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Fiber-Optic Networks

Fiber-Optic Networks. Xavier Fernando Ryerson Communications Lab. OSI – 7 Layer Model. This Course. Network Categories. Optical Networks are categorized in multiple ways: All Optical (or Passive Optical) Networks Vs Optical/Electrical/Optical Networks Based on service area

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Fiber-Optic Networks

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  1. Fiber-Optic Networks Xavier Fernando Ryerson Communications Lab

  2. OSI – 7 Layer Model This Course

  3. Network Categories Optical Networks are categorized in multiple ways: • All Optical (or Passive Optical) Networks Vs Optical/Electrical/Optical Networks • Based on service area • Long haul, metropolitan and access network • Wide area (WAN), metropolitan area (MAN) or local area network (LAN) • Depending on the Protocol • SONET, Ethernet, ATM, IP • Number of wavelengths • single wavelength, CWDM or DWDM

  4. Long Haul Network Long/Metro & Access Networks

  5. Global Network Hierarchy

  6. Different Network Specs Core - Combination of switching centers and transmission systems connecting switching centers. Access- that part of the network which connects subscribers to their immediate service providers LWPF : Low-Water-Peak Fiber, DCF : Dispersion Compensating Fiber, EML : Externally modulated (DFB) laser

  7. Local Area / Access Networks Local-area networks • Interconnection on number of local terminals • Main technologies: Ethernet, Fast Ethernet, Gigabit Ethernet (better for multiple access) • Usually passive star or bus networks Access networks • The first (or last) network segment between customer premises and a WAN or MAN • Usually owned by a Local Exchange Carrier • PON is getting popular • Fiber-copper technologies: HFC (fiber-coaxial cable) or DSL (fiber-twisted pair) • Fiber-wireless and free-space optics are also used

  8. Metropolitan-area/regional-area networks • A MAN or RAN covers a North American metropolitan area, or a small to medium-sized country in Europe or Asia • Optical ring/mesh topologies with adequate back-up and protection • Main technologies: SONET, ATM, Gigabit & 10-Gigabit Ethernet, DWDM • Non-optical technologies: T1, T3, Frame Relay • Several LANs could be connected to MAN

  9. Wide-Area Networks (WAN) • Long haul inter-city connections • Either government-regulated or in the public network environment • WANS originated in telephony • Main technologies: SONET/SDH, ATM, WDM • Voice circuits vs. data packets • Non-optical technologies:T1(1.544 Mb/s)/E1(2.048 Mb/s), DS-3 (44.736 Mb/s ), Frame Relay • Standards bodies include ITU-T, IETF, ATM Forum, Frame Relay Forum, IEEE

  10. Fiber in the Access End Fiber increasingly reaches the user

  11. PON Passive Optical Networks

  12. Passive Optical Networks • There is no O/E conversion in between the transmitter and the receiver (one continuous light path) • Power budget and rise time calculations has to be done from end-to-end depending on which Tx/Rx pair communicates • Star, bus, ring, mesh, tree topologies • PON Access Networks are deployed widely The PON will still need higher layer protocols (Ethernet/IP etc.) to complete the service

  13. Passive Optical Network(PON) Topologies BUS RING STAR

  14. Network Elements of PON • Passive Power Coupler/Splitter: Number of input/output ports and the power is split in different ratios. • Ex: 2X2 3-dB coupler; 80/20 coupler • Star Coupler: Splits the incoming power into number of outputs in a star network • Add/Drop Bus Coupler: Add or drop light wave to/from an optical bus • All OpticalSwitch: Divert the incoming light wave into a particular output

  15. Fig. 10-4: Fused-fiber coupler / Directional coupler • P3, P4 extremely low ( -70 dB below Po) • Coupling / Splitting Ratio = P2/(P1+P2) • If P1=P2It is called 3-dB coupler

  16. Definitions Try Ex. 10.2

  17. Star Coupler • Incoming total power is equally split between N outputs • Usually bidirectional • Splitting Loss = 10 Log N • Excess Loss = 10 Log (Total Pin/Total Pout)

  18. Star Network Power Budget: Worst case power budget need to be satisfied Ps-Pr= 2lc + α(L1+L2) + Excess Loss + 10 Log N + System Margin

  19. Linear bus topology Ex. 12.1

  20. Add-Drop Bus-Coupler Losses Connector loss (Lc) = 10Log (1-Fc) Tap loss (Ltap) = -10 Log (CT) Throughput loss (Lth) = -20 Log (1-CT) Intrinsic loss (Li) = -10 Log (1-Fi)

