Switching Architectures for Optical Networks

1. Switching Architectures for Optical Networks

2. SONET SONET SONET SONET DWDM DWDM Internet Reality Data Center Access Access Long Haul Metro Metro

3. Hierarchies of Networks: IP / ATM / SONET / WDM

4. Why Optical? • Enormous bandwidth made available • DWDM makes ~160 channels/ possible in a fiber • Each wavelength “potentially” carries about 40 Gbps • Hence Tbps speeds become a reality • Low bit error rates • 10-9 as compared to 10-5 for copper wires • Very large distance transmissions with very little amplification.

5. Dense Wave Division Multiplexing (DWDM) • 1 • 2 • 3 Long-haul fiber • 4 Output fibers • Multiple wavelength bands on each fiber • Transmit by combining multiple lasers @ different frequencies

6. Anatomy of a DWDM System Terminal B Terminal A D E M U X Transponder Interfaces M U X Transponder Interfaces Post- Amp Pre- Amp Line Amplifiers Direct Connections Direct Connections Basic building blocks • Optical amplifiers • Optical multiplexers • Stable optical sources

7. OC-3 OC-3 OC-12 STS-1 STS-1 STS-1 User Services & Core Transport EDGE CORE Frame Relay Frame Relay IP Router IP ATM Switch ATM Sonet ADM Lease Lines TDM Switch Users Services Service Provider Networks Transport Provider Networks

8. Core Transport Services • Provisioned • SONET circuits. • Aggregated into • Lamdbas. Circuit Origin • Carried over • Fiber optic cables. Circuit Destination OC-3 OC-3 OC-12 STS-1 STS-1 STS-1

9. WDM link Edge Router Legacy Interfaces Legacy ( e.g., PoS, Gigabit Interfaces Ethernet, IP/ATM) Interfaces Legacy Interfaces Optical Switch WDM Network: Wavelength View

10. Relationship of IP and Optical • Optical brings • Bandwidth multiplication • Network simplicity (removal of redundant layers) • IP brings • Scalable, mature control plane • Universal OS and application support • Global Internet • Collectively IP and Optical (IP+Optical) introduces a set of service-enabling technologies

11. Typical Super POP Interconnection Network SONET Core ATM Switch Voice Switch Core IP router Large Multi-service Aggregation Switch Coupler & Opt.amp DWDM + ADM OXC DWDM Metro Ring

12. Typical POP Voice Switch OXC D W D M D W D M SONET-XC

13. What are the Challenges with Optical Networks? • Processing: Needs to be done with electronics • Network configuration and management • Packet processing and scheduling • Resource allocation, etc. • Traffic Buffering • Optics still not mature for this (use Delay Fiber Lines) • 1 pkt = 12 kbits @ 10 Gbps requires 1.2 s of delay => 360 m of fiber) • Switch configuration • Relatively slow

14. 1 1 2 OADM 2 3 ’3 DCS 3 ’3 Optical Hardware • Optical Add-Drop Multiplexer (OADM) • Allows transit traffic to bypass node optically Add and Drop

15. 3 2 3 2 WC No  converters With  converters 1 New request 1 3 1 New request 1 3 Wavelength Converters • Improve utilization of available wavelengths on links • All-optical WCs being developed • Greatly reduce blocking probabilities

16. ADM ADM ADM ADM Digital Crossconnect DWDM IP ATM Multiplexer & Demultiplexer Router Switch Late 90s: Backbone Nodes

17. Problems • About 80% traffic through each node is “pass-through” • No need to electronically process such traffic • 80-channel DWDM requires 80 ADMs • Speed upgrade requires replacing all the ADMs in the node

18. Today: Optical Cross Connect (OXC) Optical Crossconnect ATM Digital Terabit Backbone Cross IP Switch Connect Router DWDM Multiplexer & Demultiplexer IP ATM Router Switch Source: JPMS

19. Wavelength Cross-Connects (WXCs) • A WDM network consists of wavelength cross-connects (WXCs) (OXC) interconnected by fiber links. • 2 Types of WXCs • Wavelength selective cross-connect (WSXC) • Route a message arriving at an incoming fiber on some wavelength to an outgoing fiber on the same wavelength. • Wavelength continuity constraint • Wavelength interchanging cross-connect (WIXC) • Wavelength conversion employed • Yield better performance • Expensive

20. Wavelength Router Wavelength Router Control Plane: Wavelength Routing Intelligence Data Plane: Optical Cross Connect Matrix Unidirectional DWDM Links to other Wavelength Routers Unidirectional DWDM Links to other Wavelength Routers Single Channel Links to IP Routers, SDH Muxes, ...

21. Optical Network Architecture Mesh Optical Network UNI UNI IP Network IP Network IP Router Control Path OXC Control unit Optical Cross Connect (OXC) Data Path

22. OXC Control Unit • Each OXC has a control unit • Responsible for switch configuration • Communicates with adjacent OXCs or the client network through single-hop light paths • These are Control light paths • Use standard signaling protocol like GMPLS for control functions • Data light paths carry the data flow • Originate and terminate at client networks/edge routers and transparently traverse the core

23. l2 l4 l3 l1 l3 l2 l4 l1 Optical Cross-connects (No wavelength conversion) All Optical Cross-connect (OXC) Also known as PhotonicCross-connect (PXC) Optical Switch Fabric

24. Optical Cross-Connect with Full Wavelength Conversion • M demultiplexers at incoming side • M multiplexers at outgoing side • Mn x Mn optical switch has wavelength converters at switch outputs Wavelength Converters l 2 l 1 l l l l l l 1, 2, ... , n 1, 2, ... , n l l 2 1 1 1 l l n n l l 1 1 l l l l l l 1, 2, ... , n 1, 2, ... , n l l 2 2 2 2 l l n n . . . . . . l l 1 n l l l l l l 1, 2, ... , n 1, 2, ... , n l l 2 1 M M l l n 2 Wavelength Wavelength Optical CrossBar Demux Mux Switch

