Re: DLT_LAPB value assignment

[<Mirko.Karanovic () ttc ca>]

-----Original Message-----
From: tcpdump-workers-owner () lists tcpdump org
[mailto:tcpdump-workers-owner () lists tcpdump org] On Behalf Of Guy Harris
Sent: August 13, 2007 1:12 PM
To: tcpdump-workers () lists tcpdump org
Subject: Re: [tcpdump-workers] DLT_LAPB value assignment

 

Mirko.Karanovic () ttc ca wrote:

> There is need to assign DLT_LAPB value for capturing of the X.25 LAPB

> traffic  and decoding it in the WireShark Protocol Analyzer.

 

1Q.   So would the packet data in a DLT_LAPB capture start with the
address 

field of the LAPB header, followed by the Control field, followed by the


Information field if any? 

 

1A: It's correct LAPB starts with Address, followed by Control, followed
by data if any.

 

 2Q: Or would it also contain an extra flag to 

indicate whether the packet is a DTE->DCE or DCE->DTE packet?

 

2A:  LAPB contains direction ( DCE to DTE or vice versa) encoded in the
Address byte. For Layer 3, decoder can decide direction knowing packet(
layer 3) type.

 

3Q:   Would the packets include the CRC at the end?

3A:   Currently, in my implementation FCS ( CRC-16) is not included.

 

 

4Q:   (I'm assuming they would *not* contain the flag octets at the
beginning 

and the end, and that all bit-stuffing would have been removed.)

4A:   That's correct.

 

With above set-up WireShark decodes my libpcap captured file, captured
using Sangoma S5142A card.

 

 

Best regards,

 

Mirko Karanovic.

 

-

This is the tcpdump-workers list.

Visit https://cod.sandelman.ca/ to unsubscribe.



The information transmitted is intended only for the person or entity to which it is addressed and may contain 
confidential and/or privileged material.  Any review retransmission dissemination or other use of or taking of any 
action in reliance upon this information by persons or entities other than the intended recipient or delegate is 
strictly prohibited.  If you received this in error please contact the sender and delete the material from any 
computer.  The integrity and security of this message cannot by guaranteed on the Internet.  The Sender accepts no 
liability for the content of this e-mail or for the consequences of any actions taken on basis of the information 
provided.  The recipient should check this e-mail and any attachments for the presence of viruses.  The sender accepts 
no liability for any damage caused by any virus transmitted by this e-mail.  This disclaimer is the property of the TTC 
and must not be altered or circumvented in any manner.
-
This is the tcpdump-workers list.
Visit https://cod.sandelman.ca/ to unsubscribe.