Communication network system, communication device, route design device, and failure recovery method

TECHNICAL FIELD

0001The present invention relates to a communication network system which switches a path to a detour path when a failure occurs, a communication device of the communication network system, a route design device, and a failure recovery method for when a failure occurs. In particular, the present invention relates to a communication network system capable of rapid detouring using minimal network resources in consideration of a plurality of failure locations when a plurality of failures occur simultaneously within a predetermined period of time in the communication network system, and capable of reversion to an original state after recovery from the failure, a communication device, a route design device, and a failure recovery method.

0002This application claims priority to and the benefit of Japanese Patent Applications No. 2008-079219 filed on Mar. 25, 2008, the disclosure of which is incorporated herein by reference.

BACKGROUND ART

0003An example of a conventional failure recovery scheme in a communication network is disclosed in Non-Patent Document 1 and Patent Document 1. This conventional failure recovery scheme in the communication network includes 1+1 protection (1+1 Unidirectional/Bidirectional Protection), 1:1 Protection, reservation type restoration (Shared Mesh Restoration), and path re-routing (LSP Re-routing), as disclosed in Non-Patent Document 1.

0004All of these failure recovery methods except for the path re-routing include previously determining preliminary routes for a currently-used route. For this reason, detouring the failure fails when multiple failures occur simultaneously on the currently used route and the preliminary route. As a result, in cases of multiple failures, the path re-routing as disclosed in Patent Document 1 has been applied.

0005Patent Document 1 discloses that when protection fails, path re-routing is performed under control of a GMPLS control unit. In such related art, a communication device includes a routing protocol unit, a topology DB for recording failures or empty bands of links reported by the routing protocol unit, and a signaling protocol unit for controlling paths.

0006Patent Document 1 also discloses the topology DB as a forwarding DB and the signaling protocol as a GMPLS control unit. Conventional path re-routing when the communication device having the above-described configuration is used is performed as follows.

0007After receiving a failure notification, the communication device deletes a currently-used path. The communication device then refers to the topology DB collected by the routing protocol to calculate a detour path that does not include failure locations. The communication device sets a new path along the detour route using a signaling protocol to recover from the communication failure.

0008However, such path re-routing has the following problems.

0009The first problem is that since it takes time for the routing protocol to notify the communication device of the failure location after the failure occurs, it is necessary to wait for a predetermined period of time in order to calculate the detour route and it takes time to recover from the failure.

0010Further, since it is impossible to detect whether the routing protocol was converged, it is not known whether a failure has occurred on the detour route calculated by referring to the topology DB of a start-point communication device. Therefore, when multiple failures occur, there is a possibility that a route including a failure location that is not present on the currently-used path is calculated, thus decreasing reliability of the calculated route.

0011The second problem is that, because a re-routing operation is dispersively performed, network resource contention may occur at intermediate communication nodes when a plurality of currently-used paths simultaneously fail. For example, referring to the network shown in <figref idref="DRAWINGS">FIG. 14</figref>, a link between communication devices B and C and a link between communication devices B and F have simultaneously failed. A communication device <b>1000</b> is disposed at a location encircled with a symbol A in <figref idref="DRAWINGS">FIG. 14</figref>. Similarly, communication devices <b>1000</b> are also disposed at locations encircled with symbols B, C, D, E, F, and G.

0012In <figref idref="DRAWINGS">FIG. 14</figref>, a transmission link between the communication device A and the communication device C is indicated by a transmission link <b>90</b>-AC.

0013Here, a detour route for a currently-used path <b>1100</b> is calculated by the communication device A and a detour route for a currently-used path <b>1200</b> is calculated by the communication device D. In the detour route calculation, the communication device A or D does not consider the detour route of the communication device D or A. Accordingly, even when a link between the communication devices D and E or a link between the communication device E and B is an insufficient-band link having a band for only one detour path, a contention route is calculated through a shortest route calculation. Accordingly, one of the communication devices fails to set the detour path. In <figref idref="DRAWINGS">FIG. 14</figref>, the communication device A sets a detour route <b>1101</b> and the communication device D sets a detour route <b>1201</b>. Accordingly, for example, a link between the communication device B and the communication device E becomes a contention link.

0014The third problem is that the currently-used path cannot be reverted to the original route after recovery from the failure. This is because the currently-used path needs to be deleted to set the detour route in order to reuse network resources other than those in a failure section that is being used by a failed currently-used path.

0015In general, the currently-used path is set as an optimal path in a range allowing the network to normally operate. For this reason, failure to revert to an original route of the currently-used path after recovery from all failures means that the optimal working state cannot be restored.

0016Non-Patent Document 1: J. Lang, Y. Rekhter, D. Papadimitriou, “RSVP-TE Extensions in Support of End-to-End Generalized Multi-Protocol Label Switching (GMPLS) Recovery,” IETF RFC4872. Chapters 5 to 11.

0017Patent Document 1: Japanese Unexamined Patent Publication, First Publication No. 2002-125711

DISCLOSURE OF INVENTION

Problem to be Solved by the Invention

0018The present invention has been achieved in view of the above circumstances, and it is a first object of the present invention to provide a communication network system, a communication device, a route design device, and a failure recovery method which is irrespective of convergence time of a routing protocol and is capable of quickly detouring a plurality of paths without resource contention for setting detour routes even in the case of multiple failures.

