While optics and electronics should be used appropriately for transmission and switching hardware, note that "intelligence'' in any network comes from "software,'' for network control, management, signaling, traffic engineering, network planning, etc.
The role of software in creating powerful network architectures for optical WDM networks is emphasized. Optical WDM Networks is a textbook for graduate level courses. Its focus is on the networking aspects of optical networking, but it also includes coverage of physical layers in optical networks.
Thus, fibers employing EDFAs for long-haul communication would on their receive fibers. However, by using the EDFA as an ele- the information stream. The network consists of a photonic switching shown in Fig.
Each end-user is con- information stream. The information streams from multiple nected to an active switch via a fiber link. The combination of sources are optically combined by the star and the signal power an end-user and its corresponding switch is referred to as a net- of each stream is equally split and forwarded to all of the nodes work node.
Ultrawide-band EDFAs. A fundamental requirement in a wavelength-routed optical network is that two or more lightpaths traversing the same fiber link must be on different wavelength channels so that they do not interfere with one another. A lightpath may span multiple fiber links, e.
A passive-star-based local optical WDM network. Each intermediate node in the lightpath essen- tially provides an all-optical bypass facility to support the light- Each node at its access station is equipped with a set of path. A transmitter at a node sends data into the network and transceivers [transmitters lasers and receivers filters ] and if a receiver receives data from the network.
A lightpath is an all-optical com- no networking problem to solve. However, it should be noted munication channel between two nodes in the network, and it that the network size should be scalable, transceivers are may span more than one fiber link. The intermediate nodes in the expensive so that each node may be equipped with only a few fiber path route the lightpath in the optical domain using their of them, and technological constraints dictate that the number active switches.
The end-nodes of the lightpath access the light- of WDM channels that can be supported in a fiber be limited to path with transmitters and receivers that are tuned to the wave- whose value is a few tens today, but is expected to improve length on which the lightpath operates. For example, in Fig.
Thus, only a lim- lightpaths are established between nodes and on wave- ited number of lightpaths may be set up on the network. The lightpath problem is, given a set of lightpaths that need to be established between nodes and is routed via active switches 1, 6, and on the network, and given a constraint on the number of wave- 7.
Note the wavelength reuse for. While shortest-path to as the wavelength-continuity property of the lightpath. This routes may be most preferable from the individual point of requirement may not be necessary if we also have wavelength view of each lightpath, note that this choice may have to be converters in the network.
Thus, one may allow several alternate routes for to switch 10 on wavelength , gets converted to wavelength lightpaths to be established [18].
A wavelength-routed wide-area optical WDM network. Instead, we focus on In this regard, note that, normally, a lightpath operates on two major carriers whose approaches are representative of the the same wavelength across all fiber links that it traverses, in industry trend and whose strategies were available to the author. Thus, two lightpaths that share a common fiber A. MONET has the following signers of next-generation lightwave networks must be aware three-layered approach.
Rings are interconnected through XCs. The long-distance network VI. Several other carriers are also developing similar local-exchange network or the long-distance network. The core is targeted flatness, etc. Electronic interfaces will run at OC and OC This approach will aid in performance monitoring, follows. As a result, the backbone network becomes transponder-based.
In an opaque archi- growth in its data traffic. In a transparent markets [21]. As to data switch port speeds, used to provide restoration, plus elementary management it has also been growing fast during the past years. It increased of interring traffic. Then, WDM can be used for optical networking, when vendor equipment interoperability, e. We briefly examine results in the shortest distance to the destination, and it these topics below. Thus, the connection request is routed one hop A.
Network Control and Management at a time, with each node along the route independently In a wavelength-routed WDM network, a control mechanism selecting the next hop based on routing information, and is needed to set up and take down all-optical connections i. Upon the arrival of a connection re- Once the request reaches the destination node, the destination quest, this mechanism must be able to select a route, assign a node sends an acknowledgment back to the source node wavelength to the connection, and configure the appropriate op- along the reverse path i.
