[0001]The technology disclosed herein relates to communication apparatuses and communication methods by which to perform communication operations in conformity with Wi-Fi peer-to-peer (P2P) specification. BACKGROUND ART [0002] Various types of information terminals such as smartphones, cell phones, and tablets have recently come standard with a communication function conforming to wireless local area network (LAN) standards, typified by Institute of Electrical and Electronic Engineers (IEEE) 802.11. The wireless LAN may be, for example, Wireless Fidelity (Wi-Fi) , Wi-Fi P2P (hereinafter, also called "Wi-Fi Direct") , or Wi-Fi CERTIFIED Miracast (for example, refer to Patent Document 1) . The information terminals with a Wi-Fi P2P function can perform printing, information sharing and synchronization, image display, and others in simple and easy operations. CITATION LIST PATENT DOCUMENT [0003] Patent Document 1: Japanese Patent Application Laid-Open No. 2016-28465 SUMMARY OF THE INVENTION PROBLEMS TO BE SOLVED BY THE INVENTION [0004] An object of the technology disclosed herein is to provide an excellent communication apparatus and communication method by which to perform favorable communication operations in conformity with the Wi-Fi P2P specification. SOLUTIONS TO PROBLEMS [0005] The technology disclosed herein is devised in view of the foregoing issue. A first aspect of the technology is a communication apparatus that supports services using Wi-Fi P2P or basic service set (BSS) connection. When either a service advertiser function or a service seeker function is to be activated, the communication apparatus activates both the service advertiser function and the service seeker function. [0006] According to a second aspect of the technology disclosed herein, the communication apparatus according to the first aspect is configured to activate the service seeker function with receipt of a seek service method by an application service platform (ASP) from a service layer in the communication apparatus as a trigger, and activate the service advertiser function as well when the service advertiser function is deactivated. [0007] In addition, a third aspect of the technology disclosed herein is a communication apparatus that supports services using Wi-Fi P2P or BSS connection. When activating only a service advertiser function, the communication apparatus starts to activate a service seeker function with receipt of a request or a query specifying a supportable service as a trigger. [0008] According to a fourth aspect of the technology disclosed herein, the communication apparatus according to the third aspect is configured to, when activating only the service advertiser function, activate the service seeker function to transmit a request or a query specifying a supportable service to another communication apparatus with receipt of a request including a hash value matching a name of a supportable service or a query including a character string indicating a name of a supportable service as a trigger. [0009] In addition, a fifth aspect of the technology disclosed herein is a communication apparatus that supports services using Wi-Fi P2P or BSS connection. When activating only a service advertiser function in a situation without a limitation on usable channels, the communication apparatus starts to activate a service seeker function to transmit a request or a query specifying a supportable service on all supportable channels.with no receipt of a request or a query specifying a supportable service on a social channel within a predetermined period of time as a trigger. [0010] According to a sixth aspect of the technology disclosed herein, the communication apparatus according to the fifth aspect is configured to deactivate the service seeker function with no receipt of a response to the request or the query transmitted by using the service seeker function within a second predetermined period of time as a trigger. [0011] In addition, a seventh aspect of the technology disclosed herein is a communication apparatus that supports services using Wi-Fi P2P or BSS connection. When activating both a service seeker function and a service advertiser function in a situation without a limitation on usable channels, the communication apparatus transmits a request or a query specifying a supportable service on all supportable channels with no receipt of a response to a request or a query specifying a supportable service transmitted by itself on a social channel within a predetermined period of time or with no receipt of a request or a query specifying a supportable service on the social channel within a predetermined period of time as a trigger. [0012] In addition, an eighth aspect of the technology disclosed herein is a communication apparatus that supports services using Wi-Fi P2P or BSS connection. When activating both a service seeker function and a service advertiser function in a situation without a limitation on usable channels, the communication apparatus transmits by itself a request or a query sp.eciXying a supportable service and waits for receipt of a response to the request or the query transmitted by itself or a request or a query specifying a supportable service on a social channel, and then transmits a request or a query specifying a supportable service on all supportable channels. [0013} According to a ninth aspect of the technology disclosed herein, the communication apparatus according to the eighth aspect is configured to, after asking a user to confirm 5 SP367878WO00 transmission of a request or a query on channels other than the social channel or after a lapse of a predetermined period of time/ transmit a request or a query on all the supportable channels. 5 [0014] In addition, a tenth aspect of the technology disclosed herein is a communication apparatus that supports services using Wi-Fi P2P or BSS connection. When activating only a service advertiser function in a situation where a usable 10 channel is limited to an operating channel, the communication apparatus starts to activate a service seeker function to transmit a request or a query specifying a supportable service on the operating channel with receipt of a request or a query specifying a supportable service on the operation channel as 15 a trigger. [0015] In addition, an eleventh aspect of the technology disclosed herein is a communication apparatus that supports services using Wi-Fi P2P. When activating both a service 20 seeker function and a service advertiser function in a situation where a usable channel is limited to an operating channel, the communication apparatus transmits a probe request frame and.