0019A second object of the present invention is to provide a communication network system, a communication device, a route design device, and a failure recovery method capable of reverting to an originally used route after recovery from failure.

Means for Solving the Problem

0020(1) The present invention has been made to solve the above-described problems. According to an aspect of the present invention, there is provided a communication network system comprising a plurality of communication devices each comprising a switching unit which switches traffic routes, and transmission links which connects the plurality of communication devices, wherein a start-point communication device of the plurality of communication devices comprising: a storage unit which previously stores information of a plurality of detour paths corresponding to but having routes different from a working path that is transferring traffic between the start-point communication device and an endpoint communication device; and a setting unit which receives a failure notification when a failure occurs in the working path, selects a detour path that is switchable and has the highest priority from among the plurality of detour paths stored in the detour path information storage unit, and then sets relevant communication devices among the plurality of communication devices along the route of the detour path to recover from the failure.

0021(2) In the communication network system according to the aspect of the present invention, the plurality of detour paths stored in the storage unit of the start-point communication device are registered as paths for which reserving of bands and setting of the switching units are not performed in the communication devices along the route of the detour path, and when a failure affecting the detour path occurs, the communication device that has detected the failure or the communication device that has received the failure notification notifies the start-point communication device of a failure location.

0022(3) In the communication network system according to the aspect of the present invention, a requested band of the path is 0 in signaling for setting the detour path.

0023(4) In the communication network system according to the aspect of the present invention, the storage unit of the start-point communication device comprises a working path database which stores the working paths and a detour path database which stores information of the detour paths, and the setting unit of the start-point communication device: stores information of the currently-used path that has been used as the working path in the detour path database as a detour path during the failure, stores information of the detour path used as the working path in the working path database, and refers to the information of the detour path to perform signaling for setting the detour path as a working path when switching to the detour path, and also stores the information of the currently-used path from the detour path database in the working path database after recovery from the failure, and refers to the information of the relevant currently-used path to revert to the currently-used path.

0024(5) In the communication network system according to the aspect of the present invention, the communication network system further comprises a route design device which calculates routes of detour paths that do not contend with each other when a failure occurs in calculation of the detour paths corresponding to different currently-used paths, wherein the route design device calculates routes of the detour paths that are previously set in the start-point communication device.

0025(6) According to another aspect of the present invention, there is provided a communication device in a communication network system comprising a plurality of communication devices each comprising a plurality of transmission interfaces which converts main signals so as to have a predetermined transfer format for transmission and reception, multiplexing/demultiplexing units which multiplexes the main signals transmitted from the relevant transmission interfaces or demultiplexing received signals, and a switching unit which switches routes for the main signals; and transmission links which connects the plurality of communication devices, the communication device comprising: a detour path selecting unit which selects a detour path that is switchable and has the highest priority from among a plurality of detour path candidates when a failure occurs in a working path that is transferring traffic; and a signaling unit which sets the communication devices along a route of the detour path selected by the detour path selecting unit.

0026(7) In the communication device according to the aspect of the present invention, the communication device further comprises: a path management unit which manages the routes of the working path and the detour path; and a failure notification party management unit which determines a party to be notified when a failure in the detour path or the working path is detected.

0027(8) According to further another aspect of the present invention, there is provided a route design device in a communication network system having a plurality of communication devices each comprising a switching unit which switches traffic routes, and transmission links which connects the plurality of communication devices, the route design device comprising: a route calculation unit which refers to topology information of the communication network to calculate a route from a start-point communication device to an endpoint communication device; and a detour path adjusting unit which adjusts detour paths to prevent contention from occurring between the detour paths when the detour paths are calculated.

0028(9) According to further another aspect of the present invention, there is provided a failure recovery method in a communication network system comprising a plurality of communication devices each comprising a switching unit which switches traffic routes, and transmission links which connects the plurality of communication devices, wherein a start-point communication device of the plurality of communication devices: sets a plurality of detour paths corresponding to but having routes different from a working path that is transferring traffic between the start-point communication device and an endpoint communication device, and selects a detour path that is switchable and has the highest priority from among the plurality of detour paths when a failure occurs in the working path and then sets communication devices along a route of the detour path to recover from the failure.

0029(10) In the failure recovery method according to the aspect of the present invention, when switching to the detour path, the start-point communication device stores information of a currently-used path that has been used as the working path as a detour path during the failure, and reverts to the currently-used path after recovery from the failure.

EFFECT OF THE INVENTION

0030According to the present invention as described above, paths that do not reserve bands on detour route candidates are made to be set and then reported to a communication device that performs switching in consideration of affective failures only. Accordingly, when not only a single failure, but also multiple failures occur, failure locations can be rapidly determined without using a routing protocol to set detour paths.

0031In addition, according to the present invention, a plurality of detour paths can be designed by a detour route adjusting function. Therefore, when a plurality of failures occur, all detour routes can be set without causing network resource contention between the plurality of detour paths.

0032Further, according to the present invention, reversion after recovery from the failure is possible by managing currently-used paths and detour paths separately from each other and storing the paths used when the failure occurs in a detour path DB. Therefore, reversion to the original route after recovery from the failure is possible.

BRIEF DESCRIPTION OF THE DRAWINGS

0033<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram showing a network configuration according to a first embodiment of the present invention.

0034<figref idref="DRAWINGS">FIG. 2</figref> is a block diagram showing a configuration of a communication device according to the first embodiment of the present invention.

