Path changing system and method for use in ATM communication apparatus

• US 5,600,630 A
• Filed: 08/25/1994
• Issued: 02/04/1997
• Est. Priority Date: 08/31/1993
• Status: Expired due to Fees

• Current Assignee: Hitachi Communication Systems Incorporated (Hitachi, Ltd.), Hitachi, Ltd.
• Original Assignee: Hitachi Communication Systems Incorporated (Hitachi, Ltd.), Hitachi, Ltd.
• Inventors: Takase, Akihiko, Takahashi, Setsuo, Takano, Masataka, Oka, Yoji
• Primary Examiner(s): Olms, Douglas W.
• Assistant Examiner(s): Jung, Min
• Application Number:
  US08/296,334
• Time in Patent Office: 894 Days
• Field of Search: 370/16, 370/60.1, 370/94.1, 370/94.2, 370/60, 370/94.3, 370/54, 371/8.1, 371/8.2, 371/11.1, 371/11.2
• US Class Current: 370/218
• CPC Class Codes: H04L 2012/5619 Network Node Interface, e.g. tandem connections, transit switching
• CPC Class Codes: H04L 2012/5627 Fault tolerance and recovery
• CPC Class Codes: H04L 41/0659 by isolating or reconfiguring faulty entities
• CPC Class Codes: H04L 41/40 using virtualisation of network functions or resources, e.g. SDN or NFV entities
• CPC Class Codes: H04L 45/10 Routing in connection-oriented networks, e.g. X.25 or ATM
• CPC Class Codes: H04L 45/22 Alternate routing
• CPC Class Codes: H04L 45/28 using route fault recovery
• CPC Class Codes: H04L 49/25 Routing or path finding in a switch fabric
• CPC Class Codes: H04L 49/256 Routing or path finding in ATM switching fabrics
• CPC Class Codes: H04L 49/30 Peripheral units, e.g. input or output ports
• CPC Class Codes: H04L 49/3009 Header conversion, routing tables or routing tags
• CPC Class Codes: H04L 49/3081 ATM peripheral units, e.g. policing, insertion or extraction
• CPC Class Codes: H04L 49/309 Header conversion, routing tables or routing tags
• CPC Class Codes: H04L 49/555 Error detection
• CPC Class Codes: H04L 49/557 Error correction, e.g. fault recovery or fault tolerance

Abstract

An ATM path changing system and method for use in an ATM communication apparatus and ATM communication network are provided which can set an alternating route in the event of a failure occurring in a transmission line or VP. A header converter in a line controller includes a plurality of output path routing tables, a selector, a comparator, a register for failure RTG and a register for failure VPI and when the contents of the register for failure RTG or VPI coincides with a RTG or VPI of the output path routing tables, an output is selected in accordance with the contents of a selected emergency-route RTG or VPI register.

Claims

1. A communication apparatus wherein connecting information included in cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines by converting at least one of an output connection and an output line, comprising:

a plurality of routing information storing apparatuses each for storing information of an output connection, an output line or both corresponding to one piece of input connecting information;

an equipment information registering apparatus for storing information indicative of states such as a failure, of said output line, an output communication apparatus, a communication apparatus of interest or communication equipment comprised of a combination thereof; and

a selecting apparatus for selecting any one of said plurality of routing information storing apparatus based on correspondence between the contents of said equipment information registering apparatus and said plurality of routing information storing apparatus,

whereby in the event of a failure occurring in said output line, the output communication apparatus, the communication apparatus of interest or a combination thereof, an output line, an output connection or an output apparatus is selected in self-control fashion from said plurality of routing information storing apparatuses in accordance with the failure.

2. A communication network comprised of a plurality of communication apparatuses wherein connecting information included in cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines by converting at least one of an output connection and an output line, and including a managing apparatus for managing said plurality of communication apparatuses and a plurality of transmission lines, each communication apparatus including:

a plurality of routing information storing apparatus each for storing information on an output connection, an output line or both in correspondence to an input cell; and

an equipment information storing apparatus for storing states, such as a failure, of an output line, an output communication apparatus, a communication apparatus of interest or communication equipment comprised of a combination thereof.

said managing apparatus being operative to set precedently a plurality of alternating output connections, output lines or both in said plurality of routing information storing apparatuses, correspondingly, to one piece of input connection information, in accordance with the states of the output communication apparatus, the communication apparatus of interest or the communication equipment,

whereby an output line, an output connection or an output apparatus is selected in self-control fashion from said plurality of routing information storing apparatuses in accordance with the stored state of the output communication apparatus to be transmitted and received between communication apparatuses, the stored state of the communication apparatus of interest or the stored state of the communication equipment, so as to perform communication in said communication network by taking an alternating transmission line or an output connection.

3. An ATM communication apparatus wherein connecting information included in cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines by converting at least one of a path identifier and a channel identifier, comprising:

a plurality of output path routing tables for storing an output path identifier, an output channel identifier and an output line corresponding to one input path identifier or channel identifier;

a failure information register for storing failure information indicative of a failure in an output line, output paths, output channel or a combination thereof;

a comparator for comparing the contents of said failure information register with the contents of said output path routing tables; and

a selecting circuit responsive to an output of said comparator to select any one of said plurality of output path routing tables,

whereby in the event of a failure in said output line, said output path, said output channel or a combination thereof, a normal output line, a normal output path, a normal output channel or a combination thereof is selected from said plurality of output path routing tables.

4. An ATM communication apparatus wherein connecting information included in cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines by converting at least one of a path identifier and a channel identifier, comprising:

a plurality of output path routing tables for storing an output path identifier, an output channel identifier and an output line corresponding to one input path identifier or channel identifier;

a failure information register for storing failure information indicative of a failure in at least one of an output line, output path, and output channel;

a comparator for comparing the contents of said failure information register with the contents of said output path routing tables; and

a selecting circuit responsive to an output of said comparator to select any one of said plurality of output path routing tables,

whereby in the event of a failure occurring in said at least one of said output line, said output path, and said output channel, at least one of a normal output line, a normal output path and a normal output channel is selected from said plurality of output path routing tables.

5. An ATM communication apparatus wherein connecting information included in cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines by converting at least one of a path identifier and a channel identifier, comprising:

a plurality of output path routing tables for storing an output path identifier, an output channel identifier and an output line corresponding to one input path identifier or channel identifier;

a failure information register for storing failure information indicative of a failure in an output line, an output path, an output channel or a combination thereof;

a comparator for comparing the contents of said failure information register with the contents of said output path routing tables; and

a selecting circuit responsive to an output of said comparator to select any one of said plurality of output path routing tables,

whereby in the event of a failure occurring in said output line, said output channel, said output channel or said combination thereof, a normal output line, a normal output path, a normal output channel or a combination thereof is selected from said plurality of output path routing tables.

6. An ATM communication apparatus wherein connecting information included in cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines by converting at least one of a path identifier and a channel identifier, comprising:

a plurality of output path routing tables for memorizing an output path identifier, an output channel identifier and an output line corresponding to one input path identifier;

a first failure information register for storing failure information indicative of a failure in said output line;

a second failure information register for storing failure information indicative of a failure in said output path;

a third failure information register for storing failure information indicative of a failure in said output channel;

a first comparator for comparing the contents of said first failure information register with the contents of said output path routing tables;

a second comparator for comparing the contents of said second failure information register with the contents of said output path routing tables;

a third comparator for comparing the contents of said third failure information register with the contents of said output path routing tables; and

selecting circuits responsive to outputs of said first, second and third comparators to select any one of said plurality of output path routing tables,

whereby in the event of a failure occurring in said output line, said output path, said output channel or a combination thereof, a normal output line, a normal output path, a normal output channel or a combination thereof is selected from said plurality of output path routing tables.

