Multiplex communications – Channel assignment techniques – Arbitration for access to a channel
Reexamination Certificate
1998-05-01
2001-10-02
Cangialosi, Salvatore (Department: 2661)
Multiplex communications
Channel assignment techniques
Arbitration for access to a channel
C370S447000
Reexamination Certificate
active
06298067
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to arbitration between ports on a network, and in particular to methods and systems for arbitrating between ports on a hub.
2. Description of Related Art
Computer networks are called upon to handle increasingly higher speeds of data transmission. Computer networks often involve numerous end stations coupled together in a hub for communication with each other. Such hubs may represent a bottleneck for efficiency in transmission between the various end stations or other elements of the network. A hub often includes a number of ports, which are coupled to the end stations or other devices in the computer network. Ports are then coupled to other ports via a bus within the hub. Some hubs used in computer networks are repeating hubs and others are switching hubs.
Within the hub, ports must transmit and receive onto the common bus. Conflicts may occur when the various ports attempt to simultaneously transmit from the same bus. One system for resolving conflicts between entities sharing a common transmission medium is the carrier sensed multiple access with collision detect (CSMA-CD) scheme. Under such a scheme, entities attempting to transmit over the shared medium attempt to transmit over the medium and if a conflict occurs then the entities do not transmit at that time. Such a scheme may involve inefficiencies in the use of the transmission medium. More efficient and robust systems for sharing media such as a bus within a hub are needed.
As computer networks increase in speed, components within network devices may be called upon to operate at higher speeds. Clocks for controlling operation of such high speed components are important. However, physical limitations of a bus may prevent the bus from running at a desired clock speed.
SUMMARY
The invention includes a distributed arbitration scheme for an internal bus network device. Ports in a network device determine which port in a set of ports may broadcast a packet onto a bus in the network device. An embodiment of the invention is a method of transmitting data between a set of ports sharing a bus in hub. The set of ports includes a first port, and the method comprises the first port receiving a packet, the first port requesting the bus, and, if another port is requesting the bus, the first port transmitting the packet to the bus if the first port has not transmitted a packet later than the another port requesting the bus.
According to an aspect of the invention, the first port transmits based on port numbers of respective ports requesting the bus. According to another aspect of the invention, the first port does not transmit if another port requesting the bus has a lower port number. According to another aspect of the invention, the first port transmits based on whether a buffer coupled to another port is full.
According to various embodiments of the invention, the hub comprises a fiber module or the hub comprises a 100 base SX module.
An embodiment of the invention includes a method of transmitting data between a set of ports sharing a bus in an Ethernet hub. The set of ports including a first port. The first port enters a first state if the first port has received the packet and the first port wins an arbitration with other ports requesting the bus. The packet is transmitted after the first port has entered the first state. The port exits the first state, and after exiting the first state, enters a wait state and remains in the wait state until no other port is requesting the bus.
An aspect of the invention includes entering a second wait state if the first port does not win the arbitration. A further aspect of the invention includes exiting the second wait state after a particular time interval.
An embodiment of the invention includes an Ethernet hub. The hub includes a plurality of ports coupled to a bus. Respective ports have logic that, if a port has received a packet and the port has not transmitted a packet during the current cycle, causes the port to request the bus and transmit the packet if the port wins an arbitration with other ports in the plurality of ports requesting the bus. According to an aspect of the invention, the current cycle ends when no port is requesting the bus.
According to an aspect of the invention a plurality of buffers is coupled to respective ports, and the hub includes logic to cause the port to not transmit the packet if a buffer among the respective buffers is full.
According to an aspect of the invention, the hub includes respective lines coupled to respective ports and requesting the bus comprises driving a respective line. According to another aspect of the invention, respective ports include logic to detect the states of the lines to determine whether the respective ports win the arbitration.
The plurality of ports comprises 8 ports according to an aspect of the invention, and ports in the plurality of ports comprise application specific integrated circuits (ASICs) according to another aspect of the invention.
REFERENCES:
patent: 4560985 (1985-12-01), Strecker et al.
patent: 5519837 (1996-05-01), Tran
patent: 5905877 (1999-05-01), Guthrie et al.
patent: 6061360 (2000-05-01), Miller et al.
IEEE Draft P802.3z/D2, “Media Access Control (MAC) Parameters, Physical Layer, Repeater and Management Parameters for 1000 Mb/s Operation”, LAN MAN Standards Committee of the IEEE Computer Society, IEEE, New York, Feb. 19, 1997.
3 Com Corporation
Cangialosi Salvatore
McDonnell & Boehnen Hulbert & Berghoff
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