The key of Cool Optics’ solution is to switch off the communication during idle time. This seems easy. This is however not done today, because re-starting the network takes long synchronization time. Cool Optics found a solution for this issue.
The Cool Optics solution targets a significant improvement in energy consumption of data communication. This energy is mainly consumed in network IC’s (stack and transceiver).
In almost all network protocols for fast communication, the bits performing the protocol, flow continuously, regardless if there is actual data or idle periods. This is to maintain network synchronization, preventing re-starting of the network after each idle period, which costs a lot of resynchronization time. This means the data stack and the transceiver consume always full power. Most of the time, this is useless power, as most links have an average data load between 1 and 10%.
The FP7 EU project ADDAPT (“Adaptive Data and Power Aware Transceivers for Optical Communications”) has developed a basic concept of a transceiver, that can be switch off, and resynchronizes again within nanoseconds after having been switched on again. This enables considerable energy savings. This concept has no notion of data-protocols, and/or how to interpret them.
Cool Optics has extended the concept of the transceiver further into the network stack, particularly for the Ethernet protocol (it applies to a range of other protocols as well), leading to an integrated energy management solution, resulting in efficient usage of energy while maintaining low latency for the data stream.
The Cool Optics technology will work on the current standards like PAM-4 and NRZ.
Of course, additional savings can be achieved using the Cool Optics transceiver, with it unique fast synchronization capability.
Bit Error Rate (BER) is an important factor influencing latency in data communication. The present PAM-4 standards have a BER of approx. 10-5. This BER requires Forward Error Correction (FEC) which not only introduces appr. 100 nsec latency but also 40% more energy consumption and chip area compared to a solution without FEC.
The NRZ modulation standard may apply to some applications. The efficiency of data transport is lower than PAM-4, but on the other hand, the BER of the Cool Optics technology will be lower (10^-12 ) and therefore does not need an FEC, which saves as discussed above 100 nsec latency, and 40% energy and IC area. In both cases, the Cool Optics technology can be applied.
In the first place, due to this fast switching time (10 nsec), the system can be switched off during more time, thus achieving more energy savings. That in itself provides a great advantage over the existing EE solutions such as Deep Sleep and Fast wake. (see clause 78 in IEEE 802.3).
The results can be seen in the graph below, in which the relative differences between the solutions are depicted
Ref: ADDAPT 2017
The current load on communication lanes today is normally between 1 and 10%.
The Cool Optics solution will save up to 60% energy in the network stack, (typically 100 mW/Gbps), and brings a reduction of 20 mW/Gbps (typical) to potentially 1 mW/Gbps if the cool optics transceiver is also applied.
Alternative scenarios are the IEEE standards Fast Wake for optical fiber networks, and Deep Sleep for copper networks. With the Cool Optics Transceiver, a type of “Deep Sleep” can be achieved for optical networks.
Let us assume an average load of 10%. Below you will find a table about how the various technologies compare to each other.
The graph and table above depict the difference between the standardized EE solutions and Cool Optics’ solution.
In case of a standard transceiver the On-Off time is slightly better, but the savings slightly less, as the Transceiver is not switched off in that case.
The second USP is fast synchronization. In some cases, the prediction can start the synchronization, before the actual data traffic coming from the host, actually hits the transceiver. In those cases, the Cool Optics on/off mechanism is latency-free.
In more complex situations, there will be some latency, but this will be limited to several 10’s of nanoseconds for the more complex situations.
The basic concept of Cool Optics technology is shown below:
- The ITPA™ idle time prediction algorithms, controlling the Lock & Link™ mechanism.
- The Lock & Link mechanism, taking care of switching on and off the stack, while taking care of synchronization.
- The Lock & Link mechanism, optionally taking care of switching on and off the Fast Link™ mechanism if this is implemented in the transceiver.
- The Fast LinkTM mechanism in the transceiver, taking care of switching the transceiver on and off on a controlled manner, and of fast capturing of the incoming data stream after a new start.