An addition to the standards for network interface modules proposed by Nikhef will play an important role in the introduction of ultra-precise timing in data networks.
“This brings the ideas about sub-nanosecond timing a lot closer to reality,” says Peter Jansweijer of Electronics Technology at Nikhef. Over the past five years, he has been working on an additional chapter 13 for the standard for SFP modules of the Storage Networking Industry Association, SNIA.
Nikhef and Jansweijer have long been closely involved in the development of White Rabbit technology, a method for synchronizing components of a fiber optic network to within less than a nanosecond. A consortium has been formed for this purpose, including CERN.
Sub-nanosecond
Sub-nanosecond timing is essential for some large scientific instruments such as telescopes or detectors like those at CERN. But such precision is also becoming increasingly important for data traffic and telecommunications. The maximum timing error for connected transmission masts is currently 5 nanoseconds, but a standard of 0.2 nanoseconds has already been defined; the trend is toward greater precision.
SFP modules are pluggable network interface modules that connect the optical fiber network to the electronics. In data networks and data centers, these are widely used, easily replaceable, pluggable modules for converting electrical signals into light and vice versa.
In networks with ultra-precise timing, the delays between the electrical and optical inputs and outputs of each network interface module play an essential role. When replaced, the accuracy of the network’s time synchronization can be lost, requiring a new time calibration.
Storage
Manufacturers of network interface modules can measure the delays of their modules in advance and store this data on a chip in the network interface module itself. Chapter 13 of standard SFF-8472 describes in detail how this information must be stored in order to be universally usable.
Calibration is then no longer necessary; the system incorporates the information into the calculations used to synchronize the clocks in the network. How these calculations are performed is described in the next version of the IEEE-1588 standard, which is still under development.
Jansweijer: “This eliminates the need to recalibrate after replacing a network interface module and brings you a lot closer to the reality of data networks, where you want to be able to replace components without any hassle.”
The new SFF-8472 standard was preceded by much discussion with major telecom providers such as Nokia and Ericsson. That took time, but Jansweijer now believes that it is precisely because of the large market share of telecom providers that the agreed standard can be put into practice quickly.
