One document matched: draft-schmidt-multimob-pmipv6-mcast-deployment-04.xml
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docName="draft-schmidt-multimob-pmipv6-mcast-deployment-04"
ipr="trust200902">
<front>
<title abbrev="Multicast Listeners in PMIPv6">A Minimal Deployment Option
for Multicast Listeners in PMIPv6 Domains</title>
<author fullname="Thomas C. Schmidt" initials="T C." surname="Schmidt">
<organization>HAW Hamburg</organization>
<address>
<postal>
<street>Berliner Tor 7</street>
<city>Hamburg</city>
<code>20099</code>
<country>Germany</country>
</postal>
<email>schmidt@informatik.haw-hamburg.de</email>
<uri>http://inet.cpt.haw-hamburg.de/members/schmidt</uri>
</address>
</author>
<author fullname="Matthias Waehlisch" initials="M." surname="Waehlisch">
<organization>link-lab & FU Berlin</organization>
<address>
<postal>
<street>Hoenower Str. 35</street>
<city>Berlin</city>
<code>10318</code>
<country>Germany</country>
</postal>
<email>mw@link-lab.net</email>
</address>
</author>
<author fullname="Suresh Krishnan" initials="S." surname="Krishnan">
<organization>Ericsson</organization>
<address>
<postal>
<street>8400 Decarie Blvd.</street>
<city>Town of Mount Royal</city>
<region>QC</region>
<country>Canada</country>
</postal>
<email>suresh.krishnan@ericsson.com</email>
</address>
</author>
<date day="8" month="February" year="2010" />
<workgroup>MULTIMOB Group</workgroup>
<abstract>
<t>This document describes deployment options for activating multicast
listener functions in Proxy Mobile IPv6 domains without modifying
mobility and multicast protocol standards. Similar to Home Agents in
Mobile IPv6, PMIPv6 Local Mobility Anchors serve as multicast
subscription anchor points, while Mobile Access Gateways provide MLD
proxy functions. In this scenario, Mobile Nodes remain agnostic of
multicast mobility operations.</t>
</abstract>
<note title="Requirements Language">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref
target="RFC2119">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section title="Introduction">
<t>Proxy Mobile IPv6 (PMIPv6) <xref target="RFC5213"></xref> extends
Mobile IPv6 <xref target="RFC3775"></xref> by network-based management
functions that enable IP mobility for a host without requiring its
participation in any mobility-related signaling. Additional network
entities, i.e., the Local Mobility Anchor (LMA), and Mobile Access
Gateways (MAGs), are responsible for managing IP mobility on behalf of
the mobile node (MN).</t>
<t>With these routing entities in place, the mobile node looses
transparent end-to-end connectivity to the static Internet, and in the
particular case of multicast communication, group membership management
as signaled by the Multicast Listener Discovery protocol <xref
target="RFC3810"></xref>, <xref target="RFC2710"></xref> requires a
dedicated treatment at the network side, see <xref
target="I-D.deng-multimob-pmip6-requirement"></xref>.</t>
<t>Multicast routing functions need a careful placement within the
PMIPv6 domain to augment unicast transmission with group communication
services. <xref target="RFC5213"></xref> does not explicitly address
multicast communication, whereas bi-directional home tunneling, the
minimal multicast support arranged by MIPv6, cannot be applied in
network-based management scenarios: A mobility-unaware node will
experience no reason to initiate a tunnel with an entity of mobility
support.</t>
<t>This document describes options for deploying multicast listener
functions in Proxy Mobile IPv6 domains without modifying mobility and
multicast protocol standards. Similar to Home Agents in Mobile IPv6,
PMIPv6 Local Mobility Anchors serve as multicast subscription anchor
points, while Mobile Access Gateways provide MLD proxy functions. Mobile
Nodes in this scenario remain agnostic of multicast mobility operations.