- -[0061] 25 At a transmission time, the amplifier unit 415 amplifies the analog signal input from the wireless interface unit 414 to predetermined power, and sends the same to the antenna 416. In addition, at a reception time, the amplifier unit 415 performs low-noise amplification of the signal input from the 30 antenna 416 to predetermined power, and outputs the same to the wireless interface unit 414. At least either the 21 SP367878WO00 transmission-time function or the reception-time function of the amplifier unit 415 may be included in the wireless interface unit 414. [0062] 5 The power supply unit 404 includes a battery power source or a stationary power source (commercial power source or the like) that supplies power to the components of the communication apparatus 400. [0063] 10 Subsequently, problems with conventional P2Ps device discovery will be described. [0064] In WFA-prescribed P2Ps, the roles of service seeker and service advertiser are defined in device discovery and service 15 discovery, (as described above). The service seeker can display a UI of a list of discovered partner devices, and attempts connection to the device selected by the user through the UI of the service seeker. However, the service advertiser only returns information regarding services supported by 20 itself but cannot generate a device list screen, and thus the user cannot select the device via the UI of the service advertiser. [0065] The foregoing prescription is applicable without 25 problem to a service that is favorably functional with a combination of one device serving as a seeker and the other as an advertiser. For example, in a print service, a personal computer (PC) as a print server is a seeker and a printer is an advertiser. The print server as a seeker attempts to 30 discover printers and connect to the printer selected by the user. In addition, the printer as an advertiser only needs 22 SP367878WO00 to return information regarding the print service supported by itself to the print server and does not need to present a device list to the user or attempt connection to the selected print server. 5 [0066] However, in a case of a display service and the like that allows screen sharing between devices, it is necessary to make a mechanism in which the partners can be selected by each other f romboth the source transmitting screen information 10 and the sink receiving the screen information from the source and displaying the same. For example, in a case of outputting images from a smartphone and displaying the same on a large screen such as a television, it is preferred that the device as destination of image output can be selected from the 15 smartphone and the smartphone as image source can be selected in reverse from the television. Specifically, in a use case of Wi-Fi Display Release 2 (hereinafter, referred to as WFD R2) as a WFA-developed display transmission technology through one-on-one wireless communications, both the devices of source 20 and sink need to support both seeker and advertiser. If the procedure and operating method for supporting both the functions are not properly determined, compatibility problems may occur. [0067] 25 In short, the WFD R2 devices need to be capable of : activating both a service seeker and a service advertiser simultaneously. However, the devices here refer to both source and sink. [0068] 30 The service seeker and the service advertiser are defined in theP2Ps technical specification "Wi-Fi Peer-to-Peer 23 SP367878WO00 Service Technical Specification". In addition, the technical specification is publicly available free of charge . However, the P2Ps technical specification only states that, when the ASP receives a seek service method, the device starts to operate 5 as a service seeker, and when the ASP receives an advertise service method, the device starts to operate as a service advertiser. That is, as of the filing of the subject application, the procedure and operating method for the devices to support both service seeker and service advertiser in device 10 discovery are not clearly defined. [0069] Meanwhile, when a device simply activates both service seeker and service advertiser, the device operates as a service seeker to continuously transmit a probe request until 15 discovering a partner device, which increases power consumption and load on the wireless communication media. To avoid this problem, for example, if a device simply switches between the time for activating the service seeker function and the time for activating the service advertiser function, 20 the device is less likely to be discovered by other P2Ps devices supporting the service or is less likely to discover other P2Ps devices supporting the service. This is contradictory to the..original purpose for activating both service seeker and service advertiser for mutual discovery. Further, if the 25 service seeker function is always activated, at each discovery of a partner device, a list of discovered partner devices and a UI for asking the user to confirm connection are displayed, which may be annoyance to the user. [0070] 30 In addition, the P2Ps specification prescribes only Wi-Fi P2P as a means for connection of the second layer. With 24 SP367878WO00 this prescription, even if a terminal connected to an AP attempts to offer a service through the AP, the service cannot be implemented due to incapability of device discovery and service discovery. Accordingly, some function extension is 5 desired to implement device discovery and service discovery using BSS connection to the AP. [0071] Therefore, there are proposed herein a procedure and operating method for a WFD R2 device to support both seeker 10 and adviser in device discovery v/ith an extension to the P2Ps technical specification. [0072] For reference, to implement the procedure and the operating method described later, the communication apparatus 15 400 illustrated in Fig. 4 can activate service seeker and service advertiser simultaneously in the control unit 402, and controls the starting of the service seeker operation. [0073] It is first assumed that a WFD R2 device activates the 20 service advertiser function by default. As a modification example, when the ASP receives an advertise service method as usual, the device starts to activate the service advertiser function. ■■ --. [0074] 25 Based on the foregoing assumption, the following points (1) to (3) regarding the procedure or operating method for a WFD R2 device will be described. [0075] Point (1) 30 When the ASP in the WFD R2 device receives at least either a seek service method or an advertise service method, the device 25 SP367878WO00 activates the service seeker function. In addition, when the service advertiser is off at that time, the device activates the service advertiser function as well. [0076] 5 In short, when either the service advertiser function or the service seeker function is to be activated, the WFD R2 device activates both the functions. In particular, the device avoids operating only as a service seeker. Accordingly, the device can discover partner devices as a service seeker, 10 and also can be discovered by the partner devices as a service advertiser. [0077] Fig. 5 illustrates a sequence example of operations for setting up a WFD R2 device to activate both the service 15 advertiser function and the service seeker function. [0078] The device B operates as a service seeker with receipt of a seek service method from the service layer by the ASP in the device B as a trigger. The device B transmits a probe 20 request frame to other devices to perform a device discovery process, and the like as described above with reference to Fig. 3, which is not illustrated in the drawing or described here in detail. At that time, if the service advertiser is off in the device B, the ASP issues an advertise service method 25 to itself to allow the device B to operate as a service advertiser as well. [0079] In addition, the device B operates as a service advertiser with receipt of an advertise service method from the service 30 layer by the ASP in the device A as a trigger. The device A waits for receipt of a probe request from another device, 26 SP367878WO00 and the like as described above with reference to Fig. 3, which is not illustrated in the drawing or described here in detail. If the service seeker is off in the device A at that time, the ASP in the device A issues a seek service method to itself 5 to allow the service A to serve as a service seeker as well. [0080] Fig. 6 illustrates in flowchart form, a procedure of operations for setting up a WFD R2 device to activate both the functions of service advertiser and service seeker. 