Multicast delivery destination designation procedure, sending station and receiving station

Abstract

Multicast delivery destination designation method for designating a delivery destination between a transmitting station (11) performing a multicast transmission via a satellite (2) and a plurality of receiving stations (12), wherein the multicast delivery destination designation method comprises: - a delivery destination designation step for sending delivery destination designation information from the receiving station (12) to the sending station (11), wherein the delivery destination designation information refers to a multicast address to which a delivery per multicast address is requested from a communication terminal (4) connected to the receiving station (12); - a delivery destination table generation step for generating, by the sending station (11), a multicast delivery destination table in which a multicast address to which delivery is requested by the communication terminal (4) is assigned to the communication terminal (4), from the delivery destination designation information received by the plurality of receiving stations (12); and - a delivery destination referencing step to reference the multicast delivery destination table when the transmitting station (11) performs the multicast transmission via the satellite (2).

Description

TECHNICAL AREA

[0001] The present invention relates to a method for designating the delivery destination of multicast transmissions, a transmitting station and a receiving station for multicast transmissions. STATE OF THE ART

[0002] Traditionally, a communication system optimizes communication bands by dividing the destinations of a notification into small groups to reduce the load on multicast communication (e.g., see PTL 1). In typical multicast communication handled over a general LAN, the destinations of the notification can be dynamically changed using protocols such as IGMP (Internet Group Management Protocol) and MLD (Multicast Listener Discovery) by dividing the destinations into small groups.

[0003] This also applies to delivery destination control, which exhibits similar flexibility and is implemented in multicast communications over satellite links (communication links) of a satellite communication system. Furthermore, in some multicast communications, instead of a station communication device (a network device at a receiving station, such as a switching node) connected to a network (communication link), unconditionally delivering multicast data (multicast packets) to a communication terminal connected to the station communication device (the receiving station), the station communication device (the network device at the receiving station, such as a switching node) delivers a multicast packet to a specific communication terminal (e.g., see PTL 2 or 3).

[0004] Examples of satellite communication systems include the so-called DAMA system (Demand Allocation Multiple Access) (e.g., see PTL 4). In the DAMA satellite communication system, a central control station allocates lines from the ground station to several ground stations (either transmitting or receiving), and the ground stations conduct data communication (IP communication) via satellite links. With DAMA, connections are allocated on demand and can be released for reassignment after use. Thus, DAMA ensures continuous communication. Because of this characteristic, the DAMA satellite communication system is typically independent of fixed-line connections, such as mobile phone connections, even in emergencies or disasters, and is therefore frequently used for disaster relief applications due to its suitability for emergency communication.

[0005] PTL 5 discloses a system and method for supporting Internet Protocol (IP) multicast in mesh TDMA satellite networks using a centralized route server architecture that conserves link bandwidth and minimizes latency. Individual satellite terminals forward multicast IP traffic to destination terminals based on information provided by the route server. Multicast routing protocols only need to be supported on the route server, thus minimizing the CPU and memory resources required on the end devices. Channel capacity for multicast traffic can be allocated statically or dynamically, fully utilizing the broadcast capabilities of the medium.

[0006] PTL 6 discloses devices and methods for managing a global forwarding table in a distributed switch. A particular method may include managing a global forwarding table in a distributed switch. The distributed switch may contain a plurality of switch forwarding units. The method may start a timer for an entry in the global forwarding table, and the entry may contain a multicast destination address and corresponding multicast membership information. The method may also, in response to the expiration of the entry's timer, check at least one hit status to determine whether at least one switch forwarding unit of the plurality of switch forwarding units has forwarded multicast data to the corresponding multicast membership information of the entry's multicast destination address.The procedure can also determine whether the entry is a cast-out candidate, based on the hit status. DOCUMENTS ON THE STATE OF TECHNOLOGY PATENT LITERATURE PTL 1: Published Japanese patent application JP 2000-324 155 A PTL 2: Published Japanese patent application JP 2007-274 456 A PTL 3: Published Japanese patent application JP 2009-55 244 A PTL 4: Published Japanese patent application JP 2007-208 630 A PTL 5: US 6 894 990 B1 PLT 6: US 2013 / 0 182 707 A1 BRIEF DESCRIPTION OF THE INVENTIONAL PROBLEM

[0007] One problem with a system that performs multicast data communication over satellite communication is that the system must reduce the transmission of unnecessary multicast data (multicast packets) to a receiving station via a satellite link. This is because if the speed of the satellite link is low (e.g., spread spectrum), the transmission of unnecessary multicast data leads to a bottleneck of the connection.

[0008] In the conventional DAMA satellite communication system, multicast data is sent to all receiving stations connected to the transmitting station via satellite links, and unnecessary multicast data is discarded at each receiving station. Therefore, if the bandwidth for satellite links is narrow, as described above, and a packet is even sent to receiving stations that do not need to receive multicast data, the bandwidth of the satellite link can be limited, hindering communication options other than multicasting.

