Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
2000-02-29
2003-12-02
Ton, Dang (Department: 2661)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S438000, C370S460000
Reexamination Certificate
active
06658016
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to packet switching fabrics for use in data communications networks. Specifically, the present invention pertains to a packet switching fabric having a plurality of switching devices arranged in a ring topology and operating in accordance with an output queuing controlled packet transfer protocol.
DESCRIPTION OF THE PRIOR ART
Switching devices are essential components of data communication networks including local area networks (LANs), such as ETHERNET, and wide area networks (WANs). Common switching devices include cross bar switching devices, and packet switching fabrics. A packet switching fabric is an interconnection architecture which uses multiple stages of switches to route transactions between a source address and a destination address of a data communications network. A packet switching fabric may have a variety of different architectures, or topologies.
Cross bar switching devices typically include a plurality of N input ports, a plurality of N output ports, and a switching matrix having redundant interconnection resources requiring a complexity of N×N for selectively connecting the input ports to the output ports. One problem with cross bar switching devices is achieving scalability of the number of network ports. Because of the N×N complexity of the interconnection resources, exponential costs are incurred when increasing the number of network ports of a cross bar switching device.
Because packet switching fabrics include multiple switching devices, fabrics provide better scalability than crossbar switches because each of the switching devices of the fabric includes a plurality of network ports, and the number of switching devices of the fabric may be increased in order to increase the number of network connections for the switch. However, prior art packet switching fabrics usually have a bus topology including a back plane, or bus, having a plurality of slots for cards including the network ports. One problem with such switching devices is modularity. While a number of cards having additional network ports may be inserted into slots of the back plane to increase the total number of network ports, the maximum number of cards which may be added is limited because the back plane may support only a limited number of cards due to loading effects on the back plane. Therefore, the modularity problem of bus architecture packet switching fabrics imposes a limit on the scalability of the number of network ports of the fabric.
Typically, each device of a switching fabric includes a plurality of switching devices each including: network ports for transmitting and receiving data packets to and from network nodes via network communication links; and internal data link ports for transmitting and receiving data packets to and from other switch devices of the fabric. The switching devices of a switching fabric may be configured in any one of a variety of topologies, or architectures. In a switching fabric having a ring architecture, the devices are configured in a ring topology. Because each connection in a ring architecture switching fabric is a point to point link, ring architecture switching fabrics allow for higher frequencies and greater throughput between devices than bus architecture fabrics.
Typical prior art ring architecture switching fabrics are controlled by a token ring protocol wherein only one device of the ring transmits data at a time. Therefore, prior art ring architecture switching fabrics are not commonly used for network switching which requires high data throughput. An important objective of the present invention is to provide a ring architecture packet switching fabric which is capable of concurrently processing an increased number of packet transfer operations between a large number of source network nodes and corresponding destination network nodes, thereby allowing for greater switching throughput.
Each switching device of a switching fabric reads header information of a data packet, received from a source node via one of its network ports, in order to dynamically route the data packet to an appropriate destination network port, or ports, which is communicatively to a destination node specified by a destination address carried in the header information of the data packet. The destination network port may be a local network port of the same switching device, having the source port at which the packet is received, or maybe a network port of another switching device of the fabric. The process of transferring a data packet received at a network port of a source device to a network port of a destination device is referred to herein as a packet transfer operation. In order to transfer data from a source device to a destination device, an internal source-destination channel path coupling the source port to the destination port is required.
In many data communications networks, and particularly in local area networks, (e.g., ETHERNET), when a destination node of the network begins receiving a data packet, the transmission of the data packet to that node cannot be interrupted, even by transmission of an idle signal. Therefore, transmission of a data packet from a destination output port of a switching fabric to a corresponding destination node must not be interrupted. Therefore, most switching fabrics include transmit buffers at each network port which are large enough to store a whole packet of data. However, this is undesirable because the use of large buffers limits the number of network ports which can be implemented on an integrated circuit chip.
Another objective of the present invention is to provide a ring architecture packet switching fabric wherein each integrated circuit switching device of the fabric has higher integration thereby allowing for an increased number of network ports.
A further objective of the present invention is to provide a packet switching fabric providing convenient scalability wherein the total number of network ports supported by the fabric may be scaled up without incurring exponential costs such as in cross bar switching devices.
Yet another objective of the present invention is to provide a packet switching fabric which provides higher data transfer rates via source-destination channel paths established between switching devices of the fabric thereby allowing for cut-through packet transfer between a source device and a corresponding destination port. Achieving this objective of the present invention also provides a packet switching fabric wherein each switching device of the fabric has an increased number of ports.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a ring architecture packet switching fabric wherein each integrated circuit switching device of the fabric has higher integration thereby allowing for an increased number of network ports.
Another object of the present invention is to provide a packet switching fabric providing convenient scalability wherein the total number of network ports supported by the fabric may be scaled up without incurring exponential costs such as in cross bar switching devices.
A further object of the present invention is to provide a packet switching fabric which provides higher data transfer rates via source-destination channel paths established between switching devices of the fabric thereby allowing for cut-through packet transfer between a source device and a corresponding destination port.
Yet another object of the present invention is to provide a packet switching fabric which provides reduced delays in packet transfer operations, and therefore faster switching.
Briefly, a presently preferred embodiment of the present invention comprises a packet switching fabric including means forming a data ring, means forming a control ring, and means forming a plurality of data communication network links each having at least one network node coupled thereto. The packet switching fabric further includes a plurality of output queuing controlled switching devices coupled together by the dat
Chao Jason
Dai William
Liu Yao-Ching
Broadcom Corporation
Phan Tri H.
Ton Dang
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