10 [0081] When the ASP receives a seek service method from the service layer in the device (step S601: Yes), the ASP checks if the operation of the service seeker is off in the device (step S602). Then, when the operation of the service seeker 15 is off (step S602: Yes) , the ASP issues a seek service method to itself in the device (step S603), and the device turns on the operation of the service seeker (stepS604) . In thismanner, the device operates as a service seeker. [0082] 20 At that time, the ASP checks if the operation of the service advertiser is off in the device (step S605) . Then, when the operation of the service advertiser is off (step S605: Yes), the ASP issues an advertise service method to itself inthedevice (stepS606), and the device turns on the operation 25 of the service advertiser (step S607). [0083] Point (2) When activating only the service advertiser function on the P2P interface side, the WFD R2 device activates the 30 service seeker function as well immediately upon receipt of a probe request frame including a hash value matching a service 27 SP367878WO00 supportedby itself (forexample, Miracast Sink) . Asaresult, the device can transmit by itself a probe request frame to other devices. [0084] 5 Without starting the service seeker, the WFD R2 device cannot search for a partner device by itself or create a device list to be displayed on the device itself. Accordingly, the device activating only the service advertiser function can activate the service seeker function as well as described above 10 to create a device list to be displayed on the device itself and provide the UI to the user. [0085] Fig. 7 illustrates a sequence example of operations for setting up the WFD R2 device A activating only the service 15 advertiser function on the P2P interface side to activate the service seeker function as well. [0086] The device B starts to activate the service seeker function with receipt of a seek service method from the service 20 layer by the ASP in the device B as a trigger. Then, the device B transmits a probe request frame including a hash value of the name of the service searched for by itself to other devices . [0087] The device A activates only the service advertiser 25 function upon receipt of an advertise service method from the service layer by the ASP in the device A. Here, it is assumed that the hash value of the service name included in the probe request frame received from the device B matches a service supported by the device A. The device A returns a probe 30 response frame to the device B, continues to perform the service discovery process with the device B, and the like as described 28 SP367878WO00 above with reference to Fig. 3, which is not illustrated in the drawing or described here in detail. At that time, the ASP in the device A issues a seek service method to itself to allow the device A to activate the service seeker function 5 as well. [0088] Then, the device A can transmit a probe request frame including a hash value of the name of the service searched for by itself to other devices, receive a probe response frame 10 from a devxce with a matching hash value (assuming as the device B) , and provide a UI of a device list based on the search result to the user. [0089] Fig. 8 illustrates in flowchart form, a procedure of 15 operations for setting up a WFD R2 device activating only the service advertiser function on the P2P interface side to activate the service seeker function as well. [0090] When operating as a service advertiser (stepS801: Yes), 20 the device waits for receipt of a probe request frame from another device (operating as a service seeker) (step S802) . [0091] Then, upon receipt of a probe request frame from another device (step S802: Yes), the device performs hash matching 25 to determine whether a hash value of the service name included in the received probe request frame matches a service supported by the device itself (step S803). [0092] Here, when there is no match between the hash values 30 (step S804: No) , the device can determine that the received probe request frame specifies a service not supported by the 29 SP367878WO00 device itself. In this case, the device returns to step S801 and continues to operate only as a service advertiser. [0093] Meanwhile, when there is a match with the hash value 5 of the service name (step S804 : Yes) , the device can determine that the received probe request frame specifies a service supportable by the device itself. In this case, the ASP in the device issues a seek service method to itself (step S805) to allow the device to activate the service seeker function 10 as well (step S806). [0094] In this manner, the device activating only the service advertiser function activates the service seeker function as well with receipt of a probe request frame with a matching 15 hash value as a trigger. Accordingly, the device can transmit a probe request frame by itself, receive a probe response frame to the probe request frame, generate a device list to be displayed on the device itself, and provide the UI to the user. [0095] 20 There may be a modification example in which similar operations are performed on the basic service set (BSS) connection side. That is, when activating only the service advertiser function on the BSS interface side, the WFDR2 device activates the service seeker function as well immediately upon 25 receipt of a multicast domain name system (DNS) query (mDNS query) including a character string corresponding to a service supportedby itself (forexample, Miracast Sink) . Asaresult, the device can transmit an mDNS query by itself, receive an mDNS response from another device having received the mDNS 30 query including the corresponding character string, and generate a device list to be displayed on the device itself, 30 SP367878WO00 on the basis of the search results of device discovery and service discovery. [0096] Point (3) 5 The WFD R2 device controls operations depending on the presence or absence of limitation on usable channels and the operational state of the service advertiser or the service seeker of the device. [0097] 10 Under