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Telecommunications Concepts

Chapter 3.2 Packet Switched Store and Forward Networks. Telecommunications Concepts. Contents. Store and Forward Networks X25 Frame Relay ATM. Contents. Store and Forward Networks X25 Frame Relay ATM. Point to Point Networks. Normal Operation Mode : Store & Forward

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Telecommunications Concepts

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  1. Chapter 3.2 Packet Switched Store and Forward Networks TelecommunicationsConcepts

  2. Contents • Store and Forward Networks • X25 • Frame Relay • ATM

  3. Contents • Store and Forward Networks • X25 • Frame Relay • ATM

  4. Point to Point Networks Normal Operation Mode : Store & Forward Commonly used in Wide-Area Networks The Network itself has considerable storage capacity

  5. The 3 lower OSI layersFor Store & Forward Networks Internet 3 Network 2 Data Link Control 1 Physical

  6. Contents • Store and Forward Networks • X25 • Frame Relay • ATM

  7. Standardized, multivendor interface for packet switched networks. Initially published by CCITT in 1974 Major revisions in 1976, 1978, 1980, 1984, 1988. Provides common procedures between a DTE and a packet switched DCE for Establishing a connection to the network Exchanging data with another DTE releasing the connection Can be used for direct DTE-DTE connection X25 and related standards

  8. X25 and related standards Virtual Circuit DTE DTE X25 X25 Packet switched data network The standard does not specify the internal operation of the packet switched data network. It is however possible, and common practice, to use also the X25 protocols between nodes inside the data network

  9. X25 Applications :Public Packet Switched Data Networks Main purposes : Connect terminals to mainframe Interconnect mainframes X75 Example : Belgacom's DCS PSTN/ ISDN PAD PAD public PAD private PAD

  10. Public PAD X25 Applications :Private Packet Switched Data Networks Example: old Banksys network PSTN /ISDN Private PAD

  11. Public networks Very successful in France (Transpac) Quite successful throughout Europe Marginal in the rest of the world Private networks dominant technology: Seventies : proprietary networks Eighties in Europe : X25 Nineties : IP X25 in the world

  12. Uyless Black X25 and related protocols IEEE Computer Society press, 1991. ISBN 0-8186-8976-5 ISBN 0-8186-5976-9 (microfiche) X25 Reference

  13. Contents • Store and Forward Networks • X25 • Frame Relay • ATM

  14. Frame Relay Origin: Developed to allow fast packet switching in ISDN channels. Simple protocols allow very high data rates. Frame Relay has replaced X25 in high-speed packet switching independently from ISDN

  15. Facts : Transmission errors have been significantly reduced Most high-speed links are seldom switched Design consequences : Simplify error handling Separate connection management and data transmission Main Frame Relay characteristics : Layer 2 : Error detection but no correction Permanent virtual circuits through layer 2 entities Layer 3 : empty on data transmission protocol stack Frame Relay

  16. Switching in Frame Relay Any transport or internet protocol switching node Data protocol Signaling protocol (possibly manual) Network management

  17. All frames have Frame Check Sequence. Bad frames are not relayed Upper layers have to handle the missing frames A transport layer designed for a connectionless network service can handle such missing frames. Frame RelayError Correction:

  18. Risks: Unfairness Congestion Collapse Frame Relay Flow Control Basic mechanism : Frame Discarding Transport protocol Frame Relay layer

  19. At set-up, committed rate is negotiated (CIR) Frames in excess of committed rate have “Discard Eligible” bit set. Frames with DE bit set discarded first. Users can voluntarily set the DE bit. Congestion notification bits in each frame to warn upper layers. Frame Relay Flow Controladditional mechanisms :

  20. Philip Smith Frame Relay : Principles and Applications Addison-Wesley, 1993 ISBN 0-201-62400-1 References

  21. Contents • Store and Forward Networks • X25 • Frame Relay • ATM

  22. Convergence of telecommunication networks Telephone Cable TV Data Dominant application : Video On Demand High Definition TV : 155 Mb/s Four different programs per home Broadband ISDNDominant ideas in the early 80's

  23. Broadband ISDN A single, universal, communications network

  24. Dominated by the HDTV requirements 600 Mb/s throughput to every home Fiber to the home Simple protocols implemented in hardware Guaranteed Quality Of Service Connection oriented protocol General purpose network HDTV, LDTV, Voice, Data Different service classes Very low data-rate applications (meter reading) Multiplexing of very different data-rates Low multiplexing overhead Broadband ISDNDesign Specifications

  25. Designed for broadband ISDN Dissociates completely data transfer and signaling Provides virtual circuits at the physical layer, supporting directly the application layers Uses very small, fixed size packets, called "cells” Unique protocol for a universal BISDN network. Used in the interface between network and end-user. Used inside the network between nodes Asynchronous Transfer Mode

  26. Data encapsulated in small (53 bytes) cells Long low priority packet can not block service of high priority packet Very different throughputs can be multiplexed Header decoding and cell handling simple Hardwired switches Very high throughputs possible Communication by Virtual Circuits Established through separate signaling network Addressing etc handled by signaling network QOS negotiation through signaling network ATM technology

  27. Virtual Path & Virtual Channel Virtual Path Transmission Path Virtual Channel

  28. ATM in the OSI modelwith ad-hoc signaling Any Application Protocol switch ATM Signaling protocol Network management

  29. ATM Interfaces UNI NNI

  30. ATM cell format Header Data(48 bytes) VPI GFC VPI VCI VCI PT PT CLP CLP HEC HEC Network Node Interface User Node Interface

  31. ATM Adaptation Layer Service Classes Constant Variable Connection Connectionless Type of Service Bit Rate Bit Rate Oriented Data Oriented Data Class A Class B Class C Class D Timing coordination Required Not Required Bit Rate Constant Variable Connection Mode Connection Oriented Connectionless

  32. ATM Adaptation Layer Data encapsulation Higher layer PDU pad AAL ATM header pad AAL

  33. HDTV Broadcasters not willing to invest in HDTV Public prefers diversity over technical quality Video on demand can't compete with video rental Digital Signal Processing Video compressed into 1.5 Mb/s XDSL allows up to 6 Mb/s over copper local loop Internet Explosive success of cheap, low quality but very diversified universal communications network Broadband ISDNThe situation in the 90's

  34. Huge research investments by vendors Data transfer protocols mature Signaling immature : target market ??? No push from Telco's Privatization restricts long term developments New operators compete with low cost technology (Voice over IP, …) Corporate backbones / high throughput LAN's Only possibility to recover quickly some of the huge investments made in ATM research ATMThe situation in the 90's

  35. X X ATM bridges for Ethernet ATM switch X

  36. X X X ATM bridges for Ethernet WAN with ATM over SDH

  37. M.De Prycker Asynchronous Transfer Mode : Solutions for broadband ISDN. Ellis Horwood 1993. Web sites: http://www.atmforum.com Official web site of ATM forum http://www.atm25.com/ATM_Reference.html Links to many sites on ATM References

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