Accrediting the problem space of multicast mobility <xref
target="I-D.irtf-mobopts-mmcastv6-ps"></xref>, this document does not
address specific optimizations and efficiency improvements of multicast
routing in network-centered mobility beyond base potentials, as such
solutions would require changes to the base specification of <xref
target="RFC5213"></xref>.</t>
</section>
<section title="Terminology">
<t>This document uses the terminology as defined for the mobility
protocols <xref target="RFC3775"></xref> and <xref target="RFC5213">
</xref>, as well as the multicast edge related protocols <xref
target="RFC3810"></xref> and <xref target="RFC4605"></xref>.</t>
</section>
<section title="Overview">
<t>The reference scenario for multicast deployment in Proxy Mobile IPv6
domains is illustrated in <xref target="fig1"></xref>.</t>
<figure anchor="fig1"
title="Reference Network for Multicast Deployment in PMIPv6">
<artwork><![CDATA[ +-------------+
| Content |
| Source |
+-------------+
|
*** *** *** ***
* ** ** ** *
* *
* Fixed Internet *
* *
* ** ** ** *
*** *** *** ***
/ \
+----+ +----+
|LMA1| |LMA2| Multicast Anchor
+----+ +----+
LMAA1 | | LMAA2
| |
\\ //\\
\\ // \\
\\ // \\ Unicast Tunnel
\\ // \\
\\ // \\
\\ // \\
Proxy-CoA1 || || Proxy-CoA2
+----+ +----+
|MAG1| |MAG2| MLD Proxy
+----+ +----+
| | |
MN-HNP1 | | MN-HNP2 | MN-HNP3
MN1 MN2 MN3]]></artwork>
</figure>
<t>An MN in a PMIPv6 domain will decide on multicast group membership
management completely independent of its current mobility conditions. It
will submit MLD Report and Done messages following application desires,
thereby using its link-local source address and multicast destination
addresses according to <xref target="RFC3810"></xref>, or <xref
target="RFC2710"> </xref>. These link-local signaling messages will
arrive at the currently active MAG via one of its downstream local
(wireless) links. A multicast unaware MAG would simply discard these MLD
messages.</t>
<t>To facilitate multicast in a PMIPv6 domain, an MLD proxy function
<xref target="RFC4605"></xref> needs to be deployed on the MAG that
selects the tunnel interface corresponding to the MN's LMA for its
upstream interface (cf., section 6 of <xref target="RFC5213"></xref>).
Thereby, each LMA-to-MAG tunnel interface defines an MLD proxy domain at
the MAG, containing all downstream links to MNs that share this LMA.
According to standard proxy operations, MLD Report messages will be
forwarded under aggregation up the tunnel interface to its corresponding
LMA.</t>
<t>Serving as the designated multicast router or an additional MLD
proxy, the LMA will transpose any MLD message from a MAG into the
multicast routing infrastructure. Correspondingly, the LMA will
implement appropriate multicast forwarding states at its tunnel
interface. Traffic arriving for groups under subscription will arrive at
the LMA, which it will forward according to all its group/source states.
In addition, the LMA will naturally act as an MLD querier, seeing its
downstream tunnel interfaces as multicast enabled links.</t>
<t>At the MAG, MLD queries and multicast data will arrive on the
(tunnel) interface that is assigned to a group of access links as
identified by its Binding Update List (cf., section 6 of <xref
target="RFC5213"></xref>). As specified for MLD proxies, the MAG will
forward multicast traffic and initiate related signaling down the
appropriate access links to the MNs. In proceeding this way, all
multicast-related signaling and the data traffic will transparently flow
from the LMA to the MN on an LMA-specific tree, which is shared among
the multicast sources.</t>
<t>In case of a mobility handover, the MN (unaware of IP mobility) will
refrain from submitting unsolicited MLD reports. Instead, the MAG is
required to maintain group memberships in the following way. On
observing a new MN on a downstream link, the MAG sends a General MLD
Query. Based on its outcome and the multicast group states previously
maintained at the MAG, a corresponding Report will be sent to the LMA
aggregating group membership states according to the proxy function.
