Title of Invention: CONTROL DEVICE, COMMUNICATION SYSTEM, COMMUNICATION 5 CONTROL METHOD, AND NON-TRANSITORY COMPUTER READABLE MEDIUM STORING PROGRAM Technical Field [0001] 10 The present invention relates to a control device, a communication system, a communication control method, and a non-transitory computer readable medium storing a program. Background Art [0002] 15 As the information technology progresses in recent years, a demand for data communication traffic is increasing. Under this circumstance, broadband communication in a network and reduction in operation cost have been required. [0003] 20 In wireless systems utilizing a frequency of a millimeter wave band or the like, broadband transmission can be performed. A network constituted of radio links such as an FWA (Fixed broadband Wireless Access) employing these wireless systems is utilized in a mobile phone network or the like. 25 [0004] Communication quality of a radio link varies depending on an SNR (Signal to Noise Ratio) of a receiving signal. In order to implement further broadband communication using a radio link, an adaptive modulation technique has been paid attention to. The adaptive 2 modulation technique is a technique, in which a modulation method having a highest transmission efficiency is adaptively obtained from a radio condition of a radio link for using the modulation method. Use of the adaptive modulation technique makes it possible to perform optimum 5 wireless communication depending on the radio environment. Enhancement of frequency efficiency can be expected by performing optimum wireless communication depending on the radio environment. Citation List Patent Literature 10 [0005] PTL 1: Japanese Laid-open Patent Publication No. 2012-65135 Summary of Invention Technical Problem [0006] 15 In a radio link having an adaptive modulation function, the transmission rate changes by an external factor such as the weather. When band control is not performed when the transmission rate is lowered in a radio link, a band that is consumed by a piece of traffic lost in the radio link, which turns out to be a bottle neck, may be wasted. 20 [0007] PTL 1 discloses a transport control system, in which the amount of traffic flowing through a network is monitored, and a difference in traffic amount between the start node and the end node is measured to find a piece of traffic wasted in the network. This technique, however, requires 25 constant monitoring of the traffic amount, and takes time to specify the radio link, which turns out to be a bottle neck. [0008] In other words, in the aforementioned technique, when the transmission rate of a radio link changes, it is not possible to efficiently 3 perform band control. [0009] In view of the above-described circumstances, the present invention has been made, and a main object of the invention is to provide a control 5 device, a communication system, a communication control method, and a non-transitory computer-readable medium storing a program, which enable to efficiently perform band control when the transmission rate of a radio link changes. Solution to Problem 10 [0010] A control device according to an aspect of the present invention is a control device for controlling a band of each piece of traffic between communication devices having an adaptive modulation function, including: a throughput calculation means which receives information relating 15 to a transmission rate change, and calculates a predicted end-to-end throughput of each piece of traffic, on the basis of the information and a table which includes a degree of priority and a band index of each piece of traffic; an adjustment means which calculates a missing band of each piece 20 of traffic and/or an unused band of a radio link connecting between the communication devices, when band setting is performed on the basis of the predicted throughput, and decides band distribution with respect to each piece of traffic, on the basis of the table and the missing band and/or the unused band; and 25 a setting transmission means which transmits the band distribution decided by the adjustment means to the communication devices. [0011] A communication system according to another aspect of the present invention includes a plurality of communication devices having an 4 adaptive modulation function, and a control device which controls a band of each piece of traffic between the plurality of communication devices, wherein each of the plurality of communication devices executes the 5 adaptive modulation function, and transmits a transmission rate change to the control device, and the control device includes: a throughput calculation means which receives information relating to a transmission rate change, and calculates a predicted 10 end-to-end throughput of each piece of traffic, on the basis of the information and a table which includes a degree of priority and a band index of each piece of traffic; an adjustment means which calculates a missing band of each piece of traffic and/or an unused band of a radio link connecting 15 between the communication devices, when band setting is performed on the basis of the predicted throughput, and decides band distribution with respect to each piece of traffic, on the basis of the table and the missing band and/or the unused band; and a setting transmission means which transmits the band 20 distribution decided by the adjustment unit to the plurality of communication devices. [0012] A communication control method according to yet another aspect of the present invention is a communication control method for setting a band 25 of each piece of traffic between communication devices having an adaptive modulation function, including: receiving information relating to a transmission rate change, and calculating a predicted end-to-end throughput of each piece of traffic, on the basis of the information and a table which includes a degree of priority 5 and a band index of each piece of traffic; and calculating a missing band of each piece of traffic and/or an unused band of a radio link connecting between the communication devices, when band setting is performed on the basis of the predicted throughput, and 5 deciding band distribution with respect to each piece of traffic, on the basis of the table and the missing band and/or the unused band. [0013] A non-transitory computer-readable medium storing a program according to still another aspect of the present invention is a non-transitory 10 computer-readable medium storing a program which causes a computer to calculate a band of each piece of traffic between communication devices having an adaptive modulation function, the program causing the computer to execute: a throughput calculating step of receiving information relating to a 15 transmission rate change, and calculating a predicted end-to-end throughput of each piece of traffic, on the basis of the information and a table which includes a degree of priority and a band index of each piece of traffic; and an adjusting step of calculating a missing band of each piece of 20 traffic and/or an unused band of a radio link connecting between the communication devices, when band setting is performed on the basis of the predicted throughput, and deciding band distribution with respect to each piece of traffic, on the basis of the table and the missing band and/or the unused band. 25 Advantageous Effects of Invention [0014] According to the invention, it is possible to provide a control device, a communication system, a communication control method, and a non-transitory computer-readable medium storing a program, which enable 6 to efficiently control band control when the transmission rate of a radio link changes. Brief Description of Drawings [0015] 5 Fig. 1 is a block diagram illustrating a configuration of a wireless system in a first exemplary embodiment; Fig. 2 is a diagram illustrating a relationship between a modulation method of a radio link and a transmission rate in the first exemplary embodiment; 10 Fig. 3 is a diagram illustrating an example of traffic to be handled in the wireless system in the first exemplary embodiment; Fig. 4 is a block diagram illustrating a configuration of a path control device 101 in the first exemplary embodiment; Fig. 5 is a flowchart illustrating a flow of a process to be carried 15 out by the path control device 101 in the first exemplary embodiment; Fig. 6A is a conceptual diagram illustrating a communication state in the first exemplary embodiment; Fig. 6B is a diagram illustrating a band of each piece of traffic in the first exemplary embodiment; 20 Fig. 7 A is a conceptual diagram illustrating a communication state in the first exemplary embodiment; Fig. 7B is a diagram illustrating a band of each piece of traffic in the first exemplary embodiment; Fig. 8A is a conceptual diagram illustrating a communication state 25 in the first exemplary embodiment; and Fig. 8B is a diagram illustrating a band of each piece of traffic in the first exemplary embodiment. Description of Embodiments [0016] 7