Jonathan P. Lang

An analysis of oblivious and adaptive routing in optical networks with wavelength translation

We present an analysis for both oblivious and adaptive routing in regular, all-optical networks with wavelength translation. Our approach is simple, computationally inexpensive, accurate for both low and high network loads, and the first to analyze adaptive routing with wavelength translation in wavelength division multiplexed (WDM) networks while also providing a simpler formulation of oblivious routing with wavelength translation. Unlike some previous analyses which use the link independence blocking assumption and the call dropping (loss) model (where blocked calls are cleared), we account for the dependence between the acquisition of wavelengths on successive links of a sessions path and use a lossless model (where blocked calls are retried at a later time). We show that the throughput per wavelength increases superlinearly (as expected) as we increase the number of wavelengths per link, due both to additional capacity and more efficient use of this capacity; however, the extent of this superlinear increase in throughput saturates rather quickly to a linear increase. We also examine the effect that adaptive routing can have on performance. The analytical methodology that we develop can be applied to any vertex and edge symmetric topology, and with modifications, to any vertex symmetric (but not necessarily edge symmetric) topology. We find that, for the topologies we examine, providing at most one alternate link at every hop gives a per-wavelength throughput that is close to that achieved by oblivious routing with twice the number of wavelengths per link. This suggests some interesting possibilities for network provisioning in an all-optical network. We verify the accuracy of our analysis for both oblivious and adaptive routing via simulations for the torus and hypercube networks.

A virtual circuit deflection protocol

We propose a communication protocol, called the virtual circuit deflection (VCD) protocol, which combines some of the individual characteristics of virtual circuit switching and deflection routing. An advantage of the VCD protocol over previous (datagram) deflection schemes is that deflections in the former occur on a per session basis (or a per subsession basis, if sessions need to be split to find adequate capacity on the outgoing links), while in the latter, they occur on a per packet basis. This makes packet resequencing at the destination considerably easier to accomplish in the VCD protocol than in datagram deflection schemes. The VCD protocol exploits the storage arising from the high bandwidth-delay product of optical fibers to provide lossless communication with little buffering at the switches and without the need for advance reservations. This makes it particularly suitable for networks that use optical switching, where buffers are expensive to implement with current optical technology. We present a simple implementation of the VCD protocol for such networks, which requires only limited buffering, accomplished through the use of a minimal number of optical delay lines. We also analyze the performance of the protocol for the Manhattan Street network topology by using new analytical models. In particular, we examine the effect of the traffic load and the network size on the throughput and the length of the paths followed by the sessions, and compare the analytical results obtained with corresponding simulation results. The results indicate that the VCD protocol is efficient under both light and heavy traffic conditions, especially when the link capacities are large compared to the basic rate of individual sessions, as is expected to be the case in future multigigabit networks.

Performance of path protection in IP/optical core mesh networks with source-routed GMPLS protocols

Performance of 1:1 path protection times in the range of 100-200 msec are reported with optimum design parameters implemented in a large continental optical network. Protection time depends heavily on the network (size, topology, length of the traffic demands) under consideration, the algorithm used for fault mitigation, and switching and processing times at nodes. Standardized generalised multiprotocol label switching (GMPLS) signaling, routing, and LMP protocols can be used to implement a variety of desired protection and restoration mechanisms for traffic recovery to meet various service requirements.

The /spl lambda/-scheduler: A multiwavelength scheduling switch

We propose a new multiwavelength almost all-optical switch architecture called the /spl lambda/-scheduler that uses wavelength division multiplexing (WDM) internally to fold the switch architecture in both the space and time domains to reduce the hardware complexity and to improve the signal characteristics through the switch. The /spl lambda/-scheduler preserves the packet order for a given input-output pair, is consistent with virtual circuit switching, and when combined with appropriate connection and flow control protocols, provides lossless communication for bursty (or nonconstant rate) traffic, provided the traffic satisfies certain smoothness properties. The /spl lambda/-scheduler uses novel scheduling and wavelength assignment algorithms, in conjunction with a series of feed-forward delay blocks, to avoid packet collisions within the switch or at the switch outputs. We present two implementations of the /spl lambda/-scheduler when the number of internal wavelengths k equal the number of inputs (and outputs) N to the switch. In the compressed /spl lambda/-scheduler, the N internal wavelengths are used to fold the architecture in the time domain, which reduces the total number of delay blocks for the switch by 2N log N. In the collapsed /spl lambda/-scheduler, the N internal wavelengths are used to fold the architecture in the space domain, which reduces the number of delay blocks and total fiber length used for delays by a factor of N. We examine the insertion loss for both /spl lambda/-scheduler implementations and discuss the trade-offs between the reduction in overall component count and the improvement in the signal characteristics.

A new analysis for wavelength translation in regular WDM networks

We present a new analysis of wavelength translation in regular all-optical WDM networks, that is simple, computationally inexpensive, and accurate for both low and high network loads. In a network with k wavelengths per link, we model the output link by an auxiliary M/M/k/k queueing system. We then obtain a closed-form expression for the probability P/sub succ/ that a session arriving at a node at a random time successfully establishes a connection from its source node to its destination node. Unlike previous analyses, which use the link independence blocking assumption, we account for the dependence between the acquisition of wavelengths on successive links of the sessions path. Based on the success probability, we show that the throughput per wavelength increases superlinearly (as expected) as we increase the number of wavelengths per link; however the extent of this superlinear increase in throughput saturates rather quickly. This suggests some interesting possibilities for network provisioning in an all-optical network. We verify the accuracy of our analysis via simulations for the torus and hypercube networks.

Intelligent optical networking with photonic cross connections

Optical amplification and dense wavelength division multiplexing (DWDM) have fundamentally changed optical transport networks. Now that these technologies are widely adopted, the bottleneck has moved from the outside line plant to nodal central offices, where electrical switching equipment has not kept pace. While OEO technology was (and still is) necessary for grooming and traffic aggregation, the transport network has dramatically changed, requiring a dramatic rethinking of how networks need to be designed and operated. While todays transport networks carry remarkable amounts of bandwidth, their optical layer is fundamentally static and provides for only simple point-to-point transport. Efficiently managing the growing number of wavelengths can only be achieved through a new breed of networking element. Photonic switching systems (PSS) can efficiently execute these functions because they are bit rate, wavelength, and protocol transparent. With their all-optical switch cores and interfaces, PSS can switch optical signals at various levels of granularity wavelength, sub band, and composite DWDM fiber levels. Though cross-connect systems with electrical switch cores are available, they perform these functions at very high capital costs and operational inefficiencies. This paper examines enabling technologies for deployment of intelligent optical transport networks (OTN), and takes a practical perspective on survivability architecture migration and implementation issues.

An Analysis of Deflection-Based Wormhole Routing with Virtual Channels

We analyze a new wormhole routing scheme, which we call the wormhole deflection with virtual channels (abbreviated WDVC) scheme, that combines wormhole routing with virtual channels and deflection routing to provide efficient lossless communication. We use new analytical models to analyze the performance of the WDVC scheme for the Manhattan Street (MS) network topology. In particular, we examine the effect of the traffic load and the number of virtual channels on the throughput and the length of paths followed by the worms, and compare the analytical results obtained with corresponding simulation results. Our results indicate that wormhole deflections combined with virtual channels is efficient under both light and heavy traffic loads, especially when the number of virtual channels on a link is large.