Additional Reports can be omitted, whenever multicast forwarding states
previously established at the new MAG already cover the subscriptions of
the MN.</t>
<t>In summary, the following steps are executed on handover:</t>
<t><list style="numbers">
<t>The MAG-MN link comes up and the MAG discovers the new MN.</t>
<t>Unicast address configuration and PMIPv6 binding are performed,
the MAG can determine the corresponding LMA.</t>
<t>Following IPv6 address configuration, the MAG SHOULD send an
(early) MLD General Query to the new downstream link as part of its
standard multicast-enabled router operations.</t>
<t>The MAG SHOULD determine whether the MN is admissible to
multicast services, and stop here otherwise.</t>
<t>The MAG adds the new downstream link to the MLD proxy instance
with up-link to the corresponding LMA.</t>
<t>The corresponding Proxy instance triggers an MLD General Query on
the new downstream link.</t>
<t>The MN Membership Reports arrive at the MAG, either in response
to the early Query or to that of the Proxy instance.</t>
<t>The Proxy processes the MLD Report, updates states and reports
upstream if necessary.</t>
</list></t>
<t>After Re-Binding, the LMA is not required to issue a General MLD
Query on the tunnel link to refresh forwarding states. Multicast state
updates SHOULD be triggered by the MAG, which aggregates subscriptions
of all its MNs (see the call flow in <xref
target="fig:callflow"></xref>).</t>
<figure anchor="fig:callflow" height=""
title="Call Flow of Multicast-enabled PMIP">
<artwork><![CDATA[MN1 MAG1 MN2 MAG2 LMA
| | | | |
| Join(G) | | | |
+--------------->| | | |
| | Join(G) | | |
| |<---------------+ | |
| | | | |
| | Aggregated Join(G) | |
| +================================================>|
| | | | |
| | Mcast Data | | |
| |<================================================+
| | | | |
| Mcast Data | Mcast Data | | |
|<---------------+--------------->| | |
| | | | |
| | < Movement to MAG2 & PMIP Binding Update > |
| | | | |
| | |--- Rtr Sol -->| |
| | | | |
| | | MLD Query | |
| | |<--------------+ |
| | | | |
| | | Join(G) | |
| | +-------------->| |
| | | Aggregated Join(G)
| | | +===============>|
| | | | |
| | Mcast Data | | |
| |<================================================+
| | | | Mcast Data |
| | | |<===============+
| Mcast Data | | | |
|<---------------+ | Mcast Data | |
| | |<--------------+ |
| | | | |
]]></artwork>
</figure>
<t></t>
<t>These multicast deployment considerations likewise apply for mobile
nodes that operate with its IPv4 stack enabled in a PMIPv6 domain.
