Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-12-09
2001-12-11
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S449000, C370S452000, C370S455000, C709S251000
Reexamination Certificate
active
06330245
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to stackable hubs for packet-switched communication systems, particularly ‘Ethernet’ systems. Stackable hubs are composed of a selectable plurality of hub units which can be connected together to form, functionally, a single hub.
BACKGROUND OF THE INVENTION
It is known to connect hubs in a closed system to enable a user to be connected to any unit in the stack and to enable the stack to be managed as a single logical entity. It is necessary to provide some means of arbitration between requests by the units for access to the ring. It is known to provide a ring communication system in which a unit having data to transmit monitors frames circulating on the ring and if a token bit in a frame header indicates that the token is ‘free’ the unit may transmit and also set the token bit so that other units may not transmit while the unit that has set the token still has ‘possession’ of the ring. A system of this nature can include a priority indication which prevents the issue of a free token. This inhibition is chiefly intended to allow synchronous data packets to take precedence over asynchronous data packets, as described in U.S. Pat. No. 4,482,999.
BRIEF SUMMARY OF THE INVENTION
The present invention is based on a ring arbitration system in which the arbitration signals, particularly requests for the grant of access, grants of access and indications of priority are inserted in a packet header (particularly an Ethernet packet header) in place of preamble fields in the packet. The system, which preferably includes requests for access and grants for a multiplicity of priority levels and will be described in greater detail below, is capable of providing a fair arbitration for a multiplicity of priority levels for asynchronous data transfer. The system does not use a contentious technique such as collision detection and in its preferred form enables a high utilisation of available bandwidth.
In a preferred form of the invention, a data network hub unit is stackable with other such units, to constitute a hub in which each of the units can supply data packets to network data destinations and receive data packets from network data sources, and to form a closed data transmission ring, which enables packets received at any unit to be transmitted from any other unit. The hub unit includes arbitration control means responsive to packet headers circulating on said ring and the arbitration control means is operative.
(i) when the hub unit acts a master unit to supply data packets, to modify data packets to provide them each with an arbitration header which includes a grant field, a request priority field, capable of indicating various different level of priority, and a grant priority field,
(ii) when the hub unit is acting as the master unit and has no more data packets to supply to the ring to respond to an arbitration header which has a set priority field by settling the grant field and setting the grant priority field;
(iii) when the hub unit is not the master unit but has data packets to place on the ring, to respond to arbitration headers by setting a request in a request priority field; and
(iv) when the hub unit is not the master unit but has data packets to send, to respond to an arbitration header which has the grant field set and a grant priority field indicating a priority level correspondingly to the priority requested by this unit to become the master unit.
Various features of the invention will be apparent from the following description of a detailed example.
REFERENCES:
patent: 5053946 (1991-10-01), Jain
patent: 5070501 (1991-12-01), Shimizu
patent: 5274637 (1993-12-01), Sakamura
patent: 5784648 (1998-07-01), Duckwall
Brewer Steven
Stapleton Nicholas M.
Walker Christopher A.
3Com Technologies
Hsu Alpus H.
Nixon & Vanderhye P.C.
Qureshi Afsar M.
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