3 ms·

The Empire Strikes Back: Or AT&Ts Micro Cell Strategy Pt2--Response from ATT

18 points by jboydyhacker 16y ago

tptacek 16y ago
I like the notion that someone at AT&T thinks we should appreciate the fact that they don't micro-bill us for usage on our own wifi networks. You just know somebody at AT&T has a Word doc with 1000 revisions in it outlining exactly how they might do that.
tjarratt 16y ago
I haven't read much about this, but I don't see how AT&T can justify charging you for the base station hardware as well as its continued use. If using the device does not use any of their services or network and is ONLY between your cell phone and ISP, what benefit does AT&T bring that warrants them charging you for using two goods/services (the micro-cell base station and your ISP's bandwidth) that you have already paid for? This is a classic bait and switch, as far as I can tell.
- wmf 16y ago
  The prevailing theory is that AT&T is too incompetent to meter traffic based on source; since the double-billing is not intentional they don't have to justify it. Of course, now that they've been informed of the problem they have to either fix it or somehow justify not fixing it (I predict that "it's not cost-effective to rewrite the billing system to save a few dollars for a few people using femtos the wrong way").
  - chrisbolt 16y ago
    They can definitely meter traffic based on source. You can get unlimited free calling with your microcell for $20/month.
grogers 16y ago
The MSC is part of the core network, and it handles circuit switched calls/data, the SGSN is also part of the core network, and it handles packet switched data. When AT&T is telling you not to use your femtocell for data, it isn't just because it puts an extra strain on their network, its also significantly slower than if you just used the wifi you probably already have to begin with. The extra hops it has to go through - from the femtocell, through your ISP, to AT&T's SGSN, GGSN, then out to AT&T's ISP, make it seem silly to want to use a femtocell for data. In addition, I don't see any reason they can't charge you for the femtocell, even though it is using your ISP's resources you already paid for, it still adds value to your service. The SIP gateways that providers like T-Mobile use seem like a better alternative to femtocell's anyways. With these, your voice and data both go over wifi, and only the voice will enter the core network. When you need to be paged on a mobile termination, the core network knows you are registered as a SIP guy, so it just sends you a SIP INVITE which reaches you over your wifi. When you roam back into the cell coverage area, it goes back to normal.
jonah 16y ago
It seems this is the core of the question: Is your 3G DATA going through AT&T's core systems on its way to the internet or is it splitting out at the microcell and going directly to the wider internet? If it's the latter - then it's nuts that they are charging against your data cap for usage that doesn't even traverse their network. If it's the former, (which I suspect it is), whether it's just or not, they'd be within their right to charge for the transit load on their systems.
- grogers 16y ago
  When you send packets of data out of your phone, there are several layers that are added onto your IP packet. Here is a basic diagram of the different nodes in the RAN and CN and which layers they operate on: UE<->NodeB (Uu): <your data> | PDCP | RLC | MAC | <L1 radio stuff> NodeB<->RNC (Iub): <your data> | PDCP | RLC | MAC | FP | <L2 stuff depending on IP/ATM/etc> RNC <-> SGSN (Iu): <your data> | GTP | UDP | IP | <L2 stuff> SGSN <-> GGSN (Gn): <your data> | GTP | UDP | IP | <L2 stuff> GGSN <-> Internet (Gi): <your data> (finally!) At some points your data's UDP/TCP headers might be compressed/uncompressed but thats the basic idea. Something needs to perform the functions performed by all these nodes. "Traditionally" the femtocell is a combination of the RNC/NodeB (aka the Radio Access Network). Clearly it is possible to add core network functionality to the femtocell, but not only is it probably not worth it, the security implications are tricky (you would have to expose your HLR directly to the internet to be able to talk to the femtocell - instead of just your SGSN, which you would likely have special CN nodes for talking to femtocells). So it is almost guaranteed to be the former. And it makes AT&T's recommendations make alot more sense. You don't even need to assume any malice in them.
  - jonah 16y ago
    Googling madly ... http://en.wikipedia.org/wiki/GPRS_Core_Network http://en.wikipedia.org/wiki/GPRS_Core_Network http://en.wikipedia.org/wiki/Network_switching_subsystem http://en.wikipedia.org/wiki/Network_switching_subsystem ... OK, makes some sense now. Their recommendations make sense. It's actually nice of them to recommend using WiFi where available (though you'd hope people would be smart enough to figure that out on their own.) Looking at it from a bottleneck/financial perspective I wonder where the constraints are that cause them to want/need to limit data usage. If it's just the UE<->NodeB (Uu) bandwidth, then the femtocell addresses that and maybe they could prorate the data coming through it, if it's farther up the string then it's understandable.

