Control apparatus, communication system, switch controlling method and program

CROSS-REFERENCE TO RELATED APPLICATION

0001The present application asserts priority rights based on JP Patent Application No. 2012-053265 filed on Mar. 9, 2012, the contents thereof being incorporated by reference into the present application. This invention relates to a control apparatus, a communication system, a switch controlling method and a program and, more particularly, to a control apparatus, a communication system, a switch controlling method and a program for managing centralized control of a communication device(s) on a network.

BACKGROUND

Technical Field

0002Recently, it has become possible to collect the statistics information on the traffic volume on the flow basis or to effect load distribution by managing path control on the flow basis. This may be implemented by the controller performing centralized management of the flow tables of the switches on the network. An example of such technique is the OpenFlow shown in Non-Patent Document 1.

0003Patent Document 1 discloses a method of improving the efficiency in the communication of applications pre-defined by HTTP (Hyper-Text Transfer Protocol), FTP (File Transfer Protocol) or others, by removing an address table at an aging time interval proper to each application.

0004Patent Document 2 discloses a method that dynamically changes timeout time of a session, depending on the session rate, so as to enable protocol processing to be performed without causing overflow of a session memory at the time of high-load accessing.

0005Patent Document 3 discloses a method that takes account of the number of empty flow entries in a plurality of switches arranged on a communication network to decide a flow path so as to suppress the occurrence of entry overflow.

CITATIONS LIST

Patent Documents

0000<ul id="ul0001" list-style="none"><li id="ul0001-0001" num="0006">Patent Document 1: JP Patent Kohyo Publication No. 2003-526279A</li><li id="ul0001-0002" num="0007">Patent Document 2: JP Patent Kokai Publication No. 2006-279531A</li><li id="ul0001-0003" num="0008">Patent Document 3: JP Patent Kokai Publication No. 2010-161473A</li></ul>

Non-Patent Documents

0000<ul id="ul0002" list-style="none"><li id="ul0002-0001" num="0009">Non-Patent Document 1: Nick McKeown and three others, “OpenFlow: Enabling Innovation in Campus Networks”, [online], [searched on February 14, Heisei 24 (2012)], Internet <URL: http://www.openflow.org/documents/openflow-wp-latest.pdf></li><li id="ul0002-0002" num="0010">Non-Patent Document 2: “OpenFlow Switch Specification” Version 1.1.0 Implemented (Wire Protocol 0x02), [online], [searched on February 14, Heisei 24 (2012)], Internet <URL: http://www.openflow.org/documents/openflow-spec-v1.1.0.pdf></li></ul>

SUMMARY

Technical Problem

0011The following analysis is given by the present invention. A communication device, represented by an OpenFlow switch, disclosed in Non-Patent Documents 1, 2, is able to forward a flow at a high speed as the flow is identified by exploiting an ASIC (Application Specific Integrated Circuit) flow table. However, there persists a problem that the number of flow entries, registrable in the ASIC flow table, is small and, if an upper limit of the number is exceeded, processing by software has to be performed, so that the transfer performance is considerably lowered. There are also cases wherein, depending on setting of the flow occurrence time interval or the aging time values, flow table removal and registration for the same flows occur repeatedly, thus increasing the overhead. Hence, it becomes necessary to reduce the number of times of flow entry registration and removal as the flow table overflow is suppressed.

0012In the method of Patent Document 1, an address table is removed at an aging time interval proper to a known application, however, a problem persists that the method is not effective against unknown applications.

0013In the method of Patent Document 2, the session information can not be selectively removed depending on the session characteristic. Hence, the method suffers a problem that, if a high-load access state is continued, the session information which, if retained, would yield better results in point of the efficiency, is removed, resulting in a state of a still higher load due to repetition of registration and removal of the session information and consequent increase in the overhead.

0014Furthermore, in the method of Patent Document 3, flow entry erasure is carried out at a preset timeout interval, so that, in a switch where the flow is concentrated, such as a core switch having only a smaller number of substitution paths, flow entry overflow tends to be produced.

0015It is an object of the present invention to provide a control apparatus, a communication system, a switch control method and a program capable of contributing to reducing the occurrence of the above mentioned flow table overflow phenomenon.

Solution to Problem

0016According to a first aspect of the present invention, there is provided a control apparatus comprising a communication device controller that acts on a set of flow entries retained by one communication device of a group of communication device(s) to control the group of the communication device(s), and a flow statistics information management unit that gathers and manages the flow statistics information collected by the communication device per flow entry. If a new flow is encountered, the communication device controller finds an estimated lifetime of the new flow based on the flow statistics information, and sets a flow entry, having set an aging time consistent with the estimated lifetime, on the communication device(s) on a path of the new flow.

0017According to a second aspect of the present invention, there is provided a communication system including a control apparatus and a communication device(s), in which the control apparatus comprises a communication device controller that acts on a set of flow entries retained by one communication device of a group of communication device(s) to control the group of the communication device(s) and a flow statistics information management unit that gathers and manages the flow statistics information collected by the communication device per flow entry. On occurrence of a new flow, the communication device controller finds an estimated lifetime of the new flow based on the flow statistics information, and sets a flow entry, having set an aging time consistent with the estimated lifetime, on the communication device(s) on a path of the new flow. The communication device(s) processes a packet using the flow entry as set from the control apparatus

0018According to a third aspect of the present invention, there is provided a method for controlling a communication device, in which the method comprises the steps of a control apparatus including a communication device controller that acts on a set of flow entries retained by one communication device of a group of communication device(s) to control the group of the communication device(s) and a flow statistics information management unit that gathers and manages the flow statistics information collected by the communication device(s) per flow entry, finding, on occurrence of a new flow, an estimated lifetime of the new flow based on the flow statistics information, and setting a flow entry, having set an aging time consistent with the estimated lifetime, on the communication device(s) on a path of the new flow. The present method is tied to a particular machine which is a control apparatus controlling the communication device(s) on the network.

