[INFO] My findings pertaining to WiFi calling

unforgiven512

Senior Member
Oct 28, 2008
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Erie, PA
unforgivendevelopment.com
So, I've decided to give WiFi calling a spin (despite having a solid 4 bars of sweet, sweet HSPA+ sitting at my desk). I'd like to share my findings with you guys.

Firstly, I've looked into the bandwidth used by WiFi calling, by watching my router's information page.

Here is a screenshot of an active call


The very first section is me tapping on the mic, while waiting on hold with HTC (that's a whole 'nother story). The second part, silently listening to their boring hold music/we appreciate your call as a valued customer crap, the third part, a two-way, engaged conversation, and finally, me giving her my name, ticket number, etc, while she silently listened.

By the way, despite the green line being stated as "in", it is actually the outbound (upstream) bandwidth from my WAN interface. It's reporting as "in" because the data is flowing out of the WLAN chip on my phone, in to the WLAN interface (wl0) on the router, then going through the bridge (br0), and out the WAN port (vlan2) on my router. And, in effect, the red line would be incoming (downstream) data on my WAN, and it is flowing out of wl0 into my phone. Hope that makes sense. Also, my computer that I was viewing this info from did not fudge the results at all, I am connected via wl1 (the 5 GHz interface), and my G2 was the only client on the 2.4 GHz interface.

During this call, there was also some other traffic flowing in/out of the WAN interface (traffic from my PC, broadcast messages, and what not). Nothing extreme. The maximum bandwidth used at any point in the call was about 80kbps (kilobits per socond) in either direction. I am going to go out on a limb here and guess latency is more important to call quality than available bandwidth.

I do not have packet-level QoS enabled in my router, however, I do have WMM/WME (Wireless Multimedia Extensions) enabled, with DD-WRT's default settings. I am unsure if Kineto's UMA app tags the frames with the necessary information for it to be prioritized by WMM/WME. I guess I will look into that later.

From a subjective point of view, the woman I was speaking with sounded crystal clear, quite possibly better than a typical UMTS/GSM based call. I also asked her how I sounded on her end, and her response was "absolutely gorgeous". Then, we got back to the actual conversation, and about 30 seconds later, the call dropped. Hmph. The call drop log in SETTINGS --> ADVANCED SETTINGS --> CALL DROP LOG is as follows:

Code:
CD-12 ISP Problems
2010:11:04:11:06:18:336
Perhaps we can find reference to all of the error codes somewhere, and find out exactly what went wrong?

Well, that just about sums up my findings and information for now. I will be looking deeper into this, and how we can make it better, and more stable. I will also try to keep this post updated with my findings, as well as those of others, so you do not have to read through many pages to find all of the information.
 
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khaosxiii

Senior Member
Feb 26, 2009
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Cool!


Yeah latency is allways goign to be key - in a few aspects:

High latency is a problem: this would be due to you saying something and it not getting to the other end in time (this is why wifi calling over 3/4g is a bad idea).
If it takes too long it's discarded (choppyness) as we can't retransmit parts of a conversation over other parts that are already occuring in real time.
Drops: If a packet drops it's gone, it's not retransmitted - this is UDP, the reason being, again if you say something and it doesn't get there - there is no reason to retransmit it as you are already on to the next word in your sentance.
Of course in a TCPIP situation, for example accessing a website - if your initial request drops it's just retransmitted, several times if neccessary - the only thing you notice is waiting an extra half of a second for a page to load.
Jitter:is the variation in latency. If your latency is jumping all over from 40ms to 120+ms and back again then you will also experience issues. If there is slightly higher but consistent latency on a connection then this is likley better then a high varation in jitter.

I wonder what all codecs they're all using to transmit ... if it's straight voip or what?

:cool:
 

StanSimmons

Member
Jul 16, 2009
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I wonder what all codecs they're all using to transmit ... if it's straight voip or what?

:cool:
It isn't VoIP.

It is GSM over IP. GAN/UMA/WiFi Calling takes the normal GSM packets and encapsulates them in IP packets and send them thru an encrypted tunnel back to the carrier's (TMO) network. Once at the carrier network, the GSM packets are stripped out of the IP packets and handled like any other GSM call.
 

linkmaster_6

Senior Member
Feb 26, 2009
139
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If you are worryed about latency then turn QOS on, on your router and set your phone to have a static ip when you are at home. Thats what i did for our VOIP router at my house. Should work the same with your phone you would think