Distributed routing protocols for ATM extended Banyan networks

It is well known that a multistage banyan network, which is a single-path blocking structure, becomes rearrangeable nonblocking in a circuit-switching environment if the number of its stages is increased so as to obtain a Benes network. Banyan networks, provided with a shared queue in each switching element, have often been proposed as the core of an interconnection network for an ATM packet switching environment. In this scenario, if the classical interstage backpressure protocols are used, adding stages to a banyan network can even degrade the banyan network performance, in spite of the multipath capability given by the additional stages. A class of new simple interstage protocols is here defined to operate in the added stages of the banyan network so that a sort of sharing of the queueing capability in each added stage is accomplished. Large improvements in the traffic performance of these extended banyan networks are obtained, especially in the region of offered loads providing a low packet loss probability     

Optical Network Survivability: Protection Techniques in the WDM Layer

This paper is an introduction to survivability of WDM networks. All the main optical protection techniques proposed as far as now for the WDM layer are classified and reviewed. In particular, commonly adopted protection strategies for ring and mesh networks are explained. Moreover, off-line planning of WDM networks able to support path protection is briefly introduced. Finally, an example of heuristic network-capacity optimization is presented, discussing results obtained by considering a case-study network.     

Strictly Nonblocking $f$-Cast Photonic Networks

The multicast capability and crosstalk issue need to be deliberately considered in the design of future high performance photonic switching networks. In this paper, we focus on the photonic switching networks built on the banyan-based architecture and directional coupler technology. We explore the capability of these networks to support general f-cast traffic, which covers the unicast traffic (f = 1) and multicast traffic (f = N) as special cases, and determine the conditions for these networks to be f-cast strictly nonblocking under various crosstalk constraints. In particular, we propose an optimization framework to determine the nonblocking condition of an f-cast photonic network when a general crosstalk constraint is imposed.     

Architectures and performance of optical packet switching nodes for IP networks

As new bandwidth-hungry Internet protocol (IP) services are demanding more and more capacity, transport networks are evolving to provide a reconfigurable optical layer in order to allow fast dynamic allocation of wavelength-division-multiplexing (WDM) channels. To achieve this goal, optical packet-switched systems seem to be strong candidates as they allow a high degree of statistical resource sharing, which leads to an efficient bandwidth utilization. In this paper, we propose an architecture for optical packet-switched transport networks, together with an innovative switching node structure based on the concept of per-packet wavelength routing. The traffic performance of such node when loaded by a typical IP traffic is evaluated through computer simulation; packet loss probability and average delay performance are shown for various load conditions.     

Multistage shuffle networks with shortest path and deflectionrouting for high-performance ATM switching: the closed-loop shuffleout

A new class of switching architectures for broadband packet networks, called shuffleout, is described and analyzed. Shuffleout is basically an output-queued architecture with a multistage interconnection network built out of unbuffered b×2b switching elements. Its structure is such that the number of cells that can be concurrently switched from the inlets to each output queue equals the number of stages in the interconnection network. The switching element operates the cell self-routing adopting a shortest path algorithm which, in case of conflict for interstage links, is coupled with deflection routing. The basic version of this architecture is called open-loop shuffleout. This paper describes the closed-loop shuffleout architecture with 2×4 switching elements in which cells that have crossed the whole interconnection network re-enter the network as long as they are not successfully routed to the addressed switch outlet. This result is accomplished by adding to the basic open-loop structure recirculation paths so that each packet can cross several times the interconnection network. Two different solutions are proposed to implement such functionality, the buffered closed-loop shuffleout and the expanded closed-loop shuffleout architecture. Both these solutions aim at reducing the number of stages in the network, compared to the open-loop structure, so as to reduce the complexity of the switch internal wiring and to simplify the output queue interface     

