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L1 - 1 © P. Raatikainen Switching Technology / 2004 Switching Technology S38.165 Pertti Raatikainen, research professor VTT Information Technology pertti.raatikainen@vtt.fi L1 - 2 © P. Raatikainen Switching Technology / 2004 General • Lecturer: Pertti Raatikainen, research professor /VTT email: pertti.raatikainen@vtt.fi • Exercises: Kari Seppänen, snr. research scientist /VTT email: kari.seppänen@vtt.fi • Information: http://www.netlab.hut.fi/opetus/s38165 L1 - 3 © P. Raatikainen Switching Technology / 2004 Goals of the course • Understand what switching is about • Understand the basic structure and functions of a switching system • Understand the role of a switching system in a transport network • Understand how a switching system works • Understand technology related to switching • Understand how conventional circuit switching is related to packet switching L1 - 4 © P. Raatikainen Switching Technology / 2004 Course outline • Introduction to switching – switching in general – switching modes – transport and switching • Switch fabrics – basics of fabric architectures – fabric structures – path search, self-routing and sorting L1 - 5 © P. Raatikainen Switching Technology / 2004 Course outline • Switch implementations – PDH switches – ATM switches – routers • Optical switching – basics of WDM technology – components for optical switching – optical switching concepts L1 - 6 © P. Raatikainen Switching Technology / 2004 Course requirements • Preliminary information – S-38.188 Tietoliikenneverkot or S-72.423 Telecommunication Systems (or a corresponding course) • 13 lectures (á 3 hours) and 7 exercises (á 2 hours) • Calculus exercises • Grating – Calculus 0 to 6 bonus points – valid in exams in 2004 – Examination, max 30 points L1 - 7 © P. Raatikainen Switching Technology / 2004 Course material • Lecture notes • Understanding Telecommunications 1, Ericsson & Telia, Studentlitteratur, 2001, ISBN 91-44-00212-2, Chapters 2-4. • J. Hui: Switching and traffic theory for integrated broadband networks, Kluwer Academic Publ., 1990, ISBN 0-7923-9061-X, Chapters 1 - 6. • H. J. Chao, C. H. Lam and E. Oki: Broadband Packet Switching technologies – A Practical Guide to ATM Switches and IP routers, John Wiley & Sons, 2001, ISBN 0-471-00454-5. • T.E. Stern and K. Bala: Multiwavelength Optical Networks: A Layered Approach, Addison-Wesley, 1999, ISBN 0-201-30967-X. L1 - 8 © P. Raatikainen Switching Technology / 2004 Additional reading • A. Pattavina: Switching Theory - Architecture and Performance in Broadband ATM Networks, John Wiley & Sons (Chichester), 1998, IBSN 0-471-96338-0, Chapters 2 - 4. • R. Ramaswami and K. Sivarajan, Optical Networks, A Practical Perspective, Morgan Kaufman Publ., 2nd Ed., 2002, ISBN 1- 55860-655-6. L1 - 9 © P. Raatikainen Switching Technology / 2004 Introduction to switching Switching Technology S38.165 http://www.netlab.hut.fi/opetus/s38165 L1 - 10 © P. Raatikainen Switching Technology / 2004 Introduction to switching • Switching in general • Switching modes • Transport and switching L1 - 11 © P. Raatikainen Switching Technology / 2004 Switching in general ITU-T specification for switching: “The establishing, on-demand, of an individual connection from a desired inlet to a desired outlet within a set of inlets and outlets for as long as is required for the transfer of information.” inlet/outlet = a line or a channel L1 - 12 © P. Raatikainen Switching Technology / 2004 Switching in general (cont.) • Switching implies directing of information flows in communications networks based on known rules • Switching takes place in specialized network nodes • Data switched on bit, octet, frame or packet level • Size of a switched data unit is variable or fixed L1 - 13 © P. Raatikainen Switching Technology / 2004 Why switching ? • Switches allow reduction in overall network cost by reducing number and/or cost of transmission links required to enable a given user population to communicate • Limited number of physical connections implies need for sharing of transport resources, which means – better utilization of transport capacity – use of switching • Switching systems are central components in communications networks L1 - 14 © P. Raatikainen Switching Technology / 2004 Full connectivity between hosts Full mesh Number of links to/from a host = n-1 Total number of links = n(n-1)/2 L1 - 15 © P. Raatikainen Switching Technology / 2004 Centralized switching Number of links to/from a host = 1 Total number of links = n L1 - 16 © P. Raatikainen Switching Technology / 2004 Switching network to connect hosts Number of links to/from a host = 1 Total