2 phonelines

[viper610]

Does anyone know if 5Mb DSL can support 2 lines at the same time?

[zombie999]

Do a speed test and post results. If your DSL is regular 800K upload, you can have up to 6 lines, no problem.
http://voiptest.nuvio.com/

[laurent]

Long answer: It depends a lot on the codec you choose for your outbound, as some are optimized for bandwidth (G729) and others for quality (pcm).

In the case of G729a, which is what I use, my router tells me a live call with continous talking takes about 6 kilobytes per second. My ordinary DSL line (5M/800k) could therefore, in ideal conditions with the wind in your back and going downhill, support perhaps a good dozen outbound channels (so, calls) at the same time.

Of course real life make it far from that. My actual bandwidth upstream is closer to half what I'm supposed to have, and there's a good 10-15% of "room" there should be to ensure immediate packet delivery (no delays in transit).

Short answer: yes.

[zombie999]

In the case of G729a, which is what I use,

Don't forget that FPL will not allow G729 on incoming, so "dozen calls" will not work.

[laurent]

incoming bandwidth on most DSL links is as almost ten times the bandwidth of the upstream. Whatever codec FPL uses for our inbound, his 5 Mbps link will certainly sustain as many call as his upstream can handle under g729a!

Also, in the 2 minutes call test I just ran on 3G with Siphone, download had about the same usage as upload, so their codec (is it g711?) seems just as good bandwidth wise...

[tbrummell]

incoming bandwidth on most DSL links is as almost ten times the bandwidth of the upstream. Whatever codec FPL uses for our inbound, his 5 Mbps link will certainly sustain as many call as his upstream can handle under g729a!

Also, in the 2 minutes call test I just ran on 3G with Siphone, download had about the same usage as upload, so their codec (is it g711?) seems just as good bandwidth wise...

I think you are a tad confused. On an inbound call, FPL wants g711 as we all know. We also all know that this requires approx 100kps of bandwidth. I think the part you are confused/ignorant about, is it is 100kpbs *symmetrical*. Both ways.....up and down. So your 400k is good for 4 calls. Just trying to point you in the right direction.

And, using g729 is around 8k for the voice stream, but with overhead packets it actually comes out to be around 40kpbs in the real world. g711 actually is 64kpbs but in real world with overhead is past 80kpbs, it's easier to just say 100k for the math.

[viper610]

thats awesome thanks guys

[laurent]

Okay let's clarify because I indeed was not clear enough, and I was wrong about codecs mixup. I thought different codecs could be used in the same call, but as tbrummell pointed out, when a codec is picked, it's used for both legs of the call.

Therefore, I clarify:

For outgoing calls, we can use the G729 codec. The actual measured real-world data use is 191 Kilo-Bytes per minute (3 Kilo-Bytes per second), or about 11 Mega-Bytes per hour in EACH direction (reception and transmission). The codec is used for both legs of the call, so speed is the same for RX and TX.

5 minutes test call over 3G with voice & music in each phone:

5mincall-g729.png (8.25 KiB) Viewed 12866 times

For incoming calls, FPL enforces the G711 codec. The actual measured real-world data use is 614 Kilo-Bytes per minute (10 Kilo-Bytes per second), or about 36 Mega-Bytes per hour in EACH direction.

Same 5 minutes test call over 3G:

5mincall-g711.png (8.26 KiB) Viewed 12866 times

Suppose this Bell DSL i'm sitting on right now, 5Mbps/640Kbps. Actual measured data transfers, in Kilo-Bytes per second, is 625 Kilo-Bytes/s downstream and 75 Kilo-Bytes/s upstream. Now I'm using all the same base for comparisons, measured Kilo-Bytes per second.

Since my bottleneck is upstream, and leaving some room to breathe (20%), I could sustain either:
- 6 incoming calls (because of G711 codec both ways), or
- 20 outgoing calls (thanks to G729 codec both ways)

This test includes overhead because it's a real call, not theorical bitrates, and is measured at the data provider (the phone itself's 3G data use measurements). Unless this measurement is unreliable, I think my test is pretty accurate.

[laurent]

Also one interesting thing to point out is that when I disable all codecs except 729 in siphon, I can't receive calls Why wouldn't FPL accept this codec for inbound calls if they recommend it for outbound? Seems counter-productive, as people might experience problems receiving calls while making them works fine (when bandwidth issues exist).

[tbrummell]

Also one interesting thing to point out is that when I disable all codecs except 729 in siphon, I can't receive calls Why wouldn't FPL accept this codec for inbound calls if they recommend it for outbound? Seems counter-productive, as people might experience problems receiving calls while making them works fine (when bandwidth issues exist).

I had the exact same thought. Only FPL tech people can answer that one. The only answer I myself can think of is they want inbound sound quality to sound as good as possible as a new user this would be one of the first things they check. Other then that, I have no idea why they force 711 on inbound. I wish they supported wideband, I have phones that have 722 and they sound excellent.

PS: I avoid 729 at all costs, I think it sounds like crap.

[laurent]

You know, I thought my brain was broken previously as call quality seems to differ from time to time, but couldn't see why. I now realize that all my incoming calls sounded great because of G711, and my outbound calls worse because of G729. As my DSL can handle the measured bandwidth easily, I'll switch off G729 from my prefered vocoders and go straight for 711.

Also, FunkyTown already pointed out that 711 was a great compromise of quality and bandwidth, and recommended we use it. Is think even DTMF can go through 711 as audio, right?

[tbrummell]

Is think even DTMF can go through 711 as audio, right?

Yes it does/can. As long as your DTMF option is set as Inband, otherwise it will go out of band as a SIP message.

[zombie999]

Okay let's clarify because I indeed was not clear enough, and I was wrong about codecs mixup. I thought different codecs could be used in the same call, but as tbrummell pointed out, when a codec is picked, it's used for both legs of the call.

It's true that different codecs can be used on the same call. One for upstream and one for downstream channel. But FPL does not negotiate that way.

Also, FunkyTown already pointed out that 711 was a great compromise of quality and bandwidth, and recommended we use it. Is think even DTMF can go through 711 as audio, right?

G711 does NOT compromise. It provides lowest latency and best quality (except for 722). Compromising is going with any compressed codec. And the only thing that FPL supports is G729 on outgoing (which indeed could sound better).

[laurent]

Awesome, so I'm switching my ATA to G711 immediately! Just tested it with Siphon and I can make outbound calls in 711, so that's the one I'll get in the ATA too.

EDIT: Wow the difference is incredible. Codecs from 1972 for the win!

Double-edit: I just did a very interesting test. Placed a phone call on G711 (outbound) while capturing bandwidth at the router. This is the DSL side:

As we can see, it tops at just about 10KB per second each direction.

The interesting part, is when observing the ethernet side:

Wow! I knew ethernet frames added some overhead, and that since voip packets are very small, it could add a lot of overhead. But this is just insane! 150% increase!

At least back on the DSL side, the actual data is back to original size, consuming reasonable bandwidth.

[zik]

hi is it 711a or 711u ?

[zombie999]

G711u

G711a does not work on FPL.
They are both similar. One is american and the other is european flavour.