0019According to a forth aspect of the present invention, there is provided a program for causing a control apparatus including a communication device controller that acts on a set of flow entries retained by one communication device of a group of communication device(s) to control the group of the communication device(s) and a flow statistics information management unit that gathers and manages the flow statistics information collected by the communication device per flow entry, to perform the processing of finding, on occurrence of a new flow, an estimated lifetime of the new flow based on the flow statistics information, and the processing of setting a flow entry, having set an aging time consistent with the estimated lifetime, on the communication device(s) on a path of the new flow. It is noted that the program can be recorded on a computer readable recording medium. That is, the present invention can be implemented as a computer program product.

Advantageous Effect of the Invention

0020According to the present invention, it is possible to contribute to reducing the flow table overflow phenomenon in a communication device that identifies a flow by an entry registered in a flow table.

BRIEF DESCRIPTION OF THE DRAWINGS

0021<figref idref="DRAWINGS">FIG. 1</figref> is a schematic view for illustrating the synopsis of an exemplary embodiment of the present invention.

0022<figref idref="DRAWINGS">FIG. 2</figref> is a block diagram showing a configuration of a communication system according to an exemplary embodiment 1 of the present invention.

0023<figref idref="DRAWINGS">FIG. 3</figref> is a schematic view showing a configuration of a flow entry to be set in a switch of the exemplary embodiment 1 of the present invention.

0024<figref idref="DRAWINGS">FIG. 4</figref> is a tabulated view for illustrating the topology information stored in a topology memory of a controller according to the exemplary embodiment 1 of the present invention.

0025<figref idref="DRAWINGS">FIG. 5</figref> is a tabulated view for illustrating the flow table information stored in a flow entry memory of the controller according to the exemplary embodiment 1 of the present invention.

0026<figref idref="DRAWINGS">FIG. 6</figref> is a tabulated view for illustrating the flow entry information stored in a flow entry memory of the controller according to the exemplary embodiment 1 of the present invention.

0027<figref idref="DRAWINGS">FIG. 7</figref> is a tabulated view for illustrating the statistics information stored in a flow statistics memory of the controller according to the exemplary embodiment 1 of the present invention.

0028<figref idref="DRAWINGS">FIG. 8</figref> is a flowchart showing the operation (flow entry setting) of the communication system according to the exemplary embodiment 1 of the present invention.

0029<figref idref="DRAWINGS">FIG. 9</figref> is a flowchart showing the operation (aging processing) of the communication system according to the exemplary embodiment 1 of the present invention.

0030<figref idref="DRAWINGS">FIG. 10</figref> is a block diagram showing a configuration of a communication system according to an exemplary embodiment 2 of the present invention.

0031<figref idref="DRAWINGS">FIG. 11</figref> is a tabulated view for illustrating the statistics information stored in a flow characteristic setting memory of a controller according to the exemplary embodiment 2 of the present invention.

0032<figref idref="DRAWINGS">FIG. 12</figref> is a flowchart showing the operation (flow entry setting) of the communication system according to the exemplary embodiment 2 of the present invention.

0033<figref idref="DRAWINGS">FIG. 13</figref> is a flowchart showing the operation (aging processing) of the communication system according to the exemplary embodiment 2 of the present invention.

PREFERRED MODES FOR CARRYING OUT THE INVENTION

0034Initially, the synopsis of the present invention will be explained with reference to the drawings. It is noted that symbols used in the synopsis for reference to the drawings are simply illustrations to assist in understanding and are not intended to limit the present invention to the modes illustrated.

0035Referring to <figref idref="DRAWINGS">FIG. 1</figref>, an exemplary embodiment of the present invention may be implemented by a control apparatus <b>10</b> controlling a plurality of communication devices <b>20</b>A to <b>20</b>D. More specifically, the control apparatus includes a communication device controller <b>12</b> that acts on the flow entries retained by the communication devices <b>20</b>A to <b>20</b>D to control a group of the communication devices, and a flow statistics information management unit <b>11</b>. The flow statistics information management unit gathers and manages the flow statistics information collected by the communication devices <b>20</b>A to <b>20</b>D per flow entry. When a new flow is encountered, the communication device controller <b>12</b> finds an estimated lifetime of the new flow, such as XXms, based on the flow statistics information, while setting, on a communication device(s) on the path of the new flow, a flow entry in which an aging time consistent with the estimated lifetime has been set. This aging time, which is the ‘Idle Timeout value’ of the Non-Patent Document 2, may, for example, be YYms. By so setting the flow entry, if no relevant packet is received for longer than YYms as from the time of the setting, the flow entry is removed by aging processing.

0036By setting not the aging time, decided on the communication system scale, but the aging time consistent with the estimated lifetime of the new flow, the flow entry highly likely to be statistically unnecessary can be removed at an earlier time. On the other hand, the flow entry, highly likely to be statistically necessary, may be retained for longer time.

0037This suppresses the occurrence of the flow table overflow phenomenon in the communication devices <b>20</b>A to <b>20</b>D. In addition, the frequency of occurrence of the flow entry setting requests may be reduced.

