a method of flow control for
network for network data transfers.
• Data Link Layer uses sliding window algorithm, which allows a
sender to have more than one unacknowledged packet “in
flight” at a time, which improves network throughout.

22. Key Concepts of the Sliding
Window
Both the sender and receiver maintain a
finite size buffer to hold outgoing and
incoming packets from the other side.
Every packet sent by the sender, must be
acknowledged by the receiver. The sender
maintains a timer for every packet sent, and
any packet acknowledged in a certain time,
is resent.
The sender may send a whole window of
packets before receiving an
acknowledgement for the first packet in the
window. This results in higher transfer rates,
as the sender may send multiple packets
without waiting for each packet’s
acknowledgement.
The Receiver advertises a window
size that tells the sender how
much data it can receive, in order
for the sender not to fill up the
receiver buffers.
Efficiency can also be improved by
making use of the full-duplex line.
B
A

24. GO BACK ‘N”
It is used when the transmission time for frames is large or the bandwidth
is too large.
When either the bandwidth or the round trip delay is large, we need to
increase the size of sending window.
In networking if a task is often began before the previous task ended.
This is known as PIPELING.

25. Example 1
Assume that, in a Stop-and-Wait AEQ system, the
bandwidth of the line is 1 Mbps, and 1 bit takes 20 ms to
make a round trip. What is the bandwidth-delay
product? If the system data frames are 1000 bits in
length, what is the utilization percentage of the link?

26. Solution
The bandwidth-delay product is
The system can send 20,00 bits during the time it takes for the data to go
from the sender to the receiver and then back again. However, the system sends only
1000 bits. We can say that the link utilization is only 1000/20,000, or 5 percent.
For this reason, for a link with a high bandwidth or long delay, the use of Stop-and-
Wait ARQ wastes the capacity of the link.

28. What is Selective Protocol?
The Selective repeat(SR) protocol is a sliding window-
based data link layer protocol. Following are some
features of SR protocol: The sender window size is
always the same as the receiver window size.

29. Why Selective Repeat Protocol?

30. SELECTIVE REPEAT PROTOCOL
 In this protocol, both the sender
and receiver maintain a window of
outstanding and acceptable
sequence numbers, respectively.
 The sender’s window size starts
out at 0 and grows to some
predefined maximum.
 The receiver’s window, in contrast,
is always fixed in size and equal to
the predetermined maximum.
 The receiver has a buffer reserved
for each sequence number within
its fixed window.

31. Example Of Selective Repeat
Receiver must keep track holes’ in the
sequence of delivered frames.
Sender must maintain one timer per
outstanding packet