Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-02-25
2002-12-31
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S412000, C370S429000, C370S452000, C709S251000, C710S004000, C710S052000, C710S120000, C711S202000
Reexamination Certificate
active
06501761
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to an expandable modular network switch for routing data between network stations.
2. Description of Related Art
Computer networks transfer data between computers or other types of network stations that are connected through buses to input/output (I/O) ports of a network hub or switch. A network hub is simply a repeater for receiving a data transmission at any of its I/O ports and for rebroadcasting the data transmission outward on all of its other I/O ports. Thus all network stations connected to a network hub receive all data transmissions sent to the hub. A header in each data transmission indicates the intended destination station for the data transmission, and on receiving a data transmission, each network station looks at the data transmission header to determine whether it should accept or ignore an incoming data transmission. Network hubs do not make efficient use of the bandwidth of network buses because most of the data transmission traffic a network station receives may be intended for another station.
A network switch also has I/O ports that may be connected to several network stations, but a network switch routes an incoming data transmission arriving at one I/O port only to the particular I/O port serving the network station that is to receive the data transmission. A network switch makes more efficient use of network bus bandwidth because each network station normally receives only the data transmission traffic directed to it, unless more than one station share the same switch I/O port. Since the data transmission header only indicates the destination station's network address, and does not indicate which I/O port serves the network station, the network switch must be able to translate between each network station's network address and address of the particular I/O port that serves the destination station. Network switches therefore typically include address translation units including lookup tables which convert network station addresses to I/O port addresses. Each data transmission header also includes the network address of the station sending the data transmission. Sophisticated network switches automatically learn each station's network address and build their address translation tables by reading the source address included in the header of each incoming data transmission and making note of the I/O port on which the data transmission arrived.
U.S. Pat. No. 5,754,791 entitled “Network Switch with Broadcast Support”, issued Jul. 21, 1998 to Dahlgren et al describes a network switch that allows a network station to broadcast a data transmission to all network stations. The broadcasting station sets the destination address included in the data transmission header to a particular “broadcast” address. The network switch receiving the data transmission responds to the broadcast address by broadcasting the data transmission outward on all I/O ports. Also, when an incoming data transmission is addressed to a network station having a network address that a network switch has not yet learned, the network switch may broadcast the data transmission outward from all of its I/O ports in the same manner as a network hub so that each network station can examine the data transmission header and accept it if it has the correct data transmission address.
Since a network switch has a limited number of I/O ports, it can serve only a limited number of network stations. However when some of the I/O ports of a network switch are linked to I/O ports of other network switches, they form a larger network switch that can serve a larger number of network stations. One problem with interconnecting smaller network switches to form a larger network switch arises when the smaller switches don't share their address translation information. While one network switch may have logged a particular network station's address logged into its address translation table, other network switches which have not yet received a data transmission from that particular network station may not have logged the network address into their address translation tables. When a network switch receives a data transmission directed to an unmapped network address, it doesn't know which I/O port is to forward the data transmission and therefore must broadcast that data transmission outward on all of its I/O ports. Since broadcasting a data transmission ties up system resources, it would be beneficial if the various network switches could share the address translation information that they acquire.
Some prior art systems a single, central address translation server linked by a parallel bus to all network switches for mapping network addresses to the ports. Whenever a switch receives a data transmission it consults the address translation server to determine how to route the data transmission and also provides the server with information it needs to map network addresses of new stations. A central address translation server system cuts down on the need for broadcasting data transmissions because address translation information gathered by all switches is shared by all other switches. But under high traffic conditions the bandwidth of the parallel bus interconnecting the address translation server to the various network switches or the operating speed of the server itself can limit network throughput as the various switches compete for access to the address translation server.
Another inefficiency associated with interconnecting multiple network switches is that each switch along the route of a data transmission through a set of interconnected switches has to retranslate the address. The time required to translation addresses several times can increase the total time required to route a data transmission through the switches.
What is needed is network switch architecture that allows multiple interconnected network switches to be easily interconnected, which allows the network switch to share address translation information without overloading a central address translation server, and which minimizes the number of times an address must be translated when routed through several interconnect network switches. In this way, multiple switches can be interconnected or “stacked” such that they act as a single large switch.
SUMMARY OF THE INVENTION
A modular network switch in accordance with the present invention routes data transmissions between a set of network stations, each network station having a unique network address. The switch includes a set of switch modules, with each module including a set of I/O ports, each I/O having a unique port ID. Each I/O port may be linked to a network bus for conveying data transmissions to and from one more of the network stations.
In accordance with one aspect of the invention, all network switch modules are interconnected in series by a ring bus to form a loop network of switch modules. The ring bus connection to each switch module includes a set of incoming data lines through which each switch module may receive data transmissions from a preceding module of the loop network and a set of outgoing data lines through which each switch module may forward data transmissions to a next module of the loop network.
In accordance with another aspect of the invention, the ring bus also includes a set of ID lines. When a switch module is added to the network switch, each port of that module assigns itself a unique port ID by communicating with ports of other modules via those ID lines bus to learn their port IDs and then assigning itself an unassigned port ID.
In accordance with a further aspect of the invention, each switch module includes its own address translation unit for mapping the network address of each said network station to a port ID of the I/O port to which the network station is linked. The switch module consults its own address translation unit to determine how to route data transmissions though the module. The address translation unit updates its address mapping w
Hemming Robert D.
Pannell Donald Robert
Bedell Daniel J.
Fairchild Semiconductor Corporation
Hsu Alpus H.
Smith-Hill and Bedell
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