Wireshark · Ethereal-dev: Re: [Ethereal-dev] Fields and protocols relationships

[Stefano Pettini <spettini@xxxxxxxxxxxxxxxxxxxxx>]

Michael Tuexen wrote:

> does this mean that the protocol fields at one layer depend on the
> upper layer but there is no indication at this layer what the upper
> layer is? Sounds a bit 'special'?

After a careful reading of RFC 3450 ... well ... I'm wrong :-)

ALC is a "composite protocol". It's composed of many "building block", 
that can be reused by protocols other than ALC (NORM, for example, is 
another protocol of this kind). Not every building block is a protocol: 
for example some of them are algorithms for congestion control and error 
correction.

LCT is one of these building blocks, and it defines LCT specific 
extensions and "outer protocol" extensions. LCT is not a real protocol, 
you won't find LCT packets on the net, but only ALC packets containing 
LCT headers and fields. If I dissect an ALC packet, I know that the 
"outer protocol" of LCT is the ALC itself.

I posted my question since I confused the outer protocol with the upper 
layer protocol.

Of course ALC headers don't depend of the protocol transported by ALC 
itself.

Thanks.

Stefano