The document discusses the data link layer and outlines its key functions and design considerations. It covers three main services provided by the data link layer to the network layer: unacknowledged connectionless, acknowledged connectionless, and acknowledged connection-oriented. It also discusses framing of data, error detection and correction techniques, and elementary and sliding window protocols used at the data link layer. The goal is to study how the data link layer provides reliable and efficient communication between network layers on different machines.
Lecture slides from the 3rd-year module on Computer Networks at the University of Birmingham, UK.
This presentation covers the Data-Link layer of the networks stack, primarily Error Control, Flow Control and Framing.
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.
Lecture slides from the 3rd-year module on Computer Networks at the University of Birmingham, UK.
This presentation covers the Data-Link layer of the networks stack, primarily Error Control, Flow Control and Framing.
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.
Slides for my talk at the OSGi Community Event / Eclipse Con Europe 2012.
See http://www.eclipsecon.org/europe2012/sessions/universal-declarative-services for abstract.
Show the basics of inheritance and polymorphism in object-oriented programming. Introductory. Part of Industrial Logic's Object-Oriented Design Workshop. http://industriallogic.com/shop
Iterator - a powerful but underappreciated design patternNitin Bhide
Iterator design pattern is described in GoF ‘Design Patterns’ book. It is used at many places (e.g. Sql Cursor is a ‘iterator’), C++ standard template library uses iterators heavily. .Net Linq interfaces are based IEnumerable (i.e. iterator). However, I don’t see projects creating/using ‘custom’ iterator classes. Many problems can be solved ‘elegantly’ by use of customized iterators. This talk is about ‘power of iterators’ and how custom iterators can solve common problems and help create modular/reusable code components.
Key Discussion Points
Typical examples of iterators in common use.
Kind of problems that can be ‘elegantly’ solved with iterators
When to use custom iterators?
How write custom iterators in C++/C#
From webinar I did on TechGig
http://www.techgig.com/expert-speak/Iterator-a-powerful-but-underappreciated-pattern-449
This is the subject slides for the module MMS2401 - Multimedia System and Communication taught in Shepherd College of Media Technology, Affiliated with Purbanchal University.
Pg. 03Question Three Assignment 3Deadline Thurs.docxkarlhennesey
Pg. 03
Question Three
Assignment 3
Deadline: Thursday [email protected] 23:59
[Total Mark for this Assignment is 6]
Network Management
IT340
College of Computing and Informatics
Question One
3 Marks
Learning Outcome(s):
LO3: Evaluate different SNMP tools, network statistics tools, and protocol analyzer for network management.
Compare between the three cryptographic algorithms DES, IDEA and RSA by filling the following table:
Stands for
Type
Key size
Advantage
DES
Data Encryption Standard
symmetriccryptography (secret key cryptography)
56-bit key
1- Designed for efficient hardware implementation.
2- faster than asymmetric Cryptography such as RSA.
IDEA
international Data encryption Algorithm
symmetric cryptography (secret key cryptography)
128-bit key
1- More secure than DES. it uses a 128 bits key which is double than the key size of the DES
2- functions efficiently in software implementation.
RSA
Rivest–Shamir–Adleman
Asymmetric Cryptography
( Public Key Cryptography)
512-bit key
1- used to encrypt secret key
2- More secure than DES , IDEA
Question Two
1.5 Marks
Learning Outcome(s):
LO4: Understand the importance of broadband networking services and technologies.
Compare ATM and MPLS broadband protocol in terms of class of Quality of Service (QoS) to satisfy different kinds of traffic.
Answer
Four classes of traffic have been defined in ATM network to implement quality of service.