PMIPv6 can provide an IPv4 home address mobility support <xref
target="I-D.ietf-netlmm-pmip6-ipv4-support"></xref>. Such mobile node
will use IGMP <xref target="RFC2236"></xref>,<xref target="RFC3376">
</xref> signaling for multicast, which is handled by an IGMP proxy
function at the MAG in an analogous way.</t>
<t>Following these deployment steps, multicast management transparently
inter-operates with PMIPv6. It is worth noting that multicast streams
can possibly be distributed on redundant paths that lead to duplicate
traffic arriving from different LMAs at one MAG, and can cause multiple
data transmissions from an MAG over one wireless domain to different MNs
(see <xref target="A-Eval"></xref> for further considerations).</t>
</section>
<section title="Deployment Details">
<t>Multicast activation in a PMIPv6 domain requires to deploy general
multicast functions at PMIPv6 routers and to define its interaction with
the PMIPv6 protocol in the following way:</t>
<section title="Operations of the Mobile Node">
<t>A Mobile Node willing to manage multicast traffic will join,
maintain and leave groups as if located in the fixed Internet. No
specific mobility actions nor implementations are required at the
MN.</t>
</section>
<section title="Operations of the Mobile Access Gateway">
<t>A Mobility Access Gateway is required to assist in MLD signaling
and data forwarding between the MNs which it serves, and the
corresponding LMAs associated to each MN. It therefore needs to
implement an instance of the MLD proxy function <xref
target="RFC4605"></xref> for each upstream tunnel interface that has
been established with an LMA. The MAG decides on the mapping of
downstream links to a proxy instance (and hence an upstream link to an
LMA) based on the regular Binding Update List as maintained by PMIPv6
standard operations (cf., section 6.1 of <xref
target="RFC5213"></xref>). As links connecting MNs and MAGs change
under mobility, MLD proxies at MAGs MUST be able to dynamically add
and remove downstream interfaces in its configuration.</t>
<t>On the reception of MLD reports from an MN, the MAG MUST identify
the corresponding proxy instance from the incoming interface and
perform regular MLD proxy operations: it will insert/update/remove a
multicast forwarding state on the incoming interface, and state
updates will be merged into the MLD proxy membership database. An
aggregated Report will be sent to the upstream tunnel of the MAG when
the membership database <xref target="RFC4605">(cf., section 4.1 of
</xref>) changes. Conversely, on the reception of MLD Queries, the MAG
proxy instance will answer the Queries on behalf of all active
downstream receivers maintained in its membership database. Queries
sent by the LMA do not force the MAG to trigger corresponding messages
immediately towards MNs. Multicast traffic arriving at the MAG on an
upstream interface will be forwarded according to the
group/source-specific forwarding states as acquired for each
downstream interface within the MLD proxy instance. At this stage, it
is important to stress that IGMP/MLD proxy implementations capable of
multiple instances are expected to closely follow the specifications
of section 4.2 in <xref target="RFC4605"></xref>, i.e., treat proxy
instances in isolation of each other while forwarding.</t>
<t>In case of a mobility handover, the MAG will continue to manage
upstream tunnels and downstream interfaces as foreseen in the PMIPv6
specification. It MUST dynamically associate new access links to proxy
instances that for a MN provide up-link to its corresponding LMA. In
addition, it MUST assure consistency of its up- and downstream
interfaces that change under mobility with MLD proxy instances and its
multicast forwarding states. The MAG will detect the arrival of a new
MN by receiving a router solicitation message and by an upcoming link.
To learn about multicast groups subscribed by a newly attaching MN,
the MAG sends a General Query to the MN's link. Querying an upcoming
interface is a standard operation of MLD queriers (see <xref
target="A-InitMLD"></xref>) and performed immediately after address
configuration. In addition, an MLD query SHOULD be initiated by the
proxy instance, as soon as a new interface has been configured for
downstream. In case, the access link between MN and MAG goes down,
interface-specific multicast states change. Both cases may alter the
composition of the membership database, which then will trigger
corresponding Reports towards the LMA. Note that the actual observable
state depends on the access link model in use.</t>
<t>An MN may be unable to answer MAG multicast membership queries due
to handover procedures, or its report may arrive before the MAG has
configured its link as proxy downstream interface. Such occurrences
are equivalent to a General Query loss. To prevent erroneous query
timeouts at the MAG, MLD parameters SHOULD be carefully adjusted to
the mobility regime. In particular, MLD timers and the Robustness
Variable (see section 9 of <xref target="RFC3810"></xref>) MUST be
chosen to be compliant with the time scale of handover operations and
proxy configurations in the PMIPv6 domain.</t>
<t>In proceeding this way, the MAG is entitled to aggregate multicast
subscriptions for each of its MLD proxy instances. However, this
deployment approach does not prevent multiple identical streams
arriving from different LMA upstream interfaces. Furthermore, a per
group forwarding into the wireless domain is restricted to the link
model in use.</t>
</section>
<section title="Operations of the Local Mobility Anchor">
<t>For any MN, the Local Mobility Anchor acts as the persistent Home
Agent and at the same time as the default multicast querier for the
corresponding MAG. It implements the function of the designated
multicast router or a further MLD proxy. According to MLD reports
received from a MAG (on behalf of the MNs), it
establishes/maintains/removes group/source-specific multicast
forwarding states at its corresponding downstream tunnel interfaces.