0038It is also possible for the communication device controller <b>12</b> to set a flow entry provided with aging time as account is taken not only of the estimated lifetime of the flow but also of whether or not the new flow in question is such flow that occurs periodically. For example, the flow of SNMP (Simple Network Management Protocol) polling from a network management server to a router on the network is featured by the fact that it occurs frequently but has a shorter lifetime. The time interval between occurrences of successive flows depends on the setting in the network management server and differs from one network environment to another. There may possibly be many other flows having similar characteristics, such as KeepAlive communication between applications. If a shorter aging time is set for the flows generated at a shorter time interval or duration, the result is the excessively increased number of times of flow entry registration requests to the controller. Thus, for these flows, it is desirable to set the aging time so as to be at least longer than the time interval between occurrences of successive flows.

0039The communication device controller <b>12</b> may take into account a flow table use ratio (or an empty flow table ratio) of each switch on the flow path to decide the aging time. For example, a shorter aging time value can be set for a communication device having a higher flow table use ratio (or a lower empty flow table ratio). By so doing, the flow entry may be removed only after a shorter time to lower the flow table use ratio. Conversely, a longer aging time value can be set for a communication device having a lower flow table use ratio (or a higher empty flow table ratio). In this manner, the flow entry may be retained for longer time to suppress the flow entry setting requests, viz., to reduce the load on the control apparatus.

0040Such correction of the aging time in the increasing or decreasing direction in response to the flow table use ratio (or the empty flow table ratio) may be implemented by adding a correction term that makes use of the flow table use ratio or the empty flow table ratio or by using the flow table use or empty ratio as a correction coefficient.

0041It is also desirable that the same value is set as the aging time value for the total of the communication devices on the path of a given flow, as shown in <figref idref="DRAWINGS">FIG. 1</figref>. By so doing, the flow entries may be removed on the total of the switches on the path simultaneously.

Exemplary Embodiment 1

0042An exemplary embodiment 1 of the present invention will now be detailed with reference to the drawings. <figref idref="DRAWINGS">FIG. 2</figref> depicts a block diagram showing a configuration of a communication system according to the exemplary embodiment 1 of the present invention. Referring to <figref idref="DRAWINGS">FIG. 2</figref>, the exemplary embodiment 1 of the present invention includes a controller <b>100</b>, equivalent to the above mentioned control apparatus and configured for controlling the switches on a network <b>200</b>, and the network <b>200</b> in which a group of switches <b>201</b> to <b>206</b>, as species of the above mentioned communication device, are arrayed. The controller is equivalent to the above mentioned control apparatus and configured for controlling the switches on the network.

0043The controller <b>100</b> is responsive to the new flow reception notification (Packet-In) from the switches <b>201</b> to <b>206</b> to register flow entries therein. The switches <b>201</b> to <b>206</b> forward a received packet in accordance with a flow entry registered in each of the switches.

0044The network <b>200</b> includes the switches <b>201</b> to <b>206</b>, which are interconnected in order for forwarding data. The controller <b>100</b> and the switches <b>201</b> to <b>206</b> are interconnected for control. Each of the switches <b>201</b> to <b>206</b> may be an OpenFlow switch specified in Non-Patent Documents 1, 2.

0045The flow entries include match conditions for flows, the counter information for matched flows (traffic volume) and instructions, as shown in <figref idref="DRAWINGS">FIG. 3</figref>. As the flow match conditions, the following packet header information may be specifically designated. For example, a flow may be specified using, for example, a transmission source IP address, a destination IP address, a protocol, a transmission source TCP/UDP port number or a destination TCP/UDP port number. As the counter information, the number of packets that matched the match conditions and the number of bytes, that is, the traffic volume, are recorded. As the instructions, the processing contents applied to the packets that matched the matching conditions, for example, packet forwarding from the specified port or header rewriting, are specified. These flow entries are stored in the flow tables of the switches <b>201</b> to <b>206</b>.

0046The controller <b>100</b> includes a topology memory <b>101</b>, a topology management unit <b>102</b>, a flow entry memory <b>103</b>, a flow entry management unit <b>104</b>, a flow statistics information memory <b>105</b>, a flow statistics information management unit <b>106</b> and a switch control unit <b>107</b>. Such controller <b>100</b> may be implemented by adding the functions, which will hereinafter be explained, to the OpenFlow controller, shown in the Non-Patent Documents 1, 2, as a basic structure.

0047The respective parts of the controller <b>100</b> operate substantially as follows: The topology memory <b>101</b> has stored the connection states of the switches <b>201</b> to <b>206</b> on the network <b>200</b>. The connection states of the network may be represented by sets of the names of the ports and the switches connected to both ends of the links, and link bandwidths, as shown for example in <figref idref="DRAWINGS">FIG. 4</figref>.

0048The topology management unit <b>102</b> collects the connection information of the switches <b>201</b> to <b>206</b>, by means such as LLDP (Link Layer Discovery Protocol), and causes it to be stored in the topology memory <b>101</b>.

0049The flow entry memory <b>103</b> has stored, for each switch, the number of flow tables registered (number of registered entries), an upper limit of the flow tables registered (the maximum number of registrable entries) and the flow table use ratio (number of registered entries/maximum number of registrable entries), as shown in <figref idref="DRAWINGS">FIG. 5</figref>. The flow entry memory <b>103</b> also has stored the registered flow table entries in the switches <b>201</b> to <b>206</b>, as shown in <figref idref="DRAWINGS">FIG. 6</figref>. Although the flow table use ratio is used in the example of <figref idref="DRAWINGS">FIG. 5</figref>, the empty flow table ratio (number of empty entries/the number of maximum registrable entries) may also be used.

