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

[Guy Harris <guy@xxxxxxxxxxxx>]

Eduardo Escudero Sánchez 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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