Network device with multicast forwarding data

Details Network device with multicast forwarding data Network device with multicast forwarding data

1999-04-26

2003-03-25

Yao, Kwang Bin (Department: 2664)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S432000

Reexamination Certificate

active

06539022

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a communications network that transmits messages therein. The present invention especially relates to the transmission of multicast packets in such a network.
BACKGROUND OF THE INVENTION
FIG. 1
shows a conventional hierarchically organized communications network
10
. In particular, the communications network has a wide area network (WAN), such as the Internet, at the highest level of the hierarchy. A campus network
15
is interconnected to the WAN by a router r
1
. The campus network
15
is so called because it is typically located at a single geographic campus of several buildings. The interconnections may include any combination of wires, coaxial cables, optical fibers, circuit switches, packet switches, etc. The router r
1
interconnects a backbone network of the campus network
15
to the WAN. Connected to the backbone network are additional routers r
2
, r
3
and r
4
. Each additional router r
2
, r
3
and r
4
connects a respective subnetwork A, B or C to the backbone network. The campus network
15
is at a middle level of the hierarchy and subnetworks A, B and C of the campus network
15
are at a lower level in the hierarchy. The subnetworks A, B, C are typically isolated to a single, small geographic area such as an office building or floor of an office building. The WAN, on the other hand, typically sprawls from geographic area to geographic area. The WAN itself typically includes a number of routers (not shown) for routing communications from campus network to campus network.
The communication between routers on the WAN and on the backbone network is illustratively achieved according to the Internet protocol (IP). (Herein, protocol means a collection of semantic and syntactic rules obeyed by the devices which communicate according to the protocol).
The router r
2
is connected to bridges b
1
and b
2
of the subnetwork A, the router r
3
is connected to bridge b
3
of the subnetwork C. Each bridge b
1
-b
4
is connected to one or more network segments or collision domains which illustratively are local area networks (LANs). The bridge b
1
is connected to network segments L
1
and L
2
, the bridge b
2
is connected to network segments L
2
, L
3
and L
4
, the bridge b
3
is connected to network segments L
5
, L
6
and L
7
and the bridge b
4
is connected to network segment L
8
. Each network segment L
1
-L
8
comprises one or more interconnected host computers h
1
-h
17
. The network segment L
1
includes hosts h
1
, h
2
and h
3
, the network segment L
2
includes the host h
4
, the network segment L
3
includes the hosts h
5
, h
6
and h
7
, the network segment L
4
includes the host h
8
, the network segment L
5
includes the host h
9
, the network segment L
6
includes the hosts h
10
and h
11
, the network segment L
7
includes the hosts h
12
, h
13
and h
14
and the network segment L
8
includes the hosts h
15
, h
16
and h
17
. The network segments L
1
-L
8
may be Ethernet LANs, token ring LANs or FDDI LANs, for example.
Communication may be achieved locally within each network segment L
1
-L
8
according to one of a number of protocols. Since most deployed network segments L
1
-L
8
are Ethernet LANs, the Ethernet protocol for communication is used to illustrate the invention. According to the Ethernet protocol, each host computer is connected via an I/O interface to a common broadcast medium which broadcast medium may be carried by a coaxial cable, unshielded twisted pairs of wires, etc. A host communicates on the medium by transmitting a bitstream organized into packets
FIG. 2
illustrates an illustrative packet
20
, which comprises a header section
22
and a payload section
24
. A host which desires to communicate writes data in the payload section
24
, and an address of the intended recipient host in the header section
22
. (Illustratively, all hosts on a network segment are assigned a unique identifier or address). If the common broadcast medium is not currently being used, then the host transmits its packet
20
from an I/O interface connected to the host onto the common broadcast medium. If the common broadcast medium is currently being used by another host to transmit a packet, then the host waits until the common broadcast medium is available. The transmitted packet
20
is received at the I/O interface of each other host on the network segment. Each host then examines the destination address written in the header section
22
of the packet
20
. If the destination address matches the destination address of the host, the host accepts the packet
20
and may examine the contents of the payload section
24
. If the destination address does not match, the host discards the packet
20
.
It is possible that two hosts of the same network segment may attempt to transmit a packet concurrently. If this happens, a collision is said to occur. According to the Carrier Sense Multiple Access with Collision Detection (CSMA/CD) protocol, in the event of a collision, each host transmits a jamming signal for a specified period of time and waits a variable amount of time before reattempting transmission of its packet. See U.S. Pat. No. 5,355,375. Collisions are only possible within an individual collision domain or network segment. For instance, the communication amongst the hosts h
1
-h
3
and bridge b
1
in the network segment L
1
does not effect the communication amongst the host h
4
and bridge b
1
in the network segment L
2
. The delay incurred in transmitting a packet on a network segment (as caused by collisions or otherwise) increases with the increase of communications traffic on each segment.
Sometimes it is desirable to communicate from a host in one network segment to a host in another network segment of the same subnetwork. Such communication may be achieved using the bridges b
1
-b
4
. The bridge enables inter-segment communication while isolating the two network segments so that they operate as independent collision domains. The bridges b
1
-b
4
also can enable communication between network segments that communicate according to different protocols. For instance, the bridge b
1
can enable communication by the host h
4
in the network segment L
2
, which is a Token Ring LAN, with the host h
2
in the network segment L
1
, which is an Ethernet LAN.
The bridges within a subnetwork (e.g., the bridges b
1
-b
2
in the subnetwork A) pass control packets between each other to determine the best route for reaching each host in each attached network segment. Thereafter, each bridge receives each packet transmitted on its attached network segments. If the bridge (e.g., bridge b
1
) receives a packet from one network segment (e.g., L
1
) containing a destination address of a host in another network segment, (e.g., the host h
8
in network segment L
4
) the bridge transmits the packet in another attached network segment on a route to the network segment that contains the destination host. For instance, the route from host h
1
in network segment L
1
to the host h
8
in the network segment L
4
illustratively comprises: h
1
-L
1
-b
1
-L
2
-b
2
-L
4
-h
8
. Thus, the bridge b
1
retransmits a packet received from host h
1
destined to host h
8
on network segment L
2
.
In addition to enabling inter-segment communication within a subnetwork, the bridges enable the hosts in one subnetwork to communicate with the hosts in other subnetworks. To that end, IP (Internet protocol) addresses may be assigned to each host which includes the destination host's address in the particular subnetwork concatenated to at least a unique address that is assigned to the subnetwork in which the destination host is located. As an example, suppose the host h
1
in the subnetwork A wishes to transmit a packet to the host h
15
in the subnetwork C. The host h
1
writes the IP address of the node h
15
(which includes at least the destination address of the subnetwork C concatenated to the destination address of the host h
15
) in a packet and transmits the packet on its network segment L
1
. The packet is received

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