Telecommunications Concepts Chapter 3 2 Packet Switched Store

Telecommunications Concepts Chapter 3. 2 Packet Switched Store and Forward Networks 1 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Contents • • 2 Store and Forward Networks X 25 Frame Relay ATM 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Contents • • 3 Store and Forward Networks X 25 Frame Relay ATM 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Point to Point Networks Normal Operation Mode : Store & Forward Commonly used in Wide-Area Networks The Network itself has considerable storage capacity 4 10 -01 -K. Steenhaut & J. Tiberghien - VUB

The 3 lower OSI layers For Store & Forward Networks Internet 3 Network 2 1 5 Data Link Control Physical 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Contents • • 6 Store and Forward Networks X 25 Frame Relay ATM 10 -01 -K. Steenhaut & J. Tiberghien - VUB

X 25 and related standards • 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 7 10 -01 -K. Steenhaut & J. Tiberghien - VUB

X 25 and related standards Virtual Circuit DTE X 25 DTE Packet switched data network X 25 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 X 25 protocols between nodes inside the data network 8 10 -01 -K. Steenhaut & J. Tiberghien - VUB

X 25 Applications : Public Packet Switched Data Networks Main purposes : Connect terminals to mainframe Interconnect mainframes Example : Belgacom's DCS PSTN/ ISDN 9 PAD public PAD X 75 PAD private PAD 10 -01 -K. Steenhaut & J. Tiberghien - VUB

X 25 Applications : Private Packet Switched Data Networks Example: old Banksys network PSTN /ISDN Public PAD 10 Private PAD 10 -01 -K. Steenhaut & J. Tiberghien - VUB

X 25 in the world • 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 : X 25 » Nineties : IP 11 10 -01 -K. Steenhaut & J. Tiberghien - VUB

X 25 Reference Uyless Black X 25 and related protocols IEEE Computer Society press, 1991. ISBN 0 -8186 -8976 -5 ISBN 0 -8186 -5976 -9 (microfiche) 12 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Contents • • 13 Store and Forward Networks X 25 Frame Relay ATM 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Frame Relay Origin: Developed to allow fast packet switching in ISDN channels. Simple protocols allow very high data rates. Frame Relay has replaced X 25 in high-speed packet switching independently from ISDN 14 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Frame Relay • 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 15 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Switching in Frame Relay Any transport or internet protocol switching node Data protocol Network management 16 Signaling protocol (possibly manual) 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Frame Relay Error Correction: • 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. 17 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Frame Relay Flow Control Basic mechanism : Frame Discarding Transport protocol Frame Relay layer Risks: 18 Unfairness Congestion Collapse 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Frame Relay Flow Control additional mechanisms : • 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. 19 10 -01 -K. Steenhaut & J. Tiberghien - VUB

References Philip Smith Frame Relay : Principles and Applications Addison-Wesley, 1993 ISBN 0 -201 -62400 -1 20 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Contents • • 21 Store and Forward Networks X 25 Frame Relay ATM 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Broadband ISDN Dominant ideas in the early 80's • Convergence of telecommunication networks – Telephone – Cable TV – Data • Dominant application : Video On Demand – High Definition TV : 155 Mb/s – Four different programs per home 22 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Broadband ISDN A single, universal, communications network 23 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Broadband ISDN Design Specifications • 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 24 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Asynchronous Transfer Mode • 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 enduser. – Used inside the network between nodes 25 10 -01 -K. Steenhaut & J. Tiberghien - VUB

ATM technology • 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 26 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Virtual Path & Virtual Channel Virtual Path Transmission Path 27 Virtual Channel 10 -01 -K. Steenhaut & J. Tiberghien - VUB

ATM in the OSI model with ad-hoc signaling Any Application Protocol switch 28 Network management ATM Signaling protocol 10 -01 -K. Steenhaut & J. Tiberghien - VUB

ATM Interfaces UNI NNI 29 10 -01 -K. Steenhaut & J. Tiberghien - VUB

ATM cell format Header Data(48 bytes) VPI GFC VPI VCI PT PT CLP HEC User Node Interface 30 HEC Network Node Interface 10 -01 -K. Steenhaut & J. Tiberghien - VUB

ATM Adaptation Layer Service Classes Timing coordination Bit Rate Connection Mode 31 Constant Variable Connectionless Bit Rate Oriented Data Class A Type of Service Class B Class C Class D Required Constant Not Required Variable Connection Oriented Connectionless 10 -01 -K. Steenhaut & J. Tiberghien - VUB

ATM Adaptation Layer Data encapsulation Higher layer PDU pad AAL ATM header 32 pad AAL 10 -01 -K. Steenhaut & J. Tiberghien - VUB

Broadband ISDN The situation in the 90's • 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 33 10 -01 -K. Steenhaut & J. Tiberghien - VUB

ATM The situation in the 90's • 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 34 10 -01 -K. Steenhaut & J. Tiberghien - VUB

ATM bridges for Ethernet ATM switch X X X 35 10 -01 -K. Steenhaut & J. Tiberghien - VUB

ATM bridges for Ethernet X X X WAN with ATM over SDH 36 10 -01 -K. Steenhaut & J. Tiberghien - VUB

References • 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. atm 25. com/ATM_Reference. ht ml » Links to many sites on ATM 37 10 -01 -K. Steenhaut & J. Tiberghien - VUB