7. An ATM communication apparatus wherein connecting information included in cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines which include a plurality of output paths, and a plurality of output channels, comprising:

a plurality of output path routing tables for storing an output path identifier, an output channel identifier and an output line corresponding to one input path identifier or channel identifier;

a failure information register for storing failure information indicative of a failure in said output line, output path, output channel or a combination thereof;

an identifier for indicating which of said output line, said output path, said output channel and a combination thereof the output failure belongs to;

a comparator for comparing the contents of said failure information register and said identifier with the contents of said output path routing tables; and

a selecting circuit responsive to an output of said comparator to select any one of said plurality of output path routing tables,

whereby in the event of a failure occurring in said output line, said output path, said output channel or a combination thereof, a normal output line, a normal output path, a normal output channel or a combination thereof is selected from said plurality of output path routing tables.

8. The ATM communication apparatus according to claim 7 further including a plurality of failure information registers and identifiers and in the event of failures occurring in any one of the plurality of output lines, the plurality of output paths, and the plurality of output channels, the system selecting normal output lines, output paths, output channels or a combination thereof from said plurality of output path routing tables to take alternating lines, paths or channels.

9. The ATM communication apparatus according to claim 7 wherein said output path routing tables include a single output path routing table for storing a plurality of output path identifiers, output channel identifiers and output lines corresponding to one input path identifier or channel identifier and, the system further including an access controller apparatus for controlling a sequence of reading said plurality of pieces of information stored in said single output path routing table, whereby said single output path routing table is read a plurality of times so that in the event of failures occurring in the plurality of output lines, output paths, output channels or a combination thereof, the access controller selects normal output lines, output paths, output channels or a combination thereof from said single output path routing table to take alternating lines, paths, or channels.

10. A communication path changing method for an ATM communication network comprised of a plurality of ATM communication apparatus, a managing apparatus for managing said plurality of ATM communication apparatus and transmission lines, each of said plurality of ATM communication apparatus being adapted to realize the function to multiplex and switch a plurality of digital lines by converting a path identifier, a channel identifier or both and adding internal routing information of system to an ATM cell and having a changing system including a plurality of output path routing tables for storing an output path identifier, an output channel identifier and an output line corresponding to one input path identifier or channel identifier, a failure information register for storing failure information indicative of a failure in said output line, a comparator for comparing the contents of said failure information register with the contents of said output path routing tables, and a selecting circuit responsive to an output of said comparator to select any one of said plurality of output path routing tables, so that in the event of a failure occurring in said output line, a normal output line is selected from said plurality of output path routing tables,

precedently setting a plurality of alternating output path identifiers, output channel identifiers and output lines taken in an event of a failure occurring in an output line, an output path, an output channel or a combination thereof in said plurality of output path routing tables provided in each ATM communication apparatus by means of said managing apparatus, and each ATM communication apparatus inter-station failure information transmitted and received between communication apparatus and said path changing system of said ATM communication apparatus of interest to select a normal output line, a normal output path, a normal output channel or a combination thereof from said routing tables and performing communication in said ATM communication network by taking an alternating line, path or channel.

11. A communication path changing method for an ATM communication network comprised of a plurality of ATM communication apparatus, a managing apparatus for managing said plurality of ATM communication apparatus and transmission lines, each of said plurality of ATM communication apparatus being adapted to realize the function to multiplex and switch a plurality of digital lines by converting a path identifier, a channel identifier or both and adding internal routing information of system to an ATM cell and having a changing system including a plurality of output path routing tables for storing an output path identifier, an output channel identifier and an output line corresponding to one input path identifier or channel identifier, a failure information register for storing failure information indicative of a failure in said output path, a comparator for comparing the contents of said failure information register with the contents of said output path routing tables, and a selecting circuit responsive to an output of said comparator to select any one of said plurality of output path routing tables, so that in the event of a failure occurring in said output path, a normal output path is selected from said plurality of output path routing tables, comprising:

precedently setting a plurality of alternating output path identifiers, output channel identifiers and output lines taken in an event of a failure occurring in an output line, an output path, an output channel or a combination thereof in said plurality of output path routing tables provided in each ATM communication apparatus by means of said managing apparatus, and each ATM communication apparatus using inter-station failure information transmitted and received between communication apparatus and said path changing system of said ATM communication apparatus of interest selecting a normal output line, a normal output path, a normal output channel or a combination thereof from said routing tables and performing communication in said ATM communication network by taking an alternating line, path or channel.

12. A communication path changing method for an ATM communication network comprised of a plurality of ATM communication apparatus, a managing apparatus for managing said plurality of ATM communication apparatus and transmission lines, each of said plurality of ATM communication apparatus being adapted to realize the function to multiplex and switch a plurality of digital lines by converting a path identifier, a channel identifier or both and adding internal routing information of system to an ATM cell and having a changing system including a plurality of output path routing tables for storing an output path identifier, an output channel identifier and an output line corresponding to one input path identifier or channel identifier, a failure information register for storing failure information indicative of a failure in said output channel, a comparator for comparing the contents of said failure information register with the contents of said output path routing tables, and a selecting circuit responsive to an output of said comparator to select any one of said plurality of output path routing tables, so that in the event of a failure occurring in said output channel, a normal output channel is selected from said plurality of output path routing tables, comprising:

precedently setting a plurality of alternating output path identifiers, output channel identifiers and output lines taken in the event of a failure occurring in an output line, an output path, an output channel or a combination thereof in said plurality of output path routing tables provided in each ATM communication apparatus by means of said managing apparatus, and each ATM communication apparatus inter-station failure information transmitted and received between communication apparatus and said path changing system of said ATM communication apparatus of interest a normal output line, a normal output path, a normal output channel or a combination thereof from said routing tables and performing communication in said ATM communication network by taking an alternating line, path or channel.

13. A communication path changing method for an ATM communication network comprised of a plurality of ATM communication apparatus, a managing apparatus for managing said plurality of ATM communication apparatus and transmission lines, each of said plurality of ATM communication apparatus being adapted to realize the function to multiplex and switch a plurality of digital lines by converting a path identifier, a channel identifier or both and adding internal routing information of system to an ATM cell and having a changing system including a plurality of output path routing tables for storing an output path identifier, an output channel identifier and an output line corresponding to one input path identifier or channel identifier, a first failure information register for storing failure information indicative of a failure in said output line, a second failure information register for storing failure information indicative of a failure in said output path, a third failure information register for storing failure information indicative of a failure in said output channel, a first comparator for comparing the contents of said first failure information register with the contents of said output path routing tables, a second comparator for comparing the contents of said second failure information register with the contents of said output path routing tables, a third comparator for comparing the contents of said third failure information register with the contents of said output path routing tables, and selecting circuits responsive to outputs of said first, second and third comparators to select any one of said plurality of output path routing tables, so that in the event of a failure occurring in said output line, said output path, said output channel or a combination thereof, a normal output line, a normal output path, a normal output channel or a combination thereof is selected from said plurality of output path routing tables, comprising:

setting a plurality of alternating output path identifiers and output channel identifiers and output lines taken in an event of failure occurring in an output line, an output path, an output channel or a combination thereof in said plurality of output path routing tables provided in each ATM communication apparatus by means of said managing apparatus, and each ATM communication apparatus using inter-station failure information transmitted and received between communication apparatus and said path changing system of said ATM communication apparatus of interest selecting a normal output line, a normal output path, a normal output channel or a combination thereof from said routing tables and performing communication in said ATM communication network by taking an alternating line, path or channel.

