Design of a Switched Broad-Band Communications Network for Interactive Services

The congestion in broad-band communications networks resulting from the increased demand for interactive services is considered. It is shown that services such as a video library could not be provided to the majority of subscribers in a conventional CATV network. A design is developed for a space division multiplex broad-band network which can be expanded at minimum cost to meet an increasing demand for interactive services. The network contains two signal distribution networks: a cablecast system similar to the Rediffusion system, and a switched communication network providing point-to-point circuits for both one-way and two-way services. All broad-band signals are transmitted to the subscribers in the 1- to 10-MHz spectrum, permitting the use of twisted pair video cables and a minimum number of cable amplifiers. The broad-band cable network (BCN) is organized around 15 local switching exchanges and one central exchange. Multipoint switches in local exchanges under wired-logic circuit control connect individual subscriber communication lines to any channel. Crosspoint matrix switching groups in the local and central exchanges connect communication circuits in the broad-band communication network under programmed computer control. This network is accessed via links terminating on one channel of the multiposition switches. Per-subscriber costs are estimated to be 190 dollars for a cablecast system serving 3800 subscribers. Additional expenditures per subscriber of 40 dollars for fixed costs and 40 dollars for variable costs would provide interactive services. The range of interactive services provided would be extremely flexible, including both one-way video library service and point-to-point two-way communications.     

An architecture for frame integrity optical TDM switching

An architecture for optical time-division-multiplexing (TDM) switching which makes more efficient use of hardware is presented. The number of switches used is very close to the theoretical minimum. Lithium niobate switches, with fiber delay lines for storage, are used throughout, and the architecture allows the bit rate and wavelength transparency of these devices to be exploited. The networks are mathematically equivalent to Benes and Waksman networks, and they are constructed using recursive definitions which are justified mathematically. The use of `feedforward' rather than `feedback' delays produces superior crosstalk performance and more uniform attenuation than existing designs. The networks may be dilated in a similar way to dilated Benes networks, yielding vastly improved crosstalk performance at the expense of using roughly twice as many switches     

The Effects of Management Traffic on the Local Call Processing Performance of ATM Switches Using Queue Network Models and Jackson's Theorem

This paper considers a TMN‐based management system for the management of public ATM switching networks using a four‐level hierarchical structure consisting of one network management system, several element management systems, and several agent‐ATM switch pairs. Using Jackson's queuing model, we analyze the effects of one TMN command on the performance of the component ATM switch in processing local calls. The TMN command considered is the permanent virtual call connection. We analyze four performance measures of ATM switches—utilization, mean queue length and mean waiting time for the processor directly interfacing with the subscriber lines and trunks, and the call setup delay of the ATM switch—and compare the results with those from Jackson's queuing model.     

A Two-Stage Rearrangeable Broadcast Switching Network

A new rearrangeable broadcast switching network has been invented. In its simplest form, the network has two stages. For larger networks, the switches in each stage can be replaced with two-stage networks to reduce crosspoint cost. The invention is based on an innovative approach of connecting each inlet channel to a multiplicity of first-stage switches according to a predetermined connection pattern. The network grows easily and has simple path hunt and rearrangement algorithms. It provides a general solution for any nonblocking broadcast switching application. Fewer crosspoints are required than in any other known two- or three-stage rearrangeable broadcast network. The connection arrangement exemplifies a topic heretofore unaddressed in combinatorial theory.     

Binomial Switching Networks for Concentration and Distribution

In this paper a new class of switching networks is presented for concentration and distribution interconnection assignments between disjoint sets of input and output terminals. These networks are called binomial switching networks because of their structural association with the binomial distribution. Binomial networks are uniform in that all connecting paths are of equal length and are such that cycles or iterations through stages of the network are not permitted, and binomial networks are rearrangeable in that implementing an additional path through the network for a new connection can require the rearranging of existing paths. It is shown that an upper bound on the number of such rearrangements is closely related to the number of stages in the network. A sparse crossbar switch construction of the binomial switching network is presented which contains crossbar switches in which it is not possible to connect each switch input to each switch output. Finally, the number of crosspoints needed for such networks for sufficiently large numbers of input and output terminals is seen to be less than the classical, benchmark alternatives for both concentration and distribution assignments.     

