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OSI and TCP MODELS of Networking
 

OSI and TCP MODELS of Networking

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It illustrates the difference of OSI model with TCP model for communications.

It illustrates the difference of OSI model with TCP model for communications.

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  • a distributed-queue dual-bus network (DQDB) is a distributed multi-access network that (a) supports integrated communications using a dual bus and distributed queuing, (b) provides access to local or metropolitan area networks
  • (Routing is the process of selecting paths in a network along which to send network traffic.)
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OSI and TCP MODELS of Networking OSI and TCP MODELS of Networking Presentation Transcript

  • The Theoretical Network
  • OSI Model • Networks are complicated structures with many interrelated parts. • To identify the various parts that makeup networks and how they work together , it is useful to have a network model. • International standard organization (ISO) established a committee in 1977 to develop a reference model for understanding computer network 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. • Communication Architecture provides Strategy for connecting host computers and other communicating equipment and defines necessary elements for data communication between devices. • OSI model is a layer architecture design and It is easy to debug network applications in a layered architecture network. • Term “open” denotes the ability to connect any two systems which conform(obey the rules) to the reference model and associated standards.
  • • 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 path of moving information between computers over a network medium into SEVEN smaller and more manageable functions . • This separation into smaller more manageable functions is known as layering.
  • 7 Layers of OSI Reference Model 07 06 05 → → → 04 → 03 → 02 → 01 → Provides services that directly support user applications Translates data formats and adds encryption Establishing and maintaining connections Adds identifiers to processes and deals with error-handling information Handles internetwork sequencing ,addressing and routing Adds error checking information and organizes bits into frames Transmits and receives bits over physical media
  • Physical Layer • Responsible for sending bits from one computer to another. • Deals with physical connection to the network and with transmission and reception of signals. • Covers all mechanical, electrical, functional and procedural aspects for physical communication , Such as voltage levels, timing of voltage changes, maximum transmission distances, physical connectors, and other similar attributes are defined by physical layer specifications.
  • Data link Layer • Data link layer attempts to provide reliable communication over the physical layer interface. • Create and detect frame boundaries. • Handle errors by implementing an acknowledgement and retransmission scheme. • Implement flow control. • Supports points-to-point communication. • Supports simplex, half-duplex or full-duplex communication.
  • Network Layer • Implements routing of frames (packets) through the network. • Defines the best possible path the packet should take from the source to the destination. Handles overcrowding in the network. • Defines logical addressing so that any endpoint can be identified • translates logical network physical machine addresses. addresses into
  • 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 sequence. data units are delivered in • Ensures that there is no loss or duplication of data units.
  • 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. • a logical connection to be established on an enduser’s request. • Any necessary log-on or password validation is also handled by this layer. • Session layer is also responsible for terminating the connection. • also provide check-pointing mechanism • data can be checkpoint. retransmitted from the last
  • 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 ,data translation, interpretation of graphics command.
  • Application Layer • Application layer interacts with application programs and is the highest level of OSI model. • such as file transfer, electronic mail, remote login etc. • When a programmer writes an application program that uses network services ,application program will access this layer.
  • Communication between Layers • Moving from the top, down - messages get larger and larger ! ! A message is passed down, and the lower layer adds a header to it. This is called encapsulation. • Moving from the bottom, up - messages get smaller and smaller ! ! A message is first stripped of it's header, and then the inner contents (the "data" portion) is passed up. This is "decapsulation".
  • Although there is officially no layer 0 or 8 conceptuall y they exist as the physical link (the cable) and the User, as shown below. Note how the packets get larger as each successive layer adds it's own header to the packet that was handed down to it from the layer above.
  • IEEE 802 categories • The institute of IEEE in February 1980 formed a project called project 802 to help define certain LAN standards, though “802” is sometimes associated with the date the first meeting was held — February 1980. • IEEE 802 refers to a family of IEEE standards dealing with local area networks and metropolitan area networks.
  • • IEEE 802 splits the OSI Data Link Layer into two sub-layers named Logical Link Control (LLC) and Media Access Control (MAC), so that the layers can be listed like this: 1. Data link layer i. LLC Sub layer ii. MAC Sub layer 2. Physical layer • The IEEE 802 family of standards is maintained by the IEEE 802 LAN/MAN Standards Committee (LMSC). The most widely used standards are for the Ethernet family, Token Ring, Wireless LAN, Bridging and Virtual Bridged LANs. An individual Working Group provides the focus for each area.
