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jjx is offline jjx
2009-11-20 , 01:39
Posts: 474 | Thanked: 283 times | Joined on Oct 2009 @ Oxford, UK
#21
Originally Posted by chemist View Post
Example: you are somewhere with CDMA (HSPA) and you provider decided to use at the train-station another radio-station type as downtown (because of the amount of people or something) it could happen you drop connection and reconnect while entering to its radio zone, maybe you get more speed, maybe the provider gets more channels (users).
Yes, I've noticed that happening.

It is a good reason why modern applications should use robust protocols which can tolerate change of IP address and dropped TCP connections, without breaking the application's connection.
 
TA-t3 is offline TA-t3
2009-11-20 , 10:46
Posts: 3,841 | Thanked: 1,079 times | Joined on Nov 2006
#22
Originally Posted by jjx View Post
It is a good reason why modern applications should use robust protocols which can tolerate change of IP address and dropped TCP connections, without breaking the application's connection.
TCP/IP by itself supports this, or rather, doesn't care about the physical layer. Years ago I could disconnect the PPP phone networking on my laptop, close the laptop and go home. In the middle of a remote data transfer. Then come back the day after, open the laptop, connect the cellphone, re-dial the system. Data transfer continued.

As long as the same laptop had Windows on it this was broken though, because Windows insisted on shutting down any TCP/IP connections if the physical network broke. Which happened all the time with the cellphone, so I had to restart data transfers all the time and got a phone bill which could have bought several laptops. Manager not happy.
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jjx is offline jjx
2009-11-27 , 05:10
Posts: 474 | Thanked: 283 times | Joined on Oct 2009 @ Oxford, UK
#23
Originally Posted by TA-t3 View Post
TCP/IP by itself supports this, or rather, doesn't care about the physical layer. Years ago I could disconnect the PPP phone networking on my laptop, close the laptop and go home. In the middle of a remote data transfer. Then come back the day after, open the laptop, connect the cellphone, re-dial the system. Data transfer continued.
TCP/IP can't resume a connection if your IP address changes. That was unusual in the old days, but now it's common. I've seen it happening sometimes when hopping from one 3G base station to the next, and of course it always changes IP address when switching between 3G and WLAN.

Also, fwiw, TCP/IP doesn't do very well if your connection is down for, say, 30 seconds. It may recover, but it'll sometimes take another 30 seconds to notice after the connection comes back. If your connection is down for 120 seconds, TCP/IP won't recover at all if there is any outgoing data in flight, because it'll time out.

That's what I was getting at: Robust protocols can handle a change of IP address and long downtimes. For example, IM protocols. If well done, you just have a pause until it reconnects when the connection is back, and you carry on the same chat rather seamlessly.
 
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tso is offline tso
2009-11-27 , 05:26
Posts: 4,783 | Thanked: 1,253 times | Joined on Aug 2007 @ norway
#24
one thing to consider in all this is that with GSM/GPRS/EDGE you cant do data and voice at the same time. get a voice call while the data stream is ongoing, if your lucky it will cut the data stream and go to call, if your unlucky the caller will be passed to voicemail or get a busy signal.

thats the thing about UMTS/HSPA, it can do data while doing voice (thats basically what a video call is doing), so one can for instance look up a phone number if its a unknown caller. hell, maybe have the system refuse the call if the number is on a database of known sales numbers...
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TA-t3 is offline TA-t3
2009-11-27 , 11:05
Posts: 3,841 | Thanked: 1,079 times | Joined on Nov 2006
#25
Originally Posted by jjx View Post
TCP/IP can't resume a connection if your IP address changes. That was unusual in the old days, but now it's common. I've seen it happening sometimes when hopping from one 3G base station to the next, and of course it always changes IP address when switching between 3G and WLAN.
This is true. It can be handled though, by layering a virtual network on top of the physical network, for example.

Also, fwiw, TCP/IP doesn't do very well if your connection is down for, say, 30 seconds. It may recover, but it'll sometimes take another 30 seconds to notice after the connection comes back. If your connection is down for 120 seconds, TCP/IP won't recover at all if there is any outgoing data in flight, because it'll time out.
Er, no, it doesn't. Not at all. You may add a timeout at another layer (e.g. ssh often has one), but there's not one inherent for delayed data. TCP/IP's timers start to pop in when you're disconnecting (there's one typically at 120 seconds, another near 15 minutes etc.)
If it couldn't survive a 120 second holdup during data streaming it wouldn't be very useful in a lot of normal, day-to-day conditions. TCP/IP was _designed_ to survive such things. I wasn't kidding when I described my over-the-night resurrection of a data transfer.
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shadowjk is offline shadowjk
2009-11-29 , 00:44
Posts: 1,258 | Thanked: 672 times | Joined on Mar 2009
#26
Note that he said "if there is any outgoing data in flight". Also applies to incoming data in flight.

Personally on N810 I use openvpn connecting to a server of mine. Connections are migrated without breaking from wlan to bluetooth-cellphone-edge/3g when I move about.
 
agogo is offline agogo
2009-11-29 , 07:32
Posts: 74 | Thanked: 25 times | Joined on Nov 2009 @ Bahrain
#27
How about a 3G/2G toggling widget?
 
chrisp7 is offline chrisp7
2009-11-29 , 11:14
Posts: 515 | Thanked: 193 times | Joined on Oct 2009
#28
Originally Posted by agogo View Post
How about a 3G/2G toggling widget?
Its not a very intuitive solution. Maybe suggest that as a different app?
 
chrisp7 is offline chrisp7
2009-11-29 , 11:15
Posts: 515 | Thanked: 193 times | Joined on Oct 2009
#29
Originally Posted by tso View Post
one thing to consider in all this is that with GSM/GPRS/EDGE you cant do data and voice at the same time. get a voice call while the data stream is ongoing, if your lucky it will cut the data stream and go to call, if your unlucky the caller will be passed to voicemail or get a busy signal.

thats the thing about UMTS/HSPA, it can do data while doing voice (thats basically what a video call is doing), so one can for instance look up a phone number if its a unknown caller. hell, maybe have the system refuse the call if the number is on a database of known sales numbers...
I didnt know that, good point. - Is the N900 designed to cut the connection with an incoming call (2G/EDGE/GPRS)?
 
Aweb is offline Aweb
2009-11-29 , 14:45
Posts: 62 | Thanked: 24 times | Joined on Nov 2009 @ France
#30
Originally Posted by chrisp7 View Post
I didnt know that, good point. - Is the N900 designed to cut the connection with an incoming call (2G/EDGE/GPRS)?
N900 supports class A GPRS, which mean you can do audio and data at the same time, but your provider may not (in France, none does). Normally, they have Class B which will tell the phone there's a call and stop the data.

More information there : http://en.wikipedia.org/wiki/General...rvice#Hardware
 

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