14. A communication path changing method for an ATM communication network comprised of a plurality of ATM communication apparatus, a managing apparatus for managing said plurality of ATM communication apparatus and transmission lines, each of said plurality of ATM communication apparatus being adapted to realize the function to multiplex and switch a plurality of digital lines by converting a path identifier, a channel identifier or both and adding internal routing information of system to an ATM cell and having a changing system including a plurality of output path routing tables for storing an output path identifier, an output channel identifier and an output line corresponding to one path identifier or channel identifier, a failure information register for storing failure information indicative of a failure in said output line, output path, output channel or a combination thereof, an identifier for indicating which of said output line, said output path, said output channel and a combination thereof the output failure belongs to, a comparator for comparing the contents of said failure information register and said identifier with the contents of said output path routing tables, and a selecting circuit responsive to an output of said comparator to select any one of said plurality of output path routing tables, so that in the event of a failure occurring in said output line, said output path, said output channel or a combination thereof, a normal output line, a normal output path, a normal output channel or a combination thereof is selected from said plurality of output path routing tables, comprising:

setting a plurality of alternating output path identifiers, output channel identifiers and output lines taken in an event of a failure occurring in an output line, an output path, an output channel or a combination thereof in said plurality of output path routing tables provided in each ATM communication apparatus by means of said managing apparatus, and each ATM communication apparatus using inter-station failure information transmitted and received between communication apparatus and said path changing system of said ATM communication apparatus of interest selecting a normal output line, a normal output path, a normal output channel or a combination thereof from said routing tables and performing communication in said ATM communication network by taking an alternating line, path or channel.

15. A communication path changing method according to claim 14 wherein a plurality of failure information registers and identifiers are provided and in the event of failures occurring in a plurality of output lines, selecting a plurality of output paths, a plurality of output channels or a combination thereof from said plurality of output path routing tables to take alternating lines, paths or channels.

16. A communication path changing method according to claim 14 wherein said output path routing tables include a single output path routing table for storing a plurality of output path identifiers, output channel identifiers and output lines corresponding to one input path identifier or channel identifier and an access controller apparatus for controlling the sequence of reading said plurality of pieces of information stored in said single table, the method further including reading said single output path routing table a plurality of times, and in the event of failures occurring in a plurality of output lines, output paths, output channels or a combination thereof, selecting normal output lines, output paths, output channels or a combination thereof from said single output path routing table to take alternating lines, paths, or channels.

17. A path changing system for use in a cell switching system wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines, comprising:

(1) a first memory connected to at least one of input digital lines for storing (A) internal routing information indicative of output digital lines and (B) connecting information on output cells, in association with connecting information included in input cells;

(2) a second memory connected to at least one of the input digital lines for storing (A) internal routing information indicative of output digital lines different from the output digital lines indicated by the information stored in said first memory and (B) connecting information on output cells, in association with the connecting information included in the input cells;

(3) a third memory connected to at least one of the input digital lines for storing, when one of the output digital lines is faulty, internal routing information indicative of the faulty output digital line;

(4) a comparator connected to at least one of the input digital lines for comparing internal routing information read out from said first and second memories with internal routing information read out from said third memory;

(5) a first selector connected to at least one of the input digital lines for outputting either of connecting information and internal routing information read out from said first memory and connecting information and internal routing information read out from said second memory; and

,

(6) a second selector connected to at least one of the input digital lines for outputting an output from said first selector only when connecting information of the input cells are to be rewritten and only when internal routing information are to be added and for outputting the input cells,

wherein (A) internal routing information indicative of output digital lines and (B) connecting information on an output cell are read out according to connecting information included in a cell input from an input digital line from said first and second memories so that, when one of the output digital lines indicated by the read out internal routing information is faulty, causing an associated comparator to produce a match signal, a first selector is controlled to cause contents of the memory storing the internal routing information to which no match signal is produced in said comparator to be output to a second selector, whereby the cell having the connecting information rewritten and having internal routing information added thereto to indicate a normal output digital line is output into the system from said second selector to allow said cell to be output therefrom to the normal output digital line.

18. A path changing system for use in a cell switching system wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, comprising:

(1) a first memory connected to at least one of input digital lines for storing (A) connecting information indicative of output paths and (B) internal routing information, in association with connecting information included in input cells;

(2) a second memory connected to at least one of the input digital lines for storing (A) connecting information indicative of output paths different from the output paths indicated by the information stored in said first memory and (B) internal routing information, in association with the connecting information included in the input cells;

(3) a third memory connected to at least one of the input digital lines for storing, when one of the output paths is faulty, connecting information indicative of the faulty output path;

(4) a comparator connected to at least one of the input digital lines for comparing the connecting information read out from said first and second memories with the connecting information read out from said third memory;

(5) a first selector connected to at least one of the input digital lines for outputting either of (A) connecting information and internal routing information read out from said first memory and (B) connecting information and internal routing information read out from said second memory; and

,

(6) a second selector connected to at least one of the input digital lines for outputting outputs from said first selector only when connecting information of the input cells are to be rewritten and only when internal routing information is to be added and for outputting the input cells as they are at the other timings,

wherein (A) connecting information indicative of output paths and (B) internal routing information are read out according to connecting information included in a cell input from an input digital line from first and second memories so that, when one of the output paths indicated by the read-out connecting information is faulty, causing an associated comparator to produce a match signal, a first selector is controlled to cause contents of the memory storing the connecting information to which no match signal is produced in said comparator to be output to said second selector, whereby the cell having the connecting information rewritten to indicate a normal output connection and having internal routing information added thereto is output into the system from said second selector to allow said cell to be output therefrom to the normal output path.

19. A path changing system for use in a cell switching system wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, comprising:

(1) a first memory connected to at least one of the input digital lines for storing (A) connecting information indicative of output paths and (B) internal routing information indicative of output digital lines, in association with connecting information included in input cells;

(2) a second memory connected to at least one of the input digital lines for storing (A) connecting information indicative of output paths different from the output paths indicated by the information stored in said first memory and (B) internal routing information indicative of output digital lines different from the output digital lines indicated by the information stored in said first memories, in association with the connecting information included in the input cells;

(3) a third memory means connected to at least one of the input digital lines for storing (A) connecting information indicative of output paths different from the output paths indicated by the information stored in said first and second memories and (B) internal routing information indicative of output digital lines different from the output digital lines indicated by the information stored in said first and second memories, in association with the connecting information included in the input cells;

(4) a fourth memory connected to at least one of the input digital lines for storing, when one of the output paths is faulty, internal routing information indicative of the faulty output path;

(5) a fifth memory connected to at least one of the input digital lines for storing connecting information indicative of one of the output connections which is faulty;

(6) a first comparator connected to at least one of the input digital lines for comparing connecting information read out from said first, second and third memories with connecting information read out from said fifth memory means;

(7) a second comparator connected to at least one of the input digital lines for comparing internal routing information read out from said first, second and third memories with internal routing information read out from said fourth memory;

(8) a first selector connected to at least one of the input digital lines, for outputting either of connecting information and internal routing information read out of said first memory and connecting information and internal routing information read out from said second memory;

(9) a second selector connected to at least one of the input digital lines, for outputting either of (A) an output of said first selector and (B) connecting information and internal routing information read out from said third memory; and

,

(10) a third selector connected to at least one of the input digital lines, for outputting outputs from said second selector only when connecting information of the input cells are to be rewritten and when the internal routing information is to be added and for outputting the input cells,

wherein (A) connecting information indicative of output paths and (B) internal routing information are read out according to connecting information included in a cell input from an input digital line from said first and second memories so that, said first comparator producing a match signal when one of the output paths indicated by the read out connecting information is faulty, a first selector is controlled to cause contents of the memory storing the connecting information to which no match signal is produced in a first comparator to be output to said second selector, and when both of an output digital line indicated by the internal routing information read out from a third memory and an output digital line indicated by the internal routing information stored in the memory storing connecting information to which no match signal is produced in said first comparator are faulty, causing the second comparator to produce a match signal, said second selector causing contents of the memory storing the connecting information to which no match signal is produced in said second comparator to be output to said third selector, whereby the cell having the connecting information rewritten to indicate a normal output path and having internal routing information added thereto is outputted into the system from said second selector to the normal output path.

