[clug] Poor PPPd performance

[Craig Bates]

Hi people,

I've got an interesting problem that I've run out of ideas to solve, so 
I thought perhaps somebody here can help me out:)

I'm working on radio link project that runs embedded Linux on an ARM9 
platform. Four PPP sessions originated on windows PCs go over the air 
and are terminated on the ARM9.   The software that takes care of the 
air link connects to the 4 PPPd processes via pseudo TTYs. So PPPd 
thinks it is talking to a TTY and the other end looks like a file 
descriptor that the airlink software reads and writes to. So PPP is 
transported by a lower layer of software. Much like PPP is transported 
by Ethernet or ATM in DSL.  I hope that makes sense...

Anyway this works ok until one tries downloading an uploading at the 
same time in which case PPPd fails write much data to the pseudo tty. 
I.e. downloads become very slow, but uploads remain about the same. The 
system is working in the 256kbit/sec sort of area and the hardware and 
airlink is full duplex.

CPU power does not seem to be a problem. The system is capable of doing 
up and down loads on different PPP sessions at the same time, just not 
the same one. Load average is about 0.4.

So perhaps somebody with some experience with plugging PPP into other 
software can help me out.   Is there a better way of interfacing PPPd 
into other software for transport?

Thanks in advance! Craig