Port within a multi-port bridge including a buffer for...

Details Port within a multi-port bridge including a buffer for... Port within a multi-port bridge including a buffer for...

1999-03-19

2004-06-15

Pham, Chi (Department: 2663)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

Reexamination Certificate

active

06751225

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a multi-port bridge for a local area network. More particularly, the invention relates to a port within a multi-port bridge for a local area network having a buffer for storing routing information relating to data packets received in the port.
BACKGROUND OF THE INVENTION
Nodes of a local area network (LAN) are typically interconnected by a shared transmission medium. The amount of data traffic that the shared transmission medium can accommodate, however, is limited. For example, only one node at a time can successfully transmit data to another node over the shared transmission medium. If two or more nodes simultaneously attempt to transmit data, a data collision occurs, which tends to corrupt the data being transmitted. Thus, nodes that share a transmission medium are considered to be in a same collision domain.
A multi-port bridge allows simultaneous communication between nodes of the LAN by segmenting the LAN into multiple collision domains (also referred to as network segments or LAN segments), each segment having a corresponding transmission medium.
FIG. 1
illustrates a conventional local area network including a multi-port bridge
10
. The multi-port bridge
10
has eight ports A-H, though the number of ports can vary. Each port A-H is connected to a segment
11
-
18
of the LAN. Each segment
11
-
18
typically includes one or more nodes
19
-
34
, such as a workstation, a personal computer, a data terminal, a file server, a printer, a facsimile, a scanner or other conventional digital device. Each of the nodes
19
-
34
has an associated node address (also referred to as a medium access control (MAC) address) which uniquely identifies the node. The nodes
19
-
34
are configured to send data, one to another, in the form of discrete data packets.
When the LAN operates according to Ethernet standards, such as the Institute of Electrical and Electronics Engineers (IEEE) 802.3 standard, data is communicated in the form of discrete packets.
FIG. 2
illustrates a conventional IEEE 802.3 data packet
40
. The data packet
40
includes an eight byte long pre-amble
41
which is generally utilized for synchronizing a receiver to the data packet
40
. The pre-amble
41
includes seven bytes of pre-amble and one byte of start-of-frame. Following the pre-amble
41
, the data packet
40
includes a six-byte-long destination address
42
, which is the node address of a node which is an intended recipient for the data packet
40
. Next, the data packet
40
includes a six-byte-long source address
43
, which is the node address of a node which originated the data packet
40
. Following the source address
43
is a two-byte length field
44
. Following the length field
44
is a data field
45
. The data field
45
can be up to 1500 bytes long. Finally, the data packet
40
includes a two-byte frame check field
46
which allows a recipient of the data packet
40
to determine whether an error has occurred during transmission of the data packet
40
.
When a node (source node) sends data to another node (destination node) located on its same segment of the LAN (intra-segment communication), the data is communicated directly between the nodes without intervention by the multi-port bridge
10
and is known as an intra-segment packet. Therefore, when the multi-port bridge
10
receives an intra-segment packet, the multi-port bridge
10
does not bridge the packet (the packet is filtered). When a node (source node) sends a data packet to another node (destination node) located on a different segment (inter-segment communication), the multi-port bridge
10
appropriately forwards the data packet to the destination node.
More particularly, the multi-port bridge
10
(
FIG. 1
) receives each data packet
40
(FIG.
2
) and must determine whether the data packet
40
is for intra-segment communication or inter-segment communication, and if the data packet
40
is for inter-segment communication, the multi-port bridge
10
must determine to which port (destination port) the data packet
40
is to be directed based upon the destination address
42
contained in the data packet
40
. This can be accomplished by utilizing a look-up table which associates the destination address
42
included in the packet
40
to a port of the multi-port bridge
10
. Conventionally, the look-up table is constructed by executing a learning cycle and, then, a look-up cycle for each received data packet
40
. During the learning cycle, the source address
43
from the data packet
40
is stored in the table in association with the identification of the source port. Then, during the look-up cycle, the destination address
42
is utilized to look-up data stored during the learning cycle for a prior packet so as to identify the appropriate destination port for the packet
40
.
Problems can arise, however, when the capabilities of the multi-port bridge
10
are exceeded by network demand. When data packets
40
are received by the multi-port bridge
10
at a rate that is higher than the rate at which the multi-port bridge
10
can appropriately perform a learning cycle and a look-up cycle for each packet
40
and, then, forward the packet, the multi-port bridge
10
becomes a source of network congestion. This problem is exacerbated as network users place increasing demands on the network.
Therefore, what is needed is improved technique for increasing the data packet handling capacity in a multi-port bridge for a local area network.
SUMMARY OF THE INVENTION
The invention is a port within a multi-port bridge for a local area network (LAN) having a buffer (referred to herein as a “vector buffer”) for storing routing information (referred to herein as “receive vectors”) relating to data packets received in the port. The multi-port bridge includes a plurality of ports, each port for receiving data packets from, and transmitting data packets to, an associated segment of the LAN. The ports are coupled to each other via a communication bus included in the multi-port bridge. In the preferred embodiment, the communication bus includes two independently operable portions (referred to herein as a “data bus” and a “look-up bus”) which communicate data packets and look-up information in parallel. A look-up table is coupled to the look-up bus for correlating destination node addresses from packets received by the multi-port bridge to an appropriate port (destination port) of the multi-port bridge to which the packet is to be routed. In addition, a packet buffer is coupled to the data bus for temporarily storing data packets being communicated among the ports of the multi-port bridge.
When a packet is received by a port (source port) from its associated segment of the LAN, the packet is received into a receive buffer of the port. The receive buffer can preferably store more than one data packet. A destination and source address included in the packet are utilized to update the look-up table (referred to herein as a “learning cycle”) and to identify an appropriate destination port for the packet (referred to herein as a “look-up cycle”). The learning and look-up cycles are preferably performed by the source port communicating with the look-up table via the look-up bus. The vector buffer stores a receive vector for the packet which indicates whether the look-up table has been updated in response to the packet and whether the appropriate destination port for the packet has been identified. Once the destination port has been identified, the identification of the destination port is stored in the receive vector for the packet and the packet is ready for communication to the destination port via the data bus.
While a data packet is being communicated to the appropriate destination port for the packet, the appropriate destination port for one or more additional data packets received in the port subsequently can be identified. Accordingly, an advantage of the present invention is that operations for multiple data packets received by the port can be performed simultaneously (in parallel), thus,

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