20. A path changing system for use in a cell switching system wherein connecting information included in cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines, comprising:

(1) a first memory connected to at least one of input digital lines for storing (A) connecting information indicative of output paths and (B) internal routing information indicative of output digital lines, in association with the connecting information included in input cells;

(2) a second memory connected to at least one of the input digital lines for storing (A) connecting information indicative of output paths different from the output paths indicated by the information stored in said first memory and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in said first memory, in association with the connecting information included in the input cells;

(3) a third memory connected to at least one of the input digital lines for storing when a fault occurs in one of the output digital lines, (A) internal routing information indicative of the faulty output digital line and (B) information indicative of said fault in the output digital lines and also storing, when a fault occurs in one of the output paths, connecting information indicative of said fault in the output paths;

(4) a comparator connected to at least one of the input digital lines for comparing, when the information stored in said third memory indicates an output digital line fault, internal routing information read out from said first and second memories with internal routing information read out from said third memory and for comparing, when the information stored in said third memory means indicates an output path fault, connecting information read out from said first and second memories with connecting information read out from said third memory;

(5) a first selector connected to at least one of the input digital lines for outputting either of connecting information and internal routing information read out from said first memory and connecting information and internal routing information read out from said second memory; and

,

(6) a second selector connected to at least one of the input digital lines for outputting outputs from said first selector only when connecting information of the input cells are to be rewritten and only when internal routing information are to be added and for outputting the input cells as they are at the other timings,

wherein (A) connecting information indicative of output digital lines and output paths and (B) internal routing information are read out according to connecting information included in a cell input from an input digital line from said first and second memories so that, when one of the output digital lines indicated by the read out internal routing information is faulty or when one of the output paths indicated by the read out connecting information is faulty, causing a comparator to produce a match signal, a first selector is controlled to cause contents of the memory storing internal routing information or connecting information to which no match signal is produced in said comparator to be outputted to said second selector, whereby the cell having connecting information rewritten to indicate a normal output digital line and output path and having internal routing information added thereto, is outputted into the system and thus is outputted therefrom to the normal output digital line or normal output path.

21. A path changing system for use in a cell switching system wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, comprising:

(1) a first memory connected to at least one of input digital lines for storing (A) connecting information indicative of output paths and (B) internal routing information indicative of output digital lines, in association with connecting information included in input cells;

(2) a second memory connected to at least one of the input digital lines for storing (A) connecting information indicative of output paths different from the output paths indicated by the information stored in said first memory and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in said first memory, in association with the connecting information included in the input cells;

(3) a third memory connected to at least one of the input digital lines for storing, when a plurality of output digital lines are faulty, a plurality of internal routing information indicative of the faulty output digital lines;

(4) comparators connected to at least one of the input digital lines and also for respective one of the plurality of information stored in said third memory for comparing internal routing information read out from said first and second memories with internal routing information read out from aid third memories;

(5) a first selector connected to at least one of the input digital lines for outputting ether of connecting information and internal routing information read out from said first memory and connecting information and internal routing information read out from said second memory; and

,

(6) a second selector connected to at least one of the input digital lines for outputting outputs of said first selectors when connecting information of the input cells are to be rewritten and when internal routing information are to be added, and for outputting the input cells as they are at the rest of times,

wherein (A) connecting information indicative of output paths and (B) internal routing information indicative of output digital lines are read out from first and second memories according to connecting information included in a cell input from an input digital line so that, when one of the output digital lines indicated by the read out internal routing information is faulty, causing one of said comparators to produce a match signal, a first selector is controlled to cause contents of the memory storing internal routing information to which no match signal is produced in all of said comparators to be output to a second selector, whereby the cell having internal routing information rewritten to indicate a normal output digital line is output from said second selector into the system and thus is output therefrom to the normal output digital line.

22. A path changing system for use in a cell switching system wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, comprising:

(1) a first memory connected to at least one of input digital lines for storing (A) a plurality of connecting information indicative of a plurality of different output paths and (B) a plurality of internal routing information indicative of a plurality of different output digital lines, in association with connecting information included in the input cells;

(2) a second memory connected to at least one of the input digital lines for storing, when a plurality of output digital lines or a plurality of output paths or both thereof are faulty, and, when the fault occurs in the output digital lines, internal routing information indicative of the faulty output digital lines and information indicative of occurrence of the faulty output digital lines and for storing, when the fault occurs in the output paths, connecting information indicative of the faulty output paths and information indicative of the occurrence of the faulty output paths;

(3) comparators connected to at least one of the input digital lines and also for respective one of the information stored in said second memory for comparing, when the information stored in said second memory indicates an output digital line fault, internal routing information read out from said first memory with internal routing information read out from said second memory and, when the information stored in said second memory indicates an output path fault, connecting information read out from said first memory with connecting information read out from said second memories;

(4) a control circuit connected to at least one of the input digital lines for controlling said first memory to read out one of the information stored in said first memory according to connecting information included in the input cells and for controlling, when receiving a match signal from said comparators, said first memory to read out information other than the information previously read out according to the connecting information included in the input cells; and

,

(5) a selector connected to at least one of the input digital lines for outputting an output from said first memories only when connecting information of the input cells are to be rewritten and when internal routing information are to be added and for outputting the input cells as they are at the other times,

wherein one of pairs of connecting information and internal routing information indicative of output paths and output digital lines, respectively, is read out from a first memory according to connecting information included in a cell input from an input digital line so that, when an output digital line indicated by the read out internal routing information is faulty or when an output path indicated by the read out connecting information is faulty, causing one of said comparator to produce match signal, information other than the previously read out information is read out from said first memory, which in turn causes the comparator to produce no match signal with regard to the thus read out information and the thus read out information is output to said selector, and the cell having the connecting information rewritten to indicate a normal output path and having internal routing information indicative of a normal output digital line added thereto is output into the system and thus is output therefrom to the normal output digital line and the normal output path.

