[Bridge-mib] RE: Support of LAN FCS in Ethernet packet over ATM AAL5.

Nurit Sprecher <nurit.sprecher@SeabridgeNetworks.com> Thu, 27 June 2002 08:18 UTC

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From: Nurit Sprecher <nurit.sprecher@SeabridgeNetworks.com>
To: Nurit Sprecher <nurit.sprecher@SeabridgeNetworks.com>, "'Manuel Stol'" <ManuelS@AlliedData.com>, "'PPPoE Mailing List (E-mail)'" <pppoe@ipsec.org>
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Date: Thu, 27 Jun 2002 10:29:42 +0200
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Subject: [Bridge-mib] RE: Support of LAN FCS in Ethernet packet over ATM AAL5.
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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@ietf.org'.org'; 'hubmib@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


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