Self-healing network with distributed failure restoration capabilities

• US 5,235,599 A
• Filed: 07/26/1990
• Issued: 08/10/1993
• Est. Priority Date: 07/26/1989
• Status: Expired due to Fees

• Current Assignee: NEC Corporation
• Original Assignee: NEC Corporation
• Inventors: Nishimura, Yasuyo, Hasegawa, Satoshi, Sakauchi, Hideki
• Primary Examiner(s): Beausoliel, Jr., Robert W.
• Assistant Examiner(s): Hua, Ly V.
• Application Number:
  US07/556,718
• Time in Patent Office: 1,111 Days
• Field of Search: 371/11.2, 371/8.2, 370/16, 370/16.1, 370/85.9, 340/825.01, 340/825.03, 340/827
• US Class Current: 714/4.21
• CPC Class Codes: G06F 11/1415 at system level
• CPC Class Codes: G06F 11/2007 using redundant communication media
• CPC Class Codes: H04L 1/22 using redundant apparatus to increase reliability
• CPC Class Codes: H04L 45/00 Routing or path finding of packets in data switching networks routing or path finding in wireless networks H04W40/00
• CPC Class Codes: H04L 45/20 Hop count for routing purposes, e.g. TTL
• CPC Class Codes: H04L 45/26 Route discovery packet
• CPC Class Codes: H04L 45/28 using route fault recovery
• CPC Class Codes: H04L 69/40 for recovering from a failure of a protocol instance or entity, e.g. service redundancy protocols, protocol state redundancy or protocol service redirection management of faults, events, alarms or notifications in data switching networks H04L41/06
• CPC Class Codes: H04Q 2213/13141 Hunting for free outlet, circuit or channel
• CPC Class Codes: H04Q 2213/13178 Control signals
• CPC Class Codes: H04Q 2213/13213 Counting, timing circuits
• CPC Class Codes: H04Q 2213/13296 Packet switching, X.25, frame relay
• CPC Class Codes: H04Q 2213/13388 Saturation signaling systems

Abstract

In the event of a failure on a transmission line, a sender, or a terminal node of the failed line, broadcasts CONTROL packets to each of all adjacent tandem nodes, containing a hop count and node trace data. In response to a CONTROL packet, each tandem node increments the hop count of the packet, updates its node trace data, makes a record of all arriving CONTROL packets, and broadcasts copies of each arriving CONTROL packet to adjacent nodes if the hop count is smaller than a prescribed value. A chooser, which is the other terminal node of the failed line, responds to CONTROL packets from a given node for sending back to the given node as many RETURN packets as there are failed channels. Each tandem node makes a record of all arriving RETURN packets, checks the node trace data of each RETURN packet against that of the CONTROL packets in the record to detect if there is a spare channel to an adjacent node on a route to the sender with a least hop count, transmits each RETURN packet to it if a spare channel is detected, or causes retransmission of a RETURN packet from the chooser to another tandem node if no spare channel is detected. The sender responds to each RETURN packet by switching a link from a failed channel to a spare channel indicated by the packet. An END packet is sent back from the sender to each tandem node along which the RETURN packet travelled between the chooser to the sender. On reaching the chooser, the END packet is used to switch a link from a failed channel to a spare channel indicated by the received END packet.

Claims

1. A failure restoration method for a communications network having first and second nodes and a plurality of third nodes, said first, second and third nodes being interconnected by lines having regular and spare channels, wherein said plurality of third nodes are interconnected by spare channels and capable of linking the spare channels for establishing an alternate route between said first and second nodes, comprising the steps of:

a) transmitting, in response to a failure in regular channels terminating at said first node, as many CONTROL packets as there are failed regular channels from said first node to all adjacent ones of said third nodes, each of said CONTROL packets containing a hop count indicating the number of nodes through which the CONTROL packet has travelled and node trace data indicating identifications of nodes through which the CONTROL packet has travelled;

b) making a record of all CONTROL packets arriving at each of said third nodes, and broadcasting copies of a received CONTROL packet from each third node to adjacent nodes located along routes toward said second node if the hop count of the received packet is smaller than a prescribed value, each copy of CONTROL packets containing an incremented hop count and an updated version of the node trace data;

c) responsive to copies of CONTROL packets arriving at said second node, transmitting as many RETURN packets from the second node to a given third node as there are CONTROL packets received from said given third node, each of said RETURN packets containing a route index number, node trace data indicating identifications of nodes through which the RETURN packet has travelled and a spare channel identifier indicating a spare channel which leads to said given third node and forms part of an alternate route for one of said failed channels;

d) making a record of all RETURN packets arriving at said given third node, checking the node trace data of each of the received RETURN packets against the node trace data of the received CONTROL packets in said record to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count and forms part of said alternate route, transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected, and returning a negative acknowledgement packet on a line through which the received RETURN packet was transmitted to cause retransmission of a RETURN packet to another third node if no spare channel is detected, each copy of RETURN packet containing a copy of the route index number, an updated version of the node trace data and an updated version of the spare channel identifier indicating said detected spare channel;

e) responsive to receipt of each copy of RETURN packet, switching a link of said first node from one of said failed channels to a spare channel indicated by the spare channel identifier of the received copy of RETURN packet, and transmitting therefrom an END packet to said indicated spare channel, said END packet containing a copy of said route index number, a failed channel identifier indicating the failed channel of said link and a copy of said spare channel identifier;

f) responsive to receipt of said END packet, making a search through the RETURN packets in said record to detect a RETURN packet having a route index number identical to the route index number of said END packet, establishing a new link through spare channels respectively indicated by the spare channel identifiers of the received END packet and the detected RETURN packet, and transmitting a copy of the received END packet through the new link to said second node, said copy of END packet containing said failed channel identifier and a copy of the spare channel identifier of the received END packet; and

g) responsive to receipt of each copy of END packet, switching a link of said second node from a failed channel to a spare channel indicated respectively by the failed channel identifier and the spare channel identifier of the received copy of END packet.

3. A failure restoration method as claimed in claim 1 or 2, wherein said failed regular channels are assigned different levels of priority, and the step (e) switches the link from said failed channel to said spare channel according to the priority assigned to the failed regular lines.

4. A failure restoration method as claimed in claim 1 or 2, wherein each of said CONTROL packets transmitted from said first node further contains a fault location identifier indicating the location of said line failure in said network for allowing each of said third nodes to discriminate between received packets according to the fault location identifiers of line failures which occur simultaneously at different locations of the network.

5. A failure restoration method as claimed in claim 1 or 2, wherein each of said CONTROL packets transmitted from said first node further contains a priority identifier indicating priority given to each one of said failed regular channels, and each of said RETURN packets transmitted from said second node includes a copy of said priority identifier, wherein each of said third nodes examines the priority identifier contained in a received RETURN packet if a spare channel indicated by the spare channel identifier of the received RETURN packet is already reserved by a transmitted RETURN packet and returns a negative acknowledgment packet to the node from which the RETURN packet was received to cause retransmission of a RETURN packet to another third node if the priority of said received RETURN packet is lower than the priority of said transmitted RETURN packet.

6. A failure restoration method as claimed in claim 1 or 2, wherein said second node makes a record of all CONTROL packets received from said third nodes, makes a search through the node trace data of all CONTROL packets in said record in response to said negative acknowledgment packet to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count, and transmits a RETURN packet to said adjacent node containing a spare channel identifier indicating the detected spare channel.

2. A failure restoration method for a communications network having first and second nodes and a plurality of third nodes, said first, second and third nodes being interconnected by lines having regular and spare channels, wherein said plurality of third nodes are interconnected by spare channels and capable of linking the spare channels for establishing an alternate route between said first and second nodes, comprising the steps of:

a) transmitting, in response to the occurrence of said line failure, a CONTROL packet from said first node to all adjacent ones of said third nodes, said CONTROL packet containing a hop count indicating the number of nodes through which the CONTROL packet has travelled, node trace data indicating identifications of nodes through which the CONTROL packet has travelled, and an available spare channel count indicating the number of spare channels available at said first node;

b) making a record of all CONTROL packets arriving at each of said third nodes, and broadcasting as many copies of a received CONTROL packet from each third node to adjacent nodes located along routes toward said second node as there are spare channels indicated by the received CONTROL packet if the hop count of the received CONTROL packet is smaller than a prescribed value, each copy of CONTROL packets containing an incremented hop count, an available spare channel count indicating the number of available spare channels, and an updated version of the node trace data;

c) responsive to copies of CONTROL packets arriving at said second node from a given one of said third nodes, transmitting as many RETURN packets from the second node to said given third node as there are spare channels indicated by the available spare channel count of the received copy of CONTROL packet, each of said RETURN packets containing a route index number, node trace data indicating identifications of nodes through which the RETURN packet has travelled and a spare channel identifier indicating a spare channel which leads to said given third node and forms part of an alternate route for one of said failed channels;

d) making a record of all RETURN packets arriving at said given third node, checking the node trace data of each of the received RETURN packets against the node trace data of the received CONTROL packets in said record to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count and forms part of said alternate route, transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected, and returning a negative acknowledgement packet on a line through which the received RETURN packet was transmitted if no spare channel is detected to cause retransmission of a RETURN packet to another third node, each copy of RETURN packet containing a copy of the route index number, an updated version of the node trace data and an updated version of the spare channel identifier indicating said detected spare channel;

e) responsive to receipt of each copy of RETURN packet, switching a link of said first node from one of said failed channels to a spare channel indicated by the spare channel identifier of the received copy of RETURN packet, and transmitting therefrom an END packet on the indicated spare channel, said END packet containing a copy of said route index number, a failed channel identifier indicating the failed channel of said link and a copy of said spare channel identifier;

f) responsive to receipt of said END packet, searching through the RETURN packets in said record to detect a RETURN packet having a route index number identical to the route index number of said END packet, establishing a new link through spare channels respectively indicated by the spare channel identifiers of the received END packet and the detected RETURN packet, and transmitting a copy of the received END packet through the new link which leads to said second node, said copy of END packet containing said failed channel identifier and a copy of the spare channel identifier of the received END packet; and

g) responsive to receipt of each copy of END packet, switching a link of said second node from a failed channel to a spare channel indicated respectively by the failed channel identifier and the spare channel identifier of the received copy of END packet.

