Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-03-19
2004-05-18
Nguyen, Chau (Department: 2663)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S401000
Reexamination Certificate
active
06738384
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 technique for optimizing cut-through for broadcast and multi-cast data packets in a multi-port bridge for a local area network.
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
.
A broadcast packet is one that is intended by its originating node to be received by every other node of the LAN. Accordingly, when the multi-port bridge
10
receives a broadcast packet, the packet is directed to all ports of the multi-port bridge
10
. An example of a broadcast packet is a “keep alive” packet. In accordance with the IEEE 802.3 standard, each node periodically broadcasts a “keep alive” packet which informs the other nodes of the LAN of the continued presence of the sending node in the LAN.
A multi-cast packet is one that is intended to be received by each of a selected group of nodes of a LAN. For example, a virtual LAN (VLAN) may include a subset of nodes of a larger LAN. When a node included in the VLAN group sends a packet, the packet can be multi-cast to each other member of the VLAN group. Typically, a multi-cast packet is identified when the first bit of its destination address is a logical one. The source address of a multi-cast packet identifies the originating node which can then be utilized to identify the VLAN group of which the originating node is a member.
A uni-cast packet is one which is intended to be received by a single destination node. Typically, a uni-cast packet is identified by the first bit of the destination address for the packet being a logical zero. The destination node for the uni-cast packet is identified by the remaining bits of the destination address included in the packet.
Because “keep alive” packets are sent throughout the LAN with regularity, the multi-port bridge
10
tends to devote a significant portion of its packet handling capacity to forwarding of such “keep alive” packets. This reduces the ability of the multi-port bridge
10
to forward other packets to their intended destinations. Thus, problems can arise 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 operation and a look-up operation 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. What is further needed is a technique for reducing the demand placed on such a multi-port bridge for forwarding broadcast and multi-cast data packets.
SUMMARY OF THE INVENTION
The invention is a technique for optimizing cut-through for broadcast and multi-cast data packets in a multi-port bridge for a local area network (LAN). The multi-port bridge includes a plurality of ports which are each coupled to a data bus. Packet buffers are also coupled to the data bus for temporarily storing data packets undergoing transfer between the ports. A source port for a data packet receives the packet from a segment of the LAN associated with the source port and stores it in the packet buffers. A packet stored in the packet buffers can be retrieved by an appropriate destination port for the packet and loaded into a first-in, first-out transmit packet store included in the destination port. As the packet is being loaded into the transmit packet store, the packet is transmitted to the segment of the LAN associated with the destination port. A packet can also be received by the destination port directly from the source port while the source port is storing the packet in the packet buffers, assuming the transmit packet store of the destination port is not currently occupied by another packet being transmitted by the destination port.
A broadcast packet store is also provided in the destination port for receiving broadcast and multi-cast data packets directly from the source port while the source port is storing such a broadcast or multi-cast packet in the packet buffers, even when the destination port is busy transmitting a prior packet. The broadcast or multi-cast packet can then be transmitted to the segment of the LAN associated with the destination port when the destination port completes transmitting the prior packet.
A broadcast packet controller included in the destination port is normally dormant and becomes active when the following conditions are present: (1) the destination port is currently busy transmitting another packet; (2) a broadcast or multi-cast packet is received by another port; and (3) the broadcast packet store of the destination port is empty. When these conditions are all present, the broadcast packet controller stores the broadcast or multi-cast packet in t,he broadcast packet store when the packet appears on the data bus while it is being stored in the packet buffers by the source port. In addition, the broadcast packet controller conditions the destination port to transmit the packet from the broadcast packet store when the port becomes available to transmit the packet.
Because each broadcast and multi
George Keith M.
Haverstock & Owens LLP
Nguyen Chau
Sony Corporation
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