Optical Networks: from fiber transmission to photonic switching

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1 Optical Networks: from fiber transmission to photonic switching Fabio Neri and Marco Mellia TLC Networks Group Electronics Department tel tel Introduction to optical networks - 1

2 Course program outline Introduction and motivations Signal propagation in optical fibers Components for photonic systems First-generation optical networks Broadcast-and-select WDM optical networks Multi-hop WDM networks Wavelength-routing networks Optical access networks Protocol architectures in optical networks Network management, reliability and fault recovery Optical packet switching Introduction to optical networks - 2

3 References I Books on optical communication systems: G. P. Agrawal, Fiber Optic Communication Systems, John Wiley, 1997 M. M.-K. Liu, Principles and Applications of Optical Communications, McGraw Hill, 1996 J. D. Gibson (Ed.), The Communications Handbook, CRC Press, 2002 L. G. Kazovsky, S. Benedetto, A. Willner, Optical Fiber Communication Systems, Artech House, 1996 Introduction to optical networks - 3

4 References II Books on all-optical networks: R. Ramaswami and K. N. Sivarajan, Optical Networks A Practical Perspective, 2 nd Edition, Morgan Kaufmann, 2002 T. E. Stern and K. Bala, Multiwavelength Optical Networks, Addison Wesley, 1999 P.E. Green, Fiber-optic networks, Prentice-Hall, 1993 B. Mukherjee, Optical WDM Networks, Springer, 2006 [B. Mukherjee, Optical communication networks, McGraw-Hill, 1997] Introduction to optical networks - 4

5 Major achievements in optics 1966: first optical fibers were developed at Corning labs, showing great potential in telecommunication systems 1970: the first stable uncooled semiconductor laser was demonstrated at AT&T labs 1978: the first single mode fiber operating in the 1.55 μm window was developed at NTT labs 1987: the first Erbium-doped fiber amplifier was developed at Southampton University 1996: more than km of optical fiber cables deployed in the US, for a total amount of more than 20 million km of optical fibers (source: Federal Communications Commission - FCC) 2000: telcos are deploying 400 fibers cables, offering a potential capacity of hundreds of Tbit/s (Petabit/s) using WDM technology Introduction to optical networks - 5

6 Optical fibers + Bandwidth (up to THz) + Low attenuation (fraction of db/km) + Immunity to external electromagnetic interference + Thin and flexible + Less dangerous than metal conductor (no fire hazards) + Cheaper than traditional copper-based systems + More protection against intrusions - Connection and interfacing more difficult - Dispersions - Non linear effects Introduction to optical networks - 6

7 Fiber attenuation Attenuation (db/km) Rayleigh scattering Optical fiber Infrared absorption UV absorption Wavelength (nm) First window 850 nm a=1.2 db/km Second window 1310 nm a=0.4 db/km Third window 1550 nm a=0.2 db/km 1800 Introduction to optical networks - 7

8 Transmission systems evolution I First generation MMF Regenerator (1970) Rx Mbit/s LED Tx 10 km First experimental systems using optical fibers Wideband optical source (LED) Multi-mode fiber Opto-electronic regenerator (OEO) every 10km Bit rate smaller than 100 Mbit/s Introduction to optical networks - 8

9 Transmission systems evolution II Second generation (1980) 1.31 μm MM Laser Tx SMF 50 km Rx Few 100 Mbit/s to 1 Gbit/s Second generation Laser source (multi-mode laser, 1310 nm) Single-mode fiber Optoelectronic regenerator every 50 km Bit rate up to 1 Gbit/s Introduction to optical networks - 9

10 Transmission systems evolution III Third generation (1990) 1.55 μm SM Laser Tx SMF 100 km Rx 2.5 Gbps to 10 Gbps Third generation Laser source (single mode, 1550 nm) Single-mode fiber operating in the minimum attenuation window (3rd window at 1550 nm) Optoelectronic regenerators every 100 km Bit rate up to 10 Gbit/s Introduction to optical networks - 10

11 Transmission systems evolution IV Fourth generation (1995) SM DFB Laser Tx (λ 1 ) SM DFB Laser Tx (λ 2 ) SM DFB Laser Tx (λ 3 ) MUX SMF 100 s km EDFA DeMUX Rx Rx Rx Fourth generation Wavelength Division Multiplexing (WDM) Coarse WDM (CWDM) Dense WDM (DWDM) Optical amplifiers are used instead of opto-electronic regenerators Introduction to optical networks - 11