7. A failure restoration method for a communications network having first and second nodes, and a plurality of third nodes interconnected by regular and spare channels and capable of establishing links through the spare channels for establishing an alternate route between said first and second nodes, said third nodes being located between said first and second nodes, a series of said channels between said first and second nodes forming a path, each of said channels having a different bandwidth, comprising the steps of:

a) detecting, in response to a failure in a path, a spare channel from said first node to each of adjacent ones of said third nodes having a required bandwidth equal to or greater than the bandwidth of the failed path, and transmitting a CONTROL packet from said first node to each of adjacent third nodes if a spare channel having said required bandwidth is detected, said CONTROL packet containing a hop count indicating the number of nodes through which the CONTROL packet has travelled, node trace data indicating identifications of nodes through which the CONTROL packet has travelled, a bandwidth identifier indicating said required bandwidth, and a fault path identifier indicating one of said failed paths;

b) responsive to receipt of each of said CONTROL packets,

(i) making a record of CONTROL packets arriving at each of said third nodes,

(ii) detecting a spare channel from each of said third nodes to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the received CONTROL packet, and

(iii) transmitting a copy of each received CONTROL packet to each adjacent node if a spare channel having said bandwidth is detected and if the hop count of the received CONTROL packet is smaller than a prescribed value, each transmitted copy of CONTROL packet containing updated versions of the hop count, node trace data, and copies of the required bandwidth and fault path identifier;

c) responsive to each copy of CONTROL packet arriving at said second node from a given one of said third nodes, transmitting a RETURN packet from said second node to said given third node, said RETURN packet containing a spare channel identifier indicating a spare channel which leads to said given third node and forms part of an alternate route, an updated version of the node trace data, and a copy of the fault path identifier;

d) at said given third node, responsive to receipt of RETURN packet,

(i) making a record of all RETURN packets arriving at said given third node,

(ii) checking the node trace data of each arriving RETURN packets against the node trace data of the received CONTROL packets to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count and forms part of the alternate route,

(iii) transmitting a copy of each received RETURN packet from said given third node to said adjacent node if a spare channel is detected, and

(iv) returning a negative acknowledgment packet to said second node if no spare channel is detected to cause retransmission of a RETURN packet from the second node to another third node, said copy of RETURN packet containing updated versions of the node trace data and spare channel identifier indicating the detected spare channel and a copy of said fault path identifier;

e) at said first node, responsive to receipt of each copy of RETURN packet,

(i) switching a link of said first node from one of said failed paths to a spare channel indicated by the spare channel identifier of the received copy of RETURN packet, and

(ii) transmitting therefrom an END packet on the indicated switched spare channel, said END packet containing a fault path identifier indicating the failed path of said link and a copy of the spare channel identifier;

f) responsive to receipt of each END packet arriving at each of said third nodes located along a route toward said second node,

(i) making a search through the node trace data of all RETURN packets in said record,

(ii) detecting a RETURN packet whose fault path identifier is identical to the fault path identifier of the received END packet,

(iii) establishing a new link through spare paths respectively indicated by the spare path identifiers of the detected RETURN packet and the received END packet, and

(iv) transmitting a copy of the received END packet to an adjacent node through the new link to said second node, said copy of END packet containing copies of the fault path identifier and spare path identifier of the received END packet; and

g) at said second node, responsive to receipt of the copy of END packet, switching a link of said second node from one of said failed paths indicated by the fault path identifier of the received copy of END packet to a spare channel indicated by the spare channel identifier contained therein.

8. A failure restoration method as claimed in claim 7, wherein each of said CONTROL packets transmitted from said first node further contains a priority identifier indicating priority given to each one of said failed regular paths, and each of said RETURN packets transmitted from said second node includes a copy of said priority identifier, wherein each of said third nodes examines the priority identifier contained in a received RETURN packet if a spare path indicated by the spare path identifier of the received RETURN packet is already reserved by a transmitted RETURN packet and returns a negative acknowledgment packet to the node from which the RETURN packet was received to cause retransmission of a RETURN packet to another third node if the priority of said received RETURN packet is lower than the priority of said transmitted RETURN packet.

9. A failure restoration method as claimed in claim 7, wherein said second node makes a record of all CONTROL packets received from said third nodes, makes a search through the node trace data of all CONTROL packets in said record in response to said negative acknowledgment packet to detect whether there is a spare path to an adjacent node located on a route leading to said first node with a least hop count, and transmits a RETURN packet to said adjacent node containing a spare path identifier indicating the detected spare path.

10. A failure restoration method for a communications network having a plurality of nodes interconnected by regular and spare path sections, there being a plurality of subnetworks each comprising first and second terminal nodes and an intermediate node, the intermediate node providing a link between regular path sections to establish a regular path between said first and second terminal nodes, the nodes of each subnetwork functioning as third nodes of one or more of other subnetworks for establishing a link between spare path sections to form an alternate route between the first and second terminal nodes of said other subnetworks, each of said path sections having a different bandwidth, comprising the steps of:

a) responsive to occurrence of a line failure on one of the regular path sections of said regular path in one of said subnetworks,

(i) transmitting a RELEASE packet from one of said terminal nodes of said subnetwork to the intermediate node thereof to clear a link so that another path section of said regular path is made available for use as a spare path section,

(ii) detecting a spare path section from said first terminal node of said subnetwork to each of adjacent ones of said third nodes having a required bandwidth equal to or greater than the bandwidth of said failed regular path, and

(iii) transmitting a CONTROL packet from said first node to each of adjacent third nodes if a spare path section having said required bandwidth is detected, said CONTROL packet containing a hop count indicating the number of nodes through which the CONTROL packet has travelled, node trace data indicating identifications of nodes through which the CONTROL packet has travelled, a bandwidth identifier indicating said required bandwidth, and a fault path identifier indicating said failed regular path;

b) responsive to receipt of each of said CONTROL packets, making a record of all CONTROL packets arriving at each of said third nodes, detecting a spare path section from each of said third nodes to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the received CONTROL packet, and transmitting a copy of each received CONTROL packet to each adjacent node if a spare path section having said bandwidth is detected and if the hop count of the received CONTROL packet is smaller than a prescribed value, each transmitted copy of CONTROL packet containing updated versions of the hop count, node trace data, and copies of the required bandwidth and fault path identifier;

c) responsive to each copy of CONTROL packet arriving at said second node from a given one of said third nodes, transmitting a RETURN packet from said second node to said given third node, said RETURN packet containing a spare path identifier indicating a spare path section located on a route leading to said given third node and forms part of an alternate route, an updated version of the node trace data, and a copy of the fault path identifier;

d) at said given third node,

(i) making a record of all RETURN packets arriving at said given third node,

(ii) checking the node trace data of each arriving RETURN packets against the node trace data of the received CONTROL packets to detect whether there is a spare path section to an adjacent node located on a route leading to said first terminal node of said subnetwork with a least hop count and forms part of the alternate route,

(iii) transmitting a copy of each received RETURN packet from said given third node to said adjacent node if a spare path section is detected, and

(iv) or returning a negative acknowledgment packet to said second node if no spare path section is detected, to cause retransmission of a RETURN packet from the second node to another third node, said copy of RETURN packet containing updated versions of the node trace data and spare path section identifier indicating the detected spare path section and a copy of said fault path identifier;

e) at the first terminal node of said subnetwork, responsive to receipt of each copy RETURN packet,

(i) switching a link of said first terminal node of said subnetwork from said failed regular path to a spare path section indicated by the spare path section identifier of the received copy of RETURN packet, and

(ii) transmitting therefrom an END packet to said switched spare path section, said END packet containing a fault path identifier indicating the failed regular path of said link and an updated version of the spare path section identifier indicating said switched spare path section;

f) responsive to receipt of each END packet arriving at each of said third nodes located along a route toward said second terminal node of said subnetwork,

(i) searching through the node trace data of all RETURN packets in said record and detecting a RETURN packet whose fault path identifier is identical to the fault path identifier of the received END packet,

(ii) establishing a new link through spare path sections respectively indicated by the spare path section identifiers of the detected RETURN packet and the received END packet, and

(iii) transmitting a copy of the received END packet to an adjacent node on said new link to said second node, said copy of END packet containing copies of the fault path identifier and spare path identifier of the received END packet; and

g) at the second terminal node of said subnetwork, responsive to receipt of the copy of END packet, switching a link of said second terminal node of said subnetwork from said failed regular path indicated by the fault path identifier of the received copy of END packet to a spare path section indicated by the spare path section identifier contained therein.

