Breakthrough technologies for the high-performance electrical ATMswitching system

A high-performance electrical asynchronous transfer mode (ATM) switching system is described with the goal of Tb/s ATM switching. The first step system was to use advanced Si-bipolar very large scale integrated (VLSI) technologies and the multichip technique. 1.0 μm bipolar SST technologies and Cu-polyimide multilayer MCM realized a 160 Gb/s throughput ATM system. The performance limitations of the 160 Gb/s system were power supply/cooling and module interconnection. The new ATM switching system, named OPTIMA-1, adopted optical interconnection/distribution to overcome the limitations and achieve 640 Gb/s. The system uses high-performance complementary metal-oxide-semiconductor (CMOS) devices and optical wavelength division multiplexing (WDM) interconnection. Combining OPTIMA-1 with optical cell-by-cell routing functions, i.e., photonic packet routing, can realize variable bandwidth links for 5 Tb/s ATM systems. This paper first reviews high-performance electrical ATM (packet) switching system architecture and hardware technologies. In addition, system limitations are described. Next, the important breakthrough technology of optical WDM interconnection is highlighted. These technologies are adopted to form OPTIMA-1, a prototype of which is demonstrated. The key technologies of the system are advanced 80 Gb/s CMOS/MCM, electrical technologies, and 10 Gb/s, 8 WDM, 8×8 optical interconnection. Details of implementation technologies are also described. Optical cell-by-cell (packet-by-packet) routing is now being studied. From the architectural viewpoint, dynamic link bandwidth sharing will be adopted. In addition, an AWG that performs cell-by-cell routing and a distributed large scale ATM system are realized. Optical routing achieves the 5 Tb/s needed in future B-ISDN ATM backbone systems     

Large-scale WDM star-based photonic ATM switches

This paper describes the large-scale photonic asynchronous transfer mode (ATM) switching systems being developed in NTT Laboratories. It uses wavelength division multiplexing (WDM) techniques to attack 1 TB/s throughput. The architecture is a simple star with modular structure and effectively combines optical WDM techniques and electrical control circuits. Recent achievements in important key technologies leading to the realization of large-scale photonic ATM switches based on the architecture are described. We show that we can obtain a 320 Gb/s system that can tolerate the polarization and wavelength dependencies of optical devices. Our experiments using rack-mounted prototypes demonstrate the feasibility of our architecture. The experiments showed stable system operation and high-speed WDM switching capability up to the total optical bandwidth of 12.8 nm, as well as successful 10 Gb/s 4×4 broadcast-and-select and 2.5 Gb/s 16×16 wavelength-routing switch operations     

Packet-by-packet wavelength-routing interconnect technique for 5Tbit/s switching system

A packet-by-packet wavelength-routing interconnect technique for a 5 Tbit/s switching system with a three-stage architecture has been demonstrated. The technique uses an optical wavelength division multiplexing (WDM) link and dynamic bandwidth-sharing among wavelengths. The inter-stage, electro-optical interconnection subsystem was fabricated using very compact 2.5 Gbit/s, eight-wavelength WDM transmitters/receivers and an arrayed-waveguide grating router     

Practical implementation and packaging technologies for alarge-scale ATM switching system

The practical implementation of a trial large-scale asynchronous transfer mode (ATM) switching system and its packaging technologies are described. The architecture of the ATM switching system is discussed with an emphasis on system scalability. A building block architecture in which switching capacity can be expanded in a modular fashion is introduced. The design of the ATM switching system, including the ATM switch element, is described. The implementation of the VLSIs for the ATM switch which realize a highly modular system is explained. Bit-slice techniques are effectively used to realize a high-speed switch element as a CMOS VLSI chipset. An edge-to-edge orthogonal packaging technique is also presented     

Wavelength-exchanging cross connects (WEX)-a new class of photonic cross-connect architectures

All-optical wavelength division multiplexing (WDM) networks are expected to realize the potential of optical technologies to implement different networking functionalities in the optical domain. A key component in WDM networks is the optical switch that provides the basic functionality of connecting input ports to output ports. Existing WDM switches make use of space switches and wavelength converters (WCs) to realize switching. However, this not only increases the size and the complexity of the switch but also bears heavily on the cost. In this paper, the authors propose a new class of photonic switch architectures called wavelength-exchanging cross connect (WEX) that provides several advantages over existing switches by enabling a single-step space switching and wavelength conversion and thus eliminating the need for a separate conversion stage. This greatly enhances the switch architecture by reducing its size and complexity. The new class of cross-connect architectures is based on the proposed concept of a wavelength-exchange optical crossbar (WOC). The WOC concept is realized using the simultaneous exchange between two optical signals. The proposed WEX architecture is highly scalable. To establish scalability, the authors present a systematic method of developing instances of the switch architectures of an arbitrary large size.     

