Re: traffic classification (was: [16NG] FW: Review of the ipv6-over-ipv6cs draft)

[Alexandru Petrescu <alexandru.petrescu at motorola.com>]

Jari Arkko wrote:
> Hi,
>
> Some thoughts on the substantive points raised by Pekka's review:
[...]
> > It is not clear if traffic classification is adequately specified 
> > (or is it specified elsewhere?) and some miscellaneous issues.
>
> Specified elsewhere. This needs to be made clearer.

I think it _may_ be relevant here.  IPv6 has a Traffic Class field with
defined values (see rfc2474 for 6bit DSCP, and rfc2597 for AF Assured
Forwarding values).  802.16 has Service Class service flow encodings
(11.13.4 in 802.16-1004).  The mapping between the two should be
specified here I believe.

Basically one would need to define mappings between DSCPs and 802.16
Service Flow encodings.  Remark the mapping is not straightforward
because DSCP uses 6bit while service field is on 4bit.  But not all
values from 6bit need to be encoded either.

I think 802.16 spec doesn't define these mappings.  Although they do
define filter in the CS that interprets the IPv6 Traffic Class field.

I think we need advice from QoS community on this.

Alex

> > substantial -----------
> >
> > ==> looking at the other "IPv6 over foo" documents, this document 
> > doesn't specify or mention the following: - link-local address 
> > generation  (exactly as described in RFC2464, I suppose?) - unicast
> >  and multicast address mapping
> >
> > Maybe these don't require much text but an explicit note might be a
> >  good thing to have.
>
> Yes.
>
> > Hence the point-to-point link model for IPv6 operation over the IP 
> > specific part of the Packet CS in 802.16 is recommended.  A unique 
> > IPv6 prefix(es) per link (MS) is also recommended.
> >
> > ==> you don't discuss what will happen if these recommendations are
> >  not followed, in fact, the whole document assumes they are adhered
> >  to.  Either this should be discussed or the recommendations should
> >  be made stronger (requirements).
>
> They should be requirements.
>
> > 6.3.  Maximum transmission unit in 802.16
> >
> > [...]  The Max value of the IPv6 MTU for 802.16 is 2038 bytes and 
> > the minimum value of 1280 bytes.  The default MTU for IPv6 over 
> > 802.16 SHOULD be the same as specified in RFC2460 which is 1500 
> > octets.  RFC2461 defines an MTU option that an AR can advertise to 
> > an MN.  If an AR advertises an MTU via the RA MTU option, the MN 
> > should use the MTU from the RA.
> >
> > ==> Should the last sentence use uppercase keywords? ==> However, 
> > if the MS is a router, RA is basically ignored in this kind of 
> > context.  Hence, this approach of non-default MTU configuration 
> > seems applicable between host and a router only.
>
> This should be made clear in the text -- perhaps with appropriate 
> warning label that discourages such usage. (If Wimax Forum wants to 
> do that due to the MTU of the backend tunnels, it would be their 
> conscious choice.)
>
> Jari
>
>
>
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