0035<figref idref="DRAWINGS">FIG. 3</figref> is a block diagram showing a configuration of a detour route adjusting device according to the first embodiment of the present invention.

0036<figref idref="DRAWINGS">FIG. 4</figref> is a flowchart showing a path setting procedure according to the first embodiment of the present invention.

0037<figref idref="DRAWINGS">FIG. 5</figref> is a flowchart showing a failure detouring procedure according to the first embodiment of the present invention.

0038<figref idref="DRAWINGS">FIG. 6</figref> is a block diagram showing information replacement between a currently-used path and a detour path according to the first embodiment of the present invention.

0039<figref idref="DRAWINGS">FIG. 7</figref> is a flowchart showing a detour route adjusting procedure according to the first embodiment of the present invention.

0040<figref idref="DRAWINGS">FIG. 8</figref> is a block diagram showing an example of detouring a single failure according to the first embodiment of the present invention.

0041<figref idref="DRAWINGS">FIG. 9</figref> is a table representing states of detour paths when a single failure occurs according to the first embodiment of the present invention.

0042<figref idref="DRAWINGS">FIG. 10</figref> is a block diagram showing an example of detouring multiple failures according to the first embodiment of the present invention.

0043<figref idref="DRAWINGS">FIG. 11</figref> is a table representing states of detour paths when multiple failures occur according to the first embodiment of the present invention.

0044<figref idref="DRAWINGS">FIG. 12</figref> is a block diagram showing an example of detouring multiple failures by adjusting multiple paths according to the first embodiment of the present invention.

0045<figref idref="DRAWINGS">FIG. 13A</figref> shows path information T<b>430</b> in a working path DB <b>131</b> and a detour path DB <b>132</b> when a failure occurs in a communication device A.

0046<figref idref="DRAWINGS">FIG. 13B</figref> shows path information T<b>440</b> in a working path DB <b>131</b> and a detour path DB <b>132</b> when a failure occurs in a communication device D.

0047<figref idref="DRAWINGS">FIG. 14</figref> is a block diagram showing network resource contention in conventional path re-routing.

REFERENCE SYMBOLS

0000<ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0000"><ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0048"><b>50</b>: network</li><li id="ul0002-0002" num="0049"><b>90</b>: transmission link</li><li id="ul0002-0003" num="0050"><b>100</b>: communication device</li><li id="ul0002-0004" num="0051"><b>110</b>: communication device hardware unit</li><li id="ul0002-0005" num="0052"><b>111</b>: switch unit</li><li id="ul0002-0006" num="0053"><b>112</b><i>a </i>to <b>112</b><i>h</i>: transmission I/F unit</li><li id="ul0002-0007" num="0054"><b>113</b><i>a</i>, <b>113</b><i>b</i>: client I/F unit</li><li id="ul0002-0008" num="0055"><b>114</b><i>a </i>to <b>114</b><i>d</i>: multiplexing and demultiplexing unit</li><li id="ul0002-0009" num="0056"><b>120</b>: communication device software unit</li><li id="ul0002-0010" num="0057"><b>121</b>: path management unit</li><li id="ul0002-0011" num="0058"><b>122</b>: failure notification party management unit</li><li id="ul0002-0012" num="0059"><b>123</b>: XC control monitoring unit</li><li id="ul0002-0013" num="0060"><b>124</b>: detour path selection procedure</li><li id="ul0002-0014" num="0061"><b>125</b>: failure link analysis unit</li><li id="ul0002-0015" num="0062"><b>126</b>: signaling unit</li><li id="ul0002-0016" num="0063"><b>127</b>: control I/F unit</li><li id="ul0002-0017" num="0064"><b>128</b>: out-band control line</li><li id="ul0002-0018" num="0065"><b>129</b>: in-band control line</li><li id="ul0002-0019" num="0066"><b>131</b>: working path DB</li><li id="ul0002-0020" num="0067"><b>132</b>: detour path DB</li><li id="ul0002-0021" num="0068"><b>133</b>: notification party DB</li><li id="ul0002-0022" num="0069"><b>140</b>: detour route adjusting device</li><li id="ul0002-0023" num="0070"><b>141</b>: route calculation unit</li><li id="ul0002-0024" num="0071"><b>142</b>: detour route adjusting unit</li><li id="ul0002-0025" num="0072"><b>143</b>: request receiving unit</li><li id="ul0002-0026" num="0073"><b>145</b>: currently-used path information</li><li id="ul0002-0027" num="0074"><b>146</b>: all detour path information</li><li id="ul0002-0028" num="0075"><b>147</b>: topology information</li><li id="ul0002-0029" num="0076"><b>10</b>, <b>50</b>: working path</li><li id="ul0002-0030" num="0077"><b>20</b>, <b>30</b>, <b>40</b>, <b>60</b>: detour path</li><li id="ul0002-0031" num="0078">T<b>400</b> to T<b>440</b>: table information</li></ul></li></ul>

BEST MODE FOR CARRYING OUT THE INVENTION

0079Embodiments of the present invention will now be described with reference to accompanying drawings.

0080<figref idref="DRAWINGS">FIG. 1</figref> is a block diagram showing a network configuration according to a first embodiment of the present invention. <figref idref="DRAWINGS">FIG. 2</figref> is a block diagram showing a configuration of a communication device <b>100</b> according to the first embodiment of the present invention. <figref idref="DRAWINGS">FIG. 3</figref> is a block diagram showing a configuration of a detour route adjusting device <b>140</b> (route design device) according to the first embodiment of the present invention.

