[Bluez-users] hcidump and l2cap questions

[Bluez-users] hcidump and l2cap questions

[Sean Loh]

Hi,

I'm streaming audio from one computer to another
computer  using the pan profile.

1. I would like to see bnep packets being filtered
through hcidump. But when i put the bnep filter on,
hcidump does not print out anything. It only seems to
print out acl and l2cap data. Why is that? How am I
able to see bnep packet info?

2. I notice that even if i send udp packets that have
55000 bytes. The maximum packet length that turns up
on hcidump is 1500 bytes. Shouldn't it be 55000 bytes
because the max mtu for an l2cap packet is 65535
bytes?

thanks

bluez rules



		
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Re: [Bluez-users] hcidump and l2cap questions

[Marcel Holtmann]

Hi Sean,

> I'm streaming audio from one computer to another
> computer  using the pan profile.
> 
> 1. I would like to see bnep packets being filtered
> through hcidump. But when i put the bnep filter on,
> hcidump does not print out anything. It only seems to
> print out acl and l2cap data. Why is that? How am I
> able to see bnep packet info?

simply call "hcidump -x" and be happy. However if you miss the initial
l2cap_connect_req the dynamic channel assignment don't works.

> 2. I notice that even if i send udp packets that have
> 55000 bytes. The maximum packet length that turns up
> on hcidump is 1500 bytes. Shouldn't it be 55000 bytes
> because the max mtu for an l2cap packet is 65535
> bytes?

The L2CAP uses segmentation and we use a MTU of 1691. Start thinking a
little bit about the Ethernet frame size and so on.

Regards

Marcel




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Re: [Bluez-users] hcidump and l2cap questions

[Sean Loh]

Hi again Marcel,

Thanks for the quick response!!!!

1. Does that mean that bluez constantly fragments all
upperlayer protocols to a max of 1500 bytes?

2. What does the parameters of these hcidump mean?
1098027478.336048 < BNEP: Compressed(0x02|0)
    [proto 0x0800]

As usual thanks a lot..!!!!


--- Marcel Holtmann <marcel@holtmann.org> wrote:

> Hi Sean,
> 
> > I'm streaming audio from one computer to another
> > computer  using the pan profile.
> > 
> > 1. I would like to see bnep packets being filtered
> > through hcidump. But when i put the bnep filter
> on,
> > hcidump does not print out anything. It only seems
> to
> > print out acl and l2cap data. Why is that? How am
> I
> > able to see bnep packet info?
> 
> simply call "hcidump -x" and be happy. However if
> you miss the initial
> l2cap_connect_req the dynamic channel assignment
> don't works.
> 
> > 2. I notice that even if i send udp packets that
> have
> > 55000 bytes. The maximum packet length that turns
> up
> > on hcidump is 1500 bytes. Shouldn't it be 55000
> bytes
> > because the max mtu for an l2cap packet is 65535
> > bytes?
> 
> The L2CAP uses segmentation and we use a MTU of
> 1691. Start thinking a
> little bit about the Ethernet frame size and so on.
> 
> Regards
> 
> Marcel
> 
> 
> 



		
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Re: [Bluez-users] hcidump and l2cap questions

[Marcel Holtmann]

Hi Sean,

> 1. Does that mean that bluez constantly fragments all
> upperlayer protocols to a max of 1500 bytes?

this is only specific if you use BNEP, because it is an Ethernet
emulation and you can use IP on top of it.

> 2. What does the parameters of these hcidump mean?
> 1098027478.336048 < BNEP: Compressed(0x02|0)
>     [proto 0x0800]

I haven't looked up the protocol value for 0x0800, but I guess you get a
BNEP packet with an IP frame as payload.

Regards

Marcel




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