Patent Publication Number: US-2021176176-A1

Title: Traffic optimization apparatus, communication system, traffic optimization method, and program

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present invention is a National Stage of International Application No. PCT/JP2018/022149 (filed on Jun. 11, 2018), and is based upon and claims the benefit of the priority of Japanese Patent Application No. 2017-116119 (filed on Jun. 13, 2017), the disclosures of which are incorporated herein in their entirety by reference. 
    
    
     FIELD 
     The present invention relates to a traffic optimization apparatus, a communication system, a traffic optimization method, and a program. More specifically, the invention relates to a traffic optimization apparatus, a communication system, a traffic optimization method, and a program for performing optimization of a traffic that flows through a network. 
     BACKGROUND 
     Smartphones and mobile data communication services have become widespread and use of tethering has expanded. As a method of the tethering, the method of the tethering using Wi-Fi (registered trademark), a USB (Universal Serial Bus), Bluetooth (registered trademark) or the like can be selected. Under such a background, a configuration of using the Internet from a tablet terminal or a personal computer via a smartphone, in particular, has increased. 
     A communication terminal (such as a smartphone) that is providing a tethering service generates a data traffic having a property (of a timing or an amount) which is different from that in a case where only the communication terminal is used. The difference of this data traffic arises from an application difference, for example. While a data traffic of an application when the smartphone is directly used is mainly for an SNS (Social Networking Service), moving picture viewing, or the like, a tethering using device (such as a laptop personal computer or a tablet terminal) can often generate data transfer for version up of an operating system or a large-amount file. As another cause, a difference of an amount of data at a time of the moving picture viewing due to a difference between the screen size (of the smartphone: about 5 inches) and the screen size of (the tablet: about 10 inches) may also be pointed out. 
     Accordingly, an increase in a tethering traffic has become a significant target of consideration for a company that provides a data communication service for the smartphone when network design and service design are performed. When the consideration is made, it is essential to make effective use of limited network resources (such as a communication band) of a telecommunications carrier and to provide a fair service (that is appropriate for the price) to a user. 
     Thus, there is a handling method of permitting or blocking an inflow of the tethering traffic. That is, by charging another charge for the tethering, for example, only the tethering traffic of a user who has paid for the tethering is permitted to pass. This prevents an inflow of the traffic of the tethering outside of contract and avoids frequent occurrence/normalization of a state where a large amount of network resources is consumed by abuse of the tethering. 
     Each of Patent literatures 1 and 2 discloses an example of a technology whereby the tethering traffic inflow control described above is performed. Patent Literature 1 discloses a communication terminal that can control communication of each of other apparatuses configured to communication-connect to networks, using a tethering function. According to the Literature, this communication terminal provides the tethering function to each of the other apparatuses. Then, it is described that this communication terminal controls permission of the communication according to a control policy stored in a storage part in advance and based on at least one of attribute information, a communication destination, interface type information of a corresponding one of the connected networks of these other apparatuses. 
     Patent Literature 2 discloses a method for processing a data session to be executed by using a user device that has been tethered in a network. Specifically, in the method described in the Literature, a process of receiving, by a network element, the indicator of the tethered device, which has been originated from a request message from the user device, is performed. Then, a process of detecting this indicator by the network element is performed. Further, based on this indicator, a process of executing one of rejecting the data session requested by the user device or managing the data session requested by the user device is performed. 
     Patent Literature 3 discloses an identification apparatus that can identify the connection configuration of a terminal apparatus. Specifically, this identification apparatus includes a communication monitoring part  11  configured to acquire information of a communication packet to be monitored and a terminal type acquisition part (such as a communication protocol analysis part  12 ) configured to acquire information indicating the type of the terminal apparatus that has transmitted the communication packet. This identification apparatus further includes a connection configuration detection part configured to detect the connection configuration of the terminal apparatus, based on a TTL (Time To Live) value included in the information of the communication packet that is acquired by the communication monitoring part  11  and the information indicating the type of the terminal apparatus that is acquired by the terminal type acquisition part. 
     [PTL 1] International Publication No. WO2014/142299
 
[PTL 2] JP Patent Kohyo Publication No. JP2011-520383A
 
[PTL 3] JP Patent Kokai Publication No. JP2014-209674A
 
     SUMMARY 
     The following analysis has been given by the present invention. The control of the tethering traffic in each of Patent Literatures 1 and 2 is permission control at a point of the inflow of the traffic. When a user pays the another charge for the tethering, the tethering traffic flows to the side of the network without alteration. Then, the tethering traffic that has flown in is to be handled like a smartphone traffic. 