IEEE802 .11/ the assigned bandwidth is divided into a plurality of channels. One of the channels is assigned as the social channel for use in service discovery, and the other channels are used in general communication operations. As described above, among these channels, in particular, the 15 channel for use in the connection to the AP on the BSS interface side, the channel operating as a P2P client for use in the connection to a P2P group owner (P2P GO) , or the channel operating as P2P GO by itself will be called operating channel. [0098] 20 The case where there is no limitation on usable channels specifically means the case where the device is not associated with the AP or the P2P GO, is not operating as P2P GO, or is associated.with an access point operating outside the social channel or is a member of the P2P group but can shift to the 25 social channel other than the operating channel in a time-division manner. [0099] Meanwhile, the case where there is a limitation on usable channels specifically means the case where the device is 30 associated with the AP or the P2P GO or the device is operating as P2P GO by itself, and the operating channel is not the social 31 SP367878WO00 channel and cannot shift to the social channel in a time-division manner to transmit or receive data. In this case, the frame transmitting and receiving operations are limited to the operating channel. 5 [0100] (3-1) The WFD R2 device operating only the service advertiser function for the P2P interface in a case without a limitation on usable channels waits only for a predetermined period of time for receipt of a probe request frame including 10 a hash value matching a service supported by itself on the social channel. When receiving no probe request frame, the WFD R2 device activates the service seeker function as well to perform scanning (that is, transmitting a probe request frame, waiting for reception of a probe response frame, and 15 waiting for receipt of a probe request frame) on all the supportable channels. [0101] When a timeout occurs, the WFD R2 device activates the service seeker function as well to start active searching for 20 partner devices on other channels. In addition, the WFD R2 device remains activating the service advertiser function and can be discovered by partner devices on the other channels. In addition,, in a case where the WFD R2 device as a service seeker cannot discover any partner device in a second 25 predetermined period of time, the device may deactivate the service seeker function. [0102] The service advertiser function basically waits for receipt of a probe request frame, performs hash matching upon 30 receipt of a probe request frame, and returns a probe response frame in a case where there is a match. Meanwhile, the service 32 SP367878WO00 seeker function transmits a probe request frame by itself, which leads to increase in power consumption by the transmission power and requires the use of communication media at a transmission time. Therefore, upon occurrence of a 5 timeout after the second predetermined period of time, the service seeker function is deactivated to lower power consumption of the device and save wireless communicationmedia (avoid a traffic jam). [0103] 10 Fig. 9 is a flowchart of a procedure of operations for setting up a WFD R2 device activating only the service advertiser function on the P2P interface side in a situation without a limitation on usable channels to activate the service seeker function as well. 15 [0104] The WFD R2 device activating only the service advertiser function waits for receipt of a probe request frame on the social channel (step S901). [0105] 20 When the device can receive a probe request frame on the social channel (step S901: Yes) before occurrence of a timeout after a predetermined period of time (step S902: No) , the device performs hash matching to determine whether a hash value included in the received probe request frame matches 25 a service supported by the device itself (step S903). [0106] Here, when there is a match between the hash values (step S904: Yes) , the device can determine that the received probe request frame specifies a service supportable by the device 30 itself. In this case, the device returns a probe response frame to the other device (stepS905), and activates the service 33 SP367878WO00 seeker function as well immediately (step S906). [0107] Meanwhile, when the device cannot receive a probe request frame including a hash value matching a service supported by 5 the device itself on the social channel within a predetermined period of time {step S904: No and step S902: Yes), the ASP in the device issues a seek service method to itself to allow the device to activate the service seeker function as well (step S906). Subsequently, the device starts operation of 10 the service seeker function while continuing to operate as a service advertiser. [0108] As a service seeker, the device performs scanning (that is, transmitting a probe request frame and waiting for 15 reception of a probe response frame) on all the supportable channels (step S907). When a timeout occurs, the device activates the service seeker function as well to start active searching for partner devices on other channels . In addition, the device remains activating the service advertiser function 20 and can be discovered by partner devices on the other channels . [0109] The device performs repeatedly the scanning operation on all the channels only for the second predetermined period of time (step S910: No) . In the meantime, the device remains 25 activating the service advertiser function as well and can be discovered by partner devices on the other channels. For reference, in the processing procedure described in Fig. 9, the timeout mechanism for waiting for a predetermined period of time is used as a stop condition, but the use of any other 30 stop condition, such as the maximum number of scanning attempts, would be similar in substance. B9A 34 SP367878WO00 [0110] Then, when the device can receive a probe response frame on any of the channels and discover a desired partner device (step S908: Yes) within the second predetermined period of 5 time (step S910: No) , the device provides, as a search result, aUIof a list of partner devices discovered through the service layer and- the application, to the user (step S909). [0111] Meanwhile, in a case where the device cannot discover 10 any partner device in the second predetermined period of time (step S910: Yes), that is, when a timeout occurs, the device deactivates the service seeker function (step S911). [0112] There may be a modification example in which similar 15 operations are performed on the BSS connection side. That is, the WFD R2 device activating only the service advertiser function for the BSS interface waits for receipt of an mDNS query including a hash value matching a service supported by itself for a predetermined period of time, and when receiving 20 no mDNS query, the device activates the service seeker function to actively search for partner devices by transmitting an mDNS query including a character string corresponding to the service searched