0050The flow entry management unit <b>104</b> is responsive to a request from the switch control unit <b>107</b> to update the information of the flow entry memory <b>103</b>. If, on receipt of a new flow reception notification, the flow entry management unit has registered a corresponding flow entry in each of the switches <b>201</b> to <b>206</b>, the flow entry management unit increments the number of registered flow tables for the relevant switch(es) of the table of <figref idref="DRAWINGS">FIG. 5</figref>. Also, the flow entry management unit re-calculates the flow table use ratio, while adding the flow entry to the table of <figref idref="DRAWINGS">FIG. 6</figref>. On receipt of a notification for flow table removal due to aging from the switches <b>201</b> to <b>206</b>, the flow entry management unit <b>104</b> decrements the number of the flow table(s) registered for the relevant switches in the table of <figref idref="DRAWINGS">FIG. 5</figref> to re-calculate the flow table use ratio, while removing the flow entry at the same time from the table of <figref idref="DRAWINGS">FIG. 6</figref>.

0051To verify the flow characteristic, the flow statistics information memory <b>105</b> has stored the statistics information on the flow basis. The flow statistics information has stored, from one flow to another, the flow information (from “transmission source IP address” to “destination TCP/UDP port number”), an average flow table registration time interval, an average aging time value, and an average count number per aging, as shown in <figref idref="DRAWINGS">FIG. 7</figref>.

0052The flow statistics information management unit <b>106</b> is responsive to a request from the switch control unit <b>107</b> to update the information of the flow statistics information memory <b>105</b>. If, on receipt of the new flow reception notification, the flow statistics information management unit <b>106</b> has registered the flow tables in the switches <b>201</b> to <b>206</b>, the flow statistics information management unit re-calculates the number of times of flow table registration per apparatus time in the relevant entries of the flow statistics information, and updates the average flow table registration time interval. Moreover, the flow statistics information management unit <b>106</b> re-calculates the average aging time from the as-set value of the aging time and updates it. It is noted that, in re-calculating the number of times of flow table registration and the aging time values, such a method which uses an exponential smoothing method to put weight on the nearest value may be used. If notified from the switches <b>201</b> to <b>206</b> about the removal of the flow entry due to aging, the flow statistics information management unit <b>106</b> re-calculates the average count value from the counter information of the so removed flow entry. In re-calculating the count value, such a method which uses an exponential smoothing method to put weight on the nearest value may be used.

0053On receipt of the new flow reception from the switches <b>201</b> to <b>206</b>, the switch control unit <b>107</b> determines the flow path based on the information concerning the network connection states in the topology memory <b>101</b> and the information concerning the flow table use ratio in the flow entry memory <b>103</b>. As for details of the path determining method, reference may be made to a method stated in Patent Document 3.

0054The switch control unit <b>107</b> also determines the aging time value of the flow based on the maximum value of the flow table use ratio of the switches on the path, as found from the information in the flow entry memory <b>103</b>, and on the information on the average flow table registration time interval, the average aging time value and the average count value in the flow statistics information memory <b>105</b>. From the above information, the switch control unit generates a flow entry and requests each switch on the path to register the flow entry that has set therein the above mentioned aging time. After completion of the registration, the switch control unit <b>107</b> requests the flow entry management unit <b>104</b> and the flow statistics information management unit <b>106</b> to update the information.

0055On receipt of a flow table removal notification from the switches <b>201</b> to <b>206</b>, the switch control unit <b>107</b> requests the flow statistics information management unit <b>106</b> to update the information, specifically, to update the average count number. The switch control unit <b>107</b> also makes an update request to the flow entry management unit <b>104</b>, specifically, a request to update the number of the registered flow tables and the flow table use ratio in the flow table memory <b>103</b>. The switch control unit also requests removing the relevant flow table entry.

0056The switches <b>201</b> to <b>206</b> forward the packet received, or otherwise, in accordance with the flow entries registered therein. If there is no flow entry having match conditions matched to the received packet, the switches <b>201</b> to <b>206</b> transmit a new flow reception notification to the controller <b>100</b>, and forward the flow or otherwise in accordance with the instructions from the controller <b>100</b>. If once the flow entry has been registered from the controller <b>100</b> in response to the new flow reception notification, the ensuing packets of the same flow are forwarded in accordance with the flow entries registered in the switches <b>201</b> to <b>206</b>, as the counter information of the flow entries is sequentially incremented. The aging time value is set in each flow entry, such that, if the state of non-communication persists for the so set time duration, the switches <b>201</b> to <b>206</b> remove the relevant flow entries. If the flow entries have been removed due to aging, the switches <b>201</b> to <b>206</b> notify the controller <b>100</b> of the removal and about the counter information for the so removed flow entries.

0057It is noted that the respective parts (processing means) of the controller <b>100</b>, shown in <figref idref="DRAWINGS">FIG. 1</figref>, may also be implemented by a computer program which causes a computer constituting the controller <b>100</b> to execute the above mentioned respective processing operations with the use of the computer's hardware.

0058The operation of the exemplary embodiment 1 of the present invention will now be detailed with reference to the flowcharts shown in <figref idref="DRAWINGS">FIG. 8</figref>, <b>9</b>. Initially, a sequence of operations to be performed on occurrence of a new flow will be explained with reference to the flow chart of <figref idref="DRAWINGS">FIG. 8</figref>. In the following explanation, it is assumed that the switch <b>201</b> has received a new packet.

0059On receipt of the packet (step A-<b>1</b>), the switch <b>201</b> searches, from its flow table, the flow entry having match conditions matched to the received packet (step A<b>2</b>).