     In a network of a telecommunications carrier, optimization of a traffic (such as data compression or transfer speed control) may be performed. In this case as well, a smartphone traffic and a tethering traffic are handled without distinction. Also when optimization control is performed based on charging policy information for each user, which has been obtained from a PCRF (Policy and Charging Rules Function), by cooperation between a traffic optimization apparatus and the PCRF, a policy for each user is applied. That is, there is a problem that after the smartphone traffic and the tethering traffic have flown into the network of the telecommunications carrier, fine optimization in accordance with a traffic characteristic cannot be performed for each of the smartphone traffic and the tethering traffic. 
     An object of the present invention is to provide a traffic optimization apparatus, a communication system, a traffic optimization method, and a program that can contribute to enrichment of means for performing optimization of a tethering traffic from a viewpoint different from that of the above-mentioned control at the inflow point. 
     According to a first aspect, there is provided a traffic optimization apparatus comprising a tethering detection part configured to identify, based on packet header information of a packet flowing in a network to which a communication terminal configured to provide a tethering service to one or more other devices is connected, a tethering traffic from each of the one or more other devices via the communication terminal, a policy selection part configured to select a communication policy to be applied to the identified tethering traffic, and a traffic optimization part configured to apply, to the tethering traffic, a process associated with the selected communication policy. 
     According to a second aspect, there is provided a communication system comprising the above-mentioned traffic optimization apparatus and a policy management apparatus configured to provide, to the traffic optimization apparatus, the communication policy to be applied to the identified tethering traffic. 
     According to a third aspect, there is provided a traffic optimization method comprising the steps of identifying, based on packet header information of a packet flowing in a network to which a communication terminal configured to provide a tethering service to one or more other devices is connected, a tethering traffic from each of the one or more other devices via the communication terminal, selecting a communication policy to be applied to the identified tethering traffic, and applying, to the tethering traffic, a process associated with the selected communication policy. This method is linked to a specific machine which is the traffic optimization apparatus that is disposed in the network to which the communication terminal configured to provide the tethering service to the one or more other devices is connected. 
     According to a fourth aspect, there is provided a program for a computer disposed in a network to which a communication terminal configured to provide a tethering service to one or more other devices is connected, the program causing the computer to execute the processes of identifying, based on packet header information of a packet flowing in the network, a tethering traffic from each of the one or more other devices via the communication terminal, selecting a communication policy to be applied to the identified tethering traffic, and applying, to the tethering traffic, a process associated with the selected communication policy. This program can be recorded on a computer-readable (non-transient) storage medium. That is, the present invention can also be embodied as a computer program product. 
     According to the present invention, it becomes possible to optimize the tethering traffic. That is, the present invention converts the tethering service provision apparatus described in the Background Art to the one in which functional improvement has been achieved in terms of traffic control of the tethering service provision apparatus. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a diagram for describing a configuration of an exemplary embodiment of the present invention. 
         FIG. 2  is a diagram for explaining operations of the exemplary embodiment of the present invention. 
         FIG. 3  is another diagram for explaining operations of the exemplary embodiment of the present invention. 
         FIG. 4  is a diagram illustrating a configuration of a first exemplary embodiment of the present invention. 
         FIG. 5  is a table illustrating an example of communication policy information that is acquired from a PCRF by a traffic optimization apparatus in the first exemplary embodiment of the present invention. 
         FIG. 6  is a diagram for explaining traffics to be processed by the apparatus for traffic optimization in the first exemplary embodiment of the present invention. 
         FIG. 7  is a sequence diagram for explaining operations of the first exemplary embodiment of the present invention. 
         FIG. 8  is another sequence diagram for explaining operations of the first exemplary embodiment of the present invention. 
         FIG. 9  is a diagram illustrating a configuration of a second exemplary embodiment of the present invention. 
         FIG. 10  is a table for explaining the held state of each result of determination by a traffic optimization apparatus in the second exemplary embodiment of the present invention. 
