Subject: Proxy announcement !

From: "Hesham Soliman (ERA)" <[email-masked]>
Date: Wed, 4 Jul 2001 15:56:16 +0200

All, 

A new draft on IPv6 Cellular hosts requirements was submitted today. 
Until it's announced, you can view it here:

http://standards.ericsson.net/Hesham/draft-manyfolks-ipv6-cellular-host-00.txt

I'm doing this for Jari (one of the author) as he's away. 

Cheers,
Hesham
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From: Claude Castelluccia <[email-masked]>
Date: Thu, 05 Jul 2001 09:58:25 +0200

Hello ,

This is a very interesting draft but I would suggest to change the title.
Something like "Minimum IPv6 Functionality for a 3GPP Host" would
be more accurate...
Some of the sections are very specific to the 3GPP architecture and can not
be generalized to Cellular hosts (that could used IEEE802.11, Bluetooth, blabla
types
of networks..)

Regards,
Claude.

--

----------------------------------------
Claude CASTELLUCCIA, INRIA Rhone-Alpes
ph:  +33 4.76.61.52.15 (fax: 52.52)
http://www.inrialpes.fr/planete/

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From: Jun-ichiro itojun Hagino <[email-masked]>
Date: Thu, 05 Jul 2001 17:41:07 +0900

>> I'm doing this for Jari (one of the author) as he's away.

	here are a couple of comments.

itojun

2.1 RFC1981 - Path MTU Discovery for IP Version 6

>   If Path MTU Discovery is not implemented, then the uplink packet
>   size MUST be limited to 1280 octets (standard limit in [IPv6]).
>   However, the cellular host MUST be able to receive packets with size
>   up to the link MTU.

	The text (3rd and 4th line) is unclear (is it after the reassembly
	or before?  or am I badly confused?), and may conflict with RFC2460
	depending on the link MTU for the cellular host.  ???

RFC2460 page 25
>   A node must be able to accept a fragmented packet that, after
>   reassembly, is as large as 1500 octets.  A node is permitted to
>   accept fragmented packets that reassemble to more than 1500 octets.
>   An upper-layer protocol or application that depends on IPv6
>   fragmentation to send packets larger than the MTU of a path should
>   not send packets larger than 1500 octets unless it has assurance that
>   the destination is capable of reassembling packets of that larger
>   size.

2.10 RFC2710 - Multicast Listener Discovery (MLD) for IPv6

	(MLD6 is SHOULD) what happens if a cellular node doesn't emit MLD?
	will the upstream router always flood multicast datagrams to cellular
	hosts?

2.11 RFC2711 - IPv6 Router Alert Option

	in 2.4, it is specified that a cellular host will not be come a router.
	therefore, there should be no need to implement the receiver side
	of the router alert option,

2.17 DNS

	what do you mean by "DNS proxy" service?  if you still use DNS-
	formatted traffic from the cellular hosts, you would need to
	support DNS protocol anyways.  do you mean an HTTP proxy?  if so,
	how would you support name resolution for other protocols?
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From: "Gerben Kuijpers (TED)" <[email-masked]>
Date: Thu, 05 Jul 2001 14:53:53 +0200

Thanks for your comments, response inline.

> >   the destination is capable of reassembling packets of that larger

This is before reassembly. Let's try to clarify this with an example. Consider
the following situation:

                 link MTU=1500                path MTU=1500
cellular host A <--------------> router <--- ... network ... ---> host B

The cellular host A communicates with host B. Host A does not do Path MTU
discovery, but host B does. Host A will have to limit its packet size to 1280
bytes, while host B finds a path MTU of 1500 and will send packets up to that
size. Maybe its a bit unclear, since we're stating the obvious that a host must
be able to receive packets with size up to its link MTU.

>         will the upstream router always flood multicast datagrams to cellular

A cellular host that wants to join multicast groups with a scope larger than
link-scope will have to notify the upstream router in some way. Probably MLD is
the best way to do this. When no notification is sent to the upstream router,
you're right, flooding is the only option, but not preferable.

