Cascade control system for networks units

A stackable network unit including:

• a multiplicity of ports for receiving and forwarding data packets;
• and
• at least two cascade ports for the transmission of data packets to and from other units in a stack;
• control logic for forwarding control messages to and receiving control messages from the next succeeding and the next following units in the stack, said control messages including operational status information;
• and
• a switching engine for directing packets received at a port of said unit to at least one other port of said unit;
• wherein the unit is responsive to control data from said messages to control the switching engine to redirect data packets otherwise intended for one cascade port to a different cascade port.

A control device for transmitting and receiving control frames of status and control data for a cascaded stack of network units, comprising:

• means for transmitting control frames and receiving control frames at a first port;
• means for receiving and transmitting control frames at a second port;
• means for detecting absence of valid control frames at the first port to cause loop-back of data intended for the first port to provide control frames forwarded from the second port;
• and
• means for detecting absence of valid control frames at the second port to cause loop-back of data intended for the second port to provide control frames forwarded from said first port.

A stack of network units comprising:

• a plurality of network units, each network unit including a multiplicity of ports including at least one cascade port for receiving and forwarding addressed data packets and a switching engine responsive to address data within packets to direct packets received by the network unit to at least one of the ports;
• at least one cascade data path for the transmission of address data packets between the network units, including at least one cascade port on each network unit and communication links which couple a cascade port of one network unit to a cascade port of the next network unit;
• a control device for each network unit, these control devices providing a control path for the transmission of control frames including control data between the network units, each control device comprising means for transmitting control frames to the control device of the adjacent succeeding network unit and receiving control frames therefrom and means for receiving control frames from the control device of the adjacent previous network unit and transmitting control frames thereto and means responsive to the absence of control frames from one or other of the adjacent network units to cause loop-back of control data instead of forwarding control frames to the respective adjacent network unit;
• and
• means responsive to control data from said control frames to alter the operation of the switching engine in respect of directing data packets to the cascade port.