At the same time, it procures for aggregated multicast membership
maintenance at its upstream interface. Based on the
multicast-transparent operations of the MAGs, the LMA experiences its
tunnel interfaces as multicast enabled downstream links, serving zero
to many listening nodes. Multicast traffic arriving at the LMA is
transparently forwarded according to its multicast forwarding
information base.</t>
<t>On the occurrence of a mobility handover, the LMA will receive
Binding Lifetime De-Registrations and Binding Lifetime Extensions that
will cause a re-mapping of home network prefixes to Proxy-CoAs in its
Binding Cache (see section 5.3 of <xref target="RFC5213"></xref>). The
multicast forwarding states require updating, as well, if the MN
within an MLD proxy domain is the only receiver of a multicast group.
Two cases need distinction:</t>
<t><list style="numbers">
<t>The mobile node is the only receiver of a group behind the
interface at which a De-Registration was received: The membership
database of the MAG changes, which will trigger a Report/Done sent
via the MAG-to-LMA interface to remove this group. The LMA thus
terminates multicast forwarding.</t>
<t>The mobile node is the only receiver of a group behind the
interface at which a Lifetime Extension was received: The
membership database of the MAG changes, which will trigger a
Report sent via the MAG-to-LMA interface to add this group. The
LMA thus starts multicast distribution.</t>
</list></t>
<t>In proceeding this way, each LMA will provide transparent multicast
support for the group of MNs it serves. It will perform traffic
aggregation at the MN-group level and will assure that multicast data
streams are uniquely forwarded per individual LMA-to-MAG tunnel.</t>
</section>
<section title="IPv4 Support">
<t>An MN in a PMIPv6 domain may use an IPv4 address transparently for
communication as specified in <xref
target="I-D.ietf-netlmm-pmip6-ipv4-support"></xref>. For this purpose,
LMAs can register IPv4-Proxy-CoAs in its Binding Caches and MAGs can
provide IPv4 support in access networks. Correspondingly, multicast
membership management will be performed by the MN using IGMP. For
multicast support on the network side, an IGMP proxy function needs to
be deployed at MAGs in exactly the same way as for IPv6. <xref
target="RFC4605"></xref> defines IGMP proxy behaviour in full
agreement with IPv6/MLD. Thus IPv4 support can be transparently
provided following the obvious deployment analogy.</t>
<t>For a dual-stack IPv4/IPv6 access network, the MAG proxy instances
SHOULD choose multicast signaling according to address configurations
on the link, but MAY submit IGMP and MLD queries in parallel, if
needed. It should further be noted that the infrastructure cannot
identify two data streams as identical when distributed via an IPv4
and IPv6 multicast group. Thus duplicate data may be forwarded on a
heterogeneous network layer.</t>
</section>
<section title="Multicast Availability throughout the Access Network">
<t>There may be deployment scenarios, where multicast services are
available throughout the access network independent of the PMIPv6
infrastructure. Direct multicast access at MAGs may be supported
through native multicast routing, within a flat access network that
includes a multicast router, via dedicated (tunnel or VPN) links
between MAGs and designated multicast routers, or by deploying AMT
<xref target="I-D.ietf-mboned-auto-multicast"></xref>.</t>
<t>Multicast deployment can be simplified in these scenarios. A single
proxy instance at MAGs with up-link into the multicast cloud, for
instance, could serve group communication purposes. MAGs could operate
as general multicast routers or AMT gateways, as well.</t>
<t>These solutions have in common that mobility management is covered
by the dynamics of multicast routing, as initially foreseen in the
Remote Subscription approach sketched in <xref