The mechanism must also be able back to the node from which it received the connection to provide updates to reflect which wavelengths are currently request. Upon receiving the ACK, each node along the reverse being used on each fiber link so that nodes may make informed path conFigs. The source node routing decisions. This control mechanism can either be central- begins transmitting data after it receives the acknowledgment.
Distributed systems are usually more robust If a node along the path is unable to reserve the desired than centralized systems; so they are generally more preferred. The nodes on the minimize 1 the blocking probability of connection requests, 2 reverse path will release the reserved wavelengths as they the connection setup delays, and 3 the bandwidth used for con- receive the negative acknowledgment.
The source node may trol messages; as well as to maximize the scalability of such then reattempt the connection on a different wavelength. If networks [23]. Once a connection is schemes which have been examined in the literature. Each node receiving an The second approach is proposed by us in [23], and we refer to update message may then update its routing table.
We describe the Both schemes can be implemented using a separate channel, two approaches below. Alternately, In the link-state approach which may be implemented using the control information can be carried in-band, as in multipro- the open shortest path first OSPF algorithm , each node main- tocol label switching MPLS , whose wavelength-routing ver- tains the complete network topology, including information on sion is referred to as MP lambda switching.
Besides supporting which wavelengths are in use on each fiber link. Upon the arrival the signaling protocol and the network-topology and status up- of a connection request, a node utilizes the topology information date protocol, the control channel should also have the ability to to select a route and a wavelength.
Once the route and wave- discover and recover from faults, which we explain below. Fault Management vation requests to each node in the route. If an intermediate node In a wavelength-routed WDM network as well as in other is able to reserve the wavelength on the appropriate link, it sends networks , the failure of a network element e.
If all of cross-connect, etc. The appropriate switches are then Studies have been conducted to examine different approaches to configured at each node, and the connection is established. If protect WDM optical networks from single fiber-link failures.
See, for example, each node on the route in order to release the reserved resources. We also remark When a connection is established or torn down, each node in- that our discussion on fault management will be very brief volved in the connection broadcasts a topology-update message because this is just one of several topics that are covered in this which indicates any changes in the status of wavelengths being paper.
In the distributed-routing approach, routes are selected in a There are several approaches to ensure fiber-network sur- distributed fashion without knowledge of the overall network vivability. Survivable network architectures are based either on topology. Each node maintains a routing table which specifies dedicating backup resources in advance, or on dynamic restora- the next hop and the cost associated with the shortest path to tion.
In dedicated-resource survivability which includes auto- each destination on a given wavelength. The cost may reflect matic protection switching and self-healing rings [30], [31] , the hop counts or actual fiber-link distances. The routing table is disrupted network service is restored by utilizing the dedicated established by employing a distributed Bellman—Ford algorithm network resources.
In dynamic restoration, the spare-capacity [25]. Generally, dynamic restoration schemes C. The schemes have a faster restoration time and provide guarantees connections i. However, we can extend the lightpath con- We will examine three approaches to protecting against cept to point-to-multipoint, i. A light tree enables a transmitter at a survivability approach called 1 1 protection, and two dy- node to have many more logical neighbors, thereby leading to a namic approaches called link restoration and path restoration.
Again, for detailed discussions on this subject, please consult A collection of light trees embedded on an optical WDM back- the literature, e. However, the corresponding network 1 : 1 versus M : N versus 0 : 1 protection, etc.
Each of these will require multicast-capable optical switches and more power approaches has different wavelength-capacity requirements and budget to combat the effect of power losses due to signal split- blocking performance. So far, research studies have focused ting. These tradeoffs, including an integer linear program ILP on single-link failures, which are the most common form of formulation of the problem, are examined in [29], [32]. Upon a link failure on the primary path, the end- games, Internet news distribution, e-mail mailing lists, etc.
A multicast-capable WDM WAN should not only The source and destination nodes of the connections support efficient routing for multicast traffic, but it may also traversing the failed link are oblivious to the link failure. To realize multicast-capable route around the link, for each wavelength that traverses WDM WANs, we need to develop novel multicast-capable the link.
