Krishna Bala

Congestion control for high speed packet switched networks

The authors suggest and investigate a general input congestion control scheme that takes into account a broad spectrum of network issues. As a preventive congestion control strategy, a leaky-bucket-type scheme operating on a session basis that limits the sessions average rate and the burstiness is proposed. This restrictive control is combined with an optimistic bandwidth usage scheme which works by marking packets into two different colors, green and red. The packets are marked so that the average green packet rate entering the network is at the reserved average rate. The average red packet rate represents traffic in excess of this guaranteed average rate and is sent to further utilize unused bandwidth in the network. Both types of packets are further filtered by a spacer which limits the peak rate at which the packets enter the network. The marked packets are then sent into the network, where they are treated according to their color, using at each intermediate node a simple threshold policy.<<ETX>>

Capacity performance of dynamic provisioning in optical networks

This paper describes an architecture and analyzes the performance of dynamic provisioning of lightpaths in an optical network. In dynamic provisioning, a lightpath is set up in real-time without rearranging the working and protection routes of existing lightpaths, and without the knowledge of future lightpath provisioning events. This paper develops a general model of the physical topology of the optical network, and outlines routing approaches for dynamic provisioning of lightpaths. It analyzes via simulations the performance of dynamically provisioned unprotected, 1+1 protected and mesh-restored lightpaths. The analysis of the efficiency of network utilization of dynamic provisioning focuses on the spare capacity needed for protection, and in particular focuses on the impact of sharing of wavelength channels for mesh-restored lightpaths. The main conclusion from the performance studies is that significant capacity gains are achieved with sharing of wavelength-channels for mesh-restored lightpaths with dynamic provisioning even for sparse topologies, and even at moderate loads.

An architecture for a wavelength-interchanging cross-connect utilizing parametric wavelength converters

This paper proposes an architecture for a wavelength-interchanging cross-connect (WIXC) that can be used as a switching node of strictly transparent and scalable networks with all-optical routing and all-optical wavelength conversion capabilities. This architecture utilizes all-optical parametric wavelength converters based on difference-frequency-generation (DFG) or four-wave mixing (FWM), although this work focuses only on the implementation using difference-frequency-generation wavelength converters. The proposed WIXC architecture exploits the unique wavelength mapping properties of parametric wavelength converters: mirror image mapping and simultaneous multichannel wavelength conversion. The derivation of this architecture involves application of a space/wavelength transformation to the classical Benes switch fabric. The connection setup for the resulting architecture follows the well established looping algorithm, and the architecture is scalable in both the ports and the wavelengths. The scaling occurs in an orderly fashion, which allows modular upgrades of WIXCs for cost-effective evolution of the networks. The unique properties of the parametric wavelength converter including transparent and multichannel conversion capabilities result in a WIXC architecture that requires fewer wavelength converters while maintaining scalability and transparency.

Algorithms for routing in a linear lightwave network

Routing algorithms are proposed for setting up calls on a circuit-switched basis in linear lightwave networks (LLN), i.e., networks composed only of linear components, including controllable power combiners and dividers, and possibly linear (non-regenerative) optical amplifiers. The overall problem is decomposed into three subproblems: (1) physical path allocation, (2) checking for violations of the special optical constraints on the allocated physical path, and (3) channel assignment. Only point to point connections are considered. The physical path allocation technique uses the K-shortest path algorithm and tries to minimize the number of sources potentially interfering with each other, as a result of the incoming call. A channel assignment heuristic that tends to spread out calls evenly among the available channels works better than one that tries to maximize channel reuse.<<ETX>>

Acousto-optic tunable filters (AOTFs) for multiwavelength optical cross-connects: crosstalk considerations

Acousto-optic tunable filters (AOTF) have been investigated as a potential basis for multiwavelength cross-connects in optical networks. In this paper, we discuss crosstalk issues, some of which are common to other cross-connect technologies, and some of which are unique to the AOTF, which will determine the suitability of the AOTF technology for this application. In particular we show how the interactions between wavelength channels make the AOTF sensitive to switch architectures, we conclude that significant performance improvements will be required to diminish crosstalk if the AOTF is to be useful in any but small-size cross-connects, even when spare and wavelength dilation are used.

Multicasting in a linear lightwave network

Dynamic routing algorithms are proposed for setting up multicast connections in a linear lightwave network (LLN). The problem of finding a physical path for the multicast connection so as to satisfy all the constraints in the LLN is shown to be NP-complete, and a heuristic approach is presented. An algorithm is presented that decomposes the LLN into edge disjoint trees with at least one spanning tree. A multicast call is allocated a physical path on one of the trees, using the smallest component tree (SCT) or the minimum interference tree (MIT) criterion. Finally, the call is allocated the least used channel from among channels that can be allocated to it. The best performance (low blocking probability) is obtained when the LLN is decomposed into many spanning trees, each of them having a small diameter. It is also found that the selection of trees for each call using the MIT criterion exhibits better performance than with the SCT criterion.<<ETX>>

Cycles in wavelength routed optical networks

Signals in wavelength routed optical networks can oscillate in closed cycles resulting in adverse effects on network operation. In particular, amplified spontaneous emission from erbium doped fiber amplifiers can form recirculating loops that lead to amplifier saturation and oscillations. Searching, enumerating and eliminating these closed cycles becomes a problem that the network designer must address. A variety of cross-connect technologies are studied and shown to result in oscillating cycles in the network. Topological and technological approaches based on Eulerian network theory and other methods are proposed to eliminate these cycle problems.

Invited: Routing Strategies for Capacity-Efficient and Fast-Restorable Mesh Optical Networks

Wavelength division multiplexed (WDM)-based mesh network infrastructures that route optical connections using intelligent optical cross-connects (OXCs) are emerging as the technology of choice to implement the next generation core optical networks. In these architectures a single OXC is capable of switching tens of terabits of traffic per second. With such data transfer rates at stake, it becomes increasingly challenging for carriers to (1) efficiently and cost-effectively operate and manage their infrastructure, and (2) cope with network failures while guaranteeing prescribed service level agreements (SLAs) to their customers. Proper routing of primary and backup paths is a critical component of the routing and restoration architecture required to meeting these challenges. In this paper we review some of the various strategies and approaches proposed so far to intelligently route connections while at the same time providing guaranteed protection against various types of network failures. We explore the tradeoffs associated with these approaches, and investigate in particular different, sometimes competing aspects, such as cost/capacity required, level of protection (link vs. node failure), restoration time, and complexity of route computation.

A parametric wavelength interchanging cross-connect (WIXC) architecture

This letter presents an architecture for a wavelength interchanging cross-connect (WIXC) using parametric wavelength converters. The architecture exploits the unique properties of the difference frequency generating (DFG) parametric wavelength converter, including its transparency to signal format and its ability to convert multiple wavelengths simultaneously, The WIXC is shown to be scalable and rearrangeably nonblocking. Furthermore, connection setup is performed by the well-known looping algorithm used for Benes networks.

Scalability of a novel wavelength assignment algorithm for WDM shared protection rings

Summary form only given. Ring topologies have recently emerged as the preferred architectures for wavelength-division multiplexing (WDM) networks because of the survivability capabilities they provide and the fact that their capacity can be shared by all the nodes connected to a ring. This report focuses on four-fiber WDM self-healing ring (SHR) architectures in which restoration from a failure is achieved using automatic protection switching loop-back systems. A similar approach is also usable for two-fiber WDM SHRs except that the number of wavelengths required doubles.