Lubo Tancevski

Output power and SNR swings in cascades of EDFAs for circuit- and packet-switched optical networks

A simple dynamic model of the erbium-doped fiber amplifier (EDFA) that includes self-saturation by amplified spontaneous emission (ASE) is used to analyze the power and signal-to-noise ratio (SNR) transients in wavelength division multiplexed (WDM) optical networks in which signals cross chains of EDFAs from source to destination. The model, which consists of solving sequentially one ordinary differential equation per amplifier, is used to (1) determine power and SNR excursions in the surviving channels along a chain of 35 EDFAs during isolated add-drop events in a 16-channel WDM circuit switching scenario and (2) run Monte Carlo simulations of the first five EDFAs of the same chain fed by burst-mode packet switching traffic on each of the 16 channels. Each packet source is modeled as an ON-OFF asynchronous transfer mode (ATM) source, with ON and OFF times having a heavy-tailed Pareto distribution. The aggregate source model is asymptotically self-similar, and well describes multimedia packet communications. The results are used to examine the influence of average network utilization and source ON-OFF time variance on the probability density function of signal power and SNR at each EDFA output. We demonstrate that self-similar traffic generates sizable power and SNR swings, especially at low network utilization. The simulations also indicate sizable broadening of the power and SNR density functions along the cascade of EDFAs, reaching levels in excess of 9 dBm and 4 dB for the power and SNR swings, respectively, at the 5th EDFA. The effect becomes more pronounced for longer EDFA chains. Such a large broadening may imply serious system impairments in burst-mode WDM packet networks.

Impact of polarization-mode dispersion on the design of wavelength-routed networks

In this letter, we address the impact of polarization-mode dispersion on the design of wavelength-routed optical networks. A mathematical formulation of the problem is provided which optimizes the cost of the network comprising the total number of regenerators and additional installed fiber for a given traffic forecast. The hill-climbing search algorithm is employed with random restarts. Numerical examples show the efficiency of the heuristic, especially in networks with nonhomogeneous fiber quality.

Routing in all-optical packet switched irregular mesh networks

The performance of packet switching wavelength routed optical networks critically depends on packet contentions at the intermediate routers. This paper shows through simulations that deflection routing is an effective technique for packet switching wavelength routed optical networks with irregular meshed topologies. It is shown that multiple path routing (MPR) as the deflection rule mitigates the blocking of packets substantially in cross-connected all-optical networks leading to a significant reduction in hardware volume and cost of all-optical IP routers. The effectiveness of the blocking reduction critically depends on the network topology, and meshed topologies with a high number of interconnections benefit of the largest gain from deflection routing.

Network optimization with transmission impairments-based routing

We propose routing algorithms, within the MP/spl lambda/S paradigm, which support transmission impairments. Through simulation, we demonstrate substantial savings in terms of electronic equipment cost. These savings are achieved by incorporating the physical aspects of optical devices into the route computation process.

Optical packet switching multiple path routing

Abstract The performance of packet-switching wavelength routed optical networks critically depends on packet contentions at the intermediate routers. This paper shows through simulations that deflection routing is an effective technique for packet-switching wavelength routed optical networks with irregular meshed topologies. It is shown that multiple path routing (MPR) as the deflection rule mitigates the blocking of packets substantially in cross-connected all-optical networks leading to a significant reduction in hardware volume and cost of all-optical IP routers. The effectiveness of the blocking reduction critically depends on the network topology, and meshed topologies with a high number of interconnections benefit of the largest gain from deflection routing.

Enhancements to multi-protocol lambda switching (MP/spl lambda/S) to accommodate transmission impairments

We consider networks consisting of optical cross-connects interconnected via fiber optic links and controlled by IP routes. Optical connections are provisioned dynamically and on demand as the need for them arises due to changes in the traffic. We discuss the impact of linear effects such as polarization mode dispersion (PMD) on the design of the control plane. Constrained-routing algorithms as well as signaling protocols are developed which allow for proper label (lambda) and regeneration requests distribution. Both the architecture and the electronic equipment cost are validated, through simulation, using a new WDM-aware version of NS-2 simulator. Simulation results reveal that: (1) the feasibility of the lightpath is greatly affected by the PMD factor, especially for bit-rates exceeding 5Gbit/s; and (2) significant improvement (in terms of cost) can be achieved through intelligent route selection schemes which take into consideration physical characteristics of fiber links. These cost savings are more apparent in networks with non-homogeneous fiber quality.

Gain control in EDFA's by pump compensation

Gain control by means of pump compensation in cascades of erbium-doped fiber amplifiers (EDFAs) is analyzed. Based on analytical expressions for the 1-dB rise/fall time for the case of channels add/drop, required pump power changes at each amplifier are derived in the form of simple closed expressions. Numerical simulations of a system comprising 20 wavelength division-multiplexed channels transmitted through a cascade of 35 EDFAs are performed demonstrating the effectiveness of the gain control.

Large power swings in doped-fiber amplifiers with highly variable data

We show that doped-fiber amplifiers operated in saturation can display very fast transient dynamics and large power swings in a packet switching environment with highly variable packet interarrival times.

Asymmetric WDM all-optical packet switched routers

It is shown that asymmetric WDM all-optical routers architectures are the best candidates to reduce hardware volume and cost of all-optical networks. We show that due to the non-uniform network traffic behavior, routers require asymmetric wavelength conversion capabilities and also asymmetric buffering capacity to solve contention. This paper shows that due to the topology, packets may generate traffic bottlenecks produced by a tendency of the routing scheme to send packets with different destinations through preferred paths.

Informed dynamic shared path protection

Summary form only given. A generalized optical network consists of multiple optical cross-connects (OXC) that are interconnected via bi-directional WDM links in a general topology, often referred to as intelligent optical mesh network. A major aspect of this intelligence is the ability to provide fast provisioning and restoration. To achieve this, there is a need for a unified control plane responsible for running routing and traffic engineering protocols, achieved, for example, through the introduction of GMPLS. The control plane queries and modifies the wavelength-switching table of the cross-connect; floods the reservation tables of the cross-connect (through OSPF or IS-IS) in the network; is responsible for connection setup/tear-down through CR-LDP (or RSVP-TE). A mesh-restored lightpath in an optical network is allocated a pair of link-disjoint paths, where one of the path is the primary or working path and the other is backup or protection path that is activated only in case of failure. Each link in the primary path has dedicated capacity allocated to a connection. The protection path can also have dedicated capacity (1 + 1 restored lightpath), however that results in inefficient use of network capacity. In contrast, in shared or 1:N restored lightpath, the protection capacity is shared with the backup path for other restored connections, hence resulting in improved utilization of the network resources. The efficiency of distributed 1:N mesh restoration can be enhanced substantially by providing information about the protection topology. This information can be disseminated using extensions to OSPF. In order to keep the bandwidth of the distributed information low, only recent modifications in the protection tables need be distributed. Calculations indicate substantial savings (up to 35%) in terms of protection wavelength mileage due to much better sharing of backup resources. In addition, the scheme allows for different algorithms when choosing paths that share a link, thus potentially enabling protection in case of multiple failures.