Abstract-Optical networks with book-ahead bandwidth schedulers are being deployed to meet the high-speed and predictable-service networking requirements of applications in the scientific research community. We present an analytical model for a single-link book-ahead bandwidth scheduler, which responds to advance reservation requests with the first-available time interval in which a channel is available. The link is assumed to be divided into m channels, and time is discretized into intervals. Our proposed model is a non-homogeneous continuous-time Markov chain, which has an embedded discrete-time Markov chain. We solve the model for call congestion, mean scheduling delay, and link utilization. This model can be used by network designers to select the size of the reservation window, K, in timeinterval units, corresponding to a desired set of values for the output metrics, for a given value of m. For example, when m is 8, increasing the reservation window beyond 4 intervals does not affect the call congestion or system utilization, but causes the mean scheduling delay to increase. We show with comparative simulations that our analytical model can be used as a solution for an M/D/m/p queueing system at moderate-to-high loads.

Abstract-Resource-sharing mechanisms can be classified into the broad categories of reservation systems and queueing systems. There are key differences between the two types of systems, and each has advantages and disadvantages. In this work, these differences are characterized, and a general reservation system model (GRSM) is proposed. Under four different sets of assumptions, the GRSM is reduced to analytically tractable models for which solutions are provided. In two cases, queueing model solutions are used, and in the remaining two cases, Discrete Time Markov Chain (DTMC) models are solved. A fifth model, defined through a different set of simplifying assumptions to the GRSM, is solved with simulations. Next, several examples of commonly encountered reservation and queueing systems are identified, and analyzed using one of these four simplified analytical models, or the fifth simulation model. The purpose of these analyses is to understand why certain systems belonging to the same category of examples use reservation systems while others use queueing systems. For example, while both physicians and bank tellers are human servers, the former use reservation systems while the latter use queueing systems.

Abstract-Recently, both research-and-education networks (RENs) and commercial networks have added a dynamic circuit service. With this service, users can request and obtain dedicated bandwidth for short durations (on the order of minutes to hours). Host-to-host (cluster-to-cluster) circuits are used for large file transfers. The network nodes used for this circuit service are not pure TDM or WDM circuit switches; instead they are hybrid nodes that include Ethernet interfaces that allow for the connection of host Ethernet NICs. While as with ordinary circuit switches, cross-connections have to be provisioned prior to data transfer, the technology allows for the creation of mismatched rate circuits, in which the wide-area portion of the circuit can be matched to the (typically lower) disk-access rates, while the access links from hosts to these switches are Gb/s Ethernet. In this work, an in-depth experimental investigation is performed to gain insights into the complex interactions between the TCP layer, ON/OFF flow control at the Ethernet layer, and switch buffer sizes (the Ethernet line cards have buffers). Using a novel tool and transport protocol designed for circuits, these interactions are characterized. An interesting new dynamic was found between flow control at the data-link layer and congestion control at the transport layer. With this in-depth characterization, it is clear that automated mechanisms are necessary to not only configure end-host TCP send and receive buffer sizes as is required for high throughput across IP-routed networks, but for circuit networks, additionally, Ethernet-layer output queue (called qdisc in Linux) size needs to be set, along with flow-control related parameters within switches.

Abstract

Abstract-We are interested in exploring how to virtualize network switches in order to create multiple logical switches from one physical switch. The motivation behind this is to be able to support multiple research-and-education (R&E) projects by offering each of them a logical switch that could coexist with other R&E projects' logical switches, so that each would have the equivalent of their own switch. We propose an approach for virtualizing off-the-shelf Ethernet switches that have builtin support for creating isolated bandwidth partitions on their data-plane interfaces. Our solution is to implement two software modules that are run external to the switches, a slice scheduler and a Slice Administration Controller (SAC). We applied our approach to virtualizing a specific Ethernet switch, i.e., the Force10 E600 model. We describe our implementation, and show how a slowdown of 3% to 26%, based on the type of administrative command issued, is experienced when using the SAC.