for by itself. Inacase where the device still cannot discover any partner device in the second period of time, the 25 device may deactivate the service seeker function. Deactivation of the service seeker function due to the timeout lowers power consumption of the device and saves wireless communication media (avoid a traffic jam). [0113] 30 (3-2) The WFD R2 device activating both the functions of service seeker and service advertiser for the P2P interface 35 SP367878WO00 in a case without a limitation on usable channels transmits a probe request frame on the social channel and waits for receipt of a probe request frame from another device or receipt of a probe response frame to the probe request frame transmitted 5 by the device itself for a predetermined period of time. Then, when the device cannot discover any partner device, the device perf ormsscanning (that is, transmitting a probe request frame, waiting for receipt of a probe response frame, and waiting for receipt of a probe request frame) on all the supportable 10 channels while activating both the service seeker function and the service advertiser function. [0114] In this case, upon occurrence of a timeout, the WFD R2 device starts active search for partner devices on other 15 channels. In addition, the WFD R2 device remains activating the service advertiser function and can be discovered by partner devices on the other channels . In addition, in a case where the WFD R2 device as a service seeker cannot discover any partner device in the second predetermined period of time, 20 the device may deactivate the service seeker function. [0115] Fig. 10 is a flowchart of a procedure of operations for setting.up a WFD R2 device activating both the functions of service seeker and service advertiser on the P2P interface 25 side in a situation without a limitation on usable channels. [0116] The WFD R2 device activating both the functions of service seeker and service advertiser waits for receipt of a probe request frame from another device on the social channel (step 30 S1001)-[0117] 36 SP367878WO00 When the device can receive any probe request frame on the social channel (step S1010: Yes) before occurrence of a timeout after a predetermined period of time (step S1010 : No) , the device performs hash matching to determine whether a hash 5 value included in the received probe request frame matches a service supported by the device itself (step S1002). [0118] Here, when there is a match between the hash values (step S1003: Yes) , the device can determine that the received probe 10 request frame specifies a service supportable by the device itself. In this case, the device returns a probe response frame to the other device (step S1004), and then continues to perform a service discovery process with partner devices. Specifically, the device transmits a probe request frame on 15 the social-channel (step S1005) , and waits for receipt of a probe response frame to the probe request frame transmitted by the device itself (step S1006). [0119] Meanwhile, if the device cannot receive a probe request 20 frame or a probe response frame on the social channel within a predetermined period of time and cannot discover a partner device (step S1010: Yes), the device performs scanning (that is, transmitting-a. probe request frame) on all the supportable channels while activating both the service seeker function 25 and the service advertiser function (step S1007). For reference, the device remains activating the service advertiser function and can be discovered by partner devices on other channels. [0120] 30 Then, when the device receives a probe response frame on the social channel (step S1006: Yes) or receives a probe 37 SP367878WO00 response frame on any other channel and can discover a desired partner device (step S1008: Yes)/ the device provides a UI of a device list as a search result to the user through the service layer and the application (step S1009). 5 [0121] Meanwhile, in a case where the device cannot detect a partner device on any of the channels (step S1008: No), the device returns to step S1001 to repeatedly execute steps similar to the foregoing ones while activating both the 10 functions of service seeker and service advertiser. Alternatively, in a case where the device cannot detect a partner device (step S1008 : No) , the device may provide a search result that no partner device could be discovered to the user through the service layer and the application, and then provide 15 a UI for the userto select the continuance or discontinuance of an attempt to discover a partner device. Then, only in a case where the user selects the continuance, the device may return to step S1001, and in a case where the user does not select the continuance, the device may stop the search for 20 a partner device. To stop the search for a partner device, the device preferably deactivates the service seeker function. For reference, in the processing procedure described in Fig. 10, the timeout .mechanism for waiting for a predetermined period of time is used as a stop condition, but the use of 25 any other stop condition, such as the maximum number of scanning attempts, would be similar in substance. [0122] The common advantage of the points (3-1) and (3-2) is in that, in a case without a limitation on usable channels, 30 the WFD R2 device can discover other devices operating on channels other than the social channel and incapable of 38 SP367878WO00 shifting to another channel (WFD R2 devices and WFD Rl devices) and can be discovered by partner devices in reverse. [0123] (3-3) In a case without a limitation on usable channels, 5 the WFD R2 device activating both the functions of service seeker and service advertiser for the P2P interface transmits a probe request frame on the social channel and waits for receipt of a probe request frame from another device or receipt of a probe response frame to the probe request frame transmitted 10 by the device itself for a predetermined period of time (as in the point (3-2)) . Then/ even if the device can discover a partner device, the device preferably performs scanning on all the supportable channels while activating both the service seeker function and the service advertiser function. This 15 is intended to discover WFD R2 devices and WFD Rl device that might exist on other channels. [0124] However, before starting scanning on all the supportable channels, the device may display a 131 for the user to select 20 permitting or wishing or not the scanning on channels other than the social channel. [0125] Eig.... 11. .illustrates in flowchart form, a procedure of operations for setting up a WFD R2 device activating both the 25 functions of service seeker and service advertiser on the P2P interface side (however, scanning is surely performed on channels other than the social channel) in a situation without a limitation on usable channels. [0126] 30 The WFD R2 device activating both the functions of service seeker and service advertiser transmits a probe request frame 39 SP367878WO00 on the social channel (step S1101), waits for receipt of a probe response frame to the probe request frame transmitted by the device itself (step S1102), and waits for receipt of a probe request frame from another device (step S1103) . 