Re: [ethmac] Ethernet Standard Related queries.

[Sanjeev Sablok <sablok@agere.com>]

Mohan,

 Which document is talking, that the length/type field is 4 octets ?.
I think they may be talking about,  4 octet of QTAG prefix which
should be inserted between SA and length/type field for a Tagged frame.
If not, can u tell me the name of the document. I just want to see that.
   Regarding the DA & SA fields, they are of 6 octets. Since no conformant
implementation of IEEE 802.3  uses 2-octet addresses. Therefore
IEEE had excluded 2-octet addresses from the standard. Guys what do u think?
Sanjeev Sablok


Mohan Krishna wrote:

> Hi All.,
>    Thanks for clarifying my doubt on Preamble & SFD.
>
>    I have  a few questions regarding the ETHERNET standard:
>
> 1. Some documents specify the "Destination Address & Source Address " as 2 or 6Octets.What is the
> correct length of  D.A & S.A fields?
> 2. Also the LENGTH/TYPE field is specified as 2octets in some documents and 4 octets in other
> document.
>     I assume its always 2 octets. Correct me if I am wrong.
>
> Also I would like to know whether the copy available for download in the IEEE website (IEEE Std
> 802.3-2002® (Revision of IEEE Std 802.3®, 2000 Edition)
> is the latest one for reference.
>
> Thanks in Advance.
>
> Regards.
> Mohan
>
> Illan Glasner wrote:
>
> > Yes you are tho' keep in mind the the SFD is not 1011 but rather 10101011 as
> > many time since in FE we work in nibble boundry it is common to define pre
> > as 1010 and sfd as 1011 and in such case you need at least one pre before
> > the sfd.
> >
> > have a nice day
> >
> >    Illan
> >
> > -----Original Message-----
> > From: Karthik D [mailto:karthikd@myw.ltindia.com]
> > Sent: Friday, December 06, 2002 6:14 AM
> > To: ethmac@opencores.org
> > Cc: mkrishna@tataelxsi.co.in
> > Subject: Re: [ethmac] necessity of preamble during reception
> >
> > ** Proprietary **
> > ** High Priority **
> >
> > "RX_DV (Receive Data Valid) is driven by the PHY to indicate that the PHY is
> > presenting recovered and decoded nibbles on the RXD bundle and that the data
> > on RXD is synchronous to RX_CLK. RX_DV shall transition synchronously with
> > respect to the RX_CLK. RX_DV shall remain asserted continuously from the
> > first recovered nibble of the frame through the final recovered nibble and
> > shall be negated prior to the first RX_CLK that follows the final nibble. In
> > order for a received frame to be correctly interpreted
> > by the Reconciliation sublayer and the MAC sublayer, RX_DV must encompass
> > the frame, starting no later than the Start Frame Delimiter (SFD) and
> > excluding any End-of-Frame delimiter"
> >
> > This tells that we need to look for valid SFD rather than Preamble to
> > receive the frame.
> >
> > Hope i am correct...
> >
> > Karthik D.
> >
> > >>> mkrishna@tataelxsi.co.in 12/06/02 05:45PM >>>
> > hi all,
> >
> > I have simple doubt.During reception of a frame is it required that all
> > the preamble(i.e 6 octets) has to be received or is it suffucicient that
> > a valid SFD is received before the frame can be processed.
> >
> > Thanks in advance
> > Mohan
> >
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