Virtual path connector and virtual path tracing method and apparatus

Claim 2

A virtual path (VP) connector in an asynchronous transfer mode (ATM) network system in which a plurality of VP connectors, for relaying ATM cells sequentially according to a VP between two VP terminators, are arranged, said VP connectors also relay a series of operation and maintenance (OAM) cells as ATM cells in which operational information is entered, said VP connector comprising: detection means for detecting and taking in a rearmost OAM cell of the series of OAM cells which are relayed according to the VP between the two VP terminators based on an end flag which has been set in said rearmost OAM cell of the series of OAM cells by a preceding VP connector or a VP terminator of the two VP terminators with respect to the VP; judgement means for judging whether sufficient area exists in said rearmost OAM cell detected by said detection means for entering operational information in said rearmost OAM cell; OAM cell generating means for generating a new OAM cell when said judgement means judges that sufficient area does not exist for entering the operational information in said rearmost OAM cell detected by said detection means; and operational information affixing means for, when said judgement means judges that sufficient area exists for entering the operational information in said rearmost OAM cell, entering the operational information in said rearmost OAM cell detected by said detection means, and relaying, according to the VP, said rearmost OAM cell in which said operational information has been entered, wherein, when said judgement means judges that sufficient area does not exist for entering the operational information in said rearmost OAM cell, said operational information affixing means enters the operational information in said new OAM cell generated by said OAM cell generating means, sets an end flag in said new OAM cell generated by said OAM cell generating means, resets the end flag in said rearmost OAM cell detected by said detection means and relays, according to the VP, said rearmost OAM cell in which the end flag has been reset and said new OAM cell in which the operational information has been entered.

Claim 3

A VP connector according to claim 1, wherein said operational information affixing means enters a serial number in said new OAM cell generated by said OAM cell generating means, said serial number representing an order of said new OAM cell in the series of OAM cells.

Claim 4

A VP connector according to claim 1, wherein said operational information affixing means decides a value of said serial number to be entered in said new OAM cell generated by said OAM cell generating means, based on a serial number which has been set in said rearmost OAM cell of the series of OAM cells by the preceding VP connector or the VP terminator of the two VP terminators with in respect to the VP.

Claim 5

A VP connector according to claim 1, wherein said operational information affixing means enters error detection information for detecting any errors generated during relaying of said rearmost OAM cell, and enters said error detection information in said new OAM cell generated by said OAM cell generating means for detecting any errors generated during relaying of said new OAM cell.

Claim 6

A VP connector according to claim 4, wherein said operational information affixing means comprises: error detection means for detecting an error in said rearmost OAM cell based on said error detection information which has been set in said rearmost OAM cell of the series of OAM cells by a preceding VP connector or the VP terminator with respect to the VP; and means for setting an error flag in said rearmost OAM cell when said error of said rearmost OAM cell is detected by said error detection means, said detection means relaying said rearmost OAM cell instead of taking in said rearmost OAM cell in said VP connector when said error flag has been set in said rearmost OAM cell by a preceding VP connector or the VP terminator of the two VP terminators with respect to the VP.

Claim 7

A virtual path (VP) terminator in an asynchronous transfer mode (ATM) network system which includes an operating system for controlling a VP tracing, two VP terminators each of which receives an instruction of VP tracing operation from said operating system, and a plurality of VP connectors for relaying ATM cells sequentially according to a VP between said two VP terminators, said VP connectors also relay a series of operation and maintenance (OAM) cells as ATM cell in which operational information is entered, said VP terminator comprising: reception means for receiving an instruction of starting of VP tracing from the operating system, wherein said VP terminator is an end point of the VP; detection means for detecting a rearmost OAM cell of the series of OAM cells which are relayed from one of the VP connectors preceding VP terminator with respect to the VP; and reporting means for reporting, to the operating system, operational information entered in each of the OAM cells included in the series of OAM cells relayed from the VP connector preceding the VP terminator with respect to the VP, in response to a detection of said rearmost OAM cell by said detection means.

Claim 8

A virtual path (VP) terminator in an asynchronous transfer mode (ATM) network system which includes an operating system for controlling a VP tracing, two VP terminators each of which receives an instruction of VP tracing operation from said operating system, and a plurality of VP connectors for relaying ATM cells sequentially according to a VP between said two VP terminators, said VP connectors also relay a series of operation and maintenance (OAM) cells as ATM cell in which operational information is entered, said VP terminator comprising: reception means for receiving an instruction of starting of VP tracing from the operating system, wherein said VP terminator is an end point of the VP; detection means for detecting a rearmost OAM cell of the series of OAM cells which are relayed from one of the VP connectors preceding VP terminator with respect to the VP; and reporting means for reporting, to the operating system, operational information entered in each of the OAM cells included in the series of OAM cells relayed from the VP connector preceding the VP terminator with respect to the VP, in response to a detection of said rearmost OAM cell by said detection means.