1. Constant bit rate (CBR) used with voice
2. real-time variable bit rate (VBR-RT), used with Streaming video such as real-time video on the Internet
3. non-real-time variable bit rate (VBR-NRT), used with still images
4. Available bit rate (ABR) , used with IP data traffic
The MPLS label contains 3-bit experimental which are used to describe the class of service. Using class of service, the network treats packets differently based on the application or packet’s priority. The number of classes of quality is service provider specific, however most companies assign up to four classes of service to different types of traffic which are:
1. Class A premium traffic e.g. VOIP or Video over IP
2. Class B Critical traffic e.g. financial transactions
3. Class C business traffic e.g. database applications
4. Class C standard traffic, which is the default class e.g. web browsing
Question Three
2 Marks
Learning Outcome(s):
LO5: Differentiate between various wired and wireless broadband network access techniques.
Cite and describe any three factors to decrease digital subscriber line (DSL) speed at customer end.
Answer
1. Incorrect network configuration leads to high latency and so low speed.
2. The messy wiring used to connect the user to the DSL service provider.
3. The existence of high noise over the telephone lines which requires installing a splitter or DSL filter reduce the line interference.
4. The interfere between unwanted noise and the DSL or voice connections
5. Not using high quality filters th ...
This slide is all about OSI model of Computer Network. It was the very first standard model for Computer Network System. In this slide I have discussed about the 7 layers of OSI model.
A Deep Dive in the World of IT Networking (Part 2)Tuan Yang
For a successful career in Information Technology, a strong foundation of basic networking concepts is a must. Networking technology allows for the exchange of data between large and small information systems used primarily by various businesses.
Learn more about:
» OSI Model
» Networking Protocol
» TCP Model
» Networking and data security
h!
This an assignment about
Data_Communications_and_networking
OS I model
university of Sri Jayawardenepura (Dept.of.IT)
2nd year 2nd semester
Thank you,
This is inspired from Tom Mitchell's book on Machine Learning. You can achieve a bit exact implementation of the back propagation algorithm if you follow the code in this.
A simple client-server application in java in which a client sends a message to a server and the server tries to be funny by sending back a funny response.
Event Management System Vb Net Project Report.pdfKamal Acharya
In present era, the scopes of information technology growing with a very fast .We do not see any are untouched from this industry. The scope of information technology has become wider includes: Business and industry. Household Business, Communication, Education, Entertainment, Science, Medicine, Engineering, Distance Learning, Weather Forecasting. Carrier Searching and so on.
My project named “Event Management System” is software that store and maintained all events coordinated in college. It also helpful to print related reports. My project will help to record the events coordinated by faculties with their Name, Event subject, date & details in an efficient & effective ways.
In my system we have to make a system by which a user can record all events coordinated by a particular faculty. In our proposed system some more featured are added which differs it from the existing system such as security.
Cosmetic shop management system project report.pdfKamal Acharya
Buying new cosmetic products is difficult. It can even be scary for those who have sensitive skin and are prone to skin trouble. The information needed to alleviate this problem is on the back of each product, but it's thought to interpret those ingredient lists unless you have a background in chemistry.
Instead of buying and hoping for the best, we can use data science to help us predict which products may be good fits for us. It includes various function programs to do the above mentioned tasks.
Data file handling has been effectively used in the program.
The automated cosmetic shop management system should deal with the automation of general workflow and administration process of the shop. The main processes of the system focus on customer's request where the system is able to search the most appropriate products and deliver it to the customers. It should help the employees to quickly identify the list of cosmetic product that have reached the minimum quantity and also keep a track of expired date for each cosmetic product. It should help the employees to find the rack number in which the product is placed.It is also Faster and more efficient way.
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.
For more technical information, visit our website https://intellaparts.com
Quality defects in TMT Bars, Possible causes and Potential Solutions.PrashantGoswami42
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.
NO1 Uk best vashikaran specialist in delhi vashikaran baba near me online vas...Amil Baba Dawood bangali
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Welcome to WIPAC Monthly the magazine brought to you by the LinkedIn Group Water Industry Process Automation & Control.
