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Computer Communication Networks (Sub., Code : 10EC71)

Computer Communication Networks (Sub., Code : 10EC71). Unit - 1. Overview. Layered tasks OSI Model Layers in OSI model TCP/IP Suite Addressing Telephone and cable networks for data transmission, Telephone networks Dial up modem DSL Cable TV for data transmission. Network Models.

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Computer Communication Networks (Sub., Code : 10EC71)

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  1. Computer Communication Networks (Sub., Code : 10EC71)

  2. Unit - 1 Overview • Layered tasks • OSI Model • Layers in OSI model • TCP/IP Suite • Addressing • Telephone and cable networks for data transmission, • Telephone networks • Dial up modem • DSL • Cable TV for data transmission.

  3. Network Models

  4. 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. Sender, Receiver and, Carrier Higher Layer Middle Layer Lower layer Hierarchy Tasks must be done in the given order

  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. ISO is the organization.OSI is the model.

  6. Layers in the OSI Model “PleaseDo Not Touch Steve’sPet Alligators”

  7. Reasons For Layering • Layered networking model is advantageous because • Divides networking into less complex components • Enables programmers to specialize in a particular level • Allows upgrades to a specific layer without effecting other layers • Encourages interoperability • Allows for standardized interfaces

  8. The interaction between layers in the OSI model

  9. Reasons For Layering • Layered Architecture • Peer to peer Process • The process on each machine that communicates at a given layer are called peer-to-peer process. • Interfaces Between Layers • Interface defines the information and services a layer must provide for the layer above it. • Organization of the layers (subgroups ) • Layers 1,2, and 3 are the network support layers • 5,6, and 7 as a user support layers • Layer 4, Transport layer links the two subgroups

  10. The interaction between layers in the OSI model • The OSI model is composed of seven ordered layers. • Within a single machine each layer calls upon the services of the layer just below it. • Layer 3 uses the services of layer 2 and provide services to layer 4 • Between machines, layer x on the machine communicates with layer x on another machine. • Communication is governed by an agreed upon series of rules and conventions called protocols. (A protocol is a rule which guides how an activity should be performed, especially in the field of diplomacy. In computing, a protocol is a convention or standard that controls or enables the connection, communication, and data transfer between two computing endpoints.) • The process on each machine that communicates at a given layer are called peer-to-peer process.

  11. Physical layer • The physical layer is concerned with transmitting raw bits over a communication channel. • It deals with the mechanical, electrical, and timing interfaces, and the physical transmission medium, which lies below the physical layer. • Physical Characteristics of interfaces and media, Representation of bits, Date rate, Synchronization of bits, Physical topology, Transmission mode(eg., Simplex).

  12. Physical layer has the following responsibilities • Physical characteristics of interfaces and medium • Cable • Connectors • Interfaces • Transmission Medium • Cable/wire • Radio waves • Infrared • Fiber/glass • Representation of bits • Bits must be encoded into signals- electrical, optical. Type of encoding (binary encoding as voltages (Manchester encoding method) • Transmission of the signal on the medium • Synchronization of bits • Tx and Rx clocks must be synchonized.

  13. Physical layer has the following responsibilities • Data Rate • Duration of the bit • Physical Topology • How device are connected • Ring, Bus, Mesh, star Topology • Transmission mode • Simplex, half duplex, duplex.

  14. Physical layer

  15. Data link layer • Responsible for moving frames from one hop (node) to the next • Framing: Divides the stream of bits received from network layer into manageable data units called frames. • Physical addressing: Adds a header to the frame to define the sender and/or receiver of the frame. • Flow Control: If the receiver is slower than the transmitter • Error Control: Retransmit for damaged frames, recognition duplication • Access Control:

  16. Hop-to-hop delivery

  17. Data link layer • Data Link sublayers • Logical Link Control (LLC) layer • Defines how data is packaged (frames) • Provides the linking function between the Physical Layer and the higher layers • Media Access Control (MAC) layer • Media access method • Provides a unique identifier for the NIC (Physical address)

