Hi Ben.

   Don't laugh, and since this is just for hobbyist tinkering, what I'm trying to do is get a few old BlackBerries running.  They're 7290's, so only support GPRS, though I think they may support EDGE as well but I'm a little unsure on that. 

I never had a blackberry so I don't know either. I noticed that with almost any kind of Android phone, it's going to generate so much traffic as soon as it sees a network connection that it will saturate the GPRS itself. - I did not spend a huge amount of time making an analysis of this, but what can be observed is a LOT of re-transmissions (from both sides), and then TCP resets from the remotes. I suppose it's to be expected. the stack in the phone is not seeing ACKs quickly enough, so re-transmits. same on the other side.. (assuming the ACK as lost?) I'm no expert in TCP/IP, although I understand TCP is supposed to handle this by backing off, but I assumed what I was seeing was servers that are so busy they are configured with some kind of a "no, you're too slow and I'm not going to wait around for you" policy.

In production setups, with EDGE, and some several 100 phones connected, the same situation arises, but I did manage to get control of it by heavy use of iptables and TARPIT - only allowing traffic to IM services, and therefore letting at least those have some chance of establishing a connection.

I assume it's mainly all the phone-home stuff that gets in the way (most is https, most is to google) - Probably app stores checking for updates, sending google location logs, that kind of thing. Androids for example, won't back off if you don't resolve the DNS they ask for, (in some cases they don't care about configured DNS, they always ask 8.8.8.8 and 8.8.4.4 and if they get a NXDOMAIN or anything unexpected, they just keep on hammering away, expecting to get through.

While it'd of course be great if someone else was also playing around with GPRS/EDGE and the DUG, If it's just for hobbyist tinkering, I have successfully connected phones on the lab-desk, with EDGE at reasonable speeds, with the LimeSDR-mini and a mini desktop based on one of these: https://www.mitacmct.com/IndustrialMotherboard_PD11BI_PD11BI

But I understand your mileage may vary greatly there depending (maybe?) on the actual lime board you happen to have, the temperature and how sensitive your phones are to clock drift.

 Though you do have a good point that factoring in the cost of a -48v power supply, the 6601, DUG20, and RRUS, it'd probably be pushing $1k anyway.

   What Ericsson gear do you have?

Last but not least, even though it's not Ericsson, I have to mention of course the sysmocom icE1usb as an integral part of the system!

   Thanks much!

Good luck!

k/

-Ben