target="RFC3775"></xref>. Care must be taken to avoid service
disruptions due to tardy multicast routing operations <xref
target="I-D.irtf-mobopts-mmcastv6-ps"></xref>, and the different
possible approaches should be carefully investigated. Such work is
beyond the scope of this document.</t>
</section>
<section title="A Note on Explicit Tracking">
<t>IGMPv3/MLDv2 <xref target="RFC3376"></xref><xref target="RFC3810">,
</xref> may operate in combination with explicit tracking, which
allows routers to monitor each multicast receiver. This mechanism is
not standardized yet, but widely implemented by vendors as it supports
faster leave latencies and reduced signaling.</t>
<t>Enabling explicit tracking on downstream interfaces of the LMA and
MAG would track a single MAG and MN respectively per interface. It may
be used to preserve bandwidth on the MAG-MN link.</t>
</section>
</section>
<section title="Message Source and Destination Address">
<t>This section describes source and destination addresses of MLD
messages. The interface identifier A-B denotes an interface on node A,
which is connected to node B. This includes tunnel interfaces.</t>
<section title="Query">
<figure>
<artwork><![CDATA[ +===========+================+======================+==========+
| Interface | Source Address | Destination Address | Header |
+===========+================+======================+==========+
| | LMAA | Proxy-CoA | outer |
+ LMA-MAG +----------------+----------------------+----------+
| | LMA-link-local | [RFC2710], [RFC3810] | inner |
+-----------+----------------+----------------------+----------+
| MAG-MN | MAG-link-local | [RFC2710], [RFC3810] | -- |
+-----------+----------------+----------------------+----------+
]]></artwork>
</figure>
</section>
<section title="Report/Done">
<figure>
<artwork><![CDATA[ +===========+================+======================+==========+
| Interface | Source Address | Destination Address | Header |
+===========+================+======================+==========+
| MN-MAG | MN-link-local | [RFC2710], [RFC3810] | -- |
+-----------+----------------+----------------------+----------+
| | Proxy-CoA | LMAA | outer |
+ MAG-LMA +----------------+----------------------+----------+
| | MAG-link-local | [RFC2710], [RFC3810] | inner |
+-----------+----------------+----------------------+----------+
]]></artwork>
</figure>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document makes no request of IANA.</t>
<t>Note to RFC Editor: this section may be removed on publication as an
RFC.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>This draft does neither introduce additional messages nor novel
protocol operations. Consequently, no new threats arrive from procedures
described in this document in excess to <xref target="RFC3810"></xref>,
<xref target="RFC4605"></xref> and <xref target="RFC5213"></xref>
security concerns.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>This memo is the outcome of extensive previous discussions and a
follow-up of several initial drafts on the subject. The authors would
like to thank (in alphabetical order) Luis Contreras, Gorry Fairhurst,
Seil Jeon, Jouni Korhonen, Sebastian Meiling, Liu Hui, Imed Romdhani,
Behcet Sarikaya, Stig Venaas, and Juan Carlos Zuniga for advice, help
and reviews of the document. Funding by the German Federal Ministry of
Education and Research within the G-LAB Initiative is gratefully
acknowledged.</t>
<t></t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.3775"?>
<?rfc include="reference.RFC.5213"?>
<?rfc include="reference.RFC.3810"?>
<?rfc include="reference.RFC.4605"?>
<?rfc include="reference.RFC.2710"?>
<?rfc include="reference.I-D.ietf-netlmm-pmip6-ipv4-support"?>
<?rfc include="reference.RFC.3376"?>
<?rfc include="reference.RFC.2236"?>
</references>
<references title="Informative References">
<?rfc include="reference.I-D.irtf-mobopts-mmcastv6-ps"?>
