Archived from groups: comp.dcom.lans.ethernet (
More info?)
In article <41948af1$0$10649$8fcfb975@news.wanadoo.fr>,
"Michelot" <mhostettler@wanadooNOSPAM.fr> wrote:
>
> There is no difference between one error in the payload of one Ethernet
> frame, or one error in the payloads of 50 successive Ethernet frames
> carrying the same application layer message. At the application layer, the
> reassembled message could be discarded.
>
There is a BIG difference. Let's say that I want to send 1 million bytes
of application data. If I send it as 500 blocks of 2K bytes each, and
there is an error in one of the frames, a single 2K block must be
retransmitted (typically, at the Transport layer).
If instead I send the data as a single message of 1 million bytes and
there is an error in the frame (which I agree has the same probability
of containing an error as the 500 blocks of 2K bytes), then I must
retransmit the ENTIRE 1 million bytes over again. That's a severe
penalty for a single bit error.
> The problem with the global Ethernet stack (SNAP > LLC > MAC > xxBasex) is
> that we dont't have a complete adaptation layer. The Ethernet frame limit is
> reported to the 3-layer because there is no way to detect a floating 3-layer
> header in the Ethernet payload (each SNAP payload always begins by a level-3
> header).
>
I am not sure what you are talking about here. SNAP and LLC are rarely
used, particularly not in a TCP/IP context. (They are used for things
like AppleTalk, and NetBIOS/NetBEUI, but these are minor players today,
relative to TCP/IP.)
In the more typica, IP-over-Ethernet scheme, we use Type encapsulation,
and the IP header appears immediately following the Protocol Type field;
it does not "float".
--
Rich Seifert Networks and Communications Consulting
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