Multichannel bandwidth allocation in a broadband packet switch

The problem of bandwidth allocation in a packet switch supporting broadband services is addressed. To reduce the performance constraints imposed by limiting a data link to a single broadband packet channel, the author introduces the concept of channel group as a set of broadband packet channels that is viewed as a single data-link connection by routing entities. He uses a two-step bandwidth allocation scheme. At connection setup time, a call is allocated to a channel group. At transmission time, specific channels of a group are optimally allocated to the packets destined to the group. Because of the statistical smoothing of the large number of sources served by a channel group, the traffic performance of the switch is improved. This scheme also allows super-rate switching, i.e., the support of services with peak bandwidth exceeding the capacity of a single packet channel. The author shows the feasibility of this scheme in a Batcher-banyan switch, by implementing in hardware the bandwidth allocation at transmission time. Performance improvements obtained by this scheme are also provided in different traffic environments     

Rearrangeable f-cast multi-log2 N networks

Multi-log2 N networks (or vertically stacked banyan networks) have been an attractive class of switching networks due to their small depth O(logN), absolute signal loss uniformity and good fault tolerance property. Recently, F.K.Hwang extended the study of multi-log2 N networks to the generalf-cast case, which covers the unicast case (f = 1) and multicast case (f = N) as special cases, and determined the conditions for these networks to be f-cast strictly nonblocking when the fan-out capability is available at both the input stage and middle banyan stage. In this paper, we study the rearrangeable f-cast multilog2 N networks under both node-blocking scenario (relevant to photonic switches) and link-blocking scenario (relevant to electronic switches). In particular, we consider the following three fan-out cases in our study: 1) no restriction on fan-out capability; 2) input stage has no fan-out capability; 3) middle banyan stage has no fan-out capability. We determine the necessary conditions for the first two cases while obtaining the necessary and also sufficient condition for the third one.     

Multi-exit discriminator game for BGP routing coordination

Inter-Autonomous System (AS) links represent nowadays the real bottleneck of the Internet. Internet carriers may coordinate to efficiently balance the load, but the current practice is often based on an uncoordinated selfish routing. Firstly, we assess this issue by characterizing BGP route deviations across top-tier interconnections we could detect using recent Internet routing history data. Then, in order to improve the current practice, we present a novel game-theoretical framework to efficiently coordinate the routing on inter-AS links while modeling the non-cooperative carrier behavior. It relies on a coordinated use of the Multi-Exit Discriminator (MED) attribute of BGP, hence it is nicknamed ClubMED (Coordinated MED). We define the routing policy that shall be implemented upon Nash equilibria and Pareto-efficient profiles. We emulated the interconnection between the Internet2 and the Geant2 networks, comparing our proposition to the current BGP practice. The results show that the route stability can significantly be reinforced, the global routing cost can be significantly reduced, and the inter-AS link congestion can be avoided.     

Trading availability among shared-protected dynamic connections in WDM networks

Novel automatized management systems for optical WDM networks promise to allow customers asking for a connection (i.e., a bandwidth service) to specify on-demand the terms of the Service Level Agreement (SLA) to be guaranteed by the Network Operator (NO). In this work, we exploit the knowledge, among the other Service Level Specifications (SLS), of the holding time and of the availability target of the connections to operate shared-path protection in a more effective manner.In the proposed approach, for each connection we monitor the actual downtime experienced by the connection, and, when the network state changes (typically, for a fault occurrence, or a connection departure or arrival), we estimate a new updated availability target for each connection based on our knowledge of all the predictable network-state changes, i.e., the future connection departures. Since some of the connections will be ahead of the stipulated availability target in their SLA (credit), while other connections will be behind their availability target (debit), we propose a mechanism that allows us to “trade” availability “credits” and “debits”, by increasing or decreasing the shareability level of the backup capacity. Our approach permits to flexibly manage the availability provided to living connections during their holding times.The quality of the provided service is evaluated in terms of availability as well as probability of violation of availability target stipulated in the SLA (also called SLA Violation Risk), a recently-proposed metric that has been demonstrated to guarantee higher customer satisfaction than the classical statistical availability. For a typical wavelength-convertible US nationwide network, our approach obtains significative savings on Blocking Probability (BP), while reducing the penalties due to SLA violations. We also analytically demonstrate the proposed scheme can be highly beneficial if the monitored metric is the SLA Violation Risk instead of the availability.