Subject: [manet] Does MANET need a multicast member management protocol?

From: "Tony" <[email-masked]>
Date: Tue, 8 Nov 2005 17:35:01 +0800

hi~
 	Member Management is important in deployment of the multicast service,
	Every MANET node can be a router to forward the packets or a host to 
send/receive the packets.
	The relation between the multicast members is described by the MANET 
multicast procotol,but how did the network manager know the member 
information of some multicast group. 
 	while I have a question to ask, 
	Does MANET need a multicast member management protocol? 
	Thank you in advance. 

　　　　　　　　Tony
　　　　　　　　[email-masked]
　　　　　　　　　　2005-11-08
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From: Marshall Eubanks <[email-masked]>
Date: Tue, 8 Nov 2005 07:45:15 -0500

I may not be understanding this, but why is more than IGMP or MLD needed ?

Regards
Marshall Eubanks

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From: Brian Haberman <[email-masked]>
Date: Tue, 8 Nov 2005 17:19:29 -0500

Marshall,
      I *think* the question is whether IGMP/MLD is needed at all.  If
all MANET nodes are routers, who would they send an MLD Report
to?  Rather, when the socket option to join a group is instantiated,
the MLD module would bypass sending a Report but would notify
the multicast routing daemon that there is a locally-attached listener
to the specified group.

Regards,
Brian

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From: Marshall Eubanks <[email-masked]>
Date: Tue, 8 Nov 2005 17:38:34 -0500

Ah, well that is a different matter; it did not come across that way.

Marshall

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From: Marshall Eubanks <[email-masked]>
Date: Tue, 8 Nov 2005 21:15:48 -0500

This is why I pressed on this matter in AutoConf tonight.

Here is my take (after talking to Brian and Dave Thaler)

A Manet "node" is a router. As such, it will not run MLD and
will have to "speak"  a multicast routing protocol. HOWEVER, it may
have devices attached to it (say, by a standard 802.11 network, or by wire),
and so it will have to deal with MLD for the devices below it.

Regards
Marshall

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From: Christophe Jelger <[email-masked]>
Date: Wed, 09 Nov 2005 10:54:47 +0100

Hi all,

See some comments below.

Regards,
Christophe

 > the multicast routing daemon that there is a locally-attached listener

Actually the IGMP/MLD report sent by a node can be used as the first 
trigger to build a multicast delivery structure (tree or mesh): this 
report can indeed be heard by the neighbors of the sender of the 
IGMP/MLD report, and this in turn can trigger multicast routing. (One 
could also design a multicast "routing" protocol based on overhearing 
IGMP/MLD reports sent by neighboring nodes).

Also bypassing IGMP/MLD as described by Brian means that the IGMP/MLD 
module(s) of a node should behave differently when the node is in a 
MANET or in a "traditional" network. I don't think this is a very good 
idea because this would require to carefully handle exceptions. For 
example with IPv6 a node systematically joins ff02::1 and the solicited 
multicast address for each interface (e.g. ff02::1:ff58:9eec). Also 
quite a number of multicast addresses have already been assigned by IANA 
  for services (e.g. ff0x::110 Music-Service). So when in a MANET shall 
a node treat such things differently ? What if a node simply wants to 
receive a multicast video stream sent by its neighbor: can't we just use 
  IGMP/MLD ?

Also one technical issue is that for example in Linux the MLD stack 
registers Ethernet multicast addresses with the interface. Which means 
if one bypasses MLD, then s(he) has to create an alternative way in 
order to tell an interface which Ethernet multicast addresses it should 
join.

Marshall Eubanks wrote:
 > A Manet "node" is a router. As such, it will not run MLD and will
 > have to "speak"  a multicast routing protocol. HOWEVER, it may have
 > devices attached to it (say, by a standard 802.11 network, or by
 > wire), and so it will have to deal with MLD for the devices below it.

Remember that in current IGMP/MLD specifications a router should also 
run IGMP or MLD, and bahave according to the router behavior of these 
protocols. So again "not running MLD" would introduce a MANET-specific 
behavior which would break "normal" operations. Do we really want to 
start introducing MANET-specific stuff everywhere ?

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From: Anis LAOUITI <[email-masked]>
Date: Wed, 9 Nov 2005 13:19:42 +0100

Hello,
http://www.inria.fr/rrrt/rr-4721.html

 In this research report, we have proposed a multicast protocol for OLSR
 and WIGMP (a modified version of IGMP adapted to wireless world) to handle
 cases where not all
 the paticipants are multicast capable.

