1. Field of the Invention
This invention relates in general to fiber optic communication systems, and more particularly to a method and apparatus for providing channel provisioning and optical wavelength division multiplexing (WDM) networks.
2. Description of Related Art
In broadband communication networks, data are increasingly transmitted through glass or optical fiber lines in the form of optical signals. Over the last two decades, optical fibers have revolutionized the communications industry. Meanwhile, continuous innovations in optical components have made it possible to design and implement higher and higher bit-rate systems. Consequently, fiber designs continue to evolve in almost every segment of the network infrastructure.
The major driver for all this activity is the urgent need for more capacity. The late 1990s have seen an enormous surge in the amount of traffic on telecom networks. Networks whose capacity looked demand-proof only two or three years ago are hard-pressed to cope with this demand. Not only is traffic growing, but also there is a fundamental change in the nature of this traffic. In the 80s and early 90s, the majority of network traffic consisted of voice. The growth in this traffic was, and still is, fairly predictable. However, the growth in data traffic is now far outstripping the growth in voice, spurred on by the Internet and corporate data applications. The advent of affordable higher bandwidth access mechanisms such as digital subscriber line technology will serve to accelerate this growth. Voice and data are already equal on some routes, and it is clear that in the next decade data will dominate telecom networks.
Wavelength division multiplexing (WDM) is a technique for transmitting traffic over fiber in multiple channels. Traditional optical fiber transmission uses light of a single wavelength (i.e. color). In contrast, WDM combines multiple wavelengths of light into a single, multiplexed signal for transmission along a fiber. Each channel utilizes the full capacity of the fiber being used. WDM thus creates xe2x80x98virtual fiberxe2x80x99: carrying traffic over, for example, four WDM wavelength channels boosts the capacity of an installed fiber by four times.
WDM is now being used by telecommunication companies worldwide to dramatically boost the capacity of installed optical fiber cables. However, the effect WDM will have on the telecommunication industry is much more complex, ranging far beyond simple capacity increase in networks, even though the basic principle of the technology is very simple. Accordingly, WDM is emerging as an essential technology for allowing telecommunication networks to endure the telecommunication demands of the next century. The future growth of the Internet, the creation of new high bandwidth applications, the economics of the bandwidth market itself and the development of broadband networking are all inextricably linked with WDM technology.
As optical technology advances and the optical layer materializes in telecommunications networks, new challenges have emerged for engineers and network planners. Just as synchronous optical networks (SONET) introduced new design issues, such as optimized traffic patterns and restoration schemes, implementation of the optical layer with wavelength add-drop multiplexers (WADMs) has new difficulties. Telecommunication companies, as well as many smaller companies and new entrants to the telecommunication business are planning to deploy WADMs in their network. Thus, it is important that these new difficulties are addressed.
Perhaps the most fundamental issue associated with WADMs in optical networks is end-to-end wavelength span design. As some wavelengths are dropped and added while others pass through a site, network designers must consider the span for each wavelength to insure the required performance. Planners must predict the performance of each channel individually, especially considering that the channels added will be of higher quality than those passing through.
One of the more complex span designs is that of mesh architectures. A mesh architecture is a design where each channel may take a dynamically routed path around failures. When utilizing mesh architectures, all possible scenarios need to be evaluated to insure that for a single or multiple fiber cuts or failures, traffic on a channel is not lost because of unacceptable optical performance.
When adding and dropping individual wavelengths in the network, it becomes imperative for providers to be able to manage the network with wavelength granularity. Providers must be able to monitor the condition of each wavelength and maintain network traffic in the same manner that electrical paths are managed today. The complexity of managing wavelengths also depends on whether the provider is using dedicated wavelength paths (WP) or xe2x80x9cvirtualxe2x80x9d wavelength paths (VWP) in which the signal can change to another wavelength along the route. Ideally, the optical network will provide end to end services entirely in the optical domain, without ever converting signals into the electrical format.
The basic element in the optical network is the wavelength. As many wavelengths of signals are transported across the network, it becomes important to manage and switch each one individually. One of the benefits of optical networks is that it allows the network architecture for each wavelength to be different. For example, one wavelength may be established in the network to be part of a ring configuration, while another wavelength, using the same physical network, can be provisioned as point-to-point system. The flexibility of provisioning the network a wavelength at a time has led to two definitions of end-to-end services: wavelength paths and virtual wavelength paths.
The simplest implementation of a wavelength service in the optical network is a wavelength path (WP). Using a WP, a signal enters and exits the optical layer at the same wavelength, without ever changing to a different wavelength throughout the network. Essentially a wavelength is dedicated to connect the two endpoints together. This kind of design is typically much easier to plan for from an engineering perspective, because planners will know which wavelength will be used on all parts of the optical span. Designing is simply an issue of determining the path and calculating performance, as discussed above.
