On Thu, Jan 15, 2009 at 04:25:54PM +0000, Pedro la Peu wrote: > On Thursday 15 January 2009 03:03:12 Jason Dixon wrote: > > I have a Verizon USB720 dongle that shows up as ucom0. I intend to > > use it for connecting remotely with my X40. I'm having problems when > > packets exceed a certain size. When this happens, the return packets > > never make it back to my system. > > This is (if I understand correctly) normal.
Normal for what? I see 2.5Mbps/512Kbps with the same device in OS X. > > I can connect fine with ppp(8). I can ping remote hosts and do > > traceroutes. I can ssh to hosts and perform basic commands. Only > > when the payload exceeds ~900 bytes do things start to fail. This > > happens with almost all TCP traffic, but is most noticeable with SSH > > or HTTP. > > Have you seen tcp traffic that is not affected? Not by application type per se, only by packet size. > > And here are some simple tests. I've created a test file of zeroes, > > increasing by 10 bytes each time. It finally stalls at 930 bytes. > > I've tried it with and without vjcomp. > > As I understand it, this a characteristic of the underlying (mobile) > network, where the MTU is set by the network operator. Thus it may vary > depending on who you connect to. When run interactively, both sides say 1500. And like I mentioned, OS X doesn't exhibit any of these problems. When I have a spare moment I'll try Linux under VMware. > Once the ppp link is up set the mtu of the corresponding tun device to > something smaller than the size that fails (900 works here). I can't > find a ppp option that does the same (set mtu etc.) and I'm not clear > why the MTU has to be forced. But it's been working fine like this for > months so I don't worry about it any more :-) If I "set mru 900" it's stable. The download speed is around 300-400Kbps, which is to be expected. But it still sucks. Verizon must be using some sort of voodoo magic in their drivers. :( -- Jason Dixon DixonGroup Consulting http://www.dixongroup.net/