  Best regards

   Anis Laouiti

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From: Marshall Eubanks <[email-masked]>
Date: Wed, 9 Nov 2005 07:42:13 -0500

Hello;

> IGMP/MLD reports sent by neighboring nodes).

Note that this is not quite the behavior envisioned by the current muticast
service model, which basically is hierarchical in nature :

Local hosts send IGMP (v4) or MLD (v6) membership reports etc., which are
picked up by (one) first hop router, which generates (say) PIM join /
leave requests.

> protocols. So again "not running MLD" would introduce a MANET-specific

That is not quite what I meant, and I realize that I was not clear here.

> start introducing MANET-specific stuff everywhere ?

Exactly. That was not what I was trying to suggest). So, let me try again :

-----
A Manet "node" is a router. As such, it will have to run  a multicast
routing protocol _with other Manet nodes_ . HOWEVER, it may have
devices attached to it (say, by a standard 802.11 network, or by
wire), and so it will have to deal with MLD for the devices below it.
If other Manet nodes can also receive multicast packets from the same
devices, this means that either these nodes will have to use MLD to
perform Querier election, or the existing MLD protocol will have to be
changed.
-----

The trouble comes if the devices below a Manet node (call them
sub-nodes) are free to switch between Manet nodes dynamically (say if
they are running a mesh 802.11 sub network). Then, the set of Manet
nodes that can hear a sub-node can vary dynamically, which does not
fit well into the paradigm assumed in MLD / IGMP.

The purpose of MLD / IGMP is to insulate edge hosts from having to know about
the multicast routing protocol in use (and also to prevent them from
having the ability to directly interfere with that multicast routing
protocol). From RFC 3810

   MLD is an asymmetric protocol; it specifies separate behaviors for
   multicast address listeners (i.e., hosts or routers that listen to
   multicast packets) and multicast routers.

(The mapping between RFC3810 terminology and the terminology I am
using here is "multicast listeners" <-> "sub-nodes" and "multicast
routers" <-> "Manet nodes".)

If sub-nodes do not obtain multicasts by means of MLD / IGMP, then
boxes using currently existing  Multicast code will not be able to
hook into a Manet network as a sub-node (at least for multicast), and
it seems that they might as well become Manet nodes (maybe only
directly connected boxes should be considered sub-nodes). If sub-nodes
_are_ going to use MLD / IGMP and _are_ going to be allowed to
dynamically move from one Manet node to another, then I suspect that
MLD / IGMP will have to be updated.

Again, from RFC 3810 (the IGMP behavior is very similar)

  The router behavior depends on whether there are
   several multicast routers on the same subnet, or not.  If that is the
   case, a querier election mechanism (described in section 7.6.2) is
   used to elect a single multicast router to be in Querier state.  This
   router is called the Querier.  All multicast routers on the subnet
   listen to the messages sent by multicast address listeners, and
   maintain the same multicast listening information state, so that they
   can take over the querier role, should the present Querier fail.
   Nevertheless, only the Querier sends periodical or triggered query
   messages on the subnet, as described in section 7.1.

If sub-nodes are attached to Manet nodes using some sort of mesh
(wireless) network, then it's hard for me to see how this is going to
work as is, as I don't know how you
are going to be sure that all sub-nodes can directly interact with the
same Querier, as this implies.

It seems to me that the Manet multicast service model needs some clarification.

Regards
Marshall

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From: "Pedro M. Ruiz" <[email-masked]>
Date: Wed, 09 Nov 2005 14:40:16 -0800

We also did some similar in 2002 and 2003 with a protocol called MMARP.  
It also supports terminals not participating in the routing, IPv4 and 
IPv6, supports multiple gateways and does not require any changes to 
access routers. It is also been validated both in simulations and real 
testbeds.

There is a Linux implementation running all these features (plus some 
secure routing enhancements) in case anyone is interested.

Some info:

Pedro M. Ruiz, Antonio F. Gomez-Skarmeta, "Integrated IP Multicast in 
Mobile Ad Hoc Networkis with Multiple Attachments to Wired IP Networks", 
In proc. of the 15th IEEE Symposium on Personal, Indoor and Mobile Radio 
Communications (PIMRC-2004), Barcelona, 5-8 Sept. 2004. 
(http://ants.dif.um.es/staff/pedrom/papers/Ruiz-PIMRC04.pdf)

You can also find recent enhancements to that protocol and other related 
papers in:

http://ants.dif.um.es/staff/pedrom/publications.html

Regards,

--Pedro