Subject: Question on CRC-32 (MPE)

From: "Simon Teh" <[email-masked]>
Date: Mon, 23 Aug 2004 15:30:20 +0800

Dear all members,

          Currently I'm doing a study on MPE encapsulation. I got a question
on crc-32 field. From my understanding, I know that the crc-32 is compute
from the whole datagram section including the crc-32 bit tailer, but what
I'm confusing is if we would like to compute the crc-32, what is the
original value for that field (crc-32). Hope some expert could give me some
guidance. Thanks in advance!

Best Regards,

Simon Teh

Universiti Sains Malaysia

---

From: Moritz Vieth <[email-masked]>
Date: Mon, 23 Aug 2004 10:53:14 +0200

Simon Teh wrote:
> Dear all members,
> 
>  
> 
>           Currently I’m doing a study on MPE encapsulation. I got a 
> question on crc-32 field. From my understanding, I know that the crc-32 
> is compute from the whole datagram section including the crc-32 bit 
> tailer, but what I’m confusing is if we would like to compute the 
> crc-32, what is the original value for that field (crc-32). Hope some 
> expert could give me some guidance. Thanks in advance!
> 
>  

Dear Simon,

Taking a look in the current ULE draft (draft-fair-ipdvb-ule-02) helps 
on this issue as well. The same paragraph that says for which part of 
the packet the CRC is to be calculated states:
"The Encapsulator initialises the CRC-32 accumulator register to the 
value 0xFFFF FFFF."

Regards,

Moritz

-- 
Moritz Vieth

Fraunhofer Institute for Open Communication Systems
Competence Center for Advanced Satellite Communications

Schloß Birlinghoven
D-53754 Sankt Augustin, Germany

+49-(0)2241-14-3467
[email-masked]

---

From: Gorry Fairhurst <[email-masked]>
Date: Mon, 23 Aug 2004 10:28:24 +0100

Please do note the CURRENT ULE draft is:

http://www.ietf.org/internet-drafts/draft-ietf-ipdvb-ule-01.txt

And not the version quoted - the version that you mentioned is now obsolete.

The CRC algorithm in ULE is intended to follow that for MPE (see the ISO
Spec) - please do tell us of any differences or ambiguities. The new text is
intended to be clearer - in particular there is a hex dump of a packet
encoded using ULE that may be used to verify your algorithm implementation.

Best wishes,

Gorry

On 23/8/04 9:53 am, "Moritz Vieth" <[email-masked]> wrote:

> Simon Teh wrote:
>> Dear all members,
>> 
>>  
>> 
>>           Currently I¹m doing a study on MPE encapsulation. I got a
>> tailer, but what I¹m confusing is if we would like to compute the