[0009] The present invention serves to solve the problems described above and relates to a method for designating the delivery destination for multicast transmission, a transmitting station and a receiving station that achieve a reduced transmission of unnecessary multicast packets on communication links via satellite. SOLUTION TO THE PROBLEM

[0010] The problems described above are solved by the method according to claim 1, the transmitting station according to claim 7, and the receiving station according to claim 11. ADVANTAGEOUS EFFECTS OF THE INVENTION

[0011] As described above, according to the present invention, a multicast delivery destination designation method, a sending station and a receiving station can be obtained which, by assigning a multicast address to which delivery is requested and a communication terminal for each communication terminal, achieve a reduced transmission of unnecessary multicast packets. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a functional block diagram of a communication system according to embodiment 1 of the present invention. Fig. Figure 2 is a functional block diagram of the communication system according to embodiment 1 of the present invention (a variant). Fig. Figure 3 is a functional block diagram of the communication system according to embodiment 1 of the present invention (after assignment of the connections). Fig. Figure 4 is a functional block diagram of the communication system according to embodiment 1 of the present invention (after assignment of the connections). Fig. Figure 5 is an exemplary sequence diagram of the communication system according to embodiment 1 of the present invention. Fig. Figure 6 is an exemplary sequence diagram of a communication system according to embodiment 2 of the present invention. DESCRIPTION OF THE EXECUTION FORMS Execution form 1

[0012] In the following, a communication system, a communication method, a multicast delivery destination designation method, a transmitting station and a receiving station according to embodiment 1 of the present invention are described with reference to the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. 5. In the figures, the same reference numerals are used to refer to identical or similar components, and their detailed descriptions are omitted. The communication system according to embodiment 1 is suitable for a DAMA satellite communication system.

[0013] A description is given with reference to a DAMA satellite communication system. The communication system according to embodiment 1 has several ground stations 1, including a transmitting station 11 and a receiving station 12, a satellite 2 (satellite station 2), and a control station 3. Communication terminals 4 (multicast transmitting terminal 4a, multicast receiving terminal 4b), each connected to the transmitting station 11 and the receiving station 12, can be included in the communication system according to embodiment 1.

[0014] According to the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. At control station 3, a DAMA control device 31 receives a request for the allocation of connections of the satellite communication system from ground station 1 via a control channel modem 32 and satellite 2 via a control channel 33. The DAMA control device 31 notifies ground station 1 via control channel 33 of a communication link 5 assigned to ground station 1. The ground stations 1, each assigned a connection, conduct multicast communications with each other.

[0015] Transmitting station 11 is one of the ground stations 1 and performs multicast transmission to several receiving stations 12 via satellite 2. Since a request is made for the allocation of a communication link via control channel 33, control channel 33 is also referred to as CSC channel 33. CSC stands for Common Signaling Channel.

[0016] According to the Fig. 1, Fig. 2, Fig. 3, Fig. 4 to Fig. 5. The transmitting station 11 has a transmitting and receiving unit 13, a delivery destination table storage unit 14, a communication modem 15, a satellite gateway 16, and a ground station control unit 17 (located on the transmitting station 11 side). The ground station control unit 17 controls the transmitting and receiving unit 13 and the delivery destination table storage unit 14.

[0017] The ground station control unit 17 controls the operation of ground station 1, which serves as ground station 1 (and requests the assignment of a connection to the satellite communication system), and the operation of ground station 1, which serves as transmitting station 11. The receiving station 12 has a receiving station transmit and receive unit 18, a storage unit 19, a communication modem 20, a satellite gateway 21, and a ground station control unit 22 (on the receiving station 12 side).

[0018] The ground station control unit 22 controls the transmit and receive unit 18 of the receiving station and the storage unit 19 for delivery destination designation information. The ground station control unit 22 controls the operation of ground station 1, which serves as ground station 1 (and requests the assignment of a connection from the satellite communication system), and the operation of ground station 1, which serves as receiving station 12.

[0019] The in Fig. The functional block diagram of the communication system shown in 2, according to embodiment 1, is a variant of the one shown in Fig. 1 function block shown. Fig. Figure 2 illustrates a case in which the control station 3 has the functionality of the ground station 1 (transmitting station 11). In other words, in this case, the control station control unit 17b in the transmitting station 11 has the functionality of the control station 3 in addition to the functionality of the ground station control unit 17.

[0020] While the case in which the control station 3 has the functionality of the ground station 1 (receiving station 12) is not shown in the figure, in this case a control station control unit 18b in the receiving station 12 has the functionality of the control station 3 in addition to the functionality of the ground station control unit 17.

[0021] The transmitting and receiving unit 13 of the transmitting station receives the delivery destination designation information 191 from several receiving stations. The delivery destination designation information 191 refers to a multicast address to which a delivery per multicast address is requested by a communication terminal 4 (multicast receiving terminal 4b) connected to the receiving station 12. Based on the delivery destination designation information received from several receiving stations 12, the storage unit 14 generates and stores a multicast delivery destination table 141 in which a multicast address to which a delivery is requested by a communication terminal 4 (multicast receiving device 4b) connected to the receiving station 12 is assigned to the communication terminal 4 (multicast receiving device 4b).

[0022] The transmit and receive unit 13 of the transmitting station is connected to a communication terminal 4 (multicast transmit terminal 4a). The transmit and receive unit 13 of the transmitting station has the communication modem 15 (modem 15) and the satellite GW 16 (satellite gateway 16). The communication modem 15 (modem 15) is connected to an antenna contained in the transmitting station 11 and sends and receives data (delivery destination information 191, multicast packets) via the communication link 5 (satellite link 5).

