ULE-01 : Destination Address Field

[alain.ritoux@6wind.com]

About the Destination Address Field :

1) Destination Indicator
For early implementors, a position for this flag should be chosen
quickly ! For exempel, it could be possible to catch another bit
out of the Length Field. It leaves 14 bits for the lengh field
itself, allowing 16K SNDU

.-----------------------   SNDU   ------------------------.
+---+---+-----------------------------------------+--------+
| D | R | Length | Type |            PDU          | CRC-32 |
+---+---+-----------------------------------------+--------+

4.x Destination Field

The most significant bit of the Length Field is a flag indicating
the presence of a destination field, with the following semantic :
  1 : destination field absent
  0 : destination field present

One exception is transmission of an End Indicator (see 4.y), in which
this bit MUST be set to the value of 1.

And so th Length Field description would become
"A 15-bit value that ..." --> "A 14-bit value that ..."



2) Presence of Destination Address Field

"This field MUST be carried for IP unicast packets destined to
routers" This may be a little bit too much, and in contradiction
wtih the following sentence : "MAY omit ... receivers able to use
a discriminator field (e.g. the destination address)"

in the case the Receiver is a CPE that know what network is behind
him (P::/48), it cans filter packet on this basis, hence it is able
to discriminate without MAC @, even if it is a router.

Now to the question how does the encapsulator know about this, I
think it can be solved because there is some address resolution
(static, table, whatever) that provides P::/48 --> PID,MAC
If MAC == 00:00:00:00:00:00, the the encapsulator omit the destination
address field
At in the receiver side, there must be a configuration knob to
allow/forbid IP(v6)-SNDU packets to be acepted without Destination
Address field present.
In the described case, if the receiver is in a position, where it
CAN SAFELY filter out of the destination IP(v6) address, it allows
the recpetion of such SNDU

In the case where the receiver has not enough knowledge to filter
properly at IP-level, the knob is off, and all IP(v6) packets sent
within an SNDU without the destination Address Field are silently
discard.
Of course the (knob == 1) has to be in sync with the (MAC@ == 0) !

So I would say:
"This field SHOULD be carried for IP unicast packets destined to ..."

Your thoughts ?

Regards.
Alain.

--
Alain RITOUX
Tel +33-1-39-30-92-32
Fax +33-1-39-30-92-11
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