On self-routing in Clos connection networks

A self-routing connection network is a switching device where the routing of each switch can be determined in terms of the destination addresses of its inputs alone, i.e. independent of the routing information regarding the other switches in the network. One family of connection networks that were considered in the literature for self-routing are Clos networks. Earlier studies indicate that some Clos networks can be self-routed for certain permutations. In this paper, it is proved that the only category of Clos networks that can be self-routed for all permutations are those with at most two switches in their outer stages     

New architectures for optical TDM switching

A systematic theoretical study of architectures for optical TDM switching, using lithium niobate optical switches and optical fiber delay lines for storage, is undertaken. The architectures allow the bit rate and wavelength transparency of these devices to be exploited. A technique involving recursive definition and proof is used to define the networks, which are mathematically related to Benes and Waksman networks. This produces architectures that are very different from existing optical TDM networks. They exhibit economical use of components, which reaches the theoretical minimum in some cases. The use of feed-forward rather than feed-back delays give these networks superior crosstalk performance and more uniform attenuation than existing designs.<>     

一种新颖的ZVZCS双管正激变换器

本文提出了一种新颖的、利用辅助电路实现零电压、零电流开关的双管正激变换器。其中,有源钳位辅助电路用来实现主开关管上的零电压开通,同时使该变换器的占空比拓展到50%以上;变压器副边的辅助电路用来实现主开关管以及副边二极管的零电流关断。因此,该变换器中全部开关管均工作在软开关状态下。与其他软开关双管正激变换器相比,该变换器具有结构简单、所用元器件最少等优点。最后,经过一台250W的样机检验,该变换器效率最高可达95.7%,非常适合IGBT应用的场合。     

On the performance of different node configurations in multi-fiber optical packet-switched networks

With the development of optical packet-switching (OPS) technologies, multi-fiber OPS networks will play an important role in the future data transmissions. In such networks, instead of constructing some extremely expensive node configurations with strictly non-blocking switching function, a more practical solution is multi-board switches that contain a number of small-sized switching boards. In this article, we have evaluated the performance of several different multi-board switches, based on the following two main objectives: (i) better understanding the effects of different connection schemes between switching boards and optical buffers and (ii) investigating possible schemes for achieving comparable performance to that of the ideal, strictly non-blocking switches. Extensive simulation results have shown that unlike circuit-switched net- works, multi-board OPS cannot easily perform comparably to the strictly non-blocking switch by having slightly more fibers per link. Also, such a problem can be tackled by several different approaches. The most efficient one is to equip the switch with more buffers rather than to increase the switching-board size or to enhance the buffer sharing between different switching boards.     

Optical cross-connect system in broad-band networks: system conceptand demonstrators description

A network robust to future evolution in network topologies or transmission formats and bit rates, which would be achieved by introducing an all-optical transparent layer in the transport network hierarchy is considered. The transparency would permit use of physically common fiber lines and nodes for different transmission hierarchies and/or formats. A transparent network could be achieved by combining photonic switching with electronic switching technology in the network nodes. A combination of wavelength routing and space-division switching in the optical layer would increase the capacity, as well as the flexibility in a network, allowing routing with higher granularity within the optical layer. Two optical cross-connect demonstrators have been set up. One demonstrates protection switching and restoration of traffic in a future transport network, and the other demonstrates routing of subscriber signals to different service switches in a local exchange. Space switches, tunable lasers and filters are the key technologies used to obtain enhanced flexibility     

Semi-rearrangeably nonblocking operation of Clos networks in themultirate environment

We study the semi-rearrangeably nonblocking (SRN) operation of asymmetrical three-stage Clos (1953) switching networks in the multirate environment. We develop a basic algorithm that balances the established connections among middle-stage switches by performing a small number of rearrangements per disconnection. For this algorithm, we first derive general conditions under which rearranging from a single middle-stage switch is sufficient to achieve SRN operation. In the most general case, however, a sequence of rearrangements from several middle-stage switches may be required for SRN operation. An algorithm to achieve this sequence of rearrangements is presented and its correctness is proved. The minimum resource requirements to achieve SRN operation, in terms of the number of middle-stage switches, are derived for various cases     

Filters for High-Speed Diode Modulators and Demodulators

The relationship between switching time, transient suppression, and filter complexity is derived for filter-type diode switches, along with the theoretical minimum switching time. Design criteria are developed for high-speed switches and detectors in waveguide and TEM transmission lines.     

The “packing” and the “scheduling packet”switch architectures for almost all-optical lossless networks

This paper proposes two almost all-optical packet switch architectures, called the “packing switch” and the “scheduling switch” architecture, which when combined with appropriate wait-for-reservation or tell-and-go connection and how control protocols provide lossless communication for traffic that satisfies certain smoothness properties. Both switch architectures preserve the order of packets that use a given input-output pair, and are consistent with virtual circuit switching, The scheduling switch requires 2klogT+k² two-state elementary switches (or 2klogT+2klogk elementary switches, if a different version is used) where k is the number of inputs and T is a parameter that measures the allowed burstiness of the traffic. The packing switch requires very little processing of the packet header, and uses k²logT+klogk two-state switches. We also examine the suitability of the proposed architectures for the design of circuit switched networks. We find that the scheduling switch combines low hardware cost with little processing requirements at the nodes, and is an attractive architecture for both packet-switched and circuit-switched high-speed networks     

Switch minimisation for a simple bidirectional network

Describes a method for generating a one-stage, one-sided switching network with the minimum number of switches for any required level of connectivity. The fact that the method generates optimal networks is established by proving appropriate lower bounds. This generalises recent work of Newbury     

Multirate non-blocking generalized three-stage Clos switching networks

This paper studies the non-blocking switching operation of generalized three-stage Clos (1953) switching networks in the multirate environment. The analysis presented determines the minimum number of the second-stage switches required for strictly non-blocking operation of such networks at call setup. Both the discrete and the continuous bandwidth cases are considered. For the discrete bandwidth case, sufficient and necessary conditions are derived. For the continuous bandwidth case, only sufficient conditions are given, which, in some cases, also constitute necessary conditions. The results given are, in some cases, generalizations of existing results, but they also include new results.     