0060If the flow entry having the match conditions matched to the received packet has been found (Yes of the step A<b>2</b>), the switch <b>201</b> processes the received packet in accordance with the contents of the instruction field of the flow table, and increments the counter information of the flow table. The switch then returns to the initial state (step A<b>3</b>).

0061If conversely the flow entry matched to the received packet has not been found (No of the step A<b>2</b>), the switch <b>201</b> transmits a packet reception notification (new flow reception notification) to the controller <b>100</b> (step A<b>4</b>).

0062On receipt of the packet reception notification, the switch control unit <b>107</b> of the controller <b>100</b> decides on the path of the packet received by the switch <b>201</b> based on the information concerning the network connection states in the topology memory <b>101</b> and on the flow table use ratio in the flow entry memory <b>103</b>. As for details of the path determining method, reference may be made to a method stated in Patent Document 3. Here, it is assumed that a path from the switch <b>201</b> to the switch <b>203</b>, thence to the switch <b>205</b> and thence to the switch <b>206</b>, for example, has been selected (step A<b>5</b>).

0063The switch control unit <b>107</b> determines the aging time value of the flow, based on the information concerning the maximum value of the flow table use ratio in the switches on the path, as found from the flow entry memory <b>103</b>, and on the information concerning an average flow table registration time interval, an average aging time value and an average count number in the flow statistics information memory <b>105</b> (step A<b>6</b>). The average aging time value of the relevant flow may, for example, be directly used as the aging time value.

0064The aging time value may also be set in the following manner as necessary. If the maximum value of the flow table use ratio of a given switch on the path exceeds a preset threshold value, that is, there is not much allowance in the empty state for the flow tables in any of the switches on the path, a preset minimum aging time value may be set for the flow whose average count number is less than a preset average count number. As for other flows (flows whose average count numbers are not less than the count number), the aging time value may be found by a preset calculation formula: an average aging time value×(1−maximum value of the flow table use ratio on the path)×a preset coefficient. For example, if, in the state of <figref idref="DRAWINGS">FIG. 4</figref> to <figref idref="DRAWINGS">FIG. 6</figref>, the upper threshold value is 75% and the coefficient is 2, the aging time value may be found by 300×(1−0.8)×2=120 sec. In this manner, an aging time is set, which is lesser by 180 seconds than if the average aging time is directly set.

0065If, on the other hand, the maximum value of the flow table use ratio in the switch(es) on the path is less than the lower threshold value, that is, there is a flow table allowance in the total of the switches on the path, the average flow table registration time interval may directly be used as the aging time value for flows whose average flow table registration time interval is within a preset range. For other flows (flows in each of which the average flow table registration time interval is not less than a preset upper threshold value), the aging time value may be found by a formula: average aging time value×(1−maximum value of the flow table use ratio on the path)×a preset coefficient.

0066The switch control unit <b>107</b> generates a flow entry in which the aging time calculated as above has been set, and requests each of the switches <b>201</b>, <b>203</b>, <b>205</b> and <b>206</b> on the path to register the flow entry (step A<b>7</b>).

0067On completion of the registration, the switch control unit <b>107</b> requests the switch <b>201</b> to transmit the received packet at its port of connection to the switch <b>203</b> (Packet-Out message of Non-Patent Document 2). The received packet is then forwarded from the switch <b>203</b> to the switch <b>205</b> and thence to the switch <b>206</b> in accordance with the flow entries of the switches on the path. The switch control unit <b>107</b> also requests the flow entry management unit <b>104</b> and the flow statistics information management unit <b>106</b> to update the information (step A<b>8</b>).

0068The flow entry management unit <b>104</b> is responsive to the request from the switch control unit <b>107</b> to update the information in the flow entry memory <b>103</b>. The flow entry management unit increments the number of the registered flow tables in the switches <b>201</b>, <b>203</b>, <b>205</b> and <b>206</b> and re-calculates the flow table use ratio, while adding the flow entry to the table of <figref idref="DRAWINGS">FIG. 6</figref> (step A<b>9</b>).

0069The flow statistics information management unit <b>106</b> is responsive to a request from the switch control unit <b>107</b> to update the information in the flow statistics information memory <b>105</b>. The flow statistics information management unit re-calculates the average flow table registration time interval of the relevant entry of the flow statistics information, while re-calculating the average aging time value from the so set aging time. In re-calculating the flow table registration time interval and the aging time value, such a method which uses an exponential smoothing method to put weight on the nearest value may be used (step A<b>10</b>).

0070Reversion is then made to the initial state. If a new packet is received, processing is continued in accordance with a similar sequence of operations.

0071The flow entry aging processing will now be explained with reference to the flowchart of <figref idref="DRAWINGS">FIG. 9</figref>. Here, the aging processing for the flow entry for the switch <b>201</b> will be explained, as an example, with the aging time value of the flow entry of interest being 300 sec.

0072The switch <b>201</b> periodically monitors the counter information of the flow entry registered in the flow table (step A<b>11</b>).

0073The switch <b>201</b> checks whether or not the counter value has changed within the aging time value of the flow entry, which is here 300 sec (step A<b>12</b>). If the counter information of the flow entry has changed within the time specified by the aging time value (Yes of the step A<b>12</b>), the switch returns to the step A<b>11</b> to continue the monitoring.

0074If the counter information of the flow entry has not changed within the time specified by the aging time value (No of the step A<b>12</b>), the switch <b>201</b> removes the flow entry (step A<b>13</b>).

0075The switch <b>201</b> delivers the counter information of the removed flow entry to the controller <b>100</b>, while also notifying the controller <b>100</b> of the fact of removal of the flow entry (step A<b>14</b>).

