The data link layer, or layer 2, is the second layer of the seven-layer OSI model of computer networking. This layer is the protocol layer that transfers data between adjacent network nodes in a wide area network (WAN) or between nodes on the same local area network (LAN) segment.
INTRODUCTION
WHAT IS OSI?
OSI MODEL
TYPES OF LAYERS
PHYSICAL LAYER
DATA LINK LAYER
NETWORK LAYER
TRANSPORT LAYER
SESSION LAYER
PRESENTATION LAYER
APPLICATION LAYER
INTRODUCTION
WHAT IS OSI?
OSI MODEL
TYPES OF LAYERS
PHYSICAL LAYER
DATA LINK LAYER
NETWORK LAYER
TRANSPORT LAYER
SESSION LAYER
PRESENTATION LAYER
APPLICATION LAYER
Network layer - design Issues ,Store-and-Forward Packet Switching, Services Provided to the Transport Layer, Which service is the best , Implementation of Service , Implementation of Connectionless Service , Implementation of Connection-Oriented Service
Channelization is a multiple-access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations. The three channelization protocols are FDMA, TDMA, and CDMA
The network layer is responsible for routing packets from the source to destination. The routing algorithm is the piece of software that decides where a packet goes next (e.g., which output line, or which node on a broadcast channel).For connectionless networks, the routing decision is made for each datagram. For connection-oriented networks, the decision is made once, at circuit setup time.
Routing Issues
The routing algorithm must deal with the following issues:
Correctness and simplicity: networks are never taken down; individual parts (e.g., links, routers) may fail, but the whole network should not.
Stability: if a link or router fails, how much time elapses before the remaining routers recognize the topology change? (Some never do..)
Fairness and optimality: an inherently intractable problem. Definition of optimality usually doesn't consider fairness. Do we want to maximize channel usage? Minimize average delay?
When we look at routing in detail, we'll consider both adaptive--those that take current traffic and topology into consideration--and nonadaptive algorithms.
Network layer - design Issues ,Store-and-Forward Packet Switching, Services Provided to the Transport Layer, Which service is the best , Implementation of Service , Implementation of Connectionless Service , Implementation of Connection-Oriented Service
Channelization is a multiple-access method in which the available bandwidth of a link is shared in time, frequency, or through code, between different stations. The three channelization protocols are FDMA, TDMA, and CDMA
The network layer is responsible for routing packets from the source to destination. The routing algorithm is the piece of software that decides where a packet goes next (e.g., which output line, or which node on a broadcast channel).For connectionless networks, the routing decision is made for each datagram. For connection-oriented networks, the decision is made once, at circuit setup time.
Routing Issues
The routing algorithm must deal with the following issues:
Correctness and simplicity: networks are never taken down; individual parts (e.g., links, routers) may fail, but the whole network should not.
Stability: if a link or router fails, how much time elapses before the remaining routers recognize the topology change? (Some never do..)
Fairness and optimality: an inherently intractable problem. Definition of optimality usually doesn't consider fairness. Do we want to maximize channel usage? Minimize average delay?
When we look at routing in detail, we'll consider both adaptive--those that take current traffic and topology into consideration--and nonadaptive algorithms.
Python is an object-oriented programming language created by Guido Rossum in 1989. It is ideally designed for rapid prototyping of complex applications. It has interfaces to many OS system calls and libraries and is extensible to C or C++. Many large companies use the Python programming language, including NASA, Google, YouTube, BitTorrent, etc.
Linux is the best-known and most-used open source operating system. As an operating system, Linux is software that sits underneath all of the other software on a computer, receiving requests from those programs and relaying these requests to the computer's hardware.
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Student information management system project report ii.pdfKamal Acharya
Our project explains about the student management. This project mainly explains the various actions related to student details. This project shows some ease in adding, editing and deleting the student details. It also provides a less time consuming process for viewing, adding, editing and deleting the marks of the students.