0081A network <b>50</b> in <figref idref="DRAWINGS">FIG. 1</figref> includes communication devices <b>100</b>-<i>i </i>(where i denotes identifiers of the communication devices), and transmission links <b>90</b>-<i>ij </i>(where i and j denote identifiers of the communication devices at both ends of the transmission link) which connects the communication devices.

0082In <figref idref="DRAWINGS">FIG. 1</figref>, each of i and j may be any one of A, B, C, D, E, F, and G. The communication device <b>100</b>-A is shown as the encircled A in <figref idref="DRAWINGS">FIG. 1</figref>. The other communication devices <b>100</b>-B to <b>100</b>-G are also shown in the same manner.

0083The detour route adjusting device <b>140</b> is disposed to adjust the detour routes on the network <b>50</b>.

0084The communication device <b>100</b>-A of <figref idref="DRAWINGS">FIG. 1</figref> has the configuration of the communication device <b>100</b> shown in <figref idref="DRAWINGS">FIG. 2</figref>. Similarly, the other communication devices <b>100</b>-B to <b>100</b>-G have the configuration of the communication device <b>100</b> shown in <figref idref="DRAWINGS">FIG. 2</figref>.

0085The communication device <b>100</b> shown in <figref idref="DRAWINGS">FIG. 2</figref> includes a communication device control hardware unit <b>110</b> and a communication device control software unit <b>120</b>. The communication device control software unit <b>120</b> operates on a control infrastructure having a processor and volatile/nonvolatile memories. Here, the configuration of the control infrastructure is not separately shown.

0086The communication device control hardware unit <b>110</b> includes a switch unit <b>111</b>, transmission interface (I/F) units <b>112</b><i>a </i>to <b>112</b><i>h </i>(also referred to as transmission I/F units), client interface units <b>113</b><i>a </i>and <b>113</b><i>b </i>(also referred to as client I/F units), and multiplexing and demultiplexing units <b>114</b><i>a </i>to <b>114</b><i>d. </i>

0087The switch unit <b>111</b> switches main signal routes. The transmission I/F units <b>112</b><i>a </i>to <b>112</b><i>h </i>convert the main signals switched by the switch unit <b>111</b> so as to have a predetermined transfer format for transmission and reception to and from other communication devices.

0088The client I/F units <b>113</b><i>a </i>and <b>113</b><i>b </i>are connected to respective client devices and convert signals so as to have a predetermined transfer format for signal transmission and reception. The multiplexing and demultiplexing units <b>114</b><i>a </i>to <b>114</b><i>d </i>perform multiplexing or demultiplexing on the main signals output from the transmission I/F units <b>112</b><i>a </i>to <b>112</b><i>h. </i>

0089For example, different optical wavelengths, optical transport network (OTN), optical network/synchronous digital hierarchy (SONET/SDH), Ethernet (registered trademark), asynchronous transfer mode (ATM), frame relay (FR) and so on are used as the transfer formats of the transmission I/F units <b>112</b><i>a </i>to <b>112</b><i>h </i>and the client I/F units <b>113</b><i>a </i>and <b>113</b><i>b. </i>

0090The communication device <b>100</b> has an in-band control line <b>129</b> which exchanges control signals with adjacent communication devices using some channels of the transmission link.

0091The communication device software unit <b>120</b> includes a path management unit <b>121</b>, a failure notification party management unit <b>122</b>, an XC control monitoring unit <b>123</b>, a detour path selecting unit <b>124</b>, a failure link analysis unit <b>125</b>, a signaling unit <b>126</b>, and a control interface unit (also referred to as a control I/F unit) <b>127</b>.

0092The communication device software unit <b>120</b> stores a working path DB <b>131</b>, a detour path DB <b>132</b>, and a notification party DB <b>133</b>.

0093The path management unit <b>121</b> is also referred to as a setting unit. In addition, the working path DB <b>131</b>, the detour path DB <b>132</b>, and the notification party DB <b>133</b> are referred to as storage units.

0094The signaling unit <b>126</b> executes a signaling protocol which sets a path between the communication devices or notifying the communication device of the failure of the path. The control I/F unit <b>127</b> converts the signaling protocol into control information.

0095Here, an example of the signaling protocol may include RSVP-TE or CR-LDP.

0096The control I/F unit <b>127</b> transmits and receives control information using any one or both of an out-band control line <b>128</b> separate from the transmission link <b>90</b> via which the main signals are transmitted and the in-band control line <b>129</b> multiplexed to the same transmission link for the main signals.

0097The path management unit <b>121</b> manages the working paths and the detour paths which are set. The XC control monitoring unit <b>123</b> controls the switch unit <b>111</b>, the transmission I/F units <b>112</b><i>a </i>to <b>112</b><i>h</i>, and the client I/F units <b>113</b><i>a </i>and <b>113</b><i>b</i>, and detects the failure of the units.

0098The failure notification party management unit <b>122</b> manages parties to be notified of a failure detected by the XC control monitoring unit <b>123</b> when the failure affects the working path or the detour path. The failure link analysis unit <b>125</b> analyzes the path failure.

0099Among all communication devices on the working path/detour path, a notification party (start-point communication device) to be notified of a failure when the failure occurs is stored in the notification party database (also referred to as a notification party DB) <b>133</b>. In addition, in a communication device switching the path, the working path and the detour path are stored in the working path database (also referred to as a working path DB) <b>131</b> and the detour path database (also referred to as a detour path DB) <b>132</b>, respectively.