Scalable WDM access network architecture based on photonic slotrouting

This paper introduces an approach to solving the fundamental scalability problem of all-optical packet switching wavelength-division multiplexing (WDM) access networks. Current optical networks cannot be scaled by simply adding nodes to existing systems due to the accumulation of insertion losses and/or the limited number of wavelengths. Scalability through bridging requires, on the other hand, the capability to switch packets among adjacent subnetworks on a wavelength basis. Such a solution is, however, not possible due to the unavailability of fast-switching wavelength sensitive devices. In this paper, we propose a scalable WDM access network architecture based on a recently proposed optical switching approach, termed photonic slot routing. According to this approach, entire slots, each carrying multiple packets (one on each wavelength) are “transparently” routed through the network as single units so that wavelength sensitive data flows can be handled using fast-switching wavelength nonsensitive devices based on proven technologies. The paper shows that the photonic slot routing technique can be successfully used to achieve statistical multiplexing of the optical bandwidth in the access network, thus providing a cost-effective solution to today's increasing bandwidth demand for data transmissions     

WDM knockout switch with multi-output-port wavelength-channelselectors

This paper proposes the photonic knockout switch that uses wavelength division multiplexing (WDM). The proposed switch uses two types of WDM switching: broadcast-and-select (B and S) switching and wavelength routing. To extend the size of the knockout switch concentrator, a multi-output-port wavelength-channel selector is used, which enables us to reduce the number of optical gates and wavelength routers. Simple and distributed contention control becomes possible in the optical domain through the use of the wavelength-routing switch. In this switch, coherent crosstalk is a serious problem. We measured the bit error rates of a four-output-port wavelength-channel selector. The power penalty due to the presence of coherent crosstalk is less than 1 dB     

A distributed and scalable routing table manager for the next generation of IP routers

In recent years, the exponential growth of Internet users with increased bandwidth requirements has led to the emergence of the next generation of IP routers. Distributed architecture is one of the promising trends providing petabit routers with a large switching capacity and high-speed interfaces. Distributed routers are designed with an optical switch fabric interconnecting line and control cards. Computing and memory resources are available on both control and line cards to perform routing and forwarding tasks. This new hardware architecture is not efficiently utilized by the traditional software models where a single control card is responsible for all routing and management operations. The routing table manager plays an extremely critical role by managing routing information and in particular, a forwarding information table. This article presents a distributed architecture set up around a distributed and scalable routing table manager. This architecture also comes provides improvements in robustness and resiliency. The proposed architecture is based on a sharing mechanism between control and line cards and is able to meet the scalability requirements for route computations, notifications, and advertisements. A comparative scalability evaluation is made between distributed and centralized architectures in terms of required memory and computing resources.     

用时分交换技术构建IPOVERWDM网络

采用波分复用(WDM)光通信技术来传输IP数据，能够充分利用WDM技术带来的高带宽和优良的交换性能来处理IP业务，从而提高网络的传输性能。在波分复用光网络中，光纤的可用波长数目限制了网络接入用户的数量，并使网络设备的成本和复杂度提高，采用时分与波分相结合的交换技术，可以有效地提高信道的波长利用率，增加信道容量。本文介绍了一种IP OVER WDM网络结构，在光网络层采用了时分复用和波分复用相结合的交换方式。讨论了其网络结构和工作原理，并对网络性能的改进提出了一些建议。该网络具有传输效率高、结构简单、易于管理的特点。     

On the limits of electronic ATM switching

This article discusses the principal advantages and limitations of electronic switching in asynchronous transfer mode (ATM) networks. Key design parameters of ATM switch implementations are defined, and their relationships with respect to performance, complexity, and cost are modeled and discussed. Design and implementation experience is reported on a very high-performance four-input, four-output ATM switch that has been designed as part of the DARPA-sponsored “Thunder and Lightning” project at the University of California, Santa Barbara. This research project is focused on the design and prototype demonstration of ATM links and electronic switches operating at 40 Gb/s per link (TDM), with potential scalability to 100 Gb/s. Such aggressive link rates are near the implementation limits for electronic ATM switches; they place severe requirements on switch architecture, particularly the buffering scheme     

