Loop-back in dual ring network

Claim 2

A loop-back method for a ring network as claimed in claim 1 wherein working paths are established on a predetermined one of the said two ring lines.

Claim 3

A loop-back method for a ring network as claimed in claim 1 wherein each working path is established independently on either one of the two ring lines.

Claim 4

A loop-back method for a ring network as claimed in claim 2 or claim 3, wherein each protection path is assigned with the same identity number or position as that of the corresponding working path and all paths on one transmission line are looped back to the corresponding paths on the other transmission line.

Claim 5

A loop-back method for a ring network as claimed in claim 2 or claim 3, wherein each path is looped back separately.

Claim 6

A loop-back method for a ring network as claimed in claim 5, wherein working paths are looped back but protection paths are discarded.

Claim 7

A loop-back method for a ring network as claimed in claim 5, wherein protection paths at positions corresponding to the parts of the failed line downstream of a failure are discarded.

Claim 8

A loop-back method for a ring network as claimed in claim 1, wherein loop-back is made at an upstream node on the failed transmission line.

Claim 9

A loop-back method for a ring network as claimed in claim 1, wherein loop-back is made at nodes on both sides of the failed point.

Claim 10

A ring network comprising at least two ring lines having opposite transmission directions and plural nodes arranged on the two ring lines, including means on the said plural nodes for introducing information to a path indicated by a path identity number of the information or a time slot position of a periodic frame, which is characterized in that the said two ring lines are constructed in a manner that a working path between a transmission node and a receiving node is established on one of the two lines, and a protection path of open ring form is established on the other ring line extending from the said receiving node or a node which is one node upstream thereof to the said receiving node, receiving terminals for the two ring lines at the receiving node being connected by a multiplexer, and the said plural nodes are provided with means for looping-back the information on one working path established on a line to the corresponding protection path when a failure is detected on the said line.

Claim 11

A ring network including a plurality of node units connected in series, in a ring, by a plurality of sections of a first transmission line and a plurality of sections of a second transmission line, the sections of the first and second transmission lines each linking adjacent node units, the node units being capable of passing data sequentially around the ring in a first direction, by way of the sections of the first transmission line, from any one node unit serving as an input node to any other node unit serving as an output node, and the node units being capable of passing data sequentially around the ring in the opposite direction to the first direction by way of the sections of the second transmission line, each node unit being capable of cooperating with each adjacent node unit to detect a defect in one of the sections of the first transmission line and, when the node unit is the one immediately upstream of the defect, of effecting connection between the section of the first transmission line immediately upstream of the defective section and the section of the second transmission line which is adjacent to the section of the first transmission line which is immediately upstream of the defective section of line.

Claim 12

A ring network as claimed in claim 11, wherein each node unit is capable of effecting connection between the section of the first transmission line immediately downstream of the defective section of line and the section of the second transmission line which is adjacent to the section of the first transmission line immediately downstream of the defective section of line when the node unit is the one immediately downstream of the defective line.

Claim 13

A ring network as claimed in claim 11 or claim 12, wherein each node unit includes a link map providing data for its transfer connections during normal operation and for its transfer connections when a defect occurs in a section of the first transmission line immediately downstream of that node unit.

Claim 14

A ring network as claimed in claim 13, wherein the link map of each node unit provides data for its transfer connections when a defect occurs in a section of the first transmission line immediately upstream of that node unit.

Claim 15

A ring network as claimed in any one of claims 11 to 14, wherein each node unit includes a multiplexer for selecting data for transmission to its output port when that node unit serves as an output node.