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Re: [bluetooth-dev] resend: Qestions on packet loss and SDP
Le Mercredi 23 Mai 2001 16:27, Mandana Amiri a écrit :
> Sorry for the resend, but I appreciate if someone can address my questions.
> I'm running axis stack on both sides with ericsson modules over UART. I
> have 2 doubts that I hope someone can clarify for me.
> I was trying to send a file over using rf_send (rfcomm_send_data) and then
> on the receiving end receive with bt_receive_top. But packets were dropped
> at the other end without any notification. Let's say if I sent 4
> packets:1,2,3,4. Only 3 packets were received: 1,2,4 and no errors. So I
> had to implement a protocol to add a sequence number to my packets and send
> a 1 byte acknowledge for each packet to prevent packet loss. As a result
> the file transfer is very very slow.
> Now I wonder if this should be handled automatically through lower layers
> by retransmit or other mechanisms so the higher layer(my application layer)
> shouldn't have to worry about. Please let me know what am I missing here,
> (probably more spec. related than Axis related).
Ok. Inside the Bluetooth baseband an acknoledge/retransmit mechanism is
implemented so that no packet is lost. Your problem looks very strange to me.
It is probably not a UART packet : if one byte is missed, then the stack
should complain and not "drop" any acl packet. There must be someting inside
For your information, the protocols used over rfcomm (like PPP) do not
implement a (sequence number, acknoledge)/retransmit scheme for the
packets... they are supposed to be transmitted properly.
> My second question is on SDP implementation and the spec. is not clear to
> me. I've ported axis stack to PC and also to an embedded processor. The way
> SDP is implemented in Axis stack, it uses fork/exec which I don't have in
> any of these environments.
What operating system are you using then ? What changes have you done to the
stack ? That could explain a lot of things on the rfcomm side... If you want
help from us (or at least from me...), send all the information about your
system, instead of just resending the same questions...
> My goal is to run Axis only on receiving side
> and be able to run DigiAnswer or Ericsson BlueExplorer on the other side. I
> need only minimum SDP support so my bt device can be discovered by such
> applications so they can start sending me
> files. I'm looking for some tips on how to do this and which procedures to
The SDP support provided by the axis stack should work fine for that.
> THanks in advance,
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