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Wavelength selection based on wavelength availability
The document discusses wavelength selection in multi-fiber Wavelength Division Multiplexing (WDM) networks, detailing the structure and benefits of both single and multi-fiber systems. It emphasizes the importance of dynamic light path establishment and the challenges in routing and wavelength assignment, including wavelength continuity and distinct wavelength constraints. Two types of reservation protocols, forward and backward, are analyzed for their efficiency in minimizing connection blocking probability, with a proposed scheme that selects the least used wavelength to optimize performance.
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Introduction to wavelength selection based on availability in multi-fiber WDM networks, presented by Hrudya.B.Kurup.
Discusses Wavelength Division Multiplexing (WDM) and All Optical Networks (AONs), comparing single and multi-fiber WDM networks.
Explains WDM principles, advantages like increased capacity, protocol support, reliability, and wavelength reuse.
Describes the structure and functionality of wavelength routed networks with optical cross-connects and AONs.
Details the phases of data transfer in WDM AONs including light path setup, data transfer, and takedown.
Explains the RWA problem, including constraints like wavelength continuity and distinct wavelength.
Discusses traffic assumptions in RWA (static and dynamic) and strategies to manage blocking probability using converters.
Explains centralized vs. distributed control mechanisms for managing light paths and wavelength availability.
Introduces the need for dynamic wavelength selection protocols, including reservations and control mechanisms.
Describes the forward reservation process, its high blocking probability, and its mechanism of locking wavelengths.
Illustrates backward reservation through an example showing wavelength selection based on availability.
Presents a scheme for selecting wavelengths to minimize blocking by smoothing usage across links.
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Wavelength selection based on wavelength availability
- 1. WAVELENGTH SELECTION BASEDON WAVELENGTH AVAILABILITY IN MULTI-FIBER WDM NETWORKS Presented by Hrudya.B.Kurup
- 2. TOPICS COVERED WDM andAONs Data Transfer Mechanism in WDM AONs Wavelength Selection based on Wavelength Availability in MultiFiber WDM Networks
- 3.
- 4. SINGLE AND MULTIFIBER 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
- 7. WAVELENGTH DIVISION MULTIPLEXING Wavelengthdivision 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.
- 8. BENEFITS OF WDM IncreaseCapacity 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 links Reliability very reliable and safe. very low crosstalk
- 9. WAVELENGTH ROUTED NETWORK Awavelength routing network consist of optical cross connects (OXCs) - serves for switching and routing Data can be sent through light paths from source to destination. Each light path is assigned a dedicated wavelength
- 11. OPTICAL CROSS-CONNECT (OXC) Opticalswitch Can connect optical signal on input ports to output ports OXC can Switch to same wavelength Switch to the different wavelength In such cases OCX should be equipped with wavelength converters.
- 12. ALL-OPTICAL NETWORKS (AONS) Specialkind of optical networks Path between communicating nodes remains entirely optical. These paths are called light paths, which use the same wavelength on all the links along a path.
- 13. Data Transfer Mechanismin WDM AONs
- 14. DATA TRANSFER IN WDMAONs, 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
- 15. ROUTING AND WAVELENGTHASSIGNMENT (RWA) For successful data transmission A route has to be found An appropriate wavelength has to be assigned between transmitter and receiver This is called the routing and wavelength assignment (RWA)
- 16. RWA PROBLEMS There are2 problems in the RWA Wavelength continuity constraint Distinct wavelength constraint
- 17. WAVELENGTH CONTINUITY CONSTRAIN Whenthe 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.
- 18. DISTINCT WAVELENGTH CONSTRAIN Ifall light paths using the same link (fiber), then the light path should be allocated to different wavelengths.
- 19. RWA problem canbe classified into two traffic assumptions: Static RWA problem Static Light path Establishment (SLE) traffic requirements are known in advance and Dynamic RWA Dynamic Light path Establishment (DLE) The order of light path requests arrive randomly .
- 20. DYNAMIC LIGHT PATHESTABLISHMENT (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.
- 21. Dynamic RWA problem routingsub problem wavelength assignment sub problem
- 22. ROUTING ASSIGNMENT Fixed Routing asingle 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.
