02 network models

network models, Protocol layering, TCP/IP protocol suite, The OSI model.

1. Network Model 1

2. Outline 2.1 PROTOCOL LAYERING 2.1.1 Scenarios 2.1.2 Principles of Protocol Layering 2.1.3 Logical Connections 2.2 TCP/IP PROTOCOL SUITE 2.2.1 Layered Architecture 2.2.2 Layers in the TCP/IP Protocol Suite 2.2.3 Description of Each Layer 2.3 THE OSI MODEL 2.3.1 OSI versus TCP/IP 2.3.2 Lack of OSI Model’s Success 2

3. Layered Tasks Computer networks are complex systems Tasks involve varieties of hardware and software components, and protocols Networking task is divided into several subtasks, or layers. 3

4. Why layering? Networks are complex! We need a way to organize the structure of network functionalities and to reduce the design complexities Benefits of layering Interoperability Reuse Hiding underlying details 2- 4

5. Protocol interfaces Each protocol offers an interface to its users, and expects one from the layers on which it builds Syntax and semantics Data formats Interface characteristics, e.g. IP service model Protocols build upon each other Add value E.g., a reliable protocol running on top of IP Reuse E.g., OS provides TCP, so apps don’t have to rewrite 2- 5

6. Real World Example Communication between managers of two companies 6 Communicate

7. Logical Connection Communication takes place thru many layers 7 Logical communication Secretary: types a letter Delivery boy: drops the letter Secretary: reads and reports the message Delivery boy: takes the letter Post office: Processes and routes the letter Postal truck

8. Layer Model Layer N uses services provided by Layer N -1 8 Layer N Layer N Using services Providing services Logical communication path HOST A HOST B Layer N-2 Layer N-2 Layer N-1 Layer N-1 Virtual Communication System Layer N protocol

9. Why Layers? Guidelines for protocol developments Reference model Modularity Eases maintenance and updating of systems A change in one layer is transparent to the rest Is layering always the best thing to do? Maybe not  cross-layer optimization 9

10. Network Model Network models are responsible or   establishing a connection among the sender and receiver and transmitting the data. There are two computer network models on which data communication process relies : OSI Model TCP/IP Model  . 10

11. TCP/IP Model The TCP/IP model was developed prior to the OSI model . The TCP/IP model is not exactly similar to the OSI model . The TCP/IP model consists of five layers: the application layer, transport layer, network layer, data link layer and physical layer . The first four layers provide physical standards, network interface, internetworking, and transport functions that correspond to the first four layers of the OSI model and these four layers are represented in TCP/IP model by a single layer called the application layer . TCP/IP is a hierarchical protocol made up of interactive modules, and each of them provides specific functionality. 11

12. TCP/Internet Layer Model Application Layer Transport Layer Network Layer Data Link Layer Physical Layer 12 The Internet Protocol Stack User Transmission Medium Hardware Software

13. TCP/IP Model: the Internet model Application Transport Network Data link Physical 1 2 3 4 Network Data link Physical Application Transport Network Data link Physical 5 Each layer relies on services from layer below Each layer exports services to layer above Interface between layers defines interaction Hides implementation details Layers can change without disturbing other layers 2- 13

14. TCP/IP Model: the Internet model A pplication: supporting network applications FTP, SMTP, HTTP T ransport: application-application data transfer TCP, UDP N etwork: routing of datagrams from source to destination. Node-node data transfer IP, routing protocols Data Link: data transfer between neighboring network elements PPP, Ethernet P hysical: bits “on the wire” 2- 14

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17. Application Layer It is the topmost layer in the TCP/IP model . It is responsible for handling high-level protocols, issues of representation . This layer allows the user to interact with the application . It facilitates the user to use the services of the network . It is used to develop network-based applications . It provides user services like user login, naming network devices, formatting messages, and e-mails, transfer of files etc . When one application layer protocol wants to communicate with another application layer, it forwards its data to the transport layer . 17

18. Application Layer The only layer to interact with user 18 Responsible for providing services to the user SMTP HTTP FTP SMTP HTTP FTP Data Data H5 Application Layer to Transport from Transport Data H5 Data Logical communication

19. Transport Layer The transport layer is a 4 th  layer from the top . It is responsible for end to end data transmission service using connection oriented or either through connection-less protocols . TCP and UDP are two transport layer protocols that provide a different set of services to the network layer . It provide multiplexing/ demultiplexing service . It also provides other services such as reliable data transfer, bandwidth guarantees, and delay guarantees. 19

20. Transport Layer Duties/services Service-point addressing/Port Address Segmentation and reassembly Connection control Flow control (end-to-end) Error control (end-to-end) 20 Responsible for delivery of a message from one process to another

21. Transport Layer Services Segmentation  : Large data is divided into smaller segments at the senders end and then these smaller segments are recombined in exact format before it is received at receivers end . Error Control  : Distortion, Un-delivery of data packets and noise in data packets results in error and this is prevented using Transport Layer too and this feature is called Error Control . Flow Control  : Transport-Layer ensures that faster data transmission and slow data absorption or slow data transmission and faster data absorption must not occur . Transport-Layer performs  Multiplexing  &  De-multiplexing . Connection Control : Connection oriented  service using TCP (Transmission Control Protocol) Protocol & Connection less service using UDP (User Data-gram Protocol) Protocol are performed by transport layer. 21

22. Transport Layer 22 Transport Layer Data Data 1 Data 2 Data 3 H4 H4 H4 to Network Data Data 1 Data 2 Data 3 H4 H4 H4 from Network (segments) Process Process … Process Process … PORT # PORT #

23. Network Layer Duties/services Logical addressing Routing 23 Responsible for the delivery of packets from the original source to the destination