[0023] Satellite GW 16 acts as a gateway to communication link 5 (satellite link 5). The transmit and receive unit 13 of the transmitting station refers to the multicast delivery destination table 141 and sends a multicast packet from communication terminal 4 (multicast transmitting terminal 4a) to the receiving station 12, which is a delivery destination.

[0024] Receiving station 12 is one of the receiving stations that receive the multicast transmission from transmitting station 11 via satellite 2. The receiving stations are collectively referred to as receiving station 12. There are n receiving stations, including receiving station 121, receiving station 122, ..., receiving station 12n-1, and receiving station 12n, where n is a positive integer. The description is given here with reference to n = 3.

[0025] The receiving station's transmit and receive unit 18 is connected to the communication terminal 4 (multicast receiving terminal 4b). The receiving station's transmit and receive unit 18 includes the communication modem 20 (modem 20) and the satellite gateway 21 (satellite gateway 21). The communication modem 20 (modem 20) is connected to an antenna contained in the receiving station 12 and transmits and receives data (delivery destination information 191, multicast packets) via the communication link 5 (satellite link 5).

[0026] In the Fig. 1, Fig. 2 to Fig. The communication link 5 (satellite link 5), indicated by the dash-dot line, is a link assigned between transmitting station 11 and receiving station 121. The communication link 5 (satellite link 5), indicated by the dot-dot-dash line, is a link assigned between transmitting station 11 and receiving station 122. The communication link 5 (satellite link 5), indicated by the dashed line, is a link assigned between transmitting station 11 and receiving station 123.

[0027] The storage unit 19 stores the delivery destination designation information 191, which refers to a multicast address to which delivery per multicast address is requested by the communication terminal 4 (multicast receiving terminal 4b) which is connected to the local receiving station 12. The transmit and receive unit 18 of the receiving station sends the delivery destination designation information 191 to the transmitting station 11, and the receiving station 12 receives the multicast packet sent by the transmitting station 11 on the basis of the mapping (multicast delivery destination table 141) between (i) the multicast address requested for delivery by the communication terminal 4 (multicast receiving device 4b) contained in the local receiving station 12 and other receiving stations (receiving station 121, ... , receiving station 12n), and (ii) the communication terminal 4 (multicast receiving device 4b).

[0028] With reference to Fig. 1 and Fig. Section 2 describes the connection assignment in the communication system according to embodiment 1 (a communication method). The ground station 1 sends a request to the control station 3 for the assignment of a connection via control channel 33. As described above, the control station 3 receives the request for the assignment of a connection of the satellite communication system from the ground station 1 via control channel 33.

[0029] Control station 3 notifies ground station 1 about communication link 5, which is assigned to ground station 1 (link assignment step). Next, with reference to the Fig. 3, Fig. 4 to Fig. 5 the designation of a multicast delivery destination (a multicast delivery destination designation method according to embodiment 1) in the communication system (the communication method) after the assignment of the connection according to embodiment 1 is described.

[0030] The in Fig. 3 and Fig. The transmitting station 11 shown in Figure 4 is connected to the multicast transmitting terminal 4a, which generates and transmits multicast data. The multicast transmitting terminal 4a can be part of the transmitting station 11. Modem 15 is provided for each of the receiving stations 121, 122, and 123, respectively, and sends / receives data to / from satellite 2. Satellite gateway 16 sorts the transmission data into a suitable communication link 5 (satellite link 5). The in Fig. 3 and Fig. 4 Receiving station 12 shown (receiving station 121, receiving station 122, receiving station 123) is connected to the multicast receiving terminal 4b, which receives multicast data.

[0031] The multicast receiving terminal 4b can be part of the receiving station 12. Modem 20 sends / receives data to / from satellite 2. Satellite GW 21 sends the received data to the multicast receiving terminal 4b. In multicast IP communication, where the multicast transmitting terminal 4a uses the communication link 5 (satellite link 5), satellite GW 21 acts as a gateway and sends the data via the transmitting and receiving unit 13 of the transmitting station to the receiving station 12. Fig. Figure 4 illustrates a case in which a multicast packet is delivered (sent) to receiving station 121, receiving station 122, and receiving station 123. The dashed lines in Fig. The four directions shown are flow directions of the multicast packet.

[0032] An example sequence of the multicast delivery destination designation procedure according to embodiment 1 is shown in Fig. 5 shown. In other words, Fig. Figure 5 shows an example sequence for naming a delivery destination between the transmitting station 11, which performs the multicast transmission via satellite 2, and several receiving stations 12. Before entering the example sequence, the receiving station 12 first sends the delivery destination designation information 191 to the transmitting station 11 (step of naming the delivery destination), where the delivery destination designation information 191 refers to a multicast address to which delivery is requested per multicast address by the multicast receiving terminal 4b connected to the receiving station 12.

[0033] Specifically, receiving station 12 outputs delivery destination information 191, which indicates that multicast receiving terminal 4b wishes to receive the message at a specific multicast address. Subsequently, satellite GW 21 in receiving station 12 transmits delivery destination information 191 via modem 20 and satellite link 5 to transmitting station 11. Delivery destination information 191 describes a multicast address at which multicast receiving terminal 4b wishes to receive the message. Delivery destination information 191 is stored in storage unit 19.

