One document matched: draft-ietf-multimob-pmipv6-source-04.xml
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<rfc category="std" docName="draft-ietf-multimob-pmipv6-source-04"
ipr="trust200902">
<front>
<title abbrev="Multicast Senders in PMIPv6">Mobile Multicast Sender
Support in Proxy Mobile IPv6 (PMIPv6) Domains</title>
<author fullname="Thomas C. Schmidt" initials="T C." role="editor"
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="Shuai Gao" initials="S." surname="Gao">
<organization>Beijing Jiaotong University</organization>
<address>
<postal>
<street></street>
<city>Beijing</city>
<region></region>
<code></code>
<country>China</country>
</postal>
<phone></phone>
<facsimile></facsimile>
<email>shgao@bjtu.edu.cn</email>
<uri></uri>
</address>
</author>
<author fullname="Hong-Ke Zhang" initials="H." surname="Zhang">
<organization>Beijing Jiaotong University</organization>
<address>
<postal>
<street></street>
<city>Beijing</city>
<region></region>
<code></code>
<country>China</country>
</postal>
<phone></phone>
<facsimile></facsimile>
<email>hkzhang@bjtu.edu.cn</email>
<uri></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>
<date />
<workgroup>MULTIMOB Group</workgroup>
<abstract>
<t>Multicast communication can be enabled in Proxy Mobile IPv6 domains
via the Local Mobility Anchors by deploying MLD Proxy functions at
Mobile Access Gateways, via a direct traffic distribution within an
ISP's access network, or by selective route optimization schemes. This
document describes the support of mobile multicast senders in Proxy
Mobile IPv6 domains for all three scenarios. Protocol optimizations for
synchronizing PMIPv6 with PIM, as well as a peering function for MLD
Proxies defined. Mobile sources always 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 (MIPv6) <xref target="RFC6275"></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 called the Local Mobility Anchor (LMA), and
Mobile Access Gateways (MAGs), are responsible for managing IP mobility
on behalf of the mobile node (MN). An MN connected to a PMIPv6 domain,
which only operates according to the base specifications of <xref
target="RFC5213"></xref>, cannot participate in multicast communication,
as MAGs will discard group packets.</t>
<t>Multicast support for mobile listeners can be enabled within a PMIPv6
domain by deploying MLD Proxy functions at Mobile Access Gateways, and
multicast routing functions at Local Mobility Anchors <xref
target="RFC6224"></xref>. This base deployment option is the simplest
way to PMIPv6 multicast extensions in the sense that it follows the
common PMIPv6 traffic model and neither requires new protocol operations
nor additional infrastructure entities. Standard software functions need
to be activated on PMIPv6 entities, only, at the price of possibly
non-optimal multicast routing.</t>
<t>Alternate solutions leverage performance optimization by providing
multicast routing at the access gateways directly, or by selective route
optimization schemes. Such approaches (partially) follow the business
model of providing multicast data services in parallel to PMIPv6 unicast
routing.</t>
<t>Multicast listener support satisfies the needs of receptive use cases
such as IPTV or server-centric gaming on mobiles. However, current
trends in the Internet enfold towards user-centric, highly interactive
group applications like user generated streaming, conferencing,
collective mobile sensing, etc. Many of these popular applications
create group content at end systems and can largely profit from a direct
data transmission to a multicast-enabled network.</t>
<t>This document describes the support of mobile multicast senders in
Proxy Mobile IPv6 domains subsequently for the base deployment scenario
<xref target="RFC6224"></xref>, for direct traffic distribution within
an ISP's access network, as well as for selective route optimization
schemes. The contribution of this work reflects the source mobility
problem as discussed in <xref target="RFC5757"></xref>. Mobile Nodes in
this setting remain agnostic of multicast mobility operations.</t>
</section>
<section title="Terminology">
<t>This document uses the terminology as defined for the mobility
protocols <xref target="RFC6275"></xref>, <xref target="RFC5213">
