Accurate time stamp

I'd like to be able to accurately time stamp a data packet. The data packet will be transmitted to another computer and then that computer will transmit the data packet back and it should then be timestamped with the updated time. The transmission medium isn't important whether it is wirless or cable. What is important here is that the packet is sent when it is time stamped and timestamped immediately when recieved, that is nothing in terms of the computer normal funtions gets in the way of the time stamp - I want to know when the packet leaves and when it arrives back. The time accuracy is very important, ideally I'd like kind of nano second accuracy!! The system also needs to be consistent that is the software takes the same amount of time to run every time - so need to deal with interupts etc to make susre they don't mess up the time stamping. I'm told this can be achieved via UTC supplied from GPS receiver. ## Deliverables 1) Complete and fully-functional working program(s) in executable form as well as complete source code of all work done. 2) Deliverables must be in ready-to-run condition, as follows (depending on the nature of the deliverables): a) For web sites or other server-side deliverables intended to only ever exist in one place in the Buyer's environment--Deliverables must be installed by the Seller in ready-to-run condition in the Buyer's environment. b) For all others including desktop software or software the buyer intends to distribute: A software installation package that will install the software in ready-to-run condition on the platform(s) specified in this bid request. 3) All deliverables will be considered "work made for hire" under U.S. Copyright law. Buyer will receive exclusive and complete copyrights to all work purchased. (No GPL, GNU, 3rd party components, etc. unless all copyright ramifications are explained AND AGREED TO by the buyer on the site per the coder's Seller Legal Agreement). 4)Need to specify the development environment clearly so I can replicate it and be sure it's working. ## Platform Windows Ideally I'd like C# but this might not be possible to achieve the accurracy I'm looking for. Whatever is used I'd like very well commented code.