[Bluez-devel] How to know the packet loss ratio of SCO socket

[Bluez-devel] How to know the packet loss ratio of SCO socket

[Jui-Hao Chiang]

Hi, all:
as the title said, I am writing a simple server-client socket program for SCO
connection. While client is sending the SCO packet to server, it attaches a
sequence number to it. Then I want server to estimate the packet loss.
[Client program is as the following]
for (i = 0; i < 48, i++) buf[i] = 0x7f;
while (1) {
  *(uint32_t *)buf = htobl(seq);
  *(uint32_t *)(buf+4) = htobs(48);
  if (send(sockfd, buf, 48, 0) < 0) break;
  seq++;
  usleep(1)
}

However, on the server side, the data is total different, and I am not able to
get the sequence number (the hcidump -x also shows different data content as I
expect. Also, it's weird that the content is repeated)

Is this data encoded? or is there anyway to know the packet loss ratio of the
SCO connection?

Bests,
Jui-Hao


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Re: [Bluez-devel] How to know the packet loss ratio of SCO socket

[Jui-Hao Chiang]

> for (i = 0; i < 48, i++) buf[i] = 0x7f;
Sorry, just a typo, it should be (for i = 6; i< 48; i++)



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Re: [Bluez-devel] How to know the packet loss ratio of SCO socket

[Marcel Holtmann]

Hi Jui-Hao,

> as the title said, I am writing a simple server-client socket  
> program for SCO
> connection. While client is sending the SCO packet to server, it  
> attaches a
> sequence number to it. Then I want server to estimate the packet loss.
> [Client program is as the following]
> for (i = 0; i < 48, i++) buf[i] = 0x7f;
> while (1) {
>  *(uint32_t *)buf = htobl(seq);
>  *(uint32_t *)(buf+4) = htobs(48);
>  if (send(sockfd, buf, 48, 0) < 0) break;
>  seq++;
>  usleep(1)
> }
>
> However, on the server side, the data is total different, and I am  
> not able to
> get the sequence number (the hcidump -x also shows different data  
> content as I
> expect. Also, it's weird that the content is repeated)
>
> Is this data encoded? or is there anyway to know the packet loss  
> ratio of the
> SCO connection?

SCO are voice connections and they are CVSD encoded. It is not a  
reliable data transport. Use L2CAP or RFCOMM for that.

Regards

Marcel



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Re: [Bluez-devel] How to know the packet loss ratio of SCO socket

[Jui-Hao Chiang]

Hi, Marcel
> 
> SCO are voice connections and they are CVSD encoded. It is not a  
> reliable data transport. Use L2CAP or RFCOMM for that.
> 
> Regards
> 
> Marcel

I think you are right.
My original purpose is to test the voice quality when 12 SCO server-client pairs
are running in the same room (which means 12 small piconets contending the
channel, although each pair has its own frequency hopping pattern).

Is there any good way to gather the voice quality information? (actually I don't
know how to tell a voice qualify is "acceptable" to human ears. is there any
good references?)

Thanks,
Jui-Hao


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Re: [Bluez-devel] How to know the packet loss ratio of SCO socket

[Marcel Holtmann]

Hi,

> > SCO are voice connections and they are CVSD encoded. It is not a  
> > reliable data transport. Use L2CAP or RFCOMM for that.
>
> I think you are right.
> My original purpose is to test the voice quality when 12 SCO server-client pairs
> are running in the same room (which means 12 small piconets contending the
> channel, although each pair has its own frequency hopping pattern).
> 
> Is there any good way to gather the voice quality information? (actually I don't
> know how to tell a voice qualify is "acceptable" to human ears. is there any
> good references?)

I have no idea. However you will see interference if the devices are
close. SCO consumes a fixed amount bandwidth.

Regards

Marcel



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