Cascade control system for network units
View Patent ↗Cascade control logic for use in a switch or other network unit that can be used in a cascaded stack can maintain normally a point-to-point half-duplex connection for control data with each of the next preceding and next succeeding units in the cascade. Each cascade logic device is organised so that for one direction, conveniently called the up direction, a device is a master and in the other direction the device is a slave in respect of the control path. A control device will generate master control frames in the up direction and deliver slave control frames in the down direction. The control device is organised so that in the absence of reception of valid control frames on a control link control data which would otherwise be sent out on that link is looped back within the control device. In this manner the control device can maintain under normal circumstances two virtual control channels which can ‘self-heal’ notwithstanding the failure or powering-down of a unit in the cascade. Status information represented by the control frames can be used to control a switching engine to provide self healing of the data path in the cascade.
1. A control device for transmitting and receiving control frames of status and control data for a cascaded stack of network units coupled by a data path for addressed data packets, comprising:
means for transmitting control frames and receiving control frames at a first port, said control frames each including control data;
means for receiving and transmitting control frames at a second port, said first and second ports defining a control path separate from said data path;
means for detecting absence of valid control frames at the first port to cause loopback of control data intended for the first port to provide control frames forwarded from the second port;
means for detecting absence of valid control frames at the second port to cause loop-back of control data intended for the second port to provide control frames forwarded from said first port;
first storage means for storing data from control frames received at said second port and for providing data for control frames forwarded from the first port, wherein the first storage means comprises a first set of storage registers for data from control frames received at the second port and a second set of storage registers for providing control data for control frames forwarded from the first port;
second storage means for storing control data from control frames receiving at said first port and for providing control data for control frames forwarded from said second port, the second storage means comprises a third set of registers for control data received from control frames at the first port; wherein the second set of registers and the first port are selectively coupled to the third set of storage registers and the third set of storage registers and the second port are selectively coupled to the first set of storage registers; and wherein
the loop-back of control data intended for the first port extends from the first storage means to the second storage means and the loop-back of control data intended for the second port extends from the second storage means to the first storage means.
2. A stack of networks 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 data packets to direct data packets received by the network unit to at least one of the ports;
at least one cascade data path for the transmission of addressed 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 separate from said data 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;
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; and
wherein each network unit has at least two cascade ports and each unit is responsive to control data from said control messages to control the switching engine to redirect data packets otherwise intended for one cascade port of the network unit to a different cascade port of the same network unit.