Trame ethernet II et taille des données

Marsh Posté le 02-01-2009 à 23:19:44

Bonjour :hello:

Par simple curiosité je ne comprends pas comment, dans une trame ethernet v2, l'ordinateur fait pour distinguer la fin des données des octets de bourrage, du CRC ou d'éventuels parasites puisqu'il ne dispose pas d'un champ longueur.

Merci d'avance de vos réponses

Marsh Posté le 02-01-2009 à 23:19:44

Marsh Posté le 27-03-2013 à 15:44:41

Marsh Posté le 24-02-2019 à 03:40:43

up car je sais toujours pas

Marsh Posté le 24-02-2019 à 05:29:43

Citation :

The Physical Coding Sublayer is responsible for delimiting the frames, and sending them up to the MAC layer.

In Gigabit Ethernet, for example, the 8B/10B encoding scheme uses a 10 bit codegroup to encode an 8-bit byte. The extra two bits tell whether a byte is control information or data. Control information can be Configuration, Start_of_packet, End_of_packet, IDLE, Carrier_extend, Error_propagation.

That is how a NIC knows where a frame start and ends. This also means that the length of the frame is not known before it has fully decoded, analogous to a NULL-terminated string in C.

https://serverfault.com/questions/8 [...] a-frame-is

Citation :

The control symbols within 8b/10b are 10b symbols that are valid sequences of bits (no more than six 1s or 0s) but do not have a corresponding 8b data byte.

https://en.wikipedia.org/wiki/8b/10 [...] ol_symbols

Citation :

The end of a frame is signaled by loss of carrier or by a special symbol or sequence in the line coding scheme for a particular Ethernet physical layer, so the length of the frame does not always need to be encoded as a value in the Ethernet frame.

https://en.wikipedia.org/wiki/EtherType#Overview

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