Method and system of multicast routing for groups with a single transmitter

• US 5,517,494 A
• Filed: 09/30/1994
• Issued: 05/14/1996
• Est. Priority Date: 09/30/1994
• Status: Expired due to Term

• Current Assignee: Apple Computer Incorporated (Apple Inc.)
• Original Assignee: Apple Computer Incorporated (Apple Inc.)
• Inventors: Green, Mark A.
• Primary Examiner(s): Safourek, Benedict V.
• Application Number:
  US08/316,081
• Time in Patent Office: 592 Days
• Field of Search: 395/200, 395/325, 370/58.1, 370/54, 370/60, 370/85.13, 370/85.14
• US Class Current: 370/408
• CPC Class Codes: H04L 12/185 with management of multicast group membership

Abstract

A method of implementing a multicast routing protocol in routers is provided to manage the assignment of multicast transport addresses and to forward data from a single transmitting endpoint to multiple receiving endpoints. This method in conjunction with a method for implementing the multicast routing protocol as a transport protocol layer service for endpoints provides an internet wide multicast transport service. The multicast transport service provides the capability of transmitting data from a single source to multiple receivers on interconnected networks efficiently and without having to send duplicate copies of the data on any single network. Routers and endpoints transmit and receive multicast packets in a manner which is independent of the network layer datagram protocols used by the multicast transport service. Multicast control packets are exchanged using a multicast transaction protocol which allows routers and endpoints to execute transactions in a manner that does not require either routers to know the state of specific endpoints or endpoints to know the state of specific routers.

Claims

1. A method for creating a multicast distribution tree in a computer system, comprising the steps of:

transmitting, by a listener computer, coupled by a common network, to a first designated router, a join group request which includes a multicast address which contains a network number that identifies a particular network and which requests data from the particular network,

scanning, by the first designated router, the forwarding table of the first designated router to locate the particular multicast request included in the join group request, to determine whether the first designated router is currently receiving data from the particular multicast address, and if not, then

scanning, by the first designated router, the routing table of the first designated router to locate the network number contained in the particular multicast address and a corresponding second designated router, coupled to a network common to that of the first designated router, for receiving data from the particular network, and

requesting, by the first designated router, transmission of data from the particular network through the second designated router.

2. The method of claim 1, further comprising the step of:

transmitting, by the first designated router, data to the listener computer to start receiving data, if the first designated router is currently receiving data from the particular network.

3. The method of claim 1, further comprising the steps of:

scanning, by the second designated router, the forwarding table of the first designated router to locate the particular multicast request included in the join group request, to determine whether the second designated router is currently receiving data from the particular multicast address, and if not, then

scanning, by the second designated router, the routing table of the second designated router to locate the network number contained in the particular multicast address and a corresponding third designated router, coupled to a network common to that of the second designated router, for receiving data from the particular network, and

requesting, by the second designated router, transmission of data from the particular network through the third designated router.

4. The method of claim 3, further comprising the steps of:

scanning, by the third designated router, of the forwarding table of the first designated router to locate the particular multicast request included in the join group request, to determine whether the third designated router is currently receiving data from the particular multicast address, and if not, then

scanning, by the third designated router, the routing table of the third designated router to locate the network number contained in the particular multicast address and a corresponding fourth designated router, coupled to a network common to that of the third designated router, for receiving data from the particular network, and

requesting, by the third designated router, transmission of data from the particular network through the fourth designated router.

5. A method for multicasting data in a computer system, comprising the steps of:

transmitting, by a source computer, a create request to a first designated router coupled to a first network common to the source computer;

creating, by the first designated router, a multicast address corresponding to data transmitted by the source computer; and

transmitting, by the source computer, data including said multicast address upon the first network.

6. The method of claim 5, wherein the multicast address includes a network number and a socket number, wherein the socket number corresponds to a particular source computer.

7. The method of claim 6, wherein each network is identified by network numbers within a predetermined numerical range.

8. The method of claim 6, wherein the socket number assigned to a particular source computer is based on a random number.

9. The method of claim 5, further comprising the steps of:

transmitting, by the designated router, a query to adjacent routers at predetermined time intervals to determine if listener computers, present on networks adjacent to the designated router, are currently receiving data from a particular network;

checking for responses to the transmitted query; and

terminating, by the designated router, transmission of data from adjacent networks that, during a predetermined amount of time following transmission of the query, have provided no response.

10. The method of claim 5, further comprising the step of:

storing multicast addresses in a forwarding table in the designated router.

11. The method of claim 10, further comprising the steps of:

receiving a join request, from a second router on a second network adjacent to the first designated router, to the first designated router to start forwarding data from a network having a particular multicast address; and

checking, by the first designated router, a routing table to confirm if the first designated router is receiving data having the particular multicast address; and

if so, forwarding the data having the particular multicast address to the second designated router.

12. The method of claim 5, wherein the multicast address includes a network number and a socket number.

13. The method of claim 12, wherein the router generates the multicast address.

14. The method of claim 12, further comprising the step of:

deleting unused data from the forwarding table in response to changing activity of the networks.

15. The method claim 5 utilizing transport layer routing that is independent of network layer unicast routing, and further comprising the steps of:

initializing a routing table of a router;

sending a distance vector request on each port of the router coupled to a network;

updating the routing table in response to receiving a distance vector request; and

sending, in response to the distance vector request, a distance vector which reflects changing activity of networks coupled to the router.

16. The method of claim 15, wherein the router coupled to the network is a designated router.

17. The method of claim 5, further comprising the step of:

identifying receiving and sending computers by a multicast address that is transmitted in the multicast data.

18. An apparatus for creating a multicast distribution tree, comprising:

a common network;

a designated router coupled to the common network;

listener computer means, coupled to the common network, for transmitting, to the first designated router, a join group request which includes a multicast address which contains a network number that identifies a particular network and which requests data from the particular network;

said first designated router including

means for scanning the forwarding table of the first designated router to locate the particular multicast request included in the join group request to determine if the first designated router is receiving data from the particular multicast address;

means for scanning a first routing table when the first designated router is not currently receiving data from the particular network, to locate the network number contained in the particular multicast address and a corresponding second designated router, coupled to a network common to that of the first designated router, for receiving data from the particular network; and

means for requesting transmission of data from the particular network through the second designated router, if the first designated router is not currently receiving data from the particular network.