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  #1  
Old 02-10-2012, 03:33 PM
Machine Elf Machine Elf is offline
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cell phones: why is there a transmit/receive delay?

When I speak to someone over my cell phone, there is a tiny but noticeable delay (compared to when I use a land line), either in the sending of my words to my partner, or in the sending of their words to me. It's just a tiny fraction of a second, but often it's enough to screw up the cadence of a conversation.

What is the source of this delay? A/D conversion within the phone? Encoding for transmission? Something else?

What of these sources is not present in conventional landlines?
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  #2  
Old 02-11-2012, 11:52 PM
CTburns CTburns is offline
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I can't speculate as to the answer, but I've noticed that too and hate having a conversation on a cell phone because of it!
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Old 02-12-2012, 09:03 AM
beowulff beowulff is online now
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It's all of the above.
Modern cell phones use packetized data. This implies a small but unavoidable latency in the audio. Add to this the delays in every step along the way - digitizing, compression, transmission, routing, reception, decompression, buffering, D/A and you end up with a delay of around 1/3 of a second or so.
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Old 02-12-2012, 12:48 PM
IAmNotSpartacus IAmNotSpartacus is offline
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Quote:
Originally Posted by beowulff View Post
It's all of the above.
Modern cell phones use packetized data. This implies a small but unavoidable latency in the audio. Add to this the delays in every step along the way - digitizing, compression, transmission, routing, reception, decompression, buffering, D/A and you end up with a delay of around 1/3 of a second or so.
This. It's DSP- Digital Signal Processing. They have to convert your voice to 1s and 0s based on the appropriate codec in the vocoder, and then have to deconvert it from 1s and 0s back to an analog signal for the speaker.
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Old 02-12-2012, 02:00 PM
Fear Itself Fear Itself is offline
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"Give it a second! It's going into SPACE!!"

~~thanx Louis C.K.
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Old 02-12-2012, 02:15 PM
scr4 scr4 is online now
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Originally Posted by Fear Itself View Post
"Give it a second! It's going into SPACE!!"

~~thanx Louis C.K.
But it doesn't goo into space. Not even inter-continental calls go into space anymore, they go through submarine cables. That's why the time lag on inter-continental calls is much shorter than it used to be.
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Old 02-12-2012, 02:19 PM
Baron Greenback Baron Greenback is offline
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Originally Posted by scr4 View Post
But it doesn't goo into space. Not even inter-continental calls go into space anymore, they go through submarine cables. That's why the time lag on inter-continental calls is much shorter than it used to be.
Why did they use satellites at all given that the cables have been there for a lot longer? Was it a capacity thing, now resolved by fibre or whatever?
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Old 02-12-2012, 02:20 PM
Fear Itself Fear Itself is offline
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Originally Posted by scr4 View Post
But it doesn't goo into space. Not even inter-continental calls go into space anymore, they go through submarine cables. That's why the time lag on inter-continental calls is much shorter than it used to be.
So, you are saying I can't trust a stand up comedian for the truth about digital electronics?
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Old 02-13-2012, 07:57 AM
Colophon Colophon is offline
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Originally Posted by scr4 View Post
But it doesn't goo into space. Not even inter-continental calls go into space anymore, they go through submarine cables. That's why the time lag on inter-continental calls is much shorter than it used to be.
I don't care if the delay is shorter. They had submarine cables in Victorian times, dammit. I want my phone call to go into SPACE!
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  #10  
Old 02-13-2012, 08:54 AM
Hermitian Hermitian is offline
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Originally Posted by Baron Greenback View Post
Why did they use satellites at all given that the cables have been there for a lot longer? Was it a capacity thing, now resolved by fibre or whatever?
Yea, they only had limited capacity before (when the cables looked like this).

Fiber means that you can put an amazing amount of data through, so telephone calls are a no-biggie.
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  #11  
Old 02-13-2012, 05:58 PM
Blakeyrat Blakeyrat is offline
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Quote:
Originally Posted by Machine Elf View Post
When I speak to someone over my cell phone, there is a tiny but noticeable delay (compared to when I use a land line), either in the sending of my words to my partner, or in the sending of their words to me. It's just a tiny fraction of a second, but often it's enough to screw up the cadence of a conversation.

What is the source of this delay? A/D conversion within the phone? Encoding for transmission? Something else?

What of these sources is not present in conventional landlines?
Cellphones are packet-switched (like your Internet connection, your USB bus, your cable TV-- well pretty much all data is packet-switched now), which means as the "phone lines" approach capacity, the latency increases.

Basically, the cell tower you (or your callee) was using was overloaded.
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  #12  
Old 02-13-2012, 09:24 PM
GameHat GameHat is offline
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Don't landlines have this delay as well?

I'm thinking of my boss and my former boss, both of whom have offices across from my cube (triangular).

When they're both on a conference call, both on speakerphone - there's a stadium echo effect when current boss (who has a big booming voice) speaks and there's a small fractional second delay from when he speaks to when I hear it from the speaker of former boss.

EDIT: or is that just the delay of the conference call "server" or whatever telco calls it?

Last edited by GameHat; 02-13-2012 at 09:25 PM..
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