12 Transmission systems evolution 1970 P λ LED Tx MMF 10 km Regenerator Rx Mbit/s P P P λ λ λ 1.31 μm MM Laser Tx 1.55 μm SM Laser Tx SM DFB Laser Tx (λ 1 ) SM DFB Laser Tx (λ 2 ) SM DFB Laser Tx (λ 3 ) MUX SMF 50 km SMF 100 s km SMF 100 km EDFA Rx Rx Few 100 Mbit/s to 1 Gbit/s 2.5 Gbps to 10 Gbps DeMUX Rx Rx Rx Introduction to optical networks - 12

13 Multiplexing techniques Time Division Multiplexing (TDM) Up to 40 Gbit/s in the electronic domain Optical Time Division Multiplexing (OTDM) TDM of different streams directly in the optical domain e.g. 16 channels at 10 Gbit/s = 160 Gbit/s Wavelength Division Multiplexing (WDM) Similar to frequency division multiplexing Gbit/s or Gbit/s Space Division Multiplexing (SDM) e.g. more than one fiber in a single cable, or more than one path in a network (Optical) Code Division Multiplexing (CDM/OCDM) code identifies a transmitter Introduction to optical networks - 13

14 Wavelength-division multiplexing WDM Wavelength division multiplexing N digital channels on N differents wavelengths Optical Spectrum Definitions: λ 1 λ 2 λ N λ Coarse-WDM: two different wavelengths, usually 1310 and 1550 nm, or few different wavelengths with large channel spacing (~ 20 nm) Dense-WDM (DWDM): large number of wavelengths in the 1550 nm range, thin channel spacing (~ 1 nm) Introduction to optical networks - 14

15 WDM techniques WDM techniques are more natural in the optical domain A partitioning of the optical bandwidth is necessary since information flows are originated and terminated in the electronic domain, even if they traverse several switching points in the optical domain If WDM and optical switching are adopted, transparent, end-toend channels may be offered to users. These channels are called lightpaths. If distances are large, there can be the need for signal Regeneration (termed 1R), often coupled with a Reshaping (2R) and Resynchronization (3R) of digital pulses Lightpaths may be transparent (all-optical) or opaque (allowing regeneration 2R or 3R) Introduction to optical networks - 15

16 Submarine systems Trans-oceanic submarine systems reach maximum values of the bandwidth-distance product: TAT 12/13: (TransATlantic link) in operation since 1995, maximum distance 6200 km, original capacity 5 Gb/s per fiber TPC 5: (TransPaCific link) in operation since 1996, maximum distance 8200 km, capacity 5 Gb/s per fiber TAT 14: in operation since December 2000, 16 WDM 2.5 Gb/s TPC 6: up to 640Gb/s using WDM channels Introduction to optical networks - 16

17 Optical fiber capacity State of the art: Systems in operation: up to 8 10 Gb/s (8 WDM channels SONET OC-192, SDH STM-64 ) Commercial offers: up to Gb/s (Cisco, Nortel, Ciena, Lucent, Alcatel, Pirelli, etc.) Lab records: 10.9 Tbit/s over 100 km (Alcatel: Gb/s); 2.4 Tbit/s over 6200 km (TyCom: Gb/s) Technical goals of current R&D: Development of commercial 40 Gb/s systems in WDM technology Specification of 100 Gb/s systems New technologies to increment the usable optical bandwidth (e.g., large-bandwidth optical amplifiers) Introduction to optical networks - 17

18 Optical fibers A single fiber can carry all peak-hour telephone traffic generated in the US Today the total traffic carried by installed fibers is much smaller than the available fiber capacity There are solutions to provide high capacity in the private environment (e.g. Ethernet), and in backbone systems (e.g. SONET/ SDH), but still there is still a bandwidth bottleneck in access and metropolitan segments (ADSL is not enough!) Introduction to optical networks - 18

19 From optical transmissions to optical networks Optical fibers are nowadays the preferred physical medium for distances above 1km and capacities larger than hundreds of Mbit/s Optical fibers as massively used on high capacity backbone links (Sonet/SDH transport networks) in LANs (e.g. FDDI, Gigabit Ethernet) Optical fibers are starting to be used in access networks ( last mile, FTTC, FTTB, FTTH) The large available bandwidth has increased the complexity on electronic devices used to manage the network Need to implement switching functions in the optical domain Introduction to optical networks - 19

20 All-optical networks All-optical networks exploit optical the domain not only for transmission, but also to implement switching, routing and management functions Avoid the electronic bottleneck due to optical to electronic conversions Electronic routers are available today up to Terabit capacity, with I/O links up to 40Gb/s but they are too complex, too big, too power consuming, and too expensive. We are reaching the fundamental limitations of the electronic domain Introduction to optical networks - 20

21 The beauty of the prism λ white λ green λ g (1) λ v (1) λ g (2) λ red λ yellow λ g (2) λ v (2) λ v (2) λ g (1) λ v (1) A prism is an all-optical switching element, very cheap, that offers huge capacity! Introduction to optical networks - 21