Claim 9

A VP terminator according to claim 6, wherein said reporting means reports, to said operating system, operational information entered in each of the OAM cells included in the series of OAM cells which have been relayed from the VP connector preceding the VP terminator with respect to the VP, in response to an occurrence of an event indicating that a predetermined time period starting at a time point when said reception means receives said instruction of starting of VP tracing has elapsed before said detection means detects said rearmost OAM cell of the series of OAM cells.

Claim 10

An asynchronous transfer mode (ATM) network system which includes an operating system for controlling a virtual path (VP) tracing, two VP terminators each of which receives an instruction of VP tracing operation from said operating system and a plurality of VP connectors for relaying ATM cells sequentially according to a VP between said two VP terminators, said VP connectors also relay a series of OAM cells each of which is an ATM cell in which operational information is entered, wherein the VP terminator being arranged at a start point of the VP comprises: first reception means for receiving an instruction of starting of VP tracing in which the VP terminator is a start point of the VP from said operation system, and transmission means for transmitting, in response to reception of said instruction by said first reception means, an OAM cell including an end flag being set and operational information of the VP terminator at the start point of the VP, to the VP connector succeeding the VP terminator arranged at the start point of the VP; wherein each of said VP connectors comprises: first detection means for detecting a rearmost OAM cell of the series of OAM cells which are relayed, according to the VP, based on an end flag which has been set in said rearmost OAM cell of the series of OAM cells by a preceding VP connector or a VP terminator with respect to the VP, judgement means for judging whether sufficient area exists for entering operational information in said rearmost OAM cell detected by said first detection means, OAM cell generating means for generating a new OAM cell when said judgement means judges that sufficient area does not exist for entering said operational information in said rearmost OAM cell, and operational information affixing means for, when said judgement means judges that sufficient area exists for entering said operational information in said rearmost OAM cell, entering said operational information in said rearmost OAM cell detected by said first detection means and relaying, according to the VP, said rearmost OAM cell in which said operational information has been entered, wherein, when said judgement means judges that sufficient area does not exist for entering said operational information in said rearmost OAM cell, said operational information affixing means enters said operational information in said new OAM cell generated by said OAM cell generating means, sets an end flag in said new OAM cell generated by said OAM cell generating means, resets the end flag in said rearmost OAM cell detected by said detection means and relays, according to the VP, said rearmost OAM cell in which the end flag has been reset and said new OAM cell in which said operational information has been entered; and wherein, the VP terminator arranged at an end point of the VP comprises: second reception means for receiving instruction of starting of VP tracing in which the VP terminator is an end point of the VP from said operation system, second detection means for detecting said rearmost OAM cell of the series of OAM cells which are relayed from a VP connector preceding the VP terminator with respect to the VP based on an end flag which has been set in said rearmost OAM cell of the series of OAM cells by a previous VP connector or a VP terminator of the two VP terminators with respect to the VP, and reporting means for reporting, to said operating system, operational information entered in each of the OAM cells included in the series of OAM cells relayed from the VP connector preceding the VP terminator with respect to the VP, in response to a detection of said rearmost OAM cell by said second detection means.

