Subject: [nemo] NEMO Multicast Issues

From: "Daniel NEGRU" <[email-masked]>
Date: Wed, 26 Nov 2003 14:18:15 +0100

Hi all,

I am a Ph.D student in CNRS-PRISM Laboratory at the University of Versailles and I'm very interested in Network Mobility, especially concerning multicast issues on mobile networks.
I was wondering if it would be possible for a MR to join to any multicast groups with its care-of-address when it is in a visited network. I suppose yes but section 5.7 of the basic support made me have a doubt.

Thanks,
Daniel.

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From: Vijay Devarapalli <[email-masked]>
Date: Wed, 26 Nov 2003 11:02:44 -0800

Daniel NEGRU wrote:
> Hi all,
> 
> I am a Ph.D student in CNRS-PRISM Laboratory at the University of Versailles 
> and I'm very interested in Network Mobility, especially concerning multicast 
> issues on mobile networks.
> I was wondering if it would be possible for a MR to join to any multicast 
> groups with its care-of-address when it is in a visited network. I suppose 
> yes but section 5.7 of the basic support made me have a doubt.

section 5.7 only restricts the Mobile Router when it comes to
joining the All Routers Multicast group. it doesnt talk about
any other multicast group.

Vijay

---

From: Vijay Devarapalli <[email-masked]>
Date: Wed, 26 Nov 2003 11:02:44 -0800

Vijay

---

From: Greg Daley <[email-masked]>
Date: Thu, 27 Nov 2003 12:07:49 +1100

Hi Daniel,

At this stage, I'm not sure how much work
has been done on this.

The section 5.7 says that in the visited network the
NEMO MR is treated as a host (not as a router).
This is consistent with all of the other NEMO work.

In order to get multicast data streams in the visited
access network, it's certainly possible to do MLD/IGMP
proxying as defined (for fixed routers in):

http://www.ietf.org/internet-drafts/draft-ietf-magma-igmp-proxy-04.txt

The primary issues (which also relate to NEMO) are topological.
Proxying doesn't have a full tree view of the multicast routing
state (there's a discontinuity at the MLD Proxy), and relies
upon manual topology information to ensure this (determining
upstream and downstream interfaces).

Actually, NEMO would not require a strict tree topology
above it (it needs only be a DAG), but the multicast
subscription needs to be selectively performed so that
only one copy of a packet arrives on a particular downstream
interface.

Since the topology information in NEMO comes for free
(we know our ingress and egress interfaces, which correspond to
the downstream and upstream interfaces), it is plausible to
allow MLD proxying on MRs, without significant further work.
Even the mobility is unlikely to cause issues, since an
egress interface is still an interface (until we come home).

Within the NEMO, amongst the routers it may be possible
to run a routing protocol, with the MR providing RPF neighbor
capability on it's ingress link.  It can then arbitrate
whether the actual reception comes from the visited network
or over teh home tunnel.

Of course this only works for multicast reception.
Transmission is possibly a more diffcult thing due to the
fact that the packets are unlikely to be topologically
correct in the visited network (although there's been some
work on that with Mobile sources).

Tunneling multicast routing to the Home network is simple
enough,  but if multicast from the visited network is
desirable and reliable, it's certainly possible with NEMO.
The rest is policy decisions, which I'm not very good at.

At this stage, I'm not not sure if others have written this
up in a draft, though.

Greg

Daniel NEGRU wrote:
> Hi all,
>  
> I am a Ph.D student in CNRS-PRISM Laboratory at the University of 
> Versailles and I'm very interested in Network Mobility, especially 
> concerning multicast issues on mobile networks.
> I was wondering if it would be possible for a MR to join to any 
> multicast groups with its care-of-address when it is in a visited 
> network. I suppose yes but section 5.7 of the basic support made me have 
> a doubt.
>  
> Thanks,
> Daniel.

---

From: Greg Daley <[email-masked]>
Date: Thu, 27 Nov 2003 12:07:49 +1100

Hi Daniel,

Greg

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From: Christophe Janneteau <[email-masked]>
Date: Thu, 27 Nov 2003 10:28:44 +0100

Hi Daniel, Greg,

> http://www.ietf.org/internet-drafts/draft-ietf-magma-igmp-proxy-04.txt

Exactly! We also have been working recently on the problem of delivering
IP multicast to nodes in a moving network. "IGMP/MLD-based multicast
forwarding" (referenced by Greg) is indeed an interesting approach that
can be deployed within the moving network (including MR) in order to
enable this capability. This allows the MR to collect group membership
information from within the nemo and subscribe itself to those groups
through the visited network. With this approach, the MR behaves like a
Mobile Node from the visited network perspective, using "remote
subscription" through its egress interface to support handover of
multicast flows.

As mentioned by Greg, this approach has some limitations (e.g. manual
configuration of the tree-like topology) but has also many advantages
IMHO. Here are few of them:

o Enable "global mobility": MR is using MLD towards the visited network
(as a Mobile Node), and not a multicast routing protocol. Thus avoiding
interoperability issues when MR roams into a domain supporting a
multicast routing protocol different from the one at home.
o Optimal routing, even with nested MRs.
o Per-flow handover possible, for MR equipped with multiple egress
interfaces
o Independent of the base NEMO support (unicast).
o No need to run a multicast routing protocol within the moving network.
o Easy to implement

This makes the approach interesting for vehicular environments, where
the intra-vehicular network topology is small to medium.

We have been implementing and experimenting this approach as part of the
OverDRiVE project (http://www.ist-overdrive.org) on top of the LIVSIX
IPv6 stack (http://www.nal.motlabs.com). This is to be demonstrated next
week during the HyWiN workshop in Turin
(http://www.comnets.rwth-aachen.de/~o_drive/HyWiN2003/index.html).

> work on that with Mobile sources).

The MLD-based Multicast Forwarding has some kind of support for sources
in the Moving Network. It can route packets from a source located within
the NEMO towards receivers also located in the same NEMO without
problem. However, as mentioned by Greg, when it comes to reach receivers
in the Internet, then tunnelling of the packets through the MR-HA is
required to pass RPF checks.

> At this stage, I'm not not sure if others have written this

We were planning to write a draft in the coming weeks, to share our
experience of this approach with the working group (if any interest).

Bye
Christophe.

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From: Christophe Janneteau <[email-masked]>
Date: Thu, 27 Nov 2003 10:28:44 +0100

Hi Daniel, Greg,

Bye
Christophe.