Subject: [mobile-ip] moving on with the multicast issue (#63)

From: Jari Arkko <[email-masked]>
Date: Tue, 20 Aug 2002 15:34:21 +0300

A discussion has taken place on and off-list about the
multicast mechanisms in MIPv6 and exactly what the base
RFC must say and allow.

The main discussion item has been whether to allow
sending only via the HA, or also locally. We have
come up with the following proposal in the discussion:

1. We clarify in the draft that HAO is not allowed for
    CoA-sourced multicast traffic.

    Reason: reduces complexity and we simply don't know how to
    do this at this time.

2. We allow HA tunneling AND CoA sourced traffic, but add
    an applicability statement that describes what limitations
    these mechanisms have.

    Reason: This does not prevent anything, but warns the
    implementers so that they can think about the implications
    for the multicast routing infrastructure. Later, when
    we have better technology we can revisit this statement.

3. We require MLD to be run without HAO.

    Reason: This makes multicast traffic that uses care-of
    address equivalent to any other local traffic. Also
    implied by item 1.

-----text for 1------

   (1) send directly on the foreign link being visited

=>

   (1) Send directly on the foreign link being visited.
       The application is aware of the care-of address
       and uses it for multicast traffic just like any
       other stationary address. The mobile node MUST NOT
       use Home Address destination option in such traffic.

-----text for 2-------

Note that direct sending from the foreign link is only
applicable whilst the MN is at that foreign link. This
is because the associated multicast tree is specific to
that source location and any change of location and source
address will invalidate the source specific tree or branch
and the application context of the other multicast
group members.

This specification does not provide mechanisms to enable such
local multicast session to survive hand-off, and to seamlessly
continue from a new CCoA on each new foreign link. Any
such mechanism, developed as an extension to this
specification, needs to take into account the impact of
fast moving mobile nodes on the Internet multicast
routing protocols and their ability to maintain the
integrity of source specific multicast trees and branches.

Whilst the use of reverse tunnelling can ensure that multicast trees are
independent of the MN's movement, in some case such tunnelling can have
adverse affects. The latency of specific types of multicast
applications such as multicast based discovery protocols will
be impacted when the RTT between the foreign subnet and the HA
is significant compared to that of the topology to be
discovered. In addition, the delivery tree from the HA in such
circumstances relies on unicast encapsulation from the HA to the
MN and is therefore bandwidth inefficient compared to the native
multicast forwarding in the foreign multicast system.

-----text for 3------

    If the multicast applications depend on the
    address of the joining node, the mobile node MAY treat the router as
    a correspondent node and establish a binding with it.  The mobile
    node can then use the Home Address destination option in the sent
    control messages.

=>

    The mobile node MUST NOT use the Home Address destination option
    when sending MLD packets [ref].

---

From: "Alan O'Neill" <[email-masked]>
Date: Wed, 21 Aug 2002 08:51:04 -0400

Fine with me..

-----text for 1------

=>

-----text for 3------

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