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. > 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? > Here is my ppp.conf: Basically identical to mine. > 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. I have a couple of Huawei USB HSDPA modems from two UK mobile networks and see the exact same symptoms. However, sometimes when roaming on a foreign network the problem did not occur. > Any suggestions are greatly appreciated. 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 :-)
