Connection-Oriented Networks - Harry Perros1 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 Perros2 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 Perros3 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 Perros4 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 Perros5 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. payloadhdr Wavelength i input port j Optical packet hdr CPU Optical switch payload hdr Re-combined Wavelength i output port j

Connection-Oriented Networks - Harry Perros6 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. Output ports payload Optical Switch Input ports

Connection-Oriented Networks - Harry Perros7 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 Perros8 Techniques for resolving contention in an optical switching optical buffering, exploiting the wavelength domain, and using deflection routing.

Connection-Oriented Networks - Harry Perros9 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 Perros10 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. FDLs

Connection-Oriented Networks - Harry Perros11 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 Perros12 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: –T he end-to-end delay for an optical packet may be unacceptably high. –Optical p ackets may have to be re-ordered at the destination

Connection-Oriented Networks - Harry Perros13 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 Perros14 A space switch fabric architecture Packet encoder Space switch Packet buffer 1 1 W 1 N 0 d d 1 N 0 d 0 d N 1 W 1 N 0 d 0 d 1 N 0 d 0 d *T N d*T 0 d 0*T d*T 0 d...

Connection-Oriented Networks - Harry Perros15 Packet encoder 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. 1 1 W N 1 W... Tunable wavelength converter De-mux

Connection-Oriented Networks - Harry Perros16 Space switch splitter Optical gate 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 1 N 0 d d 1 N 0 d 0 d 1 N 0 d 0 d 1 N 0 d 0 d 0... Input Port 1 Input Port N Output Port 1 Output Port N d d

Connection-Oriented Networks - Harry Perros17 Packet buffer 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, 1 0*T N d*T 0 d 0*T d*T 0 d... i coupler FDL i...

Connection-Oriented Networks - Harry Perros18 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. Optical Burst Switching

Connection-Oriented Networks - Harry Perros19 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. Control Unit Input WDM fibers Output WDM fibers … Switch fabric … … … … …

Connection-Oriented Networks - Harry Perros20 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 Perros21 A B End-device SETUP Burst SETUP Burst offset time

Connection-Oriented Networks - Harry Perros22 A B time offset Burst is transmitted without knowing if the connection has been successfully established Offset = Sum of processing at each OXC + 1 configuration delay On-the fly connection setup Control packet Burst Processing time of control packet

Connection-Oriented Networks - Harry Perros23 A B time offset 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 Burst Processing time of control packet

Connection-Oriented Networks - Harry Perros24 A B Confirmed connection setup 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 time Control packet Burst

Connection-Oriented Networks - Harry Perros25 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 Perros26 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 Perros27 A B time offset Immediate setup, timed release Control packet Burst Processing time of control packet Time during which resources were allocated A B offset Immediate setup, explicit release Control packet Burst Re;ease packet

Connection-Oriented Networks - Harry Perros28 A B time offset Delayed setup, timed burst Control packet Burst Processing time of control packet Time during which resources were allocated

Connection-Oriented Networks - Harry Perros29 Classification of reservation/release schemes 1.Immediate setup/explicit release 2.Immediate setup/timed release 3.Delayed setup/explicit release 4.Delayed setup/ timed release

Connection-Oriented Networks - Harry Perros30 Control packet Burst offset time Immediate setup, explicit release Burst Arrival No other bursts are accepted during this time A new burst will be accepted if its control packet arrives after the end of the current burst Scheduling bursts in an OBS node

Connection-Oriented Networks - Harry Perros31 Control packet Burst offset time Immediate setup, timed release Burst Arrival No other bursts are accepted during this time A new burst will be accepted if its control packet arrives prior the end of the current burst offset Control packet

Connection-Oriented Networks - Harry Perros32 SETUP Burst offset time Delayed setup, timed release: void filling Burst Arrival A new bursts is accepted during this time if it fits A new burst will be accepted if its control packet arrives prior the end of the current burst offset SETUP

Connection-Oriented Networks - Harry Perros33 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 Perros34 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 Perros35 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 Perros36 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 Perros37 The Jumpstart architecture 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.

Connection-Oriented Networks - Harry Perros38 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 Perros39 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 Perros40 On-the-fly connection setup Time Burst A SETUP ACK RELEASE CONNECT B

Connection-Oriented Networks - Harry Perros41 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 Perros42 SESSION DECLARATION SESSION ACK KEEP ALIVE SESSION RELEASE Persistent connection setup Data transfer Tear down SESSION DECLARATION SESSION DECLARATION SESSION ACK KEEP ALIVE SESSION RELEASE SESSION RELEASE SESSION ACK B A 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. Persistent connections

Connection-Oriented Networks - Harry Perros43 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 Perros44 Common headerHardpath IEsSoftpath IEsCRC 32 Protocol type Protocol version Message type Message length Softpath IEs offset IE mask... Hardpath IEs Number of softpath IEs... TLVs Header flags Message format

Connection-Oriented Networks - Harry Perros45 Addressing 0x1A0x1B 0x01 0x02 0x0E 0x03 0x0B 0x001F 0x001 0x000F 0x035 Domain 0xA Domain 0xB OBS top Domain Hierarchical addresses, similar in spirit to the NSAP address format

Connection-Oriented Networks - Harry Perros46 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 Perros47 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 Perros48 JITPAC 155Mb/s UTP Ethernet OBS OXC ATM Network Ethernet Network Ethernet 10BaseT Ethernet 10/100 ATM Interface MPC8260 Altera EP20K400 FPGA SDRAM DIMM Module (64 Meg) Flash 16M SDRAM 4M 60x Bus Local Bus Serial Port 1 Serial Port 2

Connection-Oriented Networks - Harry Perros49 The routing architecture OXC JITPAC Data plane Control plane

Connection-Oriented Networks - Harry Perros50 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 Perros51 The routing architecture for control messages The control plane was implemented on an electrical packet-switched network. The primary routing goal is the computation of shortest paths between JITPAC controllers to enable the efficient exchange of control messages. To that effect a link-state protocol such as OSPF or IS-IS can be used to establish paths for control messages.

Connection-Oriented Networks - Harry Perros52 Routing architecture for data bursts A centralized architecture is used for computing paths for data bursts within a network domain. The path computation is the responsibility of the Routing Data Node (RDN), a server attached to one of the OBS nodes. It is responsible for –collecting routing information regarding the data plane, –computing the burst forwarding tables for each JITPAC controller, and –downloading the tables to the JITPAC controllers.