Re: [Linux-ATM-General] General doubt in ATM

[chas w. - C. <ch...@cm...>]

On Thu, 19 Aug 2010 19:49:15 +0530
mahendra varman <mah...@gm...> wrote:

> Hi
> 
> Is that possible to find what is the VPI and VCI value of a received
> cell from the trailer or by another means ?.

the vpi/vci is only contained in the header and most of the hardware
does not expose this in the aal5 layer.

> 1. Suppose in real time if the receiver does not know by what vpi/vci
> value the transmitter is sending then how to find from the received
> cells ?

you need an atm analyzer/capture device.  some hardware has the ability
to receive all the cells regardless of vpi/vci and deliver them to the
user.  however, this usually cant be done at line speed since it would
typically generate an interrupt per cell and require quite a bit of cpu
to handle a full rate oc3, 64-bytes at a time.  the pca200e has a
special firmware for this.  not sure about any other card.

> 2. Another query is In ethernet reception we can say broadcast address
> and it will receive from any address. Similarly is there any option to
> open aread such that it will receive cell of any vpi/vci value ?

nope.  a general solution might be to open all the possible vpi/vci
values for a card and poll() on all the open fd's.  ugly but
manageable.  however, most of the atm cards have a limit to the number
of bits you can split between vpi and vci so they cannot snoop the 
whole spectrum of possible cells.

> 
> Thanks
> Mahendra
>