Sachpazis:Terzaghi Bearing Capacity Estimation in simple terms with Calculati...Dr.Costas Sachpazis
Terzaghi's soil bearing capacity theory, developed by Karl Terzaghi, is a fundamental principle in geotechnical engineering used to determine the bearing capacity of shallow foundations. This theory provides a method to calculate the ultimate bearing capacity of soil, which is the maximum load per unit area that the soil can support without undergoing shear failure. The Calculation HTML Code included.
About
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
Technical Specifications
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
Key Features
Indigenized remote control interface card suitable for MAFI system CCR equipment. Compatible for IDM8000 CCR. Backplane mounted serial and TCP/Ethernet communication module for CCR remote access. IDM 8000 CCR remote control on serial and TCP protocol.
• Remote control: Parallel or serial interface
• Compatible with MAFI CCR system
• Copatiable with IDM8000 CCR
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
Application
• Remote control: Parallel or serial interface.
• Compatible with MAFI CCR system.
• Compatible with IDM8000 CCR.
• Compatible with Backplane mount serial communication.
• Compatible with commercial and Defence aviation CCR system.
• Remote control system for accessing CCR and allied system over serial or TCP.
• Indigenized local Support/presence in India.
• Easy in configuration using DIP switches.
CFD Simulation of By-pass Flow in a HRSG module by R&R Consult.pptxR&R Consult
CFD analysis is incredibly effective at solving mysteries and improving the performance of complex systems!
Here's a great example: At a large natural gas-fired power plant, where they use waste heat to generate steam and energy, they were puzzled that their boiler wasn't producing as much steam as expected.
R&R and Tetra Engineering Group Inc. were asked to solve the issue with reduced steam production.
An inspection had shown that a significant amount of hot flue gas was bypassing the boiler tubes, where the heat was supposed to be transferred.
R&R Consult conducted a CFD analysis, which revealed that 6.3% of the flue gas was bypassing the boiler tubes without transferring heat. The analysis also showed that the flue gas was instead being directed along the sides of the boiler and between the modules that were supposed to capture the heat. This was the cause of the reduced performance.
Based on our results, Tetra Engineering installed covering plates to reduce the bypass flow. This improved the boiler's performance and increased electricity production.
It is always satisfying when we can help solve complex challenges like this. Do your systems also need a check-up or optimization? Give us a call!
Work done in cooperation with James Malloy and David Moelling from Tetra Engineering.
More examples of our work https://www.r-r-consult.dk/en/cases-en/
Forklift Classes Overview by Intella PartsIntella Parts
Discover the different forklift classes and their specific applications. Learn how to choose the right forklift for your needs to ensure safety, efficiency, and compliance in your operations.
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COLLEGE BUS MANAGEMENT SYSTEM PROJECT REPORT.pdfKamal Acharya
The College Bus Management system is completely developed by Visual Basic .NET Version. The application is connect with most secured database language MS SQL Server. The application is develop by using best combination of front-end and back-end languages. The application is totally design like flat user interface. This flat user interface is more attractive user interface in 2017. The application is gives more important to the system functionality. The application is to manage the student’s details, driver’s details, bus details, bus route details, bus fees details and more. The application has only one unit for admin. The admin can manage the entire application. The admin can login into the application by using username and password of the admin. The application is develop for big and small colleges. It is more user friendly for non-computer person. Even they can easily learn how to manage the application within hours. The application is more secure by the admin. The system will give an effective output for the VB.Net and SQL Server given as input to the system. The compiled java program given as input to the system, after scanning the program will generate different reports. The application generates the report for users. The admin can view and download the report of the data. The application deliver the excel format reports. Because, excel formatted reports is very easy to understand the income and expense of the college bus. This application is mainly develop for windows operating system users. In 2017, 73% of people enterprises are using windows operating system. So the application will easily install for all the windows operating system users. The application-developed size is very low. The application consumes very low space in disk. Therefore, the user can allocate very minimum local disk space for this application.
Final project report on grocery store management system..pdfKamal Acharya
In today’s fast-changing business environment, it’s extremely important to be able to respond to client needs in the most effective and timely manner. If your customers wish to see your business online and have instant access to your products or services.