number of links depends on used network topology L1 - 17 © P. Raatikainen Switching Technology / 2004 Hierarchy of switching networks Local switching network Long distance switching network To higher level of hierarchy L1 - 18 © P. Raatikainen Switching Technology / 2004 Sharing of link capacity Space Division Multiplexing (SDM) 1 2 n ...3 ...Physical link CH 1 CH 2 CH n Physical link 1 2 n ...3 Space to be divided: - physical cable or twisted pair - frequency - light wave L1 - 19 © P. Raatikainen Switching Technology / 2004 Sharing of link capacity (cont.) 1 2 n ...1 2 n ...1 2 3 n 1 2 … ... n-1 Synchronous transfer mode (STM) k Overhead Payload Asynchronous transfer mode (ATM) 1 2 n ...1 2 n ...1 2 n 1 ... idle 2 1 idle Time Division Multiplexing (TDM) L1 - 20 © P. Raatikainen Switching Technology / 2004 Main building blocks of a switch Input Interface Card #1 put Interface Card #1 Input interface #1 Switch fabric Output Interface Card #1 Ou put Interface Card #1 Output interface #1 Switch control • input signal reception • error checking and recovery • incoming frame disassembly • buffering • routing/switching decision • switching of data units from input interfaces to destined output interfaces • limited buffering • buffering, prioritizing and scheduling • outgoing frame assembly • output signal generation and transmission • processing of signaling/connection control information • configuration and control of input/output interfaces and switch fabric L1 - 21 © P. Raatikainen Switching Technology / 2004 Heterogeneity by switching • Switching systems allow heterogeneity among terminals – terminals of different processing and transmission speeds supported – terminals may implement different sets of functionality • and heterogeneity among transmission links by providing a variety of interface types – data rates can vary – different link layer framing applied – optical and electrical interfaces – variable line coding L1 - 22 © P. Raatikainen Switching Technology / 2004 Basic types of witching networks • Statically switched networks – connections established for longer periods of time (typically for months or years) – management system used for connection manipulation • Dynamically switched networks – connections established for short periods of time (typically from seconds to tens of minutes) – active signaling needed to manipulate connections • Routing networks – no connections established - no signaling – each data unit routed individually through a network – routing decision made dynamically or statically L1 - 23 © P. Raatikainen Switching Technology / 2004 Development of switching technologies 1950 1960 1990 1980 1970 2000 2020 2010 SPC, analog switching Crossbar switch Manual SPC - stored program control Step-by-step SPC, digital switching Broadband, electronic Broadband, optical Source: Understanding Telecommunications 1, Ericsson & Telia, Studentlitteratur, 2001. L1 - 24 © P. Raatikainen Switching Technology / 2004 Development of switching tech. (cont.) • Manual systems – in the infancy of telephony, exchanges were built up with manually operated switching equipment (the first one in 1878 in New Haven, USA) • Electromechanical systems – manual exchanges were replaced by automated electromechanical switching systems – a patent for automated telephone exchange in 1889 (Almon B. Strowger) – step-by-step selector controlled directly by dial of a telephone set – developed later in the direction of register-controlled system in which number information is first received and analyzed in a register – the register is used to select alternative switching paths (e.g. 500 line selector in 1923 and crossbar system in 1937) – more efficient routing of traffic through transmission network – increased traffic capacity at lower cost L1 - 25 © P. Raatikainen Switching Technology / 2004 Development of switching tech. (cont.) • Computer-controlled systems – FDM was developed round 1910, but implemented in 1950’s (ca. 1000 channels transferred in a coaxial cable) – PCM based digital multiplexing introduce in 1970’s – transmission quality improved – costs reduced further when digital group switches were combined with digital transmission systems – computer control became necessary - the first computer controlled exchange put into service in 1960 (in USA) – strong growth of data traffic resulted in development of separate data networks and switches – advent of packet switching (sorting, routing and buffering) – N-ISDN network combined telephone exchange and packet data switches – ATM based cell switching formed basis for B-ISDN – next step is to use optical switching with electronic switch control – all