24. Network Layer 24 Network Layer Data from Transport to Data Link Data to Transport from Data Link Data H3 Data H3 (packet)

25. Network Layer 25 Network 1 Network 6 Network 5 1.1 1.2 6.6 6.1 6.3 5.7 5.2 Network 3 3.8 3.3 Router Data 1.1 5.7 1.1, 1.2, 6.1, 5.7, ... are logical addresses R1 R3 R2

26. Data Link Layer Framing: The data link layer divides the stream of bits received from the network layer into manageable data units called frames. Physical addressing: If frames are to be distributed to different systems on the network, the data link layer adds a header to the frame to define the sender and/or receiver of the frame. If the frame is intended for a system outside the sender's network, the receiver address is the address of the device that connects the network to the next one. Flow control (hop-to-hop): A receiving node can receive the frames at a faster rate than it can process the frame. Without flow control, the receiver's buffer can overflow, and frames can get lost. To overcome this problem, the data link layer uses the flow control to prevent the sending node on one side of the link from overwhelming the receiving node on another side of the link. Error control (hop-to-hop): The data link layer adds reliability to the physical layer by adding mechanisms to detect and retransmit damaged or lost frames. It also uses a mechanism to recognize duplicate frames. Error control is normally achieved through a trailer added to the end of the frame. Access control :. When two or more devices are connected to the same link, data link layer protocols are necessary to determine which device has control over the link at any given time. 26

27. Data Link Layer 27 Data Link Layer Data from Network to Physical Data to Network from Physical Data H2 Data H2 (frame) T2 T2 Responsible for transmitting frames from one hop (node) to the next

28. Data Link Layer 28 3B A3, 3B, 82, 9F, ... are physical addresses 9F 82 A3 Data 9F T2 A3 Data H2

29. Data Link Layer 29 Network 1 Network 6 Network 5 1.1 1.2 6.6 6.1 6.3 5.7 5.2 Network 3 3.8 3.3 Data 1.1 5.7 97 32 25 79 62 54 74 12 88 Data 1.1 5.7 25 97 Data 1.1 5.7 62 79 Data 1.1 5.7 74 54 R1 R3 R2

30. Physical Layer Physical Layer is the bottom-most layer. It is associated with the electrical, mechanical and transmission media . P hysical layer deals with all the physical devices that can be used for data communication. 30 The physical layer is responsible for movements of individual bits from one hop (node) to the next

31. Physical Layer 31 Physical Layer Data from Data Link to Data Link Data 01001011 01001011 Transmission medium (bits)

32. Physical Layer Functions Physical characteristics of interfaces and medium Representation of bits: Data consists of a stream of bits (sequence of 0s or 1s) with no interpretation. Data rate: T he number of bits sent per second. Synchronization of bits: the sender and the receiver clocks must be synchronized . Line configuration: Point to Point or Multipoint Physical topology: Bus/ Star/Mesh… Transmission mode: Simplex/Half/Full 32

33. The Big Picture 33 L5 data H5 L4 data H4 L3 data H3 L2 data T2 H2 0111011010101001010101001 L5 data H5 L4 data H4 L3 data H3 L2 data T2 H2 0111010101010010101010101 5 4 3 2 1 5 4 3 2 1 Transmission medium

34. Network D.L. P.L. D.L. P.L. Network D.L. P.L. D.L. P.L. Internet Model Application Transport Network Data Link Physical 34 Application Transport Network Data Link Physical Transmission medium sender router router receiver

35. Internet Model 35

36. Protocol Suites A set of protocols must be constructed to ensure that the resulting communication system is complete and efficient Each protocol should handle a part of communication not handled by other protocols How can we guarantee that protocols work well together? Instead of creating each protocol in isolation, protocols are designed in complete, cooperative sets called suites or families 36 36

37. Internet Protocol Suite 37 Layer Protocols Application HTTP, FTP, Telnet, SMTP, ... Transport TCP, UDP, SCTP, ... Network IP (IPv4), IPv6, ICMP, IGMP, ... Data Link Ethernet, Wi-Fi, PPP, ... Physical RS-232, DSL, 10Base-T, ...

38. OSI Model OSI stands for Open System Interconnection . Before networks came into existence, computers could only communicate from the same manufacturers .  OSI was designed by ISO (International Organization for Standardization) in late 1970 ’s. To break this barrier so that Computers from different manufacturer could communicate with each other . OSI is a “ Layered Approach ”, which is a logical representation of how Data Communication should occur. 38

39. OSI Model OSI has 7 different layers Two new layers is added Presentation Layer Session Layer It is divided into two groups, Top 3 layers defines how application within end stations will communicate with each other and with the user ( Software Layer ). Bottom 4 layers defines how actually data is transferred ( Hardware Layer ). https://www.youtube.com/watch?v=fiMswfo45DQ 39 7.Application Layer 6.Presentation Layer 5.Session Layer 4.Transport Layer 3.Network Layer 2.Data Link Layer 1.Physical Layer User Transmission Medium

40. Session Layer This layer is responsible for establishment of connection, maintenance of sessions, authentication and also ensures security . Duties/services Dialog Controller : Allows the two processes to establish, use and terminate a connection. Communication in half-duplex or full-duplex . Synchronization : allows a process to add checkpoints data is re-synchronized  Session recovery 40

41. Presentation Layer A Presentation layer is mainly concerned with the syntax and semantics of the information exchanged between the two systems . It acts as a data translator for a network . This layer is a part of the operating system that converts the data from one presentation format to another format . The Presentation layer is also known as the syntax layer. 41

42. Presentation Layer functions Duties/services Data translation:  For example, ASCII to EBCDIC . Encryption/Decryption Compression: Reduces the number of bits that need to be transmitted on the network. 42