22 Why optical networking? Traffic Growth: ~100% per year e.g.: Amsterdam Internet Exchange Point traffic Introduction to optical networks - 22

23 Networked Hosts Introduction to optical networks - 23

24 Why optical networks? Bandwidth demand and availability double every 12 months Moore law: processing power doubles every 18 months? Performance and cost limits are in the information electronic processing and switching, not in the transmission capacity Introduction to optical networks - 24

25 Bandwidth is no longer a problem! Introduction to optical networks - 25

26 What are optical networks? There is no unique meaning for the term optical networks. Some people use this term to refer to quite different architectures: First generation optical networks cheap, medium capacity LANs (FDDI, Ethernet) Access networks (FTTH) Backbone networks (SONET/SDH) Second generation optical networks Access or backbone high capacity networks, with some all-optical functionalities These different architectures exhibit different problems at various levels (components, transmission, networking) In this course we mainly refer to high-speed backbone (WAN) technologies: capacities larger than 1 Gb/s per channel, WDM technology, narrowband lasers and single mode transmissions Introduction to optical networks - 26

27 Taxonomy of optical networks 1 st generation: optical fibers replace copper transmission media international standards SONET/SDH FDDI Gbit Ethernet 2 nd generation: routing and switching in the optical domain all-optical networks international standards ITU G.872 Architecture of optical transport networks ITU G.ASON, Architecture for the Automatic Switched Optical Network Introduction to optical networks - 27

28 First generation networks Today s switches: Optical fiber inputs/outputs network node 3R E/O Interface 3R Electronic 3R O/E Crossconnect E/O Interface or ADM Interface 3R E/O Interface Characteristics: 3R signal regeneration with OEO conversion information processing entirely in the electronic domain Introduction to optical networks - 28

29 Second generation networks The wavelength routing approach Network nodes Optical links Transparent lightpath #1 Transparent lightpath #2 RX TX RX TX Introduction to optical networks - 29

30 Second generation networks The key device is the optical cross-connect DeMux λ 0, λ 1,... λ n DeMux Optical cross connect Mux λ 0, λ 1,... λ m λ 0, λ 1,... λ n DeMux Mux λ 0, λ 1,... λ m Introduction to optical networks - 30

31 Limits of optical components To deploy all-optical networks, a number of major problems of optical components and systems are still to be solved: there is no optical equivalent of electronic random-access memories very limited information processing capabilities various (non-linear) transmission impairments, particularly for reconfigurable optical channels high cost (in all senses) of the optical interfacing Introduction to optical networks - 31

32 Optical networks architectures Two main classes of networks will be considered: λ 1 λ 2 λ TX/RX 3 λ 1 λ 2 λ 3 λ 2 star coupler λ 1 λ 1 λ 2 λ 3 WDM crossconnect lightpath TX/RX λ 1 λ 2 λ 3 TX/RX λ 1 λ 2 single-hop network (e.g. broadcast-and-select) wavelength conversion? multi-hop network (e.g.wavelength routing) Introduction to optical networks - 32

33 Optics in different network segments Backbone networks (wavelength routing: optical-cross-connect and WDM links) Metropolitan area networks (broadcast-andselect architectures, rings and WDM stars) Access networks (Passive Optical Networks - PONs) Introduction to optical networks - 33

34 Segments of public networks Submarine Network Central Office (CO) Local Access Network Last/First Mile : from the user to the nearest central office Metropolitan Local-exchange Network Connections among closely located central offices Long Haul Interexchange (backbone) Network Introduction to optical networks - 34

35 Network Architectures Access: LAN (Eth, GbE, 10GbE), xdsl, PON (EPON, GPON), FTTx, PLC,... DECT, GSM, HSCSD, GPRS, EDGE, 3G (UMTS),... WLAN: WiFi (IEEE a,b,g) ( Wireless MAN: WiMAX (IEEE ) ( p2p microvawe, terrestrial, satellite, free space optics, etc. Metro: SDH, Metro Ethernet, ATM, MPLS, Metro Access: aggregate the traffic from access networks classical approaches (SONET/SDH aggregation rings, RPR, Full Ethernet, Pt2Pt Optical Ethernet) METRO Core: ROADM with CWDM or DWDM Transport (Backbone, Core) DW/OTN, (ng)sdh/sonet, ASON, GMPLS, ASTN Introduction to optical networks - 35

36 GEANT European network Introduction to optical networks - 36

37 ESnet (2003) Introduction to optical networks - 37

38 AArnet (Australia 2004) connections + SXTransPORT (Trans Pacific Optical Research Testbed) Introduction to optical networks - 38