[0034] The delivery destination designation step is performed at least after the establishment of the communication link 5 between the transmitting station 11 and several receiving stations 12 via satellite 2. In other words, the transmitting and receiving unit 18 of the receiving station sends the delivery destination designation information at least after the communication link 5 to the transmitting station 11 via satellite 2 has been established.

[0035] Similarly, the transmitting and receiving unit 13 of the transmitting station receives the delivery destination designation information 191 at least after the establishment of the communication link 5 to the receiving station 12 via satellite 2. If the delivery destination designation step is performed during the initial communication after the establishment of the communication link 5, the transmission of unnecessary multicast packets immediately after the establishment of the communication link 5 can be reduced.

[0036] In this case, the transmitting and receiving unit 18 of the receiving station sends the delivery destination designation information 191 during the initial communication after the communication link 5 has been established. Similarly, the transmitting and receiving unit 13 of the transmitting station receives the delivery destination designation information 191 during the initial communication after the communication link 5 has been established.

[0037] In Fig. Figure 5 also shows the multicast delivery destination table 141 when no delivery destination identifier information 191 is present. In other words, even if the delivery destination identifier step is missing (the initial state), a delivery destination referencing step can be performed as described below. From the delivery destination identifier information 191 received by several receiving stations 12, the sending station 11 generates the multicast delivery destination table 141, in which a multicast address to which delivery is requested from the multicast receiving terminal 4b is assigned to the multicast receiving terminal 4b (delivery destination table generation step).

[0038] In particular, when receiving the delivery destination designation information 191 from the receiving station 12, the satellite GW 16, which is contained in the transmitting station 11, reads the multicast address written in the delivery destination designation information 191, and a receiving station 12 that corresponds to this multicast address is registered in the multicast delivery destination table 141.

[0039] Note that the delivery destination designation step can be performed each time the delivery destination designation information 191 is changed. In other words, the transmit and receive unit 18 of the receiving station can send the delivery destination designation information 191 each time the delivery destination designation information 191 is changed.

[0040] The multicast delivery destination table 141 contains, for each multicast receiving terminal 4b, the mapping between a multicast address to which delivery is requested and the receiving station 12 connected to the multicast receiving terminal 4b. The satellite GW 16, contained in the transmitting station 11, manages the multicast delivery destination table 141 and has the function of sending the multicast packet to a modem within the transmitting station 11. Fig. 1 and Fig. Figure 2 illustrates this functionality of the satellite GW 16 separately as Delivery Destination Table Storage Unit 14 (Storage Unit 14).

[0041] In the Fig. In the multicast delivery destination table 141 shown in Figure 5, the correspondence between a multicast address, which is a destination of the multicast packet, and the receiving station 12, which wants to receive the delivery at that multicast address, is written. Initially, no receiving station 12 is specified for a multicast address in the table.<Multicast-Zustellungsbestimmungsorttabelle 1> in Fig. 5 registered.

[0042] When transmitting station 11 performs a multicast transmission via satellite 2, reference is made to the multicast delivery destination table 141 (the delivery destination referencing step). Specifically, when the multicast transmitting terminal 4a sends a multicast packet, satellite GW 16, which is contained in transmitting station 11, reads (refers to) a destination address of the multicast packet. The multicast delivery destination referencing procedure according to embodiment 1 may further include a delivery step.

[0043] The multicast delivery destination designation procedure, which includes the delivery step, can also be called the communication procedure. A connection assignment step can be added to the communication procedure. The delivery step sends the multicast packet to the receiving station 12, which is a delivery destination obtained from the multicast delivery destination table 141, read (referenced) in the delivery destination referencing step.

[0044] In the delivery step, the multicast delivery destination table 141 is searched for an address, and if receiving station 12 (multicast receiving terminal 4b) is registered, a multicast packet is sent to this receiving station 12, but not to any other stations. If no receiving station 12 (multicast receiving terminal 4b) is registered for the address contained in the multicast delivery destination table 141 in the delivery step, satellite GW 16, which is contained in transmitting station 11, discards the multicast packet if no receiving station 12 (multicast receiving terminal 4b) is registered. In other words, the transmitting station's transmit and receive unit 13 refers to the multicast delivery destination table 141 and discards the multicast packet if no delivery destination is found.

[0045] The method for designating the delivery destination for multicast delivery according to embodiment 1 is described with reference to Fig. 5 described in more detail. Fig. Figure 5 illustrates four multicast delivery destination tables 141: < Multicast Delivery Destination Table 1>; < Multicast Delivery Destination Table 2>; < Multicast Delivery Destination Table 3>; and < Multicast Delivery Destination Table 4>.

[0046] Fig. Figure 5 illustrates a case in which a form (pre-registration form) is pre-registered with three assumed multicast addresses (destination multicast addresses), namely AA.BB.CC.DD, EE.FF.GG.HH, and WW.XX.YY.ZZ. The multicast delivery destination table 141 is not limited to these. The multicast delivery destination table 141 need not be in the form of a pre-registration and may initially contain zero entries, and a new multicast address may be registered in the table (multicast delivery destination table 141) (an additional registration form).

