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CS 268: Optical Networks

CS 268: Optical Networks. Ion Stoica April 21, 2004. (Based in part on slides from Ed Bortolini (Network Photonics), Ling Huang (UC Berkeley), Shivkumar Kalyanaraman (RPI), Larry McAdams (Cisco)). SONET. SONET. SONET. SONET. DWDM. DWDM. Big Picture. Data Center. Metro. Long Haul.

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CS 268: Optical Networks

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  1. CS 268:Optical Networks Ion Stoica April 21, 2004 (Based in part on slides from Ed Bortolini (Network Photonics), Ling Huang (UC Berkeley), Shivkumar Kalyanaraman (RPI), Larry McAdams (Cisco))

  2. SONET SONET SONET SONET DWDM DWDM Big Picture Data Center Metro Long Haul Metro Access Access

  3. Overview • Optical Transmission • Dense Wavelength Division Multiplexing (DWDM) • Synchronous Optical Network (SONET) • Generic Framing Procedure (GFP)

  4. Optical Transmission Transmitted data waveform Waveform after 1000 km

  5. Fiber Attenuation • Telecommunications industry uses two windows: 1310 & 1550 nm • 1550 window is preferred for long-haul applications • Less attenuation • Wider window • Optical amplifiers 1550 window 1310 window l

  6. Dispersion • Dispersion causes the pulse to spread as it travels along the fiber • Chromatic dispersion • Light propagation in material varies with the wavelength • Degradation scales as (data-rate)2 (Figure from http://lw.pennnet.com/)

  7. Dispersion • Modal dispersion • Only for fiber that carry multiple light rays (modes) • Different modes travel at different speeds • Multimodal fiber used only for short distances

  8. Overview • Optical Transmission • Dense Wavelength Division Multiplexing (DWDM) • Synchronous Optical Network (SONET) • Generic Framing Procedure (GFP)

  9. DWDM 2.488 Gbps (1) 1310/1510 nm 2.488 Gbps (16) λ1 λ2 λ3 λ4 λ5 λ16 1530-1565 nm ramge 1310/1510 nm 16*2.488 Gbps = 40 Gbps 16 uncorrelated vawelengths 16 stabilized, correlated vawelengts

  10. Terminal Terminal Terminal Terminal Terminal Terminal Terminal Terminal Terminal Terminal DWDM System Design 40-80 km Regenerator - 3R (Reamplify, Reshape and Retime) 120 km Optical Amplifiers (OA) OA amplifies all ls

  11. 15xx nm 1310 nm 1310 nm Reamplify Reshape Retime Rx Tx External Modulator Laser Rx DWDM System Design 1550 0 0 1551 1 1 1552 2 2 1553 3 Optical Combiner 3 DWDM Filter 1554 4 4 1555 5 5 Amplify 1556 6 6 1557 7 7 15xx nm

  12. All-opticalOXC DWDM Fibersin DWDM Fibersout DWDM Demux DWDM Demux DWDM Mux DWDM Mux All-Optical Switching • Natively switch s while they are still multiplexed • Eliminate redundant optical-electronic-optical conversions

  13. 1-D MEMS • MEMS: Micro-electromechanical systems • 1-Dimensional array of micro-mirrors • 1 mirror per wavelength • Digital control; no motors

  14. Input & Output fiber array Wavelength Dispersive Element 1-D MEMS Micro-mirror Array Input Fiber Output Fiber 1 Output Fiber 2 Digital MirrorControl Electronics 1011 Optical Switch • 1-input 2-outoput illustration with four wavelengths • 1-D MEMS with dispersive optics • Dispersive element separates the ’s from inputs • MEMS independently switches each  • Dispersive element recombines the switched ’s into outputs

  15. Optical Switch

  16. Optical Add-Drop Multiplexer • Add-drop one l • Each l is associated with a fixed add/drop port • Used to implement ring topologies MUX DEMUX

  17. Overview • Optical Transmission • Dense Wavelength Division Multiplexing (DWDM) • Synchronous Optical Network (SONET) • Generic Framing Procedure (GFP)

  18. SONET • Encode bit streams into optical signals propagated over optical fiber • Uses Time Division Multiplexing (TDM) for carrying many signals of different capacities • A bit-way implementation providing end-to-end transport of bit streams • All clocks in the network are locked to a common master clock • Multiplexing done by byte interleaving

  19. Synchronous Transport Signal (STS) • First two bytes of each frame contain a special bit pattern that allows to determine where the frame starts • Receiver looks for the special bit pattern every 810 bytes • Size of frame = 9x90 = 810 bytes Data (payload) overhead 9 rows Synchronous Payload Envelope (SPE) 90 columns SONET STS-1 Frame

  20. Encoding • Overhead bytes are encoded using Non-Return to Zero • high signal  1; low signal  0 • To avoid long sequences of 0’s or 1’s the payload is XOR-ed with a special 127-bit patter with many transitions from 1 to 0 • Duration of a frame is 125 µsec (51.84 Mbps for STS-1)

  21. SONET Overhead Processing • Three layers of overhead • Path overhead (POH): end-to-end transport • Line overhead (LOH): mux-to-mux transport • Section overhead (SOH): adjacent network element Section Section Section Section Intermediate Multiplexer (ADM or DCS) DEMUX Regenerator Regenerator MUX Line Line Path

  22. STS-1 Frame Format • Two-dimensional: 9*80 = 810 bytes • Time Frame: 125 µsec • Rate: 810*8 bit/125 µsec = 51.84 Mbps • For STS-3 only the number of columns changes (3*80 = 270) 90 Bytes Or “Columns” 9 Rows Small Rectangle =1 Byte