  21. Star, Tree & Bus Networks • Tree networks are widely deployed in the access front • Tree couplers are similar to star couplers (expansion in only one direction; no splitting in the uplink) • Bus networks are widely used in LANs • Ring networks (folded buses with protection) are widely used in MAN • Designing ring & busnetworks are similar

  22. Linear Bus versus Star Network • The loss linearly increases with N in bus (ring) connections while it is almost constant in start (tree) networks (Log(N))

  23. Synchronous Optical Network SONET

  24. Brief History • Early (copper) digital networks were asynchronous with individual clocks resulting in high bit errors and non-scalable multiplexing • Fiber technology made highly Synchronous Optical Networks (SONET) possible. • SONET standardized line rates, coding schemes, bit-rate hierarchies and maintenance functionality

  25. Synchronous Optical Networks • SONET is the TDM optical network standard for North America (called SDH in the rest of the world) • De-facto standard for fiber backhaul networks • OC-1 consists of 810 bytes over 125 us; OC-n consists of 810n bytes over 125 us • Linear multiplexing and de-multiplexing is possible with Add-Drop-Multiplexers

  26. SONET/SDH Bandwidths

  27. Synchronous Optical Networks • SONET is the TDM optical network standard for North America (It is called SDH in the rest of the world) • We focus on the physical layer • STS-1, Synchronous Transport Signal consists of 810 bytes over 125 us • 27 bytes carry overhead information • Remaining 783 bytes: Synchronous Payload Envelope

  28. SONET/SDH Bit Rates

  29. Digital Transmission Hierarchy (T-Standards) Additional framing bits stuffed at each level to achieve synchronization Not possible to directly add/drop sub-channels DS3 DS2 DS1 Predominant before optical era

  30. Fig. 12-5: Basic STS-1 SONET frame

  31. Fig. 12-6: Basic STS-N SONET frame STS-N signal has a bit rate equal to N times 51.84Mb/s Ex: STS-3  155.52 Mb/s

  32. SONET Add Drop Multiplexers ADM is a fully synchronous, byte oriented device, that can be used add/drop OC sub-channels within an OC-N signal Ex: OC-3 and OC-12 signals can be individually added/dropped from an OC-48 carrier

  33. SONET/SDH Rings • SONET/SDH are usually configured in ring architecture to create loop diversity by self healing • 2 or 4 fiber between nodes • Unidirectional/bidirectional traffic flow • Protection via line switching (entire OC-N channel is moved) or path switching (sub channel is moved)

  34. 2-Fiber Unidirectional Path Switched Ring Node 1-2 OC-3 Node 2-4; OC-3 Ex: Total capacity OC-12 may be divided to four OC-3 streams

  35. 2-Fiber UPSR • Rx compares the signals received via the primary and protection paths and picks the best one • Constant protection and automatic switching

  36. 4-Fiber Bi-directional Line Switched Ring (BLSR) All secondary fiber left for protection Node 13; 1p, 2p 31; 7p, 8p

  37. BLSR Fiber Fault Reconfiguration In case of failure, the secondary fibers between only the affected nodes (3 & 4) are used, the other links remain unaffected

  38. BLSR Node Fault Reconfiguration If both primary and secondary are cut, still the connection is not lost, but both the primary and secondary fibers of the entire ring is occupied

  39. Generic SONET network Large National Backbone City-wide Local Area Versatile SONET equipment are available that support wide range of configurations, bit rates and protection schemes

  40. Do the rest

  41. Network Terminologies

  42. Some Terms Topology – logical manner in which nodes linked Switching – transfer of information from source to destination via series of intermediate nodes; Circuit Switching – Virtual circuit established Packet Switching – Individual packets are directed Switch – is the intermediate node that stream the incoming information to the appropriate output Routing – selection of such a suitable path Router – translates the information from one network to another when two different protocol networks are connected (say ATM to Ethernet)

  43. The Optical Layer The OL is a wavelength based concept lies just above the physical layer

  44. Optical Cross Connects

  45. WDM Networks • Single fiber transmits multiple wavelengths  WDM Networks • One entire wavelength (with all the data) can be switched/routed • This adds another dimension; the Optical Layer • Wavelength converters/cross connectors; all optical networks • Note protocol independence

  46. WDM Networks • Broadcast and Select: employs passive optical stars or buses for local networks applications • Single hop networks • Multi hop networks • Wavelength Routing: employs advanced wavelength routing techniques • Enable wavelength reuse • Increases capacity

  47. WDM P-P Link Several OC-192 signals can be carried, each by one wavelength

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