COMPUTER NETWORKS-1 (BTCS-403) By Baljinder Singh Assistant Professor (I.T)

1. COMPUTER NETWORKS-1 (BTCS-403) By Baljinder Singh Assistant Professor (I.T) Beant College of Engg. & Technology, Gurdaspur

2. CONTENTS • Introduction Computer Networks • OSI & TCP/IP Reference Model • Layering, TCP/IP, Internet Addresses, DNS, Client Server Model, Port Numbers. • Link Layer Ethernet & IEEE 802( SLIP, PPP).

3. INTRODUCTION

4. Computer Network • A computer n/w is a group of communicating entities that uses a common network protocol to exchange data and share resources with each other over a communication medium. These communicating entities can be differentiated into end systems or intermediate systems. • End System(Computer, Telephone, Laptop, etc…) • Intermediate System(Repeater, Hub, Bridges, Router)

5. Contt… • Computer Network can be classified into different types on the basis of the…. • Geographical Extent(LAN, MAN, WAN). • Physical Interconnection of hosts(Network Topologies(Bus, Ring, Star, Tree, Mesh). • Type of communication path used • Manner of data transmission among hosts over this communication path.

6. Uses of Computer Networks • Resource Sharing • Communication Medium • Reliability • Scalability • Money Saving • E-Commerce • Online Banking Etc.

7. Business Applications of Networks • A network with two clients and one server.

8. Business Applications of Networks (2) • The client-server model involves requests and replies.

9. Mobile Network Users

10. Types of Networks • Local Area Networks • Metropolitan Area Networks • Wide Area Networks • Wireless Networks

11. Broadcast Networks • Types of transmission technology • Broadcast links • Point-to-point links

12. Classification of interconnected processors by scale.

13. Local Area Networks • Two broadcast networks • (a) Bus • (b) Ring

14. Metropolitan Area Networks • A metropolitan area network based on cable TV.

15. Wide Area Networks • Relation between hosts on LANs and the subnet.

16. Wide Area Networks (2) • A stream of packets from sender to receiver.

17. Wireless Networks • Categories of wireless networks: • System interconnection • Wireless LANs • Wireless WANs

18. Wireless Networks (2) • (a) Bluetooth configuration • (b) Wireless LAN

19. Network Software • Protocol Hierarchies • Design Issues for the Layers • Connection-Oriented and Connectionless Services • Service Primitives • The Relationship of Services to Protocols

20. Network SoftwareProtocol Hierarchies • Layers, protocols, and interfaces.

21. Design Issues for the Layers • Addressing • Error Control • Flow Control • Multiplexing • Routing

22. Services to Protocols Relationship • The relationship between a service and a protocol.

23. Reference Models • The OSI Reference Model • The TCP/IP Reference Model

24. Reference Models The OSI Reference Model.

25. Network Communication Protocols • In order to standardize these protocols and also to provide a framework for their development, some standard reference models were developed. These network models are based on the concept of layering. • The n/w protocols are structured into set of layers, with each layer responsible for a different fact of communication. • A layered architecture lies in the ability to independently design, build or modify the functions and services of each layer without effecting the other layers. • It reduces the complexity of n/w operations by dividing them into simpler components • It also enable multi-vendor integration by dividing standard interfaces.

26. Protocols & Standards • A protocol is a set of rules that govern data communication. A protocol define what is communicated, how it is communicated & when to communicated. Key elements are. 1. Syntax 2. Semantics 3. Timing • Syntax refers to structure or format of the data, order they presented. • 1st 8-bit address of sender • 2nd 8-bit address of receiver • Rest of stream of message • Semantics refers to the meaning of each section of bits, how is particular pattern interpreted. • Timing refers two things:- 1. When data should be sent 2. How fast it can be send.

27. Contt… • Standards are essentials in creating and maintaining an open and competitive market for equipment manufacturers and also in guaranteeing national & international inter operability of data & telecommunications technology & processes. There are two types • de-facto(By fact or by convention) • de-jure(By law by regulation) • RFCs(Request for Comment) All the official standards in the internet community are published as RFC. Additionally there are lot of RFCs that are not official standards but published for information purposes. Each RFC ranges from 1 page to almost 200 pages. Each RFC is identified by a number.

28. OSI REFERENCE MODEL

29. Communication Architecture • Strategy for connecting host computers and other communicating equipment. • Defines necessary elements for data communication between devices. • A communication architecture, therefore, defines a standard for the communicating hosts. • A programmer formats data in a manner defined by the communication architecture and passes it on to the communication software. • Separating communication functions adds flexibility, for example, we do not need to modify the entire host software to include more communication devices.

30. Layer Architecture • Layer architecture simplifies the network design. • It is easy to debug network applications in a layered architecture network. • The network management is easier due to the layered architecture. • Network layers follow a set of rules, called protocol. • The protocol defines the format of the data being exchanged, and the control and timing for the handshake between layers.

31. Open Systems Interconnection (OSI) Model • International standard organization (ISO) established a committee in 1977 to develop an architecture for computer communication. • Open Systems Interconnection (OSI) reference model is the result of this effort. • In 1984, the Open Systems Interconnection (OSI) reference model was approved as an international standard for communications architecture. • Term “open” denotes the ability to connect any two systems which conform to the reference model and associated standards.