11. A self-healing communications network having a plurality of nodes interconnected by lines having regular and spare channels, two of said nodes functioning as first and second nodes when a line failure occurs on a regular channel interconnecting said first and second nodes, and the other nodes functioning as third nodes and capable of linking spare channels for establishing an alternate route between said first and second nodes, each of said nodes comprising:

means, responsive to the occurrence of said line failure, for transmitting as many CONTROL packets to all adjacent nodes as there are failed regular channels when functioning as said first node, each of said CONTROL packets containing a hop count indicating the number of nodes through which the CONTROL packet has travelled and node trace data indicating identifications of nodes through which the CONTROL packet has travelled, including,

means for incrementing the hop count of an arriving CONTROL packet,

means for updating the node trace data of the arriving CONTROL packet,

means for making a record of all arriving CONTROL packets, and

means for broadcasting copies of each arriving CONTROL packet to adjacent nodes if the hop count of each arriving CONTROL packet is smaller than a prescribed value;

means, responsive to copies of arriving CONTROL packets from a given adjacent node, for transmitting as many RETURN packets to said given node as there are said arriving CONTROL packets when functioning as said second node, each of said RETURN packets containing a route index number, node trace data indicating identifications of nodes through which the RETURN packet has travelled and a spare channel identifier indicating a spare channel leading to an adjacent node and forms part of an alternate route for one of said failed channels;

means for making a record of all arriving RETURN packets when functioning as one of said third nodes, checking the node trace data of each of the arriving RETURN packets against the node trace data of the received CONTROL packets in said record to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count and forms part of said alternate route, transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected, and returning a negative acknowledgment packet on a line through which the received RETURN packet was transmitted to cause retransmission of a RETURN packet to another third node if no spare channel is detected, each copy of RETURN packet containing a copy of the route index number, an updated version of the node trace data and an updated version of the spare channel identifier indicating said detected spare channel;

means, responsive to receipt of each copy of RETURN packet when functioning as said first node, for switching a link from one of said failed channels to a spare channel indicated by the channel identifier of the received copy of RETURN packet, and transmitting an END packet in a direction parallel to said switched spare channel, said END packet containing a copy of said route index number, a failed channel identifier indicating the failed channel of said link and a spare channel identifier indicating the switched spare channel;

means, responsive to receipt of said END packet when functioning as one of said third nodes, for making a search through the RETURN packets in said record to detect a RETURN packet having a route index number identical to the route index number of said END packet, establishing a new link through spare channels respectively indicated by the channel identifiers of the received END packet and the detected RETURN packet, and transmitting a copy of the received END packet on the new link to said second node, said copy of END packet containing said failed channel identifier and a copy of the spare channel identifier of the received END packet; and

means responsive to receipt of each copy of END packet when functioning as said second node for switching a link from one of the failed channels to a spare channel indicated respectively by the failed channel identifier and the spare channel identifier of the received copy of END packet.

13. A self-healing communications network as claimed in claim 11 or 12, wherein said failed regular channels are assigned different levels of priority, and wherein each of said nodes, when functioning as said first node, switches the link from said failed channel to said spare channel according to the priority assigned to the failed regular channels.

14. A self-healing communications network as claimed in claim 11 or 12, wherein each of said CONTROL packets transmitted from each node when functioning as said first node further contains a fault location identifier indicating the location of said failure in said network for allowing each of said third nodes to discriminate between received packets according to the fault location identifiers of failures which occur simultaneously at different locations of the network.

15. A self-healing communications network as claimed in claim 11 or 12, wherein each of said CONTROL packets transmitted from a node functioning as said first node further contains a priority identifier indicating priority given to each one of said failed regular channels, and each of said RETURN packets transmitted from a node functioning as said second node includes a copy of said priority identifier, wherein each of said nodes when functioning as one of said third nodes, includes means for examining the priority identifier contained in a received RETURN packet if a spare channel indicated by the spare channel identifier of the received RETURN packet is already reserved by a transmitted RETURN packet and returns a negative acknowledgment packet to the node from which the RETURN packet was received to cause retransmission of a RETURN packet to another third node if the priority of said received RETURN packet is lower than the priority of said transmitted RETURN packet.

16. A self-healing communications network as claimed in claim 15, wherein each node, when functioning as said second node, includes means for making a record of all arriving CONTROL packets, making a search through the node trace data of all CONTROL packets in said record in response to said negative acknowledgment packet to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count, and transmitting a RETURN packet to said adjacent node containing a spare channel identifier indicating the detected spare channel.

12. A self-healing communications network having a plurality of nodes interconnected by regular and spare channels, two of said nodes acting as first and second nodes when a line failure occurs on a regular channel interconnecting said first and second nodes, and other nodes functioning as third nodes capable of linking spare channels for establishing an alternate route between said first and second nodes, each of said nodes comprising:

means, responsive to the occurrence of said line failure, for transmitting a CONTROL packet to all adjacent nodes when functioning as said first node, said CONTROL packet containing a hop count indicating the number of nodes through which the CONTROL packet has travelled and node trace data indicating identifications of nodes through which the CONTROL packet has travelled, and a spare channel count indicating the number of available spare channels, including;

means for incrementing the hop count of an arriving CONTROL packet,

means for updating the node trace data of the arriving CONTROL packet,

means for making a record of all arriving CONTROL packets, and

means for broadcasting copies of each arriving CONTROL packet to adjacent nodes if the hop count of each arriving CONTROL packet is smaller than a prescribed value;

means, responsive to receipt of said CONTROL packet, when functioning as a third node, for broadcasting as many copies of the received CONTROL packet as there are spare channels indicated by the received CONTROL packet, said copy of said CONTROL packet containing a spare channel count;

means, responsive to each copy of arriving CONTROL packet from a given adjacent node, for transmitting as many RETURN packets to said given node as there are spare channels indicated by the spare channel count of said arriving CONTROL packet when functioning as said second node, each of said RETURN packets containing a route index number, node trace data indicating identifications of nodes through which the RETURN packet has travelled and a spare channel identifier indicating a spare channel which leads to a given third node and forms part of an alternate route for one of said failed channels;

means for making a record of all arriving RETURN packets when functioning as one of said third nodes and checking the node trace data of each of the arriving RETURN packets against the node trace data of the received CONTROL packets in said record to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count and forms part of said alternate route, transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected, and returning a negative acknowledgment packet on a channel through which the received RETURN packet was transmitted to cause retransmission of a RETURN packet to another third node if no spare channel is detected, each copy of RETURN packet containing a copy of the route index number, an updated version of the node trace data and an updated version of the spare channel identifier indicating said detected spare channel;

means, responsive to receipt of each copy of RETURN packet when functioning as said first node, for switching a link from one of said failed channels to a spare channel indicated by the channel identifier of the received copy of RETURN packet, and transmitting an END packet to said switched spare channel, said END packet containing a copy of said route index number, a failed channel identifier indicating the failed channel of said link and a spare channel identifier indicating the switched spare channel;

means, responsive to receipt of said END packet when functioning as one of said third nodes, for making a search through the RETURN packets in said record to detect a RETURN packet having a route index number identical to the route index number of said END packet, establishing a link between spare channels respectively indicated by the channel identifiers of the received END packet and the detected RETURN packet, and transmitting a copy of the received END packet on said new link to said second node, said copy of END packet containing said failed channel identifier and a copy of the spare channel identifier of the received END packet; and

means responsive to receipt of each copy of END packet when functioning as said second node for switching a link from one of the failed channels to a spare channel indicated respectively by the failed channel identifier and the spare channel identifier of the received copy of END packet.

17. A self-healing communications network having a plurality of nodes interconnected by regular and spare paths, two of said nodes functioning as first and second nodes when a line failure occurs on a regular path interconnecting said first and second nodes, and the other nodes functioning as third nodes capable of linking spare paths for establishing an alternate route between said first and second nodes, each of said paths being formed by a series of channels having a different bandwidth, each of said nodes comprising:

means, responsive to occurrence of said line failure, for detecting a spare channel to each adjacent node having a required bandwidth equal to or greater than the bandwidth of one of failed paths when functioning as said first node, and transmitting a CONTROL packet to each adjacent node if a spare channel having said required bandwidth is detected, said CONTROL packet containing a hop count indicating the number of nodes through which the CONTROL packet has travelled, node trace data indicating identifications of nodes through which the CONTROL packet has travelled, a bandwidth identifier indicating said required bandwidth, and a fault path identifier indicating one of said failed path;

means, responsive to receipt of each arriving CONTROL packet when functioning as one of said third nodes, for detecting a spare channel to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the arriving CONTROL packet, including

means for making a record of all arriving CONTROL packets,

means for incrementing the hop count of the arriving CONTROL packet,

means for updating the node trace data of the arriving CONTROL packet,

means for making a record of all arriving CONTROL packets, and

means for retransmitting a copy of each arriving CONTROL packet to adjacent nodes if a spare channel having said required bandwidth is detected and if the hop count of the arriving CONTROL packet is smaller than a prescribed value;

means, responsive to each copy of CONTROL packet arriving at said second node from a given third node when functioning as said second node, for transmitting a RETURN packet to said given third node, said RETURN packet containing a spare channel identifier indicating a spare path which leads to said given third node and forms part of an alternate route, an updated version of the node trace data, and a copy of the fault path identifier;

means for checking the node trace data of each arriving RETURN packets against the node trace data of the arriving CONTROL packets, when functioning as one of said third nodes, to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count and forms part of the alternate route, updating the arriving RETURN packet in respect to the node trace data and spare channel identifier so that the spare channel identifier contains the detected spare channel and the fault path identifier thereof is copied, for making a record of all arriving RETURN packets, transmitting the updated packet as a copy of the received RETURN packet to said adjacent node if a spare channel is detected, and returning a negative acknowledgment packet to said second node if no spare channel is detected to cause retransmission of a RETURN packet from the second node to another third node;

means, responsive to receipt of each copy of arriving RETURN packet when functioning as said first node for switching a link from one of said failed paths to a spare channel indicated by the spare channel identifier of the received copy of RETURN packet, and transmitting an END packet to said switched spare path, said END packet containing a fault path identifier indicating the failed path of said link and an updated version of the spare path identifier indicating said switched spare path;

means, responsive to receipt of each arriving END packet when functioning as one of said third nodes located along a route toward said second node, for making a search through the node trace data of all RETURN packets in said record and detecting a RETURN packet whose fault path identifier is identical to the fault path identifier of the received END packet, establishing a new link through spare channels respectively indicated by the spare path identifiers of the detected RETURN packet and the received END packet, and transmitting a copy of the received END packet to an adjacent node on said new link to said second node, said copy of END packet containing copies of the fault path identifier and spare path identifier of the received END packet; and

means, responsive to receipt of the copy of END packet when functioning as said second node, for switching a link from one of said failed paths indicated by the fault path identifier of the received copy of END packet to a spare channel indicated by the spare channel identifier contained therein.

