[atlas] probe resolution, overhead, or ...?
Stelios M. steliosm at gmail.com
Wed Jun 20 11:04:07 CEST 2012
Hello Philip. Ping relies heavily on the system's CPU. That is why it is considered unreliable for measuring when you are pinging CPU loaded machines/devices. The CPU on the probe is a n ARM7TDMI running at 55MHz, based on information from this link: http://www.digi.com/products/wireless-wired-embedded-solutions/solutions-on-module/digi-connect/digiconnectme#specs Regards, Stelios Mersinas On Wed, Jun 20, 2012 at 11:48 AM, Philip Homburg <philip.homburg at ripe.net>wrote: > On 6/20/12 9:11 , Randy Bush wrote: > >> we want to use atlas probes in an experiment. being prudent (you can >> tell it was not i), we decided to try to get some basic calibration. >> one run was just on a local LAN. >> >> three hosts on the same gige switch >> o probe 2285 >> o psg.com, a not very fancy or fast freebsd 9 box with intel/pro1000 >> gige ports >> o bbgp.psg.com, a funky older freebsd 9 box with bge gige >> >> probe 2285 pinging bbgp.psg.com, average RTT: 1.5606994382 , number >> of pings: 356*3 >> >> psg.com pinging bbgp.psg.com, average RTT: 0.253424332344 , number of >> pings: 674 >> >> has anyone done similar probe calibration experiments? does anyone have >> any clue as to why the difference? >> >> >> Just to confirm my suspicion, I tried to other way around: > > This is an old AMD64 running FreeBSD pinging an Atlas probe on the same > LAN: > $ ping 126.96.36.199 > PING 188.8.131.52 (184.108.40.206): 56 data bytes > 64 bytes from 220.127.116.11: icmp_seq=0 ttl=64 time=2.515 ms > 64 bytes from 18.104.22.168: icmp_seq=1 ttl=64 time=0.913 ms > 64 bytes from 22.214.171.124: icmp_seq=2 ttl=64 time=0.915 ms > 64 bytes from 126.96.36.199: icmp_seq=3 ttl=64 time=0.929 ms > > And this is the same FreeBSD box pinging a Celeron 766 MHz, running a > micro kernel operating system, also on the same LAN: > $ ping prism > PING prism.hq.phicoh.net (188.8.131.52): 56 data bytes > 64 bytes from 184.108.40.206: icmp_seq=0 ttl=96 time=0.364 ms > 64 bytes from 220.127.116.11: icmp_seq=1 ttl=96 time=0.210 ms > 64 bytes from 18.104.22.168: icmp_seq=2 ttl=96 time=0.211 ms > 64 bytes from 22.214.171.124: icmp_seq=3 ttl=96 time=0.214 ms > > This does not involve any of the Atlas software, just the ucLinux kernel > running on the probe. > > My conclusion is: probes are just very slow. > > They are fine for measuring multi millisecond delays on WAN links but not > for sub-millisecond delays on local links. > > > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://www.ripe.net/ripe/mail/archives/ripe-atlas/attachments/20120620/1091f442/attachment.html>