<?rfc include="reference.I-D.deng-multimob-pmip6-requirement"?>
<?rfc include="reference.I-D.ietf-mboned-auto-multicast"?>
<?rfc include="reference.I-D.zuniga-multimob-smspmip"?>
</references>
<section anchor="A-InitMLD" title="Initial MLD Queries on Upcoming Links">
<t>According to <xref target="RFC3810"></xref> and <xref
target="RFC2710"></xref> when an IGMP/MLD-enabled multicast router
starts operating on a subnet, by default it considers itself as Querier
and sends several General Queries. Such initial query should be sent by
the router immediately, but could be delayed by a (tunable) Startup
Query Interval (see Sections 7.6.2. and 9.6. of <xref
target="RFC3810"></xref>).</t>
<t>Experimental tests on Linux and Cisco systems have revealed immediate
IGMP Queries following a link trigger event (within a fraction of 1 ms),
while MLD Queries immediately followed the autoconfiguration of IPv6
link-local addresses at the corresponding interface.</t>
</section>
<section title="State of IGMP/MLD Proxy Implementations">
<t>The deployment scenario defined in this document requires certain
proxy functionalities at the MAGs that implementations of <xref
target="RFC4605"></xref> need to contribute. In particular, a
simultaneous support of IGMP and MLD is needed, as well as a
configurable list of downstream interfaces that may be altered during
runtime, and the deployment of multiple proxy instances at a single
router that can operate independently on separated interfaces.</t>
<t>A brief experimental trial undertaken in February 2010 revealed the
following divergent status of selected IGMP/MLD proxy
implementations.</t>
<t><list style="hanging">
<t hangText="Cisco Edge Router">Software-based commodity edge
routers (test device from the 26xx-Series) implement IGMPv2/v3 proxy
functions only in combination with PIM-SM. There is no support of
MLD Proxy. Interfaces are dynamically configurable at runtime via
the CLI, but multiple proxy instances are not supported.</t>
<t hangText="Linux igmpproxy">IGMPv2 Proxy implementation that
permits a static configuration of downstream interfaces (simple bug
fix required). Multiple instances are prevented by a lock
(corresponding code re-used from a previous DVMRP implementation).
IPv6/MLD is unsupported. Project page:
http://sourceforge.net/projects/igmpproxy/.</t>
<t hangText="Linux gproxy">IGMPv3 Proxy implementation that permits
configuration of the upstream interface, only. Downstream interfaces
are collected at startup without dynamic extension of this list. No
support of multiple instances or MLD. Project page:
http://potiron.loria.fr/projects/madynes/internals/perso/lahmadi/igmpv3proxy/.</t>
<t hangText="Linux ecmh">MLDv1/2 Proxy implementation without IGMP
support that inspects IPv4 tunnels and detects entcapsulated MLD
messages. Allows for dynamic addition of interfaces at runtime and
multiple instances. However, downstream interfaces cannot be
configured. Project page: http://sourceforge.net/projects/ecmh/</t>
</list></t>
</section>
<section anchor="A-Eval"
title="Comparative Evaluation of Different Approaches">
<t>In this section, we briefly evaluate two basic PMIP concepts for
multicast traffic organization at LMAs: In scenario A, multicast is
provided by combined unicast/multicast LMAs as described in this
document. Scenario B directs traffic via a dedicated multicast LMA as
proposed in <xref target="I-D.zuniga-multimob-smspmip"></xref>, for
example.</t>
<t>Both approaches do not establish native multicast distribution
between the LMA and MAG, but use tunneling mechanisms. In scenario A, a
MAG is connected to different multicast-enabled LMAs, and can receive
the same multicast stream via multiple paths depending on the group
subscriptions of MNs and their associated LMAs. This problem, a.k.a.
tunnel convergence problem, may lead to redundant traffic at the MAGs.
