AT&T 3G MicroCell: A Comprehensive Exploration
by Brian Klug on April 1, 2010 1:55 AM EST- Posted in
- Smartphones
- AT&T
- Microcell Review
- Mobile
I mentioned earlier that voice and data both work fine, as long as you're inside the MicroCell's coverage radius. So what happens if you step outside? In theory and per advertising, your call is supposed to transition "seamlessly" to the nearest macrosite. In fact, the first time I tried walking out of location 1, it transitioned perfectly! I then proceeded to spend over a half hour trying to repeat my initial success...
The Theory of Handovers
But before I dive into the problems I experienced, let's briefly touch on some of the tech behind it. There are two types of handover that happen on a cellular network: soft and hard handovers. In a soft handover, the phone is continually talking to multiple macrocells at the same time - the transition happens seamlessly because you're already connected and communicating with towers you're going to handover to. This is a make-before-break transition. The transition is simply a matter of choosing which one has the best link quality, and this is generally how most transitions happen because it's robust.
The other case is a hard handover - this is less seamless break-before-make transition that's nearly instantaneous in practice, but still perceptible if you know what to look for. In a hard handover, the phone literally releases its active connection and transitions to another. Also of relevance are so-called vertical handoffs - these are transitions that happen across network technologies, in this case from UMTS to GSM, though other cross-technology handovers are possible as well. There's a huge amount of complexity to these systems; effectively handing off users while maintaining voice and data sessions is a challenging multidimensional problem. One that's often taken entirely for granted because of just how well we're used to it working.
So you can imagine my surprise when I discovered that the handover from femtocell back to public 3G wasn't just rough, it's downright crude. First of all, virtually every femtocell handover is of the hard variety, and in practice almost all of the ones I saw were also vertical, from UMTS (3G) to GSM (2G). During that long provisioning process, I mentioned that the femtocell is building a rough list of all the macrocells it can see. Hopefully, it can see a few of both 3G and 2G variety, which it passes onto the phone in the form of a neighbor list. The phone also builds out its own neighbor list, which you can see some of in the Field Trial (*3001#12345#*) dialer application. It's been gimped significantly since the iPhone 2G, but there's still enough here to get the point across:
Neighbor Cells - Just like advertised
Anyhow, when you leave the femtocell's radius, if there's a macrocell in range and your phone can hard handover to it, the call continues. Hopefully this is what happens, otherwise the call drops. Of course, the big caveat here is that if you're installing the femtocell in a place with little to no signal (why it's there in the first place) handover is going to be a difficult prospect. That's why I tried the AT&T MicroCell both in an area with good existing coverage, and one with poor coverage. The results at both were equally disappointing.
AT&T advertises an effective range of 5000 square feet. This seems about right, but it's signal dependent. Location one is just over of 2000 square feet, and continual femtocell coverage barely makes it across two rooms. Location two is effectively 5000 square feet, and femtocell coverage includes the whole house, guest house, and most of both long driveways. Again, this is largely in part because the femtocell is sitting atop existing 3G spectrum - there's no spectrum overlay just for microcells yet. The result is that if signal is bad where you are, your microcell range is larger. Conversely, if signal is already reasonable, you're not going to see more than a room or two of microcell coverage. It's a complex problem akin to the cell breathing phenomenon, and I think AT&T's 3G MicroCell product is doing a lot of ranging at setup.
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dkapke - Thursday, April 1, 2010 - link
I can't speak for what AT&Ts plans are, but I think what a lot of you aren't seeing, at least in terms of Sprint, is I LOVE their femtocell. Not because I can't get service or have crappy coverage, but because it allows UNLIMITED calls. I can get their cheapest plan, eliminate the home phone, and so long as I'm not driving between 6a-6p all of my calls are free. I work from home so this is great.So, all of you saying this is AT&Ts method of uncongesting their network - yes, that's true. But you're missing a very valid argument FOR these - unlimited calling. I guess you have to determine how often you're at home and how many minutes you use at home before night/weekend calling kicks in, but for those of us who work from home, these are awesome and well worth the $20. Oh, and when my kids come down for the summer and spend all day on the phone while they're sitting around at the house...yeah...it pays for itself very quickly.
