Link discovery, verification, and failure isolation in an optical communication system

1. A method for determining unknown optical communication links between two adjacent network elements in an optical communication system, each network element comprising a number of transmit interfaces and a number of receive interfaces, the method comprising:

generating an optical signal at a first one of the network elements, the optical signal being transmitted over one of its transmit interfaces;

receiving the optical signal at one of:

a receive interface of a second one of the network elements; and

a receive interface of said first one of the network elements; and

detecting an established, but previously unknown, optical communication link between a transmit interface of the first one of the network elements and the receive interface of the second one of the network elements and a corresponding optical communication link between a transmit interface of the second one of the network elements and the receive interface of the first one of the network elements based upon at least the received optical signal,

wherein the optical signal comprises an identity pattern that uniquely identifies a transmit port of the first one of the network elements, and

wherein detecting the established, but previously unknown, optical communication link between the transmit interface of the first one of the network elements and the receive interface of the second one of the network elements comprises:

recovering the identity pattern from the received optical signal; and

detecting the established, but previously unknown, optical communication link based upon the recovered identity pattern,

wherein detecting the established, but previously unknown, optical communication link based upon the recovered identity pattern comprises:

obtaining a table that maps each of a number of identity patterns to a corresponding transmit interface of the first one of the network elements; and

determining from the table that the recovered identity pattern maps to the transmit interface of the first one of the network elements, and

wherein the table further maps each identity pattern and corresponding transmit interface of the first one of the network elements to a corresponding receive interface of the first one of the network elements, and wherein detecting the established, but previously unknown, optical communication link between the transmit interface of the second one of the network elements and the receive interface of the first one of the network elements comprises:

inferring the established, but previously unknown, optical communication link from the mapping in the table.

2. The method of claim 1 , wherein the optical signal comprises at least one of:

a sustained light on condition;

a sustained light off condition;

a plurality of successive light on and light off conditions that vary according to a predetermined pattern;

an optical signal that is modulated according to a predetermined data sequence;

an optical signal that is modulated according to a pilot tone;

an optical signal at an unused wavelength;

amplified spontaneous emission noise;

an alarm signal; and

an optical signal that produces an invalid received signal at the receive interface.

3. The method of claim 1 , wherein generating the optical signal at the first one of the network elements comprises:

instructing the first one of the network elements to generate the optical signal by the second one of the network elements using a predetermined protocol.

4. The method of claim 1 , wherein generating the optical signal at the first one of the network elements comprises:

allocating a test transmitter; and

crossconnecting the test transmitter to the transmit interface of the first one of the network elements.

5. The method of claim 1 , wherein receiving the optical signal at the receive interface of the first one of the network elements comprises:

receiving the optical signal at the receive interface of the second one of the network elements; and

causing the optical signal to be looped back from the receive interface of the second one of the network elements to the transmit interface of the second one of the network elements.

6. The method of claim 1 , wherein receiving the optical signal at the receive interface of the first one of the network elements comprises:

allocating a test receiver; and

crossconnecting the test receiver to the receive interface of the first one of the network elements.

7. An optical communication system comprising:

a plurality of interconnected network elements, each network element comprising a number of transmit interfaces and a number of receive interfaces;

means for automatically discovering established, but previously unknown, optical communication links between adjacent network elements; and

means for verifying the optical communication links;

means for generating defect indications by a number of network elements in response to a failure;

means for receiving the defect indications by at least one photonic cross-connect device among the plurality of interconnected network elements; and

means for isolating the failure in the optical communication system based upon the defect indications received by the at least one photonic cross-connect device.

8. The optical communication system of claim 7 , wherein the means for automatically discovering established, but previously unknown, optical communication links between adjacent network elements comprises:

means for causing a first one of the network elements to generate an optical signal over one of its transmit interfaces;

means for causing the optical signal to be received at one of:

a receive interface of a second one of the network elements; and

a receive interface of said first one of the network elements; and

means for detecting an optical communication link between a transmit interface of the first one of the network elements and the receive interface of the second one of the network elements and a corresponding optical communication link between a transmit interface of the second one of the network elements and the receive interface of the first one of the network elements based upon at least the received optical signal.