Why is there no latency in local phone calls?

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simon14

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#9422 14-Sep-2006 15:31

How come there is no latency what so ever when making a loacal phone call? But on the internet and through cell phones, there is a noticeable amount of latency?

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#46161 14-Sep-2006 15:43

There is latency but on a local call the latency is so low most people can't recognise it.

If you want to test it talk to someone while you've both got your TV on the same channel. You should be able to hear a fractional delay in the audio for the TV.

Jp.

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simon14

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#46164 14-Sep-2006 15:53

I did a test once, I got my nieghbours cordless phone and bought it round to my house, i called my phone and had both phones up to my ear, as I talked my voice came out at exactly the same time, i couldnt notice any latency at all.

The tv test isnt accurate because TV itself can have latency, for example Sky is a few seconds behind analogue TV.

Bung

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#46168 14-Sep-2006 16:12

Make the most of a telephone system designed for voice while we still have it. From memory the round trip delay Wgtn - Auck is around 9ms so you'd be hard pressed to hear any delay on a true local call.

jpwise

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#46170 14-Sep-2006 16:20

Yeah, I was debating mentioning UHF vs cable/sky, but hadn't edited it yet.

Lol, what I'd give for a 9ms ping in a game a quake.. I normally play with a ~69ms ping on quake, and you can feel the difference to within 15ms or so generally for gameplay. Slight OT, but yeah. :)

Jp.

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juha

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#46171 14-Sep-2006 16:21

Actually, that is an interesting question. I was wondering earlier how much difference putting calls over a packet-switched network rather than a circuit-switched one makes?

Juha

simon14

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#46192 14-Sep-2006 18:10

My experience with VoIP is that the sound quality is better with VoIP, but latency is worse than standard telephone calls.

Xnet, for example, run all thier call centre calls through VoIP, and i can notice a delay when I'm talking with them. It can be annoying because you go to say soemthing, but they have already started to talk.... hopefully this will be fixed once interleaving can be turned off.

sbiddle

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#46193 14-Sep-2006 18:29

Any latency below 50ms will not really be detectible for voice calls, in an ideal network configuration you'll have less than 20ms latency anyway.

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Bung

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#46195 14-Sep-2006 18:32

If delay is noticable then there'll still be plenty assuming that interleaving is ~16ms in each direction.

simon14

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#46197 14-Sep-2006 18:41

So with interleaving turned off, we should get -32ms of latency reduced from our conntectionss current ping rate?

For example, If i currently get 45ms, if i had interleaving turned off, I would get 13ms?

barf

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#46199 14-Sep-2006 18:48

re interleaving: here is an ICMP ping result from an ADSL connection through TelstraClear (which I assume has interleaving turned off).

stuart@server:~$ ping -c4 geekzone.co.nz
PING geekzone.co.nz (210.48.73.74) 56(84) bytes of data.
64 bytes from geekzone.co.nz (210.48.73.74): icmp_seq=1 ttl=114 time=30.9 ms
64 bytes from geekzone.co.nz (210.48.73.74): icmp_seq=2 ttl=114 time=28.2 ms
64 bytes from geekzone.co.nz (210.48.73.74): icmp_seq=3 ttl=114 time=28.7 ms
64 bytes from geekzone.co.nz (210.48.73.74): icmp_seq=4 ttl=114 time=29.9 ms

--- geekzone.co.nz ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3029ms
rtt min/avg/max/mdev = 28.273/29.502/30.957/1.059 ms

heh this makes a good advert for TCL

Sniffing the glue holding the Internet together

simon14

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#46200 14-Sep-2006 19:39

Foudn this forum of a guy who is on XTRA and had his interleaving turned off.

http://www.gpforums.co.nz/thread/334768/?s

He shows some ping rates as low as 15ms through his ADSL connection.

Fraktul

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#46212 14-Sep-2006 21:57

You will typically see 12-25ms on an ADSL connection with no interleaving with small packet sizes and a decent connection rate. Lowering the speed the ADSL physical trains at like Telecom has done has added latency by way of serialization delay, minor however.

Increasing the speed and turning interleaving off is a dual whammy, if your line has a decent SNR to begin with and you dont begin dropping packets that is.

Fraktul

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#46213 14-Sep-2006 21:58

barf: re interleaving: here is an ICMP ping result from an ADSL connection through TelstraClear (which I assume has interleaving turned off).

stuart@server:~$ ping -c4 geekzone.co.nz
PING geekzone.co.nz (210.48.73.74) 56(84) bytes of data.
64 bytes from geekzone.co.nz (210.48.73.74): icmp_seq=1 ttl=114 time=30.9 ms
64 bytes from geekzone.co.nz (210.48.73.74): icmp_seq=2 ttl=114 time=28.2 ms
64 bytes from geekzone.co.nz (210.48.73.74): icmp_seq=3 ttl=114 time=28.7 ms
64 bytes from geekzone.co.nz (210.48.73.74): icmp_seq=4 ttl=114 time=29.9 ms

--- geekzone.co.nz ping statistics ---
4 packets transmitted, 4 received, 0% packet loss, time 3029ms
rtt min/avg/max/mdev = 28.273/29.502/30.957/1.059 ms

heh this makes a good advert for TCL

Was that sold from Telstra Clear or wholesaled from them out of interest?

antoniosk

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#46221 14-Sep-2006 23:13

The ping times on a UBS connection is about 66-69ms... 63-65 for Telecom latency, balance for TCL ISP layer.

On-net - TelstraClear has it's own copper network in the business districts - the ping times are much better as this shows.

Check out my opening thoughts for my geekzone blog - http://www.geekzone.co.nz/antoniosk/337 - for a potted history of where 50ms came from for acceptable voice quality. Amazing stuff.

Now try designing a service that can deliver that reliably - the best customer edge equipment (that doesn't cost a fortune) delivers in around 20ms (then add another 20ms for the return path....)

Now consider this.

High quality voice (what we get now on copper) is delivered using a G711a encoding. This requires a connection capable of about 80-90Kbps.

But 3G calls on UMTS only utilise 12.2kbps for the actual vox piece. GSM calls utilise 8Kbps.

The technology used to encode, decode and correct for errors is VERY good. And the human brain is VERY good at 'filling-in' the blanks - so if you think you heard "tree", on balance you probably did.

And the latency on a mobile call is quite horrible compared to wireline, but it works and people persevere.

Bung

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#46231 15-Sep-2006 07:20

antoniosk:
Check out my opening thoughts for my geekzone blog - http://www.geekzone.co.nz/antoniosk/337 - for a potted history of where 50ms came from for acceptable voice quality. Amazing stuff.

Your history only seems to go back 20 years which is nothing in terms of telephony history. Don't believe that some US Engineers just pulled 50ms out of their oops (thin air). There have been many studies done. I think the ITU (CCITT) G Series has some.

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