19. A self-healing communication network as claimed in claim 17 or 18, wherein each of said CONTROL packets transmitted from said first node further contains a priority identifier indicating priority given to each one of said failed regular paths, and each of said RETURN packets transmitted from said second node includes a copy of said priority identifier, wherein each of said third nodes includes means for examining the priority identifier contained in a received RETURN packet if a spare path indicated by the spare path identifier of the received RETURN packet is already reserved by a transmitted RETURN packet and returning a negative acknowledgment packet to the node from which the RETURN packet was received to cause retransmission of a RETURN packet to another third node if the priority of said received RETURN packet is lower than the priority of said transmitted RETURN packet.

20. A self-healing communications network as claimed in claim 17 or 18, wherein said second node includes means for making a record of all CONTROL packets received from said third nodes, making a search through the node trace data of all CONTROL packets in said record in response to said negative acknowledgment packet to detect whether there is a spare path to an adjacent node located on a route leading to said first node with a least hop count, and transmitting a RETURN packet to said adjacent node containing a spare path identifier indicating the detected spare path.

21. A self-healing communications network as claimed in claim 19, wherein each of said nodes includes means for transmitting said packets of any type according to the priority identifier of a packet to be transmitted.

18. A self-healing communications network having a plurality of nodes interconnected by lines having regular and spare path sections, there being a plurality of subnetworks each comprising first and second terminal nodes and an intermediate node, the intermediate node providing a link between regular path sections to establish a regular path between said first and second terminal nodes, the nodes of each subnetwork function as third nodes of one or more of the other subnetworks for establishing a link between spare path sections to form an alternate route between the first and second terminal nodes of said other subnetworks, each of said path sections having a different bandwidth, each of said nodes comprising:

means, responsive to occurrence of a line failure on one of the regular path sections of said regular path in one of said subnetworks, for transmitting a RELEASE packet to said intermediate node to cause said intermediate node to clear a link so that another path sections of said regular path is made available for use as a spare path section, detecting a spare path section to each adjacent node having a required bandwidth equal to or greater than the bandwidth of said failed regular path, transmitting a CONTROL packet to each adjacent node if a spare path section having said required bandwidth is detected, said CONTROL packet containing a hop count indicating the number of nodes through which the CONTROL packet has travelled, node trace data indicating identifications of nodes through which the CONTROL packet has travelled, a bandwidth identifier indicating said required bandwidth, and a fault path identifier indicating said failed regular path;

means, responsive to receipt of each arriving CONTROL packet when functioning as one of said third nodes, for making a record of all arriving CONTROL packets, detecting a spare path section to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the arriving CONTROL packet, and transmitting a copy of each received CONTROL packet to each adjacent node if a spare path section having said bandwidth is detected and if the hop count of the received CONTROL packet is smaller than a prescribed value, each transmitted copy of CONTROL packet containing updated versions of the hop count, node trace data, and copies of the required bandwidth and fault path identifier;

means, responsive to each copy of arriving CONTROL packet from a given third node when functioning as said second node, for transmitting a RETURN packet to said given third node, said RETURN packet containing a spare path section identifier indicating a spare path section which leads to said given third node and forms part of an alternate route, an updated version of the node trace data, and a copy of the fault path identifier;

means for checking the node trace data of each arriving RETURN packets against the node trace data of the received CONTROL packets, when functioning as one of said third nodes, to detect whether there is a spare path section to an adjacent node located on a route leading to said first terminal node with a least hop count and forms part of the alternate route, making a record of all arriving RETURN packets, transmitting a copy of each received RETURN packet from said given third node to said adjacent node if a spare path section is detected, and returning a negative acknowledgment packet to a line through which the received RETURN packet was transmitted if no spare path section is detected to cause retransmission of a RETURN packet to another third node, said copy of RETURN packet containing updated versions of the node trace data and spare path section identifier indicating the detected spare path section and a copy of said fault path identifier;

means, responsive to receipt of each copy of arriving RETURN packet when functioning as said first node, for switching a link from said failed regular path to a spare path section indicated by the spare path identifier of the received copy of RETURN packet, and transmitting therefrom an END packet in a direction parallel to said switched spare path section, said END packet containing a fault path identifier indicating the failed regular path of said link and an updated version of the spare path identifier section indicating said switched spare path section;

means, responsive to receipt of each arriving END packet when functioning as one of said third nodes located along a route toward said second terminal node, for making a search through the node trace data of all RETURN packets in said record and detecting a RETURN packet whose fault path identifier is identical to the fault path identifier of the received END packet, establishing a new link through spare path sections respectively indicated by the spare path identifiers section of the detected RETURN packet and the received END packet, and transmitting a copy of the received END packet to an adjacent node on said new link to said second node, said copy of END packet containing copies of the fault path identifier and spare path identifier of the received END packet; and

means, responsive to receipt of the copy of arriving END packet when functioning as second node, for switching a link from said failed regular path indicated by the fault path identifier of the received copy of END packet to a spare path section indicated by the spare path identifier section contained therein.

22. A failure restoration method for a communications network having first and second nodes and a plurality of third nodes, said first, second and third nodes being interconnected by lines having regular channels and spare channels, said third nodes being located between said first and second nodes, said regular and spare channels terminating at said first and second nodes, the method comprising the steps of:

a) responsive to a failure in regular channels terminating at said first node, transmitting from the first node as many CONTROL packets as there are failed regular channels to adjacent ones of said third nodes;

b) broadcasting copies of a received CONTROL packet from each third node to adjacent nodes;

c) at said second node, responsive to each copy of CONTROL packets arriving thereat, transmitting a RETURN packet therefrom to a given third node;

d) at said given third node, responsive to said RETURN packet,

(i) determining whether there is a spare channel to an adjacent node located on a route leading to said first node,

(ii) transmitting a copy of the received RETURN packet to said adjacent node if a spare channel is detected, and

(iii) returning a negative acknowledgement packet on a line through which said received RETURN packet was transmitted to cause retransmission of a RETURN packet to another third node if no spare channel is detected;

e) at said first node, responsive to receipt of each copy of RETURN packet,

(i) switching a link of the first node from one of said failed channels to a spare channel extending to said given third node thereby establish a switched channel, and

(ii) transmitting an END packet to the switched channel;

f) at said given third node, responsive to receipt of said END packet,

(i) establishing a new link through the switched channel and a spare channel to the second node, and

(ii) transmitting a copy of the received END packet to said second node through the spare channel of the new link; and

g) at said second node, responsive to receipt of each copy of END packet, switching a link of the second node from a failed channel to the new link.

26. A failure restoration method as claimed in claim 22, 23, 24 or 25, wherein said failed regular channels are assigned different levels of priority, and the step (e) includes providing the switching (e) (i) of said link in an order specified by the assigned priority of the failed regular channels.

27. A failure restoration method as claimed in claim 22, 23, 24 or 25, further comprising, at said first node, the steps of inserting into each of said CONTROL packets transmitted therefrom a fault location identifier indicating the location of said failure in said network for allowing each of said third nodes to discriminate between received packets according to different locations of failures which occur simultaneously in the network.

28. A failure restoration method as claimed in claim 22, 23, 24 or 25, further comprising the steps of:

at said first node, inserting, into each of said CONTROL packets transmitted therefrom a priority identifier indicating priority given to each one of said failed regular channels;

at said second node, inserting into each of said RETURN packets transmitted therefrom a copy of said priority identifier; and

at each of said third nodes, examining the priority identifier contained in a received RETURN packet if a spare channel indicated by the spare channel identifier of the received RETURN packet is already reserved by a transmitted RETURN packet and returning a negative acknowledgement packet to the node from which the RETURN packet was received to cause retransmission of a RETURN packet to another third node if the priority of said received RETURN packet is lower than the priority of said transmitted RETURN packet.

29. A failure restoration method as claimed in claim 22, 23, 24 or 25, further comprising, at said second node, the steps of:

recording all CONTROL packets received from said third nodes;

searching through the CONTROL packets in said record in response to said negative acknowledgement packet to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count; and

transmitting a RETURN packet to said adjacent node containing a spare channel identifier indicating the detected spare channel.