Mini-slot TDM WDM optical networks

In recent years, optical transport networks have evolved from interconnected SONET/WDM ring networks to mesh-based optical WDM networks. Time-slot wavelength switching is to aggregate the lower rate traffic at the time-slot level into a wavelength in order to improve bandwidth utilization. With the advancement of fiber-optics technologies, continual increase of fiber bandwidth and number of wavelengths in each fiber, it is possible to divide a wavelength in a fiber into time-slots, and further divide a time-slot into mini-slots so that the fiber bandwidth can be more efficiently utilized. This article proposes a router architecture with an electronic system controller to support optical data transfer at the mini-slot(s) of a time-slot in a wavelength for each hop of a route. The proposed router architecture performs optical circuit switching and does not use any wavelength converter. Each node in the mini-slot TDM WDM optical network consists of the proposed router architecture. Three different network topologies are used to demonstrate the effectiveness and behavior of this type of network in terms of blocking probability and throughput.     

On Guaranteed Smooth Switching for Buffered Crossbar Switches

Scalability considerations drive the evolution of switch design from output queueing to input queueing and further to combined input and crosspoint queueing (CICQ). However, CICQ switches with credit-based flow control face new challenges of scalability and predictability. In this paper, we propose a novel approach of rate-based smoothed switching, and design a CICQ switch called the smoothed buffered crossbar or sBUX. First, the concept of smoothness is developed from two complementary perspectives of covering and spacing, which, commonly known as fairness and jitter, are unified in the same model. Second, a smoothed multiplexer sMUX is designed that allocates bandwidth among competing flows sharing a link and guarantees almost ideal smoothness for each flow. Third, the buffered crossbar sBUX is designed that uses the scheduler sMUX at each input and output, and a two-cell buffer at each crosspoint. It is proved that sBUX guarantees 100% throughput for real-time services and almost ideal smoothness for each flow. Fourth, an on-line bandwidth regulator is designed that periodically estimates bandwidth demand and generates admissible allocations, which enables sBUX to support best-effort services. Simulation shows almost 100% throughput and multi-microsecond average delay. In particular, neither credit-based flow control or speed-up is used, and arbitrary fabric-internal latency is allowed between line cards and the switch core, simplifying the switch implementation.     

大容量路由器交换网络结构的研究

随着Internet的不断发展,对网络带宽的需求急剧增长,同时随着波分复用技术的产生和发展,传输链路已不再是限制骨干网发展的因素,因而作为业务结点的路由器就成为"瓶颈".文中对大容量路由器体系结构中的关键组成部分交换网络进行了研究,研究并比较了几种适合于构建大容量交换网络的网络拓扑.     

A fast decoupled approach for optimum TDM assignment in constrainedhierarchical switching systems

A three-tiered digital switching hierarchy is considered in which traffic from remote users is grouped, concentrated into time-multiplexed lines, and then transmitted to a central location for interconnection by a central space division switch. While the configuration provides efficient sharing of both transmission and switching resources, the TDM (time-division multiplexing) assignment problem for a conventional time-space-time (T-S-T) switch can become quite formidable due to the various hierarchical constraints. A time-slot assignment strategy is proposed that circumvents this problem by temporarily storing the incoming traffic at the central switch. Unlike the traditional T-S-T approach, the in-bound and out-bound assignments are entirely decoupled, which greatly simplifies the assignment process and produces a fast circuit switching capability. Necessary and sufficient conditions governing the assignability of traffic to the three-tiered switching system are stated and proved, and a block diagram of the proposed switching architecture is presented     

Scalable optical switch with internal fiber network

We present architecture of a large dynamic optical packet/burst switch comprising a number of smaller switching fabrics that are interconnected by internal fiber links. The switching fabrics are based on the broadcast-and-select architecture, while the internal interconnection network is a full mesh. An extensive performance study has been performed and results regarding scalability, packet/burst loss rate and achievable throughput for four scheduling algorithms are shown.     