25. Cross-Connect Incoming Interface Incoming Wavelength Outgoing Interface Outgoing Wavelength l1 l3 Wavelength Router with O/E and E/O

26. O/E O/E O/E O/E O/E O/E O/E O/E O/E O-E-O Crossconnect Switch (OXC) Outgoing fibers Incoming fibers Individual wavelengths O O Demux Mux E/O E 1 1 E/O E/O E/O 2 2 E/O WDM (many λs) E/O N E/O N E/O E/O Switches information signal on a particular wavelength on an incoming fiber to (another) wavelength on an outgoing fiber.

27. Optical core network Opaque (O-E-O) and transparent (O-O) sections Transparent optical island E/O O/E Client signals O O O O E E O to other nodes from other nodes O O O O O E E O Opaque optical network

28. Capable of status monitoring Optical signal regenerated – improve signal-to-noise ratio Traffic grooming at various levels Less aggregated throughput More expensive More power consumption Unable to monitor the contents of the data stream Only optical amplification – signal-to-noise ratio degraded with distance No traffic grooming in sub-wavelength level Higher aggregated throughput ~10X cost saving ~10X power saving OEO vs. All-Optical Switches OEO All-Optical

29. Large customers buy “lightpaths” A lightpath is a series of wavelength links from end to end. optical fibers One fiber Repeater cross-connect

30. Hierarchicalswitching: Node with switches of different granularities O O A. Entire fibers O Fibers Fibers “Express trains” O O B. Wavelength subsets O E O C. Individual wavelengths O “Local trains”

31. GAN links Wide Area Network (WAN) WAN : Up to 200-500 wavelengths 40-160 Gbit/s/l wavebands (> 10 l) OXC: Optical Wavelength/Waveband Cross Connect

32. Packet (a) vs. Burst (b) Switching

33. MAN (Country / Region) IP packets optical burst formation

34. Optical Switching Technologies • MEMs – MicroElectroMechanical • Liquid Crystal • Opto-Mechanical • Bubble Technology • Thermo-optic (Silica, Polymer) • Electro-optic (LiNb03, SOA, InP) • Acousto-optic • Others… Maturity of technology, Switching speed, Scalability, Cost, Relaiability (moving components or not), etc.

35. MEMS Switches for Optical Cross-Connect Proven technology, switching time (10 to 25 msec), moving mirrors is a reliability problem.

36. WDM “transparent” transmission system (O-O nodes) Wavelengths disaggregator Wavelengths aggregator O O O O O O Fibers multiple λs Optical switching fabric (MEMS devices, etc.) Tiny mirrors Incoming fiber Outgoing fibers

37. Upcoming Optical Technologies • WDM routing is circuit switched • Resources are wasted if enough data is not sent • Wastage more prominent in optical networks • Techniques for eliminating resource wastage • Burst Switching • Packet Switching • Optical burst switching (OBS) is a new method to transmit data • A burst has an intermediate characteristics compared to the basic switching units in circuit and packet switching, which are a session and a packet, respectively

38. Optical Burst Switching (OBS) • Group of packets a grouped in to ‘bursts’, which is the transmission unit • Before the transmission, a control packet is sent out • The control packet contains the information of burst arrival time, burst duration, and destination address • Resources are reserved for this burst along the switches along the way • The burst is then transmitted • Reservations are torn down after the burst

39. Optical Burst Switching (OBS)

40. Optical Packet Switching • Fully utilizes the advantages of statistical multiplexing • Optical switching and buffering • Packet has Header + Payload • Separated at an optical switch • Header sent to the electronic control unit, which configures the switch for packet forwarding • Payload remains in optical domain, and is re-combined with the header at output interface

41. Optical Packet Switch • Has • Input interface, Switching fabric, Output interface and control unit • Input interface separates payload and header • Control unit operates in electronic domain and configures the switch fabric • Output interface regenerates optical signals and inserts packet headers • Issues in optical packet switches • Synchronization • Contention resolution

42. Main operation in a switch: • The header and the payload are separated. • Header is processed electronically. • Payload remains as an optical signal throughout the switch. • Payload and header are re-combined at the output interface. hdr CPU payload hdr payload hdr payload Re-combined Wavelength i output port j Optical packet Wavelength i input port j Optical switch

43. Output port contention • Assuming a non-blocking switching matrix, more than one packet may arrive at the same output port at the same time. Input ports Optical Switch Output ports payload hdr . . . payload hdr . . . . . . . . . payload hdr

44. OPS Architecture: Synchronization Occurs in electronic switches – solved by input buffering Slotted networks • Fixed packet size • Synchronization stages required Sync.

45. OPS Architecture: Synchronization Slotted networks • Fixed packet size • Synchronization stages required Sync.

46. OPS Architecture: Synchronization Slotted networks • Fixed packet size • Synchronization stages required Sync.

47. OPS Architecture: Synchronization Slotted networks • Fixed packet size • Synchronization stages required Sync.

48. OPS Architecture: Synchronization Slotted networks • Fixed packet size • Synchronization stages required Sync.

49. OPS Architecture: Synchronization Sync.

50. OPS: Contention Resolution • More than one packet trying to go out of the same output port at the same time • Occurs in electronic switches too and is resolved by buffering the packets at the output • Optical buffering ? • Solutions for contention • Optical Buffering • Wavelength multiplexing • Deflection routing