01-19-2012 06:52 AM
I am making a voip application which uses UDP as a transport mechanism and everything works well for WIFI connections and the datagrams are send and received successfully.
But when I try to use 3g connections with APN some interesting results are observed:
- On a blakcberry without data plan the datagram packets are transferred successfully and the apn=wap-gprs.mtel.bg which is the apn for my carrier
- On another blackberry with data plan there are two apns detected - apn=wap-gprs.mtel.bg and apn=blackberry.net.
When I try with the first one everything is ok but with the second one I get an error on the server side that TCP is not a valid transport type for my request. So this means that somewhere in the middle there has been a conversion of the traffic from UDP to TCP. Has anyone encountered this? Is it possible to send datagrams successfully through device with data plan without this conversion.
The device is Bold 9780 os 6, non BES, GSM device.
04-06-2012 09:29 AM
The second apn is likely to be the BIS apn which does not support UDP. Here is the thing. There is really no UDP as we know it in 3G as the packets are broken up for transmittion from the BB and reassembled on the AP side. So some kind of reliable communications mechanism is used for this leg. In your case, the BIS server is attemptinig to reassmeble the packets back to a UDP packet which it probably does not understand because it is expecting TCP packets.