[0047] Although no specific information is provided in the additional registration form, the multicast address itself can be registered in the multicast delivery destination table 141 if the delivery destination label information 191 is added. This does not require prior acquisition of the multicast addresses themselves and provides flexibility when adding / removing the receiving station 12 to / from the multicast delivery destination table 141.

[0048] Next, the pre-registration form is described. The delivery destination designation information 191 is then explained in sequence.<Multicast-Zustellungsbestimmungsorttabelle 1> ,<Multicast-Zustellungsbestimmungsorttabelle 2> ,<Multicast-Zustellungsbestimmungsorttabelle 3> and<Multicast-Zustellungsbestimmungsorttabelle 4> Added. The added receiving stations (12) are indicated by underlines. Zero multicast addresses are indicated as (zero).<Multicast-Zustellungsbestimmungsorttabelle 1> This illustrates that no receiving station 12 is registered in the multicast delivery destination table 141, i.e., that no silent participant is present. Therefore, the sending station 11 discards the multicast packet.

[0049] The<Multicast-Zustellungsbestimmungsorttabelle 2> This illustrates that the multicast receiving terminal 4b, which is connected to receiving station 121, is registered as a silent participant for the multicast address AA.BB.CC.DD. Initially, receiving station 121 communicates with sending station 11 and updates the multicast delivery destination table 141 so that the multicast address AA.BB.CC.DD is registered as delivery destination label information 191. This enables the sharing of delivery destination label information between sending station 11 and receiving station 121.

[0050] When a multicast packet needs to be sent to the multicast address AA.BB.CC.DD, sending station 11 references the multicast delivery destination table 141. Since receiving station 121 is registered for the multicast address AA.BB.CC.DD, sending station 11 knows that a silent subscriber is present at receiving station 121 and sends the multicast packet from multicast sending terminal 4a to receiving station 121. Receiving station 121 (multicast receiving terminal 4b) receives this multicast packet.

[0051] The <Multicast Delivery Destination Table 3> shows that the multicast receiving terminal 4b, which is connected to receiving station 122, is additionally registered as a silent participant for the multicast address AA.BB.CC.DD. Initially, receiving station 122 communicates with sending station 11 and updates the multicast delivery destination table 141 so that the multicast address AA.BB.CC.DD is registered as delivery destination identifier information 191. This enables the sharing of delivery destination identifier information between sending station 11 and receiving station 122.

[0052] When a multicast packet needs to be sent to the multicast address AA.BB.CC.DD, sending station 11 references the multicast delivery destination table 141. Since receiving stations 121 and 122 are registered for the multicast address AA.BB.CC.DD, sending station 11 knows that a silent subscriber is present at both stations and sends the multicast packet from multicast sending terminal 4a to both stations. Receiving stations 121 (multicast receiving terminal 4b) and 122 (multicast receiving terminal 4b) then receive this multicast packet.

[0053] The <Multicast Delivery Destination Table 4> shows that the multicast receiving terminal 4b, connected to receiving station 123, is additionally registered as a silent participant for the multicast address EE.FF.GG.HH. Initially, receiving station 123 communicates with sending station 11 and updates the multicast delivery destination table 141, so that the delivery destination identifier information 191 is registered for the multicast address EE.FF.GG.HH. This enables the sharing of delivery destination identifier information between sending station 11 and receiving station 123.

[0054] When a multicast packet needs to be sent to the multicast address EE.FF.GG.HH, the sending station 11 references the multicast delivery destination table 141. Since the receiving station 123 is registered for the multicast address EE.FF.GG.HH, the sending station 11 knows that a silent subscriber is present at the receiving station 123 and sends the multicast packet from the multicast transmit terminal 4a to the receiving station 123.

[0055] Receiving station 123 (multicast receiving terminal 4b) receives this multicast packet.

[0056] Consequently, no unnecessary multicast packet is sent via communication link 5 to receiving station 121 and receiving station 122. If a multicast packet needs to be sent to the multicast address AA.BB.CC.DD, a procedure similar to that described in <Multicast Delivery Destination Table 3> is followed. Consequently, no unnecessary multicast packet is sent via communication link 5 to receiving station 123.

[0057] While the delivery destination naming step can be performed each time the delivery destination name information 191 is changed (including an update) when the receiving station 12 has changed the delivery destination name information 191 (including an update) after the sending station 11 has performed the multicast communication, the delivery destination naming step can proceed as follows.

[0058] If the multicast packet sent by transmitting station 11 does not belong to the multicast address to which delivery is requested per multicast address by multicast receiving station 4b due to a change in the delivery destination label information 191, the receiving station's transmit / receive unit 18 discards the multicast packet. In response to the multicast packet sent by transmitting station 11 being discarded as the trigger, the receiving station's transmit / receive unit 18 can forward the changed delivery destination label information 191 to transmitting station 11.

[0059] As such, the communication system, the communication method, the multicast delivery destination designation method, the transmitting station and the receiving station according to embodiment 1 refer to the satellite communication system that performs the multicast communication, in which multicast data is sent via satellite links 5, while transmitting station 11 and receiving stations 12 of the multicast data are connected via satellite links 5.

[0060] Depending on a multicast data delivery request from receiving station 12, transmitting station 11 can restrict the destination to which the multicast data is sent. The multicast data delivery request from receiving station 12 can be made via satellite link 5 when transmitting station 11 and receiving station 12 are connected, and the destination to which the multicast data is sent can be restricted by transmitting station 11 because the connection between transmitting station 11 and receiving station 12 is established via satellite link 5.

