Re: [tcpdump-workers] where does PCAP timestamp before or after the
Hi, We want to know where/when does PCAP put the timestamp (from not so accurate kernel time) on to the packets. I already know, it does when the kernel sees the packet. The question is: Is it after or before the MAC scheduler? I mean, does it in TR or RX buffers or at higher protocol layers take place? Under Linux (at least 2.6.x) the received packets are timestamped in netif_rx() direcly after the driver has setup a sk_buff for the packet. This is before the receiving interrupt is distributing the sk_buff (the struct in which the Linux kernel stores packets) to the interested receivers of which one is the sniffing socket as they call it within the linux kernel and another is the TCP/IP stack (ip_rcv()). For the sending of the packet i am not sure, but i think this happens directly before the packet it handed to the driver function. But what exactly is the MAC scheduler? I have not yet heard of it. mfG Fabian Schneider -- Fabian Schneider, Technische Universität München address: Boltzmannstr. 3, 85748 Garching b. Münchenn e-mail: [EMAIL PROTECTED], WWW: http://www.net.in.tum.de/~schneifa phone: +49 89 289-18012, mobile: 0179/2427671- This is the tcpdump-workers list. Visit https://lists.sandelman.ca/ to unsubscribe.
Re: [tcpdump-workers] where does PCAP timestamp before or after the MAC scheduler?
On Thu, Mar 30, 2006 at 12:17:47PM +0200, Debrei Gabor wrote: Hello! We want to compare 802.11 MAC schedulers performance, to decide how much the Media Access takes. Many 802.11 MACs put a microsecond timestamp on received frames. Some wireless drivers in *BSD will load that timestamp into the radiotap capture header. In principle (maybe in fact), Linux can do the same. Sadly, 802.11 MACs do not stamp transmitted frames. That would be very useful! Dave We want to know where/when does PCAP put the timestamp (from not so accurate kernel time) on to the packets. I already know, it does when the kernel sees the packet. The question is: Is it after or before the MAC scheduler? I mean, does it in TR or RX buffers or at higher protocol layers take place? (If it takes place in the buffers the use of HW monitoring devices the only way of measuring? ) Thanks, I am looking forwad to Your answers. Gabor _ Digit?lis f?nyk?pez?g?pek rendk?v?li csomagaj?nlatokkal, fot?kidolgoz?s m?r 25,- Ft-t?l FotoMarket, m?r 5 ?ve az ?n fot?szolg?lat?ban! www.fotomarket.hu - This is the tcpdump-workers list. Visit https://lists.sandelman.ca/ to unsubscribe. -- David Young OJC Technologies [EMAIL PROTECTED] Urbana, IL * (217) 278-3933 - This is the tcpdump-workers list. Visit https://lists.sandelman.ca/ to unsubscribe.