5 [0127] When the devxce can receive a probe request frame on the social channel (step S1103: Yes) before occurrence of a timeout after a predetermined period of time (stepSllll: No), the device performs hash matching to determine whether a hash 10 value included in the received probe request frame matches a service supported by the device itself (step S1104) . [0128] Here, when there is a match between the hash values (step S1105: Yes), the device can determine that the received probe 15 request frame specifies a service supportable by the device itself. In this case, the device returns a probe response frame to the other device (step S1106). [0129] After a lapse of a predetermined period of time, the 20 device provides the result of search for partner devices on the social channel to the user in step S1107. At that time, in a case where the device cannot receive a probe request frame or a probe, response frame or cannot discover a partner device on the social channel (step Sllll: Yes), the device provides 25 the search result that no partner device could be discovered on the social channel to the user. Meanwhile, in a case where the device receives a probe request frame on the social channel (step S1103: Yes), detects a match between the hash values (step S1105: Yes), and returns a probe response frame to the 30 received probe request frame (stepS1106), the device provides the search result that one or more devices could be discovered 40 SP367878WO00 to the user. Further, in step S1107, the device displays a UI for the user to select permitting or wishing or not scanning on channels other than the social channel to check if to perform scanning on channels other than the social channel. 5 [0130] In a case of performing no scanning on channels other than the social channel (step S1108: No), the device deactivates the service seeker function and operates only the service advertiser function, and returns to the probe request 10 frame waiting state. Alternatively, the device may return to step S1101 to repeatedly execute steps similar to the foregoing ones while activating both the functions of service seeker and service advertiser. [0131] 15 In a case of performing scanning on channels other than the social channel (step S1108: Yes), the device performs scanning (that is, transmitting a probe request frame, waiting for receipt of a probe request frame, and waiting for receipt of a probe request frame) on all the supportable channels while 20 activating both the service seeker function and the service advertiser function (step S1109) . For reference, the device remains activating the service advertiser function and can be discovered by partner devices on other channels. [0132] 25 Finally, when the device can receive a probe response frame on the social channel or any other channel and discover a desired partner device (stepS1109: Yes), the device provides a UI of a device list as search result to the user through the service layer and the application (step Si110) . 30 [0133] Meanwhile, in a case where the device cannot detect a 41 SP367878WO00 partner device on any of the channels (step S1109: No), the device returns to step S1101 to repeatedly execute steps similar to the foregoing ones while activating both the functions of service seeker and service advertiser. 5 Alternatively, the device may deactivate the service seeker function and operate only the service advertiser function, and returns to the probe reguest frame waiting state. For reference, in the processing procedure described in Fig. 11, the timeout mechanism for waiting for a predetermined period 10 of time is used as a stop condition, but the use of any other stop condition, such as the maximum number of scanning attempts, would be similar in substance. [0134] (3-4) In a case where there is a restriction on usable 15 frequencies, that is, the frame transmitting and receiving operations are limited to the operating channel, the WFD R2 device activating only the service advertiser function for the P2P interface waits for receipt of a probe reguest frame on the operating channel. The device activates the service 20 seeker function as well immediately upon receipt of a probe request frame including a hash value matching a service supportedby itself (forexample, Miracast Sink) . Asaresult, the device.can transmit a probe request frame on the operating channel to discover partner devices by itself. 25 [0135] Fig. 12 illustrates in a flowchart form, a procedure of operations for setting up a WFD R2 device activating only the service advertiser function on the P2P interface side in a situation with a limitation on usable channels to activate 30 the service seeker function as well. [0136] 42 SP367878WO00 The WFD R2 device activating only the service advertiser function waits for receipt of a probe request frame on the social channel (step S1201) . [0137] 5 When receiving a probe request frame on the social channel (step S1201: Yes), the device performs hash matching to determine whether a hash value included in the received probe request frame matches a service supported by the device itself (step S1203). 10 [0138] When there is no match between the hash values (step S1204: No) , the device returns to step S1201 to continue only the operation of the service advertiser function and wait for receipt of probe request frames from other devices. 15 [0139] Meanwhile/ when there is a match between the hash values (step S1204: Yes) , the device can determine that the received probe request frame specifies a service supportable by the device itself. In this case, the device returns a probe 20 response frame (step S1205). Further, the ASP in the device issues a seek service method to itself to allow the device to activate the service seeker function as well (step S1206) . Subsequently, the device starts the operation of the service seeker function as well while operating as a service advertiser 25 on the operating channel. [0140] (3-5) In a case where there is a restriction on usable frequencies, that is, the frame transmitting and receiving operations are limited to the operating channel, the WFD R2 30 device activating both the functions of service seeker and service advertiser for the P2P interface transmits a probe 43 SP367878WO00 request frame on the operating channel and waits for receipt of a probe request frame from another device or waits for a probe response frame to the probe request frame transmitted by the device itself. 