Triplet architecture in a multi-port bridge for a local area...

Details Triplet architecture in a multi-port bridge for a local area... Triplet architecture in a multi-port bridge for a local area...

1998-03-30

2001-07-03

Vu, Huy D. (Department: 2733)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S392000, C370S413000

Reexamination Certificate

active

06256313

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a multi-port bridge for a local area network. More particularly, the invention relates to controlling flow of data packets among the ports of a multi-port bridge.
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), each segment having a corresponding transmission medium.
FIG. 1
illustrates a conventional local area network (LAN) including a multi-port bridge
10
. The multi-port bridge
10
in this example has eight ports #
1
-
8
, though the number of ports can vary. Each port #
1
-
8
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 which uniquely identifies the node. The nodes
19
-
34
are configured to send data, one to another, in the form of 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 length field
44
. Following the length field is a data field
45
. The data field
45
can be up to 1500 bytes long. Finally, the data packet
40
includes a four-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 the 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), however, the multi-port bridge
10
appropriately forwards the data packet to the destination node.
When a node (source node) sends data to another node (destination node) located on the same segment of the LAN (intra-segment communication), the data is communicated directly between the nodes without intervention by the multi-port bridge
10
. 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), however, the multi-port bridge
10
appropriately forwards the data packet to the destination node.
Data packets received by the multi-port bridge
10
are generally stored temporarily within the multi-port bridge
10
before being forwarded to the appropriate destination node by the multi-port bridge
10
. Problems can arise, however, when the capabilities of the multi-port bridge are exceeded by network demand. When data packets 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 forward the packets, the network becomes congested. This problem is exacerbated as network users place increasing demands on the network.
Therefore, what is needed is improved technique for controlling the flow of data in a multi-port bridge for a local area network.
SUMMARY OF THE INVENTION
The invention is a method and apparatus for controlling flow of data packets among the ports of a multi-port bridge. The multi-port bridge includes a switch engine, a dynamic random access memory and a plurality of ports, all of which are interconnected by a high speed communication bus. The switch engine includes a memory controller and a bus controller, each being a finite state machine. The bus controller controls access to the communication bus by collecting requests from the ports and granting the requests according to an appropriate priority. The memory controller provides an interface between the memory and the communication bus. The memory includes look-up tables utilized for appropriately directing data packets among the ports, packet buffers utilized for temporarily storing packets and mailboxes for providing an interface between the switch engine and an external processor.
Each port includes a port controller, a MAC transceiver, a receive buffer, a transmit buffer and a triplet buffer. Packets received from a LAN segment by the transceiver are directed to the communication bus through the receive buffer, while packets to be transmitted over the LAN segment are directed to the transceiver through the transmit buffer. The triplet buffer stores memory pointers, referred to herein as “triplets,” for data packets being queued in the packet buffers of the memory.
A data packet originating from a node (source node) in a segment of the LAN is received by the receive buffer of a corresponding one of the ports (source port) of the multi-port bridge. As the packet is still being received, the look-up tables are utilized to determine which is the appropriate destination port for the packet based upon the destination address. A result of performing the look-up is a “triplet” which includes three fields: a first field containing the identification of the source port, a second field containing the identification of the destination port, and a third field containing a starting address assigned to the incoming packet in the packet buffers of the memory.
If the source port and the destination port are the same, this indicates that the source and destination nodes are on the same segment of the LAN (intra-segment communication) and the packet is filtered. Otherwise, the memory controller places the triplet on the communication bus which is monitored by each port. If the port identified as the destination port in the triplet is not currently busy transmitting or receiving another packet, the destination port will configure itself to receive the packet directly from the source port (cut-through).
However, if the triplet buffer in the port identified as the destination port in the triplet is nearly full, the bus controller of the destination port applies a jam request signal to the communication bus. The source port will receive the jam request and, in response, will discard the incoming packet and also send a jam signal over its associated segment. The jam signal will cause the node (source node) which is the source of the packet to discontinue sending the packet and attempt to r

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