Description

APPARATUS AND METHOD FOR ROUTING X-CAST IP

DATAGRAM

Technical Field

[1] The present invention relates to an X-cast (explicit multicast) routing communication of an IP (Internet Protocol) packet data, and in particular, to indicate a destination IP address for routing of an IP packet data. Background Art

[2] A data transmission method in an Internet protocol network includes largely a unicast method and a multicast method. The unicast method indicates an address of a data receiver in an IP header of an IP data packet and allows routers in the network to transmit the IP data packet to the corresponding receiver of the address indicated in the IP header. The multicast method indicates an address of a multicast group in a header of an IP data packet and allows routers in the network to copy and transmit a multicast IP data packet to a plurality of receivers of the multicast group at the same time. Therefore, the unicast method is a one-to-one transmission method, and the multicast method is a one-to-many transmission method.

[3] As mentioned above, the multicast method is a one-to-many transmission method, and thus it is advantageous to provide, for example a movie information, with which a plurality of receivers can share. However, the multicast method allows routers in the network to copy a multicast IP data and route the multicast IP data to another router or receiver, thereby resulting in overload.

[4] And, the multicast method is effective in the case that a multicast group includes a plurality of receivers, but ineffective in the case that a multicast group includes a small number of receivers. That is, the multicast method suffers routers' overload in transmitting the same information to a plurality of receivers simultaneously, and thus uses a network so inefficiently to be applied to a small number of receivers (for example, a multi-party audio conference of an Internet phone, a network game or a multi-party video conference).

[5] An X-cast method has been suggested to solve the disadvantages of the multicast method. The X-cast method allows a sender to designate a small number of receivers simultaneously, to whom the sender intends to transmit an IP data packet. In the X-cast method, an X-cast header is added between an IP header and a transport header in the IP data packet and addresses of the receivers are inserted in the X-cast header. Here, the IP header contains an X-cast address information informing that it is an X-cast method, and routers in the network detect a transmission channel of the IP data packet,

i.e. a next router using the X-cast address information.

[6] The routers at the side of the receivers in the network receive the X-cast IP data packet and route the IP data packet to each receiver by a unicast method using the address information of the receivers in the X-cast header. Therefore, unlike the conventional multicast method, the X-cast method does not perform a multicast routing, and thus routers' overload in transmitting an IP data packet can be considerably reduced, and in particular, it is possible to transmit data only to a small number of receivers designated by a sender.

[7] However, the conventional X-cast method should indicate the overall destination IP address in an X-cast header, and thus as the number of receivers increases, the length of the X-cast header increases accordingly.

[8] In order to solve the problem, Korean Laid-open Patent Publication No.

2003-19668 (Document 1) discloses a method for transmitting a multicast data using X-cast.

[9] That is, in the Document 1, to transmit the same data to receivers of a multicast group, a multicast IP data packet, in which an IP header contains an address of the multicast group, is provided to a router at the side of a sender, and the router at the side of the sender converts the multicast IP data packet to an X-cast IP data packet using an address of a router at the side of the receiver and provides the X-cast IP data packet to the router at the side of the receiver, and the router at the side of the receiver converts the X-cast IP data packet to a multicast IP data packet again and provides the multicast IP data packet to the receivers using multicast.

[10] In the above-mentioned Document 1, the address information of the router at the side of the receiver and address information of the multicast group are recorded in the X-cast header of the X-cast IP data packet.

[11] As described above, in order to solve the inherent system overload problem of the multicast method, the Document 1 suggests to convert the multicast IP data packet to the X-cast IP data packet and transmit the converted X-cast IP data packet in routing between the router at the side of the sender and the router at the side of the receiver.

[12] However, the Document 1 fails to solve another inherent problem of the X-cast method, i.e. the length of the X-cast header increases in proportion to the number of receivers.

Disclosure of Invention Technical Problem

[13] An object of the present invention is to provide a method for reducing the length of an X-cast header of an X-cast datagram.

[14] That is, the present invention provides a destination IP address indicating method

that allows an X-cast header with a shorter length than that of a conventional X-cast header.

[15] Other objects and advantages of the present invention will be described below, and understood through embodiments of the present invention. And, objects and advantages of the present invention may be realized by means and combination recited in the following claims. Technical Solution

[16] In order to achieve the above-mentioned objects, an X-cast IP datagram according to an aspect of the present invention includes an IP header, an X-cast (explicit multicast) header, a transport header and a payload field, and the X-cast header has a destination IP address area including at least one first destination IP address field containing a network address and a host address; and at least one second destination IP address field containing a flag bit string and a host address, the flag bit string indicating that the second destination IP address field has the same network address as that of the first destination IP address field.