  23. Section Overhead (SOH) Path Overhead (POH): Floating; can begin anywhere Line Overhead (LOH) STS-1 Headers 90 Bytes Or “Columns” 9 Rows

  24. First 3 lines in the header Main functions Framing (A1, A2) Monitor performance Local orderwire (E1): select repeater/terminal within communication complex Proprietary OAM (Operation, Administration, and Maintenance) (F1) Section Overhead (SOH) A1 =0xF6 A2 =0x28 J0/Z0 STS-ID B1 BIP-8 E1 Orderwire F1 User D1 Data Com D2 Data Com D3 Data Com SOH 87 B 3 B

  25. Last 3 lines in the header Main functions Locating payload (SPE) in the frame (H1, H2) Muxing and concatenating signals Performance monitoring Automatic protection switch (K1, K2) Switchover in case of failure Line maintenance Line Overhead (LOH) H1 Pointer H2 Pointer H3 Pointer Act B2 BIP-8 K1 APS K2 APS D4 Data Com D5 Data Com D6 Data Com D7 Data Com D8 Data Com D9 Data Com D10 Data Com D11 Data Com D12 Data Com S1 Sync M0 REI E1 Orderwire LOH 87 B 3 B

  26. 1st column in SPE Main functions Info about SPE content Performance monitoring Path status Path trace SPE can start anywhere in the current frame and span the next one Avoids buffer management complexity & artificial delays Path Overhead (POH) J1 Trace B3 BIP-8 C2 Sig Label G1 Path Stat F2 User H4 Indicator Z3 Growth Z4 Growth 1st STS-1 P O H SPE 9 rows Z5 Tandem 2nd STS-1

  27. STS-N Frame Format 90xN Bytes Or “Columns” N Individual STS-1 Frames Examples STS-1 51.84 Mbps STS-3 155.520 Mbps STS-12 622.080 Mbps STS-48 2.48832 Gbps STS-192 9.95323 Gbps • Composite Frames: • Byte Interleaved STS-1’s • Clock Rate = Nx51.84 Mbps • 9 colns overhead Multiple frame streams, w/ independent payload pointers Note: header columns also interleaved

  28. STS-N: Generic Frame Format STS-N STS-1

  29. STS-Nc Frame Format 90xN Bytes Or “Columns” Transport Overhead: SOH+LOH • Concatenated mode: • Same header structure and data rates as STS-N • Not all header bytes used • First H1, H2 Point To POH • Single Payload In Rest Of SPE Current IP over SONET technologies use concatenated mode: OC-3c (155 Mbps) to OC-192c (10 Gbps) rates a.k.a “super-rate” payloads

  30. Practical SONET Architecture ADM – Add-Drop Multiplexer DCS – Digital Crossconnect

  31. Protection Technique Classification • Restoration techniques can protect the network against: • Link failures • Fiber-cables cuts and line devices failures (amplifers) • Equipment failures • OXCs, ADMs, electro-optical interface. • Protection can be implemented • In the optical channel sublayer (path protection) • In the optical multiplex sublayer (line protection) • Different protection techniques are used for • Ring networks • Mesh networks

  32. 1+1 Protection • Traffic is sent over two parallel paths, and the destination selects a better one • In case of failure, the destination switch onto the other path • Pros: simple for implementation and fast restoration • Cons: waste of bandwidth

  33. 1:1 Protection • During normal operation, no traffic or low priority traffic is sent across the backup path • In case failure both the source and destination switch onto the protection path • Pros: better network utilization • Cons: required signaling overhead, slower restoration

  34. 1:1 Ring Protection • Each channel on one ring is protected by one channel on the other ring • When faults  loop around ADM ADM ADM ADM ADM ADM ADM ADM

  35. Protection in Ring Network (Unidirectional Path Switched Ring) (Bidirectional Line Switched Ring) 1:1 Line Protection Used for interoffice rings 1+1 Path Protection Used in access rings for traffic aggregation into central office 1:1 Span and Line Protection Used in metropolitan or long- haul rings

  36. Protection in Mesh Networks • Network planning and survivability design • Disjoint path idea: service working route and its backup route are topologically diverse. • Lightpaths of a logical topology can withstand physical link failures. Working Path Backup Path

  37. Normal Operation Path Switching: restoration is handled by the source and the destination. Line Switching: restoration is handled by the nodes adjacent to the failure. Span Protection: if additional fiber is available. Line Switching: restoration is handled by the nodes adjacent to the failure. Line Protection. Path Protection / Line Protection

  38. Shared Protection • Backup fibers are used for protection of multiple links • Assume independent failure and handle single failure. • The capacity reserved for protection is greatly reduced. Normal Operation 1:N Protection In Case of Failure

  39. Overview • Optical Transmission • Dense Wavelength Division Multiplexing (DWDM) • Synchronous Optical Network (SONET) • Generic Framing Procedure (GFP)

  40. Generic Framing Procedure (GFP) • GFP provides a generic mechanism to adapt traffic from higher-layer client signals over an octet synchronous transport network (e.g., SONET)

  41. Generic Framing Procedure (GFP) • Frame-mapped • Need to know the client protocol • Associate a length to each higher level frame • Efficient: eliminate the need for byte stuffing or for block encoding (e.g., 8B/10B) • Transparent • No need to know the client protocol • Less efficient; can transmit signal even when the client is idle

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