Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-08-04
2004-07-13
Kizou, Hassan (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S369000
Reexamination Certificate
active
06763030
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to the field of digital communications. More particularly, this invention relates to switching hubs for high speed local area networks.
2. Background
Ethernet is a specific implementation of what is generally referred to as a Carrier Sense Multiple Access/Collision Detection (CSMA/CD) protocol. In accordance with such protocols, only a single station is permitted to have access to the medium at any one time. A procedure is specified to resolve conflicts resulting from concurrent access attempts by multiple sources. For Ethernet, the details of this protocol are defined by the IEEE 802.3 specification.
A typical prior local area network is comprised of a set of communication agents coupled to a common communication medium. For example, an Ethernet local area network comprises a set of Ethernet compatible communication agents coupled to a coaxial, twisted pair, or fiber optics cable as a communication medium. In such systems a communication transaction between any two of the communication agents typically prevents communication among the other communication agents during the communication transaction.
One prior method for increasing the capacity of a local area network is to employ bridge circuits. Prior art bridge circuits typically couple together segments of local area networks. Typically, each segment comprises a set of communication agents coupled to a communication medium. A bridge circuit enables communication between each of the communication mediums.
Such prior are bridge circuits typically listen for communication messages on each of the communication mediums and propagate the appropriate communication messages to the other communication medium according to the network configuration. Communication messages are commonly referred to as communication frames.
Such a prior are bridge circuit typically buffers communication frames that require propagation to another communication medium. Thereafter, the bridge circuit forwards the buffered communication frames to the appropriate destination communication agents. Unfortunately, such buffering and forwarding of communication frames between communication mediums of the local area network increases the overall latency in the communication network.
Another prior art method for increasing the capacity of a local area network is to employ a switched hub circuit. A switched hub circuit is typically arranged in a “star” configuration wherein each segment of the local area network coupled to a unique serial communication port of the switched hub circuit. The switched hub circuit typically senses incoming communication frames, determines the destinations of the incoming frames, and switches the incoming communication frames to the appropriate outbound transmission paths.
Such switched hub circuits typically allow parallel data transfer between ports as long as the data transfer paths do not conflict.
Unfortunately, the switching functions performed by such prior art switched hub circuits are complicated by certain types of communication traffic. For example, if more than one communication agent attempts to transmit to the same communication agent, the switched hub circuit must select one of the transmissions and delay the other transmissions. The delayed transmissions increase the latency in the network.
In addition, broadcast transmissions and multicast transmissions require a switched hub circuit to switch a single incoming communication frame to multiple destination communication agents even though conflicting traffic may be under way to the destination communication agents. The multicast transmissions typically conflict with other transmissions, thereby increasing delays in the network.
The data transmitted in the network physical medium is in a serial form. However in most switched hubs the data is transformed (demultiplexed) to a slower multi-bit parallel format. This conversion is necessary to enable storage of the data in memory devices in the standard format of bytes and words. This conversion is also required in order to match the data rate to the read/write speed of memories and other processing devices. For this purpose and particularly when the serial data rate is 100 megabit/sec or above, the data is converted to a 32 or even 64 bits parallel format.
In most prior switched hubs the inbound data is stored, at least temporarily, in the receiving memory. This data is then transferred to the destination port circuitry for processing and subsequent transmission. The data transfer either involves a plurality of data buses and a switching mechanism between these buses, or a common bus shared by all port circuits. A typical prior art switched hub is shown in FIG.
1
. In such a prior art switched hub, network segments b
1
-n are each coupled to a corresponding packet processing unit (PPU)
3
which in turn are coupled to cross bar switching matrix
1
. Each PPU includes a transmitter
8
, a receiver
9
, a media access controller
10
, a multiplexor
13
a
and a demultiplexor
13
b.
OBJECTS OF THE INVENTION
One object of the present invention is to provide a switching hub for a high speed communication network, especially Fast Ethernet and Gigabit Ethernet. Another object of the present invention is to provide a switching hub for a communication network that resolves conflicts among inbound communication frame that specify the same destination, thereby preventing collisions in the network.
Another object of the present invention is to provide a switching hub for a communication network that performs broadcast and/or multicast operations while avoiding collisions with conflicting communication traffic. Another object of the present invention is to provide a switching hub for a communication network that provides a flexibility in the switching hub makeup and enables system sizing and type alteration by means of replacing modules connected to a common motherboard.
These and other objects of the invention are provided by a communication system including a switched hub circuit that transfers incoming communication frames via a set of serial communication links. The switched hub circuit stores the incoming communication frames into a set of memory buffers that supply a set of outbound communication frames for transfer over the serial communication links. The switched hub circuit includes the means to decipher the destination of each message and a crossbar type switching matrix in the outbound physical layer to route the outbound transmission to the desired destination.
Other objects, features and advantages of the present invention will be apparent from the accompanying drawings, and from the detailed description that follows below.
SUMMARY OF THE INVENTION
In general, in one aspect, the invention features an apparatus for interconnecting N network segments each of which operates in accordance with a defined bus protocol such as IEEE 802.3 or similar protocols. The apparatus includes N physical interfaces to network segments, N Packet Processing Units (PPUs)
23
, a Routing Controller (RC)
21
, a Switching Matrix (SM)
1
, an Address Management Unit (AMU)
17
and a Packet Broadcast Controller
20
, as illustrated in FIG.
2
. The input from each of the N network segments
6
connects to the input port of the corresponding Packet Processing Unit
23
. The output port of each of the Packet Processing Units connects to a corresponding input in the Switching Matrix. The outbound line of each of the network segments connects to the corresponding output in the Switching Matrix. The Address Management Unit
17
and the Routing Controller
21
connect to all the Packet Processing Units via a multi-bit parallel bus
4
. The Routing Controller connects to the switching matrix
1
and controls its operation.
Each Packet Processing Unit receives packets from the network segment
6
, decodes the packet's source and destination addresses, and forwards this information to the Address Management Unit. When instructed by the Routing Controller
21
, the Packe
Regev Alon
Regev Zvi
Dickstein , Shapiro, Morin & Oshinsky, LLP
Kizou Hassan
Micro)n Technology, Inc.
Pezzlo John
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