23. A path changing system for use in an ATM communication system wherein virtual path identifiers included in ATM cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers to allow the ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to be output to a plurality of predetermined output digital lines, comprising:

(1) a first routing table connected to at least one of input digital lines for storing (A) virtual path identifiers indicative of output paths and (B) internal routing information indicative of output digital lines, in association with the virtual path identifiers included in the input ATM cells;

(2) a second routing table connected to at least one of the input digital lines for storing (A) internal routing information indicative of output digital lines different from the output digital lines indicated by the information stored in said first routing tables and (B) virtual path identifiers, in association with the virtual path identifiers included in the input ATM cells;

(3) a failure information register connected to at least one of the input digital lines for storing, when one of output digital lines is faulty, internal routing information indicative of the faulty output digital line;

(4) a comparator connected to at least one of the input digital lines for comparing internal routing information read out from said first and second routing tables with internal routing information read out from said failure information registers;

(5) a first selector circuit connected to at least one of the input digital lines for outputting either of (A) virtual path identifiers and internal routing information read out from said first routing tables and (B) virtual path identifiers and internal routing information read out from said second routing tables; and

,

(6) a second selector circuit connected to at least one of the input digital lines for outputting outputs from said first selector circuits only when the virtual path identifiers of the input ATM cells are to be rewritten and when internal routing information are to be added, and for outputting the input ATM cells as they are at the other times,

wherein (A) virtual path identifiers indicative of output paths and (B) internal routing information indicative of output digital lines are read out according to a virtual path identifier included in an ATM cell input from an input digital line from first an second routing tables so that, when one of output digital lines indicated by the read out internal routing information is faulty, causing a comparator to produce a match signal, a first selector circuit is controlled to cause contents of a routing table storing internal routing information to which no match signal is produced in said comparator to be output to a second selector circuit, whereby an ATM cell having a virtual path identifier rewritten to indicate a normal output path and having internal routing information indicative of a normal output digital line added thereto is output into the system from said second selector circuit to the normal output digital line.

24. A path changing system for use in an ATM communication system wherein virtual path identifiers included in ATM cells input from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers to allow the ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to be output to a plurality of predetermined output digital lines, comprising:

(1) a first routing table connected to at least one of input digital lines for storing (A) virtual path identifiers indicative of output paths and (B) internal routing information indicative of output digital lines, in association with the virtual path identifiers included in the input ATM cells;

(2) a second routing table connected to at least one of the input digital lines for storing (A) virtual path identifiers indicative of output paths different from the output paths indicated by the information stored in said first routing tables and (B) internal routing information, in association with the virtual path identifiers included in the input ATM cells;

(3) a failure information register connected to at least one of the input digital lines for storing, when one of the output paths is faulty, a virtual path identifier indicative of the faulty output path;

(4) a comparator connected to at least one of the input digital lines for comparing virtual path identifiers read out from said first and second routing tables with virtual path identifiers read out from said failure information registers;

(5) a first selector circuit connected to at least one of the input digital lines for outputting one of (A) virtual path identifiers and internal routing information read out from said first routing tables and (B) virtual path identifiers and internal routing information read out from said second routing tables; and

,

(6) a second selector circuits connected to at least one of the input digital lines for outputting outputs from said first selector circuits only when the virtual path identifiers of input ATM cells are to be rewritten and when internal routing information are to be added, and for outputting the input ATM cells as they are at the other times,

wherein virtual path identifiers indicative of output paths and internal routing information are read out according to a virtual path identifier included in an ATM cell input from an input digital line from first and second routing tables so that, when an output path indicated by the read out virtual path identifier is faulty, said comparator producing a match signal, a first selector circuit is controlled to cause contents of a routing table storing virtual path identifier to which no match signal is produced in a comparator to be output to a second selector circuit, whereby the ATM cell having the virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output into the system from said second selector circuit to allow the ATM cell to be output therefrom to the normal output path.

25. A path changing system for use in an ATM communication system wherein virtual path identifiers included in ATM cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers so as to allow the ATM cells to be outputted into the system, whereby the ATM cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, comprising:

(1) a first routing table connected to at least one of input digital lines for storing virtual path identifiers indicative of output paths and internal routing information indicative of output digital lines, in association with virtual path identifiers included in the input ATM cells;

(2) a second routing table connected to at least one of the input digital lines for storing (A) virtual path identifiers indicative of output paths different from the output paths indicated by the information stored in said first routing tables and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in the first routing tables, in association with the virtual path identifiers included in the input ATM cells;

(3) a third routing table connected to at least one of the input digital lines for storing (A) virtual path identifiers indicative of output paths different from the output paths indicated by the information stored in said first and second routing tables and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in said first and second routing tables, in association with the virtual path identifiers included in the input ATM cells;

(4) a first failure information register connected to at least one of the input digital lines for storing, when one of output digital lines is faulty, internal routing information indicative of the faulty output digital line;

(5) a second failure information register connected to at least one of the input digital lines for storing, when one of output paths is faulty, a virtual path identifier indicative of the faulty output path;

(6) a first comparator connected to at least one of the input digital lines for comparing virtual path identifiers read out from said first, second and third routing tables with virtual path identifiers read out from said second failure information register;

(7) a second comparator connected to at least one of the input digital lines for comparing internal routing information read out from said first, second and third routing tables with internal routing information read out from said first failure information register;

(8) a first selector circuit connected to at least one of the input digital lines for outputting one of (A) virtual path identifiers and internal routing information read out from said first routing table and (B) virtual path identifiers and internal routing information read out from said second routing table;

(9) a second selector circuit connected to at least one of the input digital lines for outputting one of (A) an output of said first selector circuits and (B) virtual path identifiers and internal routing information read out from said third routing tables; and

,

(10) a third selector circuit connected to at least one of the input digital lines for outputting outputs from said second selector circuits only when virtual path identifiers of the input ATM cells are to be rewritten and only when internal routing information is to be added and for outputting the input ATM cells as they are at the other timings,

wherein (A) virtual path identifiers indicative of output paths and (B) internal routing information indicative of output digital lines are read out according to a virtual path identifier included in an ATM cell input from an input digital line from said first and second routing tables so that, when one of the output paths indicated by the read-out virtual path identifiers is faulty, said first comparator producing a match signal, said first selector circuit is controlled to cause contents of the routing table storing virtual path identifiers to which no match signal is produced in associated first comparator to be output to associated second selector circuit, and so that, the output digital line indicated by the internal routing information stored in the routing table storing virtual path identifier to which no match signal is produced in said first comparator and the output digital line indicated by the internal routing information read out from said second routing table are faulty, causing said second comparator to produce a match signal, said second selector circuit is controlled to cause contents of the routing table storing virtual path identifiers to which no match signal is produced in said second comparator to be output to an associated third selector circuit, whereby the ATM cell having the virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output into the system from said second selector circuit to the normal output path.

26. A path changing system for use in an ATM communication system wherein virtual path identifiers included in ATM cells input from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers so as to allow the ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to a plurality of predetermined output digital lines, comprising:

(1) a first routing table connected to at least one of input digital lines for storing (A) virtual path identifiers indicative of output paths and (B) internal routing information indicating output digital lines, in association with the virtual path identifiers included in the input ATM cells;

(2) a second routing table connected to at least one of the input digital lines for storing (A) virtual path identifiers indicative of output different from the output paths indicated by the information stored in said first routing tables and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in said first routing tables, in association with the virtual path identifiers included in the input ATM cells;

(3) a failure information register connected to at least one of the input digital lines for storing, when a fault occurs in one of the output digital lines, internal routing information indicative of the output digital line fault and information indicative of said fault being in the output digital lines and also storing, when a fault occurs in one of the output paths, virtual path identifiers indicative of the faulty output virtual path and information indicative of said faulty occurrence being in the output paths;

(4) a comparator connected to at least one of the input digital lines for comparing, when the information stored in said failure information register indicates the output digital line fault, internal routing information read out from said first and second routing tables with the internal routing information read out from said failure information register and for comparing, when the information stored in said failure information register indicates an output path fault, virtual path identifiers read out from said first and second routing tables with the virtual path identifiers read out from said failure information register;