     
    
    
     PREFERRED MODES 
     First, an overview of an exemplary embodiment of the present invention will be described with reference to the drawings. A reference numeral in each drawing given in this overview is provided to each element for convenience as an example for helping understanding and does not intend to limit the present invention to the mode that has been illustrated. Also, connection lines between blocks in the drawings or the like that will be referred to in the following description include both bidirectional and unidirectional connection lines. Each one-way arrow schematically illustrates a flow of a main signal (data), and it does not exclude bidirectionality. Though there is a port or an interface at each input/output connection point in each block in each drawing, illustration of them will be omitted. 
     The embodiment of the present invention can be implemented by a traffic optimization apparatus  30  including a tethering detection part  31 , a policy selection part  32 , and a traffic optimization part  33 , as illustrated in  FIG. 1 . 
     More specifically, a communication terminal  2   a  provides a tethering service to one or more other devices (e.g.,  1   a  and  1   b  in  FIG. 1 ). The tethering detection part  31  identifies a tethering traffic from each of the one or more other devices via the communication terminal  2   a , based on information of the packet header of a packet flowing in a network to which the communication terminal  2   a  is connected. 
     As a method of identifying the tethering traffic, a traffic analysis method that is used in a DPI (Deep Packet Inspection) apparatus or the like can be used. It is a method of using that a value in a Time-To-Live (hereinafter “TTL”) field of an IP packet is an initial value which is different according to an origination, for example. If there is a variation in the TTL, the traffic can be estimated to the tethering traffic. Alternatively, as the method of identifying the tethering traffic, a different tendency, which is seen between TTL values of IP packets in a traffic when the communication terminal  2   a  is directly used and the tethering traffic, for example, can also be used. When the TTL value of a packet after having been observed for a certain period is small, the traffic can be estimated to be the tethering traffic. The reason why the TTL value differs in this way is that the number of hops in an IP path for tethering becomes larger than that for a smartphone traffic. 
     When the tethering traffic is identified, it is necessary to analyze each traffic through the communication terminal  2   a  that provides a tethering function. The IP address of an IP packet can be used for the identification through the communication terminal  2   a . Since the communication terminal  2   a  operates as a NAT router also when the tethering is performed, an origination becomes the IP address of the communication terminal  2   a . Thus, a TTL value is monitored for each communication terminal  2   a  and is recorded for a certain period as the TTL value of the traffic from the IP address. When an IP packet having a TTL value that is different from this reference value flows in from the same IP address, that flow can be estimated to be the tethering traffic from the communication terminal  2   a . This allows identification of the tethering traffic for each communication terminal  2   a.    
     More preferably, by monitoring a value in a Use-Agent (hereinafter “UA”) field of an HTTP Request message header, in addition to the TTL value, a plurality of devices that are connected from the same communication terminal  2   a  using the tethering function can be identified. 
     The policy selection part  32  selects a communication policy to be applied to the identified tethering traffic. 
     The traffic optimization part  33  applies, to the tethering traffic, a process associated with the selected communication policy. 
     It is assumed, for example, that each of a tablet-type terminal  1   a  and a PC (personal computer)  1   b  performs communication with a service provision apparatus  4 , using the tethering function of the communication terminal  2   a , as illustrated in  FIG. 2 . In this case, the traffic optimization apparatus  30  determines whether or not a traffic between the communication terminal  2   a  and the service provision apparatus  4  is the tethering traffic, based on information of the packet header of a packet that is communicated between the communication terminal  2   a  and the service provision apparatus  4 . 
     If it has been determined, as a result of the determination, that the traffic between the communication terminal  2   a  and the service provision apparatus  4  is the tethering traffic, it means that the tethering traffic from the other device via the communication terminal  2   a , could be identified. In this case, the traffic optimization apparatus  30  selects the communication policy to be applied to the identified tethering traffic. The communication policy of applying, to the tethering traffic of this type, a data transfer speed which is lower than that for any other traffic, for example, is selected. 
     Then, the traffic optimization apparatus  30  applies, to the tethering traffic, the process associated with the selected communication policy. 
     As a result, the communication policy is applied to the tethering traffic illustrated by a broken line in  FIG. 2 , for example. This makes it possible to handle the tethering traffic and a traffic other than the tethering traffic in distinction between each other and to perform optimization of the tethering traffic. On the other hand, when the communication terminal  2   a  does not provide the tethering function, as illustrated in  FIG. 3 , the traffic is not identified to be the tethering traffic, so that application of the communication policy to be applied to the tethering traffic is not performed. By the above-mentioned processes, the optimization of the tethering traffic is implemented. 