5 [0141] Fig. 13 illustrates in flowchart form, a procedure of operations for- setting up a WFD R2 device activating both the functions of service seeker and service advertiser on the P2P interface side in a situation without a limitation on usable 10 channels. [0142] The WFD R2 device activating both the functions of service seeker and service advertiser first operates as a service seeker to transmit a probe request frame on the operating 15 channel (step S1301). [0143] When receiving a probe response frame to the probe request frame (step S1302: Yes), the device provides a UI of a device list as search result to the user through the service layer 20 and the application (step S1303). [0144] After the provision of the UI of the device list (step S1303) , .when- receiving no probe response frame to the probe request frame (step S1302: No), the device then operates as 25 a service advertiser to wait for receipt of a probe request frame from another device (step S1304). [0145] When receiving no probe request frame (step S1304 : No) , the device returns to step S1301 to repeatedly transmit and 30 receive a probe request frame or probe response frame on the operating channel while activating both the functions of 44 SP367878WO00 service seeker and service advertiser. [0146] Meanwhile, when receiving a probe request frame (step S1304: Yes), the device performs hash matching to determine 5 whether a hash value included in the received probe request frame matches a service supported by the device itself (step S1305). [0147] When there is no match between the hash values (step 10 S1306: No), the device returns to step S1301 to repeatedly transmit and receive a probe request frame or probe response frame on the operating channel while activating both the functions of service seeker and service advertiser. [0148] 15 Meanwhile, when there is a match between the hash values (step S1306: Yes) , the device can determine that the received probe request frame specifies a service supportable by the device itself. In this case, the device continues the operation of the service advertiser function. That is, the 20 device returns a probe response frame to the other device (step SI307). After that, the device returns to step S1301 to repeatedly transmit and receive a probe request frame or probe response frame on the operating channel while activating both the functions of service seeker and service advertiser. 25 [0149] Meanwhile, Fig. 14 summarizes the main features of point (3) . [0150] According to the technology disclosed herein, in a case 30 where a device operates as a service seeker and a service advertiser such that the device can discover other service 45 SP367878WO00 devices compatible with the device itself and can be discovered by the other devices, it is possible to limit the time during which the device operates as a service seeker. This provides an advantage that the device can reduce power consumption and 5 prevent wasteful use of wireless communication media by decreasing the frequency with which to transmit requests or queries specifying a supportable service, without lowering the probability that the device will discover other service-supporting devices or the probability that the device 10 will be discovered by other service-supporting devices as compared to a case where the device always operates as a service seeker. Further, the device can activate the service seeker function in specific states to eliminate the possibility that the user might feel annoyed with the display of UIs of a partner 15 device list and confirmation of connection at each discovery of a partner device. INDUSTRIAL APPLICABILITY [0151] 20 The technology disclosed herein has been described in detail so far with reference to specific embodiments . However, it is self-evident that a person skilled in the art can achieve modifications and replacements of the embodiments without deviating from the substance of the technology disclosed 25 herein. [0152] The technology disclosed herein is favorably applicable to mainly communication apparatuses under the P2Ps specification, but is also similarly applicable to various 30 other communication systems in which the roles of seeker and advertiser are defined in device discovery to make it easy 46 SP367878WO00 to discover desired communication partners. [0153] In short, the technology disclosed herein has been described so far in the form of exemplification, and the 5 description herein should not be interpreted in a limited way. The claims should be considered to determine the substance of the technology disclosed herein. [0154] For reference, the technology disclosed herein can be 10 configured as described below. (1) A communication apparatus supporting services using Wi-Fi P2P or BSS connection, in which, when one of a service advertiser function and a service seeker function is to be activated, the communication apparatus activates both the 15 service advertiser function and the service seeker function. (2) The communication apparatus according to (1) , in which the communication apparatus activates the service seeker function with receipt of a seek service method from a service layer by an ASP in the communication apparatus as a trigger, 20 and activates the service advertiser function as well when the service advertiser function is deactivated. (3) A communication apparatus supporting services using Wi-Fi P2P-ar,BSS connection, in which, when activating only a service advertiser function, the communication apparatus 25 starts to activate a service seeker function with receipt of a request or a query specifying a supportable service as a trigger. (4) The communication apparatus according to (3), in which, when activating only the service advertiser function, 30 the communication apparatus activates the service seeker function to transmit a request or a query specifying a 47 SP367878WO00 supportable service to another communication apparatus with receipt of a request including a hash value matching a name of a supportable service or a query including a character string indicating a name of a supportable service as a trigger. 5 (5) A communication apparatus supporting services using Wi-Fi P2P or BSS connection, in which, when activating only a service advertiser function in a situation without a limitation on usable channels, the communication apparatus starts to activate a service seeker function to transmit a 10 request or a query specifying a supportable service on all supportable channels with no receipt of a request or a query specifying a supportable service on a social channel within a predetermined period of time as a trigger. (6) The communication apparatus according to (5), in 15 which the- -communication apparatus deactivates the service seeker function with no receipt of a response to the request or the query transmitted by using the service seeker function within a second predetermined period of time as a trigger. (7) A communication apparatus supporting services using 20 Wi-Fi P2P or BSS connection, in which, when activating both a service seeker function and a service advertiser function in a situation without a limitation on usable channels, the communication, -apparatus transmits a request or a query specifying a supportable service on all supportable channels 25 with no receipt of a response to a request or a query specifying a supportable service transmitted by itself on a social channel within a predetermined period of time or with no receipt of a request or a query specifying a supportable service on the social channel within a predetermined period of time as a 30 trigger. (8) A communication apparatus supporting services using 48 SP367878WO00 Wi-Fi P2P or BSS connection, in