Selection technique for preventing a source port from...

Details Selection technique for preventing a source port from... Selection technique for preventing a source port from...

1998-04-22

2001-10-09

Ton, Dang (Department: 2661)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

Reexamination Certificate

active

06301256

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a multi-port bridge for a local area network. More particularly, the invention relates to selection technique for filtering packets in a multi-port bridge for a local area network, thus, preventing a source port for a packet from becoming a destination port for the packet
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 scanner, a modem, a facsimile 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, 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
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
51
includes seven bytes of preamble and one byte of start-of-frame. Following the preamble
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
55
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 intrasegment 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.
The multi-port bridge
20
(
FIG. 1
) receives each data packet
50
(
FIG. 2
) and must determine whether the data packet
50
is for intra-segment communication or inter-segment communication, and if the data packet
50
is for inter-segment communication, the multi-port bridge
20
must determine which port (destination port) the data packet
50
is to be directed based upon the destination address
52
contained in the data packet
50
. This can be accomplished utilizing a look-up table. Conventionally, the look-up table is constructed by executing a learning phase for each received data packet
50
to store data in the table and by executing a look-up phase for each received data packet
50
to look-up data stored during the learning phase for a prior packet.
Once the look-up is performed, however, the packets need to be appropriately filtered. Therefore, what is needed is improved technique for filtering packets in a multi-port bridge for a local area network thereby preventing a source port from becoming a destination port for a packet.
SUMMARY OF THE INVENTION
The invention is a method of and apparatus for filtering packets in a multi-port bridge for a local area network thereby preventing a source port from becoming a destination port for a packet. 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 (uni-cast packet) or ports (multi-cast packet) 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 source port requests a look-up cycle. The source port stores indicia of whether it requested the look-up cycle. During the look-up cycle, the look-up tables are utilized to determine which one or ones of the ports are the appropriate destination ports for the packet, based upon the destination address.
Each of the plurality of ports is assigned a respective one of the signal lines of the communication bus dedicated to communicating data. A product of utilizing the look-up tables is referred to as a bit-map of the destination ports for the packet. The bit-map includes a logic level for each signal line assigned to a port wherein the logic level is indicative of whether the corresponding port is a destination port for the packet.
The bit-map is placed on the data portion of the communication bus. The co

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