     Further, when the number of tethering using devices to be connected from the same communication terminal  2   a , using the tethering function can be grasped by the monitoring of the UA field or the like, the tethering traffic in which the number of the tethering using devices is equal to or more than a predetermined number can also be made to be a target for the application of the communication policy. 
     First Exemplary Embodiment 
     Subsequently, a first exemplary embodiment of the present invention will be described in detail, using the drawings.  FIG. 4  is a diagram illustrating a configuration of the first exemplary embodiment of the present invention. Referring to  FIG. 4 , the configuration including a smartphone  2  that is connected to a network  100  via a mobile network  200  and one or more tethering using devices  1  configured to use the tethering function of this smartphone  2  is illustrated. 
     The network  100  is a network of a communications carrier that provides a mobile data communication service to the smartphone  2 . In the example in  FIG. 4 , a router  5 , a GGSN/P-GW  6 , a PCRF  7 , and a traffic optimization apparatus  30  are disposed on the side of the network  100 . 
     Each tethering using device  1  is a terminal configured to be connected to the smartphone  2  by tethering, thereby accessing the Internet, and has a function of wireless or wired tethering connection. As the tethering using device  1  as mentioned above, a tablet terminal, a laptop personal computer, or the like may be mainly pointed out. Besides, as the tethering using device  1 , a game terminal, a smartphone without a SIM (Subscriber Identify Module) may be used. As a method for connection to the smartphone  2  by the tethering, Wi-Fi (registered trademark), for example, may be used or a different method (such as a USB (Universal Serial Bus), Bluetooth (registered trademark), or the like) may be used. 
     The smartphone  2  is a terminal in a state capable of using an Internet access service that is provided by the telecommunications carrier and has the tethering function. In this exemplary embodiment, the description will be given, assuming that the smartphone  2  is used. However, a tablet terminal or the like having a mobile data communication function may be used instead of the smartphone  2 . The tethering function of the smartphone  2  includes a NAT (Network Address Translation) router function configured to relay an internet access traffic from the tethering using device  1 . The UE (User Equipment) of each of the smartphone  2  and the tethering using device  1  can receive, from a service provision apparatus  4 , a service that is referred to as an OTT (Over The Top) via the network  100 . 
     The router  5  is disposed in the network  100  and has a function of routing a mobile data communication traffic. The router  5  may be a DPI switch, a layer  3  switch, or the like. Further, control based on a communication policy provided by the PCRF  7  or the like may be performed for any data traffic including the tethering traffic described in the Background Art, in the router  5 . 
     The PCRF  7  is an abbreviation for Policy and Charging Rules Function, is disposed in the network  100 , and has a function (corresponding to that of a policy management apparatus) of managing user policies of the mobile data communication service. The user policies that are managed by the PCRF  7  can separately include a policy when the smartphone is used and a policy when the tethering is used or a communication policy for the tethering traffic. Then, the PCRF  7  responds the communication policy of a target user, in response to a policy inquiry request from the traffic optimization apparatus  30  or the like. Further, the PCRF  7  may employ a method where when communication policy content is set or changed, the PCRF  7  voluntarily notifies the set content or the changed content to the traffic optimization apparatus  30  or the like. In this exemplary embodiment, the PCRF  7  functions as an apparatus configured to provide, to the traffic optimization apparatus  30 , the communication policy for the tethering traffic. 
     The GGSN/P-GW  6  is a device that is a Gateway GPRS Support Node or a Packet Data Network Gateway, which constitutes a connecting point between the mobile network  200  and the network  100 . The GGSN/P-GW  6  performs assignment of an IP (Internet Protocol) address to a device on the side of the mobile network, or the like, for example. 
     The traffic optimization apparatus  30  includes a tethering detection part  31 , a policy selection part  32 , and a traffic optimization part  33 , is disposed in the network  100 , and performs various optimization processes to the mobile data communication traffic. 
