Patent ID: 7167441

Claim:
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.