[17] The X-cast IP datagram is handled by network apparatuses located in an IP packet network, i.e. a plurality of routers and wired or wireless data communication terminals. The network apparatuses generate or interpret the X-cast IP datagram or route the X- cast IP datagram to a next hop through the IP packet network.

[18] And, a method for routing an X-cast IP datagram through an IP packet network having at least one router according to another aspect of the present invention comprises (a) a sending terminal obtaining a network address and a host address from at least one receiving terminal belonging to the same network through the IP packet network; (b) a receiving router receiving an X-cast IP datagram containing the network address and the host address of the receiving terminal from the sending terminal, the X-cast IP datagram including an X-cast header having at least one first destination IP address field containing a network address and a host address, and at least one second destination IP address field containing a flag bit string and a host address, the flag bit string indicating that the second destination IP address field has the same network address as that of the first destination IP address field; (c) the receiving router restoring a network address of the second destination IP address field with reference to the network address of the first destination IP address field; and (d) the receiving router unicasting the X-cast IP datagram to the at least one receiver terminal belonging to the same network.

[19] At this time, preferably the first destination IP address field precedes the second destination IP address field all the time, and the flag bit string is all composed of "0".

[20] And, preferably the second destination IP address field has a smaller storage space

than that of the first destination IP address field, in particular, in the case that the first destination IP address field is N bytes long, the second destination IP address field is

N/2 bytes long. For example, the first destination IP address field may contain a network address of 3 bytes and a host address of 1 byte, and the second destination IP address field may contain a flag bit string of 1 byte and a host address of 1 byte. [21] And, in the case that a total number of the first destination IP address field and the second destination IP address field dependent on the first destination IP address field is an odd number, a final second destination IP address field may further contain a padding bit string. [22] At this time, preferably the padding bit string is all composed of "0", the first destination IP address field and the final second destination IP address field each is the same N bytes long, and the other second destination IP address field is N/2 bytes long.

Brief Description of the Drawings [23] These and other features, aspects, and advantages of preferred embodiments of the present invention will be more fully described in the following detailed description, taken accompanying drawings. In the drawings: [24] FIG. 1 is a view showing an IP packet network for routing an X-cast IP datagram according to the present invention. [25] FIG. 2 is a view showing a format of an X-cast IP datagram according to the present invention. [26] FIG. 3 is a view showing a format of a conventional X-cast header of an X-cast IP datagram. [27] FIG. 4 is a view showing a format of an X-cast header of an X-cast IP datagram according to the present invention. [28] FIG. 5 is a flow chart of a method for routing an X-cast IP datagram according to the present invention.

Best Mode for Carrying Out the Invention [29] Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. [30] FIG. 1 shows an IP packet network 106 for routing an X-cast IP datagram (or IP data packet) according to the present invention. [31] As shown in FIG. 1, the X-cast IP datagram according to the present invention is transmitted from a sending terminal 100 to a plurality of receiving terminals 102a to

102d and 104a to 104d through the IP packet network 106 of FIG. 1. [32] The sending terminal 100 is connected to a sending router 106a, and a plurality of the receiving terminals 102a to 102d and 104a to 104d are connected to a receiving router 106d. The receiving terminals 102a to 102d and 104a to 104d connected to the

receiving router 106d may be located in separate A and B networks 102 and 104, respectively. That is, the receiving terminals 102a to 102d are located in the A network 102, and the receiving terminals 104a to 104d are located in the B network 104.

[33] Although FIG. 1 shows both of the A network 102 and the B network 104 are connected to the same receiving router 106d, the A network 102 and the B network 104 may be each connected to different receiving routers.

[34] At least one intermediate routers 106b and 106c may be interposed between the sending router 106a and the receiving router 106d, and the IP datagram may be transmitted using X-cast between the sending terminal 100 and a plurality of the receiving terminals 102a to 102d and 104a to 104d via the intermediate routers 106b and 106c.

[35] For example, in the case that the sending terminal 100 transmits an X-cast IP datagram to a first receiving terminal 102a to a fourth receiving terminal 102d belonging to the A network 102, the X-cast IP datagram (or IP data packet) has a format shown in FIG. 2.

[36] That is, the X-cast IP datagram includes largely a header field and a payload field

(that is, data field), and the header field has an IP header, an X-cast header and a transport header. The header field contains information required for routing and transmission of a packet, and the payload field contains information that a sender intends to deliver to a receiver.

[37] The IP header of the X-cast IP datagram has an X-cast address recorded therein, and the X-cast address performs two functions: a first function for indicating that an IP datagram is an X-cast IP datagram, and a second function for designating a transmission path of an X-cast IP datagram. The functions of the X-cast address are well known in prior art, and thus their detailed description is omitted herein.

[38] FIG. 3 is a view showing a format of a conventional X-cast header of an X-cast IP datagram.

