Chapter 10: Optical burst switching

1. Chapter 10:Optical burst switching TOPICS • Optical packet switching • Optical burst switching • Connection setup schemes • Reservation/release of resources • Scheduling • The Jumpstart project Connection-Oriented Networks - Harry Perros

2. Optical burst switching (OBS) • It has not been standardized yet • It is regarded as a viable solution for transmitting bursts over an optical network • A connection is setup uniquely for the transmission of a single burst • OBS was preceded by an earlier scheme: optical packet switching (OPS) Connection-Oriented Networks - Harry Perros

3. Optical Packet Switching (OPS) • A WDM optical packet network consists of optical packet switches interconnected by WDM fiber links. • Optical packet switches operate in a slotted manner. • An optical packet are fixed-sized in time, but the actual transmission rate may vary, i.e., the packet size may vary Connection-Oriented Networks - Harry Perros

4. WDM optical packet switches • A WDM optical packet switch consists of the following four parts: • input interfaces • the switching fabric • output interfaces, and • the control unit. Connection-Oriented Networks - Harry Perros

5. 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 Connection-Oriented Networks - Harry Perros

6. Output port contention Assuming a non-blocking switching matrix, more than one optical packet may arrive at the same output port at the same time. Input ports Output ports Optical Switch payload . . . payload . . . . . . . . . payload Connection-Oriented Networks - Harry Perros

7. Contention resolution • Output port contention commonly arises in packet switches, and it is known as external blocking. • It is resolved by buffering all the contending packets, except one which is permitted to go out. Connection-Oriented Networks - Harry Perros

8. Techniques for resolving contention in an optical switching • optical buffering, • exploiting the wavelength domain, and • using deflection routing. Connection-Oriented Networks - Harry Perros

9. Optical buffering - The Achilles' heel of OPS! • Optical buffering currently can only be implemented using fiber delay lines (FDL). • An FDL can delay an optical packet for a specified amount of time, which is related to the length of the delay line. • FDLs are not commercially viable. Connection-Oriented Networks - Harry Perros

10. FDLs • A buffer for N packets with a FIFO discipline can be implemented using N optical delay lines of different lengths. • FDL i delays an optical packet for i timeslots. • Assuming C wavelengths, FDL i may be able to store: C*i optical packets . • Limited by the length of the delay lines, this type of optical buffer is usually small, and it does not scale up. Connection-Oriented Networks - Harry Perros

11. Exploiting the wavelength domain • External blocking may be minimized by exploiting the WDM feature on a fiber link that connects two optical switches. • Two optical packets destined to go out of the same output port at the same time can be sent out on two different wavelengths. This requires converters. • This method may have some potential since the number of wavelengths that can be coupled together onto a single fiber continues to increase. Connection-Oriented Networks - Harry Perros

12. Deflection routing • When there is a conflict between two optical packets, one will be routed to the correct output port, and the other will be routed to any other available output port. • A deflected optical packet may follow a longer path to its destination. In view of this: • The end-to-end delay for an optical packet may be unacceptably high. • Optical packets may have to be re-ordered at the destination Connection-Oriented Networks - Harry Perros

13. Optical packet switch architectures • Based on the switching fabric used, they have been classified in the following three classes: • space switch fabrics, • broadcast-and-select switch fabrics, and • wavelength routing switch fabrics. Connection-Oriented Networks - Harry Perros

14. A space switch fabric architecture 0 1 d 1 0 0*T 1 1 d N 0 . . . d*T 0 1 d d W 0 d N . . . . . . 0 1 d 1 0*T 0 N N N d 0 . . . d*T 0 1 d d W 0 d N Space switch Packet buffer Packet encoder Connection-Oriented Networks - Harry Perros

15. Packet encoder 1 1 • The switch is slotted, with N input/output ports, and W wavelengths per port • The incoming signal in input port i is demultiplexed into the W wavelengths. • Each wavelength carries a packet for that slot, and it is converted to another wavelength to avoid collisions at the destination output port. . . . W . . . 1 N . . . W De-mux Tunable wavelength converter Connection-Oriented Networks - Harry Perros

16. Space switch 0 1 d 0 . . . 0 Input Port 1 • The space switch fabric switches an optical packet to any of the N output optical buffers. • A splitter distributes the same packet to N different output fibers, one per output port. The signal on each of these output fibers is split again d+1 times, one per FDL at the destination output buffer Output Port 1 d N . . . 0 1 d d . . . 0 d N . . . . . . 0 1 d . . . 0 0 Input Port N N d Output Port N . . . 0 1 d d . . . 0 d N splitter Optical gate Connection-Oriented Networks - Harry Perros

