In WDM optical networks, a low speed traffic is often multiplexed or switched into a high speed lightpaths. In common measures, a lightpath established in traffic grooming does not consider transmission impairment. It transports traffic optically as long as possible. But optical medium is not ideal, transmission impairment like ASE noise, which degrades the signal to noise ratio, exists. To maintain an acceptable SNR level at the receiver side, the number of optical amplifiers in a lightpath should not exceed a Maximum value (M). A segment between two optical amplifiers referred as a span. In this paper, we adds span constraints to the traffic grooming problem, and present an heuristic algorithm to bring up a series of lightpaths explicitly to accommodate such traffic. From the numerical result, it could be found that it guarantees each traffic to be successfully routed. It also achieves good performance of wavelength efficiency and lightpath efficiency.
Packet Ring transport technology combines the simplicity of Ethernet and survivability of SONET and attracts more and more interests of researches. However, electrical processing cost will also be very high as data rate grows to gigabit level, which lowers its efficiency. This paper examines the value of optical bypass approach by minimizing the traffic to be processed in electrical domain. An Integer Linear Program (ILP) formulation is presented to solve this problem and results with different traffic patterns are given, which shows one more wavelength can bring notable electrical processing cost savings in the case of a small number of multiplexed wavelengths in one channel.
The rapid progress on optical performance monitoring technology makes it possible for optical network designers to guarantee the QoS quality of lightpaths in Wavelength Division Multiplexing (WDM) network. This article describes the basic idea of online QoS guarantee scheme, focusing on the distributed optical noise figure calculation algorithm and optimal design heuristic.
This paper studies the problem of virtual topology reconfiguration for changing traffic patterns in wavelength-routed network. We formulate it as an optimization problem, which tries to find out the virtual topology with least lightpath changes with network performance within given bound, when traffic demand imposed on wavelength-routed network changes. Average Packet Hop Count (APHD) is used to measure the degree of network performance. A linear formulation is presented and solved by MILP (Mixed Integer Linear Programming) method. Then we analyze the relationship between lightpath changes and degradation degree of performance. It can be seen that a large cost reduction for reconfiguration can be achieved by giving up a small amount of network performance.
In IP over WDM networks, when a failure (a link failure) occurs, the service restoration can be implemented by dynamic routing in IP layer. But it needs the virtual topology remains connected after any physical link failure. Otherwise, IP layer cannot find an alternate path to restore the service. The problem of routing logical links (lightpaths) on a physical network in a way that the logical topology remains connected in the event of single physical link failure is called survivable routing. Our aim is to find out the minimum wavelength requirement for survivable routing.
In short, we address the survivable routing problem by proposing a new ILP algorithm which works well with sparse-connected logical topologies. The necessary and sufficient conditions for survivable routing are simplified, which greatly reduces the number of survivable constraints. Based-on the simplified conditions, a new ILP formulation with K-shortest paths as alternate paths for a logical link is presented, which mainly reduces the number of variables needed to be solved. It will be demonstrated that the time needed to solve such an ILP is relatively small. Finally, numerical results are given and discussed to show the effectiveness of our algorithm.
In this paper, we discuss the load balancing issues for wavelength-routed optical networks. After a definition of load balancing factor, which evaluates the fairness of the wavelength usage on each link, a new Integer Linear Program (ILP) formulation is proposed for routing and wavelength assignment for WP and VWP-RWA scheme. As the ILP is time-consuming for large-scale networks, an effective heuristic algorithm is given. In this paper, we use three metrics to quantify the performance improvement by our method: Load balancing factor FF, wavelength requirement N<sub>λ</sub> and wavelength reusability ρ. In both WP and VWP schemes, our load balancing algorithm achieves much better performance than Fixed-shortest-path and alternate-shortest-paths routing algorithms.
The blocking performance of two types of all-optical networks: wavelength-selective (WS) and wavelength-interchangeable (WI) networks, is studied. Efficiency of different dynamic routing and wavelength assignment (RWA) algorithms, including adaptive routing algorithms and dynamic alternate routing algorithms, is investigated. Dynamic wavelength assignment combined with adaptive route selection algorithm is also presented and investigated. Numerical results show that multifiber WS networks may provide a viable and economical alternative to WI networks, and dynamic alternate routing algorithms is also a good substitute to adaptive routing algorithms. The presented dynamic wavelength assignment combined with adaptive route selection algorithms exhibit better efficiency than other ones. The study also shows that the efficiency of different dynamic RWA algorithms is dependent with different topologies, and the performance gain of wavelength conversion in regular topology is not as significant as in irregular topology networks, meanwhile, the efficiency of different dynamic RWA algorithms is closely related with the number of alternate routes.
Several tunable optical splitter techniques and some of their applications, including some prospective schemes, are discussed in this paper. It is explained by specific examples that all the variable transmission/reflection film technology, variable fiber couple length technology, acousto-optic/electro-optic deflection technology, and Mach-Zehnder interference technology are the capable technologies to realize tunable optical splitter, and tunable splitter technology to be applied to optical transmission networks, other devices and optical measurements.
A kind of multi-wavelength labeled optical packet switching technology is presented, in which optical header is consisted of several optical pulses in different wavelength that are in the same WDM optical channel band as optical signal payload. A probable scheme to realize such optical switching as well as an optical switching node structure is proposed. A simplify principle experiment has proved the possibility of such switching method.
This paper presents the design and development of a bit rate transparent 3R O/E/O transponder, which accomplishes full data rate transparency from 30Mb/s to 2.5Gb/s by signal processing in electronic domain. With the use of chipsets that perform clock recovery in several continuous bit rate ranges, we develop a clock and data regenerating circuit self-adaptive to the bit rate of input signal. Experimental results presented in the last section of this paper show us that a good bit rate-adaptive capability and good BER performance can be achieved.
The basic technology of adaptive optical amplifier is introduced in this paper. How the performance of optical amplifier may meet the needs of application system is discussed according to the amplitude and shape of the input optical signal, the amplifier automatically adjusting the operating parameters. Taking the EDFA as an example, the feasibility to be realized technology of adaptive amplifier is investigated.
How to transport the control and management information of optical networking is a major concern these days. We compare several means and arrive at a conclusion that OSC (optical supervisory channel) is a better choice. The content of OSC is given and OSC channel wavelength, bit rate and coding method are discussed. An OSC example of WDM metro network are illuminated, which demonstrates the processing operation of overheads in OSC, FDI behavior for three types of failure, and Self-management of OSC subsystem. To fulfill the demand of intelligent and distributed management of optical transport network, an OSC of OC-3 (155Mbps) channel bit rate may be needed in the near future.