RE: [ethmac] how about VLAN?

["Illan Glasner" <iglasner@zumanetworks.com>]

Hi,

	Ok now I got what you mean by this special arithmetic, and I wouldn't recommend try to find a furmola. and I will even bet that if you ever find such formula for any given packet and vlan it will not only be HUGE compare to the 32 FF and few LUT that CRC require. keep in mind crc is far from being a chksum.

why when you recive packet you want to change the vlan ?
usualy vlan will be change/insert on the trasmite.

it is true there are some cases vlan can be modify in the input as well as in the output only maybe in your case you can do it on the output and in such case save the exrta crc machine.

BTW the crc mahcine are really not so complicated. more over both generator and checker use same equation and only the wrapper of it have really minor differance.

have a nice day

   Illan


-----Original Message-----
From: jcwh@sina.com [mailto:jcwh@sina.com]
Sent: Thursday, April 04, 2002 5:13 PM
To: ethmac@opencores.org
Subject: RE: [ethmac] how about VLAN?


if we need to insert a vlan tag in a received frame.we should:
1 check the non-vlan packet is good or bad by calculate crc for it.
2 intert a VLAN tag.
3 reculate crc for the new packet.

so, we shall implement 2 CRC modules in this design. and the circuits is 
very complicated.

if we desing a special arithmetic, maybe only one crc module is needed. 
and circuits became simple?

i mean when recalculate crc, we just calculate the crc for VLAN tag, 
and use this crc value to modify the original CRC.
i don't know the details, but i think it is possible.


----- Original Message ----- 
From: "Illan Glasner" <iglasner@z... > 
To: <ethmac@o... > 
Date: Thu, 4 Apr 2002 08:38:00 -0800 
Subject: RE: [ethmac] how about VLAN? 

> 
> 
> 
> 
>    Hi, 
> 
>          I'm not sure I follow what you try to say when you write 
> special aritmetic, but basicly when you get a packet and want to 
> remove/change the vlan while you remove the vlan your crc checker 
> will check the original packet before the remove/change and NOT 
> after. 
> 
> and when sending packet if you insert/change a vlan you recalculate 
> the crc on the fly while sending it away and just override the old 
> crc with the new one. 
> 
> Notice that 64-67 byte packet with vlan that you decide to remove 
> the vlan you need to pad to prevent the packet to become less than 
> 64. 
> 
> have a nice day 
> 
>    Illan 
> 
> 
> -----Original Message----- 
> From: jcwh@s...  
> [/cgi-bin/post.cgi?cmd=new&to=jcwh%20at%20sina%20dot%
20com&msg=/ml-archive/ethmac/msg00007.shtml] 
> Sent: Thursday, April 04, 2002 1:52 AM 
> To: ethmac@o...  
> Subject: [ethmac] how about VLAN? 
> 
> 
> Is someone going to implement VLAN tag insertion and extraction in 
> this 
> mac controller? 
> 
> when inserting /extracting the VLAN tag, CRC should be calculated 
> once 
> more. 
> 
> Can we just change the old crc on some kind of spcial arithmetic 
> ,while 
> not "crc through" the whole frame? 
> 
> does someone here know this kind of arithmetic? 
> 
> thanks 
> 
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