[0061] As such, depending on a transmission request from the receiving station 12, the transmitting station 11 selects the destination to which the transmitting station 11 sends multicast data, thus eliminating the transmission of unnecessary multicast data to the receiving station, thereby reducing the amount of multicast data transmitted to the satellite link 5 and increasing the efficiency of the use of the satellite link. Design 2

[0062] In the following, a communication system, a communication method, a multicast delivery destination designation method, a transmitting station and a receiving station according to embodiment 2 of the present invention are described with reference to Fig. 6. The same reference numerals are used in the figures to refer to identical or similar components, and their detailed descriptions are not omitted. Embodiments 1 and 2 are identical in the following respects.

[0063] The satellite GW 16 (delivery destination table storage unit 14) contained in transmitting station 11 manages the multicast delivery destination table 141 and is responsible for sending a multicast packet to modem 15 within transmitting station 11, depending on the contents of the multicast delivery destination table 141. The multicast delivery destination table 141 records the correspondence between a multicast address, which is the destination of the multicast packet, and the receiving station 12, which wishes to receive the delivery at that multicast address. Initially, no receiving station is registered for a multicast address in the multicast delivery destination table 141.

[0064] The differences between embodiment 2 and embodiment 1 are primarily described. Configurations of embodiment 2, without further description, are common to embodiment 1. The communication system, the communication method, the multicast delivery destination designation method, the transmitting station, and the receiving station according to embodiment 2 receive notification from all receiving stations 12 during the initial communication for the connection between receiving stations 12 and transmitting station 11, indicating whether multicast is activated or deactivated.

[0065] Since receiving station 12 outputs the delivery destination identifier information 191, which indicates that the multicast receiving terminal 4b wishes to receive the delivery at a specific multicast address, the satellite GW 21 contained in receiving station 12 contains the delivery destination identifier information 191. During the initial communication for the connection between receiving station 12 and transmitting station 11 via the satellite link 5, which occurs after the connection is established, receiving station 12 informs transmitting station 11 whether receiving station 12 wishes to receive multicast (multicast is enabled, multicast is disabled) and to which multicast address the delivery that the multicast receiving device wishes to receive is addressed.

[0066] After receiving information that multicast is enabled at receiving station 12 during the initial communication for connecting satellite link 5 to receiving station 12, satellite GW 16, contained in transmitting station 11, reads the multicast address written in the information and registers this receiving station 12 with the multicast delivery destination table 141. If satellite GW 15, contained in transmitting station 11, receives information indicating that multicast is disabled at receiving station 12 during the initial communication for connecting satellite link 5 to receiving station 12, satellite GW 15, contained in transmitting station 11, takes no action.

[0067] Satellite GW 15 also stores information on receiving station 12, where multicast is disabled. In other words, the information indicating that multicast is enabled can be referred to as Delivery Destination Label Information 191. The information indicating that multicast is disabled can be referred to as Null Delivery Destination Label Information 191.

[0068] When the multicast transmit terminal 4a sends a multicast packet, satellite GW 15, contained in transmitting station 11, reads (references) a destination address of the multicast packet and searches the multicast delivery destination table 141 for the address. If receiving station 12 is registered for the address, satellite GW 15, contained in transmitting station 11, sends the multicast packet to that receiving station 12, but not to any other stations. If the receiving station is not registered for the address in the multicast delivery destination table 141, satellite GW 15, contained in transmitting station 11, discards the multicast packet.

[0069] The method for designating the delivery destination of the multicast delivery according to embodiment 2 is described with reference to Fig. 6 described in more detail. Fig. Figure 6 illustrates four multicast delivery destination tables 141: < Multicast Delivery Destination Table 1>; < Multicast Delivery Destination Table 2>; < Multicast Delivery Destination Table 3>; and < Multicast Delivery Destination Table 4>.

[0070] Fig. Figure 6 illustrates a case in which a form (pre-registration form) is pre-registered with three assumed multicast addresses (destination multicast addresses), namely AA.BB.CC.DD, EE.FF.GG.HH, and WW.XX.YY.ZZ. Similar to embodiment 1, the multicast delivery destination table 141 can use the additional registration form, as described in embodiment 1, instead of the pre-registration form. In the additional registration form, the multicast address, as is, is added to the multicast delivery destination table 141 by the information that multicast is enabled (delivery destination label information 191).

[0071] Thus, the additional registration form has features that do not require prior acceptance of a multicast address and do not unnecessarily increase the number of multicast addresses. In particular, one of the features of the additional registration form is that if the information indicating that multicast is disabled at receiving station 12 is received by receiving station 12 later, or during a renewed connection between sending station 11 and receiving station 12, the number of registered multicast addresses is not excessively increased by removing a multicast address that corresponds to the information indicating that multicast is disabled.

[0072] Next, the pre-registration form is described. The delivery destination designation information 191 is added sequentially during the initial communication for connecting satellite link 5 to receiving station 12 to <Multicast Delivery Destination Table 1>, <Multicast Delivery Destination Table 2>, <Multicast Delivery Destination Table 3>, and <Multicast Delivery Destination Table 4>. Added receiving stations 12 are indicated by underlines. Zero multicast addresses are indicated as (zero).