0076On receipt of the notification of flow entry removal from the switch <b>201</b>, the switch control unit <b>107</b> of the controller <b>100</b> requests the flow statistics information management unit <b>106</b> and the flow entry management unit <b>104</b> to update the information (step A<b>15</b>).

0077The flow statistics information management unit <b>106</b> is responsive to the request from the switch control unit <b>107</b> to update the information of the flow statistics information memory <b>105</b>, and re-calculates the average count number from the counter information notified. In re-calculating the count number, such a method which uses an exponential smoothing method to put weight on the nearest value may be used (step A<b>16</b>).

0078The flow entry management unit <b>104</b> is responsive to the request from the switch control unit <b>107</b> to update the information of the flow entry memory <b>103</b>. The flow entry management unit decrements the number of the registered flow tables in the switch <b>201</b>, which has made the removal notification, re-calculates the flow table use ratio and removes the relevant flow entry from the table of <figref idref="DRAWINGS">FIG. 6</figref> (step A<b>17</b>).

0079Reversion is then made to the initial state and the aging processing for the flow table is carried out by the same sequence of operations.

0080As set out above, deterioration of the packet forwarding performance may be suppressed even in a network environment coping with larger numbers of flows. The reason is that, by setting the aging time that takes account of flow characteristic, it is possible to suppress flow table overflow in the switches.

0081Moreover, according to the present exemplary embodiment, deterioration of the packet forwarding performance may be suppressed even in a case that a switch(es) that may become a deterrent from the viewpoint of flow table capacity exists on the path. The reason is that, by setting the aging time value which takes account of the flow table use ratio in the switches on the path, and which is shorter than the usual aging time value, it is possible to suppress flow table overflow in the respective switches.

0082Additionally, according to the present exemplary embodiment, the load on the controller may be suppressed in connection with a flow sent on a path having a flow table capacity allowance. For example, by setting the aging time value which takes account of the flow table use ratio in the switches on the path, that is, the aging time value longer than the usual value, the flow entry may be retained in each switch. By so doing, the number of times of requests for flow entry setting may be reduced to decrease the overhead.

Exemplary Embodiment 2

0083An exemplary embodiment 2 of the present invention, in which the aging time is set using not the flow statistics information but certain parameters specified from a network administrator, will now be detailed with reference to the drawings. <figref idref="DRAWINGS">FIG. 10</figref> depicts a block diagram showing a configuration of a communication system according to the exemplary embodiment 2 of the present invention. <figref idref="DRAWINGS">FIG. 10</figref> depicts a block diagram showing a configuration of a communication system according to the exemplary embodiment 2 of the present invention. The following explanation is centered about the points of difference from the exemplary embodiment 1.

0084Referring to <figref idref="DRAWINGS">FIG. 10</figref>, the configuration of the exemplary embodiment 2 of the present invention includes, in the controller <b>100</b>A, a flow characteristic setting memory <b>115</b> and a flow characteristic setting management unit <b>116</b>, in place of the flow statistics information memory <b>105</b> and the flow statistics information management unit <b>106</b> of the controller <b>100</b> of the exemplary embodiment 1.

0085The flow characteristic setting memory <b>115</b> has stored flow-based setting information (flow characteristic setting information) as set by the administrator. In this flow characteristic setting information, the flow occurrence time interval and the reference aging time value are set, from one flow specified by the flow information to another, as shown for example in <figref idref="DRAWINGS">FIG. 11</figref>.

0086The flow characteristic setting management unit <b>116</b> is responsive to a request from the administrator to set, change or remove the information in the flow characteristic setting memory <b>115</b>.

0087The operation of the exemplary embodiment 2 of the present invention will now be detailed with reference to flowcharts of <figref idref="DRAWINGS">FIG. 12</figref> and <figref idref="DRAWINGS">FIG. 13</figref>.

0088Initially, the operation in receiving a packet will be explained with reference to the flowchart of <figref idref="DRAWINGS">FIG. 12</figref>. In the following, it is assumed that the switch <b>201</b> has received a new packet.

0089On receipt of a packet (step B<b>1</b>), the switch <b>201</b> searches, from the flow table, a flow entry having match conditions matched to the received packet (step B<b>2</b>).

0090If a flow entry having the match conditions matched to the received packet is found (Yes of the step B<b>2</b>), the switch <b>201</b> processes the received packet in accordance with the contents of the instruction field of the flow table. After incrementing the counter information of the flow table, the switch <b>201</b> reverts to its initial state (step B<b>3</b>).

0091If conversely the flow entry having match conditions matched to the received packet has not been found (No of the step B<b>2</b>), the switch <b>201</b> transmits a packet reception notification (new flow reception notification) to the controller <b>100</b> (step B<b>4</b>).

0092On reception of the packet reception notification, the switch control unit <b>107</b> of the controller <b>100</b> determines the path of the packet, received by the switch <b>201</b>, based on the information concerning the network connection states in the topology memory <b>101</b> and the information concerning the flow table use ratio in the flow entry memory <b>103</b>. The method for determining the path, discussed in detail in Patent Document 3, may be used in determining the path, as an example. It is here assumed that a path from the switch <b>201</b> to the switch <b>203</b>, thence to the switch <b>205</b> and thence to the switch <b>206</b> has been selected (step B<b>5</b>).

0093Furthermore the switch control unit <b>107</b> determines the aging time value of the flow based on the information concerning the maximum value of the flow table use ratio of the switches on the path, as found from the flow entry memory <b>103</b>, and on the flow occurrence time interval as well as the reference aging time value in the flow characteristic setting memory <b>115</b> (step B<b>6</b>). For example, the reference aging time value for the relevant flow may directly be used as the aging time value.

