wavelength selection based on wavelength availability

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Wavelength selection based on wavelength availability in multi -fiber WDM networks



2. TOPICS COVERED WDM and AONs Data Transfer Mechanism in WDM AONs Wavelength Selection based on Wavelength Availability in MultiFiber WDM Networks 3. WDM and AONs 4. SINGLE AND MULTI FIBER WDM NETWORKS Single fiber WDM Networks Each link consists of a single fiber. Two or more light paths with the same wavelength cannot be established in the same link Multi fiber WDM Networks Each link consists of multiple fibers. The same number of light paths as fibers can be established with the same wavelength on each link 5. WAVELENGTH DIVISION MULTIPLEXING Wavelength division multiplexing (WDM) multiple wavelengths to transmit different data streams. optical spectrum, is used more efficiently Enormous bandwidth is available on fiber WDM can provide an optical transmission system with an extremely large data rate. 6. BENEFITS OF WDM Increase Capacity Same fiber employed for multiple data streams.Transparency Supports multiple protocols . Supports different bit rates. Wavelength Reuse Same wavelength can be used at different fiber linksReliability very reliable and safe. very low crosstalk 7. WAVELENGTH ROUTED NETWORK A wavelength routing network consist of optical cross connects (OXCs) - serves for switching and routingData can be sent through light paths from source to destination.Each light path is assigned a dedicated wavelength 8. OPTICAL CROSS-CONNECT (OXC) Optical switchCan connect optical signal on input ports to output portsOXC can Switch to same wavelengthSwitch to the different wavelength In such cases OCX should be equipped with wavelength converters. 9. ALL-OPTICAL NETWORKS (AONS) Special kind of optical networksPath between communicating nodes remains entirely optical.These paths are called light paths, which use the same wavelength on all the links along a path. 10. Data Transfer Mechanism in WDM AONs 11. DATA TRANSFER IN WDM AONs, to send data from source node to a destination node, three phases are to be considered Light path establishment and set-up (routing and wavelength assignment) Data transfer Light path takedown (wavelength release) This process requires the exchange of control messages.So the phases 1 and 3 requires a control protocol 12. ROUTING AND WAVELENGTH ASSIGNMENT(RWA) For successful data transmission A route has to be foundAn appropriate wavelength has to be assigned between transmitter and receiverThis is called the routing and wavelength assignment (RWA) 13. RWA PROBLEMS There are 2 problems in the RWA Wavelength continuity constraintDistinct wavelength constraint 14. WAVELENGTH CONTINUITY CONSTRAIN When the routing nodes are not capable for wavelength conversion Then the light path must use the same wavelength in all the optical segments it uses. In the absence of a free wavelength along the entire route, the connection cannot be established and it is blocked When wavelength conversion is present The only limiting factor is the bandwidth of every link. In such network, a connection is blocked only when no wavelength is available at some segment of an optical path. 15. DISTINCT WAVELENGTH CONSTRAIN If all light paths using the same link (fiber), then the light path should be allocated to different wavelengths. 16. RWA problem can be classified into two traffic assumptions: Static RWA problem Static Light path Establishment (SLE) traffic requirements are known in advanceand Dynamic RWA Dynamic Light path Establishment (DLE) The order of light path requests arrive randomly . 17. DYNAMIC LIGHT PATH ESTABLISHMENT (DLE) Objective is to choose a route and a wavelength which maximizes the probability of setting up a given connection, while at the same time attempting to minimize the blocking for future connections. 18. Dynamic RWA problem routing sub problemwavelength assignment sub problem 19. ROUTING ASSIGNMENT Fixed Routing a single fixed route is predetermined for each sourcedestination pair.Adaptive Routing Alternate-Path Routing. Relies on a set of predetermined fixed routes between a source node and a destination node When a connection request arrives, a single route is chosen from the set of predetermined routes, and a light path is established on this route. The criteria for route selection are typically based on either path length or path congestion. 