Ethereal-users: Re: [Ethereal-users] assemble ATM classical IP packets??

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From: Guy Harris <guy@xxxxxxxxxx>
Date: Thu, 16 Jan 2003 20:44:16 -0800
On Wed, Jan 15, 2003 at 11:34:46PM -0500, Balendran Bala wrote:
> Let just say that a Sun terminal receives IP-ATM cells (256 bytes
> length IP packet) on its ATM interface.  So who actually does assemble
> the packet together on the Sun terminal? Is it libpcap? Is it the h/w?.. 

The hardware (i.e., the ATM interface).

Libpcap doesn't do any reassembly of anything whatsoever - that's not
its job; its job is to filter packets (or tell the OS kernel capture
code to do so) and to deliver those packets to the application using it.
Furthermore, those packets are also supplied to the Solaris networking
stack; if the reassembly weren't done in the interface, it'd have to be
done in the networking stack as well as in libpcap.

I also don't know how much of a CPU burden it'd put on the host to have
it do cell reassembly.  (It'd have to deliver cells in large batches -
interrupting the host for ever cell would, I suspect, be insane.)