35. A failure restoration method as claimed in claim 22, 23, 24, 25, 30, 31, or 32, further comprising the steps of:

at each of said first, second and third nodes, inserting into each of said CONTROL packets a hop count indicating the number of nodes through which the CONTROL packet has travelled; and

at each of said third nodes;

examining each of said CONTROL packets,

broadcasting said copies of the CONTROL packet if the hop count of the received CONTROL packet is smaller than a predetermined value,

inserting an incremented hop count into each copy of the broadcast CONTROL packet,

making a record of all CONTROL packets arriving thereat,

searching through said record in response to receipt of a RETURN packet for detecting a CONTROL packet having a least hop count along a route having a spare channel, and

transmitting a copy of the received RETURN packet on said route.

36. A failure restoration method as claimed in claim 22, 23, 24, 25, 30, 31, or 32, further comprising the steps of:

at each of said first and third nodes, inserting node trace data into each of said CONTROL packets, the node trace data identifying the nodes through which the CONTROL packet has travelled;

at each of said second and third nodes, inserting node trace data into each of said RETURN packets, the node trace data identifying the nodes through which the RETURN packet has travelled; and

at each of said third nodes, updating the node trace data of a received packet and transmitting a copy of the received packet to those third nodes which are not indicated in the node trace data of the received packet.

37. A failure restoration method as claimed in claims 22, 23, 24, 25, 30, or 31, wherein the step (d) further comprising the step of inserting to said RETURN packet a reserved channel identifier indicating that a spare channel of a transmission line through which the RETURN packet is sent is reserved to prevent the spare channel from being accessed by other packets.

23. A failure restoration method for a communications network having first and second nodes and a plurality of third nodes, said first, second and third nodes being interconnected by lines having regular channels and spare channels, said third nodes being located between said first and second nodes, said regular and spare channels terminating at said first and second nodes, the method comprising the steps of:

a) transmitting, in response to a failure in regular channels terminating at said first node, a CONTROL packet from said first node to adjacent ones of said third nodes, said CONTROL packet indicating the number of available spare channels;

b) broadcasting copies of a received CONTROL packet from the third node to adjacent nodes each copy of CONTROL packet indicating the number of available spare channels;

c) at said second node, responsive to each copy of CONTROL packet arriving thereat from a given one of said third nodes, transmitting as many RETURN packets from the second node to said given third node as there are available spare channels indicated by the received copy of CONTROL packet;

d) at said given third node,

(i) determining whether there is a spare channel to an adjacent node located on a route leading to said first node,

(ii) transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected, and

(iii) returning a negative acknowledgment packet on a line through which said received RETURN packet was transmitted if no spare channel is detected to cause retransmission of a RETURN packet to another third node;

e) at said first node, responsive to receipt of each copy of RETURN packet,

(i) switching a link from one of said failed channels to a spare channel extending to said given third node to thereby establish a switched channel, and

(iii) transmitting an END packet to the switched channel;

f) at said given third node, responsive to receipt of said END packet,

(i) establishing a new link through the switched channel and a spare channel to said second node, and

(ii) transmitting a copy of the received END packet to the second node through the new link; and

g) at said second node, responsive to receipt of each copy of END packet, switching a link of the second node from a failed channel to the new link.

24. A failure restoration method for a communications network having first and second nodes and a plurality of third nodes, said first, second and third nodes being interconnected by lines having regular channels and spare channels, said third nodes being located between said first and second nodes, said regular and spare channels terminating at said first and second nodes, the method comprising the steps of:

a) transmitting, in response to a failure in regular channels terminating at said first node, as many CONTROL packets as there are failed regular channels from said first node to each adjacent one of said third nodes;

b) at each of said adjacent third nodes, broadcasting copies of a received CONTROL packet therefrom to adjacent nodes;

c) at said second node, responsive to each copy of CONTROL packet arriving thereat, transmitting a RETURN packet therefrom to a given third node, each of said RETURN packets containing a route index number and a spare channel identifier indicating a spare channel which leads to said given third node and forms part of an alternate route to one of said failed channels;

d) at said given third node,

(i) making a record of all RETURN packets arriving thereat,

(ii) determining whether there is a spare channel to an adjacent node located on a route leading to said first node,

(iii) transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected, and

(iv) returning a negative acknowledgment packet on a line through which received RETURN packet was received to cause retransmission of a RETURN packet to another third node if no spare channel is detected, each copy of RETURN packet containing a copy of the route index, and a spare channel identifier indicating said detected spare channel;

e) at said first node, responsive to receipt of each copy of RETURN packet,

(i) switching a link of the first node from one of said failed channels to a spare channel indicated by the channel identifier of the received copy of RETURN packet, and

(ii) transmitting therefrom an END packet on the indicated spare channel, said END packet containing a copy of said route index number, and a copy of said spare channel identifier;

f) at said given third node, responsive to receipt of said END packet,

(i) making a search through said record to detect a RETURN packet having a route index number identical to the route index number of said END packet,

(ii) establishing a new link through spare channels respectively indicated by the spare channel identifiers of the received END packet and the detected RETURN packet, and

(iii) transmitting a copy of the received END packet through the new link to said second node, said copy of END packet containing a copy of the spare channel identifier of the received END packet; and

g) at said second node, responsive to receipt of each copy of END packet, switching a link of the second node from a failed channel to a spare channel indicated by the spare channel identifier of the received copy of END packet.

25. A failure restoration method for a communications network having first and second nodes and a plurality of third nodes, said first, second and third nodes being interconnected by lines having regular channels and spare channels, said third nodes being located between said first and second nodes, said regular and spare channels terminating at said first and second nodes, the method comprising the steps of:

a) transmitting, in response to a failure in regular channels terminating at said first node, a CONTROL packet therefrom to all adjacent ones of said third nodes, said CONTROL packet indicating the number of available spare channels;

b) at each of said adjacent third nodes, responsive to receipt of a CONTROL packet from the first node, broadcasting copies of the received CONTROL packet therefrom the adjacent nodes, each copy of CONTROL packets indicating the number of available spare channels;

c) at said second node, responsive to receipt of copies of CONTROL packet arriving thereat from a given one of said third nodes, transmitting as many RETURN packets therefrom to said given third node as there are available spare channels indicated by each of the received copies of CONTROL packet, each of said RETURN packets containing a route index number and a spare channel identifier indicating a spare channel which leads to said given third node and forms part of an alternate route for one of said failed channels;

d) at said given third node,

(i) making a record of all RETURN packets arriving thereat,

(ii) determining whether there is a spare channel to an adjacent node located on a route leading to said first node,

(iii) transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected, and

(iv) returning a negative acknowledgement packet on a line through which the received RETURN packet was transmitted if no spare channel is detected to cause retransmission of a RETURN packet to another third node, each copy of RETURN packet containing a copy of the route index number and an updated version of the spare channel identifier indicating said detected spare channel;

e) at said first node, responsive to receipt of each copy of RETURN packet;

(i) switching a link of the first node from one of said failed channels to a spare channel which is indicated by the spare channel identifier of the received copy of RETURN packet, and

(ii) transmitting therefrom an END packet on the indicated spare channel, said END packet containing a copy of said route index number and a copy said spare channel identifier of the received RETURN packet;

f) at said given third node, responsive to receipt of said END packet;

(i) searching through the RETURN packets in said record to detect a RETURN packet having a route index number identical to the route index number of said END packet;

(ii) establishing a new link through spare channels respectively indicated by the spare channel identifiers of the received END packet and the detected RETURN packet, and

(iii) transmitting a copy of the received END packet through the new link to said second node, said copy of END packet containing a copy of the spare channel identifier of the received END packet; and

g) at said second node, responsive to receipt of each copy of END packet, switching a link of the second node from a failed channel to a spare channel indicated by the spare channel identifier of the received copy of END packet.

30. A failure restoration method for a communications network having first and second nodes and a plurality of third nodes, said first, second and third nodes being interconnected by lines having regular and spare channels, said third nodes being located between said first and second nodes, a series of said channels extending between said first and second node forming a path, the method comprising the steps of:

a) responsive to a failure in said path terminating at said first node;

(i) detecting a spare channel from said first node to each of adjacent ones of said third nodes having a required bandwidth equal to or greater than the bandwidth of the failed path, and

(ii) transmitting a CONTROL packet from said first node to each of adjacent third nodes if a spare channel having said required bandwidth is detected, said CONTROL packet containing a bandwidth identifier indicating said required bandwidth and a fault path identifier indicating said failed path;

b) at each of said third nodes, responsive to receipt of each of said CONTROL packets,

(i) making a record of CONTROL packets,

(ii) detecting a spare channel extending from each of said third nodes to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the received CONTROL packet, and

(iii) transmitting a copy of each received CONTROL packet to each adjacent node if a spare channel having said bandwidth is detected, each transmitted copy of CONTROL packet containing copies of the required bandwidth and fault path identifier;

c) at said second node, responsive to each copy of CONTROL packet arriving thereat from a given one of said third nodes, transmitting a RETURN packet from said second node to said given third node, said RETURN packet containing a copy of the fault path identifier;

d) at said given third node, responsive to said RETURN packet,

(i) determining whether there is a spare channel to an adjacent node located on a route leading to said first node,

(ii) transmitting a copy of the received RETURN packet from said given third node to said adjacent node if a spare channel is detected, and

(iii) returning a negative acknowledgement packet on a line through which the received RETURN packet was transmitted if no spare channel is detected to cause retransmission of a RETURN packet to another third node, said copy of RETURN packet containing a copy of said fault path identifier;

e) at said first node, responsive to receipt of each copy of RETURN packet,

(i) switching a link of the first node from said failed path to a spare channel extending to a third node to thereby establish a switched channel, and

(ii) transmitting therefrom an END packet to the second node through the switched channel, said END packet containing a fault path identifier indicating the switched channel;

f) at each of said third nodes, responsive to receipt of each END packet arriving thereat,

(i) establishing a new link through the switched channel and a spare channel to said second node, and

(ii) transmitting a copy of the received END packet to an adjacent node through said new link to said second node, said copy of END packet containing copies of the fault path identifier; and

g) at said second node, responsive to receipt of the copy of END packet, switching a link of the second node from one of said failed paths indicated by the fault path identifier of the received copy of END packet to said new link.