Although a WP is simple to implement, it can impose some limitations on the bandwidth available in the network and the cost of implementing it. One method to overcome this limitation is by using a xe2x80x9cvirtualxe2x80x9d wavelength path (VWP) in which a signal path can travel on different wavelengths throughout the network. By avoiding a dedicated wavelength for an end-to-end connection, the network can reuse and optimize wavelengths to provide the greatest amount of capacity. The flexibility provided by VWPs comes at a cost: VWPs introduce more difficulty into the network design. For networks with a large number of all-optical paths, especially in metropolitan or access networks, VWPs can introduce a large number of possible optical path sets to be calculated and planned for.
Although the main driver for WDM today is the need to increase network capacity and relieve network congestion, WDM is part of a much bigger story of the evolution of electrical networks to optical networks. Eventually, WDM is expected to be used to route traffic on individual wavelengths in all levels of the network, significantly increasing flexibility. This transition will create an optical layer. The optical layer is a new networking layer in which wavelength channels are processed and routed only by optical equipment, just as electronic multiplexers, cross connects and switches handle semi-permanent digital channels in the synchronous digital hierarchy (SDH)/SONET and asynchronous transfer mode (ATM) layers of today""s networks. As suggested above, this will involve the deployment of optical add-drop multiplexers, enabling WDM ring architectures to be constructed. In the longer term this will also require the deployment of optical cross connects to reconfigure and re-route individual wavelength channels in the network.
These recent advances in optical WDM technology are pushing this technology beyond simple point-to-point deployment and more towards applications in end-to-end networking. These trends will require more advanced network control features in order to take full advantage of the optical fiber bandwidth. Although much work has been done on static WDM network provisioning, the more important issue of network control in dynamic environments needs further investigation.
Thus, network configuration design and management in WDM networks is a crucial issue. The main concerns are designing an efficient virtual topology and effectively maintaining/adjusting it. Those skilled in the art will recognize that because physical topology design is very similar to the classical network design problem, it will not be discussed herein. Further, those skilled in the art will recognize that network configuration design and management in WDM networks is dependent on many external constraints, such as material and manpower costs, economic conditions, etc., and accordingly it will also not be discussed herein.
To date, researchers have focused on two main problems, namely virtual (logical) topology design and the related routing and wavelength assignment (RWA) problem. The former decides on the optical connectivity between different nodes, and the latter actually performs the wavelength assignment at the physical level.
Topology design for generic mesh-based networks is a complicated issue. Many authors have proposed various optimization-based approaches here, with the objectives being to maximize the offered network load and minimize performance related metrics, such as average delays, hop counts, etc. Others have also devised more heuristic-type schemes, which iteratively assign paths to heavier-traffic source-destination pairs and use network-pruning techniques to handle the remaining connection requests. One benefit of using such methods is that they can be augmented to incorporate non-linear cost metrics, such as packet delay, revenues, etc., which may be difficult to incorporate in linear optimization formulations. Other work in this area has also looked at using flow-deviation (load balancing) techniques and simulated annealing processes.
The RWA problem has also been well studied. Again, many authors have used optimization formulations to minimize various cost functions, i.e., minimize the number of wavelengths, blocking probabilities, delays, etc. For example, some work has cast the problem into integer linear (multi-commodity flow) or mixed integer type problems, and these are usually very compute-intensive.
Apart from optimization-type methods, more practical schemes for dynamic RWA problems have also been devised. In real networks, many connection setup requests arrive in random order and require fast processing. For such dynamic lightpath establishment (DLE), heuristics based on various cost metrics can be designed using shortest-path algorithms. To curtail increases in call blocking probabilities, connection re-routing heuristics can also be employed, i.e., partial/full wavelength reassignments. In addition, theoretical results in graph theory can also be used here, such as node interchange algorithms for graph coloring problem. Overall, results from such ad-hoc approaches have compared favorably with those from more complex optimization schemes.
Although many solutions have been devised for the topology design and wavelength routing problems, practical implementation concerns, however, have not been treated as thoroughly. Although this may appear as a control issue, largely orthogonal to the traffic management aspect, effective schemes are necessary here to realize the benefits of wavelength routing. As an example, any of the previously cited optimization type schemes for routing virtual path requests in a given network only lends themselves to a centralized control solution, in which a main network controller performs the channel route computation process and sends configuration updates to each optical node via logical control channels.
In such solutions, the controller entity, possibly co-located with an electronic network node, requires global (i.e., network-wide) knowledge and must be sufficiently powerful since optimization schemes are generally very compute intensive. For example, typical computation times are in the order of hundreds of seconds even for moderate network sizes and reasonable constraint sets. Such performance may be unacceptable in many practical network settings where improved response times are important. Moreover all major non-optical routing protocols for large-scale networks are based upon distributed paradigms, i.e., Internet Protocol""s (IP""s) Open Shortest Path First (OSPF) and Border Gateway Protocol (BGP), and ATM""s Private Network-Node Interface (PNNI).
Generally, it is expected that maturing optical networks will require signaling protocols of their own to provision and protect lightpath channels for a variety of higher-level networking clients. Distributed routing schemes basically implement the decision/computation process over multiple network nodes, with each optical node running a distributed control protocol. Nodes distribute information amongst themselves, such as load changes, alarm events, feature sets, etc., and use this to help in the route computation process.
