Réf. : Re: comment on ULE draft (bridging mode)

[Tarif.Zein-Alabedeen@space.alcatel.fr]

Hi Gorry,

Sorry if I have not been clear enough....
What I wanted to say is that I think the value for the TYPE field when the
FCS of the Ethernet frame is removed before it is encapsulated within the
SNDU (which is the case in the draft) should be 0x0007 and not 0x0001 (you
can check this in RFC 2684)
In fact both values indicate that the transported PDU is Ethernet. However
0x0001 indicates that the FCS is preserved and 0x0007 indicates that it is
removed.
This is the case for each bridged protocol and not only Ethernet.

What is needed is just to correct the type field in the indicated figures
of the draft

Best regards
Tarif ZEIN







Gorry Fairhurst <gorry@erg.abdn.ac.uk>@erg.abdn.ac.uk on 02/02/2004
19:24:55

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cc :
Objet :     Re: comment on ULE draft (bridging mode)




Tarif.Zein-Alabedeen@space.alcatel.fr wrote:

>This concerns §4.7.5 : bridged frame SNDU encapsulation ( fiugres 8 and 9)
>:
>The type field value in the figures is set to 0x0001.
>
Yes

> This indicates that
>the payload is an ethernet frame
>
Yes

>with preserved FCS
>
The Ethernet frame should be sent using ULE *without* an Ethernet-level
FCS as described in:

      "The Encapsulator MUST check the
        LAN-FCS value of all frames received, prior to further processing.
        Frames received with an invalid LAN FCS MUST be discarded. After
        checking, the LAN FCS is then removed (i.e., it is NOT forwarded in
        the bridged SNDU)."

http://www.ietf.org/internet-drafts/draft-fair-ipdvb-ule-02.txt

Is this the sort of behaviour that you desire?

>This leads to a redundant CRC : that of the Ethernet frame and that of the
>SNDU
>
>In Eth/AAL5, it is useual to remove the FCS field from the Eth frame
before
>encapsulating it in AAL5 PDU since AAL5 makes its own checksum
>This may also be a good thing for ULE.
>
>The coding for the type field when the FCS is not preserved is 0x0007
>(instead of 0x0001)
>
What do you mean?

>regards
>
>
>ALCATEL SPACE
>DRT/RST  --  Ingénieur Systèmes
>Tel : 0534356918  /  Fax : 0534355560
>Porte : W.220
>
>
>
Best wishes,

Gorry Fairhurst.









ALCATEL SPACE
DRT/RST  --  Ingénieur Systèmes
Tel : 0534356918  /  Fax : 0534355560
Porte : W.220