peertime v0.9.4

PeerTime

Network Peer Time Synchronization for Node.js and Browser.

About

This is a small JavaScript library for Node.js and the Browser to synchronize the time between networking peers by determining a globally-aligned local time. This is inevitable in a network of peers where exchanged data has to be locally timestamped with a globally agreed time.

Algorithm

PeerTime uses the following time synchronization protocol between a local node and a peer node:

1. REQUEST: Local node stamps its current (potentially already globally aligned) local time and sends it in a TIME-REQ (request) data frame to a peer node.

2. RESPONSE: Upon receipt of the TIME-REQ frame, peer node stamps its current (potentially already globally aligned) local time and sends it in a TIME-RES (response) data frame to the local node.

3. ADJUSTMENT: Upon receipt of the TIME-RES frame, local node subtracts its current local time from the previously sent local time and divides it by two to compute network latency. It subtracts current local time from peer time to determine communication time delta and adds in the half-latency to get the correct local time offset.

The first determined clock offset is immediately be used to adjust the local time since it will get the local time into at least the right ballpark.

The local node then repeats the above steps 1 through 3 a few times, pausing a few seconds each time. Other network communication is allowed in the interim, but should be minimized for best results.

The results of the determined local time offsets are accumulated and sorted in a lowest-latency to highest-latency order. The median latency is then determined by picking the mid-point sample from this ordered list. All samples above approximately one standard-deviation from the median are discarded and the remaining samples are averaged using an arithmetic mean. In case of multiple peers, the arithmetic average of the local time offset against all peers are taken as the final local time offset.

Installation

$ npm install peertime

Usage

See the TypeScript API definition for all details on the Application Programming Interface (API) of PeerTime.

Credits

PeerTime was inspired by a similar library named timesync and PeerTime's underlying core synchronization algorithm was derived from this library, which in turn derived it from the NTP and SNTP time synchronization protocols. The major difference between PeerTime and timesync is that PeerTime is fully agnostic to the network layer, both from a JavaScript API perspective and NPM package dependency perspective and hence can be more easily embedded into other frameworks or larger libraries.

License

Copyright (c) 2018-2021 Dr. Ralf S. Engelschall (http://engelschall.com/)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.