In this month's edition, along with this month's industry news to celebrate the 13 years since the group was created we have articles including
A case study of the used of Advanced Process Control at the Wastewater Treatment works at Lleida in Spain
A look back on an article on smart wastewater networks in order to see how the industry has measured up in the interim around the adoption of Digital Transformation in the Water Industry.
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.
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.
1. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
THE DATA LINK LAYER
Muhammad Adil Raja
Roaming Researchers, Inc.
August 25, 2014
2. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
OUTLINE
1 INTRODUCTION
2 DATA LINK LAYER DESIGN ISSUES
3 ERROR DETECTION AND CORRECTION
4 ELEMENTARY DATA LINK PROTOCOLS
5 SLIDING WINDOW PROTOCOLS
6 EXAMPLE DATA LINK PROTOCOLS
7 CONCLUSIONS
3. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
OUTLINE
1 INTRODUCTION
2 DATA LINK LAYER DESIGN ISSUES
3 ERROR DETECTION AND CORRECTION
4 ELEMENTARY DATA LINK PROTOCOLS
5 SLIDING WINDOW PROTOCOLS
6 EXAMPLE DATA LINK PROTOCOLS
7 CONCLUSIONS
4. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
OUTLINE
1 INTRODUCTION
2 DATA LINK LAYER DESIGN ISSUES
3 ERROR DETECTION AND CORRECTION
4 ELEMENTARY DATA LINK PROTOCOLS
5 SLIDING WINDOW PROTOCOLS
6 EXAMPLE DATA LINK PROTOCOLS
7 CONCLUSIONS
5. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
OUTLINE
1 INTRODUCTION
2 DATA LINK LAYER DESIGN ISSUES
3 ERROR DETECTION AND CORRECTION
4 ELEMENTARY DATA LINK PROTOCOLS
5 SLIDING WINDOW PROTOCOLS
6 EXAMPLE DATA LINK PROTOCOLS
7 CONCLUSIONS
6. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
OUTLINE
1 INTRODUCTION
2 DATA LINK LAYER DESIGN ISSUES
3 ERROR DETECTION AND CORRECTION
4 ELEMENTARY DATA LINK PROTOCOLS
5 SLIDING WINDOW PROTOCOLS
6 EXAMPLE DATA LINK PROTOCOLS
7 CONCLUSIONS
7. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
OUTLINE
1 INTRODUCTION
2 DATA LINK LAYER DESIGN ISSUES
3 ERROR DETECTION AND CORRECTION
4 ELEMENTARY DATA LINK PROTOCOLS
5 SLIDING WINDOW PROTOCOLS
6 EXAMPLE DATA LINK PROTOCOLS
7 CONCLUSIONS
8. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
OUTLINE
1 INTRODUCTION
2 DATA LINK LAYER DESIGN ISSUES
3 ERROR DETECTION AND CORRECTION
4 ELEMENTARY DATA LINK PROTOCOLS
5 SLIDING WINDOW PROTOCOLS
6 EXAMPLE DATA LINK PROTOCOLS
7 CONCLUSIONS
9. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
INTRODUCTION I
The goal is to study the design principles for the data
link layer.
To study the algorithms for achieving reliable, efficient
communication of whole units of information.
To understand communication with frames as opposed
to bits.
10. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
DATA LINK LAYER DESIGN ISSUES I
The data link layer uses the services of the physical layer to
send and receive bits over communication channels. It has
a number of functions, including:
1 Providing a well-defined service interface to the
network layer.
2 Dealing with transmission errors.
3 Regulating the flow of data so that slow receivers are
not swamped by fast senders.
To accomplish these goals, the data link layer takes the
packets it gets from the network layer and encapsulates
them into frames for transmission.
Each frame contains a frame header.
And a payload field for holding the packet.
11. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
2. Dealing with transmission errors.
3. Regulating the flow of data so that slow receivers are not swamped
DATA LINK LAYER DESIGN ISSUES II
by fast senders.
