Android: slow network during phone calls

Question

We're working on an app that streams a large amount of data out via UDP for GSM-based phones. The idea is to use it while in conjunction with a voice call. If no voice call is present, things are good. However, if a voice call is active, it seems that most of the data we're sending out simply never makes it, even on HSPA+. If we enable Wifi, then everything is good.

I'm worried that this is a physics problem, rather than a phone one. I ruled out CPU contention by inserting a log statement after we send a chunk of data, and saw that it appeared plenty of times.

Is the 3G radio capable of sending data and voice simultaneously well? We tried a speed test during a voice call and saw a huge drop in bandwidth.

score 5 · Accepted Answer · answered Jul 24 '11 at 02:26

I've run into exactly this problem on AT&T's network in the US. They simply throttle the bandwidth while the call is in progress; whether you're on 3G or H. To see how much you're getting throttled try installing speedtest.net's app and running a speed test during and outside a call.

In the bay area I see data rates as low as 30kbit/s during a call on AT&T's network. On T-Mobile it's not throttled so much (same location). A partner in Israel tried the same test and saw only slight throttling during a call -- he was still seeing 500+kbit/s using the same phone that we tested on in the US. (The same phone that got several Mbit/s outside a call in the US.)

As the poster above points out, CDMA phones can't use data concurrently with a phone call at all (but you said GSM explicitly in your post anyway).

What phones did you try this on? We didn't see this issue on the iPhone. — Matt Green, Jul 25 '11 at 22:53
We were using Android phones, HTC Desire, Nexus One, Nexus S, Inspire HD. — Fasaxc, Aug 01 '11 at 19:06

score 1 · Answer 2 · answered Jul 20 '11 at 21:18

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Yes, when you are in a call, there might be not internet connection at all. It depends on the type of network you are in. It would vary from GSM, CDMA, and also the connection type, ie. GPRS, EDGE, 3G or 4G. The 3G and upcoming 4G connections should be able to simultaneous give you network connectivity and voice calling.

answered Jul 20 '11 at 21:18

Kumar Bibek

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Thanks, but my inquiry was directed toward whether the 3G/4G simultaneous data and voice actually performs well in practice. – Matt Green Jul 22 '11 at 11:31
©Matt Green It won't because of the reasons from Kumar Bibek:-) – powder366 Jul 24 '13 at 19:28

score 0 · Answer 3 · answered Jul 22 '11 at 14:36

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Yes, the radio is capable of sending both voice and data simultaneously, but from what I understand its a limitation of the network that your phone uses. If you are on Verizon's 3g network than this is probably your problem. Below is an article that goes into some details about the differences between at&t and Verizon's networks: http://mashable.com/2011/01/11/cdma-umts-att-verizon-networks/

answered Jul 22 '11 at 14:36

Noah

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After I made the original post, we've tested the iPhone in a similar manner and found it does not suffer the limitations I've discussed. We also tested the Android devices (Atrix, Inspire) on a microcell with little improvement. Everything is pointing to a limitation of the hardware within the devices, or the underlying Android platform. – Matt Green Jul 22 '11 at 14:56
Without the testing variables its hard to say, but are you sure the iPhone / android devices were all on the same network? If its a network problem, the tests on different devices could be masking the underlying issue. Also, while a microcell on the network should boost power, I don't think it will have any effect on the protocol of the base network. – Noah Jul 22 '11 at 17:03
We're both testing on AT&T's at the same location, first iPhone, then Android. We've replicated the results elsewhere. Android reports being connected to HSPA+. – Matt Green Jul 22 '11 at 19:39

score 0 · Answer 4 · answered Jul 26 '11 at 00:48

I don't know if this case apply to the operator you are using, but for the operators in my country, they limit the bandwidth used per phone, so if the user use calls and internet connection in the same time, you must subtract the bandwidth used for the phone call, which as i know 48 Kb/s for GSM networks(as maximum) and some of operators limits the call bandwidth for 24 Kb/s and and the total available bandwidth is 64 Kb, so the rest of the bandwidth is used for internet, and i don't know the bandwidth user for 3G networks.

BTW, some phones doesn't support phone calls and internet usage in the same time

all the information above belong to personal information able to be wrong

score 0 · Answer 5 · answered Jul 27 '11 at 07:36

I do confirm the bandwith is reduced during phone calls unless you are using wifi.

This seems to come from the system, not from the operator. This because it is reported with any hardware / any operator / any country. I have searched for some official documentation regarding that but couldn't find any.

I don't think there is any way to work around that so far.

Android: slow network during phone calls

5 Answers5