Electrical computers and digital processing systems: multicomput – Computer-to-computer data routing
Reexamination Certificate
1997-06-05
2001-06-05
Geckil, Mehmet B. (Department: 2152)
Electrical computers and digital processing systems: multicomput
Computer-to-computer data routing
C709S240000, C455S432300, C455S433000, C455S435100, C370S389000, C370S392000
Reexamination Certificate
active
06243758
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to computer networks, and more specifically to group-oriented multicast routing in an internetwork, wherein the reacheable extent of multicast packets is limited within an area, called “multicast scope”.
2. Description of the Related Art
For multicast routing in an internetwork, the concept of “multicast scope” is described in a dissertation “Multicast Routing in a Datagram Internetwork” submitted to Stanford University, S. E. Deering, December 1991. An internetwork having a multicast scope (or simply scope) has the ability to limit the “scope” of a multicast transmission to reach only nearby destinations. As disclosed in “IP Version 6 Addressing Architecture” Request for Comment 1884, RFC 1884, December 1995, R. Hinden et al, a scope can be established by encapsulating a four-bit scope field in the address field of a multicast packet according to the internet protocol version 6. Using the scope field of a multicast packet, each router in the internetwork intercepts the packet and prevents it going beyond the boundary of the scope.
While there are a number of advantages for limiting the scope of a multicast, it is disadvantages for mobile hosts visiting a subnetwork external to the scope if they wish to, or are entitled to, participate in group activities within the scope. One approach is to encapsulate a multicast packet in the payload field of a unicast packet and send it from a home agent to an external mobile host. However, the number of unicast packets will increase with an increase in external mobile hosts, causing a significant increase in traffic.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a computer network capable of selectively routing multicast packets to home mobile hosts visiting a subnetwork external to a scope or foreign mobile hosts visiting a subnetwork within the scope.
According to a first aspect of the present invention, there is provided a computer network comprising a plurality of subnetworks each comprising a plurality of interconnected hosts, the subnetworks forming a multicast scope which defines a reachable extent of multicast packets, and a plurality of routers interconnecting the subnetworks and further connecting the subnetworks to an external subnetwork. Each of the hosts which form a multicast group within the scope transmits a multicast packet containing a scope field indicating that transmission of the multicast packet beyond the scope is forbidden and a boundary flag indicating whether only hosts within the scope are allowed to participate in a group activity or mobile hosts outside the scope are also allowed to participate in the group activity. Each of the routers, on receiving a multicast packet, prevents it from being transmitted beyond the scope if the scope field is contained in the received packet. A home agent located within the scope receives a multicast packet and transmits it to a mobile host visiting the external subnetwork if the boundary flag of the received packet indicates that participation in the group activity is allowed.
According to a second aspect, the present invention provides a computer network comprising a plurality of subnetworks each comprising a plurality of interconnected hosts, the subnetworks forming a multicast scope which defines a reachable extent of multicast packets, and a plurality of routers interconnecting the subnetworks and further connecting the subnetworks to an external subnetwork. Each of the hosts which form a multicast group within the scope transmits a multicast packet containing a scope field indicating that transmission of the multicast packet beyond the scope is forbidden and a group identifier identifying the group. Each of the routers, on receiving a multicast packet, prevents it from being transmitted beyond the scope if the scope field is contained in the received packet. One of the hosts within the scope transmits a control message containing a group identifier and a boundary flag indicating whether only hosts within the scope are allowed to participate in a group activity or mobile hosts outside the scope are also allowed to participate in the group activity. A home agent within the scope receives the control message, stores the group identifier and boundary flag of the received message, and subsequently receives a multicast packet, and transmits the packet to a mobile host visiting the external subnetwork if the stored subnet flag indicates that participation of outside mobile hosts in group activity is allowed when the stored group identifier coincides with the group identifier of the received packet.
According to a third aspect, the present invention provides a computer network comprising a plurality of subnetworks each comprising a plurality of interconnected hosts, the subnetworks forming a multicast scope which defines a reachable extent of multicast packets, and a plurality of routers interconnecting the subnetworks and further connecting the subnetworks to an external subnetwork. Each of the hosts which form a multicast group within the scope transmitting a multicast packet containing a scope field indicating that transmission of the multicast packet beyond the scope is forbidden and a subnet flag indicating whether only hosts attached to one of the subnetworks within the scope are allowed to participate in a group activity or mobile hosts outside the subnetwork are also allowed to participate in the particular group activity. Each of the routers, on receiving a multicast packet, prevents it from being transmitted beyond the scope if the scope field is contained in the received packet. A mobile host of the external subnetwork receives a multicast packet when visiting one of the subnetworks within the scope, and reads the contents of the received packet if the subnet flag of the received packet indicates that participation of outside mobile hosts in a group activity is allowed.
According to a further aspect, the computer network of the present invention comprises a plurality of subnetworks each comprising a plurality of interconnected hosts, the subnetworks forming a multicast scope which defines a reachable extent of multicast packets, and a plurality of routers interconnecting the subnetworks and further connecting the subnetworks to an external subnetwork. One of the hosts within the scope transmits a control message to the routers so that the control message is relayed to the subnetworks within the scope, the control message containing a multi-bit flag indicating one of a plurality of group activities. Each of the hosts which form a multicast group within the scope receives the control message, stores the multi-bit flag of the message, and transmits a multicast packet containing a scope field indicating that transmission of the multicast packet beyond the scope is forbidden and the stored multi-bit flag. Each of the routers, on receiving a multicast packet, prevents it from being transmitted beyond the scope if the scope field is contained in the received packet. A mobile host located within the scope receives the control message, stores the multi-bit flag contained therein, receives a multicast packet, and reads contents of the received packet if a multi-bit flag contained in the packet coincides with the stored multi-bit flag. Alternatively, a home agent within the scope receives the control message, stores the multi-bit flag of the message, receives a multicast packet, and transmits the received packet to a mobile host visiting the external subnetwork if a multi-bit flag contained in the received packet coincides with the stored multi-bit flag.
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patent: 5517618 (1996
Geckil Mehmet B.
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
Vaughn, Jr. William C.
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