Anthony S. Acampora

The Knockout Switch: A Simple, Modular Architecture for High-Performance Packet Switching

A new, high-performance packet-switching architecture, called the Knockout Switch, is proposed. The Knockout Switch uses a fully interconnected switch fabric topology (i.e., each input has a direct path to every output) so that no switch blocking occurs where packets destined for one output interfere with (i.e., block or delay) packets going to different Outputs. It is only at each output of the switch that one encounters the unavoidable congestion caused by multiple packets simultaneously arriving on different inputs all destined for the same output. Taking advantage of the inevitability of lost packets in a packet-switching network, the Knockout Switch uses a novel concentrator design at each output to reduce the number of separate buffers needed to receive simultaneously arriving packets. Following the concentrator, a shared buffer architecture provides complete sharing of all buffer memory at each output and ensures that all packets are placed on the output line on a first-in first-out basis. The Knockout Switch architecture has low latency, and is self-routing and nonblocking. Moreover, its Simple interconnection topology allows for easy modular growth along with minimal disruption and easy repair for any fault. Possible applications include interconnects for multiprocessing systems, high-speed local and metropolitan area networks, and local or toll switches for integrated traffic loads.

Benefits of wavelength translation in all-optical clear-channel networks

In this paper, we study the benefits of wavelength translation in all-optical networks providing clear channel circuit-switching among users. We first establish approximate analytical models for a static-routing circuit-switched network with an arbitrary topology, both with and without wavelength translation. We then study the performance of the nonblocking centralized switch, the mesh-torus network and the ring network, using the analytical models and simulation results. It is shown that the analytical models match the simulation results very well in the case of the centralized switch and the mesh network. The results of our study also show that the benefits of wavelength translation are modest for the centralized switch and the ring network. On the other hand, the results show that wavelength translation can significantly improve the performance of a large mesh-torus network.

Control and quality-of-service provisioning in high-speed microcellular networks

esign and implementation of broadband networks is one of the major focal areas in modern telecommunications. With recent developments in the field of wireless, hand-held terminals, as well as in personal communications services (PCS) [l-61, integration of mobile, wireless connections in a backbone broadband network is an essential and challenging task since mobile users may need to access the communication services offered by the fixed broadband network. This implies that wireless networks must provide packetbased t ransport and bandwidth-upon-demand, as well as support multimedia applications. Since the radio spectrum is limited, future wireless systems will have micro/picocellular architectures in order to provide the higher capacity needed to support broadband services [7-91. Due to the small coverage area of micro/picocells and characteristics of the multipath and shadow fading radio environment, hand-off events in future microcellular systemswill occur at a much higher rate as compared to today’s macrocellular systems, and control of such systems will introduce a new set of challenges. We canviewwirelessimobile connections as consisting of paths (or routes) through the broadband backbone network; and radio links between the mobile, wireless terminals and base stations (or access points) which are the interface of mobile users to the fixed backbone network. When the quality of a radio link between a wireless terminal and its access point degrades, a new access point with acceptable quality must be found (hand-off), and network control functions of both the fixed and wireless network need to be invoked. In the backbone network, hand-off requires the establishment of a new route, which transports the packets destined to (or originated from) the wireless terminal to (or from) the new access point. Here, network call processing functions need to be invoked in order to set up such a route and ensure that the newly established route maintains acceptable quality-of-service (QOS) to both the wireless connection and to pre-existing calls sharing links of the new route. Furthermore, to execute hand-off, the network call controller must first ensure that the new wireless connection does not overload the new access point and then create a radio link between the mobile terminal and the new access point. As one can see, a substantial number of call processing and control functions of the fixed and wireless network must be invoked to complete a hand-off event. If such control functions are performed in a centralized fashion, call processing of handoff events would impose a bottleneck on the capacity of future microcellular networks. In this article, we propose and study distributed control methodologies for high-speed microcellular networks based on a hierarchical grouping of backbone and wireless network resources. With our approach, a number of adjacent cells are grouped into a cell-cluster that is used for call setup and control of the radio links, and all access points in a cell-cluster belong to the same backbone network connection tree, to be used for call setup and control of the backbone portion of wireless connections.

Wireless ATM: a perspective on issues and prospects

In this article the author examines several key issues in wireless ATM and even offers possible resolutions for some. The primary differences that distinguish wireless from wireline communications are presented, together with a short summary of so-called second-generation digital cellular system concepts. The operation of a wireline ATM network, especially with regard to those aspects bearing on the feasibility of wireless extension, is briefly reviewed, as well as some key technologies which may be very important enablers for wireless ATM, and some possible approaches for enabling bandwidth on demand (the media access problem) and maintaining service quality guarantees (the cell handoff problem), respectively. Finally, a possible format for signaling and synchronization, needed to tie it all together, is presented.