Online Grocery Store is an e-commerce website, which retails various grocery products. This project allows viewing various products available enables registered users to purchase desired products instantly using Paytm, UPI payment processor (Instant Pay) and also can place order by using Cash on Delivery (Pay Later) option. This project provides an easy access to Administrators and Managers to view orders placed using Pay Later and Instant Pay options.
In order to develop an e-commerce website, a number of Technologies must be studied and understood. These include multi-tiered architecture, server and client-side scripting techniques, implementation technologies, programming language (such as PHP, HTML, CSS, JavaScript) and MySQL relational databases. This is a project with the objective to develop a basic website where a consumer is provided with a shopping cart website and also to know about the technologies used to develop such a website.
This document will discuss each of the underlying technologies to create and implement an e- commerce website.
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Maintaining high-quality standards in the production of TMT bars is crucial for ensuring structural integrity in construction. Addressing common defects through careful monitoring, standardized processes, and advanced technology can significantly improve the quality of TMT bars. Continuous training and adherence to quality control measures will also play a pivotal role in minimizing these defects.
Immunizing Image Classifiers Against Localized Adversary Attacksgerogepatton
This paper addresses the vulnerability of deep learning models, particularly convolutional neural networks
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introduce a novel volumization algorithm, which transforms 2D images into 3D volumetric representations.
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Vaccine management system project report documentation..pdfKamal Acharya
The Division of Vaccine and Immunization is facing increasing difficulty monitoring vaccines and other commodities distribution once they have been distributed from the national stores. With the introduction of new vaccines, more challenges have been anticipated with this additions posing serious threat to the already over strained vaccine supply chain system in Kenya.
Overview of the fundamental roles in Hydropower generation and the components involved in wider Electrical Engineering.
This paper presents the design and construction of hydroelectric dams from the hydrologist’s survey of the valley before construction, all aspects and involved disciplines, fluid dynamics, structural engineering, generation and mains frequency regulation to the very transmission of power through the network in the United Kingdom.
Author: Robbie Edward Sayers
Collaborators and co editors: Charlie Sims and Connor Healey.
(C) 2024 Robbie E. Sayers
2. Data Link Layer Design Issues
• Services Provided to the Network Layer
• Framing
• Error Control
• Flow Control
3.
4. Functions of the Data Link Layer
• Provide service interface to the network layer
• Dealing with transmission errors
• Regulating data flow
• Slow receivers not swamped by fast senders
5. Functions of the Data Link Layer (2)
Relationship between packets and frames.
Each frame contains a frame header,
A payload field for holding the packet, and
A frame trailer
6. Services Provided to Network Layer
(a) Virtual communication.
(b) Actual communication.
The principal service is transferring data from the network layer on the source
machine to the network layer on the destination machine.
7. Services Provided to Network Layer
Unacknowledged connectionless service.
source machine send independent frames to the destination
machine without having the destination machine acknowledge them.
Acknowledged connectionless service.
When this service is offered, there are still no logical connections used, but
each frame sent is individually acknowledged. In this way, the sender knows
whether a frame has arrived correctly.
Acknowledged connection-oriented service.
8. Services Provided to Network Layer
WAN subnet consisting of routers connected by point-to-point
leased telephone lines.
When a frame arrives at a router, the hardware checks it for
errors
Then passes the frame to the data link layer software.
The data link layer software checks to see if this is the frame
expected,
Gives the packet contained in the payload field to the routing
software.
The routing software then chooses the appropriate outgoing line
Passes the packet back down to the data link layer software,
which then transmits it
10. Framing
Data link layer must use the service provided to it by the
physical layer.
This bit stream is not guaranteed to be error free.
Data link layer to break the bit stream up into discrete
frames and compute the checksum for each frame.
When a frame arrives at the destination, the checksum is
recomputed.
If the newly-computed checksum is different from the one
contained in the frame, the data link layer knows that an
error has occurred and takes steps to deal with it
11. Framing
It is too risky to count on timing to mark the start and end of each
frame, we will look at four methods:
Character count.
Flag bytes with byte stuffing.
