Bluetooth GPRS telephone timing connection

Question

I changed my old Powerbook 15" for a new one. The serial numbers of the "Old" and the "New" are given below. The Old powerbook had an external D-Link Bluetooth and the New has a built in one.
New: Mac Powerbook 15" version 2005
Serial Number W8541NLXSWZ
Old: Mac Powerbook 15" Alu version 2002
Serial Number QT30728DN4M
I definitely have a problem with the new Blutooth device.
Actually, I am using this device for a unique purpose: when travelling once a week for a 4 hours train trip, from home to work, I am using my Blutototh T68i SonyEricsson mobile telephone to get connected via GPRS to my mail box and internet and AIM to keep in touch with my collaborators.
With my old PB and connection I could stay connected for the whole trip whaterver was the level of connection low or high.
Now with the new PB, the GPRS connection is only kept for something like 2-3 mn of inactive transmission or reception.
This is not coming from the telephone company providing the internet connection, my two PB are working, can use the same telephone and only the new PB exhibits this "feature".
My com.apple.Bluetooth.plist looks like that.
• ControllerPowerState 1
• BluetoothSystemWakeEnable 1
• OBEXFTPRootFolderLocation /Users/francistaulelle/Documents
• OBEXFileHandling 0
• EncryptionEnable 0
• OBEXOtherDataDisposition 2
¢∫ FavoriteDevices
• OBEXOtherDataSaveToLocation /Users/francistaulelle/Documents
• OBEXPIMDataDisposition 2
• PrefKeyBluetoothMenuExtraShow 1
State
• PrefPanelTabIndex 1
• DiscoverableState 1
• OBEXPIMDataSaveToLocation /Users/francistaulelle/Documents
• OBEXSecurityUpdate-2005-005 YES
• RFCOMM10BEnable 1
¢∫ RecentDevices
• AuthenticationEnable 0
• BluetoothVersionNumber 2
• kPrefKeyFileTransferEnabled 1
• ControllerPowerState 1
• BluetoothSystemWakeEnable 1
• OBEXFTPRootFolderLocation /Users/francistaulelle/Documents
• OBEXFileHandling 0
• EncryptionEnable 0
• OBEXOtherDataDisposition 2
¢∫ FavoriteDevices
• OBEXOtherDataSaveToLocation /Users/francistaulelle/Documents
• OBEXPIMDataDisposition 2
• PrefKeyBluetoothMenuExtraShow 1
State
• PrefPanelTabIndex 1
• DiscoverableState 1
• OBEXPIMDataSaveToLocation /Users/francistaulelle/Documents
• OBEXSecurityUpdate-2005-005 YES
• RFCOMM10BEnable 1
¢∫ RecentDevices
• AuthenticationEnable 0
• BluetoothVersionNumber 2
• kPrefKeyFileTransferEnabled 1
I know a colleague that has written a little script to keep the connection awake, but I think this parameter can be set somewhere.
But I guess that the key to myproblem is in one of the parameters above. Which one?
The problem is especially annoying because since few months I am using a vpn connection and when the blutooth deconnects the internet connexion everything has to be started up again, every 2-3 mn !!!!!
I have read also on MacNN Forums > Hardware - Troubleshooting and Discussion > PowerBook > Bluetooth hardware suddenly not found - 17" pb
that blued.plist could/sould be removed in /private/var/root/Library/Preferences/ but I did not find any blued.plist.

Answer 1

I have to correct you. GPRS is very wired when it comes to computer connections. Rather than a network fault it is a mobile phone fault. You do not talk PPP with the network but with a GPRS/UMTS modem. It is like dialling into a network provider but rather you communicate with your phone's PPP software stack.
Because a phone has limited memory and this was a new area for mobile phone designers, buggy PPP stacks were created and included on mobile phones.
All mobile phones will disallow TCP/IP header compression. It makes no sense because the computer to phone interface (Bluetooth, USB or PC Card) is not a bottleneck as usual. However, most are able to negotiate this correctly. If you enable this setting, the phone will tell Mac OS X's PPP something like: "No, I do not have that feature. Please do not use it." However, sometimes the answer of the phone is not understandable to Mac OS X and the connection fails at all. So changing this setting has no effect at all.
PPP echo is another beast. Personally, I see no reason for it. Apple seems to love it to get better "connection is dropped" error messages. However, again this can cause much trouble with bad PPP software stacks as found on GPRS/UMTS phones.
There are even some bad PPP stacks out there, which do not forward the correct IP addresses to Mac OS X (like with early Sony Ericsson GPRS PC Card firmwares). Then it gets really complicated…