32. OSI Reference Model • The OSI model is now considered the primary Architectural model for inter-computer communications. • The OSI model describes how information or data makes its way from application programmes (such as spreadsheets) through a network medium (such as wire) to another application programme located on another network. • The OSI reference model divides the problem of moving information between computers over a network medium into SEVEN smaller and more manageable problems . • This separation into smaller more manageable functions is known as layering.

33. OSI Reference Model: 7 Layers OSI Model

36. OSI Model OSI: A Layered Network Model • The process of breaking up the functions or tasks of networking into layers reduces complexity. • Each layer provides a service to the layer above it in the protocol specification. • Each layer communicates with the same layer’s software or hardware on other computers. • The lower 4 layers (transport, network, data link and physical —Layers 4, 3, 2, and 1) are concerned with the flow of data from end to end through the network. • The upper four layers of the OSI model (application, presentation and session—Layers 7, 6 and 5) are orientated more toward services to the applications. • Data is Encapsulated with the necessary protocol information as it moves down the layers before network transit.

37. User Level Processing Telnet, FTP, Mail Application ISO Presentation Data Representation & Syntax Presentation ISO Session Sync Points and Dialogs Session Transport Reliable End to End TCP Unreliable Thru Multi-Node Network Network X.25 Pkt, IP Reliable Across Physical Line Link LAPB, HDLC Unreliable Wire, Telco Line Physical RS232, T1, 802.x The OSI Model Layer Name Description Examples

38. Application Presentation Session Transport Network Link Physical The OSI Model The Standards Layer Name Standards X.400, Telnet, FTP, Mail ASN.1, X.409 X.225 X.224, TCP X.25 Pkt, Q.931, IP X.25 LAPB, Q.921 LAPD, ISO 3309 HDLC Reliable Across Physical Line Unreliable Wire, Telco Line Unreliable Wire, Telco Line RS232, V.35, EIA530, X.21, T1, E1

39. OSI Model Physical Layer • Provides physical interface for transmission of information. • Defines rules by which bits are passed from one system to another on a physical communication medium. • Covers all - mechanical, electrical, functional and procedural - aspects for physical communication. • Such characteristics as voltage levels, timing of voltage changes, physical data rates, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.

40. OSI Model Data Link Layer • Data link layer attempts to provide reliable communication over the physical layer interface. • Breaks the outgoing data into frames and reassemble the received frames. • Create and detect frame boundaries. • Handle errors by implementing an acknowledgement and retransmission scheme. • Implement flow control. • Supports points-to-point as well as broadcast communication. • Supports simplex, half-duplex or full-duplex communication.

41. OSI Model Network Layer • Implements routing of frames (packets) through the network. • Defines the most optimum path the packet should take from the source to the destination • Defines logical addressing so that any endpoint can be identified. • Handles congestion in the network. • Facilitates interconnection between heterogeneous networks (Internetworking). • The network layer also defines how to fragment a packet into smaller packets to accommodate different media.

42. OSI Model Transport Layer • Purpose of this layer is to provide a reliable mechanism for the exchange of data between two processes in different computers. • Ensures that the data units are delivered error free. • Ensures that data units are delivered in sequence. • Ensures that there is no loss or duplication of data units. • Provides connectionless or connection oriented service. • Provides for the connection management. • Multiplex multiple connection over a single channel.

43. OSI Model Session Layer • Session layer provides mechanism for controlling the dialogue between the two end systems. It defines how to start, control and end conversations (called sessions) between applications. • This layer requests for a logical connection to be established on an end-user’s request. • Any necessary log-on or password validation is also handled by this layer. • Session layer is also responsible for terminating the connection. • This layer provides services like dialogue discipline which can be full duplex or half duplex. • Session layer can also provide check-pointing mechanism such that if a failure of some sort occurs between checkpoints, all data can be retransmitted from the last checkpoint.

44. OSI Model Presentation Layer • Presentation layer defines the format in which the data is to be exchanged between the two communicating entities. • Also handles data compression and data encryption (cryptography).

45. OSI Model Application Layer • Application layer interacts with application programs and is the highest level of OSI model. • Application layer contains management functions to support distributed applications. • Examples of application layer are applications such as file transfer, electronic mail, remote login etc.

46. OSI Model OSI in Action • A message begins at the top application layer and moves down the OSI layers to the bottom physical layer. • As the message descends, each successive OSI model layer adds a header to it. • A header is layer-specific information that basically explains what functions the layer carried out. • Conversely, at the receiving end, headers are striped from the message as it travels up the corresponding layers.

47. TCP/IP Model OSI & TCP/IP Models

48. TCP/IP PROTOCOL SUITE

49. Introduction • The TCP/IP protocol suite allows computers of all sizes, from many different computer vendors, running totally different operating systems, to communicate with each other. What started in the late 1960s as a government-financed research project into packet switching networks has, in the 1990s, turned into the most widely used form of networking between computers. • It forms the basis for what is called the worldwide Internet, or the Internet, a wide area network (WAN) of more than one million computers that literally spans the globe.

50. TCP/IP Model Application Layer Application programs using the network Transport Layer (TCP/UDP) Management of end-to-end message transmission, error detection and error correction Network Layer (IP) Handling of datagrams : routing and congestion Data Link Layer Management of cost effective and reliable data delivery, access to physical networks Physical Layer Physical Media