0100Next, a configuration of the detour route adjusting device <b>140</b> (<figref idref="DRAWINGS">FIG. 1</figref>) will be described with reference to <figref idref="DRAWINGS">FIG. 3</figref>. The detour route adjusting device <b>140</b> has a route calculation unit <b>141</b>, a detour route adjusting unit <b>142</b>, and a request receiving unit <b>143</b>. The detour route adjusting device <b>140</b> stores all currently-used path information <b>145</b>, all detour path information <b>146</b> and topology information <b>147</b>.

0101The request receiving unit <b>143</b> receives a request to design routes of the working path and the detour path. The route calculation unit <b>141</b> calculates a route of a requested section. The detour route adjusting unit <b>142</b> adjusts the calculated routes of the detour paths between the currently-used paths.

0102The topology information <b>147</b> is information necessary for the route calculation unit <b>141</b> to calculate the route. In addition, the currently-used path information <b>145</b> is information regarding all currently-used paths which have been previously set in the network. In addition, the detour path information <b>146</b> is information regarding all detour paths.

0103Such information is managed in the detour route adjusting device <b>140</b>, or is acquired by receiving the information stored in an external server such as a network management system (NMS).

0104Next, all operations of the communication network system according to an embodiment of the present invention will be described with reference to the configuration of the communication device <b>100</b> of <figref idref="DRAWINGS">FIG. 2</figref> and flowcharts of <figref idref="DRAWINGS">FIGS. 4 and 5</figref>.

0105Paths set in the embodiment of the present invention include working paths and detour paths. A working path is one that actually reserves network resources. A detour path is one that does not reserve network resources and is set for reporting a failure.

0106In a state with no failure, the currently-used path is used as the working path. When a failure occurs in the working path, a path candidate that can be used for path re-routing is treated as the detour path in the communication device at a switching end point.

0107In addition, the currently-used path employed in the present embodiment is a path that is initially set as the working path in a state with no failure.

0108<figref idref="DRAWINGS">FIG. 4</figref> is a flowchart showing a procedure of setting the working path and the detour path.

0109The detour route adjusting device <b>140</b> calculates a route of the working path that actually flows traffic between the start-point communication device and the endpoint communication device on the path, and a route of the detour path when a failure occurs in the working path, in response to a request to set the path between the start-point communication device and the endpoint communication device, for example, by traffic demand information or a request to start communication service (step S<b>301</b>).

0110Here, the detour route adjusting device <b>140</b> is used to optimize the detour path. Further, functions of the detour route adjusting device <b>140</b> may not be set when an administrator can set the functions in consideration of the route in a relatively small communication network.

0111Next, the start-point communication device that has received the request to set the path determines working/detour attributes of the path (step S<b>302</b>). When the path is the working path, the detour route adjusting device <b>140</b> stores the route information of the working path in the working path DB <b>131</b>. Thereafter, the signaling unit <b>126</b> exchanges a signaling message along the calculated route.

0112When the signaling unit <b>126</b> of each communication device receives the signaling message in the process of exchanging the signaling message, the path management unit <b>121</b> allocates a network resource called a label while referring to the requested path band information and link vacancy information. Accordingly, the requested band is reserved by signaling along the designated route (step S<b>303</b>).

0113Further, the path management unit <b>121</b> sets cross-connection of the switch unit <b>111</b> via the XC control monitoring unit <b>123</b> based on the assigned label information (step S<b>304</b>).

0114While the cross-connection is set, the failure notification party management unit <b>122</b> stores, in the notification party DB <b>133</b>, information of the start-point communication device (the identifier of the start-point communication device) notified of a path failure when the failure is detected (step S<b>306</b>).

0115When it is determined in step S<b>302</b> that the path is the detour path, the start-point communication device stores the route information in the detour path DB <b>132</b>. The signaling unit <b>126</b> then exchanges the signaling message indicating that the requested band is 0 along the calculated route. Accordingly, signaling is performed along the designated route with the requested band of 0 (step S<b>305</b>).

0116When the signaling unit <b>126</b> of the communication device located midway on the route receives the signaling message, the signaling unit stores, in the notification party DB <b>133</b>, the information of the start-point communication device (the identifier of the start-point communication device) notified of the path failure when the failure is detected (step S<b>306</b>).

0117Here, the signaling message indicating that the requested band is 0 is issued in order to indicate that the path is the detour path and to specify that reserving of the resources in each communication device which has received the signaling message and setting of the cross-connection are not performed.

0118In the present embodiment, it is specified that reserving of the resources and setting of the cross-connection are not performed by setting the band to 0; however, the present invention is not limited thereto. For example, a flag may be used at a specific location of the signaling message, instead of setting the band to 0.

0119The path has been set through the process up to step S<b>306</b>. Monitoring of the path failure is then initiated (step S<b>307</b>). It is determined whether the failure was detected in the path that is being monitored (step S<b>308</b>).

0120When the failure is detected in monitoring the path, the start-point communication device on the failed path is retrieved from the notification party DB <b>133</b>, and information on the failed path and the failure location are transmitted via the signaling unit <b>126</b> (step S<b>309</b>).