Claim 11

An asynchronous transfer mode (ATM) network system which includes an operating system for controlling a virtual path (VP) tracing, two VP terminators each of which receives an instruction of VP tracing operation from said operating system and a plurality of VP connectors for relaying ATM cells sequentially according to a VP between said two VP terminators, said VP connectors also relay a series of OAM cells each of which is an ATM cell in which operational information is entered, wherein the VP terminator being arranged at a start point of the VP comprises: first reception means for receiving an instruction of starting of VP tracing in which the VP terminator is a start point of the VP from said operation system, and transmission means for transmitting, in response to reception of said instruction by said first reception means, an OAM cell including an end flag being set and operational information of the VP terminator at the start point of the VP, to the VP connector succeeding the VP terminator arranged at the start point of the VP; wherein each of said VP connectors comprises: first detection means for detecting a rearmost OAM cell of the series of OAM cells which are relayed, according to the VP, based on an end flag which has been set in said rearmost OAM cell of the series of OAM cells by a preceding VP connector or a VP terminator with respect to the VP, judgement means for judging whether sufficient area exists for entering operational information in said rearmost OAM cell detected by said first detection means, OAM cell generating means for generating a new OAM cell when said judgement means judges that sufficient area does not exist for entering said operational information in said rearmost OAM cell, and operational information affixing means for, when said judgement means judges that sufficient area exists for entering said operational information in said rearmost OAM cell, entering said operational information in said rearmost OAM cell detected by said first detection means and relaying, according to the VP, said rearmost OAM cell in which said operational information has been entered, wherein, when said judgement means judges that sufficient area does not exist for entering said operational information in said rearmost OAM cell, said operational information affixing means enters said operational information in said new OAM cell generated by said OAM cell generating means, sets an end flag in said new OAM cell generated by said OAM cell generating means, resets the end flag in said rearmost OAM cell detected by said detection means and relays, according to the VP, said rearmost OAM cell in which the end flag has been reset and said new OAM cell in which said operational information has been entered; and wherein, the VP terminator arranged at an end point of the VP comprises: second reception means for receiving instruction of starting of VP tracing in which the VP terminator is an end point of the VP from said operation system, second detection means for detecting said rearmost OAM cell of the series of OAM cells which are relayed from a VP connector preceding the VP terminator with respect to the VP based on an end flag which has been set in said rearmost OAM cell of the series of OAM cells by a previous VP connector or a VP terminator of the two VP terminators with respect to the VP, and reporting means for reporting, to said operating system, operational information entered in each of the OAM cells included in the series of OAM cells relayed from the VP connector preceding the VP terminator with respect to the VP, in response to a detection of said rearmost OAM cell by said second detection means.

Claim 12

An ATM network system according to claim 8, wherein the VP terminator arranged at the start point of the VP further comprises: means for entering a serial number in the OAM cell to be transmitted by said transmission means; wherein said operational information affixing means of each of said VP connectors enters a serial number into said new OAM cell generated by OAM cell generating means based on a serial number which has been set in said rearmost OAM cell of the series of OAM cells by the preceding VP connector or the VP terminator of the two VP terminators with respect to the VP; wherein said reporting means of the VP terminator arranged at an end point of the VP reports an abnormality to said operating system when each of the OAM cells of the series of OAM cells is not relayed in accordance with said serial number order from the VP connector preceding the VP terminator at the end point, said serial number representing an order of the OAM cell in the series of OAM cells.

Claim 15

A format of a cell included in a series of cells for tracing virtual path (VP), the cell being used for collecting operational information of connectors which establish a connection at a VP level within a network wherein the cell is transferred in an asynchronous transfer mode (ATM) wherein said cell for VP tracing contains an area for an end flag which indicates that each cell is a rearmost cell of a series of currently existing cells for said VP tracing.

Claim 16

A format of a cell included in a series of cells for tracing virtual path (VP), the cell being used for collecting operational information of connectors which establish a connection at a VP level within a network wherein the cell is transferred in an asynchronous transfer mode (ATM) wherein said cell for VP tracing contains an area for an end flag which indicates that each cell is a rearmost cell of a series of currently existing cells for said VP tracing.

Claim 17

A format of a cell according to claim 11, wherein said cell for said VP tracing contains an area for a serial number, said serial number indicating an order of said cell in said series of currently existing cells of said VP tracing.

Claim 18

A format of a cell according to claim 12, wherein said cell for said VP tracing contains an area for an error flag which indicates presence or absence of an error in said cell under said VP tracing.

Claim 19

A virtual path (VP) terminator in an asynchronous transfer mode (ATM) network system which includes an operating system for controlling a VP tracing operation, two of VP terminators each of which receives an instruction of VP tracing operation from said operating system, and a plurality of VP connectors for relaying ATM cells sequentially according to a VP between said two of VP terminators, said VP connectors also relay a series of operation and maintenance (OAM) cells as ATM cell in which operational information is entered, said VP terminator comprising: reception means for receiving an instruction of starting of an operation in VP tracing wherein the VP terminator is assigned as an end point of the VP tracing, from said operation system; detection means for executing a detection of a rearmost OAM cell of the series of the OAM cells which are relayed from one of the VP connectors preceding VP terminator with respect to said VP, said detection is started in response to a reception of said instruction at said reception means; and reporting means for reporting, to said operating system, the operational information entered in each of the OAM cells included in the series of OAM cells relayed from the VP connector preceding the VP terminator with respect to said VP, in response to detection of the rearmost OAM cell of the series of the OAM cells before a predetermined time period starting at a time point when said reception means receives said instruction has elapsed, wherein said reporting means reports, to said operating system, operational information entered in each of the OAM cells included in the series of OAM cells which have been relayed from the VP connector preceding the VP terminator with respect to said VP, in response to an occurrence of event indicating that said predetermined time period starting at a time point when said reception means receives said instruction has elapsed before said detection means detects the rearmost OAM cell of the series of the OAM cells.