which, when activating both a service seeker function and a service advertiser function in a situation without a limitation on usable channels, the communication apparatus transmits by itself a request or a 5 query specifying a supportable service and waits for receipt of a response to the request or the query transmitted by itself or receipt of a request or a query specifying a supportable service on a social channel, and then transmits a request or a query specifying a supportable service on all supportable 10 channels. (9) The communication apparatus according to claim 8, in which, after asking a user to confirm transmission of a request or a query on channels other than the social channel or after a lapse of a predetermined period of time, the 15 communication apparatus transmits a request or a query on all the supportable channels. (10) A communication apparatus supporting services using Wi-Fi P2P or BSS connection, in which, when activating only a service advertiser function in a situation where a usable 20 channel is limited to an operating channel, the communication apparatus starts to activate a service seeker function to transmit a request or a query specifying a supportable service on the operating channel with receipt of a request or a query specifying a supportable service on the operating channel as 25 a trigger. (11) A communication apparatus supporting services using Wi-Fi P2P, in which, when activating both a service seeker function and a service advertiser function in a situation where a usable channel is limited to an operating channel, the 30 communication apparatus transmxts a probe request frame on the operating channel and waits for receipt of a probe request 49 SP367878WO00 frame from another device or receipt of a probe response frame to the probe request frame transmitted by the device itself on the operating channel. (12) A communication method of a communication apparatus 5 supporting services using Wi-Fi P2P or BSS connection, including the steps of: starting to activate a service seeker function; and starting to activate a service advertiser function as well when the service advertiser function is deactivated. 10 (13) A communication method of a communication apparatus supporting services using Wi-Fi P2P or BSS connection, including the steps of: activating a service advertiser function to wait for receipt of a request or a query specifying a supportable service 15 from another communication apparatus; and starting to activate a service seeker function to transmit a request or a query specifying a supportable service with receipt of a request or a query specifying a supportable service as a trigger. 20 (14) A communication method of a communication apparatus supporting services using Wi-Fi P2P or BSS connection in a situation without a limitation, on usable channels, including the steps, .of J ,. activating a service advertiser function to wait for 25 receipt of a request or a query specif ying a supportable service from another device on a social channel; starting to activate a service seeker function with no receipt of a request or a query specifying a supportable service within a predetermined period of time as a trigger; and 30 transmitting a request or a query specifying a supportable service on all supportable channels. 50 SP367878WO00 (15) A communication method of a communication apparatus supporting services using Wi-Fi P2P or BSS connection in a situation without a limitation on usable channels, including the steps of: 5 activating both a service seeker function and a service advertiser function; waiting for receipt of a response to a request or a query specifying a supportable service transmitted by itself on a social channel; and 10 transmitting a request or a query specifying a supportable service on all supportable channels with no receipt of a response to the request or the query transmitted by itself within a predetermined period of time or with no receipt of a request or a query specifying a supportable service within 15 a predetermined period of time as a trigger. (16) A communication method of a communication apparatus supporting services using Wi-Fi P2P or BSS connection in a situation without a limitation on usable channels, including the steps of: 20 activating both a service seeker function and a service advertiser function; transmitting a request or a query specifying a supportable service on a social channel; waiting for receipt of a response to the request or the 25 query transmitted by itself or a request or a query specifying a supportable service; and transmitting a request or a query specifying a supportable service on all supportable channels. (17) A communication method of a communication apparatus 30 supporting services using Wi-Fi P2P or BSS connection in a situation where a usable channel is limited to an operating 51 SP367878WO00 channel, including the steps of: activating a service advertiser function to wait for receipt of a request or a query specifying a supportable service from another device on the operating channel; 5 starting to activate a service seeker function with receipt of a request or a query specifying a supportable service on the operating channel as a trigger; and transmitting a request or a query specifying a supportable service on the operating channel. 10 (18) A communication method of a communication apparatus supporting services using Wi-Fi P2P in a situation where a usable channel is limited to an operating channel, including the steps of: activating both a service seeker function and a service 15 advertiser function; transmitting a probe request frame on the operating channel; and waiting for receipt of a probe request frame from another device or receipt of a probe response frame to the probe request 20 frame transmitted by the device itself on the operating channel. REFERENCE.SIGNS LIST [0155] 25 400 Communication apparatus 401 Data processing unit 402 Control unit 403 Communication unit 404 Power supply unit 30 411 Modulation and demodulation unit 412 Spatial signal processing unit 413 Channel estimation unit 414 Wireless interface unit 415 Amplifier unit 416 Antenna CLAIMS 1.A communication apparatus supporting services using Wi-Fi peer-to-peer (P2P) orbasicserviceset (BSS) connection, wherein, when one of a service advertiser function and a service seeker function is to be activated, the communication apparatus activates both the service advertiser function and the service seeker function. 2. The communication apparatus according to claim 1, wherein the communication apparatus activates the service seeker function with receipt of a seek service method from a service layer by an application service platform (ASP) in the communication apparatus as a trigger, and activates the . service advertiser function as v/ell when the service advertiser function is deactivated. 3 . A communication method of a communication apparatus supporting services using Wi-Fi P2P or BSS connection, comprising the steps of: starting to activate a service seeker function; and starting to activate a service advertiser function as well when the service advertiser function is deactivated.