33. A failure restoration method as claimed in claim 30, 31, or 32, further comprising the steps of:

at said first node, inserting into each of said CONTROL packets transmitted therefrom a priority identifier indicating priority given to each one of said failed regular paths;

at said second node, inserting into each of said RETURN packets transmitted therefrom a copy of said priority identifier;

at each of said third nodes, examining the priority identifier contained in a received RETURN packet if a spare channel indicated by a received RETURN packet is already reserved by a transmitted RETURN packet and returning a negative acknowledgement packet to the node form which the RETURN packet was received to cause retransmission of a RETURN packet to another third node if the priority of said received RETURN packet is lower than the priority of said transmitted RETURN packet.

34. A failure restoration method as claimed in claim 30, 31 or 32, further comprising, at said second node, the steps of:

recording all CONTROL packets received from said third nodes;

searching through all CONTROL packets in said record in response to said negative acknowledgement packet to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least count of intervening nodes; and

transmitting a RETURN packet to an adjacent node indicating the detected spare channel.

31. A failure restoration method for a communications network having first and second nodes and a plurality of third nodes, said first, second and third nodes being interconnected by lines having regular and spare channels, said third nodes being located between said first and second nodes, a series of said channels forming a path extending between said first and second nodes, the method comprising the steps of:

a) responsive to a failure in said path terminating at said first node,

(i) detecting a spare channel from said first node to each of adjacent ones of said third nodes having a required bandwidth equal to or greater than the bandwidth of the failed path, and

(ii) transmitting a CONTROL packet from said first node to each of adjacent third nodes if a spare channel having said required bandwidth is detected, said CONTROL packet containing a bandwidth identifier indicating said required bandwidth, and a fault path identifier indicating said failed path;

b) at each of said third nodes, responsive to receipt of each of said CONTROL packets,

(i) detecting a spare channel from the third node to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the received CONTROL packet, and

(ii) transmitting a copy of each received CONTROL packet to each adjacent node if a spare channel having said bandwidth is detected, each transmitted copy of CONTROL packet containing copies of the required bandwidth and fault path identifier;

c) at said second node, responsive to each copy of CONTROL packet arriving thereat from a given one of said third nodes, transmitting a RETURN packet from said second node to said given third node, said RETURN packet containing a spare channel identifier indicating a spare channel which leads to said given third node and forms part of an alternate path and a copy of the fault path identifier;

d) at said given third node,

(i) making a record of all RETURN packets arriving thereat,

(ii) determining whether there is a spare channel to an adjacent node located on a route leading to said first node,

(iii) transmitting a copy of each received RETURN packet from said given third node to said adjacent node if a spare channel is detected, and

(iv) returning a negative acknowledgement packet on a line through which the received RETURN packet was transmitted if no spare channel is detected to cause retransmission of a RETURN packet to another third node, said copy of RETURN packet containing a spare path identifier indicating the detected spare channel and a copy of said fault path identifier;

e) at said first node, responsive to receipt of each copy of RETURN packet, switching a link of the first node from said failed path to a spare channel indicated by the spare path identifier of the received copy of RETURN packet, and transmitting therefrom an END packet on the indicated spare channel, said END packet containing a fault path identifier indicating the failed path of said link and a copy of said spare channel identifier;

f) at each of said third nodes located along a route toward said second node, responsive to receipt of each END packet arriving thereat,

(i) searching through said record to detect a RETURN packet whose fault path identifier is identical to the fault path identifier of the received END packet,

(ii) establishing a new link through two spare channels respectively indicated by the spare channel identifiers of the detected RETURN packet and the received END packet, and

(iii) transmitting a copy of the received END packet to an adjacent node through the new link toward said second node, said copy of END packet containing copies of the fault path identifier and spare channel identifier of the received END packet; and

g) at said second node, responsive to receipt of the copy of END packet, switching a link of the second node from a failed path indicated by the fault path identifier of the received copy of END packet to a spare channel indicated by the spare channel identifier of the received copy of END packet.

32. A failure restoration method for a communications network having a plurality of nodes interconnected by lines having regular and spare path sections, there being a plurality of subnetworks each comprising first and second terminal nodes and an intermediate node, the intermediate node providing a connection between regular path sections to establish a regular path between said first and second terminal nodes, the nodes of each subnetwork functioning as third nodes of one or more subnetworks for establishing a link between spare path sections to form an alternate path between the first and second terminal nodes of said other subnetworks, each of said path sections having a different bandwidth, comprising the steps of:

a) responsive to a failure in said regular path in one of said subnetworks,

(i) transmitting a RELEASE packet from one of said terminal nodes of said subnetwork to the intermediate node thereof to clear a connection so that the other path section of said regular path is made available for use as a spare path section,

(ii) detecting a spare path section from said first terminal node of said subnetwork to each of adjacent ones of said third nodes having a required bandwidth equal to or greater that the bandwidth of said failed regular path, and

(iii) transmitting a CONTROL packet from said first node to each of adjacent third nodes if a spare path section having said required bandwidth is detected, said CONTROL packet containing a bandwidth identifier indicating said required bandwidth;

b) at each of said third nodes, responsive to receipt of each of said CONTROL packets,

(i) detecting a spare path section from the third node to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the received CONTROL packet, and

(ii) transmitting a copy of each received CONTROL packet to each adjacent node if a spare path section having said bandwidth is detected, each transmitted copy of CONTROL packet containing copies of the required bandwidth;

c) at said second node, responsive to each copy of CONTROL packet arriving thereat from a given one of said third nodes, transmitting a RETURN packet from said second node to said given third node, said RETURN packet containing a spare path-section identifier indicating a spare path section located on a route leading to said given third node;

d) at said given third node, responsive to receipt of said RETURN packet,

(i) determining whether there is a spare path section to an adjacent node located on a route leading to said first terminal node of said subnetwork, and

(ii) transmitting a copy of each received RETURN packet from said given third node to said adjacent node if a spare path section is detected,

(iii) returning a negative acknowledgement packet on a line through which the received RETURN packet was received if no spare path section is detected to cause retransmission of RETURN packet to another third node, said copy of RETURN packet containing a spare path section identifier indicating the detected spare path section;

e) at said first terminal node of said subnetwork, responsive to receipt of each copy of RETURN packet,

(i) switching a link of the first terminal node from said failed regular path to a spare path section indicated by the spare path section identifier of the received copy of RETURN packet, and

(ii) transmitting therefrom an END packet on the indicated spare path section;

f) at each of said third nodes located along a route toward said second terminal node of said subnetwork, responsive to receipt of each END packet arriving thereat,

(i) establishing a new link through said indicated spare path section and a spare path section to said second node, and

(ii) transmitting a copy of the received END packet to an adjacent node located on a route toward said second node; and

g) at said second terminal node of said subnetwork, responsive to receipt of the copy of END packet, switching a link of the second terminal node from a failed regular path to said new link.

38. A self-healing communications network having a plurality of nodes interconnected by lines having regular and spare channels, two of said nodes acting as first and second nodes when a failure occurs on a regular channel interconnecting said first and second nodes, and the other nodes functioning as third nodes capable of linking spare channels for establishing an alternate route between said first and second nodes, each of said nodes comprising:

means, used when functioning as said first node and responsive to a failure in regular channels terminating at said first node, for transmitting from the first node as many CONTROL packets as there are failed regular channels to adjacent third nodes;

means, used when functioning as one of said third nodes, for broadcasting copies of a received CONTROL packet to adjacent nodes;

means, used when functioning as said second node and responsive to receipt of each copy of CONTROL packet, for transmitting a RETURN packet to a given third node;

means, used when functioning as one of said third nodes, responsive to the RETURN packet, for checking the RETURN packet to determine whether there is a spare channel to an adjacent node located on a route leading to said first node, transmitting a copy of the received RETURN packet to said adjacent node if a spare channel is detected and returning a negative acknowledgement packet on a line through which said received RETURN packet was transmitted to cause retransmission of a RETURN packet to another third node if no spare channel is detected;

means, used when functioning as said first node and responsive to receipt of each copy of RETURN packet, for switching a link of the first node from one of said failed channels to a spare channel extending to said given third node to thereby establish a switched channel, and transmitting an END packet to the switched channel;

means, used when functioning as said given third node and responsive to receipt of said END packet, for establishing a new link through the switched channel and a spare channel to the second node, and transmitting a copy of the received END packet to said second node through the spare channel of the new link; and

means, used when functioning as said second node and responsive to receipt of each copy of END packet, for switching a link of the second node from a failed channel to the new link.

42. A self-healing communications network as claimed in claim 38, 39, 40 or 41, wherein said failed regular channels are assigned different levels of priority, and wherein said means active when functioning as said first node includes means for switching the link of the first node in an order specified by the assigned priority of the failed regular channels.

43. A self-healing communications network as claimed in claim 38, 39, 40 or 41, wherein:

said means, active when functioning as said first node, includes means for inserting into each of said CONTROL packets transmitted therefrom a fault location identifier indicating the location of said failure in said network; and

said means, active when functioning as one of said third nodes, includes means for discriminating between received packets according to said fault location identifier of each of the received packets.

