Another confirmation of AON (All-Optical Networks) for the future:
All-Optical Networking Consortium
WDM Description
Introduction
A significant component of our activities is the development of an operational testbed to promote the interaction of architecture, technologies, and applications. A major milestone has been achieved in that this network is now deployed in the Boston Metropolitan area and is undergoing characterization and experimental applications. The testbed is a 20-channel WDM system with a data-rate-per-wavelength ranging from 10 Mb/s to 10 Gb/s. The network is all-optical in that the transmission of data within the network does not undergo any optical-electrical conversions, although the connections or light paths may be controlled by electronics. The testbed primarily uses fast tunable laser transmitters and receivers with array technology also being developed. The architecture is hierarchical and includes
passive broadcast local area networks (LANs), passive wavelength-routed metropolitan area networks (MANs), and configurable wavelength-routed wide area networks (WANs). Ten wavelengths are partitioned for use in the LAN, and the remaining ten are shared between the MAN and WAN. Wavelength partitioning enables scalability via wavelength reuse. Two all-optical services, A- and B-Service, share the twenty channels provided in the network. An additional service, the C-Service, is used for network management, scheduling of wavelengths and time-slots, and clock distribution. We make a distinction between the architecture and the testbed. The testbed effort is key to refining the architecture as well as being existence proof of its fundamental feasibility.
All-Optical Networking
A unique property of a WDM all-optical network is the ability to do wavelength routing. Here, the path of the signal through the network is determined by the wavelength and origin of the signal, as well as the states of the network switches and wavelength changers.
Unlike other all-optical approaches, wavelength routing provides a transparent light path between network terminals. A light path is a path an optical signal traverses in the network from a source to a single destination which may include all-optical wavelength changers. Similarly, a wavelength path is the light path without wavelength changers. This transparency provides a simple way for heterogeneous users to share network resources. For example, certain wavelengths could carry analog signals with other wavelengths simultaneously being used for digital. Moreover, different network terminals may use different modulation formats and terminals may be upgraded without any network reconfiguration. As a philosophy, the network will provide bandwidth on demand and let the users determine their individual
hardware requirements.
Users, Optical Terminals, and AON Services
The AON provides three basic types of services between optical terminals (OTs): A, B, and C Services. In turn, the OTs provide more complex services like SONET connections through these services. Many different types of OTs co-exist on the AON, providing different services to the users of the AON. Note that the users of the AON may be end-users such as workstations and video servers or could be other networking equipment such as SONET Add Drop Multiplexers, ATM switches, or gateways to other networks. In the testbed and in the near future, we expect many users to be connected to an OT; however, an OT may eventually be integrated within the Input/Output section of a user's device.
A and B service are transparent services, i.e. an OT using A or B channel(s) may transmit with any data and modulation format as long as source power levels and bandwidth specifications are not exceeded at network access points. A-service is a transparent physically circuit-switched service which connects OTs with a clear light path (A-channel). The AON allows point-to-point, point-to-multipoint, simplex and duplex connections. Services that OTs might provide through A-channels are for example: point-to-point OC-192, or HIPPI connections and point-to-multipoint video transmissions.
C-service is a datagram service under which OTs can transmit a packet in a specific data and modulation format. C-service is not transparent because it must serve as a common communication link between all users of the AON. It is a signaling network that is primarily used for resource scheduling, network management, administration, and maintenance.
AON Architecture
The AON consists of a three-level hierarchy of subnetworks: Level-0 subnets, Level-1 subnets, and a single Level-2. Each subnet is itself an all-optical network capable of autonomous operation. A Level-0 subnet is a high-performance local-area network. An OT connects to a Level-0 through a fiber pair. There are many Level-0s, each of which connects to a Level-1, also through a single fiber pair. A Level-1 is a metropolitan-area network that connects a set of Level-0s using
passive wavelength routing. Level-2 is a wide-area network used to interconnect the Level-1s. There is only one Level-2, which consists of many nodes connected in a mesh topology. A Level-1 may connect to several nodes in the Level-2 through multiple fiber pairs.
