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IE 418/518: Telecommunication Concepts

IE 418/518: Telecommunication Concepts. Lecture Notes #2 Protocols and Architecture. Protocols. Used for communications between entities in different systems Must speak the same language. Key Elements of a Protocol. Syntax Data formats Signal levels Semantics Control information

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IE 418/518: Telecommunication Concepts

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  1. IE 418/518:Telecommunication Concepts Lecture Notes #2 Protocols and Architecture

  2. Protocols • Used for communications between entities in different systems • Must speak the same language

  3. Key Elements of a Protocol • Syntax • Data formats • Signal levels • Semantics • Control information • Error handling • Timing • Speed matching • Sequencing RF LINK PC SERVER

  4. Example: Three-Layer Model • Communications can be said to involve three agents:

  5. Example: Three-Layer Model • Makes sense to organize the communication task into three, relatively independent layers Comm Task

  6. Example: Three-Layer Model • Network Access Layer Functions • Exchange of data between the computer and the network • Sending computer provides address of destination to help in determining routing options • May invoke levels of service (i.e., priority) • Software used in this layer depends on type of network used

  7. Example: Three-Layer Model • Computer-Transport Layer Functions • Reliable data exchange • Data arrive at destination application • Same order in which they were sent • Independent of network being used • Independent of application

  8. Example: Three-Layer Model • Application Layer Functions • Support for different user applications • User applications refer to network applications • Examples

  9. Example: Three-Layer Model • Addressing Requirements • Two levels of addressing required • Each computer needs unique network address • Each application on a multi-tasking computer needs a unique address within the computer • Service Access Point (SAP)

  10. Protocol Architectures and Networks

  11. Protocol Data Units

  12. OSI – The Model • Open Systems Interconnection (OSI) • Developed by the International Organization for Standardization (ISO) • Seven layers • A theoretical system delivered too late! • TCP/IP is the de facto standard

  13. OSI – The Model • Layering is the key! • Each layer performs a subset of the required communication functions • Each layer relies on the next lower layer to perform more primitive functions • Each layer provides services to the next higher layer • Changes in one layer should not require changes in other layers

  14. The OSI Environment

  15. Standardization within the OSI Framework

  16. Elements of Standardization • Protocol specification • Operates between the same layer on two systems • May involve different operating system • Protocol specification must be precise • Format of data units • Semantics of all fields • Allowable sequence of PDUs • Service definition • Functional description of what is provided • Addressing • Referenced by SAPs

  17. Layer Specific Standards

  18. ISO OSI Reference Model Networkoriented Application oriented • Network Layer (3) • Data Link Layer (2) • Physical Layer (1) • Application Layer (7) • Presentation Layer (6) • Session Layer (5) • Transport Layer (4)

  19. Network-dependent Layers • Physical Layer • Concerned with the physical and electrical interfaces b/w the user equipment and the network equipment • Responsible for the transmission of bits • Always implemented using hardware • Physical layer standards • RS-232-C • RS-449 • RS-422-A • RS-423-A

  20. Network-dependent Layers • Data Link Layer • Assembles data bits into a block, or frame • Responsible for ensuring error-free, reliable transmission of data • Requests retransmission or correction if any errors occur • Example protocols • BSC • SDLC • HDLC • PPP

  21. Network-dependent Layers • Network Layer • Responsible for appropriate routing of messages across a network • Only layer concerned with types of switching networks used to route data

  22. Use of a Relay * *

  23. Application-oriented Layers • Transport Layer • Responsible for: • Monitoring the quality of the communications channel • Selecting the most cost-efficient communication service based on reliability required for a particular transmission

  24. Application-oriented Layers • Session Layer • Requests that a logical connection be established based on the end user’s request • Transfer a file • File location • File destination • Controls any necessary log-ons and passwords • Responsible for terminating connection

  25. Application-oriented Layers • Presentation Layer • Provides format and code conversion services • Printing operations • Concerned with syntax and semantics of the information transmitted • File transfers b/w heterogeneous hosts • Data compression • Data encryption

  26. Application-oriented Layers • Application layer • Provides access to the network for the end user • Remote terminal access • File transfer • Network management statistics and diagnostics can also be implemented in this layer

  27. TCP/IP Protocol Suite • Dominant commercial protocol architecture • Specified and extensively used before OSI • Developed through the US Department of Defense • Used by the Internet

  28. TCP/IP Layers • Physical Layer • Network Access Layer • Internet Layer • Transport Layer (a.k.a., Host-to-host) • Application Layer

  29. Physical Layer • Physical interface between data transmission device (e.g. computer) and transmission medium or network • Characteristics of transmission medium • Signal levels • Data rates

  30. Network Access Layer • Exchange of data between end system and network • Destination address provision • Invoking services like priority • Software depends on type of network

  31. Internet Layer (IP) • Systems may be attached to different networks • Routing functions across multiple networks • Implemented in end systems and routers

  32. Transport Layer • Reliable delivery of data • Ordering of delivery • Uses Transmission Control Protocol (TCP)

  33. Application Layer • Support for user applications • HTTP • Simple Mail Transfer Protocol (SMTP) • Telnet • FTP

  34. Operation of TCP and IP

  35. PDUs in TCP/IP

  36. Some Protocols in TCP/IP Suite

  37. OSI vs. TCP/IP

  38. Standards • Required to allow for interoperability between equipment • Advantages • Ensures a large market for equipment and software • Allows products from different vendors to communicate • Disadvantages • Freeze technology • May be multiple standards for the same thing • e.g., military vs. commercial

  39. Standards Organizations • Internet Society • ISO • International Telecommunications Union – Telecommunications Sector (ITU-T) • ATM forum

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