0094The following aging time value may also be set as necessary. In a case that the maximum value of the flow table use ratio of a given switch on the path exceeds a predetermined threshold value, that is, there is no sufficient allowance in the empty state for the flow table in a given switch on the path, the aging time value can be found by a predetermined calculation formula such as reference aging time value×(1−maximum value of the flow table use ratio on the path)×a preset coefficient. For example, if, in the state of <figref idref="DRAWINGS">FIG. 4</figref> or <figref idref="DRAWINGS">FIG. 9</figref>, the upper threshold value is 75% and the coefficient is 2, the aging time value may be calculated by 300×(1−0.8)×2=120 sec.

0095If, on the other hand, the maximum value of the flow table use ratio of the switches on the path is not greater than the lower limit value, that is, there is flow table allowance in the total of the switches on the path, the flow occurrence time interval in the flow characteristic setting memory <b>115</b> may directly be set as the aging time value.

0096The switch control unit <b>107</b> generates a flow entry, in which the aging time calculated as described above has been set, and requests the switches <b>201</b>, <b>203</b>, <b>205</b> and <b>206</b> on the path to register the flow entry (step B<b>7</b>).

0097If the registration has been finished, the switch control unit <b>107</b> requests the switch <b>201</b> to transmit the received packet to a connection port to the switch <b>203</b> (Packet-Out message in Non-Patent Document 2). Subsequently, the packet is forwarded to the switch <b>203</b>, thence to the switch <b>205</b> and thence to the switch <b>206</b> in accordance with the flow entries in the switches on the path. The switch control unit <b>107</b> also requests the flow entry management unit <b>104</b> to update the information (step B<b>8</b>).

0098The flow entry management unit <b>104</b> is responsive to a request from the switch control unit <b>107</b> to update the information in the flow entry memory <b>103</b>. The flow entry management unit increments the number of the flow table registrations in each of the switches <b>201</b>, <b>203</b>, <b>205</b> and <b>206</b> of <figref idref="DRAWINGS">FIG. 5</figref> and re-calculates the flow table use ratio, while adding the flow entry to the table of <figref idref="DRAWINGS">FIG. 6</figref> (step B<b>9</b>).

0099Then, reversion is made to the initial state. If a new packet is received, processing is performed by the same sequence of operations.

0100Next, processing for flow entry aging will be explained with reference to the flowchart of <figref idref="DRAWINGS">FIG. 13</figref>. Here, the processing for aging for the switch <b>201</b> will be explained, as an example, with the aging time value of a flow entry of interest being 30 sec.

0101The switch <b>201</b> periodically monitors the counter information of the flow entries registered in the flow table (step B<b>11</b>).

0102The switch <b>201</b> checks to see whether or not the counter information has changed within an aging time value of the flow entry, here 300 sec (step B<b>12</b>). If the counter information of the flow entry has changed within the time specified by the aging time value (Yes of the step B<b>12</b>), processing reverts to the step B<b>11</b> to continue the monitoring.

0103If the flow entry counter information has not changed during the time specified by the aging time value (No of the step B<b>12</b>), the switch <b>201</b> removes the flow entry in question (step B<b>13</b>).

0104The switch <b>201</b> informs the controller <b>100</b> about the fact of flow entry removal (step B<b>14</b>).

0105On receipt of the flow entry removal notification from the switch <b>201</b>, the switch control unit <b>107</b> of the controller <b>100</b> requests the flow entry management unit <b>104</b> to update the information (step B<b>15</b>).

0106The flow entry management unit <b>104</b> is responsive to the request from the switch control unit <b>107</b> to update the information in the flow entry memory <b>103</b>. The flow entry management unit decrements the number of the registered flow tables in the switch <b>201</b> that made the removal notification, and re-calculates its flow table use ratio, while removing the relevant flow entry from the table of <figref idref="DRAWINGS">FIG. 6</figref> (step B<b>16</b>).

0107Reversion is then made to the initial state and the flow table aging processing is carried out by the same sequence of operations.

0108According to the present exemplary embodiment, described above, deterioration in the packet forwarding performance may be suppressed, as in the exemplary embodiment 1, without collecting the statistics information from the switches on the network.

0109Although preferred exemplary embodiments of the present invention have been described in the foregoing, the present invention is not limited to the particular exemplary embodiments, and a variety of changes, substitutions or adjustments may be made without departing from the fundamental technical scope of the invention. For example, fine-textured control may be implemented by combining the above described exemplary embodiments 1 and 2 together in order to combine the flow statistics information and the parameters set by the network administrator together.

0110Certain preferred modes of the present invention will now be summarized.

[Mode 1]

0111(See the control apparatus according to the above mentioned first aspect)

[Mode 2]

0112The control apparatus according to mode 1, wherein, <br /> the communication device controller sets, as the aging time of the flow entry to be set on the communication devices on the path of the new flow, the same value for each of the communication devices on the path.

[Mode 3]

0113The control apparatus according to mode 2, further comprising <br /> a flow entry management unit that manages the flow entry retained by each communication device; <br /> the communication device controller finding the flow table use ratio or the empty flow table ratio from the number of flow entries registered or the number of empty entries in the flow table over the maximum number of registrable flow entries in each communication device; <br /> the communication device controller correcting the aging time of the flow entry to be set on the communication devices on the path of the new flow based on an average value of the flow table use ratio or the empty flow table ratio of the communication devices on the path of the new flow.