Such schemes are normally more robust, since route resolutions around failed network elements are still possible given adequate connectivity in the underlying physical graph. However, due to their decentralized nature, not all schemes, i.e., virtual topology or RWA algorithms, can be ported to practical network environments. Usually, only heuristics-based schemes, such as those using modified shortest-path algorithms, lend themselves to distributed implementations.
Not much work exists on the topic of distributed routing in WDM networks, although a sample scheme for performing wavelength routing has been specified by R. Ramaswami and A. Segall, in xe2x80x9cDistributed Network Control for Wavelength-Routed Optical Networks,xe2x80x9d Proceedings of the IEEE INFOCOM 1996, San Francisco, Calif., April 1996. Nevertheless, this scheme is limited to ATM network interworking and requires each node to maintain a detailed, complete snapshot of the global network state, i.e., basically enough information to locally resolve complete end-to-end paths. However, for large channel counts and increased signaling frequencies, this scheme is not scalable due to the excessive per-channel overheads involved, i.e., accounting, signaling, etc.
Therefore, there is a clear need for more robust, distributed channel control protocols in optical networks. These must support multiple client protocols and incorporate more scalable routing metrics (and possibly physical layer limitations).
It can be seen then that there is a need for a distributed framework to provision channels (i.e., wavelengths) in WDM networks.
It can also be seen that there is a need for a flexible channel provisioning protocol framework for providing virtual links to multiple higher layer networking clients.
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a method and apparatus for providing channel provisioning in optical wavelength division multiplexing (WDM) networks.
The present invention solves the above-described problems by providing a distributed framework to provision channels (i.e., wavelengths) in WDM networks.
A method in accordance with the principles of the present invention includes managing configuration of underlying lower layer optical devices and processing inter-mode and client messages and alarm events.
Other embodiments of a method in accordance with the principles of the invention may include alternative or optional additional aspects. One such aspect of the present invention is that the processing of inter-node messages further includes setting-up bandwidth channels between peer nodes in wavelength division multiplexing networks using a channel request message, the channel request message specifying an associated channel feature set for a requested channel, releasing a preexisting channel using a channel release message and managing a resource update message for distributing network information used for route resolution.
Another aspect of the present invention is that the channel feature set specifies attributes for the channel.
Another aspect of the present invention is that the attributes for the channel include bandwidth, quality, resilience, policy and pricing.
Another aspect of the present invention is that the setting-up includes computing a shortest-path computation in response to the channel request message.
Another aspect of the present invention is that the setting-up bandwidth channels includes using an explicit channel specification.
Another aspect of the present invention is that the explicit channel specification is made according to pre-defined policy decisions.
Another aspect of the present invention is that the channel release message frees resources associated with the released channel.
Another aspect of the present invention is that the network information includes usage and cost information.
Another aspect of the present invention is that the managing a resource update message is initiated via a trigger.
Another aspect of the present invention is that the trigger is based upon a threshold scheme.
Another aspect of the present invention is that the network information includes metrics abstracting nodal resource levels.
Another aspect of the present invention is that the metrics include average channel utilization levels.
Another aspect of the present invention is that the metrics include fine-grained multi-channel bandwidth utilization parameters.
Another aspect of the present invention is that the setting-up, releasing and managing provide flexible channel provisioning for higher layer networking protocol clients.
Another aspect of the present invention is that the setting-up, releasing and managing configure lower layer optical devices.
Another aspect of the present invention is that the setting-up includes determining at a node receiving the channel request message whether resources are available for the channel request, determining whether the node receiving the channel request message is a destination node when the resources are determined to be available for the channel request and processing the channel request message based upon the determination of whether the node receiving the channel request is a destination node.
Another aspect of the present invention is that the channel request is accepted and a channel request accept message is propagated upstream when the receiving node is the destination node.
Another aspect of the present invention is that the next hop is resolved and the channel request is propagated downstream to the resolved next hop when the receiving node is not the destination node.
Another aspect of the present invention is that a channel request block message is propagated upstream when resources for the channel request are determined to not be available.
Another aspect of the present invention is that the releasing includes freeing resources associated with the channel release message, updating a resource status, determining whether the node receiving the channel release message is a destination node and processing the channel request message based upon the determination of whether the node receiving the channel release message is a destination node.
Another aspect of the present invention is that the channel release is confirmed and a channel release confirmation message is propagated upstream when the receiving node is the destination node.
Another aspect of the present invention is that the next hop is resolved and the channel release message is propagated downstream to the resolved next hop when the receiving node is not the destination node.
Another aspect of the present invention is that the managing includes determining whether the resource update per a resource update message reflects any change in resource allocations, updating network information pertaining to resource tables and topology overview and propagating the updated network information when there has been a change in resource allocations and propagating the resource update message when there has not been a change in resource allocations.
These and various other advantages and features of novelty, which characterize the invention, are pointed out with particularity in the claims annexed hereto and form a part hereof. However, for a better understanding of the invention, its advantages, and the objects obtained by its use, reference should be made to the drawings which form a further part hereof, and to accompanying descriptive matter, in which there are illustrated and described specific examples of an apparatus in accordance with the invention.