RE: Support of LAN FCS in Ethernet packet over ATM AAL5.

One more question please. 
In case that the LAN FCS is not supported (e.g. in LLC encapsulation format
the PID is 0x00-07), does the LAN FCS appear in the packet with arbitrary
value? I guess that the LAN FCS does not appear in the packet at all in such
a case. Can you please confirm it?
Thanks again, Nurit.

		 -----Original Message-----
		From: 	Nurit Sprecher  
		Sent:	Thursday, June 27, 2002 10:19 AM
		To:	'Manuel Stol'; PPPoE Mailing List (E-mail)
		Cc:	'bridge-mib <at> ietf.org'; 'hubmib <at> ietf.org'
		Subject:	Support of  LAN FCS in Ethernet packet over
ATM AAL5.

		In RFC 2684 on Multiprotocol Encapsulation over ATM
Adaptation Layer 5, the Payload Format for Bridged Ethernet/802.3 PDUs is
defined as follows:

		                +-------------------------------+
		                |    MAC destination address    |
		                +-------------------------------+
		                |                               |
		                |   (remainder of MAC frame)    |
		                |                               |
		                +-------------------------------+
		                |  LAN FCS (if PID is 0x00-01)  |
		                +-------------------------------+
		 
		The LAN FCS option is VC dependent. 
		In case that the LAN FCS is supported, duplicate checksum
calculations are performed: one for the AAL5 frame and one for the Ethernet
frame.

		In what cases is it required/suggested/worth to support the
LAN FCS when transmitting a packet within an AAL5 packet over an ATM
network? 

		Can a bridge that resides at the end of the ATM,
de-capsulate the ATM packet and transmit the Ethernet packet over a LAN,
calculate the LAN FCS and set it in the Ethernet packet (if required)?

		Thanks in advance, 
		Nurit Sprecher