High speed bus structure in a multi-port bridge for a local...

Details High speed bus structure in a multi-port bridge for a local... High speed bus structure in a multi-port bridge for a local...

1998-02-18

2002-08-27

Nguyen, Chau (Department: 2663)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S438000

Reexamination Certificate

active

06442168

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 high speed bus structure for a multi-port bridge for controlling the flow of data packets through the multi-port bridge by using a limited number of bus commands.
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
20
. The multi-port bridge
20
in this example has eight ports A-H, though the number of ports can vary. Each port A-H is connected to a segment
21
-
28
of the LAN. Each segment
21
-
28
typically includes one or more nodes
29
-
44
, 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
29
-
44
has an associated node address which uniquely identifies the node. The nodes
29
-
44
are configured to send data, one to another.
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
50
. The data packet
50
includes an eight byte long pre-amble
51
which is generally utilized for synchronizing a receiver to the data packet
50
. The pre-amble includes seven bytes of pre-amble and one byte of start-of-frame. Following the pre-amble
51
, the data packet
50
includes a six byte long destination address
52
, which is the node address of a node which is an intended recipient for the data packet
50
. Next, the data packet
50
includes a six byte long source address
53
, which is the node address of a node which originated the data packet
50
.
Following the source address
53
is a two-byte length field
54
. Following the length field
54
is a data field
55
. The data field
55
can be up to 1500 bytes long. Finally, the data packet
50
includes a four-byte frame check field
56
which allows a recipient of the data packet
50
to determine whether an error has occurred during transmission of the data packet
50
.
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
20
and is known as an intra-segment packet. Therefore, when the multi-port bridge
20
receives an intra-segment packet, the multi-port bridge
20
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
20
appropriately forwards the data packet to the destination node.
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
20
at a rate that is higher than the rate at which the multi-port bridge
20
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 of and apparatus for controlling the flow of data packets in a multi-port bridge. The multi-port bridge includes a switch engine, a memory and a plurality of ports, all of which are interconnected by a high speed communication bus. The switch engine includes a bus controller, a memory controller and a look-up controller, each preferably being a finite state machine. The memory controller provides an interface between the memory and the communication bus. The bus controller controls access to the communication bus by collecting requests and granting the requests according to an appropriate priority. The look-up controller determines to which port each packet is to be directed based upon the destination node address for the packet. The high speed communication bus includes single bit signal lines dedicated to communicating control commands, signal lines dedicated to communicating data, and several signal lines having special purposes. For example, two signal lines are preferably dedicated to initiating access to the bus, each having a respective priority, another signal line is dedicated to jam requests (for applying backpressure), still another signal line is dedicated to the memory controller and yet another signal line is dedicated to providing a bus clock signal. 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 finite state machine, a transmit finite state machine, a receive buffer, a transmit buffer and a memory pointer 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 memory pointer buffer stores memory pointers in a queue for transmission by the port, one memory pointer for each data packet being stored 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.
The communication bus is monitored by each port. The look-up controller indicates which are the destination ports for the packet via the communication bus. 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, if the port identified as the destination port is not currently busy transmitting or receiving another packet, the destination port configures itself to receive the packet directly from the source port (cut-through).
However, if the memory pointer buffer of the destination port is nearly full, the port controller of the destination port applies a jam request signal to the communication bus. The source port receives the jam request and, in response, discards the incoming packet and also sends a jam signal over its associated segment. The jam signal causes the node (source node) which is the source of the packet to discontinue sending the packet and attempt to resend the packet after a waiting period.
Assuming the memory pointer buffer for the destination port is not nearly full (no jam request is made), the packet is loaded from the receive buffer of the source port into the packet buffers of the memory starting at the memory address identified in the memory pointer. Writing of the packet into the packet buffers preferably

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