Multicast echo removal

Details Multicast echo removal Multicast echo removal

1999-03-16

2003-04-01

Vanderpuye, Ken (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S432000

Reexamination Certificate

active

06542503

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to multicasting on a data communications network. More specifically, the present invention relates to eliminating the problem of multicast echo, where duplicates of a multicast packet are delivered to the same address.
2. The Background
Multicasting is the process by which a host or other device transmits a message or packet to a selected group of recipients. It is commonly used in broadcast networks like Ethernet networks but may be used in any type of network.
FIG. 1
is a diagram illustrating a network capable of utilizing multicasting. Host
10
is coupled via an Ethernet link to a gateway
12
. Additional hosts
14
,
16
,
18
may also be coupled to the gateway
12
via Ethernet links. Host
10
may be a member of a multicast group which also includes hosts
14
,
16
, and
18
. Thus, if host
10
transmits a packet to gateway
12
, gateway
12
will send a duplicate of the packet to the other members of the group, which include hosts
14
,
16
, and
18
.
There is a potential, however, in certain instances, for a multicasting echo problem to arise. A multicast echo occurs when two or more versions of the same packet arrive at the same destination or host.
FIG. 2
illustrates an example of how this might occur. Host
50
and host
52
are both coupled to a network access server (NAS)
56
, which may be located between the hosts
50
,
52
and a host gateway
54
. Host gateway
54
may also be coupled to hosts
58
,
60
,
62
. The problem arises if both host
50
and host
52
are members of the same multicast group. Host
50
may transmit a packet intended for each member of the multicast group. Since host
52
is on the same Ethernet segment as host
50
, the packet will be received by host
52
directly from host
50
. However, host gateway
54
will also send a duplicate of the packet to each member of the multicast group, which includes host
52
. Thus, host
52
will receive two versions of the same packet. This consumes valuable bandwidth and CPU cycles of both the gateways and the hosts.
This problem is amplified if the host gateway performs any type of routine modification on the packets, such as network address translation (NAT). NAT is a process by which a gateway modifies either the source address of destination address of a packet in order to compensate for the fact that there is a different addressing scheme on the other side of the gateway. Thus, if NAT is used in the multicast situation discussed above, it is possible for host
52
to receive two packets, identical in every way except for the fact that they have different source addresses. This has the potential to confuse or break multicast applications and confuse the end users. Thus, it is necessary to arrive at a solution which removes this potential multicast echo problem.
SUMMARY OF THE INVENTION
An apparatus is provided which processes upstream multicast packets and downstream multicast packets in a manner such as to avoid the problem of multicast echo which is generated from a host gateway. For upstream multicast packets, a method is provided which includes: extracting the source network address from the upstream multicast packet; storing said source network address in a table corresponding to the destination host gateway of the packet; and forwarding the upstream multicast packet to the destination network address. For downstream multicast packets, a method is provided which includes: accessing a table corresponding to the host gateway from which the packet was sent; determining if said source network address of the multicast packet is identical to an entry in said table; discarding the multicast packet if said source network address is identical to an entry in said table; and forwarding the multicast packet to said destination network address if said source network address is not identical to an entry in said table. This eliminates any downstream multicast packets which originated from one of the hosts coupled to the apparatus, and thus prevents multicast echo problems from occurring.


REFERENCES:
patent: 4131767 (1978-12-01), Weinstein
patent: 5243596 (1993-09-01), Port et al.
patent: 5303237 (1994-04-01), Bergman et al.
patent: 5305311 (1994-04-01), Lyles
patent: 5473607 (1995-12-01), Hausman et al.
patent: 5502725 (1996-03-01), Pohjakallio
patent: 5802047 (1998-09-01), Kinoshita
patent: 5852721 (1998-12-01), Dillon et al.
patent: 5898686 (1999-04-01), Virgile
patent: 5964850 (1999-10-01), Castell et al.
patent: 6018526 (2000-01-01), Liu et al.
patent: 6018770 (2000-01-01), Little et al.
patent: 6023724 (2000-02-01), Bhatia et al.
patent: 6081532 (2000-06-01), Faimmante

Affiliated with

Also associated with

Rating

Multicast echo removal does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Multicast echo removal, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Multicast echo removal will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3072240