Anyone know how mobile broadband dongles work?

[The Natural Philosopher]

Cos I am getting this thing to work under Linux. Its a qualcomm chipset MF622 from ZTE provided by Three..

I have been messing with it and it seems to work OK, looks a bit like a modem that is always connected..

So teh dial up logs are full of ATZ and so on, it says 'CONNECTED' ppp starts and packets flow..it even says CHAP succeeded..i.e. the name and password supplied (which everyone says are irrelevant anyway) work.

BUT I don't get any IP, or DHCP stuff and after a couple of minutes the thing 'hangs up'

This got me puzzled for a long time, till I looked at the coverage map of Three, and discovered it was only 2G or 3G, not mobile broadband, here.

Now I naively had thought that when it said 'carrier present' it meant it had an end to end connection to whatever it talks to. But I am wondering if in fact it just fakes all that locally, and the password/CHAP stuff, says its connected, goes looking for a mobile broadband signal, doesn't find it and eventually times out and issues a 'lost carrier' signal back to the pppd daemon.

I will be getting a cheap secondhand laptop to go with it shortly, but I thought I would ask anyway, to see if anyone else has invented this particular wheel..i.e. knows what happens when you fire up pppd against a working dongle that has no proper signal.

[Tim Ward]

Sounds like there is a connection then. Although the username/password are irrelevant for most (or even all) mobile data services (they identify you by IMSI) the phone doesn't know that, and IME of GPRS connections (which I've worked with and debugged at every level) there has to be some successful signalling before anything can seriously believe that the CHAP has succeeded.

There isn't a real end to end PPP negotiation, by the way, it's done with some signalling messages still in the GSM/UMTS layer three stuff, although it's quite likely to fake up normal PPP negotiation towards the client computer. Only after all this has completed does the phone switch to whatever packet transport it has for the IP. So, if you're getting PPP negotiation complete but no IP packets it sounds like you've got a perfectly good signalling connection but can't get any packet data transported.

I don't know anything about 3G, but in an area with no 3G coverage I'd expect the dongle to step down to EDGE, and if it can't find that to boring old GPRS.

[RubberBiker]

I had similar issues when using Ubuntu 8.04 (hardy heron) - linux reported connected but not getting any application level connectivity (I was using a cable-linked 3G phone). In the end it wasn't important enough to me to sort it out. However once I moved to Ubuntu 8.10 (intrepid), this included 3G modem support - and the desktop set-up widget got it right with very little fiddling (mostly issues configuring the phone handset rather than linux).

[Adrian]

"Tim Ward" gurgled happily, sounding much like they were saying:

There's very little EDGE coverage in the UK. I think O2 are the only ones with an EDGE network - and even that'll probably go sooner or later, since the iPhone 3G removes their only real need for it.

Three piggy-back off T-mobile, so there'd be no EDGE access for a Three card.

[Abo]

Yeah, it's a doddle under 8.10, just stick the dongle in, configure the accesspoint name etc. and off you go.

[Adrian]

The Natural Philosopher gurgled happily, sounding much like they were saying:

Umm, what - other than 3G - are you expecting for "mobile broadband"?

[tony sayer]

In article , Tim Ward scribeth thus

More then likely the 3G coverage seems to have only been rolled out in city areas..

Even 2G voice is lacking in quite a bit of rural Cambs even, let alone further afield;!..

[Duncan Wood]

If it's only making a 2G connection & it's configured for 3G only then nothing happens. Ringing your networks the only way you can get a real clue though, if your cell's not got any spare bandwidth you;re at the bottom of the tree & don't get any packets.

[Duncan Wood]

Dependent on configuration upto 7.2M instead of 384K.

[Theo Markettos]

It will, unless it's set to 3G or HSPA only. I don't know the ZTE dongle, but some can be set this way. 'Mobile broadband' is probably code for HSPA. If you don't get an HSPA signal you'll use 3G/UMTS or 2G/GPRS.

Three have their own 3G network. They also share 3G network with T-Mobile. When there's no Three or T-mob 3G, they use Orange 2G.

However fallback on Orange GPRS is pants. See my stats:

[dennis]

I installed a Three 3g dongle for someone six weeks ago. The first dongle was duff and didn't work. I could get a 2G connection and send SMS messages but no IP connection. The second dongle worked first time.

When I took it back there was a second person swapping an identical dongle so either they are unreliable or there was a network fault that cleared by the time I got the second dongle.

Can't help you with linux though, this was windows.

[Adrian C]

Hope not, there are other non 3G/3G+ handsets that support EDGE. Blackberry's for one.

[Tim Ward]

After a fashion ... I'm not entirely convinced that it follows the GSM specs correctly re cell reselection algorithm, and I think this is something to do with EDGE.

[Adrian]

Adrian C gurgled happily, sounding much like they were saying:

Like mine. And the Nokia 9300i I had before. Neither of which got EDGE signals in the UK, because I'm not on O2. Soon as I roamed, however...

[Roland Perry]

In message , at 11:01:06 on Thu, 16 Apr 2009, Tim Ward remarked:

Really? I'm sure you do.

I have a "3" dongle, and step-down is indeed what happens.

The feature I miss the most (it's greyed out rather than completely missing, on my PC) is the ability to say "Please use only 2/2.5/3 G at the moment".

The "3" network does not preserve a connection when roaming between the various provisions, which is a problem if you've set up a tunnel when in

2G and are reasonably happy with it, until the network decides to chuck you off because it got a sniff of something faster.

[Tim Ward]

I know that a lot of the signalling is the same as GSM, but I can't get my head round how the radio works. (Yes I have read books and papers and tutorials, and still can't get it.)

That sounds a bit cheap and nasty to me. I'm sure the GPRS and 3G specs must have been designed to allow an operator to get that sort of thing right if they felt like bothering.

[Roland Perry]

In message , at 14:53:32 on Thu, 16 Apr 2009, Tim Ward remarked:

I think it's because they don't have a 2G/2.5G network and when you roam in and out of their own network (onto whoever does their fallback this week) it's too difficult to maintain the connection.

[chunkyoldcortina]

Orange have EDGE on their 2G network, in a few places.

(cam.misc dropped from list of groups)

[chunkyoldcortina]

Well "broadband" just means the opposite to baseband. An ethernet connection is not broadband but baseband (hence the names, 10BASE-2, 100BASE-T etc)

[The Natural Philosopher]

The three site makes a complete distinction between 2G, 3G and 'mobile broadband'

"2G network: gives you voice, text and picture messaging services.

3G network: gives you all of the above, plus video calling and the internet on your mobile. HSDPA network (Mobile Broadband): gives you all 2G and 3G services, plus high-speed internet access on your mobile and with your dongle (USB modem). "

Now where I am right now has zilch on the map for 'Mobile Broadband'

So I infer from the above that the USB dongle does NOT drop back to 3G/2G.

What I was hoping for was some confirmation that what I was seeing was 'a HSDPA unit that only found a 2G network' rather than 'you plonker, your ppp config sucks'

According to their map, I can at best get 2G, although I am at (relative to other places nearby) a pretty decent altitude.