Upon a failure, the end-nodes of the failed link WRS architectures and design multicast routing and wave- may participate in a distributed procedure to hunt for length assignment algorithms, as outlined below. Then, the separate signals, each on separate tion that traverses the failed link are informed about the wavelengths, are switched by an optical switch OSW.
Unicast failure possibly via messages from the nodes adjacent to signals are sent directly to OSW ports corresponding to their the link failure. The source and the destination nodes of output links, while those signals which need to be multicast are each connection independently discover a backup route sent to an OSW port connected to a splitter bank.
The splitter on an end-to-end basis such a backup path could be on bank may be enhanced to provide optical signal amplification, a different wavelength channel. When a new route and wavelength conversion, and signal regeneration for multicast wavelength channel is discovered for a connection, net- as well as unicast connections.
If no new routes and associated wavelength switch, which routes the multicast signals to their respective are discovered for a broken connection, that connection is output fiber links. Since an optical splitter is a passive device, blocked. To For a comprehensive review of the literature on the design of be detected, the optical signal power needs to be higher than a survivable optical networks, please consult the literature, e.
Another approach would be to establish a call on any light- path with a BER lower than a certain threshold, e. It is feasible to develop network-layer solutions to combat the physical-layer impairments, including laser shift, dispersion in fiber, and also impairments that affect optical components such as wavelength converters, switch architectures, etc. Transparency, in the strict sense, implies that the physical medium an optical WDM channel in our case should support end-to-end communication of data, independent Fig.
However, this requires that the physical medium preserve all information in the form of phase, 2 Multicast Routing and Wavelength Assignment: The frequency, and analog amplitude of the optical signal during multicasting problem in communication networks is often its transport through the network. Such optical transparency modeled as the Steiner tree problem in networks SPN , which is difficult to achieve in practice, especially for long-haul is defined as follows.
Given nationwide transport networks. Optical WDM Networks: Principles and Practice presents some of the most important challenges facing the optical networking community, along with some suggested solutions. Earlier textbooks in optical networking have a narrower perspective, and rapidly advancing research has created the need for fresh and current information on problems and issues in the field.
The chapters address a wide variety of topics, including the state of the art in WDM technology, physical components that make up WDM fiber-optic networks, medium access protocols, wavelength routed networks, optical access networks, network management, and performance evaluation of wavelength routing networks.
The chapters also survey critical points in past research and tackle more recent problems. Practitioners and network product engineers interested in current state-of-the-art information beyond textbook-type coverage, and graduate students commencing research in this area, will appreciate the concise - and pertinent - information presented herein.
Covers these key topics: Shared-mesh protection for optical WDM networks. Survivable traffic grooming for hierarchical optical WDM networks. Provides a comprehensive and updated account of WDM optical network systems Optical networking has advanced considerably since A host of new technologies and applications has brought a significant change in optical networks, migrating it towards an all-optical network. The first part of Optical WDM Networks: From Static to Elastic Networks provides a qualitative foundation for what follows—presenting an overview of optical networking, the different network architectures, basic concepts, and a high-level view of the different network structures considered in subsequent chapters.
It offers a survey of enabling technologies and the hardware devices in the physical layer, followed by a more detailed picture of the network in the remaining chapters.
It discusses the networking picture; network control and management, impairment management and survivability. The last section of the book covers the upcoming technologies of flex-grid and software defined optical networking. It will also be very useful to practicing professionals in communications, networking, and optical systems.
Lo, soul! The earth to be spann'd, connected by net-work From Passage to India! Walt Whitman, "Leaves of Grass", The Internet is growing at a tremendous rate today. New services, such as telephony and multimedia, are being added to the pure data-delivery framework of yesterday. Such high demands on capacity could lead to a "bandwidth-crunch" at the core wide-area network resulting in degra dation of service quality.
Fortunately, technological innovations have emerged which can provide relief to the end-user to overcome the In ternet's well-known delay and bandwidth limitations. At the physical layer, a major overhaul of existing networks has been envisaged from electronic media such as twisted-pair and cable to optical fibers - in the wide area, in the metropolitan area, and even in the local area set tings.
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