Precision Receiver Timestamping of 802.11 packets

I find the explanation of timestamping errors in

Fine-Grained Network Time Synchronization using Reference Broadcasts (also available as PDF)

Jeremy Elson, Lewis Girod and Deborah Estrin

In Proceedings of the Fifth Symposium on Operating Systems Design and Implementation (OSDI 2002), Boston, MA. December 2002. UCLA Technical Report 0200

08. (Supercedes earlier revisions from May and February 2002.)

http://lecs.cs.ucla.edu/Publications/papers/broadcast-osdi.ps

to be particularly lucid. This page assumes you are interested in receiver side timestamping.

The radiotap header is the de facto standard for reading receiver side timestamps. Drivers will supply packets with radiotap headers to the monitoring application. The monitoring application will parse the radiotap header to retrieve the receive timestamp.

The majority of my experience has been with Atheros 5212/5213 802.11abg chipsets. The driver info below is for cards based on these.

Windows

A company called CACE sells the AirPcap adapter with a custom driver. As of version 3.2.1, this seems to work well. Previous versions (3.2.0) exhibited high receive timestamps variance.

Linux

In my experience, the drivers for Linux are more flexible and certainly cheaper than Windows options. My notes for them: madwifi and ath5k