A broadband wireless access network based on mesh-connected free-space optical links

Driven by the twin forces of industry-wide deregulation and the explosive demand for Internet access and bandwidth-intensive multimedia services, broadband local access has emerged as one of the key issues in modern telecommunications. We describe a broadband local access network consisting of small, densely spaced packet-switching nodes interconnected by focused free-space optical links in a multihop mesh arrangement. Each switch serves a client, which may be an office building (containing, for example, conventional PBXs and LANs), a picocellular base station, or both. It is the responsibility of our local access network to economically and reliably extend broadband local access service (perhaps OC-3 or OC-12 for building LANs and PBXs; perhaps several tens of megabits per second to base stations) from an infrastructure end office or fiber ring add/drop multiplexer without requiring the installation of new buried optical cabling. Computed is the capacity of the multihop mesh, defined to be the maximum number of virtual connections which can be delivered to the infrastructure access point such that, independent of the traffic distribution among clients, all quality of service guarantees are maintained.

QoS provisioning in micro-cellular networks supporting multiple classes of traffic

We introduce an adaptive call admission control mechanism for wireless/mobile networks supporting multiple classes of traffic, and discuss a number of resource sharing schemes which can be used to allocate wireless bandwidth to different classes of traffic. The adaptive call admission control reacts to changing new call arrival rates, and the resource sharing mechanism reacts to rapidly changing traffic conditions in every radio cell due to mobility of mobile users. In addition, we have provided an analytical methodology which shows that the combination of the call admission control and the resource sharing schemes guarantees a predefined quality-of-service to each class of traffic. One major advantage of our approach is that it can be performed in a distributed fashion removing any bottlenecks that might arise due to frequent invocation of network call control functions.

QOS provisioning in micro-cellular networks supporting multimedia traffic

We introduce an adaptive call admission control mechanism for wireless/mobile networks supporting multimedia traffic, and discuss a number of resource sharing schemes which can be used to allocate wireless bandwidth to different classes of traffic. The adaptive call admission control reacts to changing new call arrival rates, and the resource sharing mechanism reacts to rapidly changing traffic conditions in every radio cell due to mobility of mobile users. In addition, we have provided an analytical methodology which shows that the combination of the call admission control and the resource sharing schemes guarantees a predefined quality-of-service to each class of traffic. One major advantage of our approach is that it can be performed in a distributed fashion removing any bottlenecks that might arise due to frequent invocation of network call control functions.

Protocols for optical star-coupler network using WDM: performance and complexity study

The efficiency of protocols coordinating the data transmission between the transmitter and receivers in a network of stations connected using a passive star coupler, equipped with fixed transmitters and tunable receivers, and using wavelength-division multiplexing is discussed. Two reservation-based protocols with varying degrees of signaling complexity are proposed: the dynamic allocation scheme (DAS), which dynamically assigns slots on a packet-by-packet basis, and the hybrid time-division-multiplexing (TDM) scheme (HTDM), which combines the TDM and the DAS scheme and allows both preassigned and dynamic slot assignment. Analytical results are derived for the delay performance of the two schemes and compared with that of TDM. It is shown that the performance of DAS under ideal conditions is close to optimal, but its signaling costs are exorbitantly high. On the other hand, HTDM has lower signaling needs, but has higher delays when compared to DAS. >

Polling-based media access protocols for use with smart adaptive array antennas

Use of an adaptive antenna array or a space-time processor at each base station of a wireless network can substantially abate the effects of multipath fading and co-channel interference. Among the expected benefits are higher data rates, greater frequency reuse factors, and overall higher capacity systems as needed to enable wireless multimedia services. Media access control (MAC) protocols which facilitate the deployment of such a processor have been previously proposed and studied. These MAC protocols invoke the delivery of a pilot tone from each packet access unit in the network as needed, so that the array antenna at the associated base station may rapidly adjust its weighting coefficients, or its per branch equalization coefficients, thereby ensuring subsequent reliable communication between the access unit and the base station. This paper considers two modifications to these earlier protocols, both based upon the notion of piggybacking information requests on to the actual information messages and both intended to improve utilization efficiency and mean delay performance. Results show that a maximum link utilization efficiency of 97% is readily achieved with either modification, and that this maximum utilization efficiency is independent of the number of remote users in the network. Note that the utilization efficiency refers to the throughput at maximum loading, i.e., when the remotes always have queued requests. The modifications also help in achieving a considerable reduction in the average delay in low-load regimes: for typical system parameters, the average delay at low load is only about 10% of that produced by the original schemes.

Capture division packet access: a new cellular access architecture for future PCNs

The authors describe a new cellular access architecture, known as capture-division packet access, which is a packet-oriented architecture able to support the constant bit rate traffic and variable bandwidth on demand necessary for multimedia traffic. The approach integrates the multiple access and channel reuse issues to achieve a high degree of spectral efficiency, and presents general advantages even if used for delay-constrained circuit-oriented traffic. Unlike CDMA and TDMA, wherein the effective data rate of each connection is typically a small fraction of the total radio channel allocated for PCN, the CDPA approach allows each user to access the entire channel, if necessary, for brief periods of time (packet access). Spectrum sharing is accomplished by exploiting the different path losses suffered by the various signals as they appear at the base stations (the capture effect), with co-channel interference abated through time diversity (colliding users do not successively retry in the same time interval). Results suggest that abating co-channel interference by random retransmission may be more effective than spatial isolation at cells using the same channel, as is usual in FDMA-TDMA systems.