18 points by jboydyhacker 16y ago

I like the notion that someone at AT&T thinks we should appreciate the fact that they don't micro-bill us for usage on our own wifi networks. You just know somebody at AT&T has a Word doc with 1000 revisions in it outlining exactly how they might do that.

tjarratt 16y ago

I haven't read much about this, but I don't see how AT&T can justify charging you for the base station hardware as well as its continued use. If using the device does not use any of their services or network and is ONLY between your cell phone and ISP, what benefit does AT&T bring that warrants them charging you for using two goods/services (the micro-cell base station and your ISP's bandwidth) that you have already paid for? This is a classic bait and switch, as far as I can tell.

wmf 16y ago
The prevailing theory is that AT&T is too incompetent to meter traffic based on source; since the double-billing is not intentional they don't have to justify it. Of course, now that they've been informed of the problem they have to either fix it or somehow justify not fixing it (I predict that "it's not cost-effective to rewrite the billing system to save a few dollars for a few people using femtos the wrong way").
- chrisbolt 16y ago
  They can definitely meter traffic based on source. You can get unlimited free calling with your microcell for $20/month.

grogers 16y ago

The MSC is part of the core network, and it handles circuit switched calls/data, the SGSN is also part of the core network, and it handles packet switched data. When AT&T is telling you not to use your femtocell for data, it isn't just because it puts an extra strain on their network, its also significantly slower than if you just used the wifi you probably already have to begin with. The extra hops it has to go through - from the femtocell, through your ISP, to AT&T's SGSN, GGSN, then out to AT&T's ISP, make it seem silly to want to use a femtocell for data. In addition, I don't see any reason they can't charge you for the femtocell, even though it is using your ISP's resources you already paid for, it still adds value to your service. The SIP gateways that providers like T-Mobile use seem like a better alternative to femtocell's anyways. With these, your voice and data both go over wifi, and only the voice will enter the core network. When you need to be paged on a mobile termination, the core network knows you are registered as a SIP guy, so it just sends you a SIP INVITE which reaches you over your wifi. When you roam back into the cell coverage area, it goes back to normal.

jonah 16y ago

It seems this is the core of the question: Is your 3G DATA going through AT&T's core systems on its way to the internet or is it splitting out at the microcell and going directly to the wider internet? If it's the latter - then it's nuts that they are charging against your data cap for usage that doesn't even traverse their network. If it's the former, (which I suspect it is), whether it's just or not, they'd be within their right to charge for the transit load on their systems.

grogers 16y ago
When you send packets of data out of your phone, there are several layers that are added onto your IP packet. Here is a basic diagram of the different nodes in the RAN and CN and which layers they operate on: UE<->NodeB (Uu): <your data> | PDCP | RLC | MAC | <L1 radio stuff> NodeB<->RNC (Iub): <your data> | PDCP | RLC | MAC | FP | <L2 stuff depending on IP/ATM/etc> RNC <-> SGSN (Iu): <your data> | GTP | UDP | IP | <L2 stuff> SGSN <-> GGSN (Gn): <your data> | GTP | UDP | IP | <L2 stuff> GGSN <-> Internet (Gi): <your data> (finally!) At some points your data's UDP/TCP headers might be compressed/uncompressed but thats the basic idea. Something needs to perform the functions performed by all these nodes. "Traditionally" the femtocell is a combination of the RNC/NodeB (aka the Radio Access Network). Clearly it is possible to add core network functionality to the femtocell, but not only is it probably not worth it, the security implications are tricky (you would have to expose your HLR directly to the internet to be able to talk to the femtocell - instead of just your SGSN, which you would likely have special CN nodes for talking to femtocells). So it is almost guaranteed to be the former. And it makes AT&T's recommendations make alot more sense. You don't even need to assume any malice in them.
- jonah 16y ago
  Googling madly ... http://en.wikipedia.org/wiki/GPRS_Core_Network http://en.wikipedia.org/wiki/GPRS_Core_Network http://en.wikipedia.org/wiki/Network_switching_subsystem http://en.wikipedia.org/wiki/Network_switching_subsystem ... OK, makes some sense now. Their recommendations make sense. It's actually nice of them to recommend using WiFi where available (though you'd hope people would be smart enough to figure that out on their own.) Looking at it from a bottleneck/financial perspective I wonder where the constraints are that cause them to want/need to limit data usage. If it's just the UE<->NodeB (Uu) bandwidth, then the femtocell addresses that and maybe they could prorate the data coming through it, if it's farther up the string then it's understandable.