(5) a first selector circuit connected to at least one of the input digital lines for outputting either of virtual path identifiers and internal routing information read out from said first routing tables or virtual path identifiers and internal routing information read out from said second routing tables; and

,

(6) a second selector circuit connected to at least one of the input digital lines for outputting outputs from said first selector circuits only when the virtual path identifiers of the input ATM cells are to be rewritten and only when the internal routing information are to be added and for outputting the input ATM cells as they are at the other timings;

wherein (A) virtual path identifiers indicative of the output paths and (B) internal routing information indicative of output digital lines are read out according to a virtual path identifier included in an ATM cell input from an input digital line by associated first and second routing tables so that, when one of the output digital lines indicated by the read out internal routing information is faulty or when one of the output paths indicated by the read out virtual path identifier is faulty, causing an associated comparator to produce a match signal, an associate first selector circuit is controlled to cause contents of a routing table storing internal routing information or virtual path identifiers to which no match signal is produced in said comparator to be output to a second selector circuit, whereby the ATM cell having a virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output from said second selector circuit into the system and thus is output therefrom to the normal output path.

27. A path changing system for use in an ATM communication system wherein virtual path identifiers included in ATM cells input from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers to allow the ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to be output to a plurality of predetermined output digital lines, comprising:

(1) a first routing table connected to at least one of input digital lines for storing (A) virtual path identifiers indicative of output paths and (B) internal routing information indicative of output digital lines, in association with the virtual path identifiers included in the input ATM cells;

(2) a second routing table connected to at least one of the input digital lines for storing (A) virtual path identifiers indicative of output paths different from the output paths indicated by the information stored in said first routing tables and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in said first routing tables, in association with the virtual path identifiers included in the input ATM cells;

(3) a failure information register connected to at least one of the input digital lines for storing, when a fault occurs in the plurality of the output digital lines, a plurality of internal routing information indicative of output digital lines;

(4) comparators connected to at least one of the input digital lines and also for said failure information registers for comparing the internal routing information read out from said first and second routing tables with internal routing information read out from said failure information registers;

(5) a first selector circuit connected to at least one of the input digital lines for outputting either one of (A) virtual path identifiers and internal routing information read out from said first tables and (B) virtual path identifiers and internal routing information read out from said second routing tables; and

,

(6) a second selector circuit connected to at least one of the input digital lines for outputting an output of said first selector circuits only when the virtual path identifiers of the input ATM cells are to be rewritten and only when the internal routing information are added, and for outputting the input ATM cells as they are at the other times,

wherein (A) virtual path identifiers indicative of output paths and (B) internal routing information indicative of output digital lines are read out from said first and second routing tables according to a virtual path identifier included in an ATM cell input from an input digital line so that, when one of the output digital lines indicated by the read out internal routing information is faulty, causing said comparator to produce a match signal, an associated first selector circuit is controlled to cause contents of a routing table storing the internal routing information to which no match signal is produced in any of said comparators to be output to an associated second selector circuit, whereby the ATM cell having the virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output from said associated second selector circuit into the system and thus is output therefrom to the normal output digital line.

28. A path changing system for use in an ATM communication system wherein virtual path identifiers included in ATM cells input from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers to allow said ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to be output to a plurality of predetermined output digital lines, comprising:

(1) a routing table connected to at least one of input digital lines for storing (A) a plurality of the virtual path identifiers indicative of a plurality of different output paths and (B) a plurality of internal routing information indicative of a plurality of different output digital lines, in association with virtual path identifiers included in the input ATM cells;

(2) a failure information register connected to at least one of the input digital lines, for storing, when a plurality of output digital lines or a plurality of output paths or both thereof are faulty, and, when the fault occurs in the output digital lines, internal routing information indicative of the faulty output digital lines and information indicative of the occurrence of the faulty output virtual paths and for storing, when the fault occurs in the output virtual paths, virtual path identifiers indicative of the faulty output paths and information indicative of the occurrence of the faulty output paths;

(3) comparators connected to at least one of the input digital lines and also for respective one of information stored in said failure information registers indicates the output digital line fault, internal routing information read out from said routing tables with internal routing information read out from said failure information registers and, when the information stored in said failure registers indicates the output path fault, virtual path identifiers read out from said routing tables with virtual path identifiers read out from said failure information registers;

(4) a control circuit connected to at least one of the input digital lines for controlling said routing tables to read out one of the information stored in said routing tables according to the virtual path identifiers included in the input ATM cells and for controlling, when receiving a match signal from said comparators, said routing tables to read out information other than the information previously read out according to the virtual path identifiers included in the input ATM cells; and

,

(5) a selector circuit connected to at least one of the input digital lines for outputting an output from said routing tables only when the virtual path identifiers of the input ATM cells are to be rewritten and only when the internal routing information are added, and for outputting the input ATM cells as they are at other timings,

wherein one of the virtual path identifiers indicative of output paths and internal routing information indicative of output digital lines are read out from said routing tables according to the virtual path identifiers included in an ATM cell input from an input digital line so that, when one of the output digital lines indicated by the read out internal routing information is faulty or when one of the output paths indicated by the read out virtual path identifiers is faulty, causing an associated comparator to produce a match signal, information other than previously read out information is read out from said routing tables and is output to an associated selector circuit and the ATM cell having a virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output into the system and thus is output therefrom to the normal output digital line.

29. A path changing method for use in a cell-based communication network comprising a plurality of cell switching systems wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines, and including a managing apparatus for managing said plurality of cell switching systems and a plurality of transmission lines, each of said plurality of cell switching systems having a path changing system the method comprising:

precedently loading (A) internal routing information indicative of output digital lines different from output digital lines stored in a first memory and (B) connecting information on output cells, into each of a plurality of second memories provided in each cell switching system,

storing, in a third memory connected to at least one of the input digital lines when one of the output digital lines is faulty, internal routing information indicative of the faulty output digital line;

comparing internal routing information read out from said first and second memories with internal routing information read out from said third memory;

outputting either of connecting information and internal routing information read out from said first memory and connecting information and internal routing information read out from said second memory; and

,

outputting an output only when connecting information of the input cells are to be rewritten and only when internal routing information are to be added and for outputting the input cells,

when an output digital line of a cell switching system is faulty, selecting a normal output digital line by using (A) interstation failure information transmitted and received between associated cell switching systems and (B) said path changing system, for performing communication in a cell switching network by taking an alternate transmission line or an alternate path in the transmission line, whereby the cell having the connecting information rewritten and having internal routing information added thereto to indicate a normal output digital line is output into the system to allow said cell to be output therefrom to the normal output digital line.

30. A path changing method for use in a cell-based communication network comprising a plurality of cell switching systems wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, and a managing apparatus for managing said plurality of cell switching systems and transmission lines, each of said plurality of cell switching systems having a path changing system comprising:

precedently loading (A) connecting information indicative of output paths different from output paths indicated by information stored in a first memory and (B) internal routing information, into each one of a plurality of second memories provided in each cell switching system and

storing, in a third memory connected to at least one of the input digital lines when one of the output paths is faulty, connecting information indicative of the faulty output path;

comparing the connecting information read out from said first and second memories with the connecting information read out from said third memory;

outputting either of (A) connecting information and internal routing information read out from said first memory and (B) connecting information and internal routing information read out from said second memory; and

,

outputting outputs only when connecting information of the input cells are to be rewritten When internal routing information is to be added and for outputting the input cells as they are at the other timings,

when an output path in a cell switching system is faulty, selecting a normal output path by using (A) an interstation failure information transmitted between associated cell switching systems and (B) said path changing system for performing communication in a cell switching network by taking an alternate transmission line or an alternate path in the transmission line, whereby the cell having the connecting information rewritten to indicate a normal output connection and having internal routing information added thereto is output into the system to allow said cell to be output therefrom to the normal output path.