Claim 20

A virtual path (VP) terminator in an asynchronous transfer mode (ATM) network system which includes an operating system for controlling a VP tracing operation, two of VP terminators each of which receives an instruction of VP tracing operation from said operating system, and a plurality of VP connectors for relaying ATM cells sequentially according to a VP between said two of VP terminators, said VP connectors also relay a series of operation and maintenance (OAM) cells as ATM cell in which operational information is entered, said VP terminator comprising: reception means for receiving an instruction of starting of an operation in VP tracing wherein the VP terminator is assigned as an end point of the VP tracing, from said operation system; detection means for executing a detection of a rearmost OAM cell of the series of the OAM cells which are relayed from one of the VP connectors preceding VP terminator with respect to said VP, said detection is started in response to a reception of said instruction at said reception means; and reporting means for reporting, to said operating system, the operational information entered in each of the OAM cells included in the series of OAM cells relayed from the VP connector preceding the VP terminator with respect to said VP, in response to detection of the rearmost OAM cell of the series of the OAM cells before a predetermined time period starting at a time point when said reception means receives said instruction has elapsed, wherein said reporting means reports, to said operating system, operational information entered in each of the OAM cells included in the series of OAM cells which have been relayed from the VP connector preceding the VP terminator with respect to said VP, in response to an occurrence of event indicating that said predetermined time period starting at a time point when said reception means receives said instruction has elapsed before said detection means detects the rearmost OAM cell of the series of the OAM cells.

Claim 21

A virtual path (VP) connector in an asynchronous transfer mode (ATM) network system in which a plurality of VP connectors, for relaying ATM cells sequentially according to a VP (virtual path) between two of VP terminators, are arranged, said VP connectors also relaying a series of operation and maintenance (OAM) cells as ATM cells in which operational information is entered, comprising: detection means for detecting and taking in a rearmost OAM cell of said series of the OAM cells which are relayed to the VP connector according to said VP, based on an end flag which has been set in said rearmost OAM cell of said series of the OAM cells by a preceding VP connector or the VP terminator with respect to said VP; judgement means for judging whether sufficient area exists in said rearmost cell taken in by said detection means for entering the operational information in said rearmost OAM cell; OAM cell generating means for generating a new OAM cell when said judgement means judges that sufficient area does not exist for entering the operational information in the rearmost OAM cell taken in by said detection means; and operational information affixing means for, when said judgement means judges that sufficient area exists for entering the operational information in the rearmost OAM cell, entering the operational information in the rearmost OAM cell taken in by said detection means, entering error detection information for detecting any errors of the OAM cell under the relaying in the rearmost cell taken in by said detection means, and relaying, according to said VP, said rearmost OAM cell in which said operational information has been entered, wherein, when said judgement means judges that sufficient area does not exist for entering the operational information in the rearmost OAM cell, said operational information affixing means enters the operational information in said new OAM cell generated by said OAM cell generating means, sets the end flag in the new OAM cell generated by said OAM cell generating means, resets the end flag in the rearmost OAM cell taken in by said detection means, enters error detection information for detecting any errors of the OAM cell under the relaying in the rearmost cell taken in by said detection means, enters the error detection information in said new OAM cell generated by said OAM cell generating means, and relays, according to said VP, the rearmost OAM cell in which the end flag has been reset and said new OAM cell in which said operational information has been entered and, thereby said new OAM cell becomes a new rearmost OAM cell of said series of the OAM cells.