39 GLORIAD: Global Optical Ring (US-Europe-Russia-China, 10 Gb/s) Introduction to optical networks - 39

Americas 1 Americas II South American Crossing Columbus II Columbus III Telefonica s Emergia ARCOS Maya-1 360

40 Americas 1 Americas II South American Crossing Columbus II Columbus III Telefonica s Emergia ARCOS Maya Americas Submarine Fiber-Optic Cable System of Americas Source: H.B.Newman, GNEW2004 Introduction to optical networks - 40

41 Circus viciosus 1. Content and Service 3. Transport 2. Access Introduction to optical networks - 41

42 Applications Peer-to-Peer GRIDs SAN, osan Audio and Video Broadcast VoD VoIP Telemedicine Distant Learning Video Conferencing etc. Introduction to optical networks - 42

43 Data network (Internet) applications Person to person: limited storage capabilities (eyes, ears); sensible to delay and delay variation (jitter); e.g., telephony, games, conferencing Machine to person: best-effort service possible, but require large storage at the endpoint to overcome delay variation introduced by the network; e.g., web browsing, video and audio playback Machine to machine: best-effort paradigm is accepted; e.g., , batch processing, distributed web caching, file transfers, Introduction to optical networks - 43

44 Self-similar Internet network traffic very bursty, even after several multiplexing levels Asymmetric downlink traffic is usually larger than uplink traffic if symmetric links are deployed, large part of the capacity is unused (typical of telephone systems) Static routing TCP does not tolerate well highly dynamic routing Datagram switching information is segmented in quite small packets Introduction to optical networks - 44

45 Circuit switching Resources are allocated by the network after an explicit service request from the user Circuit resources are completely devoted to the communication for its whole duration Resources are released after an explicit signaling at the end of the communication pros: Constant and limited information transfer delays cons: no resources sharing requests blocking time-based billing Introduction to optical networks - 45

46 Circuit switching Telephone network example A circuit is equivalent to a physical connection between end-points 5. Data transmission 6. Data reception 4. Call accepted 3. Call accepted 1. Call setup 2. Call advertisement Introduction to optical networks - 46

47 Packet switching In circuit switching resources are completely devoted to each communication, upon explicit request. The link capacity utilization is very low for bursty traffic Approach: segment information in small units each segment is independently transferred by the network Resources are allocated in a dynamic fashion to different information flows Introduction to optical networks - 47

48 Packet switching No static resource allocation Suited for bursty sources Similar to the postal service address P.T. P.T. P.T. Introduction to optical networks - 48

49 Packet switching Information is formatted in data units (PDU), joining user information (SDU) to protocol control information (PCI) PDU PCI SDU Pros: efficient resource utilization in case of bursty sources possible error detection along the path possible to use volume-based billing possible to use different protocols, formats, speeds along the path Cons: each node must process each packet delays are higly variable (queueing delay) packet losses and out-of-orders Introduction to optical networks - 49

50 Packet switching Contention may arise solved by means of packet storage (memories) and possibly discarding Postal service: If there is no room on the current truck, letters will be carried by next truck switch Introduction to optical networks - 50

51 Packet switching If congestion arises, the network may drop packets Automatic retransmission protocols must be implemented to recover from packet losses (e.g. TCP) when reliable services are offered Introduction to optical networks - 51

52 Switching in Internet contention resolution in the time domain, based upon statistical multiplexing, queuing and packet dropping a packet uses at most one channel at any time longest-prefix-matching on destination IP address Introduction to optical networks - 52

53 Circuit switching Circuits or packets? Static resource (pre)allocation Positional switching Packet switching Partial and progressive resource allocation Label switching Introduction to optical networks - 53

54 Switching in optical networks Optical networks are better suited to (fast) circuit switching: There is no optical memory Time-domain operations are difficult Optical switches may be slow There is a huge bandwidth WDM can be exploited to flexibly change the network topology Introduction to optical networks - 54

55 State of the art in optical switching Proposals and research in optical networks: Routing of information in the optical domain Reconfigurable optical networks Optical fault protection & restoration The frontier is optical packet switching (3 rd generation optical networks?) Introduction to optical networks - 55

56 Circuits or packets? Tomorrow? Packet optical networks or optical packet networks? Optical packet networks: Aim at mimicking the IP and Ethernet switching paradigm Still in a very preliminary phase A lot or effort (but few results) in last years Introduction to optical networks - 56

57 Tomorrow? TX/RX TX/RX Glass cloud TX/RX TX/RX When? 20xx? Introduction to optical networks - 57

Introduction To Optical Networks Optical Networks: A Practical Perspective

Introduction To Optical Networks Optical Networks: A Practical Perspective Galen Sasaki Galen Sasaki University of Hawaii 1 Galen Sasaki University of Hawaii 2 Galen Sasaki University of Hawaii 3 Telecommunications