31. In a cell-based communication network comprising a plurality of cell switching systems wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, and a managing apparatus for managing said plurality of cell switching systems and transmission lines, each of said plurality of cell switching systems having a path changing system for rerouting data, the improvement comprising:

precedently loading (A) connecting information indicative of output paths different from output paths indicated by information stored in a first memory and (B) internal routing information indicative of output digital lines different from output digital lines indicated by the information stored in said first memory, into each of a plurality of second memories provided in each cell switching system;

precedently loading (A) connecting information indicative of output paths different from the output paths indicated by the information stored in said first and second memories and (B) internal routing information indicative of output digital lines different from the output digital lines indicated by the information stored in said first and second memories, into each of a plurality of third memories of each cell switching system;

storing, in a fourth memory connected to at least one of the input digital lines when one of the output paths is faulty, internal routing information indicative of the faulty output path;

storing, in a fifth memory connected to at least one of the input digital lines, connecting information indicative of one the output connections which is faulty; and

when a fault is detected in an output digital line or an output path in a cell switching system, selecting a normal output digital line or output path by using (A) interstation failure information transmitted and received between associated cell switching systems and (B) said path changing system for performing communication in a cell switching network by taking an alternate transmission line or alternate path in the transmission line, whereby the cell having the connecting information rewritten to indicate a normal output path and having internal routing information added thereto is outputted into the system to the normal output path.

32. A path changing method for use in a cell-based communication network comprising a plurality of cell switching systems wherein connecting information included in cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched to a plurality of predetermined output digital lines, and a managing apparatus for managing said plurality of cell switching systems and transmission lines, each of said plurality of cell switching systems having a path changing system comprising:

precedently loading (A) connecting information indicative of output paths different from output paths indicated stored in a first memory and (B) internal routing information indicative of output digital lines different from output digital lines stored in said first memory, into each of a plurality of second memories in each cell switching system; and

storing, in a third memory connected to at least one of the input digital lines when a fault occurs in one of the output digital lines, (A) internal routing information indicative of the faulty output digital line and (B) information indicative of said fault in the output digital lines and also storing, when a fault occurs in one of the output paths, connecting information indicative of said fault in the output paths;

comparing, when the information stored in said third memory indicates an output digital line fault, internal routing information read out from said first and second memories with internal routing information read out from said third memory and for comparing, when the information stored in said third memory means indicates an output path fault, connecting information read out from said first and second memories with connecting information read out from said third memory;

outputting, from a first selector, either of connecting information and internal routing information read out from said first memory and connecting information and internal routing information read out from said second memory; and

,

outputting outputs from said first selector only when connecting information Of the input cells are to be rewritten and only when internal routing information are to be added and for outputting the input cells as they are at the other timings,

when a communication fault is detected in an output digital line or an output path in a cell switching system, selecting a normal output digital line or output path by using (A) interstation failure information transmitted and received between associated cell switching systems and (B) the path changing system to continue communication by taking an alternate transmission line or alternate path in the transmission line, whereby the cell having connecting information rewritten to indicate a normal output digital line and output path and having internal routing information added thereto, is outputted into the system and thus is outputted therefrom to the normal output digital line or normal output path.

33. A path changing method for use in a cell-based communication network comprising a plurality of cell switching systems wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, and a managing apparatus for managing said plurality of cell switching systems and transmission lines, each of said plurality of cell switching systems having a path changing system for rerouting communication lines, comprising:

precedently loading (A) connecting information indicative of output paths different from output paths indicated by the information stored in a first memory and (B) internal routing information indicative of output digital lines different from those indicated by information stored in said first memory, into each of a plurality of second memories of each cell switching system and

storing, in a third memory connected to at least one of the input digital lines when a plurality of output digital lines are faulty, a plurality of internal routing information indicative of the faulty output digital lines;

comparing internal routing information read out from said first and second memories with internal routing information read out from said third memories;

outputting, from a first selector, either of connecting information and internal routing information read out from said first memory and connecting information and internal routing information read out from said second memory; and

outputting outputs of said first selector when connecting information of the input cells are to be rewritten and when internal routing information are to be added, and for outputting the input cells as they are at other times,

when a digital output line in the cell switching system is faulty, said cell switching system selecting a normal output digital line by using (A) interstation failure information transmitted between associated cell switching systems and (B) said path changing system, to thereby perform communication in a cell switching network by taking an alternate transmission line or alternate path in a transmission line, whereby the cell having internal routing information rewritten to indicate a normal output digital line is output into the system and thus is output therefrom to the normal output digital line.

34. A path changing method for use in a cell-based communication network comprising a plurality of cell switching systems wherein connecting information included in cells input from a plurality of digital lines are rewritten and internal routing information are added to the cells according to the connecting information to allow said cells to be output into the system, whereby the cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, and a managing apparatus for managing said plurality of cell switching systems and transmission lines, each of said plurality of cell switching systems having a path changing system for rerouting data comprising:

precedently loading (A) a plurality of connecting information indicative of a plurality of different output paths and (B) a plurality of internal routing information indicative of a plurality of different output digital lines, into each of a plurality of first memories of each cell switching system; and

storing, in a second memory connected to at least one of the plurality of digital lines when a plurality of output digital lines or a plurality of output paths or both thereof are faulty, and, when the fault occurs in the output digital lines, internal routing information indicative of the faulty output digital lines and information indicative of occurrence of the faulty output digital lines and for storing, when the fault occurs in the output paths, connecting information indicative of the faulty output paths and information indicative of the occurrence of the faulty output paths;

comparing, when the information stored in said second memory indicates an output digital line fault, internal routing information read out from said first memory with internal routing information read out from said second memory and, when the information stored in said second memory indicates an output path fault, connecting information read out from said first memory with connecting information read out from said second memories;

controlling said first memory to read out one of the information stored in said first memory according to connecting information included in the input cells and controlling, when receiving a match signal, said first memory to read out information other than the information previously read out according to the connecting information included in the input cells; and

,

outputting an output from said first memories only when connecting information of the input cells are to be rewritten and when internal routing information are to be added and for outputting the input cells as they are at the other times,

when at least one of a digital output line and an output path in the cell switching system is faulty, said cell switching system selecting at least one of a normal output digital line and a normal output path by using (A) interstation failure information transmitted between associated cell switching systems and (B) said path changing system for continuing communication in a cell switching network by taking an alternate transmission line or alternate path in a transmission line, and the cell having the connecting information rewritten to indicate a normal output path and having internal routing information indicative of a normal output digital line added thereto is output into the system and thus is output therefrom to the normal output digital line and the normal output path.