- 23. WAVELENGTH ASSIGNMENT A lightpath 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 constraint Blocking probability increases
- 24. WAVELENGTH ASSIGNMENT CONT.. Apossible alternative to reduce blocking probability is the use of opto-electronic wavelength converters But 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
- 25. THE NETWORK CONTROL(OR SIGNALLING) Required for managing a light path Can be Centralised Distributed
- 26. CENTRALISED CONTROL A singlecontrol 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
- 27. DISTRIBUTED CONTROL Every nodeacts 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.
- 28. But, in thiskind 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.
- 29. WAVELENGTH SELECTION BASEDON WAVELENGTH AVAILABILITY IN MULTI-FIBER WDM NETWORKS
- 30. Objective To establish wavelength-continuouslight paths dynamically and efficiently so as to minimize the overall blocking probability at the cost of a nominal increase in control overhead
- 31. Assumptions The routebetween source and destination is previously known. We consider the class of optical networks without wavelength conversion facility .
- 32. WAVELENGTH RESERVATION PROTOCOL Beforetransmission 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
- 33. CONTROL MECHANISMS In orderto support distributed wavelength reservation protocols wdm networks are equipped with a shadow network in addition to the optical data network The 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.
- 34. Routers and intermediatenodes 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
- 35. FORWARD RESERVATION Source initiated Whena transmission request arrives, The source node sends a reservation (RESV ) packet to the destination node along the decided route Each node along the path processes the RESV packet and temporarily locks one or more appropriate wavelengths on the next link for connection
- 36. If no suitablewavelength 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.
- 37. In general, theforward reservation has high blocking probability because the sender nodes cannot get the wavelength information along routes. Temporary locking of wavelength.
- 39. BACKWARD RESERVATION Destination initiated whena transmission request arrives, The sender node sends a PROB packet PROB packet collects information on available wavelengths in each link along a route. It will not lock any wavelength When 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.
- 40. The RESV packetlocks the wavelength along the reverse path towards the source node If the wavelength is not found available at some intermediate node the node generate a FAIL packet to the destination and NAK packet to source The FAIL packet releases the wavelength locked so far . NAK packet informs the source about connection failure.
- 41. The backward reservationcan 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.
- 44. AN EXAMPLE OFTHE BACKWARD RESERVATION IN MULTI FIBER WDM NETWORKS
- 45. Each link consistsof 3 fibers. Firstly, the source node sends a PROB message. In this example, wavelengths {ω1, ω2, ω3 and ω4} are available on fiber1 between the source node and the intermediate node. Similarly, wavelengths {ω1, ω2} and {ω2, ω4} 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 {ω1, ω3}, { ω3, ω4}, and { ω1}, respectively.
- 46. The PROB messagecollects information on wavelength availability. After receiving the PROB message, the destination node knows that ω1, ω3 are available along the entire route. Thus, the destination node selects a wavelength from {ω1, ω3}. Then, the destination node sends RESV message to the source node in order to reserve the selected wavelength.
- 47. WAVELENGTH SELECTION SCHEME Thereceiver selects a wavelength based on wavelength availability in fibers of each link along a route between a sender node and a receiver node, which is collected by a PROB message. Specifically, the proposed scheme selects the least used wavelength along the route. By doing so, wavelength usage in each link is smoothed and thus the generation of bottleneck links is suppressed. As a result, blocking probability of lightpath establishments is expected to be reduced.
- 48. To do so,we define a cost C ω of wavelength ω along route p as follows: where x l,f,w = 0; if wavelength ω is available in fiber f of link l along route p between a sender node and a receiver node x l,f,w = 1 otherwise
- 49. In the proposedscheme, when a receiver node receives a PROB message, it selects a wavelength ω with the smallest cost Cω. Then the receiver node sends a RESV message to reserve the selected wavelength.
- 51. The cost ofω1 is 2 because ω 1 is not available on fiber 3 between the sender node and the intermediate node and on fiber 2 between the intermediate node and the receiver node. Similarly, the costs of ω 2, ω 3 and ω 4 are 3, 3 and 3, respectively. ω 2 is not available along the entire route because ω 2 is not available on all fibers in the link between the intermediate node and the receiver node. Therefore, the receiver node selects a wavelength from ω 1, ω 3 . In this case, ω 1 is selected because it has the smallest cost.