Starting and ending flags, with bit stuffing.
Physical layer coding violations.
13. Framing Flag Byte
(a) A frame delimited by flag bytes.
(b) Four examples of byte sequences before and after stuffing.
14. Framing Flag Byte
A serious problem occurs with this method when binary data, such as object programs or
floating-point numbers, are being transmitted.
It may easily happen that the flag byte's bit pattern occurs in the data.
This situation will usually interfere with the framing.
One way to solve this problem is to have the sender's data link layer insert a special
escape byte (ESC) just before each ''accidental'' flag byte in the data.
The data link layer on the receiving end removes the escape byte before the data are
given to the network layer.
This technique is called byte stuffing or character stuffing.
Thus, a framing flag byte can be distinguished from one in the data by the absence or
presence of an escape byte before it.
15. Framing Bit Stuffing
Bit stuffing
(a) The original data.
(b) The data as they appear on the line.
(c) The data as they are stored in receiver’s memory after destuffing.
16. Types of Error Single Bit Errors
In a single bit error, only 1 bit in the data unit changes:
Burst Errors
17. Error Detection and Correction
• Error-Correcting Codes
• Error-Detecting Codes
Computer data always sent in blocks of bits.
Suppose that the block size is 1000 bits and the error
rate is 0.001 per bit.
If errors were independent, most blocks would contain
an error.
If the errors came in bursts of 100 however, only one or
two blocks in 100 would be affected, on average
18. Error-Correcting Codes
Block of data sent,
Include only enough redundancy to allow the receiver to deduce that an error occurred, but
not which error, and have it request a retransmission.
it is necessary to look closely at what an error really is.
Normally, a frame consists of m data (i.e., message) bits and r redundant, or
check, bits.
Let the total length be n (i.e., n = m + r). An n-bit unit containing data and check
bits is often referred to as an n-bit codeword.
Given any two codewords, say, 10001001 and 10110001, it is possible to determine how many
corresponding bits differ.
The number of bit positions in which two codewords differ is called the Hamming distance
here 3 (Hamming, 1950).
19. Error-Correcting Codes
Error-detecting code, consider a code in which a single parity bit is
appended to the data.
The parity bit is chosen so that the number of 1 bits in the codeword
is even (or odd).
For example, when 1011010 is sent in even parity, a bit is added to
the end to make it 10110100.
With odd parity 1011010 becomes 10110101.
A code with a single parity bit has a distance 2, since any single-bit
error produces a codeword with the wrong parity.
0000000000, 0000011111, 1111100000, and 1111111111
This code has a distance 5,
Which means that it can correct double errors.
If the codeword 0000000111 arrives, the receiver knows that the
original must have been 0000011111.
If, however, a triple error changes 0000000000 into 0000000111,
the error will not be corrected properly
20. Error-Correcting Codes
The bits of the codeword are numbered consecutively, starting with
bit 1 at the left end, bit 2 to its immediate right, and so on.
The bits that are powers of 2 (1, 2, 4, 8, 16, etc.) are check bits.
The rest (3, 5, 6, 7, 9, etc.) are filled up with the m data bits.
For example, 11 = 1 + 2 + 8 and 29 = 1 + 4 + 8 + 16. A bit is
checked by just those check bits occurring in its expansion
(e.g., bit 11 is checked by bits 1, 2, and 8).
When a codeword arrives, the receiver initializes a counter to
zero. It then examines each check bit, k (k = 1, 2, 4, 8, ...), to
see if it has the correct parity. If not, the receiver adds k to the
counter
22. Lecture 4: 9-6-01 22
Error Detection – CRC
a) View data bits, D, as a binary number
b) Choose r+1 bit pattern (generator), G
c) Goal: choose r CRC bits, R, such that
– <D,R> exactly divisible by G (modulo 2)
– Receiver knows G, divides <D,R> by G. If non-zero remainder: error
detected!