[39] Referring to FIG. 3, a conventional X-cast header 300 has a destination IP address area 310 where an address information of a destination is specified, and the destination IP address area 310 includes a plurality of destination IP address fields 310a to 310c, each being N bytes long. Generally, the destination IP address field is preferably 4 bytes long.

[40] In the conventional destination IP address fields 310a to 310c of 4 bytes total as shown in FIG. 3, a network address is assigned with 3 bytes and a host address is assigned with the remaining 1 byte. That is, the conventional destination IP address fields 310a to 310c contain a network ID and a host ID.

[41] For this reason, even in the case that an X-cast IP data packet is transmitted to a plurality of receivers belonging to the same network (A network or B network) as

shown in FIG. 1, a predetermined address space (for example, 3 bytes) for recording the same network ID should be assigned to each of the destination IP address fields 310a to 310c in a repetitive way. As a result, as the number of receiver increases, an overhead size becomes larger.

[42] That is, the format of the conventional X-cast header shown in FIG. 3 has a disadvantage of inefficient use of the address space. Thus, datagram transmission is limited to receivers of a small group and can not be made to receivers of an intermediate group and a large group.

[43] In order to solve the problem, the inventors of the present invention devised a new format of an X-cast header shown in FIG. 4.

[44] Referring to FIG. 4, an X-cast header 400 according to the present invention has a destination IP address area 410 where an address information of a destination is specified, and the destination IP address area 410 includes a plurality of destination IP address fields 410a to 410c, each being N bytes long.

[45] The destination IP address fields 410a to 410c include at least one first destination

IP address field 410a containing a network address and a host address and a plurality of second destination IP address fields 410b and 410c each containing a flag bit string for indicating the same network address and a host address.

[46] An address space assigned to each of the second destination IP address fields 410b and 410c should be smaller than that of the first destination IP address field 410a. For example, preferably the address space of the second destination IP address fields 410b and 410c is half as much as that of the first destination IP address field 410a. That is, in the case that the first destination IP address field 410a is 4 bytes long (network address: 3bytes, host address: lbyte), the second destination IP address fields 410b and 410c each may be 2 bytes long (flag bit string: 1 byte, host address: lbyte).

[47] According to the present invention, a plurality of the second destination IP address fields 410b and 410c are dependent on a single first destination IP address field 410a. That is, receivers corresponding to a plurality of the second destination IP address fields 410b and 410c mean receiving terminals belonging to the same network as a receiver corresponding to the first destination IP address field 410a and having different IP addresses (i.e. host IDs) from each other.

[48] Referring to FIG. 1, in the case that a sending terminal 100 transmits an X-cast IP datagram to a plurality of receiving terminals 102a to 102d belonging to A network 102, an X-cast header of the X-cast IP datagram has a destination IP address area 410 including a single first destination IP address field 410a and a plurality of second destination IP address fields 410b and 410c. For example, when an address information corresponding to a first receiving terminal 102a is assigned to the first destination IP address field 410a, address information corresponding to second to fourth receiving

terminals 102b to 102d are assigned to the second destination IP address fields 410b and 410c. At this time, the first destination IP address field 410a contains a network address (network ID) of 3 bytes and a host address (host ID) of 1 byte, and the second destination IP address fields 410b and 410c each contains a flag bit string of 1 byte and a host address (host ID) of 1 byte.

[49] The flag bit string is configured to indicate that the second destination IP address fields 410b and 410c have the same network address as that of the first destination IP address field 410a, and for example, may be all composed of "0". Accordingly, it does not need to record the overall network address of 3 bytes, but to record the flag bit string of 1 byte in the second destination IP address fields 410b and 410c so as to specify the network address.

[50] Therefore, routers (in particular, receiving routers) 106a to 106d of an IP packet network can find a network address of a corresponding receiver through the flag bit string of the second destination IP address fields 410b and 410c of the X-cast header. That is, when a flag bit string is found in the second destination IP address fields 410b and 410c, the routers 106a to 106d of the IP packet network restore a network address of a corresponding receiver to the network address of the first destination IP address field 410a.

[51] And, according to a dependent relationship between the first destination IP address field 410a and the second destination IP address fields 410b and 410c, the first destination IP address field 410a precedes the second destination IP address fields 410b and 410c in the destination IP address area 410.

[52] And, in the case that a total number of the destination IP address fields 410a to 410c of the destination IP address area 410 is an odd number, the remaining address space of the final second destination IP address field 410c is filled with "0". For example, in the case that the first destination IP address field 410a is 4 bytes long and the second destination IP address field 410b is 2 bytes long, the final destination IP address field 410c contains a flag bit string of 1 byte, a host address of 1 byte and a padding bit string of 2 byte. The padding bit string of 2 bytes is all composed of "0".

