[16NG] Re: multicast and IPv6 over ETHCS

[Alexandru Petrescu <[e-mail]>]

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 <[e-mail] 
> <mailto:[e-mail]>>:
> 
> 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
> 
> 


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