17. Packet buffer 0*T 1 0 • A packet arrives at its destination port and it joins one of the FDLs • FDL i delays an optical packet for a fixed delay equal to i slots (T), with FDL 0 providing zero delay, . . . d*T d . . . 0*T N 0 d*T . . . d i FDL i coupler Connection-Oriented Networks - Harry Perros

18. Optical Burst Switching • Optical burst switching is a new technology that it is currently under study. It has not as yet been commercialized. • Unlike optical packet switching, it does not require optical buffering. • It can be seen as lying between optical packet switching and wavelength-routing networks. Connection-Oriented Networks - Harry Perros

19. Control Unit Switchfabric … … Output WDM fibers Input WDM fibers … … … … • An OBS network consists of OBS nodes interconnected with WDM fiber in a mesh topology. • An OBS node is an OXC which has a very low configuration time, due to the fact that connection do not stay up for a long time. Connection-Oriented Networks - Harry Perros

20. Main features of OBS networks • Each user transmits data in bursts. • For each burst, it first sends a SETUP message to the network, to announce its intention to transmit. • Transmission of the burst takes place after a delay known as offset. • The network nodes allocate resources for just this single burst. Connection-Oriented Networks - Harry Perros

21. End-device A End-device SETUP B Burst SETUP Burst offset time Connection-Oriented Networks - Harry Perros

22. On-the fly connection setup B A Burst is transmitted without knowing if the connection has been successfully established Offset = Sum of processing at each OXC + 1 configuration delay Control packet offset Burst time Processing time of control packet Connection-Oriented Networks - Harry Perros

23. A B If the offset is not long enough, then the burst may arrive at an OXC before the SETUP request, or before the OXC has a chance to configure its switch!! Control packet offset Burst time Processing time of control packet Connection-Oriented Networks - Harry Perros

24. Control packet time Burst Confirmed connection setup A B This is equivalent to circuit-switching. It incurs a round-trip delay to set up the transmission, and the delivery of the burst is guaranteed. Processing time of control packet Connection-Oriented Networks - Harry Perros

25. Reservation of resources in an OXC • Immediate setup • The switch is configured immediately after the SETUP request has been processed. • Delayed setup • The SETUP request provides information that is used to estimate when to configure the switch for the incoming burst Connection-Oriented Networks - Harry Perros

26. Release of resources in an OXC • Timed burst • The control packet contains information re. the length of the burst. This permits the OXC to know when to release its resources. • Explicit release • An OXC releases the resources allocated to a burst upon receipt of an explicit release message Connection-Oriented Networks - Harry Perros

27. Immediate setup, timed release Immediate setup, explicit release A B B A Control packet Control packet offset offset time Burst Burst Re;ease packet Processing time of control packet Time during which resources were allocated Connection-Oriented Networks - Harry Perros

28. Delayed setup, timed burst A B Control packet offset time Burst Processing time of control packet Time during which resources were allocated Connection-Oriented Networks - Harry Perros

29. Classification of reservation/release schemes • Immediate setup/explicit release • Immediate setup/timed release • Delayed setup/explicit release • Delayed setup/ timed release Connection-Oriented Networks - Harry Perros

30. Scheduling bursts in an OBS node Immediate setup, explicit release Burst Arrival Control packet Burst offset time A new burst will be accepted if its control packet arrives after the end of the current burst No other bursts are accepted during this time Connection-Oriented Networks - Harry Perros

31. Immediate setup, timed release Control packet Burst Arrival Control packet Burst offset offset time A new burst will be accepted if its control packet arrives prior the end of the current burst No other bursts are accepted during this time Connection-Oriented Networks - Harry Perros

32. Delayed setup, timed release: void filling Burst Arrival SETUP SETUP Burst offset offset time A new burst will be accepted if its control packet arrives prior the end of the current burst A new bursts is accepted during this time if it fits Connection-Oriented Networks - Harry Perros

33. Lost bursts • A burst is blocked when upon arrival at a node, its wavelength is at the output port is not free. • Solutions: • Burst is dropped • Wavelength conversion • Deflection routing Connection-Oriented Networks - Harry Perros

34. Burst assembly • Each end-device maintains a queue for each destination end-device. • Packets arriving at the end-device are placed accordingly to the destination queues, from where they are transmitted out in bursts. • When to transmit a burst: • Timer • Max/min burst size Connection-Oriented Networks - Harry Perros

35. When a timer expires, all packets in the queue are transmitted out in a single burst, as long as: Min. burst size < burst size Also, burst size < max. burst size • A burst can also be transmitted out if the queue size reaches the max. burst size before the timer expires. Connection-Oriented Networks - Harry Perros

36. Priorities • The end-device can also introduce priorities when transmitting bursts. • Each destination queue may be further sub-divided to a number of quality-of-service queues. The arriving packets are grouped into these queues, which are served according to a scheduler. • In addition, different timers and maximum/minimum burst sizes can be used for different queues. Connection-Oriented Networks - Harry Perros