[53] As such, the destination IP address area 410 of the X-cast header has at least one first destination IP address field 410a and a plurality of second destination IP address fields 410b and 410c, thereby reducing an overhead size to 50% at a maximum.

[54] Although FIG. 4 shows a single first destination IP address field 410a, the X-cast header according to the present invention may have at least two first destination IP address fields.

[55] Hereinafter, a method for routing an IP datagram having the above-mentioned X- cast header format from a sending terminal to a plurality of receiving terminals via a plurality of routers is described with reference to FIG. 5.

[56] At least one receiving terminal 102a to 102d and 104a to 104d transmits an IP data packet containing its address information (for example, class C IP address having a network ID and a host ID) to a receiving router 106d in A network 102 or B network 104 (S400).

[57] The receiving router 106d receives the IP data packet from the receiving terminal

102a to 102d and 104a to 104d, stores the IP data packet in an internal table (routing table), and multicasts the IP data packet by copying and transmitting the IP data packet to an intermediate router 106c (S402).

[58] The multicast IP data packet is transmitted to a sending router 106a via a plurality of intermediate routers 106b and 106c, and the sending router 106a forms a routing table using the IP data packet and transmits the IP data packet to a sending terminal 100 (S404).

[59] The step for copying and transmitting the IP data packet is performed by all the routers 106a to 106d in the IP packet network 106, and thus the routers 106a to 106d are all aware of the address information (network ID and host ID) of the receiving terminal 102a to 12d or 104a to 104d (S406). Therefore, the routers 106a to 106d can forward the IP data packet to the receiving terminal 102a to 102d or 104a to 104d.

[60] The sending terminal 100 generates an X-cast IP datagram destined for a plurality of receiving terminals using the address information (network ID and host ID) of the receiving terminals 102a to 12d or 104a to 104d transmitted from the sending router 106a, and transmits the X-cast IP datagram to the sending router 106a (S406).

[61] Here, the X-cast IP datagram has formats shown in FIGs. 2 and 4.

[62] That is, the X-cast IP datagram has an IP header, an X-cast header, a transport header and a payload field. At this time, the IP header contains information for indicating that the IP datagram is an X-cast datagram and information for designating a transmission path of the X-cast datagram. And, the X-cast header contains a plurality of destination IP address information to receive the IP datagram, and a format of the X- cast header of the X-cast IP datagram is shown in FIG. 4. That is, the X-cast header includes at least one first destination IP address field 410a containing a network address and a host address, and a plurality of second destination IP address fields 410b and 410c each containing a flag bit string and a host address, the flag bit string indicating that the second destination IP address fields 410b and 410c have the same network address as that of the first destination IP address field. And, a payload field contains information that a sender intends to deliver to a receiver.

[63] The sending router 106a receives the X-cast IP datagram of formats shown in FIGs.

2 and 4 from the sending terminal 100, and routes using X-cast the X-cast IP datagram to the receiving router 106d via the designated intermediate routers 106b and 106c with reference to a routing channel of the IP header (S408).

[64] The receiving router 106d receives the X-cast IP datagram from the sending router

106a and obtains the IP address information (network ID and host ID) of the receiving terminals 102a to 102d and 104a to 104d from the X-cast header of the X-cast IP datagram. At this time, in the case that a flag bit string exists in the destination IP address field, a network ID is extracted from a corresponding first destination IP address field, and a network ID of a corresponding receiver terminal is restored to the network ID (S410). Thus, the receiving router 106d can restore network IDs and host IDs of all receiving terminals.

[65] The receiving router 106d recognizes IP address information of all receiving terminals, and unicasts the X-cast IP datagram to the corresponding receiving terminals 102a to 102d and 104a to 104d (S412). Industrial Applicability

[66] As such, the present invention is very advantageous in routing using X-cast an IP data packet to a plurality of receivers belonging to the same network. In other words, receivers belonging to the same network have the same network address, and thus it does not need to repetitively record the same network address in a destination IP address field of an X-cast header. That is, it is possible to reduce the capacity of the destination IP address field of the X-cast header to 50% at a maximum using a short bit string, i.e. a flag bit string instead of the network address to be recorded repetitively. Thus, it is possible to reduce the overhead size to 50% at a maximum when routing using X-cast the IP data packet to a plurality of receivers belonging to at least one network.

[67] Therefore, it is possible to reduce the overhead size of the X-cast header in the X- cast IP datagram to 50%. As a result, the total capacity of the IP datagram is reduced, thereby reducing the network bandwidth.

[68] And, it is possible to assign more storage space to a payload field of the IP datagram.

[69] As described above, the preferred embodiments of the present invention are described in detail with reference to the accompanying drawings. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.