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This is just a quick note to report a drastic improvement in the usability of GPRS on Linux in 2G service areas (GSM not UMTS) by setting small values for PPP's MTU and MRU parameters.
I have made a quick post to the PPP board on the Pharscape.org forums, to see whether anyone knows a bit more....
Update Feb 01. 2007: Tests using Linux KPPP with a Vodafone SIM card (APN: 'internet'), both on a 2G GSM phone and in an Option Fusion GT+ datacard, suggest that Vodafone 2G GPRS doesn't need you to tweak the MTU + MRU. So either Vodafone is doing this automatically, or there's something about their UK network that makes this unnecessary.
By contrast, TMUK's 2G GPRS network (APN: 'general.t-mobile.uk') doesn't work properly unless you adjust MTU + MRU.
I've tried un-commenting 'debug' (and setting 'kdebug' to 1) in /etc/ppp/options in order to see PPP option negotiations in /var/log/debug, but although this shows a lot of stuff, it doesn't show MTU + MRU being negotiated. If I get time I'll try setting 'kdebug' to 5, but I think that will just show data packets as well.
Posted: Mon Jan 29, 2007 1:13 am Post subject: Tuning KPPP for 2G GPRS Are there any rules of thumb for this? Some quick tests of my own suggest that MRU / MTU really benefit from tweaking! This is with T-Mobile UK using a Novatel Wireless EU740 card in a non-3G service area. With default settings in KPPP: (only parameter set = "novj") ======================================= - pings work OK - but web access is almost unusable - logs show few requests reach the web server - Wireshark shows lots of repeated HTTP GET requests every few secs With mildly optimised settings in KPP: ======================== - Settings: "novj", "mru 296", "mtu 296" (nothing magic about these numbers, but "man pppd" suggests them for very slow links) - Ping times much the same - Now the web is MUCH more usable! Not quick, but fairly predictable. I'm posting this over 2G GPRS. Page fetch requests don't time out, they just take a while. Presumably this setting will reduce the speed in 3G service areas, but I guess it's probably worth it to make this thing usable. I'd be very grateful for your thoughts! And for any more tweaks, Cheers _________________ -- Martin. (Novatel Wireless EU740 on T-Mobile UK, Kubuntu Edgy Eft 2.6.17-10-generic)
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