optical switching can be seen in the horizon L1 - 26 © P. Raatikainen Switching Technology / 2004 Roadmap of Finnish networking technologies 1955 -60 -65 -70 -75 -80 -85 -90 -95 2000 Automation of long distance telephony Digital transmission Digitalization of Exchanges ISDN Data networks WWW Arpanet ---> Internet technology NMT-450 NMT-900 Circuit switching Packet sw GSM UMTS L1 - 27 © P. Raatikainen Switching Technology / 2004 Challenges of modern switching • Support of different traffic profiles • constant and variable bit rates, bursty traffic, etc. • Simultaneous switching of highly different data rates • from kbits/s rates to Gbits/s rates • Support of varying delay requirements • constant and variable delays • Scalability • number of input/output links, link bit rates, etc. • Reliability • Cost • Throughput L1 - 28 © P. Raatikainen Switching Technology / 2004 Switching modes Switching Technology S38.165 http://www.netlab.hut.fi/opetus/s38165 L1 - 29 © P. Raatikainen Switching Technology / 2004 Narrowband network evolution • Early telephone systems used analog technology - frequency division multiplexing (FDM) and space division switching (SDS) • When digital technology evolved time division multiplexing (TDM) and time division switching (TDS) became possible • Development of electronic components enabled integration of TDM and TDS => Integrated Digital Network (IDN) • Different and segregated communications networks were developed – circuit switching for voice-only services – packet switching for (low-speed) data services – dedicated networks, e.g. for video and specialized data services L1 - 30 © P. Raatikainen Switching Technology / 2004 Segregated transport Dedicated network Packet switching network Circuit switching network Voice Data Data Video Voice Data Data Video UNI UNI L1 - 31 © P. Raatikainen Switching Technology / 2004 Narrowband network evolution (cont.) • Service integration became apparent to better utilize communications resources => IDN developed to ISDN (Integrated Services Digital Network) • ISDN offered – a unique user-network interface to support basic set of narrowband services – integrated transport and full digital access – inter-node signaling (based on packet switching) – packet and circuit switched end-to-end digital connections – three types of channels (B=64 kbit/s, D=16 kbit/s and H=nx64 kbit/s) • Three types of long-distance interconnections – circuit switched, packet switched and signaling connections • Specialized services (such as video) continued to be supported by separate dedicated networks L1 - 32 © P. Raatikainen Switching Technology / 2004 Integrated transport Dedicated network Packet switching network ISDN switch Circuit switching network Signaling network ISDN switch UNI UNI Data Video Voice Data Data Video Voice Data L1 - 33 © P. Raatikainen Switching Technology / 2004 Broadband network evolution • Progress in optical technologies enabled huge transport capacities => integration of transmission of all the different networks (NB and BB) became possible • Switching nodes of different networks co-located to configure multifunctional switches – each type of traffic handled by its own switching module • Multifunctional switches interconnected by broadband integrated transmission (BIT) systems terminated onto network-node interfaces (NNI) • BIT accomplished with partially integrated access and segregated switching L1 - 34 © P. Raatikainen Switching Technology / 2004 Narrowband-integrated access and broadband-integrated transmission Ad-hoc switch Packet switch ISDN switch Circuit switch Signaling switch UNI Voice Data Data Video Ad-hoc switch Packet switch Circuit switch Signaling switch ISDN switch UNI Voice Data Data Video Multifunctional switch Multifunctional switch NNI NNI L1 - 35 © P. Raatikainen Switching Technology / 2004 Broadband network evolution (cont.) • N-ISDN had some limitations: – low bit rate channels – no support for variable bit rates – no support for large bandwidth services • Connection oriented packet switching scheme, i.e. ATM (Asynchronous Transfer Mode), was developed to overcome limitations of N-ISDN => B-ISDN concept => integrated broadband transport and switching (no more need for specialized switching modules or dedicated networks) L1 - 36 © P. Raatikainen Switching Technology / 2004 Broadband integrated transport UNI Voice Data Video UNI NNI NNI B-ISDN switch B-ISDN switch Voice Data Video L1 - 37 © P. Raatikainen Switching Technology / 2004 OSI definitions for routing and switching Routing on L3 L2 L3 L2 L3 L2 L3 L2 L3 L2 L3 L2 L3 L4 L4 Switching on L2 L2 L3 L2 L3 L2 L3 L2 L3 L2 L3 L2 L3 L4 L4 L1 - 38 © P. Raatikainen