0121Next, detouring for when failures on the working path and the detour path set in the above-described manner are received will be described with reference to <figref idref="DRAWINGS">FIG. 5</figref>. When the start-point communication device on the path receives a path failure from the communication device for which the working path or the detour path is set (step S<b>401</b>), the start-point communication device determines whether the failure is present in the working path (step S<b>402</b>).

0122When the failure notification is about the detour path, the location where the failure has occurred is analyzed to update the state of the detour path from Up to Down (step S<b>403</b>), and the process of the flowchart shown in <figref idref="DRAWINGS">FIG. 5</figref> is terminated.

0123On the other hand, when it is determined in step S<b>402</b> that the failure notification is about the working path, the detour path having the lowest priority is selected from among the detour paths having the state of Up (step S<b>404</b>). Signaling is performed with the band of 0 along the route of the working path to release the resource, and then signaling is performed along the route of the detour path to reserve the band and to perform cross-connection so that the working path is set (step S<b>405</b>).

0124In step S<b>404</b>, when failure occurs simultaneously in a plurality of locations, it is likely that the state of the detour path has not been updated. For this reason, a latency of about several tens of milliseconds may be set until the selection of the detour path is initiated for securely updating the state.

0125In step S<b>405</b>, information of the failed currently-used path is output from the working path DB <b>131</b> to the detour path DB <b>132</b>, and the set detour path is output from the detour path DB <b>132</b> to the working path DB <b>131</b>.

0126When the detour path is set using the network resources in which the failed detour path is set, the network resource (label) reserved by the currently-used path is allocated to the detour path when detour path signaling is performed.

0127At this time, as shown in <figref idref="DRAWINGS">FIG. 6</figref>, the information of the currently-used path is output to the detour path DB <b>132</b>, and the information of the detour path selected from the detour path DB <b>132</b> is output to the working path DB <b>131</b>. Because the information of the currently-used path is stored in the detour path DB <b>132</b>, it becomes possible to revert to the original route of the currently-used path after recovering from the failure.

0128A lower part of <figref idref="DRAWINGS">FIG. 6</figref> shows the case where a path is switched to a working path <b>10</b> via the multiplexing and demultiplexing unit <b>114</b><i>a</i>, the transmission I/F unit <b>112</b><i>b</i>, the switch unit <b>111</b>, the transmission I/F unit <b>112</b><i>h</i>, and the multiplexing and demultiplexing unit <b>114</b><i>d </i>to the detour path <b>20</b> via the multiplexing and demultiplexing unit <b>114</b><i>a</i>, the transmission I/F unit <b>112</b><i>b</i>, the switch unit <b>111</b>, the transmission I/F unit <b>112</b><i>f</i>, and the multiplexing and demultiplexing unit <b>114</b><i>c. </i>

0129Next, an operation of the detour route adjusting device (also referred to as a route design device) <b>140</b> that adjusts the detour route between a plurality of currently-used paths will be described with reference to <figref idref="DRAWINGS">FIGS. 3 and 7</figref>. Here, the currently-used path of the path requested to perform a new route design is referred to as a new currently-used path. In addition, the detour path of the path requested to perform a new route design is referred to as a new detour path.

0130In addition, the currently-used path that is previously set is referred to as a preset currently-used path. The detour path that is previously set is referred to as a preset detour path.

0131In the detour route adjusting device <b>140</b>, the route calculation unit <b>141</b> calculates routes of the new detour path and the new currently-used path based on a path calculation request indicating a start-point communication device and an endpoint communication device and containing band information (step S<b>501</b>).

0132Next, when the preset detour path and the new detour path are selected as the working paths due to the failure, it is determined whether contention due to the insufficient bands occurs in the link used in these detour paths (step S<b>502</b>).

0133When a contention link is present on the new detour path, a detour path that can preferentially use the contention link is determined from among the new detour path and the preset detour path. When the new detour path acquires the right to priority use, the route of the new currently-used path is responded to with the adjusted link to the preset detour path using the contention link.

0134When the preset detour path acquires the right to priority use, a link in which the preset currently-used path currently used by the preset detour path that has acquired the right to priority use is set, is responded to with the adjusted link of the new detour path.

0135According to the flowchart of <figref idref="DRAWINGS">FIG. 7</figref>, the detour route adjusting device <b>140</b> performs the following process. That is, the detour route adjusting device <b>140</b> determines whether an insufficient-band link has occurred (step S<b>503</b>).

0136When it is determined in step S<b>503</b> that an insufficient-band link has occurred, the detour route adjusting device <b>140</b> sets the right to priority use in the specific currently-used path (step S<b>504</b>), and performs a process in step S<b>505</b>.

0137On the other hand, when it is determined in step S<b>503</b> that an insufficient-band link has not occurred, the detour route adjusting device <b>140</b> terminates the process of the flowchart shown in <figref idref="DRAWINGS">FIG. 7</figref>.

0138In step S<b>505</b>, the detour route adjusting device <b>140</b> determines whether the right to priority use was acquired on the insufficient-band link (step S<b>505</b>).

0139When it is determined in step S<b>505</b> that the right to priority use was acquired, the adjustment link information of the detour path DB that is previously set is updated (step S<b>506</b>), and the process of the flowchart shown in <figref idref="DRAWINGS">FIG. 7</figref> is terminated.

0140On the other hand, when it is determined in step S<b>505</b> that the right to priority use was not acquired, the adjustment link information of the detour path DB that was newly calculated is set (step S<b>507</b>), and the process of the flowchart shown in <figref idref="DRAWINGS">FIG. 7</figref> is terminated.