Scenario B in contrast configures MAGs to establish a tunnel to a
single, dedicated multicast LMA for all attached MNs and relocates
overhead costs to the multicast anchor. This eliminates redundant
traffic, but may result in an avalanche problem at the LMA.</t>
<t>We quantify the costs of both approaches based on two metrics: The
amount of redundant traffic at MAGs and the number of simultaneous
streams at LMAs. Realistic values depend on the topology and the group
subscription model. To explore scalability in a large PMIP domain of
1,000,000 MNs, we consider the following two extremal multicast
settings.</t>
<t><list style="numbers">
<t>All MNs participate in distinct multicast groups.</t>
<t>All MNs join the same multicast groups.</t>
</list>A typical PMIP deployment approximately allows for 5,000 MNs
attached to one MAG, while 50 MAGs can be served by one LMA. Hence
1,000,000 MNs require approx. 200 MAGs backed by 4 LMAs for unicast
transmission. In scenario A, these LMAs also forward multicast streams,
while in scenario B one additional dedicated LMA (LMA-M) serves
multicast. In the following, we calculate the metrics described
above.</t>
<figure title="1,000,000 MNs are subscribed to distinct multicast groups">
<preamble>Setting 1:</preamble>
<artwork><![CDATA[ +===================+================+===================+
| PMIP multicast | # of redundant | # of sim. streams |
| scheme | streams at MAG | at LMA / LMA-M |
+===================+================+===================+
| Combined Unicast/ | 0 | 250,000 |
| Multicast LMA | | |
+-------------------+----------------+-------------------+
| Dedicated | 0 | 1,000,000 |
| Multicast LMA | | |
+-------------------+----------------+-------------------+]]></artwork>
<postamble></postamble>
</figure>
<t></t>
<figure title="1,000,000 MNs are subscribed to the same multicast group">
<preamble>Setting 2:</preamble>
<artwork><![CDATA[ +===================+================+===================+
| PMIP multicast | # of redundant | # of sim. streams |
| scheme | streams at MAG | at LMA / LMA-M |
+===================+================+===================+
| Combined Unicast/ | 4 | 50 |
| Multicast LMA | | |
+-------------------+----------------+-------------------+
| Dedicated | 0 | 200 |
| Multicast LMA | | |
+-------------------+----------------+-------------------+]]></artwork>
<postamble></postamble>
</figure>
<t>These considerations of extremal settings show that tunnel
convergence, i.e., duplicate data arriving at a MAG, does cause much
smaller problems in scalability than the stream replication at LMAs. For
scenario A it should be also noted that the high stream replication
requirements at LMAs in setting 1 can be attenuated by deploying
additional LMAs in a PMIP domain, while scenario B does not allow for
distributing the LMA-M, as no handover management is available at
LMA-M.</t>
</section>
<section title="Change Log ">
<t>The following changes have been made from
draft-schmidt-multimob-pmipv6-mcast-deployment-03. <list style="numbers">
<t>Detailed outline of multicast reconfiguration steps on handovers
added in protocol overview (section 3).</t>
<t>Clarified the details of proxy operations at the MAG along with
the expected features of IGMP/MLD Proxy implementations (section
4.2).</t>
<t>Clarified querying in dual-stack scenarios (section 4.4).</t>
<t>Subsection added on the special case, where multicast is
available throughout the access network (section 4.5).</t>
<t>Appendix on IGMP/MLD behaviour added with test reports on current
Proxy implementations.</t>
</list></t>
<t>The following changes have been made from
draft-schmidt-multimob-pmipv6-mcast-deployment-02. <list style="numbers">
<t>Many editorial improvements, in particular as response to draft
reviews.</t>
<t>Section on IPv4 support added.</t>
<t>Added clarifications on initial IGMP/MLD Queries and
supplementary information in appendix.</t>
<t>Appendix added an comparative performance evaluation regarding
mixed/dedicated deployment of multicast at LMAs.</t>
</list></t>
</section>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 05:39:02 |