To accomplish these goals, the data link layer takes the packets it gets from the
network layer And and a frame encapsulates trailer.
them into frames for transmission. Each frame
contains a frame header, a payload field for holding the packet, and a frame
trailer, as Frame illustrated management in Fig. 3-1. Frame forms management the heart forms of the the functionality
heart of what the
data link of layer the does. data In link the layer.
following sections we will examine all the above-mentioned
issues in detail.
Header Payload field Trailer
Frame
Sending machine
Receiving machine
Packet Packet
Header Payload field Trailer
Figure 3-1. Relationship between packets and frames.
FIGURE: Relationship between packets and frames.
Although this chapter is explicitly about the data link layer and its protocols,
many of the principles we will study here, such as error control and flow control,
are found in transport and other protocols as well. That is because reliability is an
12. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
SERVICES PROVIDED TO THE NETWORK LAYER I
The function of the data link layer is to provide services
to the network layer.
The rincipal service is transfering data from the network
layer on the source machine to the network layer on the
destination machine.
On the source machine is an entity, call it a process or
a program, in the network layer that hands some bits to
the data link layer for transmission to the destination.
The job of the data link layer is to transmit the bits to
the destination machine so they can be handed over to
the network layer (of the destination machine).
13. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
transmit the bits to the destination machine so they can be handed over to the net-work
layer there, as shown in Fig. 3-2(a). The actual transmission follows the
SERVICES PROVIDED TO THE NETWORK LAYER
II
path of Fig. 3-2(b), but it is easier to think in terms of two data link layer proc-esses
communicating using a data link protocol. For this reason, we will impli-citly
use the model of Fig. 3-2(a) throughout this chapter.
4
3
2
1
4
3
2
1
4
3
2
1
4
3
2
1
Host 1 Host 2 Host 1 Host 2
Virtual
data path
Actual
data path
(a) (b)
Figure 3-2. (a) Virtual communication. (b) Actual communication.
FIGURE: (a) Virtual Communication. (b) Actual communication.
The data link layer can be designed to offer various services. The actual ser-vices
14. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
SERVICES PROVIDED TO THE NETWORK LAYER
III
The data link layer can be designed to offer various
services.
The actual services that are offered vary from protocol
to protocol.
The reasonable possibilities are:
1 Unacknowledged connectionless service.
2 Acknowledged connectionless service.
3 Acknowledged connection-oriented service.
Unacknowledged connectionless service consists of
having the source machine send independent frames to
the destination machine without having the destination
machine acknowledge them.
Ethernet is a good example that provides this service.
No logical connection is established beforehand or
released afterward.
15. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
SERVICES PROVIDED TO THE NETWORK LAYER
IV
If a frame is lost due to noise on the line, no attempt is
made to detect the loss or recover from it in the data
link layer.
This class of service is appropriate when the error rate
is low.
The recovery is left to the higher layers.
It is also appropriate for real-time traffic, such as voice.
Or for other service in late data is worse than bad data.
In an acknowledged connectionless service there
are still no logical connections.
However, each frame sent is individually acknowledged.
The sender knows that whether a frame has been
arrived correctly or has been lost.
16. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
SERVICES PROVIDED TO THE NETWORK LAYER
V
If it does not arrive within a certain time interval, it can
be sent again.
The service is useful over unreliable channels, such as
wireless systems.
IEEE 802.11 is a good example of this class of service.
Providing acknowledgements in the data link layer is a
good thing, but not a requirement.
The network layer can always send a packet and wait
for it to be acknowledged by its peer on the remote
machine.
If the acknowledgement does not arrive within a certain
interval of time, the sender can send the message
again.
This strategy can be inefficient.
17. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
SERVICES PROVIDED TO THE NETWORK LAYER
VI
Links usually have a strict maximum frame length
imposed by the hardware, and known propagation
delays.
The network layer does not know these things.
The network layer might send a large packet that is
broken up into, say, 10 frames, of which 2 are lost on
average.
It would then take a very long time for the packet to get
through.