  18. Data link layer • Type ipconfig/all at command prompt

  19. Network layer • Responsible for source to destination delivery of individual packet. • Logical addressing: Physical address used only for locally • Routing:

  20. Source-to-destination delivery

  21. Transport layer • Responsible for process-to-process delivery of the entire message. • A process is an application program running on a host. • Transport layer ensures the whole message arrives intact and in order, overseeing both error control and flow control at the source-to-destination level

  22. Transport layer Transport layer has the following responsibilities • End-to-end error free transmission and delivery • Segmentation and reassembly: Divided into transmittable segments by sequence number for each segment. • Connection Control: Connectionless or connection oriented, In connection oriented it makes connection and terminates connections when data transfer completes • Flow control: End to end rather than single link • Error control: Performed between process to process rather than a single link

  23. Transport layer

  24. Session layer • Session layer has the following responsibilities • Control for data exchange • Data synchronization • Failure recovery • Communication setup and teardown • Enables two applications to have an ongoing conversation or dialog • Ability to interrupt and recover as session • SQL, RPC, X-Windows

  25. Session layer • The session layer allows users on different machines to establish sessions between them. • Sessions offer various services, including dialog control (keeping track of whose turn it is to transmit), token management (preventing two parties from attempting the same critical operation at the same time), and synchronization (check pointing long transmissions to allow them to continue from where they were after a crash).

  26. Presentation layer Presentation has the following responsibilities • Translation: Data is of text, audio or video: changed to bit stream. Different computers use different encoding system. • BMP, WAV, JPEG, MIDI, HTML, ASCII • Data encryption: To ensure privacy (Encryption, Decryption) • Data compression: To reduce the size of the file

  27. Presentation layer • Presentation layers concerned with the syntax and semantics of the information transmitted. • In order to make it possible for computers with different data representations to communicate, the data structures to be exchanged can be defined in an abstract way, along with a standard encoding to be used ''on the wire.'' • The presentation layer manages these abstract data structures and allows higher-level data structures (e.g., banking records), to be defined and exchanged.

  28. Application layer • The port numbers are divided into three ranges: the well-known ports, the registered ports, and the dynamic or private ports. The well-known ports are those from 0 through 1023. Examples include: • 20 & 21: File Transfer Protocol (FTP) • 22: Secure Shell (SSH) • 23: Telnet remote login service • 25: Simple Mail Transfer Protocol (SMTP) • 53: Domain Name System (DNS) service • 80: Hypertext Transfer Protocol (HTTP) used in the World Wide Web • 3128: Port used by some proxy servers,  Web caches and the default for the Squid cache • 110: Post Office Protocol (POP3) • 119: Network News Transfer Protocol (NNTP) • 143: Internet Message Access Protocol (IMAP) • 161: Simple Network Management Protocol (SNMP) • 443: HTTP Secure (HTTPS) • 465: SMTP Secure (SMTPS)

  29. Application layer • The application layer contains a variety of protocols that are commonly needed by users. • HTTP (Hyper Text Transfer Protocol) • Other application protocols are used for file transfer, electronic mail, and network news.

  30. Application layer • Application has the following responsibilities • Initiate request for network services • Provides network services to applications such as e-mail and Web browsers • Protocols and utilities • Telnet • FTP • DNS • SMTP • SNMP

  31. Associated TCP/IP Protocols & Services

  32. Data Encapsulation • It is a process of adding a header to wrap the data that flows down the OSI model. • Encapsulation Process • Wrapping up of data into a protocol is also known as encapsulation. • The Application layer, Presentation layer and Session layer create data from user's input. • Encapsulation actually starts at layer 4 of the OSI model where the Transport layer convert the data into segments by adding a header containing source and destination port numbers. • The Network layer convert the segments into packets (or datagram) by adding a header containing source and destination IP address. • The Data link layer convert the packets into Frames by adding a header containing source and destination MAC address and a trailer containing the Frame check sequence(FCS)used for verifying the data integrity. • The Physical layer convert the frames to bits and it is transmitted through the physical medium which can be a UTP