Claim 22

A virtual path (VP) connector in an asynchronous transfer mode (ATM) network system in which a plurality of VP connectors, for relaying ATM cells sequentially according to a VP (virtual path) between two of VP terminators, are arranged, said VP connectors also relaying a series of operation and maintenance (OAM) cells as ATM cells in which operational information is entered, comprising: detection means for detecting and taking in a rearmost OAM cell of said series of the OAM cells which are relayed to the VP connector according to said VP, based on an end flag which has been set in said rearmost OAM cell of said series of the OAM cells by a preceding VP connector or the VP terminator with respect to said VP; judgement means for judging whether sufficient area exists in said rearmost cell taken in by said detection means for entering the operational information in said rearmost OAM cell; OAM cell generating means for generating a new OAM cell when said judgement means judges that sufficient area does not exist for entering the operational information in the rearmost OAM cell taken in by said detection means; and operational information affixing means for, when said judgement means judges that sufficient area exists for entering the operational information in the rearmost OAM cell, entering the operational information in the rearmost OAM cell taken in by said detection means, entering error detection information for detecting any errors of the OAM cell under the relaying in the rearmost cell taken in by said detection means, and relaying, according to said VP, said rearmost OAM cell in which said operational information has been entered, wherein, when said judgement means judges that sufficient area does not exist for entering the operational information in the rearmost OAM cell, said operational information affixing means enters the operational information in said new OAM cell generated by said OAM cell generating means, sets the end flag in the new OAM cell generated by said OAM cell generating means, resets the end flag in the rearmost OAM cell taken in by said detection means, enters error detection information for detecting any errors of the OAM cell under the relaying in the rearmost cell taken in by said detection means, enters the error detection information in said new OAM cell generated by said OAM cell generating means, and relays, according to said VP, the rearmost OAM cell in which the end flag has been reset and said new OAM cell in which said operational information has been entered and, thereby said new OAM cell becomes a new rearmost OAM cell of said series of the OAM cells.

Claim 23

A VP (virtual path) connector defined in claim 15, wherein said operational information affixing means comprises: error detection means for detecting an error in said rearmost OAM cell taken in by said detection means, based on the error detection information which has been set in said rearmost OAM cell by a preceding VP connector or the VP terminator with respect to said VP; and means for setting an error flag in the rearmost OAM cell when the error of said rearmost OAM cell is detected by said error detection means, wherein said detection means relays the detected rearmost OAM cell instead of taking in the rearmost OAM cell in said VP connector when the error flag has been set in said rearmost OAM cell by a preceding VP connector or the VP terminator with respect to the VP.

Claim 24

An asynchronous transfer mode (ATM) network system which includes an operating system for controlling a virtual path (VP) tracing, two of VP terminators each of which receives an instruction of VP tracing operation from said operating system and a plurality of VP connectors for relaying ATM cells sequentially according to a VP between said two of VP terminators, said VP connectors also relaying a series of operation and maintenance (OAM) cells each of which is an ATM cell in which operational information is entered, wherein the VP terminator being arranged at a start point of the VP comprises: first reception means for receiving an instruction of starting of an operation in VP tracing in which the VP terminator is a start point of the VP from said operation system, and transmission means for transmitting, in response to the reception of said instruction by said first reception means, an OAM cell including an end flag being set and operational information of the VP terminator at the start point of the VP, to the VP connector arranged succeeding the VP terminator arranged at the start point of the VP; wherein each of said VP connectors comprises: first detection means for detecting a rearmost OAM cell of the series of the OAM cells which are relayed, according to the VP, based on an end flag which has been set in said rearmost OAM cell of said series of the OAM cells by a preceding VP connector or the VP terminator with respect to the VP, judgement means for judging whether sufficient area exists for entering the operational information in said rearmost OAM cell taken in by said first detection means, OAM cell generating means for generating a new OAM cell when said judgement means judges that sufficient area does not exist for entering the operational information in said rearmost OAM cell, and operational information affixing means for, when said judgement means judges that sufficient area exists for entering said operational information in said rearmost OAM cell, entering the operational information in said rearmost OAM cell and relaying, according to said VP, the rearmost OAM cell in which said operational information has been entered; wherein, when said judgement means judges that sufficient area does not exist for entering said operational information in said rearmost OAM cell, said operational information affixing means enters said operational information in said new OAM cell generated by said OAM cell generating means, sets an end flag in said new OAM cell generated by said OAM cell generating means, resets the end flag in said rearmost OAM cell taken in by said detection means and relays, according to said VP, the rearmost OAM cell in which the end flag has been reset and said new OAM cell in which said operational information has been entered; wherein the VP terminator arranged at an end point of the VP comprises: second reception means for receiving instruction of starting of an operation in VP tracing in which the VP terminator is an end point of the VP from said operation system, second detection means for detecting the rearmost OAM cell of the series of the OAM cells which are relayed from the VP connector preceding the VP terminator with respect to said VP, based on an end flag which has been set in said rearmost OAM cell of the series of the OAM cells by the previous VP connector with respect to the VP or the VP terminator arranged at the start point of the VP tracing, and reporting means for reporting, to said operating system, the operational information entered in each of the OAM cells included in the series of OAM cells relayed from the VP connector preceding the VP terminator with respect to said VP, in response to a detection of the rearmost OAM cell in said detection means; wherein said VP terminator arranged at a start point of the VP comprises means for entering a serial number in the OAM cell to be transmitted by said transmission means; wherein said operational information affixing means of each of said VP connectors enters a serial number in said new OAM cell generated by OAM cell generating means, based on the serial number which has been set in said rearmost OAM cell of said series of the OAM cells by the preceding VP connector with respect to said VP or the VP terminator arranged at the start point of the VP tracing; wherein said reporting means of said VP terminator arranged at an end point of the VP reports an abnormality to said operating system when each of the OAM cells of the series of the OAM cells is not relayed to the VP terminator at said end point in accordance with said serial number order from the VP connector preceding the VP terminator at the end point; and wherein said serial number represents an order of the OAM cell in said series of the OAM cells.

