[tcpdump-workers] some questions regarding pcap_sendpacket()

Guy Harris guy at alum.mit.edu
Wed Jun 3 12:45:33 EDT 2015

On Jun 3, 2015, at 6:16 AM, Kiran Mathews <kiranmathews20 at gmail.com> wrote:

> I am sending this mail to ask some questions regarding pcap.Im doing some
> research on synchronisation in wifi. I am trying to synchronise of two
> devices by communicating through wifi.
> So for this, i use pcap lib for sending and receving the wifi packets.
> So my question is when we sent packet using pcap_sendpacket(), whether
> function is returning the value EXACTLY after the  packet is sent or it is
> not considering the further delays by the driver??

It returns when whatever operating system call it makes returns.

On most if not all operating systems, this means it returns as soon as the packet is queued up to be sent, rather than when it's actually put on the wire/on the air.

I don't know of any way, in any OS, to wait until a packet is either put on the air or dropped (yes, if you have a medium with contention for access, if the host fails to get access to transmit after some number of tries, it'll probably give up and drop the packet for any network that provides no "guaranteed delivery" service).

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