[Twisted-Python] twisted and gprs

John Aherne johna at johnaherne.co.uk
Wed Jan 10 03:49:05 EST 2007

Carl Zmola wrote:
> John Aherne wrote:
>> Phil
>> Thanks for the reply.
>> I'm obviously missing some obvious point I think.
> I think the obvious point is that: Everything works find while the TCP 
> socket is open.  The server knows everything about the client at that 
> time.  Keep alives are sent  to keep the connection open.
> The only problem occurs when the connection is closed.  The client 
> must be responsible for re-establishing the connection, since the 
> server can not reach the client.
> To make matters more fun, the client will not always know the 
> connection is down unless the client is sending keep alives (with a 
> watchdog timer going).
> After you figure this all out, you can worry about UDP. UDP would only 
> be useful in this situation when the client is pumping data to the 
> server and does not need an immediate response, since the server may 
> not be able to send UDP data to the client.  A good example would be 
> position updates.  The client could send position updates every minute 
> via UDP and connect via TCP every 15 minutes to guarantee the messages 
> got through.
> You should probably get familiar with IP, UDP and TCP framing and byte 
> counting if you are working with GPRS.  Bytes can start to add up if 
> you don't pay attention to them.
> Carl
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Thanks for the reply.

I think the client can check its local IP address. If that has changed 
then it will know it has lost and regained its connection. It can then 
reconnect to the server. I'm not sure if this is cast in stone, but I 
can imagine a case where it might not apply.

OK, I have been looking up frame sizes etc. And I have been looking at 
the data sent through an ethernet analyser just to confirm what actually 
goes down the line.

Thansk for the advice.

John Aherne

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