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Introduction to OSI – Layer 3 and 4 Protocols

Introduction to OSI – Layer 3 and 4 Protocols. Dr. Farid Farahmand Chapters 5 and 6. Data Communication Model.

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Introduction to OSI – Layer 3 and 4 Protocols

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  1. Introduction to OSI – Layer 3 and 4 Protocols Dr. Farid Farahmand Chapters 5 and 6

  2. Data Communication Model Note that ISO is not an acronym; instead, the name derives from the Greek word iso, which means equal. Founded in 1946, ISO is an international organization composed of national standards bodies from over 75 countries. For example, ANSI (American National Standards Institute) is a member of ISO. • OSI Protocol Model • Short for Open System Interconnection developed by ISO in 1984 • ISO (International Organization for Standardization) standard for worldwide communications • Defines a seven layer networking framework for implementing protocols • Provided the data communication language rules!

  3. Data Communication Model • Protocols define the rules, methods, and standards used by the network • Voice communication standards were typically only controlled by a single company • Data communications has many different standards depending on the application

  4. OSI Model - who is in charge? http://en.wikipedia.org/wiki/Transport_layer

  5. Physical Layer Protocols (Layer 1) • Responsible for transporting the information • encapsulating information and getting it ready for transportation • They define physical interfaces, electrical parameters, pin outs, number of twists per foot, cable gauge, etc. • Examples: RS-232, V.35, RJ-48, DS3, OC-n, High Speed Serial Interface

  6. RS-233 Interfacing computer to modem Supports speeds up to 9.6 Kbps 25-pin or 9-pin interface V.35 Serial interface between the terminal and the digital communication equipment (T1) Supports speeds above 19.2 Kbps RJ-48 Physical interface for T1 and E1 Defined by G.703 standards DS3 Uses coaxial cable Supports 45 Mbps OC-n Fiber optic interface n can be 1,3,12,etc. Multimode or single mode High speed Serial Interface Supports 42 Mbps Interfacing ATM switches Physical Layer Protocols - Examples

  7. Data Link Layer Protocols (Layer 2) Data RX TX Check MAC Data Link Layer LLC Translator Network Layer • Govern routing the information through the network and ensure proper transmission of data • Consists of two sub layers • Media Access Layer • Closer to the physical layer • Checks the MAC address • 48-bit flat address • Decides if the packet must pass or sent to the LLC sub layer • Logical Link Control Layer • Passes the information to the network layer • Acts as a translating agent FR, HDLC, ATM - Layer 2 Protocol IP - Layer 3 Protocol

  8. Data Link Layer Protocols (Layer 2) • Frame and format information according to some standards • Two basic categories • Connection oriented Technology • Establishing pre-defined virtual path upon request • Many different virtual paths can reside on a physical link (like a highway system) • Example: ATM and Frame Relay Protocols • Connectionless Technology • Only source and destination addresses are defined • No pre-defined path exists between devices • The actual routing path can be different depending on the network status • Example: High-level Data Link Control (HDLC)

  9. SDLC Synchronous Data Link Control Developed by IBM for WAN Supporting mainframe machines HDLC High-level Data Link Control Developed by ISO Point-to-multi-point protocol Connectionless service PPP Point-to-point Protocol Advised by IETF Used for dial-up Internet services End-to-end connection oriented Used in Broadband technology Frame Relay Carries IP packets (encapsulated) Simple; relying on Layer 3 to handle error checking Fast (low latency) Connection oriented Supports variable length ATM Asynchronous Transfer Mode Carries a variety of data types Handle time sensitive information Fixed length packets Handles QoS Connection oriented Data Link Layer Protocols -Examples IETF: International Engineering Telecommunications Forum

  10. A Simple Analogy Physical Layer (DS3) Frame IP Packet Pkt Frame ATM Frame

  11. Network Protocol Layers (layer 3) • Transporting individual packets of information through the network end-to-end • Can route packets according to actual device address or network topology (connectionless) • Routing is done according to the network manager or by a dynamic routing protocol • Without the layer 3 all routings will be point-to-point • Examples: • Internet Protocol (IP) used on Internet • Packet-based; Connectionless • IPX developed by Novel used in LAN • Packet-based; Connectionless

  12. Transport Protocol Layers (layer 4) • Interfacing the upper layers to lower layers • Formats applications into segments • Offers end-to-end flow Read Notes on OSI Model

  13. TCP/IP Stack Protocol

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