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Wed, 26 Dec 2007

New release of the distributed storage: Groundhogs strike back: no New Year for humans!

Short changelog:

• mirroring algorithm improvements
• debug cleanups
• extended mirroring initialization
• documentation update
• name is 'Groundhogs strike back: no New Year for humans' now

/devel/dst :: Link / Comments (2)

CDMA (EVDO) vs GPRS.

Good people gave me SkyLink CDMA modem (model USB CNU-550 with EVDO support) to test internet conection in Linux and compare it against GPRS.

Well, here are my conclusions:

• CDMA works always while GPRS really sucks in the middle of the day: well, it has to be proven tomorrow, but I tested CDMA modem at about 19-00 and it worked ok, while MTS (Mobile TeleSystems in Russia) at about 12-00 worked very bad (I connected quickly, but ssh login took enormously long time).
• CDMA speed is usually about 10-16 kb/s, while GPRS is usually can not be higher than 1-2 kb/sec. More on this: I believe CDMA session can have higher speeds (pppd session requests about 900 kbit/sec), behaviour of initial login (I saw quite a few of them on different initial speeds during usual work and userspace network stack testing) shows there is some limitation on server or hardware side (i.e. SkyLink either because of special tariff scale or driver limitations, I was told there is no 16 kb/sec limitation with given card though) side (note on testing different congestion control algorithms and develop own if needed: speed downgrades to less than 10kb/sec frequently during download of the big file. SkyLink is a very interesting source of data for such development: it looks like its RTT is quite high for default (new CUBIC) congestion control, at least low-traffic but very-small-latency-wanted source (mutt over ssh on remote host without serious traffic shaping) works quite bad in this setup. Very likely it is just an empty speculation and problem is in hardware on the server (i.e. it has support for bulk streaming access at high speeds (16 kb/sec), but fails to work with low-latency applications, which work in small packets ping-pong environment)).
• CDMA USB CNU-550 modem works ok in Linux (modulo above issues) with this peers/pap-secrets files without any problems.

/other :: Link / Comments (3)