Ethereal-dev: Re: [Ethereal-dev] Not understanding something in LLC

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From: Guy Harris <guy@xxxxxxxxxxxx>
Date: Thu, 29 Jun 2006 03:20:03 -0700
Eduardo Escudero S�nchez wrote:

But i dont understand. If you go to teh standard 802.2-1998 to the 5.4.2.1 <http://5.4.2.1> for example (Format of the I - PDU) you can see in the drawing that the bits are numbered from 1 to 16 and teh only indication it gives you is that the bit numbered with 1 is the least significant byte so one can deduce from here that the most significant bit of teh conrol field is teh bit numbered with 16 so the first byte of the control field will be the byte whose eight bits are the last eigth bits of the drawing. So you can not go to the last bit of the first byte to see the type of frame because you will be seeing the value of the P/F bit, dont you?

If bits are transmitted in the order in which they're shown in 5.4.2.1; the only way in which bit 1 would be the low-order bit of the *second* octet of a 2-octet control field would be if the second octet were transmitted first.

That seems unlikely to be the case.

Note that the control field is two octets, not a single 16-bit quantity; see 3.3.2 "Control field":

The control field shall consist of one or two octets that shall be used to designate command and response functions, and shall contain sequence numbers when required.
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