  33. Data Encapsulation

  34. Data Encapsulation

  35. Summary of layers

  36. Some Data Comm. Standards

  37. TCP/IP PROTOCOL SUITE • Developed prior to the OSI model. • 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.

  38. TCP/IP and OSI model

  39. TCP/IP and OSI Model • Simple Mail Transfer Protocol (SMTP) • File Transfer Protocol (FTP) • Hypertext Transfer Protocol (HTTP) • Domain Name System (DNS) • Simple Network Management Protocol (SNMP) • Stream Control Transmission Protocol (SCTP) • Transmission Control Protocol (TCP)  • User Datagram Protocol (UDP) • Internet Control Message Protocol (ICMP) • Internet Group Management Protocol (IGMP) • Internet Protocol (IP) • Address Resolution Protocol (ARP) • Reverse Address Resolution Protocol (RARP)

  40. Physical and Data Link Layers • Covers physical interface between PC or workstation and a transmission medium or network • At the physical and data link layers, TCP/IP does not define any specific protocol. • It supports all the standard and proprietary protocols. • A network in a TCP/IP internetwork can be a local-area network or a wide-area network.

  41. Network Layer • Concerned with access to and routing data across a network for two end systems attached to the same network. • TCP/IP supports the Internetworking Protocol. • IP uses four supporting protocols : ARP, RARP, ICMP, and IGMP. • IP (Internetworking Protocol) • ARP (Address Resolution Protocol) • RARP (Reverse Address Resolution Protocol) • ICMP (Internet Control Message Protocol) • IGMP (Internet Group Message Protocol) • Internet Layer: IP provides the routing functions across the multiple networks

  42. Network Layer • IP (Internetworking Protocol) • IP is the transmission mechanism by the TCP/IP protocol. • It is unreliable connectionless protocol a best effort delivery service. • It transports data in packets called datagrams. • ARP (Address Resolution Protocol) • Is used to associate a logical address with a physical address. ARP is used to find the physical address of the node when its Internet address is known. • RARP (Reverse Address Resolution Protocol) • It allows a host to discover its Internet address when it knows only physical address. It is used when a computer is connected for the first time.

  43. Network Layer • ICMP (Internet Control Message Protocol) • ICMP is mechanism used by host and gateways to send notification of datagram problems back to the sender. • IGMP (Internet Group Message Protocol) • IGMP is used to facilitate the simultaneous transmission of message to a group of recipients.

  44. Transport Layer • Collection of mechanisms in a single and common layer • The transport layer was represented in TCP/IP by two protocols : TCP and UDP. • IP is a host-to-host protocol • TCP and UDP are transport level protocols responsible for delivery of a message from a process to another process. • UDP (User Datagram Protocol) • TCP (Transmission Control Protocol) • SCTP (Stream Control Transmission Protocol)

  45. Transport Layer • UDP (User Datagram Protocol) • UDP is the simper of the two standard TCP/IP transport protocol. It is a process to process protocol that adds only port address, checksum, error control. • TCP (Transmission Control Protocol) IP is a host-to-host protocol • TCP is a reliable stream transport protocol (connection oriented) • At the sending end message is divided into smaller units called segments. • SCTP (Stream Control Transmission Protocol) • Supports for newer applications such as voice over IP. It combiners the best features of UDP and TCP.

  46. What is TCP/IP? • Transmission Control Protocol (TCP) – uses a set of rules to exchange messages with other Internet points at the information packet level • Internet Protocol (IP) – uses a set of rules to send and receive messages at the Internet address level • TCP/IP is a result of protocol research and development conducted on experimental packet switched network by ARPANET funded by the defense advanced research projects agency (DARPA). • TCP/IP used as internet standards by the internet architecture board (IAB).

  47. IP • Connectionless protocol (I.e. no established connection between the end points that are communicating.) • Responsible for delivery the independently treated packet !!!! • TCP responsible for reassembly.

  48. Application Layer • The application layer in TCP/IP is equivalent to the combined session, presentation, and application layers in the OSI model. • Many protocols are defined at this layer. • Contains the logic needed to support the various user applications. • Separate module are required for each application

  49. Associated TCP/IP Protocols & Services

  50. RS-232

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