– Can detect all burst errors less than r+1 bits
a) Widely used in practice (ATM, HDCL)
(Cyclic Redundancy Check)
23. Lecture 4: 9-6-01 23
CRC Example
Want:
D.2r XOR R = nG
equivalently:
D.2r = nG XOR R
equivalently:
if we divide D.2r by G,
want reminder Rb
R = remainder[ ]
D.2r
G
10111010011
24. Flow and Error ControlFlow and Error Control
a) The most important responsibilities of the data link
layer are flow control and error control. these
functions are known as :
b) data link control.
25. 10.
Data link control.
Data must be checked and processed before
they can be used.
The rate of such processing is often slower
than the rate of transmission.
For this reason , each receiver has a buffer to
store incoming data until they are processed.
If buffer begin to fill up, the sender must slow
or halt transmission.
26. Flow Control
a) Necessary when data is being sent faster than it can be
processed by receiver
b) Computer to printer is typical setting
c) Can also be from computer to computer, when a processing
program is limited in capacity
d) Flow control is needed since the sending entity should not
overwhelm the receiving entity
– Recipient needs some time to process incoming packets
– If sender sends faster than recipient processes, then buffer overflow
occurs
• flow control prevents buffer overflow
26
27. 10.
Flow control refers to a set of procedures
used to restrict the amount of data that the
sender can send before waiting for
acknowledgment.
Note
28.
29. Stop and Wait Flow Control
a) Source transmits frame
b) Destination receives frame and replies with acknowledgement
(ACK)
c) Source waits for ACK before sending next frame
d) Destination can stop flow by not sending ACK
e) Works well for large frames
f) Inefficient for smaller frames
30. Stop and Wait Flow Control
a) However, generally large block of data split into small frames
– Called “Fragmentation”
• Limited buffer size at receiver
• Errors detected sooner (when whole frame received)
– On error, retransmission of smaller frames is needed
• Prevents one station occupying medium for long periods
32. Sliding Window Flow Control
a) The problem of “Stop and Wait” is not be able to send
multiple frames
b) Sliding Window Protocol allows multiple frames to be in
transit
c) Receiver has buffer of W (called window size) frames
d) Transmitter can send up to W frames without ACK
e) Each frame is numbered
– Sequence number bounded by size of the sequence number field (k
bits)
– thus frames are numbered modulo 2k
(0 … 2k-1
)
a) ACK includes number of next frame expected
37. Error Control
a) Actions to be taken against
– Lost frames
– Damaged frames
a) Automatic repeat request (ARQ) mechanism components
– Error detection
– Positive acknowledgment
– Retransmission after timeout
– Negative acknowledgement and retransmission
38. 10.
Error control : is both error detection and
correction. Error correction in data link layer is
implemented simply: anytime an error is detected
in exchange, specified frames are retransmitted.
This process is called Automatic Repeat Request
Data link control.
39. 10.
Error control in the data link layer is based
on automatic repeat request, which is the
retransmission of data.
Note
40. Error Control
Having solved the problem of marking the start and end of each
frame,
How make sure all frames delivered to the network layer
destination and proper order.
To ensure reliable delivery is to provide the sender with some
feedback about what is happening
If the sender receives a positive acknowledgement about a
frame, it knows the frame has arrived safely.
On the other hand, a negative acknowledgement means that
something has gone wrong, and the frame must be transmitted
again.
41. Error Control
When the sender transmits a frame, it generally also starts a
timer.
The timer is set to expire after an interval long enough for the
frame to reach the destination
Acknowledgement propagate back to the sender.
The frame correctly received and the acknowledgement will get
back before the timer runs out,
If either the frame or the acknowledgement is lost, the timer will
go off, alerting the sender to a potential problem.
The obvious solution is to just transmit the frame again.
To prevent this from happening, it is generally necessary to assign
sequence numbers to outgoing frames, so that the receiver can
distinguish retransmissions from originals
42. PROTOCOLS
Now let us see how the data link layer can
combine flow control , and error control to
achieve the delivery of data from one node to
another . The protocols are normally
implemented in software.
Stop-and-Wait ARQ
Go-Back-N ARQ
Selective Repeat ARQ
PROTOCOLS
43. A transmitter sends a frame then stops and waits for
an acknowledgment.