44. A self-healing communications network as claimed in claim 38, 39, 40 or 41, wherein:

said means, active when functioning as said first node, includes means for inserting into each of said CONTROL packets transmitted therefrom a priority identifier indicating priority given to each one of said failed regular channels;

said means, active when functioning as said second node, includes means for inserting into each of said RETURN packets transmitted therefrom a copy of said priority identifier; and

said means, active when functioning as one of said third nodes, for examining the priority identifier contained in a received RETURN packet if a spare channel indicated by the spare channel identifier of the received RETURN packet is already reserved by a transmitted RETURN packet and returning a negative acknowledgment packet to the node from which the RETURN packet was received to cause retransmission of a RETURN packet to another third node if the priority of said received RETURN packet is lower than the priority of said transmitted RETURN packet.

45. A self-healing communications network as claimed in claim 38, 39, 40 or 41, wherein said means, active when functioning as said second node, further includes:

means for making a record of all CONTROL packets received from said third nodes;

means for making a search through the CONTROL packets in said record in response to said negative acknowledgment packet to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least hop count; and

means for transmitting a RETURN packet to said adjacent node containing a spare channel identifier indicating the detected spare channel.

51. A self-healing communications network as claimed in claim 38, 39, 40, 41, 46, 47 or 48, wherein:

said means, active when functioning as any one of said first, second and third nodes, includes means for inserting into each of said CONTROL packets a hop count indicating the number of nodes through which the CONTROL packet has travelled; and

said means, active when functioning as one of said third nodes, includes;

means for examining each of said CONTROL packets and broadcasting said copies of the CONTROL packet if the hop count of the received CONTROL packet is smaller than a predetermined value,

means for inserting an incremented hop count into each of the broadcast CONTROL packet,

means for making a record of all CONTROL packets arriving thereat,

means for searching through said record in response to receipt of a RETURN packet for detecting a CONTROL packet having a least hop count along a route having a spare channel, and

means for transmitting a copy of the received RETURN packet on said route.

52. A self-healing communications network as claimed in claim 38, 39, 40, 41, 46, 47 or 48, wherein:

said means, active when functioning as said first node, includes means for inserting node trace data into each of said CONTROL packets, the node trade data identifying the nodes through which the CONTROL packet has travelled;

said means, active when functioning as said second node, including means for inserting node trade data into each of said RETURN packets, the node trace data identifying the nodes through which the RETURN packet has travelled,

said means, active when functioning as one of said third nodes, including means for updating the node trade data of a received packet and transmitting a copy of the received packet to those third nodes which are not indicated in the node trace data of the received packet.

39. A self-healing communications network having a plurality of nodes interconnected by lines having regular and spare channels, two of said nodes functioning as first and second nodes when a failure occurs on a regular channel interconnecting said first and second nodes, and the other nodes functioning as third nodes capable of linking spare channels for establishing an alternate route between said first and second nodes, each of said nodes comprising:

means, used when functioning as said first node and responsive to a failure in regular channels terminating at said first node, for transmitting a CONTROL packet to adjacent ones of said third nodes, said CONTROL packet indicating the number of available spare channels;

means, used when functioning as one of said third nodes, for broadcasting as many copies of a received CONTROL packet to adjacent nodes as there are spare channels indicated by the received CONTROL packet, each copy of CONTROL packet indicating the number of available spare channels;

means, used when functioning as said second node and responsive to each copy of CONTROL packet from a given one of said third nodes, for transmitting as many RETURN packets to said given third node as there are available spare channels indicated by the received copy of CONTROL packet;

means, used when functioning as one of said third nodes, for checking each of the RETURN packets to determine whether there is a spare channel to an adjacent node located on a route leading to said first node, and transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected, and returning a negative acknowledgment packet on a line through which said received RETURN packet was transmitted if no spare channel is detected to cause retransmission of a RETURN packet to another third node;

means, used when functioning as said first node and responsive to receipt of each copy of RETURN packet, for switching a link from one of said failed channels to a spare channel extending to said given third node to thereby establish a switched channel, and transmitting an END packet to the switched spare channel;

means, used when functioning as said given third node and responsive to receipt of said END packet, for establishing a new link through the switched spare channel and a spare channel to said second node, and transmitting a copy of the received END packet to the second node through the spare channel of the new link; and

means, used when functioning as said second node and responsive to receipt of each copy of END packet, for switching a link of the second node from a failed channel to the new link.

40. A self-healing communications network having a plurality of nodes interconnected by lines having regular and spare channels, two of said nodes functioning as first and second nodes when a failure occurs on a regular channel interconnecting said first and second nodes, and the other nodes functioning as third nodes and capable of linking spare channels for establishing an alternate route between said first and second nodes, each of said nodes comprising:

means, active when functioning as said first node and responsive to a failure in regular channels terminating as said first node, for transmitting as many CONTROL packets as there are failed regular channels from said first node to each adjacent one of said third nodes;

means, active when functioning as each of said adjacent third nodes, for broadcasting copies of a received CONTROL packet to adjacent nodes;

means, active when functioning as said second node and responsive to each copy of CONTROL packet, for transmitting a RETURN packet to a given third node, each of said RETURN packets containing a route index number and a spare channel identifier indicating a spare channel which leads to said given third node and forms part of an alternate route to one of said failed channels;

means, active when functioning as said given third node, for making a record of all RETURN packets arriving thereat to determine whether there is a spare channel to an adjacent node located on a route leading to said first node, transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected and returning a negative acknowledgement packet on a line through which received RETURN packet was received to cause retransmission of a RETURN packet to another third node if no spare channel is detected, each copy of RETURN packet containing a copy of the route index number, and a spare channel identifier indicating said detected spare channel;

means, active when functioning as said first node and responsive to receipt of each copy of RETURN packet, for switching a link of the first node from one of said failed channels to a spare channel indicated by the channel identifier of the received copy of RETURN packet, and transmitting therefrom an END packet on the indicated spare channel, said END packet containing a copy of said route index number, and a copy of said spare channel identifier;

means, active when functioning as said given third node and responsive to receipt of said END packet, for searching through said record to detect a RETURN packet having a route index number identical to the route index number of said END packet, establishing a new link through spare channels respectively indicated by the spare channel identifiers of the received END packet and the detected RETURN packet, and transmitting a copy of the received END packet through the new link to said second node, said copy of END packet containing a copy of the spare channel identifier of the received END packet; and

means, active when functioning as said second node and responsive to receipt of each copy of END packet, for switching a link of the second node from a failed channel to a spare channel indicated by the spare channel identifier of the received copy of END packet.

41. A self-healing communications network having a plurality of nodes interconnected by lines having regular and spare channels, two of said nodes functioning as first and second nodes when a failure occurs on a regular channel interconnecting said first and second nodes, and the other nodes functioning as third nodes capable of linking spare channels for establishing an alternate route between said first and second nodes, each of said nodes comprising:

means, active when functioning as said first node, and transmitting, in response to a failure in regular channels terminating at said first node, a CONTROL packet therefrom to all adjacent ones of said third nodes, said CONTROL packet indicating the number of available spare channels;

means, active when functioning as said adjacent third nodes and responsive to receipt of a CONTROL packet from the first note, for broadcasting copies of a received CONTROL packet therefrom to adjacent nodes, each copy of CONTROL packets indicating the number of available spare channels;

means, active when functioning as said second node and responsive to receipt of copies of CONTROL packet arriving thereat from a given one of said third nodes, for transmitting as many RETURN packets therefrom to said given third node as there are available spare channels indicated by each of the received copies of CONTROL packet, each of said RETURN packets containing a route index number and a spare channel identifier indicating a spare channel which leads to said given third node and forms part of an alternate route for one of said failed channels;

means, active when functioning as said given third node, for making a record of all RETURN packets arriving thereat, determining whether there is a spare channel to an adjacent node located on a route leading to said first node, transmitting a copy of each received RETURN packet to said adjacent node if a spare channel is detected, and returning a negative acknowledgment packet on a line through which the received RETURN packet was transmitted if no spare channel is detected to cause retransmission of a RETURN packet to another third node, each copy of RETURN packet containing a copy of the route index number and an updated version of the spare channel identifier indicating said detected spare channel;

means, active when functioning as said first node and responsive to receipt of each copy of RETURN packet, for switching a link of the first node from one of said failed channels to a spare channel which is indicated by the spare channel identifier of the received copy of RETURN packet, and transmitting therefrom an END packet on the indicated spare channel, said END packet containing a copy of said route index number and a copy of said spare channel identifier of the received RETURN packet;

means, active when functioning as said given third node and responsive to receipt of said END packet, for searching through the RETURN packets in said record to detect a return packet having a route index number identical to the route index number of said END packet, establishing a new link through spare channels respectively indicated by the spare channel identifiers of the received END packet and the detected return packet through the new link to said second node, said copy of END packet containing a copy of the spare channel identifier of the received END packet; and

means, active when functioning as said second node and responsive to receipt of each copy of END packet, for switching a link of the second node from a failed channel to a spare channel indicated by the spare channel identifier of the received copy of END packet.