     As illustrated in  FIG. 4 , the traffic optimization apparatus  30  may be disposed in such a way that each traffic that flows between the service provision apparatus  4  and each of the UEs including the smartphone  2  and the tethering using device  1  is drawn in from the router  5 . In this case, it may be so configured that the router  5  performs traffic selection according to a predetermined condition, directs the traffic that has met the condition to the traffic optimization apparatus  30  as an optimization target, and does not direct the traffic (that is a user traffic indicated by a broken line in  FIG. 6 ) that has not met the condition to the traffic optimization apparatus  30  and forwards the traffic to an original destination. With respect to the traffics (that are a user traffic indicated by a dash-dotted line in  FIG. 6  and a user traffic indicated by a solid line in  FIG. 6 ), which have been transmitted to the traffic optimization apparatus  30 , the traffic optimization apparatus  30  may forward the traffic to the service provision apparatus  4 , or may return the traffic to the router  5 . 
     It may also be so configured that the traffic optimization apparatus  30  itself is disposed at the position of the router  5  in  FIG. 4 . In this case, the traffic optimization apparatus  30  also serves as the router  5 , so that the router  5  becomes unnecessary. 
     The tethering detection part  31  has a function of monitoring each traffic between the service provision apparatus  4  and the smartphone  2  or the tethering using device  1  and determining whether that the traffic is due to the smartphone  2  or the tethering. The tethering detection part  31  also has a function of identifying the number of the tethering using devices  1 . A mechanism whereby the tethering detection part  31  identifies the tethering traffic and the number of the devices that uses the tethering traffic will be described later in detail. 
     The policy selection part  32  communicates with the PCRF  7  and acquires user policy information. More specifically, the policy selection part  32  acquires the communication policy to be applied to the tethering traffic that has been identified by the tethering detection part  31 . 
       FIG. 5  is a table illustrating an example of each communication policy information that is acquired from the PCRF  7  by the traffic optimization apparatus  30  in the first exemplary embodiment of the present invention. In the example in  FIG. 5 , content of a process (user policy) to be applied to the tethering traffic is defined for each user. In the example in  FIG. 5 , the content of the process to be applied differs according to the number of the tethering using terminals. To take an example, the user policy to be applied to a same user A differs between a case where the number of the tethering using terminals is one and a case where the number of the tethering using terminals is two. As mentioned above, the information of the user policy to be set in the PCRF  7  in advance may comprise a plurality of types. Besides the information of the user policy illustrated in  FIG. 5 , the user policy may comprise two types that are a smartphone traffic policy and a tethering traffic policy of a certain user, and three or more types of the tethering traffic policy may be further provided according to the number of simultaneously connecting devices. In the example in  FIG. 5 , the communication policy is defined for each traffic type. However, the communication policy (user policy) to be applied may be changed according to the contracted service or the payment status of each user. To take an example, the tethering traffic of the user who makes a contract using a high charge plan may be treated to be equivalent to a non-tethering traffic. 
     A “high throughput” in the user policy in  FIG. 5  means control of a throughput of the traffic optimization apparatus  30  so that a predetermined lower limit value is guaranteed for the throughout. A “low throughput” to the applied to the tethering traffic in  FIG. 5  means control of the throughput of the traffic optimization apparatus  30  so that the throughput of the traffic optimization apparatus  30  is a lower throughput than the “high throughput”. An “intermediate throughput” means a throughput intermediate between the “high throughput” and the “low throughput”. Generally, the user policy is defined according to the service policy and the charge plan of a telecommunications carrier. With respect to the user policy to be applied to the tethering traffic, the format and the defined content of the user policy can be adjusted in advance between the PCRF  7  and the traffic optimization apparatus  30 . These user policies can also be held by using system setting of the traffic optimization apparatus  30  (such that the name for each policy may just be responded from the PCRF  7  to the traffic optimization apparatus  30 ). Each user policy may be dynamically changed. To take an example, the “low throughput” of the tethering traffic policy of a certain user, which has been initially set, may be changed to the “high throughput” (according to a change in the contract content of the user). By finely determining each user policy and traffic optimization execution content corresponding to the user policy, a quality of experience appropriate to the charge can be provided. 
     In the traffic optimization apparatus  30 , the traffic optimization part  33  applies an optimization process to the tethering traffic that has been identified by the tethering detection part  31 , based on the communication policy acquired by the policy selection part  32 . 
     Each part (processing means) of the traffic optimization apparatus  30  illustrated in  FIGS. 1 and 4  can also be implemented by a computer program configured to cause a processor mounted on the traffic optimization apparatus  30  to execute each process described above, using hardware of the traffic optimization apparatus  30 . 