Stop-and-Wait ARQ has the following features:
The sending device keeps a copy of the sent frame
transmitted until it receives an
acknowledgment( ACK)
The sender starts a timer when it sends a frame. If
an ACK is not received within an allocated time
period, the sender resends it
Both frames and acknowledgment (ACK) are
numbered alternately 0 and 1( two sequence number
only)
This numbering allows for identification of frames in
case of duplicate transmission
Stop-and-Wait ARQ
44. The acknowledgment number defines the number of
next expected frame. (frame 0 received ACK 1 is
sent)
A damage or lost frame treated by the same manner
by the receiver
If the receiver detects an error in the received frame,
or receives a frame out of order it simply discards
the frame
The receiver send only positive ACK for frames
received safe; it is silent about the frames damage
or lost.
The sender has a control variable Sthat holds the
number of most recently sent frame (0 or 1). The
receiver has control variable R, that holds the
Stop-and-Wait ARQ
45. Cases of Operations:
1.Normal operation
2.The frame is lost
3.The Acknowledgment (ACK) is lost
4.The Ack is delayed
Stop-and-Wait
ARQ
46. The sender will not
send the next frame
until it is sure that the
current one is
correctly receive
sequence number is
necessary to check
for duplicated frames
Stop-and-Wait ARQ
47. 1. Stop and Wait ARQ
2. Lost or damaged frame
A damage or lost frame
treated by the same
manner by the receiver.
No NACK when frame is
corrupted / duplicate
48. 3. Lost ACK frame
Importance of frame
numbering
Stop-and-Wait ARQ
49. 10.
In Stop and-Wait ARQ, numbering frames
prevents the retaining of duplicate
frames.
Note
50. 4. Delayed ACK and lost frame
Importance of
frame numbering
Stop-and-Wait ARQ
52. Go-Back-N ARQ
a) Based on sliding window
b) If no error, ACK as usual with next frame expected
– ACKi means “I am ready to receive frame i” and “I received all
frames between i and my previous ack”
a) Sender uses window to control the number of
unacknowledged frames
b) If error, reply with rejection (negative ack)
– Discard that frame and all future frames until the frame in error
received correctly
– Transmitter must go back and retransmit that frame and all
subsequent frames
53. Go-Back-N ARQ
Example: The sender has sent frame 6 , and timer expires for frame 3(
frame 3 has not been acknowledge); the sender goes back and
resends frames 3, 4,5 and 6
54. Go-Back-N ARQ
Normal operation
How many frame scan be
transmitted Without
acknowledgment?
ACK1 is not necessary if
ACK2 is sent: Cumulative
ACK
55. Go-Back-N ARQ -
Damaged Frame
a) Receiver detects error in frame i
b) Receiver sends “reject i”
c) Transmitter gets “reject i”
d) Transmitter retransmits frame i and all subsequent frames
56. Go-Back-N ARQ
Damage or Lost Frame
Correctly received out of
order packets are not
Buffered
What is the disadvantage of
this?
57. Go-Back-N ARQ - Lost Frame
a) Frame i lost
b) Transmitter sends frame i+1
c) Receiver gets frame i+1 out of sequence
d) Receiver sends “reject i”
e) Transmitter goes back to frame i and
retransmits it and all subsequent frames
58. Go-Back-N ARQ
Damage or Lost Frame
Correctly received out of
order packets are not
Buffered
What is the disadvantage of
this?
59. 10.
Stop-and-Wait ARQ is a special case of
Go-Back-N ARQ in which the size of
the send window is 1
Note
60. Selective Repeat ARQ
Go-Back-N ARQ is inefficient of a noisy link.
In a noisy link frames have higher probability of damage , which
means the resending of multiple frames.
this resending consumes the bandwidth and slow down the
transmission .
Solution:
Selective Repeat ARQ protocol : resent only the damage frame
It defines a negative Acknolgment (NAK) that report the sequence
number of a damaged frame before the timer expires
It is more efficient for noisy link, but the processing at the receiver
is more complex