37. Jumpstart is a DoD-funded project carried out by NC State University and MCNC, an RTP-based non-profit research organization. The objectives of Jumpstart are: Define an architecture for signaling in OBS networks and demonstrate proof of concept Define a routing architecture for OBS networks and demonstrate proof of concept. The Jumpstart architecture Connection-Oriented Networks - Harry Perros

38. Features • Jumpstart uses the immediate setup with timed or explicit release. • Both on-the-fly and confirmed connection setup methods are used. • Uses out-of-band packet-based signaling (ATM network) • The signaling messages for establishment and tearing down of a connection are processed by the OBS nodes in hardware to assure fast connections. Connection-Oriented Networks - Harry Perros

39. Basic signaling messages • The following signaling messages have been defined for the basic operation of an OBS network: • SETUP • SETUP ACK • KEEP ALIVE • RELEASE • CONNECT • FAILURE Connection-Oriented Networks - Harry Perros

40. On-the-fly connection setup A B SETUP SETUP ACK SETUP SETUP Burst CONNECT Time RELEASE RELEASE RELEASE Connection-Oriented Networks - Harry Perros

41. KEEP ALIVE messages • In the case of explicit release, to guard against lost RELEASE messages, the control unit of each OBS node associates the transmission of a burst with a timer. • The control unit assumes that the transmission of a burst has been completed if the timer expires and it has not received a RELEASE message. • In view of this, when an end-device transmits a very long burst, it must periodically send to the network KEEP ALIVE messages which are used by each control unit to reset the timer. Connection-Oriented Networks - Harry Perros

42. Persistent connections • A persistent connection guarantees that a series follows the same path through the network. The following additional messages are used: • SESSION DECLARATION, • DECLARATION ACK • SESSION RELEASE. A B SESSION DECLARATION SESSION DECLARATION Persistent connection setup SESSION DECLARATION SESSION ACK SESSION ACK SESSION ACK KEEP ALIVE Data transfer KEEP ALIVE KEEP ALIVE SESSION RELEASE Tear down SESSION RELEASE SESSION RELEASE Connection-Oriented Networks - Harry Perros

43. The signaling message structure • Signaling messages are structured so that they can be partly processed in hardware and partly in software. • The information carried in a message is organized in information elements (IEs): • Hardpath IEs (processed in hardware) • Softpath IEs (processed in software) • IE structure: TLV (type, length, value) Connection-Oriented Networks - Harry Perros

44. Message format Common header Hardpath IEs Softpath IEs CRC 32 Protocol type Header flags Message type Protocol version Message length Softpath IEs offset Hardpath IEs TLVs Number of softpath IEs . . . IE mask . . . flags Connection-Oriented Networks - Harry Perros

45. Addressing • Hierarchical addresses, similar in spirit to the NSAP address format OBS top Domain Domain 0xA Domain 0xB 0x01 0x0E 0x03 0x1A 0x1B 0x035 0x001 0x001F 0x000F 0x02 0x0B Connection-Oriented Networks - Harry Perros

46. JITPAC: The Jumpstart signaling processing engine • The JITPAC processes SETUP/RELEASE messages and controls the optical fiber. • Hardware-based • Uses ATM/AAL5 frames for signaling • Controls the OXC (2D MEMS) via RPC calls done over dedicated Ethernet. Connection-Oriented Networks - Harry Perros

47. Main operation: SETUP message • JITPAC receives a SETUP message. • Using the destination address it looks up the next hop (i.e. the output port number). • Instructs the switch fabric to setup the path from input to output. • Forwards the SETUP message to the JITPAC of the next hop OXC. Connection-Oriented Networks - Harry Perros

48. Serial Port 1 Local Bus SDRAM 4M Serial Port 2 MPC8260 155Mb/s UTP ATM Network ATM Interface SDRAM DIMM Module (64 Meg) Ethernet 10/100 60x Bus Ethernet Network Altera EP20K400 FPGA Ethernet 10BaseT Flash 16M Ethernet OBS OXC JITPAC Connection-Oriented Networks - Harry Perros

49. The routing architecture JITPAC JITPAC JITPAC Control plane JITPAC JITPAC OXC OXC Data plane OXC OXC OXC Connection-Oriented Networks - Harry Perros

50. Features • Different routing architectures for control messages and data bursts are used. • Signaling messages were not considered, since they use the same routes as the data bursts. • Each JITPAC maintains two logical forwarding tables: the control forwarding table, and the burst forwarding table. • Two separate and independent path computation components were defined for the control forwarding table and the burst forwarding table. Connection-Oriented Networks - Harry Perros