0141Thus, in the present embodiment, the detour route adjusting device <b>140</b> checks and adjusts the contention link when the detour path is detoured. Accordingly, even when multiple failures occur, it is possible to acquire the route that recovers from failures of all the currently-used paths without contention between the detour paths.

0142A specific example of the above-described detouring operation will be described with reference to <figref idref="DRAWINGS">FIGS. 8 to 11</figref>. In addition, cases of a single failure, multiple failures, and multiple failures that require preventing contention with other paths will be described.

0143First, a switching example in the case of a failure will be described with reference to <figref idref="DRAWINGS">FIGS. 8 and 9</figref>. <figref idref="DRAWINGS">FIG. 8</figref> shows a detour path <b>20</b>, which is a detour route of a working path <b>10</b>, selected when the single failure occurs.

0144Specifically, the failure occurs between the communication device B and the communication device C in <figref idref="DRAWINGS">FIG. 8</figref>. Accordingly, the working path <b>10</b> via the communication device A, the communication device C, and the communication device B is switched to the detour path <b>20</b> via the communication device A, the communication device C, the communication device E, and the communication device B.

0145<figref idref="DRAWINGS">FIG. 9</figref> shows path information T<b>400</b> in the working path DB <b>131</b> and the detour path DB <b>132</b> when the failure occurs. In <figref idref="DRAWINGS">FIG. 9</figref>, the information with a priority of 0 is stored in the working path DB <b>131</b>. Information with priorities of 1 to 4 is stored in the detour path DB <b>132</b>.

0146For the path information T<b>400</b>, paths are calculated before a failure occurs and set as a currently-used path and a detour path by the above-described signaling procedure.

0147Here, the value of a cost of the link is 10. An overlapping degree indicates a route overlapping degree with currently used working paths, and the value from which the cost of an overlapped link was subtracted is set as the path cost.

0148When the failure occurs in a communication link BC (a link between a communication device B and a communication device C) for which the working path <b>10</b> is set, the XC control monitoring unit <b>123</b> of the communication device B or the communication device C detects the failure and transmits a failure notification to a communication device A that is a starting point of the working path <b>10</b>.

0149The communication device A that has received the failure notification analyzes a failure location included in the failure notification, and updates the states of path information in the working path DB <b>131</b> and the detour path DB <b>132</b>. A detour path with the lowest priority <b>1</b> (route AC to CE to EB) is selected from detour paths with a state “Up” in the updated path information of the detour path DB <b>132</b>, and the detour path <b>20</b> is set by signaling along the route.

0150By doing so, it is possible to rapidly set the detour path and detour the path with the single failure.

0151Next, a switching example in the case of multiple failures will be described with reference to <figref idref="DRAWINGS">FIGS. 10 and 11</figref>.

0152<figref idref="DRAWINGS">FIG. 10</figref> shows a detour path <b>30</b>, which is a detour route for a working path <b>10</b>, selected when two failures occur.

0153Specifically, in <figref idref="DRAWINGS">FIG. 10</figref>, failures occur between a communication device A and a communication device D, between a communication device B and a communication device C, between the communication device B and a communication device E, between the communication device B and a communication device F, and between the communication device E and a communication device G.

0154Accordingly, the working path <b>10</b> via the communication device A, the communication device C, and the communication device B is switched to the detour path <b>30</b> via the communication device A, the communication device C, the communication device E, the communication device D, the communication device F, the communication device G, and the communication device B.

0155<figref idref="DRAWINGS">FIG. 11</figref> shows path information T<b>420</b> in the working path DB <b>131</b> and the detour path DB <b>132</b> when the failure occurs. In <figref idref="DRAWINGS">FIG. 11</figref>, information with the priority of 0 is stored in the working path DB <b>131</b>. Information with priorities of 1 to 4 is stored in the detour path DB <b>132</b>.

0156For the path information T<b>420</b>, routes are calculated before the failure occurs and set as a currently-used path and a detour path by the above-described signaling procedure.

0157Here, the value of a cost of the link is 10. An overlapping degree indicates a route overlap degree with currently used working paths. In addition, the value from which the cost of an overlapped link was subtracted is set as the path cost.

0158When failure occurs in a communication link BC (a link between the communication device B and the communication device C) for which the working path <b>10</b> is set, the XC control monitoring unit <b>123</b> of the communication device B or the communication device C detects the failure and transmits a failure notification to the communication device A, which is a starting point of the working path <b>10</b>.

0159Simultaneously, when failures occur in the communication link BE (the link between the communication device B and the communication device E) of which the detour path is set, the communication link BF (the link between the communication device B and the communication device F), the communication link EG (the link between the communication device E and the communication device G), and the communication link AD (the link between the communication device A and the communication device D), the XC control monitoring unit <b>123</b> of the communication device adjacent to each link detects the failures and transmits a failure notification to the communication device A, which is the starting point of the working path <b>10</b>.

0160The communication device A that has received the failure notification analyzes failure locations included in the failure notification, and updates states of the path information in the working path DB <b>131</b> and the detour path DB <b>132</b>. A detour path with the lowest priority <b>4</b> (route AC to CE to ED to DF to FG to GB) is selected from detour paths with a state “Up” in the updated path information of the detour path DB <b>132</b>, and the detour path <b>30</b> is set by signaling along the route.

0161Even when three or more failures simultaneously occur as described above, it is possible to rapidly set the detour path and detour the failed path.

