1. Overview of Data Communications and Networking
Data communications and networking are changing the way we do business and the way we live. Business decisions have to be made ever more quickly, and the decision makers require immediate access to accurate information.
Research in data communications and networking has resulted in new technologies.
One goal is to be able to exchange data such as text, audio, and video from all
points in the world. We want to access the Internet to download and upload information
quickly and accurately and at any time.
Behrouz A. Forouzan” Data communications and Networking

2. 1. Data Communication
Communication sharing information. Sharing can be local (face to face) or remote (over distance)
Data communication: exchange of data between two devices via transmission medium (wire cable)
Communicating devices made up of : H.W( physical equipments )and S.W
Behrouz A. Forouzan” Data communications and Networking

3. Data Communication
The Effectiveness of data communication depends on :
Delivery : System must deliver data to correct destination. Data must be received by only intended device or user.
Accuracy: The system must deliver data accurately
Timeliness: the system must deliver data in a timely manner. Data delivered later are useless.
Jitter: Variation in the packet arrival time. It is the uneven delay in the delivery of audio or video packets.
Behrouz A. Forouzan” Data communications and Networking

4. Direction of data flow Simplex, half duplex and full duplex Simplex:
Communication is unidirectional. (one-way-street). Only one of the two devices on a link can transmit; the other can only receive Ex: As Keyboard (only input) and monitors only output)
Ex: As Keyboard (only input) and monitors only output)
Behrouz A. Forouzan” Data communications and Networking

5. Direction of data flow 2. half duplex :
Each station can both transmit and receive , but not at the same time. When one device is sending the other can receive and vice versa. one-lane road with two direction).

6. Direction of data flow 3. Full-Duplex:
Both stations can transmit and receive simultaneously. ( telephone network)
Like two way street with traffic flowing in both directions at the same time.

7. 2. Networks
Network is a set of devices (often referred to as nodes) connected by communication links.
A node can be a computer, printer, or any other device capable of sending and/or receiving data generated by other nodes on the network.
Network Criteria
Performance,
Reliability and
security

8. Network criteria Type of transmission media,
1. Performance:
The performance depends on :
Number of user
Type of transmission media,
Capabilities of connected H.W and the efficiency of software.
2. Reliability
Measured by frequency of failure, the time it takes to recover from failure, and network’s robustness in a catastrophe.
3. Security:
Protecting data from unauthorized access.

9. Chapter 2 Network Models
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10. 2-1 LAYERED TASKS
We use the concept of layers in our daily life. As an example, let us consider two friends who communicate through postal mail. The process of sending a letter to a friend would be complex if there were no services available from the post office.

11. Figure 2.1 Tasks involved in sending a letter

12. Network models

13. 2-2 THE OSI MODEL
Established in 1947, the International Standards Organization (ISO) is a multinational body dedicated to worldwide agreement on international standards. An ISO standard that covers all aspects of network communications is the Open Systems Interconnection (OSI) model. It was first introduced in the late 1970s.

14. ISO is the organization. OSI is the model.
Note
ISO is the organization. OSI is the model.
The purpose of OSI model is to show how to facilitate communication between two different systems without requiring change to the logic of the underling H/W and S/W.
The OSI model ( not a protocol ) that is: flexible, robust, and interoperable.
It consists of seven separate but related layers, each of which defines a part of the process of moving information across a network.

15. Figure 2.2 Seven layers of the OSI model

16. Layered Architecture OSI model consists of 7 layers.
Each layer defines a family of functions distinct from those of the other layers.
Within a single machine, each layer calls upon the services of the layer just below it.
e.g. layer 3 uses the services provided by layer 2 and provides services for layer 4.
Between machines, layer x on one machine communicate with layer x on another machine.
This communication is govern by an agreed-upon series of rules and convention called protocols.
Communication between machines is a peer-to-peer process using the protocols appropriate to a given layer.

17. Figure 2.3 The interaction between layers in the OSI model

18. Organization of the Layers
The seven layers can be thought of as belonging to three subgroups:
Layers 1,2, and 3 – physical, data link, and network – are the network support layers.
Layers 5,6, and 7 – session, presentation, and application – are user support layers; they allow interoperability among unrelated software systems.
Layer 4, the transport layer, links the two groups and ensures that what the lower layers have transmitted is in a form that the upper layers can use.
The upper OSI layers almost implemented in S/W; lowers layers are combination of S/W and H/W except for the physical layer which is mostly H/W.

19. Figure 2.4 An exchange using the OSI model
Organization of the Layers

20. Encapsulation
There is another aspect of data communications in the OSI model:
Encapsulation.
The data portion of a packet at level N-1 carries the whole packet ( data and header and maybe trailer) from level N.
The concept is called encapsulation; where level N-1 is not aware of which part of the encapsulated packet is data and which part is the header or trailer.

21. Topics discussed in this section:
2-3 LAYERS IN THE OSI MODEL
In this section we briefly describe the functions of each layer in the OSI model.
Topics discussed in this section:
Physical Layer Data Link Layer
Network Layer
Transport Layer
Session Layer
Presentation Layer
Application Layer

22. 1. Physical layer
The physical layer coordinate the functions required to carry a bit stream over a physical medium including:
Dealing with the mathematical and electrical specifications of the interfaces and transmission medium.
It defines the procedures and functions that physical devices and interfaces have to perform for transmission to occur.
The physical layer is also concerned with:
Physical characteristics of interfaces and medium.
Representation of bits
Data rate
Synchronization of bits
Line configuration
Physical topology
Transmission mode

23. Figure 2.5 Physical layer

24. 2. Data Link layer
The data link layer transforms the physical layer to reliable link.
It makes the physical layer appear error-free to the upper layer (network layer).
There are other responsibilities of data link layer include:
Framing
Physical addressing
Flow control
Error control
Access control

25. Figure 2.6 Data link layer

26. Figure 2.7 Hop-to-hop delivery

27. 3. Network layer
The network layer is responsible for the delivery of individual packets from the source host to the destination host.
If two systems are connected to the same link, there is usually no need for a network layer.
If the two systems are attached to different networks with connecting devices between the networks, there is often a need for the network layer to accomplish source-to-destination delivery.
Other responsibilities of network layer include:
Logical addressing
Routing

28. Figure 2.8 Network layer

29. Figure 2.9 Source-to-destination delivery

30. 4. Transport layer
The transport layer is responsible for the delivery of a message from one process to another.
Unlike the network layer which is source-to-destination delivery, the transport layer is process-to-process delivery of the entire message.
Other responsibilities of transport layer:
Service-point addressing
Segmentation and reassembly
Connection control
Flow control
Error control

31. Figure 2.10 Transport layer

32. Figure 2.11 Reliable process-to-process delivery of a message

33. 5. Session layer
The session layer is responsible for dialog control and synchronization.
Specific responsibilities of the session layer include:
Dialog control
Synchronization

34. 6. Presentation layer
The presentation layer is concerned with syntax and semantics of the information exchange between two systems.
Specific responsibilities of presentation layer:
Translation
Encryption
Compression

35. 7. Application layer
The application layer enables user, weather human or software, to access the network.
It provides user interfaces and support for services such as , remote file access and transfer, shared database management, and other types of distributed information services.
Specific responsibilities of presentation layer:
Network virtual terminal
File transfer, access, and management
Mail services
Directory services

36. Figure 2.14 Application layer

37. Figure 2.15 Summary of layers