Network Models. Presentation by Dr.S.Radha HOD / ECE SSN College of Engineering

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1 Network Models Presentation by Dr.S.Radha HOD / ECE SSN College of Engineering

2 Objective At the end of this section students will be able to Understand the architecture of the OSI model Understand the layers of the OSI model and their functions Understand the architecture of the TCP/IP Protocol Suite Differentiate between the OSI model and the TCP/IP Suite Differentiate between the three types of Internet addresses

3 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. Topics discussed in this section: Sender, Receiver, and Carrier Hierarchy

4 Tasks involved in sending a letter

5 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. Topics discussed in this section: Layered Architecture Peer-to-Peer Processes Encapsulation

6 Note ISO is the organization. OSI is the model.

7 Seven layers of the OSI model

8 The interaction between layers in the OSI model

9 An exchange using the OSI model

10 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

11 Physical layer

12 Note The physical layer is responsible for movements of individual bits from one hop (node) to the next.

13 Physical Layer Functions 1. Physical characteristics of interfaces and medium 2. Representation of bits 3. Data rate 4. Synchronization of bits 5. Line configuration 6. Physical topology 7. Transmission mode

14 Data link layer

15 Note The data link layer is responsible for moving frames from one hop (node) to the next.

16 Data Link Layer Functions 1. Framing 2. Physical addressing 3. Flow control 4. Error control 5. Access control

17 Hop-to-hop delivery

18 Network layer

19 Note The network layer is responsible for the delivery of individual packets from the source host to the destination host.

20 Network Layer Functions 1. Logical addressing 2. Routing

21 Source-to-destination delivery

22 Transport layer

23 Note The transport layer is responsible for the delivery of a message from one process to another.

24 Transport Layer Functions 1. Service point addressing 2. Segmentation and reassembly 3. Connection control 4. Flow control 5. Error control

25 Reliable process-to-process delivery of a message

26 Session layer

27 Note The session layer is responsible for dialog control and synchronization.

28 Session Layer Functions 1. Dialog control 2. Synchronization

29 Presentation layer

30 Note The presentation layer is responsible for translation, compression, and encryption.

31 Presentation Layer Functions 1. Translation 2. Encryption 3. Compression

32 Application layer

33 Note The application layer is responsible for providing services to the user.

34 Application Layer Functions 1. Network virtual terminal 2. File transfer, access and management 3. Mail services 4. Directory services

35 Summary of layers

36 TCP/IP PROTOCOL SUITE The layers in the TCP/IP protocol suite do not exactly match those in the OSI model. The original TCP/IP protocol suite was defined as having four layers: host-to-network, internet, transport, and application. However, when TCP/IP is compared to OSI, we can say that the TCP/IP protocol suite is made of five layers: physical, data link, network, transport, and application. Topics discussed in this section: Physical and Data Link Layers Network Layer Transport Layer Application Layer

37 TCP/IP and OSI model

38 ADDRESSING Four levels of addresses are used in an internet employing the TCP/IP protocols: physical, logical, port, and specific. Topics discussed in this section: Physical Addresses Logical Addresses Port Addresses Specific Addresses

39 Addresses in TCP/IP

40 Relationship of layers and addresses in TCP/IP

41 Example 1 In the following figure, a node with physical address 10 sends a frame to a node with physical address 87. The two nodes are connected by a link (bus topology LAN). As the figure shows, the computer with physical address 10 is the sender, and the computer with physical address 87 is the receiver.

42 Physical addresses

43 Example 2 Most local-area networks use a 48-bit (6-byte) physical address written as 12 hexadecimal digits; every byte (2 hexadecimal digits) is separated by a colon, as shown below: 07:01:02:01:2C:4B A 6-byte (12 hexadecimal digits) physical address.

44 Example 3 The following figure shows a part of an internet with two routers connecting three LANs. Each device (computer or router) has a pair of addresses (logical and physical) for each connection. In this case, each computer is connected to only one link and therefore has only one pair of addresses. Each router, however, is connected to three networks (only two are shown in the figure). So each router has three pairs of addresses, one for each connection.

45 IP addresses

46 Example 4 The following figure shows two computers communicating via the Internet. The sending computer is running three processes at this time with port addresses a, b, and c. The receiving computer is running two processes at this time with port addresses j and k. Process a in the sending computer needs to communicate with process j in the receiving computer. Note that although physical addresses change from hop to hop, logical and port addresses remain the same from the source to destination.

47 Port addresses

48 Note The physical addresses will change from hop to hop, but the logical addresses usually remain the same.

49 Example 5 A port address is a 16-bit address represented by one decimal number as shown. 753 A 16-bit port address represented as one single number.

50 Note The physical addresses change from hop to hop, but the logical and port addresses usually remain the same.

51 Summary The ISO created a model called the OSI, which allows diverse systems to communicate. The seven layer OSI model provides guidelines for the development of universally compatible networking protocols. The physical, data link and network are the network support layers. The session, presentation and application are the user support layers. The transport layer links the network support layers and the user support layers.

52 Summary The physical layer coordinates the functions required to transmit a bitstream over physical medium. The data link layer node to node delivery The network layer source to destination delivery The transport layer process to process delivery The session layer establishes, maintains and synchronizes the interactions between communicating devices. The presentation layer ensures interoperability between communicating devices through transformation of data into a mutually agreed upon format. The application layer enables the users to access the network.

53 Summary TCP/IP is a five layered hierarchical protocol suite developed before the OSI model. The TCP/IP application layer is equivalent to the combined session, presentation and application layers of the OSI model. Four levels of addresses are used in the TCP/IP protocol physical, logical, port and specific addresses. Physical (link) address is the address of a node as defined by a LAN or WAN. Logical (IP) address uniquely defined a host on the internet. The port address identifies a process on a host. A specific address is a user friendly address

54 Review Questions 1. The layer changes bits into electromagnetic signals. A) Physical B) Transport C) None of the above D) Data link 2. The physical layer is concerned with the transmission of over the physical medium. A) Programs B) Protocols C) Bits D) Dialogs 3. Mail services are available to network users through the layer. A) Data link B) Physical C) Application D) Transport 4. As the data packet moves from the lower to the upper layers, headers are. A) Added B) Rearranged C) Modified D) Subtracted

55 Review Questions 5. As the data packet moves from the upper to the lower layers, headers are. A) Removed B) Added C) Rearranged D) Modified 6. The layer lies between the network layer and the application layer. A) Data link B) Physical C) Transport D) None of the above 7. Layer 2 lies between the physical layer and the layer. A) Data link B) Network C) Transport D) None of the above 8. When data are transmitted from device A to device B, the header from A's layer 4 is read by B's layer. A) Application B) Physical C) Transport D) None of the above

56 Review Questions 9. Which layer functions as a liaison between user support layers and network support layers? A) Network layer B) Transport layer C) Physical layer D) Application layer 10. What is the main function of the transport layer? A) Process-to-process delivery B) Node-to-node delivery C) Synchronization D) Updating and maintenance of routing tables 11. Which of the following is an application layer service? A) Remote log-in B) File transfer and access C) Mail service D) All the above 12. The Internet model consists of layers. A) Three B) Five C) Seven D) Eight

57 Review Questions 13. The process-to-process delivery of the entire message is 5 responsibility of the layer. A) Physical B) Network C) Transport D) Application 14. The layer is the layer closest to the transmission medium. A) Network B) Physical C) Data link D) Transport

Chapter 2 Network Models 2.1

Chapter 2 Network Models 2.1 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 2.2 2-1 LAYERED TASKS We use the concept of layers in our daily life. As an example,