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Passive Optical Star With WDM Couplers for Hybrid Access Control and Overflow Prevention Disclosure Number: IPCOM000036450D
Original Publication Date: 1989-Sep-01
Included in the Prior Art Database: 2005-Jan-29
Document File: 5 page(s) / 82K

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This article describes a hybrid access control for a slotted passive optical star.

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Passive Optical Star With WDM Couplers for Hybrid Access Control and Overflow Prevention

This article describes a hybrid access control for a slotted passive optical star.

The invention exploits commercially available technological advances in the construction of (i) single-mode passive star couplers and (ii) wavelength division multiplexing (WDM) couplers [1], which can efficiently merge and split two distinct wave lengths. One wavelength, g1, constitutes the data channel, and the other wavelength, g2, is used for network control. The following solution has two components: (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. Passive Optical Star with WDMCouplers

Fig. 1 depicts a passive optical star with WDM couplers. The

(Image Omitted)

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 usually characterized so that it splits an input signal equally between the two outputs (3 dB attenuation).

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 / 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 circumference, by delaying the information it receives or transmits by TR - Wi, as shown in Fig. 3. As a result, all nodes can synchronize the beginning of their time slots, and can execute distributed algorithms that use the same state information.

The Time Slot: The round trip delay from the imaginary circumference to the center of the optical star, 2TR, is divided into f time slots of equal duration, i.e., f(Ts) = 2TR, The Control and Data Channels

The transmission of control and data over the star is separated into two channels. Over the data channel, using g1, a node can transmit one data packet for the duration of one time slot. Over the control channel, the nodes are using implicit signalling for access control, collision resolution and destination overflow avoidance.


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Implicit signalling means that the receiving signal is not decoded explicitly. Receiving over the control channel just requires the ability to determine, at every instant of time, if the channel is active or not. The advantage of implici...