LLDP Extension for Optimal End-to-End Optical Network Performance
Oct 21, 2017
In a linear optical network that contains multiple optical nodes, it is an operational goal to optimize the end-to-end optical network performance, measured by the receiving node’s optical BER (Bit Error Rate). And as time goes on, the receiving node’s BER can drift, due to factors such as the sending node’s transmitting optical power drifting, ambient temperature variation, equipment aging, etc. While some factors are difficult to control, such as ambient temperature variation and equipment aging, the sending node’s transmitting optical power is easily controllable and can be adjusted to compensate for the BER drifting due to other factors. So if we can continuously monitor the receiving node’s real-time BER, provide feedback to the sending node, and adjust the sending node’s transmitting optical power as needed, we can obtain the optimal end-to-end optical network performance.
The following diagram shows the relationship between the receiving node’s optical BER and the sending node’s transmitting optical power. There is a sweet spot at which the minimum BER is achieved.
This next diagram illustrates an optical network. Nodes 1 and 5 are integrated photonic line cards on two PTX chassis. Nodes 2, 3, and 4 represent inline optical amplifiers. They don’t terminate the optical signal. Their purpose is to amplify the optical signal so that the optical signal can travel longer distance between node 1 and node 5. Nodes 1 through to 5 are connected through bi-directional optical fibers. They terminate the OSC (Optical Supervisory Channel) between every node.
If node 1 knows node 5’s BER in a real-time fashion, it can continuously adjust its transmitting optical signal power to get the minimum BER on node 5; similarly, in the reverse direction, if node 5 knows node 1’s BER, it can adjust its transmitting optical signal power and get the minimum BER on node 1.
How can this be done? Puneet Jain, Domenico Di Mola, and I came up with an innovation that achieves this goal in an elegant way:
All nodes in the network run the LLDP (Link Layer Discovery Protocol). The LLDP application on each node periodically sends LLDP packets to its immediate neighbors through the OSC OC3 data path, which is terminated between each node. Each node’s application will extract the LLDP packets from the OSC OC3 data path and read/process the LLDP payloads.
On top of the basic/standard LLDP TLVs (Type-Length-Value), an extension is made to the LLDP by adding organizationally specific TLVs to LLDP payloads. The newly added organizationally-specific TLVs contain BER.
If a node doesn’t have a cross-connect (such as node 1 and node 5), it will insert its own BER in its outgoing LLDP TLVs. If a node has a cross-connect (such as nodes 2, 3, and 4), it will take its cross-connect’s BER in the incoming LLDP TLVs and send them to the downstream node in its outgoing LLDP TLVs. In the above case, node 1 (no cross-connect) will send its BER to node 2, node 2 (with cross-connect) will send node 1’s BER to node 3, and so on, and eventually, node 5 will receive node 1’s BER. Same happens in the reverse direction: node 1 will receive node 5’s BER.
After node 1 gets node 5’s BER, node 1 can use the BER as feedback to adjust its transmitting optical power and achieve the best network performance; similarly, node 5 can use node 1’s BER as feedback to adjust its transmitting optical power and achieve optimal performance.
LLDP sends LLDP packets periodically. So the end nodes steadily and continuously receive the other ends’ BER. This end-to-end optical network performance optimization is an ongoing process.
Besides BER, other optical control information, such as received optical power readings, can also be added to the LLDP’s organizationally specific TLVs for other control purposes.
This invention is a beautiful way to achieve the optimal end-to-end optical network performance, as LLDP is a simple and light-weighted protocol, and is already supported in Junos. It blends packet network (LLDP with extension) with optical network (OSC OC3 data path) very nicely. Moreover, it has been granted as a US patent:
U.S. Patent No. 9,755,956
Filing Date: November 16, 2015
Issue Date: September 05, 2017
Title: SIGNAL CHARACTERISTIC INFORMATION FOR NETWORKS
Inventor(s): Dai Song (firstname.lastname@example.org), Domenico Di Mola (email@example.com), Puneet Jain (firstname.lastname@example.org).