Method of setting up a backup path in a transport network
View Patent ↗Paths in a transport network are identified by labels (n 1 -n 4 , b 1 -b 4 ) and more than one restoration resources that can be used for setting up a particular backup path form a restoration group. Backup tables (R 1 , R 7 ) are provided, which define restoration groups per path labels (b 1 -b 4 ), only, rather than individual restoration resources. Upon initial receipt of a path label (b 1 -b 4 ), a network element ( 1 - 13 ) selects according to pre-determined rules a particular restoration resource from the restoration group defined in the backup table (R 1 -R 7 ) for this backup path label.
1. A method of setting up a backup path in a transport network, wherein the transport network comprises a number of physically interconnected network elements, the method comprising:
assigning labels to paths in the transport network;
providing pre-configured backup tables to at least some network elements in the network, the backup tables defining the assigned labels and a route through the network for the backup path;
activating the backup path at a first network element by inserting into a restoration resource available at a physical link along the route of the backup path the label of the backup path as defined by the backup table locally stored in the first network element; and
upon receipt of the backup path label at a second network element, determining an output port of the second network element for the backup path using the backup table locally stored in the second network element,
wherein a plurality of restoration resources available for the backup path form a restoration group, the backup tables define restoration groups per path labels, and the first and second network elements select a particular restoration resource from the restoration groups for the backup path according to pre-determined rules,
wherein a path in the transport network is represented by a sequence of multiplex units transmitted at a predetermined frame position within consecutive frames and wherein idle frame positions in said frames constitute said restoration resources.
2. The method according to claim 1 , wherein within a restoration group, each resource has assigned a resource number and wherein the predetermined rules include that from the selected restoration group the restoration resource with the lowest resource number shall be selected.
3. The method according to claim 1 , wherein within a restoration group, the path has assigned a priority and wherein the predetermined rules include that in case of contention the path with the higher priority is kept and the request for the path with the lower priority removed.
4. The method according to claim 1 , wherein the predetermined rules include that in the case of a contention, which one of the two network elements adjacent to the contention selects a different resource to resolve the contention.
5. The method according to claim 4 , wherein the network element having the higher node ID selects another resource to resolve the contention.
6. A network element for a transport network comprising:
at least one input port designed for the reception of a transmission signal comprising frames, wherein a sequence of multiplex units transmitted at a predetermined frame position in consecutive frames represents a path through the transport network, and wherein idle frame positions in the frames constitute restoration resources;
a low-level control facility controlling the input port and comprising a memory for storing a backup table provided to the network element, the backup table defining labels and a route through the network for a backup path;
a switch matrix for connecting the multiplex units from the input port to any of a number of output ports under the control of the low-level control facility;
wherein the low-level control facility is adapted to activate the backup path by selecting an output port from the backup table and by inserting into a restoration resource available at the selected output port the label of the backup path as defined by the backup table locally stored in the first network element;
wherein more than one restoration resources available for the backup path form a restoration group, the backup table defines restoration groups per path labels, and the low-level control facility selects a particular restoration resource from the restoration groups for the backup path according to pre-determined rules.
7. A network element for a transport network comprising:
at least one input port designed for the reception of a transmission signal comprising frames, wherein a sequence of multiplex units transmitted at a predetermined frame position in consecutive frames represents a path through the transport network, and wherein idle frame positions in the frames constitute restoration resources;
a low-level control facility controlling the input port and comprising a memory for storing a backup table provided to the network element, the backup table defining labels and a route through the network for a backup path;
a monitor assigned to the input port for checking path labels received at the input port and
a switch matrix for connecting the multiplex units from the input port to any of a number of output ports under the control of the low-level control facility;
wherein the low-level control facility is adapted to determine an output port for a backup path using the backup table upon receipt of a backup path label at the input port and to configure the switch matrix to establish an internal cross-connection between the input port and the selected output port to set up the backup path; and
wherein more than one restoration resources available for the backup path form a restoration group, the backup table defines restoration groups per path labels, and the low-level control facility selects a particular restoration resource from the restoration groups for the backup path according to pre-determined rules.
8. The method according to claim 1 , wherein the path is identified on a basis of links.
9. The method according to claim 8 , wherein the path uses different labels on each of the links.
10. The method according to claim 8 , wherein, when a failure is detected in one of the links, a first and a second node adjacent to the link insert their own respective node identification rather than the label of the path, in a reverse direction.
11. The method according to claim 1 , wherein each of the locally stored backup table includes a destination link and a next label.
12. The method according to claim 1 , wherein each of the locally stored backup tables define more backup paths than backup capacity available.
13. The method according to claim 1 , wherein the multiplex units are repeated with each successive frame in same order.
14. The method according to claim 1 , wherein the frames comprise at least one virtual container, wherein the virtual container corresponds to a higher order multiplexing unit called virtual container.
15. The method according to claim 14 , wherein the at least one virtual container comprises a path overhead and a payload section.
16. The method according to claim 15 , wherein the labels are transported in the path overhead of the multiplex units.
17. The method according to claim 1 , wherein the activating the backup path uses an internal tandem connection (ITC), which is added to the path overhead or removed from the path overhead.
18. The method according to claim 1 , wherein when a failure occurs a particular label is inserted in to the POH of an idle multiple unit.
19. The method according to claim 1 , wherein the multiplex unit corresponds to a timeslot.
20. The method according to claim 1 , wherein the multiplex unit corresponds to a set of timeslots.