46. A self-healing communications network having a plurality of nodes interconnected by lines having regular and spare channels, two of said nodes functioning as first and second nodes, and the other nodes functioning as third nodes capable of linking spare channels for establishing an alternate route between said first and second nodes, a series of said channels extending between said first and second nodes forming a path, each of said nodes comprising:

means, active when functioning as said first node and responsive to a failure in said path terminating at said first node, for detecting a spare channel from said first node to each of adjacent ones of said third nodes having a required bandwidth equal to or greater than the bandwidth of the failed path, and transmitting a CONTROL packet from said first node to each of adjacent third nodes if a spare channel having said required bandwidth is detected, said CONTROL packet containing a bandwidth identifier indicating said required bandwidth and a fault path identifier indicating said failed path;

means, active when functioning as each of said third nodes and responsive to receipt of each of said CONTROL packets, for making a record of CONTROL packets, detecting a spare channel extending from each of said third nodes to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the received CONTROL packet, and transmitting a copy of each received CONTROL packet to each adjacent node if a spare channel having said bandwidth is detected, each transmitted copy of control packet containing copies of the required bandwidth and fault path identifier;

means, active when functioning as said second node and responsive to each copy of CONTROL packet arriving thereat from a given one of said third nodes, transmitting a RETURN packet from said second node to said given third node, said RETURN packet containing a copy of the fault path identifier;

means, active when functioning as said given third node and responsive to said RETURN packet for determining whether there is a spare channel to an adjacent node located on a route leading to said first node, transmitting a copy of the received RETURN packet to said adjacent node if a spare channel is detected, and returning a negative acknowledgment packet on a line through which the received RETURN packet was transmitted if no spare channel is detected to cause retransmission of a RETURN packet to another third node, said copy of RETURN packet containing a copy of said fault path identifier;

means, active when functioning as said first node and responsive to receipt of each copy of RETURN packet, for switching a link of the first node from said failed path to a spare channel extending to a third node to thereby establish a switched channel, and transmitting therefrom an END packet to the second node through the switched channel, said END packet containing a fault path identifier indicating the switched channel;

means, active when functioning as each of said third nodes and responsive to receipt of each END packet, for establishing a new link through the switched channel and a spare channel to said second node, and transmitting a copy of the received END packet to an adjacent node through said new link to said second node, said copy of END packet containing copies of the fault path identifier; and

means, active when functioning as said second node and responsive to receipt of the copy of END packet, for switching a link of the second node from one of said failed paths indicated by the fault path identifier of the received copy of END packet to said new link.

49. A self-healing communications network as claimed in claim 46, 47 or 48, wherein:

said means, active when functioning as said first node, includes means for inserting into each of said CONTROL packets transmitted therefrom a priority identifier indicating priority given to each one of said failed regular paths;

said means, active when functioning as said second node, including means for examining the priority identifier contained in a received RETURN packet if a spare channel indicated by a received RETURN packet is already reserved by a transmitted RETURN packet and returning a negative acknowledgment packet to the node from which the RETURN packet was received to cause retransmission of a RETURN packet to another third node if the priority of said received RETURN packet is lower than the priority of said transmitted RETURN packet.

50. A self-healing communications network as claimed in claim 46, 47 or 48, wherein said means, active when functioning as said second mode, includes:

means for making a record of all CONTROL packets received from said third nodes;

means for searching through all CONTROL packets in said record in response to said negative acknowledgment packet to detect whether there is a spare channel to an adjacent node located on a route leading to said first node with a least count of intervening nodes; and

means for transmitting a RETURN packet to an adjacent node indicating the detecting spare channel.

47. A self-healing communications network having a plurality of nodes interconnected by lines having regular and spare channels, two of said nodes functioning as first and second nodes when a failure occurs on a regular channel interconnecting said first and second nodes, and the other nodes functioning as third nodes and capable of linking spare channels for establishing an alternate route between said first and second nodes, a series of said channels extending between said first and second nodes forming a path, each of said nodes comprising:

means, active when functioning as said first node and responsive to a failure in said path terminating at said first node, for detecting a spare channel from said first node to each of adjacent ones of said third nodes having a required bandwidth equal to or greater than the bandwidth of the failed path, and transmitting a CONTROL packet from said first node to each of adjacent third nodes if a spare channel having said required bandwidth is detected, said CONTROL packet containing a bandwidth identifier indicating said required bandwidth, and a fault path identifier indicating said failed path;

means, active when functioning as one of said third nodes and responsive to receipt of each of said CONTROL packets, for detecting a spare channel from the third node to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the received CONTROL packet, and transmitting a copy of each received CONTROL packet to each adjacent node if a spare channel having said bandwidth is detected, each transmitted copy of CONTROL packet containing copies of the required bandwidth and fault path identifier;

means, active when functioning as said second node and responsive to each copy of CONTROL packet arriving thereat from a given one of said third nodes, for transmitting a RETURN packet from said second node to said given third node, said RETURN packet containing a spare channel identifier indicating a spare channel which leads to said given third node and forms part of an alternate path and a copy of the fault path identifier;

means, active when functioning as said given third node, for making a record of all RETURN packets arriving thereat, determining whether there is a spare channel to an adjacent node located on a route leading to said first node, transmitting a copy of each received RETURN packet from said given third node to said adjacent node if a spare channel is detected, and returning a negative acknowledgment packet on a line through which the received RETURN packet was transmitted if no spare channel is detected to cause retransmission of a RETURN packet to another third node, said copy of RETURN packet containing a spare path identifier indicating the detected spare channel and a copy of said fault path identifier;

means, active when functioning as said first node and responsive to receipt of each copy of RETURN packet, for switching a link of the first node from said failed path to a spare channel indicated by the spare path identifier of the received copy of RETURN packet, and transmitting therefrom an END packet on the indicated spare channel, said END packet containing a fault path identifier indicating the failed path of said link and a copy of said spare channel identifier;

means, active when functioning as said first node and responsive to receipt of each copy of RETURN packet, for switching a link of the first node from said failed path to a spare channel indicated by the spare path identifier of the received copy of RETURN packet, and transmitting therefrom an END packet on the indicated spare channel, said END packet containing a fault path identifier indicating the failed path of said link and a copy of said spare channel identifier;

means, active when functioning as one of said third nodes located along a route toward said second node and responsive to receipt of each END packet arriving thereat, for searching through said record to detect a RETURN packet whose fault path identifier is identical to the fault path identifier of the received END packet, establishing a new link through two spare channels respectively indicated by the spare channel identifiers of the detected RETURN packet and the received END packet, and transmitting a copy of the received END packet to an adjacent node through the new link toward said second node, said copy of END packet containing copies of the fault path identifier and spare channel identifier of the received END packet; and

means, active when functioning as said second node and responsive to receipt of the copy of END packet, for switching a link of the second node from a failed path indicated by the fault path identifier of the received copy of END packet to a spare channel indicated by the spare channel identifier of the received copy of the END packet.

48. A self-healing communications network having a plurality of nodes interconnected by lines having regular and spare path sections, there being a plurality of subnetworks each comprising first and second terminal nodes and an intermediate node, the intermediate node providing a connection between regular path sections to establish a regular path between said first and second terminal nodes, the nodes of each subnetwork functioning as third nodes of one or more other subnetworks for establishing a link between spare path sections to form an alternate path between the first and second terminal nodes of said other subnetworks, each of said path sections having a different bandwidth, comprising:

means, active when functioning as said first node and responsive to a failure in said regular path in one of said subnetworks, transmitting a RELEASE packet from one of said terminal nodes of said subnetwork to the intermediate node thereof to clear a connection so that the other path section of said regular path is made available for use as a spare path section, detecting a spare path section from said first terminal node of said subnetwork to each of adjacent ones of said third nodes having a required bandwidth equal to or greater than the bandwidth of said failed regular path, transmitting a CONTROL packet from said first node to each of adjacent third nodes if a spare path section having said required bandwidth is detected, said CONTROL packet containing a bandwidth identifier indicating said required bandwidth;

means, active when functioning as one of said third nodes and responsive to receipt of each of said CONTROL packets, detecting a spare path section from the third node to each adjacent node having a bandwidth equal to or greater than the bandwidth indicated by the bandwidth identifier of the received CONTROL packet, and transmitting a copy of each received CONTROL packet to each adjacent node if a spare path section having said bandwidth is detected and each transmitted CONTROL packet containing copies of the required bandwidth;

means, active when functioning as said second node and responsive to each copy of CONTROL packet arriving thereat from a given one of said third nodes, for transmitting a RETURN packet from said second node to said given third node, said RETURN packet containing a spare path-section identifier indicating a spare path section located on a route leading to said given third node;

means, active when functioning as said given third node and responsive to receipt of said RETURN packet, for determining whether there is a spare path section to an adjacent node located on a route leading to said first terminal node of said subnetwork, transmitting a copy of each received RETURN packet from said given third node to said adjacent node if a spare path section is detected, and returning a negative acknowledgment packet on a line through which the received RETURN packet was received if no spare path section is detected to cause retransmission of a RETURN packet to another third node, said copy of RETURN packet containing a spare path section identifier indicating the detected spare path section;

means, active when functioning as said first terminal node of said subnetwork and responsive to receipt of each copy of RETURN packet, for switching a link of the first terminal node from said failed regular path to a spare path section indicated by the spare path-section identifier of the received copy of RETURN packet, and transmitting therefrom an END packet on the indicated spare path section;

means, active when functioning as one of said third nodes located along a route toward said second terminal node of said subnetwork and responsive to receipt of each END packet arriving thereat, for establishing a new link through said indicated spare path section and a spare path section to said second node, and transmitting a copy of the received END packet to an adjacent node located on a route toward said second node; and

means, active when functioning as said second terminal node of said subnetwork and responsive to receipt of the copy of END packet, for switching a link of the second terminal node from a failed regular path to said new link.