Optical network and arrangement and method in such network

Details Optical network and arrangement and method in such network Optical network and arrangement and method in such network

1997-12-29

2000-03-07

Negash, Kinfe-Michael

Optical: systems and elements

Deflection using a moving element

Using a periodically moving element

359110, 370405, H04B 1020, H04J 1400

Patent

active

060347988

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention concerns an optical network which is arranged to ensure communication between nodes in a lower-order loop and a higher-order loop when there is an interruption in the lower-order loop.
The invention also concerns a process for allocating channels in the aforementioned optical network.


PRIOR ART

Within the field of telecommunications there is frequently a need for very high transmission capacity. Data can be transmitted very rapidly by means of optical transmission via modulated light signals.
Large optical networks are frequently constructed as layered or hierarchical networks comprising lower-order or local loops and higher-order or central loops. The lower-order loops are formed by nodes to which a plurality of network subscribers are connected. The nodes are preferably connected to one another via two optical fibres in which messages are sent in opposite directions. Communication between nodes in different lower-order loops is performed in that the messages from and to the lower-order loops are transmitted via one or a plurality of higher-order loops. A hub disposed in the lower-order loop concentrates the traffic from the lower-order loop and transmits it to the higher-order loop. In a corresponding manner, the hub converts the traffic from the higher-order loop and transmits it to the lower-order loop in a suitable form.
A large proportion of the teletrac occurs between different lower-order loops and it is therefore important that the possibilities for communication between a lower-order loop and a higher-order loop are good. In order to ensure this communication it is already known that a plurality of hubs can be arranged in a given lower-order loop.
It is already known from U.S. Pat. No. 5,218,604 to arrange two hubs between a first ring network and a structurally similar higher-order ring network which can be compared with a local loop and a central loop. Both the first and the second ring networks comprise add/drop multiplexers (ADM) by means of which channels can be fed to or tapped from the ring networks. These consist of two lines which transmit data from and to the aforementioned ADM in two different directions, clockwise and anticlockwise in the ring networks.
Each ADM in the ring networks can communicate with both hubs in that the channels are sent in both clockwise and anticlockwise directions in the networks, i.e. the same message is sent in opposite directions on the different lines. All the channels are sent in each line to both hubs which are connected to the two lines in that a given channel received in a first hub is tapped only partially from the line, such that residual remains of this channel can continue on the line to the following hub. A first hub is arranged to transmit the channels received from the one network to a first line in the second ring network and a second hub is arranged to transmit the same channel to a second line in the second network.
A disadvantage with this known solution is that it is only intended for communication between two structurally similar ring networks which communicate only with each other. If the known solution is applied to an optical network, the ring structure causes optical noise to circulate in the ring network, which impairs signal quality. Furthermore the known solution cannot be adapted to layered networks having a plurality of different levels and a plurality of loops in each level.


DESCRIPTION OF THE INVENTION

The object of the present invention is to overcome the problem of ensuring communication between a lower-order loop and a higher-order loop when there is a cable breakdown in the lower-order loop.
This object is achieved by an optical network having one or a plurality of lower-order loops connected to a higher-order loop. The lower-order loop comprises at least one bus network with hubs and one or a plurality of nodes which are connected to one another via two optical fibres. The optical fibres in the bus network are used for transmission in different directions. Each bus network compri

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