With more service providers making considerable investments to roll out multimedia services
using IP technology, multimedia distribution, especially broadcast TV distribution over an IP network,
the so called IPTV, is expected to grow impressively over coming years. However, there are confusing
concepts and claims for this new technology: What is IPTV? Why do we need IPTV? How does it work?
What are the requirements to design an efficient IPTV network? Are there any research problems? What
are the solutions? In this paper, we will try to provide initial answers to all those questions based on our
understanding and research work.
Emerging optical networks will provide very high bandwidth connections to users. However, improving provisioning times and restoration capabilities after a network failure are important issues in evolving the optical networks. critical problems faced by optical network providers. The application of IP-based protocols to the optical network control plane has opened up new opportunities and challenges for network designers. Although much work has been done on standardization of the relevant protocols, the reliability of optical networks and their control plane needs further investigation. Based on our experience prototyping an IP based control plane, this paper discusses some general requirements and proposed solutions for reliable optical network design from a service and operational perspective. Our experiments suggest that a reliable IP based control plane for fast provisioning and restoration in optical network is feasible with careful design.
Next generation optical network technology has attracted lots of attention from both academia and industry. Large optical networks are typically partitioned into metro and core sub-networks due to the different service and technology requirements. A client optical connection may pass through multiple sub-networks, originating in a metro sub-network, traversing the core network, and accessing the destination on a different metro network. This structure is similar to current ISP networks, which may be divided into multiple routing areas for scalability. However, optical networks are different from IP networks. The difference affects the routing information that needs to be exchanged in metro/core optical networks such that IP routing protocols require significant extensions if they are to be applied in optical networks. In this paper, we focus on Metro/Core routing requirements and present a proposal to extend the current IP multi-area Open Shortest Path First (OSPF) protocol to exchange routing information over metro/core sub-network interfaces. A brief discussion of our prototype implementation is given at the end of this paper.
A major challenge of optical network design is deciding where spare capacity is needed and how much, so that interrupted traffic may be rerouted in the event of a failure. Given the optical network topology and traffic forecast, the network design needs to map the traffic forecast into optical connection demands. For each optical connection demand, two paths need to be computed, i.e., a service path and a restoration path. In most cases, optical network design mainly considers single failure. If two service paths do not share any single failure, their restoration paths can share the same capacity on any links that they have in common. In this way, the total spare capacity needed for restoration can be dramatically reduced. However, due to the layered architecture in optical networks, a pair of diverse paths in a particular layer won't necessarily be diverse when the lower layer topology is considered. For example, optical networks are typically built on top of a network of fiber spans. A single span cut in the fiber network can cause multiple link failures in the optical layer. In this paper, we investigate fiber span failure protection scenarios in mesh optical networks. Specifically, we provide an algorithm to find two fiber span disjoint paths for each demand, such that the total spare capacity allocated in the network is minimized. Another problem that arises in restoration path computation is the existence of a trap topology. In a trap topology, the pre- selected service path may not have a diverse restoration path even though two diverse paths exist in the network. For simple link-disjoint protection, the min-cost max-flow algorithm can be used to avoid this problem. For fiber span failure protection, the trap topology problem becomes complicated. We show that it is NP-hard problem to find the maximum number of fiber-span disjoint paths between two nodes. We provide two heuristic algorithms to solve this trap topology problem. We have implemented fiber span failure protection in our restoration capacity planning toolkit Cplan. We describe an application of fiber span failure protection at the end of the paper.
This paper studies the off-line wavelength assignment problem in tree optical networks that use multiple fibers in each link. In the multifiber scenario, the wavelength assignment is potentially more flexible because the same wavelength can be carried simultaneously on parallel links. However, in tree networks, our results unfortunately show that multiple fibers do not fundamentally improve problem complexity nor do they decrease the worst-case bound based on the request load. For multifiber directed or undirected binary trees, we show that the wavelength assignment problem (WAP) is NP-complete. In contract, there is a polynomial algorithm for undirected single-fiber binary trees. If path lengths are restricted to at most three, WAP in dual-fiber undirected tree networks is still NP-complete whereas if path lengths are restricted to four, WAP is any multifiber directed or undirected tree network is NP-complete. Finally, we show a tight upper bound of 3L<SUB>max</SUB>/(2k) wavelengths per fiber for any k-fiber undirected tree where L is the connection load.
This paper considers a network design problem introduced which resource allocation is performed within a Wavelength Division Multiplexing optical ring network to reduce overall equipment cost. The problem can be summarized as follows. The Add-Drop Multiplexers (ADM's) that are used to terminate lightpaths in an optical (SONET/SDH) ring are expensive and therefore a naive implementation that places ADM's for each wavelength at every node would waste expensive resources. However, by carefully assigning connections to wavelengths and routing the resulting lightpaths, one may avoid terminating all wavelengths at every node, and thereby reduce the number of ADM's needed.