[0073] The <Multicast Delivery Destination Table 1> illustrates that no receiving station 12 is registered in the Multicast Delivery Destination Table 141, i.e., that no silent participant is present. Therefore, the sending station 11 discards the multicast packet.

[0074] The <Multicast Delivery Destination Table 2> shows that the multicast receiving terminal 4b, which is connected to receiving station 121, is registered as a silent participant for the multicast address AA.BB.CC.DD. Initially, receiving station 121 communicates with sending station 11 and updates the multicast delivery destination table 141 so that the information indicating that multicast is enabled at receiving station 121 is registered for the multicast address AA.BB.CC.DD.

[0075] When a multicast packet needs to be sent to the multicast address AA.BB.CC.DD, sending station 11 references the multicast delivery destination table 141. Since receiving station 121 is registered for the multicast address AA.BB.CC.DD, sending station 11 knows that a silent subscriber is present at receiving station 121 (multicast is enabled) and sends the multicast packet from multicast transmit terminal 4a to receiving station 121. Receiving station 121 (multicast receive terminal 4b) receives this multicast packet.

[0076] The <Multicast Delivery Destination Table 3> shows that receiving station 122 has added the information that multicast is disabled at receiving station 122. Receiving station 122 communicates with sending station 11, so the information indicating that multicast is disabled at receiving station 122 is registered. In other words, receiving station 122 is not registered in the Multicast Delivery Destination Table 141. When a multicast packet needs to be sent to the multicast address AA.BB.CC.DD, sending station 11 then refers to the Multicast Delivery Destination Table 141.

[0077] Since receiving station 121 is registered for the multicast address AA.BB.CC.DD, sending station 11 knows that a silent participant is present at receiving station 121 and sends the multicast packet from multicast transmit terminal 4a to receiving station 121. Receiving station 121 (multicast receiving station 4b) receives the multicast packet. Consequently, the multicast packet is not unnecessarily sent to receiving station 122 via communication link 5.

[0078] The <Multicast Destination Table 4> illustrates that the multicast receiving terminal 4b, connected to receiving station 123, is additionally registered as a silent participant for the multicast address AA.BB.CC.DD. Initially, receiving station 123 communicates with sending station 11 and updates the multicast destination table 141 so that the information indicating that multicast is enabled at receiving station 123 is registered for the multicast address AA.BB.CC.DD.

[0079] When a multicast packet needs to be sent to the multicast address AA.BB.CC.DD, sending station 11 references the multicast delivery destination table 141. Since receiving stations 121 and 123 are registered for the multicast address AA.BB.CC.DD, sending station 11 knows that a silent subscriber is present at receiving stations 121 and 123 (multicast is enabled) and sends the multicast packet from multicast sending terminal 4a to receiving stations 121 and 123. Receiving stations 121 (multicast receiving station 4b) and 123 (multicast receiving station 4b) receive this multicast packet. Consequently, no unnecessary multicast packet is sent to receiving station 122 via communication link 5.

[0080] As such, the communication system, the communication method, the multicast delivery destination designation method, the transmitting station, and the receiving station according to embodiments 1 and 2 in the satellite communication system that performs the multicast communication, send a multicast packet only to a receiving station that needs to receive the multicast packet, and the amount of multicast packet transmission to receiving stations that do not need to receive the multicast packet is reduced, thus enabling effective use of the bandwidth of the satellite links. In particular, the transmission of unnecessary multicast packets to the receiving stations is reduced, thus enabling effective use of the bandwidth of the satellite links.

[0081] Since the communication system, the communication method, the multicast delivery destination designation method, the sending station, and the receiving station according to embodiments 1 and 2 do not send a multicast packet to receiving destinations that do not need to receive the multicast packet, the bandwidth of the satellite links can be used effectively. Consequently, there is no need for the method in which the multicast packet is sent to all receiving stations connected to the satellite links and the receiving station discards the multicast packet if it does not need it.

[0082] For example, the number of communication bands for satellite links is often less than the number of links within the ground equipment, and it is less likely that in such a case a multicast packet will be sent to receiving stations that do not need the packet, and the bandwidth of the satellite links is limited. REFERENCE MARK LIST 1 ground station (transmitting station, receiving station) 11 transmitting stations 12 receiving stations 2 satellite (satellite station) 3 Control Station 31 DAMA control unit (DAMA control, DAMA control device) 32 control channel modem 33 Control channel (CSC channel) 4 Communication terminal 4a Multicast transmit terminal 4b Multicast receiving terminal 5 Communication link (satellite link) 121 to 12n receiving station 13 Transmitting and receiving unit of the transmitting station (transmitting and receiving unit, transmitter-receiver of the transmitting station, transmitter-receiver) 14 Delivery Destination Table Storage Unit (Storage Unit, Delivery Destination Table Storage Device, Storage Device) 141 Multicast Delivery Destination Table 15 Communication modem (modem) 16 satellite gateway (satellite GW) 17 Ground station control unit (ground station control, ground station control device) 17b Control station control unit (control station control device) 18 Transmitting and receiving unit of the receiving station (transmitting and receiving unit, transmitter-receiver of the receiving station, transmitter-receiver) 18b Control station control unit (control station control, control station control device) 19 Storage unit for the delivery destination designation information (storage unit, storage device for the delivery destination designation information, storage device) 191 Delivery Destination Designation Information 20 Communication modem (modem) 21 satellite gateway (satellite GW) 22 Ground station control unit (ground station control, ground station control device)

