Link monitoring and management in optical star networks

• US 5,515,361 A
• Filed: 02/24/1995
• Issued: 05/07/1996
• Est. Priority Date: 02/24/1995
• Status: Expired due to Term

• Current Assignee: Cisco Technology, Inc. (Cisco Systems, Inc.)
• Original Assignee: International Business Machines Corporation
• Inventors: Li, Chung-Sheng, Ramaswami, Rajiv
• Primary Examiner(s): Safourek, Benedict V.
• Assistant Examiner(s): Patel, Ajit
• Application Number:
  US08/393,966
• Time in Patent Office: 438 Days
• Field of Search: 370/14, 370/15, 370/16, 370/16.1, 370/60, 370/94.3, 359/121
• US Class Current: 370/222
• CPC Class Codes: H04L 12/44 Star or tree networks

Abstract

A method and apparatus for monitoring links in an optical star network along with means for taking down a link in the event of a failure without disruption to other parts of the network, bringing back the link into operation once the failure is corrected, while adhering to eye-safety regulations. More specifically, when one link of a pair of links connecting a station to a star coupler fails, the failure is detected by a monitor and the links of the pair are connected to each other by a switch. This connection of the two links provides a look from the transmitter of the station through the pair of links and to the receiver of the station. This connection also disconnects the station from the star network. When the pair of links again become operable, a signal is detected as passing from the transmitter through the loop and back to the receiver. Detection of the signal by the receiver then results in switching the pair of links back to the star coupler, thereby reconnecting the station to the star network.

Claims

1. In a star communications network having a star coupler, and a plurality of stations connected to said star coupler, each station being connected to said star coupler by a first and second link, a method of reconfiguring said network in response to failure or successful operation of said first or second link, said method for each station comprising:

a. monitoring said first and second link for first signals being transmitted thereon, said first and second link being monitored at said star coupler and at a receiver of said each station respectively, said first signals being transmitted from said star coupler or said each station;

b. disconnecting said first and second link from said star coupler and connecting them to each other when said first signals are not detected on said first or second link, forming a loop from a transmitter of said each station through said first and second link to a receiver of said each station; and

c. reconnecting said first and second link to said star coupler and disconnecting them from each other upon detection, by said receiver, of second selected signals being transmitted from said transmitter and through said loop, thereby reconnecting said station to said star communications network upon successful operation of said first and second link.

2. In a star communications network having a star coupler, a plurality of stations connected to said star coupler, each station being connected to said star coupler by a first and second link, an apparatus for reconfiguring said network in response to failure or successful operation of said first or second link, said apparatus for each station comprising:

a. means for monitoring said first and second link for first signals being transmitted thereon, said first and second link being monitored at said star coupler and at a receiver of said each station respectively, said first signals being transmitted from said star coupler or said each station;

b. means for disconnecting said first and second link from said star coupler and connecting them to each other when said first selected signals are not detected on said first or second link, thereby forming a loop from a transmitter of said each station through said first and second link to a receiver of said each station; and

c. means for reconnecting said first and second link to said star coupler and disconnecting them from each other upon detection, by said receiver, of second signals being transmitted from said transmitter and through said loop, thereby reconnecting said each station to said star communications network upon successful operation of said first and second link.

3. In a star communications network having a star coupler, and a plurality of stations connected to said star coupler, each station being connected to said star coupler by a first and second link, an apparatus for reconfiguring said network in response to failure or successful operation of said first or second link, said apparatus for each station comprising:

a. a monitor for monitoring said first and second link for the presence of first selected signals being transmitted thereon, said first and second link being monitored at said star coupler and at a receiver of said each station respectively, said first signals being transmitted from said star coupler or said each station; and

b. a switch for disconnecting said first and second link from said star coupler and connecting them to each other when said first selected signals are not detected by said monitor on said first or second link, thereby forming a loop from a transmitter of said each station through said first and second link to a receiver of said each station, said switch also reconnecting said first and second link to said star coupler and disconnecting them from each other upon detection, by said receiver, of second selected signals being transmitted from said transmitter and through said loop, thereby reconnecting said each station to said star communications network upon successful operation of said first and second link.

4. An automatically reconfigurable fault tolerant star communications network, comprising:

a. a shared medium device;

b. a plurality of stations;

c. a plurality of links;

d. a plurality of monitors, each monitor being connected to an end of said links for detecting the presence of signals being transmitted on at least said one link; and

e. a plurality of loopback switches, each loopback switch being connected to one of said monitors and a pair of said links, which pair is connected to one of said stations,

wherein said each loopback switch interconnects a said pair of links connected to itself when its connected monitor, of said monitors, detects no first selected signals, of said signals, being transmitted on said pair of links, thereby disconnecting said each station, of said stations from said shared medium device when either link of said pair has failed, and

wherein said each loopback switch reconnects said pair of links to said shared medium device when its monitor detects second selected signals of said signals being transmitted on latter said pair of links, thereby reconnecting a station, of said stations, to said shared medium device when latter said pair are operating successfully.