     Subsequently, operations of this exemplary embodiment will be described in detail with reference to the drawings. Each of  FIG. 7  and  FIG. 8  is a sequence diagram for explaining the operations of the first exemplary embodiment of the present invention. First, with reference to  FIG. 7 , the description will be given by pointing out an example where the smartphone  2  has transmitted an HTTP (HyperText Transfer Protocol) request by itself. 
     If the message of the HTTP Request transmitted from the smartphone  2  has reached the traffic optimization apparatus  30  (steps A 1  and A 2 ), the tethering detection part  31  of the traffic optimization apparatus  30  determines the type of the traffic (whether the traffic is generated by the smartphone or tethering) (step A 3 ). Herein, since the example where the smartphone  2  has transmitted the HTTP request by itself is pointed out, the tethering detection part  31  determines that the traffic is a smartphone traffic (non-tethering traffic). 
     In the above-mentioned step A 3 , the tethering detection part  31  can determine the type of the traffic (whether the traffic is the generated by the smartphone or the tethering) by monitoring a TTL value. More preferably, a configuration can also be employed where the tethering detection part  31  performs monitoring in an HTTP layer, in addition to the monitoring of the TTL value. That is, the tethering detection part  31  restores the HTTP message, and checks a character string in the UA (User Agent) field of the HTTP message. Generally, the UA varies according to the OS or the browser of an originating device. A method of identifying the type of a traffic based on a variation state of these information can be employed. Further, if a new pattern that is different from a combination of an originating IP address and a TTL (and a UA as necessary) has been detected, an increase in the one or more tethering using devices is inferred. That is, the tethering detection part  31  can detect the number (number) of the one or more tethering using devices in accordance with the number of patterns that have been detected. 
     Subsequently, the traffic optimization part  33  of the traffic optimization apparatus  30  transmits the message of the HTTP Request to the service provision apparatus  4  (step A 4 ). Concurrently with this transmission, the policy selection part  32  of the traffic optimization apparatus  30  transmits a policy request to the PCRF  7  with the IP address of the smartphone  2  used as key information if the policy selection part  32  does not hold communication policy information of the user of the smartphone  2 . 
     If the PCRF  7  has received the policy request from the traffic optimization apparatus  30 , the PCRF  7  identifies the user to which the specified IP address has been assigned at that point, and returns, to the traffic optimization apparatus  30 , a result obtained by retrieving the communication policy information that is set for that user, as a policy response (step A 6 ). If these communications for the policy request and the policy response for acquiring user policy information of the smartphone  2  have already been performed in advance and the information of the user policy is stored in the traffic optimization apparatus  30  (and is regarded to be valid), the communication for the policy request from the traffic optimization apparatus  30  to the PCRF  7  may be omitted. 
     Thereafter, if the traffic optimization apparatus  30  receives an HTTP Response message from the service provision apparatus  4  (step A 7 ), the traffic optimization apparatus  30  performs an optimization process for the traffic, according to the communication policy for the smartphone for the user that has been acquired before from the PCRF  7  (step A 8 ). 
     Then, an HTTP Response after the optimization is transmitted to the smartphone  2  via the router  5  (steps A 9  and A 10 ). 
     Subsequently, with reference to  FIG. 8 , the description will be given by pointing out an example where the tethering using device  1  has transmitted an HTTP (HyperText Transfer Protocol) request via the smartphone  2 . As illustrated in  FIG. 8 , the HTTP request that has been transmitted from the tethering using device  1  is relayed by the smartphone  2  (steps B 0  and B 1 ) by tethering, and is further forwarded to the traffic optimization apparatus  30  by the router  5  (step B 2 ). 
     Though a flow of processes (from step B 3  to step B 9 ) where the traffic optimization apparatus  30  transmits an HTTP Response after the traffic optimization apparatus  30  has received the HTTP request is the same as that in the case of the smartphone traffic (from step A 3  to A 9  in  FIG. 2 ) described above, the following respects are different. 
     Namely, the different respects are that in step B 3 , the tethering detection part  31  detects a tethering traffic and determines the number of simultaneously connecting tethering using devices (=1) and that in step B 8 , the traffic optimization part  33  applies a traffic optimization process according to the communication policy for the tethering traffic. 