0162Next, an example of a switching process when multiple failures occur in a network having a plurality of set paths will be described with reference to <figref idref="DRAWINGS">FIGS. 12</figref>, <b>13</b>A, and <b>13</b>B.

0163<figref idref="DRAWINGS">FIG. 12</figref> shows a detour path <b>40</b> for a working path <b>10</b> and a detour path <b>60</b> for a working path <b>50</b>, which are selected when two failures occur.

0164Specifically, in <figref idref="DRAWINGS">FIG. 12</figref>, failures occur between a communication device B and a communication device C and between the communication device B and a communication device F.

0165Accordingly, the working path <b>10</b> via the communication device A, the communication device C, and the communication device B is switched to the detour path <b>40</b> via the communication device A, the communication device C, the communication device E, and the communication device B.

0166The working path <b>50</b> via the communication device B, the communication device F, and the communication device D is also switched to the detour path <b>60</b> via the communication device B, the communication device G, the communication device F, and the communication device D.

0167In <figref idref="DRAWINGS">FIG. 12</figref>, contention links are present between the communication device B and the communication device E and between the communication device F and the communication device G.

0168<figref idref="DRAWINGS">FIG. 13A</figref> shows path information T<b>430</b> in the working path DB <b>131</b> and the detour path DB <b>132</b> when the failure occurs in the communication device A. In <figref idref="DRAWINGS">FIG. 13A</figref>, information with the priority of 0 is stored in the working path DB <b>131</b>. Information with the priorities of 1 to 4 is stored in the detour path DB <b>132</b>.

0169<figref idref="DRAWINGS">FIG. 13B</figref> shows path information T<b>440</b> in the working path DB <b>131</b> and the detour path DB <b>132</b> when the failure occurs in the communication device D. In <figref idref="DRAWINGS">FIG. 13B</figref>, information with the priority of 0 and the state of “Down” is stored in the working path DB <b>131</b>. Information with the priority of 0 and the state of “Up” and information with the priorities of 1 to 4 are stored in the detour path DB <b>132</b>.

0170For the path information T<b>430</b> and T<b>440</b>, routes are calculated before a failure occurs and adjustment link information is added to prevent interference. These paths are set as working and detour paths by the above-described signaling procedure.

0171Here, the value of a cost of the link is 10. An adjustment link is information set to prevent interference with a detour route for another working path. An overlapping degree indicates a route overlapping degree with the currently used working path. In addition, the value from which the cost of the overlapped links was subtracted is set as the path cost.

0172When failures occur in the communication link BC (the link between the communication device B and the communication device C) for which the working path <b>10</b> is set and the communication link FB (the link between the communication device F and the communication device B) for which the working path <b>50</b> is set, the XC control monitoring unit <b>123</b> of the communication device adjacent to each of the links detects the failures and transmits a failure notification to the communication device A that is a starting point of the working path <b>10</b> and to the communication device D that is a starting point of the working path <b>50</b>.

0173Simultaneously, since the detour path is set for the failed communication links, both the communication device A and the communication device D can receive a failure notification for routes other than the route of the working path.

0174The communication device A that has received the failure notification analyzes failure locations included in the failure notification, and updates the states of the path information in the working path DB <b>131</b> and the detour path DB <b>132</b>. In this case, the communication device A updates the adjustment link information, as well as the route information.

0175The detour path with the lowest priority of 1 (route AC to CE to EB) is selected from routes which have the states of “Up” in the updated path information in the detour path DB <b>132</b> and for which the failures do not occur on the adjusted links, and the detour path <b>40</b> is set by signaling along the route.

0176Similarly, the communication device D that has received the failure notification analyzes failure locations included in the failure notification, and updates the states of the path information in the working path DB <b>131</b> and the detour path DB <b>132</b>. In this case, the communication device D updates the adjustment link information, as well as the route information.

0177The detour path with the lowest priority of 1 (route EF to FG to GB) is selected from routes which have the states of “Up” in the updated path information in the detour path DB <b>132</b> and for which the failures do not occur on the adjusted links, and the detour path <b>60</b> is set by signaling along the route.

0178Thus, even when two or more failures occur simultaneously, it is possible to rapidly set the detour path and detour the failed path without contention with other paths.

0179In the present embodiment, a plurality of detour paths without a reserved band are set in advance in preparation for various failures, as described above. Accordingly, even when multiple failures occur, it is possible to quickly detect failure locations regarding the detour path and rapidly set detour paths.

0180Further, it becomes possible to set the detour paths with minimal network resources by determining the cost of the detour path in consideration of the overlapping degree with the currently used working path.

0181In the present embodiment, the configuration and operation of the start-point communication device on the currently-used path that initiates the setting of the detour path have been described; however, the present invention is not limited thereto. For example, the present invention may also be applied to a segment detouring method that allows an intermediate communication device on the currently-used path to initiate the setting.

0182The embodiments of the present invention have been described with reference to the drawings; however, the detailed configuration thereof is not limited to the embodiments, and designs or the like without departing from the subject matter of the present invention are also included in the claims.

INDUSTRIAL APPLICABILITY

0183According to the present invention, in the communication network system within a communication carrier or company consisting of a plurality of nodes, the present invention may be applied as a failure recovery function to recover from multiple failures. In addition, the failure recovery function of the present invention may not only be applied to a geographically wide network but may also be used for communication between chips within a computer.