Tunable laser-based design and analysis for fractional lambda switches

Fractional lambda switching (FlambdaS) is a novel approach for traffic management over all-optical networks with sub-wavelength provisioning capability. The unique characteristic of FlambdaS is the utilization of UTC (coordinated universal time) for switching with minimum or no buffers. Several central research issues are still open in FlambdaS and need to be formally defined and analyzed. In this paper, we introduce three novel switch designs that are based on the use of tunable lasers (which can be replaced in the future with wavelength converters). First, the paper presents analytical results of scheduling feasibility, which measures the total number of possible different schedules for each switch design. Then it is shown that the architecture with the highest scheduling feasibility is strictly non blocking in the space domain. Next, the paper provides a closed form analysis of the blocking probability in the time domain, which is applicable for any strictly non-space blocking switch, using combinatorics. In addition, the paper provides measures of the switching hardware complexity, which, for the strictly non-blocking architecture, has the same switching complexity as Clos interconnection network, i.e., O(N'radic(N')) where N' is the number of optical channels.     

CoWBP capping barrier layer for sub 90 nm Cu interconnects

Electroless cobalt films have been obtained by deposition using a plating bath containing two reducing agents: dimethylamineborane (DMAB) and sodium hypophosphite. This formulation allows spontaneous activation on copper followed by auto catalytic electroless plating. CoWBP and CoBP films are proposed as diffusion barriers and encapsulation layers, for copper lines and via contacts for ULSI interconnect applications. The crystalline structure, chemical composition and oxidation states of the elements were studied, as well as the electrical resistivity, topography and morphology of the films. The film composition was characterized as a function of the solution composition; the barrier properties of the films were tested and an oxidation resistance study was conducted. The films were characterized and the results show that they can be applied as capping layers for ULSI copper metallization.     

MetaRing-a full-duplex ring with fairness and spatial reuse

The design principles of a ring network with spatial bandwidth reuse are described. A distributed fairness mechanism for this architecture, which uses low latency hardware control signals, is presented. The basic fairness mechanism can be extended for implementing multiple priority levels and integration of asynchronous with synchronous traffic. The ring is full-duplex and has two basic modes of operation: buffer insertion mode for variable-size packets and slotted mode for fixed-size packets or cells. Concurrent access and spatial reuse allow simultaneous transmissions over disjoint segments of a bidirectional ring and can increase the effective throughput by a factor of four or more. The combination of a full-duplex ring, spatial reuse, a reliable fairness mechanism, and the exploitation of advent in fiber-optic technology are the basis for the MetaRing network architecture     

Integration of synchronous and asynchronous traffic on the MetaRingand its performance study

The main motivation for developing the MetaRing architecture was to increase the throughput of a ring-based local area network beyond its single link capacity by means of spatial bandwidth reuse. We describe and evaluate a protocol for integrating two types of traffic on the MetaRing architecture. Synchronous (reserved or real-time) traffic which is periodic and requires a connection set-up and will have guaranteed bandwidth and bounded delay, and asynchronous or bursty traffic with no real-time constraints that can use the remainder of the bandwidth in a fair manner. The integration mechanism is functionally equivalent to the timed-token function in FDDI, which is a shared media ring protocol. Simulation results are also presented to show the effects of the fairness and flow control signals on the performance of the network     

End-to-end delay analysis of videoconferencing over packet-switchednetworks

Videoconferencing is an important global application-it enables people around the globe to interact when distance separates them. In order for the participants in a videoconference call to interact naturally, the end-to-end delay should be below human perception; even though an objective and unique figure cannot be set, 100 ms is widely recognized as the desired one-way delay requirement for interaction. Since the global propagation delay can be about 100 ms, the actual end-to-end delay budget available to the system designer (excluding propagation delay) can be no more than 10 ms. We identify the components of the end-to-end delay in various configurations with the objective of understanding how it can be kept below the desired 10-ms bound. We analyze these components step-by-step through six system configurations obtained by combining three generic network architectures with two video encoding schemes. We study the transmission of raw video and variable bit rate (VBR) MPEG video encoding over (1) circuit switching; (2) synchronous packet switching; and (3) asynchronous packet switching. In addition, we show that constant bit rate (CBR) MPEG encoding delivers unacceptable delay-on the order of the group of pictures (GOP) time interval-when maximizing the quality for static scenes. This study aims at showing that having a global common time reference, together with time-driven priority (TDP) and VBR MPEG video encoding, provides adequate end-to-end delay, which is (1) below 10 ms; (2) independent of the network instant load; and (3) independent of the connection rate. The resulting end-to-end delay (excluding propagation delay) can be smaller than the video frame period, which is better than what can be obtained with circuit switching     