The bandwidth of the fiber is divided into three sets: local, metro, and global. Any wavelength may be used for A- or B- service (C-service is provided out-of-band at 1.3 æm). Local wavelengths are used for intra-Level-0 connections. Frequency selective filters keep the local wavelengths within a Level-0. Metro wavelengths are used for inter-Level-0 connections for OTs that are under the same Level-1. Filters prevent the metro wavelengths from passing up to Level-2. The local and metro wavelengths can be re-used by each Level-0 and Level-1, respectively. The global wavelengths are used for access to and from the Level-2. Because Level-2 may have wavelength changers, local and metro wavelengths may be used within the Level-2; however these wavelengths cannot pass between the Level-2
and a Level-1.
Each subnet provides A, B, and C service to the subnets below it. Each subnet is responsible for its resources, e.g. bandwidth, switches, wavelength routers, wavelength changers, etc. In order to process requests for service and manage its resources, each subnet contains a Controller. The Controller is intended to permit autonomous operation if failure of a higher-level subnet occurs. Therefore, the services of a higher level controller are not used unless necessary.
Testbed Overview
The purpose of the testbed is to provide a proof-of-concept demonstration of a scalable, high-speed all-optical network using the architectural principles and technology elements described above and to provide a platform to promote the interaction of architecture, technology components, and applications. We have developed eleven optical terminals, six Level-0's, and two Level-1's. This equipment is now deployed in the Boston Metropolitan area. The nodes in Massachusetts include Digital Equipment Corporation Network Research facility in Littleton, MIT Lincoln Laboratory in Lexington, and MIT Campus in Cambridge. Several research laboratories at AT&T, DEC, MIT/LL, and MIT Campus will be participating in characterizing the network and running experimental applications.
Testbed Applications
The AON testbed is now deployed in the Boston Metropolitan area. All of the AON core bearer services and a number of network applications have been demonstrated. In particular we demonstrated rates from 10 Mb/s to 10 Gb/s A-Service connections, multiple simultaneous B-Service connections among optical terminals distributed over a metropolitan area and four separate Level-0's. We have demonstrated error-free multihop over both A- and B-Service connections.
Control of the network demonstration was accomplished using the AON distributed Network Management System built upon the AON C-Service. The capacity of the AON testbed is ~1 Tb/s. To date we have demonstrated ~130 Gb/s at once (which was limited by the number of sources available).
There are a wide range of potential applications for the AON. In the near term, most of these applications can be individually supported by electronic networks. However, the aggregation of many services and the cost, quality-of-service, flexibility, and transparency supported by AON technology may prove superior to electronic networks. We have just begun investigating applications over the AON. One experiment included a reconfigurable SONET based WAN backbone for a network of high-speed DEC FDDI and ATM packet switches (GIGAswitchr). In the testbed the GIGAswitchr trunks are implemented via single or multiple 155
Mb/s B-Service connections. At the same time B-Service was supporting multiple NTSC video (digitized at OC-3 rates) conferencing channels, a wireless LAN connection, a telemedicine imaging application and several DEC alpha workstations running a network throughput diagnostic application. A-Service at 1.244 Gb/s
was also being used to route four high speed NTSC video streams (300 Mb/s each).
Excerpts from: "A Wideband All-Optical WDM Network", IEEE Journal on Selected Areas in Communications, Vol. 14, No. 5, June 1996.<eas@ll.mit.edu>
The WDM AON Development Team
AT&T (Technology): Chris Doerr, Corrado Dragone, Ivan Kaminow, Tom Koch, Uzi Koren, Mark Haner, Adel Saleh and Bob Tkach
DEC (Architecture & Applications): Alan Kirby, Cuneyt Ozveren, Bruce Schofield and Bob Thomas
MIT Campus (Architecture): Li-Chung Chang, Angela Chiu, Steve Finn, Bob Gallager, Greg Gamble, Sofia Grubu, May Ku, Phil Lin and Stan Reiss
MIT Lincoln Lab (Test-bed, Architecture, Technology & Applications): Rick Barry, Dan Castagnozzi, Vincent Chan, Steve Finn, Roe Hemenway, Doug
Marquis, Salil Parikh, Mark Stevens and Eric Swanson
[ WDM Slide Presentation | AON Testbed Connections |
AON Homepage | MIT Lincoln Laboratory's Homepage ]
The All Optical Networking Consortium was formed by AT&T Bell Laboratories, Digital Equipment Corporation,and the Massachusetts Institute of Technology to
investigate architectures for, and build prototypes of all optical networks. The work is funded by the Defense Advanced Research Projects Agency (DARPA).
Here is the link:
ll.mit.edu |
