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Network standards


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Basic OSI Model and some protocols

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Network standards

  2. 2. De facto, de jurie Standards • Standards fall into two categories: de facto and de jure. • De facto (Latin for ‘‘from the fact’’) standards are those that have just happened, without any formal plan. HTTP, the protocol on which the Web runs, started life as a de facto standard. It was part of early WWW browsers developed by Tim Berners-Lee at CERN, and its use took off with the growth of the Web. Bluetooth is another ex-ample. It was originally developed by Ericsson but now everyone is using it. • De jure(Latin for ‘‘by law’’) standards, in contrast, are adopted through the rules of some formal standardization body. International standardization authorities are generally divided into two classes: those established by treaty among national governments, and those comprising voluntary, non- treaty organizations. In the area of computer network standards like ISO, IEEE, ASCII.
  3. 3. The Seven Layers of the OSI Model International Organization of Standardization ISO
  4. 4. Encapsulation
  5. 5. 7 Layers 7. Application Layer 6. Presentation Layer 5. Session Layer 4. Transport Layer 3. Network Layer 2. Data Link Layer 1. Physical Layer All People Seem To Need Data Processing
  6. 6. Layer7 • The application layer is the OSI layer that is closest to the user; it provides network services to the user’s applications. It differs from the other layers in that it does not provide services to any other OSI layer, but rather, only to applications outside the OSI model. Examples of such applications are spreadsheet programs, word processing programs, and bank terminal programs. If you want to remember Layer 7 in as few words as possible, think of browsers.
  7. 7. 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.
  8. 8. Layer 6 • The presentation layer ensures that the information that the application layer of one system sends out is readable by the application layer of another system. If necessary, the presentation layer translates between multiple data formats by using a common format. If you want to think of Layer 6 in as few words as possible, think of a common data format
  9. 9. 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).
  10. 10. Layer 5 • As its name implies, the session layer establishes, manages, and terminates sessions between two communicating hosts. The session layer provides its services to the presentation layer. It also synchronizes dialogue between the two hosts' presentation layers and manages their data exchange. If you want to remember Layer 5 in as few words as possible, think of dialogues and conversations.
  11. 11. 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.
  12. 12. Layer 4 • The transport layer Segments and Sequences data from the sending host's system and reassembles the data into a data stream on the receiving host's system. Layer 4 is the boundary between media-layer protocols and host-layer protocols. Layer 4 also deals with Flow Control through (Windowing) or Window Negotiation. And is responsible for the Reliability of Communication through (Acknowledgements).
  13. 13. 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.
  14. 14. Layer 3 • The network layer is a complex layer that provides connectivity and path selection between two host systems that may be located on geographically separated networks. If you want to remember Layer 3 in as few words as possible, think of path selection, routing, and logical addressing. Routers are layer 3 devices
  15. 15. 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.
  16. 16. Layer 2 • The data link layer provides reliable transit of data across a physical link. In so doing, the data link layer is concerned with physical addressing, network topology, network access, error notification, ordered delivery of frames. If you want to remember Layer 2 in as few words as possible, think of physical addressing, and topologies Switches, Bridges, and NICs are layer 2 devices
  17. 17. 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.
  18. 18. Layer 1 • The physical layer defines the electrical, mechanical, procedural, and functional specifications for activating, maintaining, and deactivating the physical link between end systems. 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. If you want to remember Layer 1 in as few words as possible, think of signals and media. Hubs, cables, and connectors are layer 1 devices
  19. 19. 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.
  20. 20. Summary of the OSI Model Layer Description
  21. 21. Encapsulation: Protocol Data Units (PDU) and Peer to Peer Communication
  22. 22. Detailed encapsulation process • All communications on a network originate at a source, and are sent to a destination. • The information sent on a network is referred to as data or data packets. If one computer (host A) wants to send data to another computer (host B), the data must first be packaged through a process called encapsulation.
  23. 23. Detailed encapsulation process Networks must perform the following five conversion steps in order to encapsulate data: 1. Build the data. 2. Package the data for end-to-end transport. 3. Add the network IP address to the header. 4. Add the data link layer header and trailer. 5. Convert to bits for transmission.
  24. 24. TCP/IP model • Unlike the proprietary networking technologies mentioned earlier, TCP/IP was developed as an open standard. • This meant that anyone was free to use TCP/IP. This helped speed up the development of TCP/IP as a standard. • Although some of the layers in the TCP/IP model have the same name as layers in the OSI model, the layers of the two models do not correspond exactly.
  25. 25. TCP/IP model Some of the common protocols specified by the TCP/IP reference model layers. Some of the most commonly used application layer protocols include the following: • File Transfer Protocol (FTP) • Hypertext Transfer Protocol (HTTP) • Simple Mail Transfer Protocol (SMTP) • Domain Name System (DNS) • Trivial File Transfer Protocol (TFTP) The common transport layer protocols include: • Transport Control Protocol (TCP) • User Datagram Protocol (UDP) The primary protocol of the Internet layer is: • Internet Protocol (IP)
  26. 26. TCP/IP model Networking professionals differ in their opinions on which model to use. Due to the nature of the industry it is necessary to become familiar with both. Both the OSI and TCP/IP models will be referred to throughout the curriculum. The focus will be on the following: • TCP as an OSI Layer 4 protocol • IP as an OSI Layer 3 protocol • Ethernet as a Layer 2 and Layer 1 technology Remember that there is a difference between a model and an actual protocol that is used in networking. The OSI model will be used to describe TCP/IP protocols. Use Ethereal to capture TCP/IP packets wrapped in an Ethernet frame
  27. 27. SLIP & PPP