     When the policies that are different according to the number of simultaneous connections of the tethering using devices  1  are given when the traffic optimization part  33  applies the optimization process in step B 8 , selection of the policy to be applied is performed, based on the number of the simultaneous connections determined by the tethering detection part  31  in step B 3 . 
     Thereafter, similar processes to those in  FIG. 7  are performed. The HTTP Response transmitted by the traffic optimization apparatus  30  is forwarded to the smartphone  2  by the router  5  (step B 10 ) and is then returned to the tethering using device  1  by being further relayed by the smartphone  2  (step B 11 ). 
     As mentioned above, in this exemplary embodiment, a plurality of the devices to be tethered from the same UE are identified when the tethering traffic is detected, based on a TTL value in an IP packet header and a value in the User-Agent field of an HTTP Request message header. This makes it possible to apply the optimization process according to the number of the simultaneous connections to the smartphone  2  as well as to determine whether or not the traffic is the tethering traffic. A time limit (time-out value) may be provided for the period of applying the communication policy by the traffic optimization part  33  described above. This makes it possible to also employ an operation of omitting detection of completion of the tethering traffic and a change in the number of the tethering using devices and regarding the communication to be ended when a time-out occurs. 
     Second Exemplary Embodiment 
     Subsequently, a description will be given about a second exemplary embodiment of the present invention which has enabled an optimization process to be performed also for a tethering traffic other than that using an HTTP, in detail, with reference to the drawings.  FIG. 9  is a diagram illustrating a configuration of the second exemplary embodiment. A configuration difference from the first exemplary embodiment illustrated in  FIG. 4  is that a determination result storage part  311  is provided at a tethering detection part  31   a  of a traffic optimization apparatus  30   a.    
     The tethering detection part  31   a  in this exemplary embodiment records each of results of estimations and identifications of a smartphone traffic and a traffic (or a tethering traffic) other than the smartphone traffic in the determination result storage part  311 , as device identification information, for a predetermined period. Then, the tethering detection part  31   a  in this exemplary embodiment uses the device identification information on the tethering traffic thus recorded in order to identify one or more tethering using devices  1 . 
       FIG. 10  is a table for explaining the held state of each result of a determination by the traffic optimization apparatus  30   a  in this exemplary embodiment. In the example in  FIG. 10 , the IP address of an origination, a TTL value, a UA value, and the result of the determination about a traffic are held when the type of the traffic is determined by the same method as that in the first exemplary embodiment. 
     After an HTTP Request header has been checked by the method described in the first exemplary embodiment and information in a UA filed has been confirmed, the information in that UA may be determined to have a one-to-one correspondence relationship with a specific TTL value. On the other hand, there are some IP packets, among IP packets that flow into the traffic optimization apparatus  30   a  from a UE, which include HTTP Request headers in their payload portions, and the other packets which do not include the HTTP Request headers. In this exemplary embodiment, the tethering detection part  31   a  can determine, among the IP packets that have subsequently flown in from a same originating IP address, the IP packet having the specific TTL value to be the one matching the device identification information that has been already recorded in the determination result storage part  311 . This makes it possible to determine the type of the traffic without waiting for restoration of an HTTP message in this exemplary embodiment. In this exemplary embodiment, the result of the determination obtained with reference to the determination result storage part  311  can be applied to an IP packet of a communication using a protocol other than the HTTP (e.g., a concealed HTTPS (Hypertext Transfer Protocol Secure) communication or a communication using a UDP (User Datagram Protocol)) as well. 
     Since the other configurations and operations are the same as those in the first exemplary embodiment, a description of the other configurations and operations will be omitted. As described above, according to this exemplary embodiment, restoration processes of HTTP messages can be partly omitted, and a traffic other than that using the HTTP can be made to be a control target. 
     Though the above description has been given about each exemplary embodiment of the present invention, the present invention is not limited to the above-mentioned exemplary embodiments, and a further variation, a further substitution, and a further adjustment may be made within the scope not departing from the basic technical concept of the present invention. To take an example, the network configuration, the configuration of each element, and the expression form of each message illustrated in each drawing are an example for helping understanding of the present invention, and the present invention is not limited to the configurations illustrated in these drawings. 