A generalized framework for analyzing time-space switched opticalnetworks

The advances in photonic switching have paved the way for realizing all-optical time switched networks. The current technology of wavelength division multiplexing (WDM) offers bandwidth granularity that matches peak electronic transmission speed by dividing the fiber bandwidth into multiple wavelengths. However, the bandwidth of a single wavelength is too large for certain traffic. Time division multiplexing (TDM) allows multiple traffic streams to share the bandwidth of a wavelength efficiently. While introducing wavelength converters and time slot interchangers to improve network blocking performance, it is often of interest to know the incremental benefits offered by every additional stage of switching. As all-optical networks in the future are expected to employ heterogeneous switching architectures, it is necessary to have a generalized network model that allows the study of such networks under a unified framework. A network model, called the trunk switched network (TSN), is proposed to facilitate the modeling and analysis of such networks. An analytical model for evaluating the blocking performance of a class of TSNs is also developed. With the proposed framework, it is shown that a significant performance improvement can be obtained with a time-space switch with no wavelength conversion in multiwavelength TDM switched networks. The framework is also extended to analyze the blocking performance of multicast tree establishment in optical networks. To the best of our knowledge, this is the first work that provides an analytical model for evaluating the blocking performance for tree establishment in an optical network. The analytical model allows a comparison between the performance of various multicast tree construction algorithms and the effects of different switch architectures     

SUCCESS-DWA: a highly scalable and cost-effective optical access network

Passive optical networks have been identified as promising access solutions that can open the first-mile bottleneck, bringing gigabits-per-second data rates to end users. Current TDM PONs enjoy low cost by sharing resources in time, but suffer from limited capacity. In the future, WDM technology may be employed to achieve high performance. In this article we introduce a novel PON employing dynamic wavelength allocation to provide bandwidth sharing across multiple physical PONs. Tunable lasers, arrayed waveguide gratings, and coarse/fine filtering combine to create a flexible new optical access solution. The network's excellent scalability can bridge the gap between conventional TDM PONs and WDM PONs. The powerful architecture is a promising candidate for next-generation optical access networks.     

Switch fabrics

We examined a spectrum of (unbuffered) switching architectures and explored various design alternatives, where each is marked by its own merits and drawbacks. A number of trade-offs between the various switching architectures in terms of their characteristics (such as performance, implementation complexity, scalability, and cost) emerge. Hence, the wide variety of available switching fabrics means that no single architecture emerges as the only winning proposition. The ultimate decision is upon the switch architect, based on the overall system design requirements and specifications.     

Concurrent round-robin-based dispatching schemes for Clos-network switches

A Clos-network switch architecture is attractive because of its scalability. Previously proposed implementable dispatching schemes from the first stage to the second stage, such as random dispatching (RD), are not able to achieve high throughput unless the internal bandwidth is expanded. This paper presents two round-robin-based dispatching schemes to overcome the throughput limitation of the RD scheme. First, we introduce a concurrent round-robin dispatching (CRRD) scheme for the Clos-network switch. The CRRD scheme provides high switch throughput without expanding internal bandwidth. CRRD implementation is very simple because only simple round-robin arbiters are adopted. We show via simulation that CRRD achieves 100% throughput under uniform traffic. When the offered load reaches 1.0, the pointers of round-robin arbiters at the first- and second-stage modules are completely desynchronized and contention is avoided. Second, we introduce a concurrent master-slave round-robin dispatching (CMSD) scheme as an improved version of CRRD to make it more scalable. CMSD uses hierarchical round-robin arbitration. We show that CMSD preserves the advantages of CRRD, reduces the scheduling time by 30% or more when arbitration time is significant and has a dramatically reduced number of crosspoints of the interconnection wires between round-robin arbiters in the dispatching scheduler with a ratio of 1//spl radic/N, where N is the switch size. This makes CMSD easier to implement than CRRD when the switch size becomes large.     

Terahipas: a modular and expandable terabit/second hierarchicallymultiplexing photonic ATM switch architecture

A terabit/second hierarchically multiplexing photonic asynchronous transfer mode (ATM) switch network architecture, called Terahipas, is proposed. It combines the advantages of photonics (a large bandwidth for transport of cells) and electronics (advanced logical functions for controlling, processing, and routing). It uses a hierarchical photonic multiplexing structure in which several tens of channels with a relatively low bit rate, say 2.4 Gb/s, are first time-multiplexed on an optical highway by shrinking the interval between optical pulses, then a number of optical highways are wavelength-multiplexed (or space-division multiplexed). As a result, the switch capacity can be expanded from the order of 100 Gb/s to the order of 10 Tb/s in a modular fashion. A new implementation scheme for cell buffering is used for eliminating the bottleneck when receiving and storing concurrent optical cells at bit rates as high as 100 Gb/s. This new architecture can serve as the basis of a modular, expandable, high-performance ATM switching system for future broad band integrated service digital networks (B-ISDN's)