[16NG] Re: multicast and IPv6 over ETHCS

2007/1/15, Alexandru Petrescu <alexandru.petrescu at motorola.com >:

Hi Jihoon,

Jihoon Lee wrote:
> Hi Alex,
>
> Sorry for my late response. Basically I agree with your opinion. An
> IPv6 node requires a link local multicast address in order to perform
>  DAD, ND, and RA.
>
> Contrary to our expectations, 802.16/16e don't support UL multicast
> (which means an MS forwards data directly to other MSs in the same
> cell).
>
> (BTW, I think I need to clarify the UL multicast I mentioned. I
> believe you already know this: the multicast/broadcast which is sent
> by an MS  to other MSs in the same cell (BS) cannot be supported in
> 802.16. However, other MSs in another cell (BS) may receive this
> since the 802.16 backhaul (WiMAX ASN) may multicast/broadcast at ETH
> or IP layer.)
>
> I agree that the document needs to specify how to deal with this
> problem.

Yes, I think the IPv6-over-ETHCS document should make clear the
assumption of IPv6 using link-layer multicast for IPv6.  I don't think
the IPv6-over-ETHCS document should solve the problem you mention above
between parenthesis (uplink mc, or mc between BSs) at link layer.

The IPv6-over-ETHCS document could list the behaviour of ETHCS it
expects.  Ie:

-when MS sends NS to a IP solicited-node multicast address the node who
has joined group must receive it.
-when BS or AR advertises an RA to all-nodes multicast address then all
SSs who have joined that group must receive it.
-mapping an IPv6 link-local multicast address should happen (eg sending
a packet to IP dst ff02::1 should have the link-layer dst
33:33:33:0:0:0:1).

The document IPv6-over-ETHCS should list what are the means for SS to
_join_ a link-layer multicast group.  There are few of them (send a
link-layer message, send a MLD message, establish a local filtering
rule, always receiving all packets, etc).

But I don't think the IPv6-over-ETHCS document should specify the
link-layer behaviour for an implementation of ETHCS link-layer
multicast.  Do you agree with this latter item?

Alex

>
> Best regards, Jihoon
>
>
> 2007/1/12, Alexandru Petrescu < alexandru.petrescu at motorola.com
> <mailto:alexandru.petrescu at motorola.com>>:
>
> Hi Jihoon, thanks for reply,
>
> Jihoon Lee wrote:
>> Hi Alex,
>>
>> Let me jump into discussion. 1) 802.16/16e MAC has no capability to
>>  do uplink multicast. In DL, 802.16 provides multicast CIDs which
>> is initiated by DSA messages. In UL, however, there is no way for
>> an MS to access others' UL data fundamentally, in 802.16 PHY/MAC.
>
> Ok.  For one, if the 802.16MAC is not capable to do bidirectional (or
>  normal) multicast then that is a big issue for IPv6-over-IPv6CS.
> (and surprisingly, apparently the document IPv6-over-IPv6CS doesn't
> seem to mention the word 'multicast'.)
>
> The issue is that a SS running IPv6 needs to multicast a NA, from
> time to time.  For DAD it needs to send a NS to a multicast address
> too.
>
>> In case of ETH over 802.16, the ETH(bridge) may cover this (an MS
>> sends multicast data in UL, and then a bridge forwards it back).
>> But, there is still a difficulty in multicasting data back except
>> for the source MS.
>
> You mean the bridge in BS?  I was thinking ETHCS in SS may offer a
> multicast interface to the IP stack.
>
> In both cases (bridge in BS or bridge in SS), I think it is not up to
>  this document to specify how the ETHCS transforms a asymmetric ul/dl
>  multicast feature into a symmetric one.  But it should be a goal for
>  ETHCS to offer such an interface to the IPv6 stack, otherwise the
> IPv6 stack won't work.  What do you think?
>
> Alex
>
>