Thread Links Date Links
Thread Prev Thread Next Thread Index Date Prev Date Next Date Index

Re: Interface reality check


To support T1X1 other types of frames aside from Ethernet format are
required. Since the format must be determined before the CRC can be located
using any part of the existing Ethernet frame to determine the format is
not a technique which works.



At 08:45 PM 4/6/00 -0700, Rick Walker wrote:
>Dear Paul,
>> "Paul Bottorff" <> writes:
>> It doesn't look like 64/66 can be extended to ANSI T1X1 systems.
>> So how is 64/66 going to extend the header mappings?  The T1X1
>> proposals relay on the <length><type><crc> to provide other frame and
>> header types for extended environments.  In particular the CRC check
>> allows validation of the <type> field giving a broad range of format
>> extensions.  The header CRC in ANSI T1X1 formats become essential for
>> the extended header fields used to address ring networks. 
>64/66 transparently supports all Ethernet packet signalling semantics.
>Ethernet packets include a two-byte <length/type> field.  The
><length/type> code is protected by CRC32 and is therefore quite
>The current mappings are:
>    L <= 1500	    	; the frame is an LLC data frame
>    L = 34,824	    	; the frame is a MAC control frame
>    L = 33,024	    	; the frame is a VLAN-tagged frame
>  none of the above 	; private use Type-frame
>This leaves a very large number of type indicators currently undefined
>by Ethernet.  I expect that they can be used to create ANSI T1X1 packet
>types if needed. 
>Best regards,
>Rick Walker 
Paul A. Bottorff, Director Switching Architecture
Enterprise Solutions Technology Center
Nortel Networks, Inc.
4401 Great America Parkway
Santa Clara, CA 95052-8185
Tel: 408 495 3365 Fax: 408 495 1299 ESN: 265 3365