Topology discovery in a dual ring network

In a telecommunications network with a ring-oriented configuration, a method of communicating network topology information among a plurality of stations on a pair of counter rotating ringlets, a respective said station having a first neighboring station in a first direction and a second neighboring station in a second direction, comprising the steps of:

• (a) sending from said respective station connected on said network, discovery messages on both ringlets to said first neighboring station in said first direction and second neighboring stations in said second direction, the discovery messages including an existing topology database stored in said respective station, said topology databases providing address and connectivity information pertaining to the stations in said network;
• and
• (b) receiving at said respective station discovery messages on both ringlets from said first and second neighboring stations without forwarding the discovery messages to stations beyond said first and second neighboring stations, the discovery messages containing topology databases stored in said first and second neighboring stations;
• (c) repeating the above steps to complete a current topology image of the network at said respective station and at each station connected in said network,
• wherein said discovery messages are sent at a predetermined timer setting Td, and wherein said address information for a station includes a unique address in said network which is a combination of the addresses of said station on both counter rotating ringlets, and
• wherein the topology image is completed once a node placed at about ½ of the ring length from said respective station receives messages containing topology information on said respective station in both said first and second directions.

In a dual ring network comprising a plurality of stations, each station connected to first and second adjacent stations by a respective pair of receive and transmit links, thereby forming first and second counter-rotating ringlets, a method of determining the topology of the network, comprising the steps of:

• (a) sending, by each operative station in the network, a first discovery message only to said first adjacent station and a second discovery message only to said second adjacent station, said discovery messages being exchanged only with said adjacent stations without forwarding the discovery messages to stations beyond said first and second adjacent stations, wherein the discovery message includes an address of the station and a status indication of the links connected to the adjacent stations;
• (b) receiving, at each station, the first and second discovery messages of its two adjacent stations;
• (c) updating, at each station from the received first and second discovery messages, the status of links connected to the adjacent stations;
• (d) sending, by each operative station, a new discovery message that includes the updated status of the links to the adjacent stations, the addresses of the adjacent stations, and any other link status or address information in the received discovery messages;
• and
• (e) repeating steps (b) to (d), until an address of a station appears twice in a discovery message, the discovery message thereby comprising the addresses and link status of all the operative stations in the network, and wherein a topology image is completed once a node placed at about ½ of the ring length from said respective station receives messages in said first and second directions containing topology information on said respective station.

In a network with a ring-oriented topology which comprises a plurality of stations linked by a first ringlet transporting traffic in one direction and a second ringlet transporting traffic in the opposite direction, a respective station comprising:

• a first interface (RxI, TxO) for transmitting traffic over the second ringlet and receiving traffic from the first ringlet;
• a second interface (RxO, TxI) for transmitting traffic over the first ringlet and receiving traffic from the second ringlet;
• a local interface for adding and dropping traffic to and from the first and second ringlets;
• a database memory for storing a topology image of the network, and
• a controller for regulating the transmission and reception of a variety of control messages onto and from the inner and outer ringlets,
• wherein said respective station is uniquely identified on said network using a combination of the addresses of said first and second interfaces, said respective station exchanging a first message only with a first neighboring station in a first direction and a second message only with a second neighboring station in a second direction, said first and second messages being exchanged without forwarding the discovery messages to stations beyond said first and second neighboring stations, and wherein a topology image of the network includes address and connectivity information for all stations connected in said network, and wherein said topology image is completed once a node placed at about ½ of the ring length from said respective station receives messages in both said first and second directions containing topology information on said respective station.