[Mode 4]

0114The control apparatus according to mode 3, wherein, <br /> in a case that the average value of the flow table use ratio is higher than a preset reference value or the empty flow table ratio is lower than a preset reference value, the aging time of the flow entry to be set on the communication device on the path of the new flow is corrected in a decreasing direction.

[Mode 5]

0115The control apparatus according to mode 3 or 4, wherein, <br /> in a case that the average value of the flow table use ratio is lower than the preset reference value or the empty flow table ratio is higher than the preset reference value, the aging time of the flow entry to be set on the communication device on the path of the new flow is corrected in an increasing direction.

[Mode 6]

0116The control apparatus according to any one of modes 1 to 5, wherein, as the estimated lifetime, an average aging time of the same flows during a past preset time duration, as found from the flow statistics information, is used.

[Mode 7]

0117The control apparatus according to any one of modes 1 to 6, wherein, the flow statistics information contains the occurrence time interval of the same flows during the past preset time period; <br /> the communication device controller in case the occurrence time interval of the same flows is shorter than a preset threshold value setting the occurrence time interval of the same flows as the aging time.

[Mode 8]

0118The control apparatus according to any one of modes 1 to 7, wherein, the flow statistics information includes an average value of the traffic volumes of the same flows during a reset past time period; <br /> the communication device controller setting a preset minimum aging time in a case that the average value of the traffic volumes of the same flows is less than a preset value.

[Mode 9]

0119The control apparatus according to mode 1, comprising, <br /> in place of the flow statistics information management unit, a flow characteristic setting memory that stores the flow characteristic setting information as set by a network administrator; <br /> the communication device controller on occurrence of a new flow setting a flow entry that has set reference aging time contained in the flow characteristic setting information in the communication device on the path of the new flow.

[Mode 10]

0120The control apparatus according to mode 9, wherein, <br /> the communication device controller sets, as the aging time of the flow entry to be set on the communication device on the path of the new flow, the same value on each of the communication devices on the path.

[Mode 11]

0121The control apparatus according to mode 10, further comprising <br /> a flow entry management unit that manages flow entries retained in each communication device; <br /> the communication device controller finding a flow table use ratio or an empty flow table ratio from the number of registered flow entries or the number of empty flow tables over the maximum number of registrable flow entries in each communication device; <br /> the communication device controller correcting the aging time of the flow entry to be set on the communication devices on the path of the new flow based on an average value of the flow table use ratio or the empty flow table ratio of the communication devices on the path of the new flow.

[Mode 12]

0122The control apparatus according to mode 11, wherein, <br /> in a case that an average value of the flow table use ratio is higher than a preset reference value or the empty flow table ratio is lower than a preset reference value, the aging time of the flow entry to be set on the communication device on the path of the new flow is corrected in a decreasing direction.

[Mode 13]

0123The control apparatus according to any one of modes 9 to 12, wherein, the flow characteristic setting information includes the flow occurrence time interval as set from a network administrator; <br /> the communication device controller setting the flow occurrence time interval as the aging time in a case that the average value of the flow table use ratio is lower than the preset reference value.

[Mode 14]

0124(See the communication system according to the above mentioned second aspect)

[Mode 15]

0125(See the communication method according to the above mentioned third aspect)

[Mode 16]

0126(See the program according to the above mentioned fourth aspect) Like the mode 1, each of the above mentioned modes 14 to 16 may be extended into modes 2 to 13.

0127The disclosures of the above mentioned Patent Documents and the Non-Patent Documents are incorporated herein by reference. The particular exemplary embodiments or examples may be changed or adjusted within the gamut of the entire disclosure of the present invention, inclusive of exemplary embodiments and modes, based on the fundamental technical concept of the invention. Moreover, a variety of combinations or selection of elements herein disclosed (elements of Exemplary Embodiments, Examples and drawings) may be made within the concept of the modes of the present invention. Viz., the present invention may include a variety of changes or corrections that may occur to those skilled in the art in accordance with the total disclosures inclusive of the modes and the drawings as well as the technical concept of the invention. In particular, as regards the ranges of numerical values set out herein, any optional numerical figures or sub-ranges contained in the ranges should be regarded as if they have in fact been specifically stated even in the absence of explicit statements.

EXPLANATION OF NUMERALS

0000<ul id="ul0003" list-style="none"><li id="ul0003-0001" num="0128"><b>10</b> control apparatus</li><li id="ul0003-0002" num="0129"><b>11</b> flow statistics information management unit</li><li id="ul0003-0003" num="0130"><b>12</b> communication device controller</li><li id="ul0003-0004" num="0131"><b>20</b>A to <b>20</b>D communication devices</li><li id="ul0003-0005" num="0132"><b>100</b>, <b>100</b>A controllers</li><li id="ul0003-0006" num="0133"><b>201</b> to <b>206</b> group of switches</li><li id="ul0003-0007" num="0134"><b>200</b> network</li><li id="ul0003-0008" num="0135"><b>101</b> topology memory</li><li id="ul0003-0009" num="0136"><b>102</b> topology management unit</li><li id="ul0003-0010" num="0137"><b>103</b> flow entry memory</li><li id="ul0003-0011" num="0138"><b>104</b> flow entry management unit</li><li id="ul0003-0012" num="0139"><b>105</b> flow statistics information memory</li><li id="ul0003-0013" num="0140"><b>106</b> flow statistics information management unit</li><li id="ul0003-0014" num="0141"><b>107</b> switch control unit</li><li id="ul0003-0015" num="0142"><b>115</b> flow characteristic setting memory</li><li id="ul0003-0016" num="0143"><b>116</b> flow characteristic setting management unit</li></ul>