A new label-based source routing for multi-ring networks

This paper presents a new source routing technique for ring and multi-ring networks, which uses short address labels. The main objectives for having this new method are that in case of one or more failures a frame will be guaranteed: (1) to be removed from the ring-termination property, and (2) to be copied at most once and only by its destinations-safety property. The scheme is based on dividing the label address space of each ring into subspaces, such that the address subspaces are physically disjoint. More specifically, each ring, in a multi-ring network, is divided into two or more parts such that adjacent address subspaces are disjoint. The route of each frame is described by a sequence of short address labels in the frame's header. The current route of a frame is determined by the first address label in its header, and it can be used for routing over at most one subspace of the ring     

A local fairness algorithm for gigabit LAN's/MAN's with spatialreuse

The authors present an algorithm to provide local fairness for ring and bus networks with spatial bandwidth reuse. Spatial bandwidth reuse can significantly increase the effective throughput delivered by the network. The proposed algorithm can be applied to any dual ring or bus architecture such as MetaRing. In the dual bus configuration, when transporting ATM cells, the local fairness algorithm can be implemented using two generic flow control (GFC) bits in the ATM cell header. In the performance it is shown that this local fairness algorithm can exploit the throughput advantage offered by spatial bandwidth reuse better than a global fairness algorithm. This is accomplished because it ensures fair use of network resources among nodes that are competing for the same subset of links, while permitting free access to noncongested parts of the network. The performance advantage of the local fairness scheme is demonstrated by simulating the system under various traffic scenarios and comparing the results to that of the MetaRing SAT-based global fairness algorithm. It is also shown that under certain traffic patterns, the performance of this algorithm achieves the optimal throughput result predicted by the known Max-Min fairness definition     

The conservative code for bit synchronization

A novel coding scheme for bit synchronization, the conservative code, is presented and analyzed. Each codeword is characterized by having a predefined number of transitions, with a known delimiting transition at the end, i.e. the number of transitions is conserved. As a result, it is possible to decode the incoming serial bit-stream without explicitly recovering the receiving clock with a phase-locked loop. Thus, it is possible to receive messages from asynchronous sources without any training period. This code can be extremely useful in communication over a passive optical star. In the analysis, the efficiency or capacity of the code is computed with two additional constraints: limited run-length and balancing. It is shown that this coding scheme is efficient when both constraints are applied. The objective of this analysis is to show that the additional constraints imposed on the encoding do not cause a significant reduction in its efficiency. The design of a serial electronic interface is described. Its goal is to maximize the interface bandwidth (greater than 1/Gb/s with GaAs technology), which is usually the bottleneck of an optical communication system. It is achieved by reducing the critical timing path to one flipflop and one NOR gate, and by having a hierarchical interface design     

Universal minimal topological dynamical systems

Rokhlin (1963) showed that any aperiodic dynamical system with finite entropy admits a countable generating partition. Krieger (1970) showed that aperiodic ergodic systems with entropy < log a, admit a generating partition with no more than a sets. In Symbolic Dynamics terminology, these results can be phrased— ℕ^ℤ is a universal system in the category of aperiodic systems, and [a]^ℤ is a universal system for aperiodic ergodic systems with entropy < log a. Weiss ([We89], 1989) presented a Minimal system, on a Compact space (a subshift of ) which is universal for aperiodic systems. In this work we present a joint generalization of both results: given ɛ, there exists a minimal subshift of [a]^ℤ, universal for aperiodic ergodic systems with entropy < log a − ɛ.     

Geodesics and almost geodesic cycles in random regular graphs

A geodesic in a graph G is a shortest path between two vertices of G. For a specific function e(n) of n, we define an almost geodesic cycle C in G to be a cycle in which for every two vertices u and v in C, the distance d_G(u, v) is at least d_C(u, v)?e(n). Let ω(n) be any function tending to infinity with n. We consider a random d‐regular graph on n vertices. We show that almost all pairs of vertices belong to an almost geodesic cycle C with e(n) = log_d?1log_d?1n+ ω(n) and |C| = 2log_d?1n+ O(ω(n)). Along the way, we obtain results on near‐geodesic paths. We also give the limiting distribution of the number of geodesics between two random vertices in this random graph. Copyright © 2010 John Wiley & Sons, Ltd. J Graph Theory 66:115‐136, 2011