Claims

[1] Multicast delivery destination designation method for designating a delivery destination between a transmitting station (11) performing a multicast transmission via a satellite (2) and a plurality of receiving stations (12), wherein the multicast delivery destination designation method comprises: - a delivery destination designation step for sending delivery destination designation information from the receiving station (12) to the sending station (11), wherein the delivery destination designation information refers to a multicast address to which a delivery per multicast address is requested from a communication terminal (4) connected to the receiving station (12); - a delivery destination table generation step for generating, by the sending station (11), a multicast delivery destination table in which a multicast address to which delivery is requested by the communication terminal (4) is assigned to the communication terminal (4), from the delivery destination designation information received by the plurality of receiving stations (12); and - a delivery destination referencing step to reference the multicast delivery destination table when the transmitting station (11) performs the multicast transmission via the satellite (2). [2] Multicast delivery destination designation method according to claim 1, comprising: a delivery step to send a multicast packet to the receiving station (12), which is a delivery destination obtained from the multicast delivery destination table referenced in the delivery destination referencing step. [3] Multicast delivery destination designation method according to claim 2, wherein the delivery step comprises discarding the multicast packet if no delivery destination is obtained from the multicast delivery destination table referenced in the delivery destination referencing step. [4] Multicast delivery destination designation method according to any one of claims 1 to 3, wherein the delivery destination designation step is carried out between the sending station (11) and the plurality of receiving stations (12) via the satellite (2), at least after the communication links (5) have been established. [5] Multicast delivery destination designation method according to any one of claims 1 to 4, wherein the delivery destination designation step is performed each time the delivery destination designation information is changed. [6] Multicast delivery destination designation method according to claim 4, wherein the delivery destination designation step is performed during a first communication after the communication links (5) have been established. [7] Transmitting station (11) for carrying out a multicast transmission to a plurality of receiving stations (12) via a satellite (2), wherein the transmitting station (11) comprises the following: - a transmitting and receiving unit (13) of the transmitting station which receives delivery destination designation information from the plurality of receiving stations (12), wherein the delivery destination designation information refers to a multicast address to which delivery is requested per multicast address from a communication terminal (4) connected to the receiving station (12);a delivery destination table storage unit (14) which, based on the delivery destination designation information received from the plurality of receiving stations (12), generates and stores a multicast delivery destination table in which a multicast address is assigned to the communication terminal (4), to which delivery is requested by the communication terminal (4), wherein the transmitting and receiving unit (13) of the transmitting station refers to the multicast delivery destination table and sends a multicast packet to the receiving station (12), which is a delivery destination. [8] Transmitting station (11) according to claim 7, wherein the transmitting and receiving unit (13) of the transmitting station discards the multicast packet if the transmitting and receiving unit (13) of the transmitting station refers to the multicast delivery destination table and no delivery destination is available. [9] Transmitting station (11) according to claim 7 or 8, wherein the transmitting and receiving unit (13) of the transmitting station receives the delivery destination designation information, at least after a communication link (5) has been established between the transmitting station (11) and the receiving station (12) via the satellite (2). [10] Transmitting station (11) according to claim 9, wherein the transmitting and receiving unit (13) of the transmitting station receives the delivery destination designation information during an initial communication after the communication link (5) has been established. [11] Receiving station (12), which is one of a plurality of receiving stations (12) that receive multicast transmission from a transmitting station (11) via a satellite (2), wherein the receiving station (12) has the following: a storage unit (19) for delivery destination identifier information, which stores delivery destination identifier information relating to a multicast address to which delivery is requested per multicast address from a communication terminal (4) connected to the receiving station (12); and - a transmit and receive unit (18) of the receiving station which sends the delivery destination designation information to the transmitting station (11) and receives a transmitted multicast packet based on the mapping between the multicast address to which delivery is requested from the communication terminal (4) and the communication terminal (4). [12] Receiving station (12) according to claim 11, wherein the transmitting and receiving unit (18) of the receiving station sends the delivery destination designation information, at least after a communication link (5) has been established between the receiving station and the transmitting station (11) via the satellite (2). [13] Receiving station (12) according to claim 11 or 12, wherein the transmitting and receiving unit (18) of the receiving station transmits the delivery destination designation information each time the delivery destination designation information is changed. [14] Receiving station (12) according to claim 12, wherein the transmitting and receiving unit (18) of the receiving station sends the delivery destination designation information during an initial communication after the communication link (5) has been established. [15] Receiving station (12) according to claim 11 or 12, wherein if the multicast packet sent by the sending station (11) does not belong to the multicast address to which delivery per multicast address is requested by the communication terminal (4) due to a change in the delivery destination designation information, the transmitting and receiving unit (18) of the receiving station discards the multicast packet. [16] Receiving station (12) according to claim 15, wherein, in response to the rejection of the multicast packet sent by the transmitting station (11), as a trigger, the transmitting and receiving unit (18) of the receiving station sends the modified delivery destination designation information to the receiving station (12).

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