  • Some Working groups Name Description IEEE 802.1 Bridging (networking) and Network Management IEEE 802.2 LLC IEEE 802.3 Ethernet IEEE 802.4 Token bus IEEE 802.5 Defines the MAC layer for a Token Ring IEEE 802.6 MANs(DQDB ) IEEE 802.7 Broadband LAN using Coaxial Cable IEEE 802.8 Fiber Optic TAG
  • Protocol Stacks • As network management is easier due to the layered architecture. • Each layer has its own a set of rules and requirements called protocol. • The protocol defines the format of the data being exchanged, and the control and timing for the handshake between layers. • Protocols that work together to provide a layer or layers of OSI model are protocol stacks or suit. • The protocol stack is an implementation of a computer networking protocol suite. The terms are often used interchangeably. Strictly notice, the suite is the definition of the protocols, and the stack is the software implementation of them.
  • • Protocol stacks are often divided into three major sections: media, transport, and applications. • A particular operating system or platform will often have two welldefined software interfaces: one between the media and transport layers, and one between the transport layers and applications. a) The media-to-transport interface defines how transport protocol software makes use of particular media and hardware types ("card drivers"). For example, this interface level would define how TCP/IP transport software would talk to Ethernet hardware. b) The application-to-transport interface defines how application programs make use of the transport layers. For example, this interface level would define how a web browser program would talk to TCP/IP transport software.
  • Internet protocol suite TCP/IP MODEL • The Internet protocol suite is the networking model and a set of communications protocols used for the Internet and similar networks. It is commonly known as TCP/IP. • The Internet protocol suite and the layered protocol stack design were in use before the OSI model was established. • It is one of the commonly used networks today.
  • The layers of the protocol suite near the top are logically closer to the user application, w hile those near the bottom are logically closer to the physical transmission of the data.
  • • It was developed by Department of defend’s Advanced projects Research Agency DARPA, an agency of the United States Department of Defense under its project on network interconnection , started in 1969. • TCP/IP provides end-to-end connectivity specifying how data should be formatted, addressed, transmitted, routed and received at the destination. • It has four layers,  The link layer  The internet layer (IP)  The transport layer  The application layer
  • • Application layer (process-to-process): This is the scope within which applications create user data and communicate this data to other processes or applications on another or the same host. This is where the higher level protocols such as HTTP (hypertext transfer protocol), etc. operate.
  • • Transport layer (host-to-host): • This is where flow-control, errorcorrection, and connection protocols exist, such as TCP. • This layer deals with opening and maintaining connections between Internet hosts.
  • Internet layer: • The internet layer has the task of exchanging data grams across network boundaries. • It defines and establishes the Internet. This layer defines the addressing and routing structures used for the TCP/IP protocol suite.
  • • Link / Network access layer: • Despite the different semantics of layering in TCP/IP and OSI, the link layer is often described as a combination of the data link layer (layer 2) and the physical layer (layer 1) in the (OSI) protocol stack • Management of reliable data delivery, • access to physical networks • Binary data transmission
  • Working As data is being sent from one computer, it will pass from the top layer to the bottom. On the receiving end, the data will then be rebuilt from the bottom layer to the top.
  • Each layer a packet of information travels through adds what is called a header. Think of it in terms of a Russian doll. • When the packet is being rebuilt on the receiving end, each header is unpackaged the same way.
  • • Since each layer of the TCP/IP model does a unique task separate of the other layers, we refer to the data package at each layer with different names. For instance, the data package at the Application Layer is called a message, while the same data package at the Internet Layer is called a datagram. • Once the data packet leaves link layer it is converted into a bit stream of electrical pulses, commonly referred to as 1’s and 0’s.
  • Difference • all transport layer in TCP implementations must choose whether or how to provide reliability. UDP(User Datagram Protocol) provides data integrity/errorless data via a checksum but does not guarantee delivery; TCP (Transmission Control Protocol) provides both data integrity and delivery guarantee by retransmitting until the receiver acknowledges the reception of the packet.
  • Connectionless vs. connection oriented protocols • These are the two ways in which communications between computers can be arranged. • Former assumes that all data will get through ,do not check delivery & sequencing . • Faster working • UDP/IP • Connectionless Network Service is an OSI Network Layer service.
  • Connectionless vs. connection oriented protocols • Later presume that some data will be lost or disordered . • Assures data delivery in sequential order by retaining data and negotiating for retransmission . • Reliable • TCP/IP
  • Which is better?  Historically, a few companies tried to create protocol stacks based on ISO/OSI, mostly throughout the 1980s (Unger man-Bass, even the early versions of Microsoft NetBEUI).  However, no implementation ever seen was "complete" in that it covered all 7 layers. The ISO/OSI model is simply more theoretical than practical.  On the other hand, the TCP/IP model is easy to implement and there are numerous implementations of it.  Either way, during the mid 1980s, it became clear that the stack of TCP/IP protocols that was built according to the TCP/IP model were winning in the market. Whatever "OSI inspired" products there were, disappeared from the market.