     To take an example, in each of the above-mentioned exemplary embodiments, the description has been given, assuming that the traffic optimization apparatus  30  ( 30   a ) acquires, from the PCRF  7 , the communication policy to be applied to the tethering traffic. It may be, however, so configured that the communication policy is acquired from a component other than the PCRF  7 . It may be so configured, for example, that the communication policy information is held in the traffic optimization apparatus  30  ( 30   a ) itself or a different apparatus and a communication policy configured to automatically reduce a tethering traffic may be set in a time zone in which the network  100  readily becomes congested. Naturally, a configuration where a network manager rewrites at any time the communication policy information can be employed. 
     In the above-mentioned exemplary embodiment, the description has been given by pointing out the example of each of the “high throughput” to the low “throughput”, as process content to be applied as each communication policy. However, different process content may be naturally defined. A communication policy of applying to a tethering traffic a compression rate which is higher than that for any other traffic, for example, may be set. Alternatively, a process of dropping a packet belonging to a specific tethering traffic, restricting a connection destination site, or the like, for example, may be performed according to the charging condition of a user or the like. 
     Finally, preferred modes of the present invention will be summarized. 
     [First Mode] 
     (See the traffic optimization apparatus according to the above-mentioned first aspect). 
     [Second Mode] 
     In the above-mentioned traffic optimization apparatus, a configuration may also be employed in which the tethering detection part determines the number of the one or more other devices that are connected via the communication terminal, based on a TTL value variation in an IP packet header and a User-Agent value in an HTTP message header, identifies the tethering traffic using the number of the one or more other devices that is equal to or more than a predetermined number, and sets the tethering traffic as a control target. 
     [Third Mode] 
     In the above-mentioned traffic optimization apparatus, a configuration may also be employed in which the tethering detection part holds the TTL value variation in the IP packet header and the User-Agent value in the HTTP message header for a predetermined period and determines the number of the one or more other devices that are connected to the communication terminal, based on the information held for the predetermined period. 
     [Fourth Mode] 
     In the above-mentioned traffic optimization apparatus, the policy selection part may also select the communication policy corresponding to the number of the one or more other devices that are connected to the communication terminal. 
     [Fifth Mode] 
     In the above-mentioned traffic optimization apparatus, a configuration may be employed in which the tethering detection part holds an originating IP address in the IP packet header and a result of the determination for a predetermined period, and determines a traffic type, based on the information held for the predetermined period. 
     [Sixth Mode] 
     In the above-mentioned traffic optimization apparatus, as the communication policy, preferably, process content of restricting a transfer speed of the tethering traffic to a transfer speed that is lower than a transfer speed of any other traffic is set. 
     [Seventh Mode] 
     In the above-mentioned traffic optimization apparatus, as the communication policy, preferably, process content of applying, to the tethering traffic, a compression rate that is higher than a compression rate of the any other traffic is set. 
     [Eighth Mode] 
     (See the communication system according to the above-mentioned second aspect). 
     [Ninth Mode] 
     (See the traffic optimization method according to the above-mentioned third aspect). 
     [Tenth Mode] 
     (See the program according to the above-mentioned fourth aspect). 
     The above-mentioned eighth to tenth modes can be developed into the second to seventh modes, like the first mode. 
     Each disclosure of the above-listed Patent Literatures is incorporated herein by reference. Modification and adjustment of each exemplary embodiment and each example are possible within the scope of the overall disclosure (including claims) of the present invention and based on the technical concept of the present invention. Various combinations and selections (including partial deletion) of various disclosed elements (including each element in each claim, each element in each exemplary embodiment and each example, each element in each drawing, and the like) are possible within the scope of the disclosure of the present invention. That is, the present invention naturally includes various variations and modifications that could be made by those skilled in the art according to the overall disclosure including the claims and the technical concept. With respect to a numerical value range described herein in particular, an arbitrary numerical value and a small range included in the numerical value range should be construed to be specifically described even unless otherwise explicitly described. 
     REFERENCE SIGNS LIST 
     
         
           1  tethering using device 
           1   a  tablet-type terminal 
           1   b  PC (personal computer) 
           2  smartphone 
           2   a  communication terminal 
           4  service provision apparatus 
           5  router 
           6  GGSN/P-GW 
           7  PCRF 
           30 ,  30   a  traffic optimization apparatus 
           31 ,  31   a  tethering detection part 
           32  policy selection part 
           33  traffic optimization part 
           100  network 
           200  mobile network 
           311  determination result storage part