20. WAVELENGTH ASSIGNMENT A light path is required to be established before data is transferred between two communicating nodes.No two light paths can share a common link using the same wavelength, known as wavelength continuity constraintBlocking probability increases 21. WAVELENGTH ASSIGNMENT CONT.. A possible alternative to reduce blocking probability is the use of opto-electronic wavelength convertersBut these converters add substantially to the cost of the network.So we need some form of network control or signalling mechanism if we do not use wave length converters 22. THE NETWORK CONTROL (OR SIGNALLING) Required for managing a light pathCan be Centralised Distributed 23. CENTRALISED CONTROL A single control centre maintains the complete network topology including wavelength usage on each link.Not feasible and reliable in large networks because A change in network topology and/or wavelength usage should be informed Immediately. if the control centre crashes, all network information is lost 24. DISTRIBUTED CONTROL Every node acts as a controller and maintains its own local database.In the event of a node crash, other nodes work as usual in the network.If there is a change in the network topology or wavelength usage, the concerned database is updated immediately. 25. But, in this kind of control, a connection request may be unnecessarily blocked due to the wavelength-continuity constraint.So an efficient distributed wavelength reservation protocol is needed for dynamic WDM networks with rapidly changing wavelength availability. 26. WAVELENGTH SELECTION BASED ON WAVELENGTH AVAILABILITY IN MULTI-FIBER WDM NETWORKS 27. Objective To establish wavelength-continuous light paths dynamically and efficiently so as to minimize the overall blocking probability at the cost of a nominal increase in control overhead 28. Assumptions The route between source and destination is previously known. We consider the class of optical networks without wavelength conversion facility . 29. WAVELENGTH RESERVATION PROTOCOL Before transmission data in optical networks, a light path have to establish by reserving a wavelength in all links along a route between a sender and a receiver.There are two types of wavelength reservation protocols which are forward reservation backward reservation 30. CONTROL MECHANISMS In order to support distributed wavelength reservation protocols wdm networks are equipped with a shadow network in addition to the optical data networkThe shadow network Used to exchange control information. Has same physical topology as data network. Operates in packet switching mode . Traffic on shadow network consist of small control packets. Lighter traffic compared to data network. 31. Routers and intermediate nodes examine these control packets and updates accordingly.Can be implemented as electronic network a virtual channel on data network can be reserved exclusively for exchanging control information 32. FORWARD RESERVATION Source initiatedWhen a transmission request arrives, The source node sends a reservation (RESV ) packet to the destination node along the decided routeEach node along the path processes the RESV packet and temporarily locks one or more appropriate wavelengths on the next link for connection 33. If no suitable wavelength is found on the next link the intermediate node sends a failure (FAIL) message back to source node.Fail packet unlocks all the wavelengths reserved so far.Otherwise at the destination one of the available wavelengths is picked up and as acknowledgement packet is send back from destination to source.On its way back to source this ACK packet permanently locks the selected wavelengths and unlocks the other wavelengths at the intermediate nodes. 34. In general, the forward reservation has high blocking probability because the sender nodes cannot get the wavelength information along routes.Temporary locking of wavelength. 35. BACKWARD RESERVATION Destination initiated when a transmission request arrives, The sender node sends a PROB packetPROB packet collects information on available wavelengths in each link along a route. It will not lock any wavelengthWhen the PROB message reaches the receiver node, the receiver node selects a wavelength from a set of available wavelengths along the entire route based on certain criteria. 36. The RESV packet locks the wavelength along the reverse path towards the source nodeIf the wavelength is not found available at some intermediate node the node generate a FAIL packet to the destination and NAK packet to sourceThe FAIL packet releases the wavelength locked so far .NAK packet informs the source about connection failure. 37. The backward reservation can reduce blocking probability more efficiently than the forward reservation because wavelength usage in all links along a route is known before selection.Furthermore, duration of reservation in the backward reservation is smaller than that in the forward reservation. 38. AN EXAMPLE OF THE BACKWARD RESERVATION IN MULTI FIBER WDM NETWORKS 39. Each link consists of 3 fibers.Firstly, the source node sends a PROB message.In this example, wavelengths {1, 2, 3 and 4} are available on fiber1 between the source node and the intermediate node.Similarly, wavelengths {1, 2} and {2, 4} are available on fiber 2 and fiber 3, respectively.Therfore wavelengths available on fiber 1, fiber 2, and fiber 3 between the intermediate node and the destination node are {1, 3},


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