Optical: systems and elements – Deflection using a moving element – Using a periodically moving element
Patent
1996-04-05
1998-06-09
Marcelo, Melvin
Optical: systems and elements
Deflection using a moving element
Using a periodically moving element
370460, 370489, H04L 1256
Patent
active
057643920
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an access control system for a multi-channel digital data transmission ring, especially for an optical ring with wavelength division multiplexing, in which a user or node is exclusively assigned as a data receiving user or node to each of the channels. In particular, the invention pertains to a node applicable in the described access control system.
BACKGROUND OF THE INVENTION
The technical field of the invention relates to communication networks for digital data transmission having a multi-channel ring topology. The networks referred to are known under the abbreviation LAN for Local Area Network, MAN for Metropolitan Area Network, and to a certain extent as WAN for Wide Area Network, respectively.
In a communication network, multiple users or nodes are interconnected by at least one transmission medium. In a ring topology, all node-to-node connections form together a circle through which the data are passed from a transmitting to a receiving node. Rings can be realized using transmission media like twisted pairs of wire, coaxial cables, or optical fibers. Several well known techniques can be employed to establish a multi-channel ring: The simplest approach is to use a number of parallel cables or fibers to interconnect the users of the ring. Another approach utilizes multiplexing techniques. In multiplexing, a common physical connection is shared between the users by dividing, for instance, the available bandwidth of of a transmitting medium into fractions exclusively accessible by one user, these fractions being either frequency fractions (frequency division multiplexing or FDM) or fractions of the complete bandwidth (time division multiplexing or TDM) referred to as time slots. The fraction of the total bandwidth is also referred to as logical channel in contrast to the physical "real" channel. While in electrical signal transmission the frequency multiplexing scheme is known as frequency division multiplexing, in optical networks the term wavelength division multiplexing (WDM) is preferred.
A WDM ring is described in the European patent application EP-A 0520494. From this application, a data transmission system is known, wherein each node is assigned to a wavelength different from other nodes, so, when it detects data on said wavelength, it receives said data for data processing, while data on other wavelengths are passed through. When the node transmits data to one of the other nodes, it generates data having the wavelength assigned to this destination node. Thus, every wavelength has the meaning of an address of the destination node. Further, to every node on the ring at least one time slot for each wavelength is assigned. Thus, the data transfer is strictly pre-coordinated or synchronized. While effectively preventing a collision of data transmitted to the channel, the fixed pre-coordination deteriorates the throughput of the channel, as transmitting users cannot take advantage of free time slots assigned to other nodes.
The method used in EP-A-0520494 and other methods allowing participation of multiple users in a network are generally known as medium access control (MAC) protocols. A MAC protocol serves to control the access of the users to the network, to direct the data from the sending or calling user to the receiving user, to prevent the loss of data, and the like. A major task of such a protocol is to guarantee a fair access of all users or nodes to the connecting network by predetermined criteria. These criteria may include the designation of priorities to certain nodes, the balance between heavy users of the network and occasional users, and managing access loads that exceed the maximum throughput of the network.
An approach (static FDM or TDM) in a MAC is to assign a portion of the transmission capacity to a certain user. However, static assignment is well known for its poor performance. Due to that reason, much work has been concentrated on dynamic bandwidth allocation methods. Two medium access schemes have won dominance in the art, one of which is based on ra
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J.A. Davis et al., "A Local Network For Experiment Support," Proceedings of the National Electronics Conference, vol. 36, pp. 356-362, 1982.
Schindler Hans Rudolf
Van As Harmen Roelof
Flynn John D.
International Business Machines - Corporation
Klett P. M.
Marcelo Melvin
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