35. A path changing method for use in an ATM communication network comprising a plurality of ATM communication apparatuses wherein virtual path identifiers included in ATM cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers to allow the ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to be output to a plurality of predetermined output digital lines, and a managing apparatus for managing said plurality of ATM communication apparatus and transmission lines, each of said plurality of ATM communication apparatus having a path changing system for rerouting data communications, comprising:

precedently loading (A) internal routing information indicative of output digital lines different from output digital lines indicated by information previously stored in a plurality of first routing tables and (B) virtual path identifiers, into each of a plurality of second routing tables provided in each ATM communication apparatus;

storing, in a failure information register connected to at least one of the plurality of digital lines when one of output digital lines is faulty, internal routing information indicative of the faulty output digital line; and

,

when a fault is detected in an output digital line of an ATM communication apparatus, said ATM communication apparatus selecting a normal output digital line by using (A) interstation failure information transmitted and received between associated ATM communication apparatuses and (B) said path changing system, and performing data communication in an ATM communication network by taking an alternate transmission line or alternate path in a transmission line, whereby an ATM cell having a virtual path identifier rewritten to indicate a normal output path and having internal routing information indicative of a normal output digital line added thereto is output into the system to the normal output digital line.

36. A path changing method for use in an ATM communication network comprising a plurality of ATM communication apparatus wherein virtual path identifiers included in ATM cells input from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers to allow the ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to be output to a plurality of predetermined output digital lines, and a managing apparatus for managing said plurality of ATM communication apparatus and transmission lines, each of said plurality of ATM communication apparatus having a path changing system comprising:

precedently loading (A) virtual path identifiers indicative of output paths different from output paths indicated by information previously stored in a plurality of first routing tables and (B) internal routing information, into each of a plurality of second routing tables provided in each ATM communication apparatus;

storing, in a failure information register connected to at least one of the plurality of digital lines when one of the output paths is faulty, a virtual path identifier indicative of the faulty output path; and

,

when a fault is detected in a virtual path of an ATM communication apparatus, said ATM communication apparatus selecting a normal output path by using (A) interstation failure information transmitted and received between ATM communication apparatuses involved and (B) said path changing system, to thereby perform communication in the ATM communication network, by taking an alternate path, whereby the ATM cell having the virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output into the system from said second selector circuit to allow the ATM cell to be output therefrom to the normal output path.

37. A path changing method for use in an ATM communication network comprising a plurality of ATM communication apparatuses wherein virtual path identifiers included in ATM cells inputted from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers so as to allow the ATM cells to be outputted into the system, whereby the ATM cells are multiplexed and switched so as to be output to a plurality of predetermined output digital lines, a managing apparatus for managing said plurality of ATM communication apparatus and transmission lines, each of said plurality of ATM communication apparatus having a path changing system comprising precedently loading (A) virtual path identifiers of output paths different from output paths indicated by information previously stored in a plurality of first routing tables and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in said plurality of first routing tables, into each of a plurality of second routing tables provided in each ATM communication apparatus and, precedently loading (A) virtual path identifiers indicative of output paths different from the output paths indicated by the information stored in said first and second routing tables and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in said first and second routing tables, into each of a plurality of third routing tables provided in each of said plurality of ATM communication apparatuses;

storing, in a first failure information register connected to at least one of the plurality of digital lines when one of the output digital lines is faulty, internal routing information indicative of the faulty output digital line;

storing, in a second failure information register connected to at least one of the plurality of digital lines when one of the output paths is faulty, a virtual path identifier indicative of the faulty output path; and

,

when an output digital line of an ATM communication apparatus is faulty, said ATM communication apparatus selecting a normal output path by using (A) interstation failure information transmitted and received between ATM communication apparatuses involved and (B) said path changing system, to thereby perform communication in an ATM communication network by taking an alternate path, whereby the ATM cell having the virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output into the system to the normal output path.

38. A path changing method for use in an ATM communication network comprising a plurality of ATM communication apparatuses wherein virtual path identifiers included in ATM cells input from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers so as to allow the ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to a plurality of predetermined output digital lines, and a managing apparatus for managing said plurality of ATM communication apparatus and transmission lines, each of said plurality of ATM communication apparatuses having a path changing system, said managing apparatus precedently loading (A) virtual path identifiers indicative of output paths different from output paths indicated by information stored in first routing tables and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in said first routing tables, into each of a plurality of second routing tables provided in each ATM communication apparatus,

storing, in a failure information register connected to at least one of the plurality of digital lines when a fault occurs in one of the output digital lines, internal routing information indicative of the output digital line fault and information indicative of said fault being in the output digital lines and also storing, when a fault occurs in one of the output paths, virtual path identifiers indicative of the faulty output virtual path and information indicative of said faulty occurrence being in the output paths;

and

when an output digital line or output path in an ATM communication apparatus is faulty, said ATM communication apparatus selecting a normal output path by using interstation failure information exchanged between ATM communication apparatuses involved and using said path changing system, to thereby perform communication in the ATM communication network by taking an alternate path, whereby the ATM cell having a virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output from said second selector circuit into the system and thus is output therefrom to the normal output path.

39. A path changing method for use in an ATM communication network comprising a plurality of ATM communication apparatuses wherein virtual path identifiers included in ATM cells input from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers to allow the ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to be output to a plurality of predetermined output digital lines, and a managing apparatus for managing said ATM communication apparatuses and transmission lines, each of said ATM communication apparatuses having a path changing system comprising:

precedently loading (A) virtual path identifiers indicative of output paths different from output paths indicated by information stored in first routing tables and (B) internal routing information indicative of output digital lines different from those indicated by the information stored in said first routing tables, into each of a plurality of second routing tables in each ATM communication apparatus, and

storing, in a failure information register connected to at least one of the plurality of digital lines when a fault occurs in the plurality of the output digital lines, a plurality of internal routing information indicative of output digital lines;

comparing the internal routing information read out from said first and second routing tables with internal routing information read out from said failure information registers;

when a fault is detected in an output digital line in an ATM communication apparatus, selecting a normal output digital line by using (A) interstation failure information transmitted between ATM communication apparatuses involved and (B) said path changing system, to thereby perform communication in the ATM communication network by exchanging data over an alternate transmission line, whereby the ATM cell having the virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output into the system and thus is output therefrom to the normal output digital line.

40. A path changing method for use in an ATM communication network comprising a plurality of ATM communication apparatuses wherein virtual path identifiers included in ATM cells input from a plurality of digital lines are rewritten and internal routing information are added to the ATM cells according to the virtual path identifiers to allow said ATM cells to be output into the system, whereby the ATM cells are multiplexed and switched to be output to a plurality of predetermined output digital lines, and a managing apparatus for managing said ATM communication apparatuses and transmission lines, each of said ATM communication apparatuses having a path changing system comprising:

precedently loading (A) a plurality of virtual path identifiers indicative of different output paths and (B) a plurality of internal routing information indicative of a plurality of different output digital lines, into each of a plurality of first routing tables included in each of said plurality of ATM communication apparatuses, and

storing, in a failure information register connected to at least one of the plurality of digital lines when a plurality of output digital lines or a plurality of output paths or both thereof are faulty, and, when the fault occurs in the output digital lines, internal routing information indicative of the faulty output digital lines and information indicative of the occurrence of the faulty output virtual paths and for storing, when the fault occurs in the output virtual paths, virtual path identifiers indicative of the faulty output paths and information indicative of the occurrence of the faulty output paths;

when a fault occurs in at least one of an output digital line and an output path in an ATM communication apparatus, said ATM communication apparatus selecting a normal output digital line by using (A) interstation failure information transmitted between ATM communication apparatuses involved in said fault and (B) said path changing system, to thereby continue data communication in the ATM communication network by exchanging data over an alternate transmission line, and the ATM cell having a virtual path identifier rewritten to indicate a normal output path and having internal routing information indicating a normal output digital line added thereto is output into the system and thus is output therefrom to the normal output digital line.