Claim 25

An asynchronous transfer mode (ATM) network system which includes an operating system for controlling a virtual path (VP) tracing, two of VP terminators each of which receives an instruction of VP tracing operation from said operating system and a plurality of VP connectors for relaying ATM cells sequentially according to a VP between said two of VP terminators, said VP connectors also relaying a series of operation and maintenance (OAM) cells each of which is an ATM cell in which operational information is entered, wherein the VP terminator being arranged at a start point of the VP comprises: first reception means for receiving an instruction of starting of an operation in VP tracing in which the VP terminator is a start point of the VP from said operation system, and transmission means for transmitting, in response to the reception of said instruction by said first reception means, an OAM cell including an end flag being set and operational information of the VP terminator at the start point of the VP, to the VP connector arranged succeeding the VP terminator arranged at the start point of the VP; wherein each of said VP connectors comprises: first detection means for detecting a rearmost OAM cell of the series of the OAM cells which are relayed, according to the VP, based on an end flag which has been set in said rearmost OAM cell of said series of the OAM cells by a preceding VP connector or the VP terminator with respect to the VP, judgement means for judging whether sufficient area exists for entering the operational information in said rearmost OAM cell taken in by said first detection means, OAM cell generating means for generating a new OAM cell when said judgement means judges that sufficient area does not exist for entering the operational information in said rearmost OAM cell, and operational information affixing means for, when said judgement means judges that sufficient area exists for entering said operational information in said rearmost OAM cell, entering the operational information in said rearmost OAM cell and relaying, according to said VP, the rearmost OAM cell in which said operational information has been entered; wherein, when said judgement means judges that sufficient area does not exist for entering said operational information in said rearmost OAM cell, said operational information affixing means enters said operational information in said new OAM cell generated by said OAM cell generating means, sets an end flag in said new OAM cell generated by said OAM cell generating means, resets the end flag in said rearmost OAM cell taken in by said detection means and relays, according to said VP, the rearmost OAM cell in which the end flag has been reset and said new OAM cell in which said operational information has been entered; wherein the VP terminator arranged at an end point of the VP comprises: second reception means for receiving instruction of starting of an operation in VP tracing in which the VP terminator is an end point of the VP from said operation system, second detection means for detecting the rearmost OAM cell of the series of the OAM cells which are relayed from the VP connector preceding the VP terminator with respect to said VP, based on an end flag which has been set in said rearmost OAM cell of the series of the OAM cells by the previous VP connector with respect to the VP or the VP terminator arranged at the start point of the VP tracing, and reporting means for reporting, to said operating system, the operational information entered in each of the OAM cells included in the series of OAM cells relayed from the VP connector preceding the VP terminator with respect to said VP, in response to a detection of the rearmost OAM cell in said detection means; wherein said VP terminator arranged at a start point of the VP comprises means for entering a serial number in the OAM cell to be transmitted by said transmission means; wherein said operational information affixing means of each of said VP connectors enters a serial number in said new OAM cell generated by OAM cell generating means, based on the serial number which has been set in said rearmost OAM cell of said series of the OAM cells by the preceding VP connector with respect to said VP or the VP terminator arranged at the start point of the VP tracing; wherein said reporting means of said VP terminator arranged at an end point of the VP reports an abnormality to said operating system when each of the OAM cells of the series of the OAM cells is not relayed to the VP terminator at said end point in accordance with said serial number order from the VP connector preceding the VP terminator at the end point; and wherein said serial number represents an order of the OAM cell in said series of the OAM cells.