Switching Technology / 2004 Switching modes • Circuit switching • Cell switching • Packet switching – Routing – Layer 3 - 7 switching – Label switching L1 - 39 © P. Raatikainen Switching Technology / 2004 Circuit switching Layer 1 Layer 1 Limited error detection Layer 1 Layer 1 Limited error detection Network edge Switching node Network edge • End-to-end circuit established for a connection • Signaling used to set-up, maintain and release circuits • Circuit offers constant bit rate and constant transport delay • Equal quality offered to all connections • Transport capacity of a circuit cannot be shared • Applied in conventional telecommunications networks (e.g. PDH/PCM and N-ISDN) L1 - 40 © P. Raatikainen Switching Technology / 2004 Cell switching • Virtual circuit (VC) established for a connection • Data transported in fixed length frames (cells), which carry information needed for routing cells along established VCs • Forwarding tables in network nodes Layer 1 Error recovery & flow control Layer 1 Layer 2 (L) Layer 2 (L) Layer 1 Layer 2 (L) Layer 2 (H) Limited error detection Layer 1 Limited error detection Network edge Switching node Network edge Error & congestion control Error & congestion control Layer 2 (L) Layer 2 (H) L1 - 41 © P. Raatikainen Switching Technology / 2004 Cell switching (cont.) • Signaling used to set-up, maintain and release VCs as well as update forwarding tables • VCs offer constant or variable bit rates and transport delay • Transport capacity of links shared by a number of connections (statistical multiplexing) • Different quality classes supported • Applied, e.g. in ATM networks L1 - 42 © P. Raatikainen Switching Technology / 2004 Packet switching Layer 1 Layer 2 Layer 3 Layer 1 Layer 2 Layer 3 Routing & mux Error recovery & flow control Layer 1 Layer 2 Layer 3 Layer 1 Layer 2 Layer 3 Routing & mux Error recovery & flow control Network edge Switching node Network edge • No special transport path established for a connection • Variable length data packets carry information used by network nodes in making forwarding decisions • No signaling needed for connection setup L1 - 43 © P. Raatikainen Switching Technology / 2004 Packet switching (cont.) • Forwarding tables in network nodes are updated by routing protocols • No guarantees for bit rate or transport delay • Best effort service for all connections in conventional packet switched networks • Transport capacity of links shared effectively • Applied in IP (Internet Protocol) based networks L1 - 44 © P. Raatikainen Switching Technology / 2004 Layer 3 - 7 switching • L3-switching evolved from the need to speed up (IP based) packet routing • L3-switching separates routing and forwarding • A communication path is established based on the first packet associated with a flow of data and succeeding packets are switched along the path (i.e. software based routing combined with hardware based one) • Notice: In wire-speed routing traditional routing is implemented in hardware to eliminate performance bottlenecks associated with software based routing (i.e., conventional routing reaches/surpasses L3-switching speeds) L1 - 45 © P. Raatikainen Switching Technology / 2004 Layer 3 - 7 switching (cont.) • In L4 - L7 switching, forwarding decisions are based not only on MAC address of L2 and destination/source address of L3, but also on application port number of L4 (TCP/UDP) and on information of layers above L4 Layer 1 Layer 2 Layer 3 Layer 1 Layer 2 Layer 3 Flow control Error recovery & flow control Layer 1 Layer 2 Layer 3 Layer 1 Layer 2 Layer 3 Routing Error recovery & flow control Network edge Switching node Network edge Layer 4 Layer 4 Layer 7 Layer 7 ......Routing Routing infoL1 - 46 © P. Raatikainen Switching Technology / 2004 Label switching Layer 1 Layer 2 Layer 3 Layer 1 Layer 2 Flow control Error recovery & flow control Layer 1 Layer 2 Layer 1 Layer 2 Layer 3 Error recovery & flow control Network edge Switching node Network edge • Evolved from the need to speed up connectionless packet switching and utilize L2-switching in packet forwarding • A label switched path (LSP) established for a connection • Forwarding tables in network nodes L1 - 47 © P. Raatikainen Switching Technology / 2004 Label switching (cont.) • Signaling used to set-up, maintain and release LSPs • A label is inserted in front of a L3 packet (behind L2 frame header) • Packets forwarded along established LSPs by using labels in L2 frames • Quality of service supported • Applied, e.g. in ATM, Ethernet and PPP • Generalized label switching scheme (GMPLS) extends MPLS to be applied also in optical networks, i.e., enables light waves to be used as LSPs