Fundamental limitations in RF switching and phase shifting using semiconductor diodes

When semiconductor diodes are used as variable impedance switching elements in RF transmission networks, the maximum power and minimum attenuation depend upon the characteristics of the diodes and the function being performed. Equations and theorems are derived which define these limits for quantized RF control networks used in on-off switches, selection switches, and phase-shift devices. The relationships are quite general and the limits are shown to apply to a wide variety of network configurations. It is shown that the maximum power of a switch is proportional to the maximum RF current of the forward-biased diode and also to the maximum RF voltage when reverse-biased. The maximum power in phase shifters is a sinusoidal function of the phase change required. Minimum attenuation depends upon the switching function performed, the frequency of operation, and a newly defined cutoff frequency which includes diode resistance in both forward-bias and reverse-bias states.     

Survey of switching techniques in high-speed networks and their performance

One of the most promising approaches for high speed networks for integrated service applications is fast packet switching, or ATM (asynchronous transfer mode). ATM can be characterized by very high speed transmission links and simple, hard-wired protocols within a network. To match the transmission speed of the network links, and to minimize the overhead due to the processing of network protocols, the switching of cells is done in hardware switching fabrics in ATM networks. A number of designs have been proposed for implementing ATM switches. Although many differences exist among the proposals, the vast majority of them are based on self-routeing multistage interconnection networks. This is because of the desirable features of multi-stage interconnection networks such as self-routeing capability and suitability for VLSI implementation. Existing ATM switch architectures can be classified into two major classes: blocking switches, where blockings of cells may occur within a switch when more than one cell contends for the same internal link, and non-blocking switches, where no internal blocking occurs. A large number of techniques have also been proposed to improve the performance of blocking and non-blocking switches. In this paper, we present an extensive survey of the existing proposals for ATM switch architectures, focusing on their performance issues.     

Subscriber Line Equipment for an Elastic Carrier Switching System

This is the third of three papers [l], [2] dealing with an elastic carrier-concentrator system. The functioning of the subscriber line equipment is described herein. The system serves 256 telephone subscriber lines by digital concentration switching and transmission of multiplexed message channels over a singleT1transmission line. The concentration switching function is nonblocking. Message channels are the individual communication links between terminals and are created on demand at the request of active subscriber lines. They are not merely inactive without service requests; they do not exist unless service is requested. The created message channels serve for their normal communication function and, in addition, carry for each line the ancillary functions of dialing, ringing, and pay-station coin disposal. Message channels are coded by delta modulation, which permits flexible digital concentration and provides a smooth tradeoff of channel quality versus the instantaneous traffic load. Each of two complementary subscriber line interface units, one per line at each end, provides the delta-modulation encoding and decoding functions for the analog voice-band signal input and output and, by overriding the delta codec, provides the desired signaling functions of dialing, ringing, etc. The line interface units provide the major equipment interface between the subscriber line and the digitalT1line. An integral test facility permits remote loop-back of any selected subscriber line unit via a test channel to the office terminals and at the same time connects the subscriber loop to an auxiliary programmed test facility which may transmit pertinent loop-test results to the office terminal.     

A resource management scheme for satellite networks

Satellite networks with dynamic bandwidth allocation capabilities (DBAC) are based on classical circuit switches. The DBAC payload allows changing the capacity of each connection dynamically, without tearing down and setting up the connection. An analysis of our DBAC satellite system performance shows a significant increase in the overall utilization factor of our system compared to a plain circuit switching solution     

Multibuffer delay line architectures for efficient contentionresolution in optical switching nodes

This paper proposes an efficient contention resolution switching architecture which can serve as the basis for all-optical switching nodes. The presented solution builds on fiber delay lines used as temporary optical storage and 2×2 space photonic switches, a solution principle also known as Quadro or switched delay lines (SDLs). The efficiency of SDLs is fundamentally linked to its storage capacity, i.e., the length of the fiber delay lines, while its cost depends on the number of 2×2 photonic switches, i.e., the number of stages in the switch. This work presents a solution that makes use of multibuffer fiber delay lines which allow multiple packets to be concurrently stored (propagated) on each line. With a novel switch control, it is shown that this solution increases the total storage capacity and significantly improves switch and network performance, without increasing the number of the 2×2 switches in the system, i.e., its cost