Address look-up mechanism in a multi-port bridge for a local...

Details Address look-up mechanism in a multi-port bridge for a local... Address look-up mechanism in a multi-port bridge for a local...

1998-06-09

2001-10-23

Harrell, Robert B. (Department: 2756)

Electrical computers and digital processing systems: multicomput

Computer-to-computer data routing

C709S238000, C709S244000, C711S200000, C711S205000, C711S216000, C713S162000

Reexamination Certificate

active

06308218

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a multi-port bridge for a local area network. More particularly, the invention relates to an address look-up mechanism in a multi-port bridge for controlling the use of a memory device as a look-up table for appropriately filtering and directing packets through the 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
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 long 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.
Accordingly, what is needed is a technique for providing a multi-port bridge with an accurate and readily available look-up table which stores information indicative of which nodes of the LAN are associated with each of port of the multi-port bridge. What is further needed is a technique for generating, accessing and maintaining the look-up table.
SUMMARY OF THE INVENTION
The invention is an address look-up mechanism in a multi-port bridge for controlling the use of a memory device as a look-up table for appropriately filtering and directing packets through the multi-port bridge. The multi-port bridge includes the memory device, a switch engine and a plurality of ports, all of which are interconnected by a high speed communication bus. The switch engine includes a look-up controller, a bus controller and a memory controller, each preferably being a finite state machine. The look-up controller implements the address look-up mechanism by generating and maintaining look-up tables in the memory device and by utilizing the look-up tables for determining to which port each packet is to be directed. 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 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 devices includes a look-up table 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. The look-up table includes learned look-up tables, a permanent look-up table and linked lists.
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 controller performs a look-up cycle on the packet and then a learning cycle.
During the learning cycle, an identification of the source port for the packet is stored in the learned look-up tables in association with a node address of the source node. Each entry is stored at a location in the learned look-up tables identified by hashing the node address. If an entry in the look-up table already exists at the hashed node address, the entry is examined to determine if the appropriate port identification is stored and to determine whether two or more nodes share a same hashed node address. If the port identification is inappropriate, it is corrected. If two nodes have the same hashed node address, then a linked entry in the linked lists is formed to appropriately identify which port is associated with each of the two nodes.
The multi-port bridge preferably implements a virtual local area network (VLAN) when the switch engine is configured in a VLAN mode. The VLAN mode allows nodes of a LAN to be arranged in VLAN groups. For example, a VLAN group can include all the workstations in a particular department of an organization. Information indicative of which nodes of the LAN are arranged into each VLAN (group is stored in the permanent tables of the memory device.
During the look-up cycle, the packet is examined to determine whether the packet is intende

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