Multiplex communications – Communication over free space – Message addressed to multiple destinations
Reexamination Certificate
1999-01-27
2002-11-05
Chin, Wellington (Department: 2664)
Multiplex communications
Communication over free space
Message addressed to multiple destinations
C370S346000, C370S390000, C370S408000, C455S414200, C455S518000, C455S519000
Reexamination Certificate
active
06477149
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to multicast group control in order for a mobile host to participate in multicast communication.
In an internet, for conducting route control of multicast communication, a router collects information that hosts in sub-networks which are directly connected to each other participate in which multicast groups. As a protocol that conducts this information collection, an IGMP (Internet Group Management Protocol) is known, for example, which is shown in “Host Extensions for IP Multicasting” by S. Deering, Request For Comment. RFC1112, August 1989. In the IGMP, the router periodically issues a membership inquiry message that requests to be informed of addresses of the multicast groups in which the hosts participate. First, each of the hosts that have received the membership inquiry message from the router starts up a timer for measuring random time. The host corresponding to the timer of which time is first up issues a membership report message including an address of the multicast group in which the host itself participates. The router grasps the address of the multicast group to be transferred to the sub-network connected thereto by receiving this membership report message. Also, the host as well as the router receives the membership report message. The host stops the timer when receiving the membership report message with respect to the multicast group in which the host itself participates, and suppresses the transmission of the overlapping membership report messages.
An example of an IGMP procedure is shown in FIG.
5
.
FIG. 5
shows an example of the case in which there are three hosts including a host
1
and a host
2
that participate in a multicast group
1
(a group
1
in the Figure), and a host
3
that participates in a multicast group
2
(a group
2
in the Figure). A router issues membership inquiry messages. First, each of the hosts that receive the membership inquiry messages from the router starts a timer for measuring random time. In
FIG. 5
, the time of the timer of the host
2
is up first, and the host
2
issues a membership report message including an address of the group
1
in which the host participates. The router grasps the existence of a host in a sub-network to be connected to the router, which participates in the group
1
, by receiving the membership report message from the host
2
. On the other hand, the host
1
and the host
3
receive the membership report message from the host
2
. Since the host
1
participates in the same group
1
in which the host
2
participates, the host
1
stops the random timer and suppresses the transmission of the overlapping membership report messages. Compared with this, the host
3
participates in the group
2
. Since the host
3
does not receive the membership report message until time of the random timer of the host
3
is up, the host
3
issues a membership report message with respect to the group
2
, and notifies the router that the host participating in the group
2
exists.
The host in which the IGMP is mounted can be realized as shown in
FIG. 6
, for example. In
FIG. 6
, a reference numeral
100
indicates an input terminal, a reference numeral
101
indicates an output terminal, a reference numeral
102
indicates an IGMP message receiving section, a reference numeral
103
indicates an IGMP message transmitting section, a reference numeral
104
indicates an IGMP message processing section, and a reference numeral
1000
indicates a participation group controlling table. In the participation group controlling table
1000
, addresses of the multicast groups in which the hosts participate are stored. A received packet is input from the input terminal
100
and is supplied to the IGMP message receiving section
102
. The IGMP message receiving section
102
extracts the IGMP message from the received packet, and outputs it to the IGMP processing section
104
. The IGMP processing section
104
forms a message to be answered using an address of the multicast group in which the host itself participates and which is controlled by the participation group controlling table
1000
, and conducts IGMP processing for realizing a procedure shown in FIG.
5
.
Also, as one of the features of multicast communication in an internet, an area capable of transferring a multicast packet, which is called a scope, is set for each multicast group. This scope can be set as a unit of a network constituting the network, and the following advantages thereof are enumerated (for example, Stephen Deering,“Multicast routing in a datagram internetwork”, Ph. D. Thesis, Stanford University, 1991):
1) It is possible to restrict a host capable of participating in as a member network by network which is connected to each other (restriction of participation host); and
2) since the same multicast addresses can be concurrently used in the multicast groups in which different scopes are defined, it is possible to effectively utilize the multicast addresses (effective utilization of multicast addresses).
Moreover, a method of applying a scope to a mobile host for conducting communication while changing a connection place to an internet is also shown in a method of conducting multicast communication of a mobile host in Japanese Patent Application No. 9-039288. For explaining this method, first, an example for realizing a mobile host on the Internet will be shown.
The mobile host on the internet is realized by a protocol shown in “IP Mobility Support” by Charles Perkins, Request For Comment: 2002, RFC2002, October 1996, for example. In this protocol, the mobile host has a universal address (home address) that does not depend on a connection place to the internet, and a temporary address (care-of address) that varies in accordance with the connection place. Moreover, in each mobile host, a node called a home agent for conducting packet transfer to the mobile host is defined. The mobile host notifies the home agent of the home address and the care-of address every time the mobile host moves to the different networks.
In case that a mobile host communicates with other mobile host (the other party), the following procedure is taken: First, when a packet is transmitted from the other party to the mobile host, the home agent intercepts the packet and transfers it to a current place where the mobile host exists, based on a set of the home address and the care-of address of which are notified by the mobile host. On the other hand, the packet that is transmitted from the mobile host to the other party is directly transmitted to the other party without passing through the home agent of the mobile host. This state is shown in FIG.
7
.
FIG. 7
shows a basic sequence in which the mobile host moves to other network while communicating with the other party, and a reference numeral
1200
indicates a sequence of a packet between the mobile host before movement and the other party, a reference numeral
1210
indicates a sequence of a packet between the mobile host after movement and the other party, and a reference numeral
1220
indicates a sequence of a packet for notifying the home agent of the home address and the care-of address when the mobile host moves. When the mobile host moves to a different network, the mobile host notifies the home agent of correspondence between the home address and the care-of address that depends on the network to which the mobile host has moved (a sequence indicated by
1220
-
a
) in FIG.
7
). When the home agent receives this notification, the home agent transmits an acknowledgment to the mobile host (a sequence indicated by
1220
-
b
) in FIG.
7
). By means of this procedure, the home agent maintains updated correspondence between the home address and the care-of address of the mobile host.
In case that the other party transmits the packet to the mobile host (
1200
-
a
) in FIG.
7
), the other party always conducts the transmission by a format of the packet as shown in
FIG. 8
regardless of a place where the mobile host is. In
FIG. 8
, a reference numeral
1
Chin Wellington
Phan M.
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