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Passive Optical Star With a Tunable Receiver for Hybrid Access Control and Overflow Prevention

IP.com Disclosure Number: IPCOM000036398D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 5 page(s) / 76K

Publishing Venue

IBM

Related People

Ofek, Y: AUTHOR

Abstract

This article describes a hybrid access control for a slotted passive optical star. Each node uses a tunable receiver and two fixed-wavelength transmitters for realizing the following control functions: (i) hybrid (random/reservation) access control with collision resolution and (ii) destination overflow prevention.

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Passive Optical Star With a Tunable Receiver for Hybrid Access Control and Overflow Prevention

This article describes a hybrid access control for a slotted passive optical star. Each node uses a tunable receiver and two fixed-wavelength transmitters for realizing the following control functions: (i) hybrid (random/reservation) access control with collision resolution and (ii) destination overflow prevention.

Given a passive optical star with one shared or multiple access data channel, we describe how to construct a control channel. The control channel makes an implicit use of multiple wavelengths. Each node has two transmitters with fixed wavelengths and one tunable receiver. The tunable receiver is used for scanning the spectrum of the transmitters in order to detect the transmitters that are active.

The signalling, with the different wavelengths, over the control channel is not decoded explicitly with a serial-to-parallel converter. Therefore, very simple digital electronic hardware is required for the control channel. The objective of this design is to exploit the abandon fiber-optic spectrum, in order to simplify the control of a multiple access data channel. Only the transmission over the data

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channel is explicitly decoded, i.e., recovering the transmitter clock with a phase- locked loop for the serial-to-parallel conversion.

Using the two fixed-wavelength transmitters, the following functions are implemented in the control channel: (i) hybrid - random/deterministic access control with collision resolution and optimal throughput of 1 (even if only one node is loaded), and (ii) destination overflow prevention which assures no packet loss as a result of an overflow.

The Passive Optical Star: Fig 1 depicts the structure of a passive optical star. The optical star is an array of single-mode star couplers organized as a perfect shuffle. It is assumed that the optical star array is built in a small area in space, so the communication over the star merges to one point in space (called the center of the star), and then broadcasts back to all its nodes. The passive star coupler is a device with two inputs and two outputs, and is usually characterized so that it splits an input signal equally between the two outputs (3 dB attenuation).

On the receiving side of each node there is a tunable filter or receiver which is used for detecting the control information.

Synchronization and Timing: The center of the star serves as a single point- of-time reference to all the n nodes of the network. All nodes are synchronized and the transmission over the passive optical star is divided into equal intervals or time slots, Ts . The Synchronization Procedure:

Let Wi be the delay of nodei from the star's center. An imaginary circle with radius R (such that TR B Wi, 1&i&n) is drawn around all the n nodes of the star. Each nodei knowing its delay from the center, can place itself on this imaginary

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circumference by delaying...