The typical topology at IP layer for a cellular network (such as 3GPP) is as
follows:

           Internet
              |
              |
              |
   ___________|__________
  |                      |
  | Upstream router      |
  |______________________|
    |      | ....... |
    |      |         |
    |      |         |
 host 1  host 2   host n

A large number of cellular hosts each have a point-to-point link to an IP router
that is part of the cellular network and acts as a gateway to the Internet for
the cellular system. The point-to-point link between the router and a cellular
host typically consist of multiple links at link-layer, including a wireless
link closest to the cellular host. Flooding will be a very inefficient for
multicast datagrams (in fact it will be a broadcast then), since a single
subscribed host could cause broadcasting of datagrams to 1000s of hosts.

For such a topology, the advantages of using multicasting (including MLD) might
be limited. A multicast datagram arriving at the router will have to be sent on
each individual point-to-point link to each cellular host subscribed to that
particular multicast group. Only the load on the link from the router to the
Internet can be reduced by multicasting. This at cost of extra load on the
(bandwidth limited) wireless links in the form of MLD signaling.

>         of the router alert option,

Good point, we'll note that.

Gerben Kuijpers

---

From: "Gerben Kuijpers (TED)" <[email-masked]>
Date: Thu, 05 Jul 2001 16:20:21 +0200

Jun-ichiro itojun Hagino wrote:
>         yes, i fully understand the situation.
>         how about adding "(before reassembly)" at the end of the paragraph,
>         just for clarity?

Agree, that will be more clear, we'll add that.

> (snip)
>         assuming that we do need to do multicasts (not just link-local):
> 
>         if you use MLD between "upstream router" and cellular hosts, you
>         may be able to cut down multicast groups the upstream router would
>         need to forward (if none of cellular host[1-n] is listening to the
>         group).
> 
>         if you don't use MLD, the "upstream router" needs to forward multicast
>         packets for every groups host[1-n] potentially join in the future.
> 
>         am i confused?

You're right, if we do need non-link-local multicast, then the upstream router
needs to be notified in some way about which multicast groups each cellular host
is listening to- Otherwise the upstream router doesn't know to which host it has
to forward specific multicast datagrams and the only option that remains is to
send each multicast datagram to each host, wasting a lot of bandwidth. MLD
between the hosts and the upstream router is a possible mechanism for notifying
the router about the multicast groups the different hosts are interested in.

Gerben Kuijpers

---

From: Jun-ichiro itojun Hagino <[email-masked]>
Date: Thu, 05 Jul 2001 22:39:15 +0900

(snip)

	am i confused?

itojun

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From: Alexandru Petrescu <[email-masked]>
Date: 05 Jul 2001 20:49:48 +0200

> http://standards.ericsson.net/Hesham/draft-manyfolks-ipv6-cellular-host-00.txt

IPv6 Jumbograms rfc2675?

Default Address selection?

I'm struck there's nothing about QoS.

You state MLD SHOULD be supported and Router Alert Option MAY be
supported.  Well, the former requires the latter I don't know where
else is the latter needed.

Alex

---

From: Gerben Kuijpers <[email-masked]>
Date: Wed, 11 Jul 2001 11:06:16 +0200 (MET DST)

-------------------------------------

> > http://standards.ericsson.net/Hesham/draft-manyfolks-ipv6-cellular-host-00.txt

We left this RFC out, because jumbograms should not be used by cellular
hosts. Maybe we should have added a section on this RFC and state there
that it should not be used by cellular hosts for the following reasons:
-typical cellular link MTUs are much smaller than 64k
-packets larger than 64k take too long to send on the relatively slow
cellular links (e.g. 64k packet on 144 kpbs link takes 3.6 seconds to
send)

> Default Address selection?

This is discussed in section 2.16. Do you miss anything there?

> I'm struck there's nothing about QoS.

What did you expect to see about QoS? Is there anything IPv6 specific
here?

> else is the latter needed.

We state that MLD is a 'SHOULD' in case the cellular host supports
multicast functionality. In that case some mechanism is needed to inform
the upstream router about which multicast groups the cellular host is
listening to. This mechanism would preferably be MLD, that's
why: 'SHOULD'.
We could add a clause that the Router Alert Option MUST be supported in
case MLD is supported. The Router Alert Option is also used by RSVP.

/Gerben Kuijpers