872 zyxwvutsrqpon IEEE JOURNAL ON SELECTED zyxwvuts AREAS IN COMMUNICATIONS, VOL. SAC-3, NO. zyxw 6, NOVEMBER 1985 An Optical Fiber-Based Integrated LAN for MAGNET’S Testbed Environment AVSHALOM PATIR, TATSURO TAKAHASHI, YOSHIHARU TAMURA, MAGDA EL ZARKI, STUDENT MEMBER, IEEE, AND AUREL A. LAZAR, MEMBER, IEEE zyxwv Abstract -MAGNET is a Network Testbed (NTB) designed to evaluate the performance of local area network architectures and protocols support- ing integrated services such as televideo,videoconferencing,telephone, computer communication, and facsimile. The integrated local area network (ILAN) presented in this paper has been designed to support the research activities intended for MAGNET. An active slotted ring topology was chosen to implement adaptive sequential-type access mechanisms that are a function of the network loading. The ILAN is based on fiber optic technology with wavelength-division multiplexing of two 100 Mbit/s chan- nels. The media-access protocol provides higher levels 9 t h the capability of implementing two modes of operation referred to as circuit-switching, and packet-switching modes, respectively. F’rovisions have also been made for implementing simultaneous scheduling as well as centralized and de- centralized access control schemes. Finally, the reconfigurable structure of the network testbed enables the study of the reliability and availability of ILAN’s. I. INTRODUCTION M AGNET is a network testbed (NTB) designed to evaluate the performance of integrated local area network (ILAN) architectures and protocols supporting services such as televideo,videoconferencing, telephone, computer communication, and facsimile. The objective is to be able to support the research activities as described in zyxwvu [2]. As such, it has to 1) be a highly reconfigurable system, 2) support a layered architecture protocol, 3) have a flexi- ble (programmable) media-access control mechanism (to support a variety of media-access procedures), 4) carry isochronous and nonisochronous traffic, and zyxwvuts 5) maintain standard interfaces to the terminals for which the service is provided. In addition, the NTB is designed to support the development of multimedia workstations (also known as integrated workstations) and benefit from, and facilitate experimentation in fiber optics for LAN’s including the was supported in part by the National Science Foundation under Grant Manuscript received January 7, 1985; revised July 28, 1985. This work CDR-84-21402 and in part by the New York State Center for Advanced Technology under Project NYSSTF CAT (84)-15 zyxwvutsr 005. University, New York, NY. He is now with the Israeli Ministry of A. Patir was with the Department of Electrical Engineering, Columbia Defense, Tel Aviv, Israel. T. Takahashi was with the Department of Electrical Engineering, ColumbiaUniversity, New York, NY. He is now with the Musashino Electrical Communication Laboratory of the Nippon Telegraph andTele- phone Corporation, Ja an Y. Tamura was witg the Department of Electrical Engineering, Col- umbia University, New York, NY. He is now with the Department of Digital Systems Development, NEC Corporation, Japan. umbia Universitv. New York. NY 10027. M. El Zarki is with the Department of Electrical Engineering, Col- A. A. Lazar Is with the Department of Electrical Engineering and Center for Telecommunications Research, Columbia University, New York. NY 10027. testing of new coding techniques and wave-division multi- plexing schemes. The ILAN that forms part of the NTB is structured to support the class of possible solutions described in [2]. The goal is to provide a system that can handle both sequential and simultaneous scheduling algorithms, and that incorpo- rates the round-robin mechanisms and allocation schemes discussed in [2]. To efficiently integrate traffic classes having different service requirements, the ILAN implements the two modes of operation that were introduced in [2] and are referred to as the circuit- and packet-switching modes. These modes are managed by a centralized network controller that has global knowledge of the loop utilization. The media-access protocol employs round-robin mechanisms that are imple- mented on a synchronous TDM optical ring structure. A variety of allocation schemes are implemented at the media level through the use of access codes ‘in the TDM slots to meet the service requirements dictated by the higher layers. These codes are used to dictate the type of traffic that a source may transmit during a slot. The slots are generated by a centralized network-controller that is responsible for network timing and synchronization. Depending upon the scheme being implemented, the controller inserts the ap- propriate access code by which a source may determine its eligibility for transmission of a specific traffic class. A variety of schemes are obtained at this level by formatting the TDM slots into cycles to which codes are designated. The transmission eligibility of a station with full buffers is based upon this cycle mechanism and associated access codes. MAGNET’S ILAN is based on two counterrotating rings. Optical links interconnect active nodes that regenerate the signal as it rotates around the loop. The above design choice was based on the following reasons: 1) Combined with the media-access scheme, high utilizations can be achieved. 2) Implementation of priority schemes on a ring for round-robin allocation mechanisms is relatively easy. 3) As each link is an independent connection, ring reconfig- uration is simple. The optical link operates on two different optical frequencies to implement the two uni- directional transmission paths. In the detailed design, expe- rience acquired in some other experimental networks (re- ported in [3], [6], [8], and [5]) was incorporated. Some of the digital circuit design developed for Fasnet was used in the implementation of the ILAN. 0733-8716/85/1100-0872$01.00 01985 IEEE