On the other hand, if individual frames are
acknowledged and retransmitted, then errors can be
corrected more directly and more quickly.
On reliable channels, such as fiber, the overhead of a
heavyweight data link protocol may be unnecessary.
18. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
SERVICES PROVIDED TO THE NETWORK LAYER
VII
However, it might be very useful on wireless channels
which are inherently unreliable.
Providing a connection oriented service is the most
reliable thing the data link layer can do.
The source and destination machines establish a
connection before any data are transferred.
Each frame sent over the connection is numbered.
Moreover, the data link layer ensures that each frame
sent is indeed received.
Moreover, it guarantees that each frame is received
exactly once.
And that all the frames are received in the right order.
Transfers go through three phases in a connection
oriented scheme:
19. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
SERVICES PROVIDED TO THE NETWORK LAYER
VIII
1 Connection establishment.
2 Frame transmission.
3 Connection release.
20. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
FRAMING I
The data link layer uses the services of the physical
layer.
The physical layer accepts a raw bitstream and tries to
deliver it to the destination.
Physical layer tries to handle noise and transmission
errors.
There is no guarantee for error-free deliveries.
The data link layer has to correct the errors.
The usual way is to break up the bit stream into frames.
The data link layer computes the checksums.
Upon arrival of a frame the checksum is recomputed.
21. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
FRAMING II
A few strategies for framing:
1 Byte count.
2 Flag bytes with byte stuffing.
3 Flag bits with bit stuffing.
4 Physical layer coding violations.
22. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
FRAMING III
198 THE DATA LINK LAYER CHAP. 3
Byte count One byte
5 1 2 3 4 5 6 7 8 9 8 0 1 2 3 4 5 6 8 7 8 9 0 1 2 3
(a)
5 1 2 3 4 7 6 7 8 9 8 0 1 2 3 4 5 6 8 7 8 9 0 1 2 3
(b)
Error
Frame 1
5 bytes
Frame 1
Frame 2
5 bytes
Frame 2
(Wrong)
Frame 3
8 bytes
Frame 4
8 bytes
Now a byte
count
Figure 3-3. A byte stream. (a)Without errors. (b)With one error.
FIGURE: A byte stream. (a) Without errors. (b) With one error.
The second framing method gets around the problem of resynchronization
after an error by having each frame start and end with special bytes. Often the
same byte, called a flag byte, is used as both the starting and ending delimiter.
This byte is shown in Fig. 3-4(a) as FLAG. Two consecutive flag bytes indicate
the end of one frame and the start of the next. Thus, if the receiver ever loses syn-chronization
23. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
FRAMING IV
SEC. 3.1 DATA LINK LAYER DESIGN ISSUES 199
FLAG Header Payload field Trailer FLAG
Original bytes After stuffing
A ESC FLAG B
A ESC ESC B
A ESC ESC ESC FLAG B
A ESC ESC ESC ESC B
A FLAG B
A ESC B
A ESC FLAG B
A ESC ESC B
(a)
(b)
Figure 3-4. (a) A frame delimited by flag bytes. (b) Four examples of byte se-quences
before and after byte stuffing.
The third method of delimiting the bit stream gets around a disadvantage of
byte stuffing, which is that it is tied to the use of 8-bit bytes. Framing can be also
be done at the bit level, so frames can contain an arbitrary number of bits made up
of units of any size. It was developed for the once very popular HDLC (High-level
Data Link Control) protocol. Each frame begins and ends with a special
bit pattern, 01111110 or 0x7E in hexadecimal. This pattern is a flag byte. When-ever
the sender’s data link layer encounters five consecutive 1s in the data, it
FIGURE: (a) A frame delimited by flag bytes. (b) Four examples of
byte sequences before and after byte stuffing.
24. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
FRAMING V
200 THE DATA LINK LAYER CHAP. 0 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 0
0 1 1 0 1 1 1 1 1 0 1 1 1 1 1 0 1 1 1 1 1 0 1 0 0 1 0
Stuffed bits
(a)
(b)
(c) 0 1 1 0 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 0 0 1 0
Figure 3-5. Bit stuffing. (a) The original data. (b) The data as they appear on
the line. (c) The data as they are stored in the receiver’s memory after destuf-fing.
FIGURE: (Bit stuffing. (a) The original data. (b) The data as they
appear on the line. (c) The data as they are stored in the
receiver’s memory after destuffing.
With both bit and byte stuffing, a side effect is that the length of a frame depends on the contents of the data it carries. For instance, if there are no bytes in the data, 100 bytes might be carried in a frame of roughly 100 bytes. however, the data consists solely of flag bytes, each flag byte will be escaped the frame will become roughly 200 bytes long. With bit stuffing, the increase
25. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
ERROR CONTROL I
How to make sure all frames are eventually delivered to
the network layer at the destination and in the proper
order.
Use of acknowledgements, retransmissions, timers and
sequence numbers.
26. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
FLOW CONTROL I
Sender transmitting faster than the receiver accepting.
Feedback based flow control.
Rate based flow control.
27. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
ERROR DETECTION AND CORRECTION I
For wireless and very old networks error rates can be
high.
Network designers add redundant data to deal with
errors.
Error Correcting Codes: Help in figuring out the
specific error that has occurred.
Error Detecting Codes: Help in figuring out if some
error has occurred or not.
The use of error correcting codes is often referred to as
FEC (Forward Error Correction).
For reliable channels error detecting codes are
normally employed.
For noisy channels, error correcting codes are used.
28. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
ERROR DETECTION AND CORRECTION II
Error correcting codes are also implemented in physical
layer.
Applied mathematics: Galois fields, properties of
sparse matrices.
29. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
ERROR-CORRECTING CODES I
Four different error-correcting codes:
1 Hamming codes.
2 Binary convolutional codes.
3 Reed-Solomon codes.
4 Low-Density Parity Check codes.
All of these codes add redundancy to the information
that is sent.
A frame consists of m data (i.e. message) bits and r
redundant (i.e. check) bits.
In a block code, the r check bits are computed solely
as a function of the m data bits with which they are
associated.
30. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
ERROR-CORRECTING CODES II
It is as if the m bits were looked up in a large table to
find their corresponding r check bits.
In a systematic code, the m bits are sent directly,
along with the check bits, rather than being encoded
themselves before they are sent.
In a linear code. the r check bits are computed as a
linear function of the m data bits.
XOR or modulo 2 addition is a popular choice.
This means that encoding can be done with operations
such as matrix multiplications or simple logic circuits.
31. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
ERROR-DETECTING CODES I
They are used for reliable channels.
Linear systematic block codes:
1 Parity.
2 Checksums.
3 Cyclic redundancy checks (CRCs).
Fletcher’s checksum.
CRC (Cyclic redundancy check).
Polynomial code.
32. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
ELEMENTARY DATA LINK PROTOCOLS I
A Utopian Simplex Protocol.
A Simplex Stop-and-Wait Protocol for an Error-Free
Channel.
A Simplex Stop-and-Wait Protocol for a Noisy Channel.
33. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
SLIDING WINDOW PROTOCOLS I
A One-Bit Sliding Window Protocol.
A Protocol Using Go-Back-N.
A Protocol Using Selective Repeat.
34. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
EXAMPLE DATA LINK PROTOCOLS I
Packet over SONET.
ADSL (Assymetric Digital Subscriber Loop).
35. The Data
Link Layer
Muhammad
Adil Raja
Introduction
Data Link
Layer Design
Issues
Error
Detection
and
Correction
Elementary
Data Link
Protocols
Sliding
Window
Protocols
Example
Data Link
Protocols
Conclusions
REFERENCES
The inspiration and figures for these slides have been taken
from, Computer Networks, Andrew S. Tanenbaum, 5th
Edition.