echtogammut - Thursday, April 1, 2010 - link
They even collaborated with AT&T on this one : http://www.wireless.att.com/learn/why/3gmicrocell/...Seriously, what really gets me about this, is I installed a booster for the last company I worked with because they were not able get calls when more than 5 data phones were in the building. I called AT&T to see if I could work with them about setting up a device similar to the microcell and they transferred me to an engineer that warned me off boosting the signal. Not that long ago they called me and offered this device to fix my reception issues and charge me for another service plan... no thank you, the booster is working fine.
kamikaze56 - Thursday, April 1, 2010 - link
I agree with all you guys saying that you wont pay for a monthly cellular bill, buy your own "cell" wich uses YOUR own internet connection.. But just remember a few facts:- First of all, this device is aimed to people who have very low to zero coverage on their house/workplace and DONT want to change carrier (Or cant due to contracts), it is not aimed to people who can change their carrier at anytime..
- Second, most of the "negative" review on this article was found on location 1 (Location in urban area, with a really good coonection, crowded spectrum etc) remember, this device is aimed to locations with Zero to Really bad coverage
- 3rd and most important: Yes, you are paying your bill, you are paying by your own cell and using your own internet connection but remember, you are just using like 1/50 part of your connection in order to REACH THE CORE NETWORK, what happens in the core network and forward its still being done by the carrier (And this part of the communication process is the one that costs more), so your basically paying for using this core network. If you dont agree with this.. DONT BUY IT
kidboodah - Thursday, April 1, 2010 - link
There seems to be a misunderstanding on the pricing of this.You pay $20 a month for unlimited minutes while connected to it. This includes up to 4 simultaneous connections.
So let's say you have a 1400 FamilyTalk plan, with 4 lines. That's $109.99 per month normally. Add the Microcell and you have Unlimited talking from home for $129.99 for all lines.
Compare this to an Unlimited Family Talk plan for $70+50+50+50....and you're saving $100 a month.
It's definitely worth the initial cost for alot of customers who are on Family plans and want unlimited service from home -- while ALSO giving them full signal strength.
taltamir - Thursday, April 1, 2010 - link
there is no such thing as a radius in square feet.Square feet is used to describe the area.
Since the area of a circle is Pie*r^2 then ((5000 ft^2)/pie)^0.5 = r
or a radius of 39.89 feet
Brian Klug - Thursday, April 1, 2010 - link
Oops, that's a typo! Fixed!-Brian Klug
Ardric - Thursday, April 1, 2010 - link
The TCP and UDP ports you've listed are only used for provisioning, when the device boots. They don't carry the voice traffic. There's no use in bothering with them. Especially HTTPS -- do you really want to elevate that for your banking site too!?The voice traffic is on the IPsec tunnel, and that's carried by the ESP protocol. ESP is IP protocol 50. There's no port number.
So ignore the TCP and UDP ports and prioritize on ESP, preferably in combination with the particular AT&T IP addresses. That's how you should set up your QoS matching.
Brian Klug - Thursday, April 1, 2010 - link
You're totally right about the provisioning ports being used only for initial setup, but the device is using IPsec NAT-T, which is definitely 4500/UDP.To be honest, all my QoS rules prioritized the device in general - I'd say doing it with a static DHCP lease IP address or MAC addy makes the most sense.
Cheers,
Brian Klug
SmCaudata - Friday, April 2, 2010 - link
With T-mobile I have UMA on my phones so I can make calls anywhere I have a wireless signal. I don't need an extra box in my home AND I can use it in the deepest basement of my work.AT&T sucks. The iPhone is the ONLY thing they have going for them.
leexgx - Friday, April 2, 2010 - link
at any time did you use 2g only (set the Phone to 3g off) as i find 3g/HSDPA mostly unreliable (more so on the Iphones not so much on windows phones with HSDPA off) problem is most phone makers set the Hand over to GSM or 2g for there phones to low and i find 3g has more problems with weaker signal (if should move to 2g when signal is below 20% back to 3g when above 35%, as when 3g gets to less then 10-20% it seems to be unreliable)