</xref> and <xref target="RFC5844"></xref>, as well as the multicast
edge related protocols <xref target="RFC3376"></xref>, <xref
target="RFC3810"></xref> and <xref target="RFC4605"></xref>.</t>
</section>
<section anchor="Base"
title="Base Solution for Source Mobility and PMIPv6 Routing">
<section title="Overview">
<t>The reference scenario for multicast deployment in Proxy Mobile
IPv6 domains is illustrated in <xref target="fig1"></xref>. MAGs play
the role of first-hop access routers that serve multiple MNs on the
downstream while running an MLD/IGMP proxy instance for every LMA
upstream tunnel.</t>
<figure anchor="fig1"
title="Reference Network for Multicast Deployment in PMIPv6 with Source Mobility">
<artwork><![CDATA[
+-------------+
| Multicast |
| Listeners |
+-------------+
|
*** *** *** ***
* ** ** ** *
* *
* 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
Multicast Sender + Listener(s)
]]></artwork>
</figure>
<t>An MN in a PMIPv6 domain will decide on multicast data transmission
completely independent of its current mobility conditions. It will
send packets as initiated by applications, using its source address
with Home Network Prefix (HNP) and a multicast destination address
chosen by application needs. Multicast packets will arrive at the
currently active MAG via one of its downstream local (wireless) links.
A multicast unaware MAG would simply discard these packets in the
absence of a multicast routing information base (MRIB).</t>
<t>An MN can successfully distribute multicast data in PMIPv6, if MLD
proxy functions are deployed at the MAG as described in <xref
target="RFC6224"></xref>. In this set-up, the MLD proxy instance
serving a mobile multicast source has configured its upstream
interface at the tunnel towards MN's corresponding LMA. For each LMA,
there will be a separate instance of an MLD proxy.</t>
<t>According to the specifications given in <xref
target="RFC4605"></xref>, multicast data arriving from a downstream
interface of an MLD proxy will be forwarded to the upstream interface
and to all but the incoming downstream interfaces that have
appropriate forwarding states for this group. Thus multicast streams
originating from an MN will arrive at the corresponding LMA and
directly at all mobile receivers co-located at the same MAG and MLD
Proxy instance. Serving as the designated multicast router or an
additional MLD proxy, the LMA forwards data to the fixed Internet,
whenever forwarding states are maintained by multicast routing. If the
LMA is acting as another MLD proxy, it will forward the multicast data
to its upstream interface, and to downstream interfaces with matching
subscriptions, accordingly.</t>
<t>In case of a handover, the MN (unaware of IP mobility) can continue
to send multicast packets as soon as network connectivity is
reconfigured. At this time, the MAG has determined the corresponding
LMA, and IPv6 unicast address configuration (including PMIPv6
bindings) has been completed. Still multicast packets arriving at the
MAG are discarded (if not buffered) until the MAG has completed the
following steps.</t>
<t><list style="numbers">
<t>The MAG has determined that the MN is admissible to multicast
services.</t>
<t>The MAG has added the new downstream link to the MLD proxy
instance with up-link to the corresponding LMA.</t>
</list>As soon as the MN's uplink is associated with the
corresponding MLD proxy instance, multicast packets are forwarded
again to the LMA and eventually to receivers within the PMIP domain
(see the call flow in <xref target="fig-callflow"></xref>). In this
way, multicast source mobility is transparently enabled in PMIPv6
domains that deploy the base scenario for multicast.</t>
<figure anchor="fig-callflow"
title="Call Flow for Group Communication in Multicast-enabled PMIP">
<artwork><![CDATA[MN1 MAG1 MN2 MAG2 LMA
| | | | |
| | Mcast Data | | |
| |<---------------+ | |
| | Mcast Data | | |
| Join(G) +================================================>|
+--------------> | | | |
| Mcast Data | | | |
|<---------------+ | | |
| | | | |
| < Movement of MN 2 to MAG2 & PMIP Binding Update > |
| | | | |
| | |--- Rtr Sol -->| |
| | |<-- Rtr Adv ---| |
| | | | |
| | | < MLD Proxy Configuration > |
| | | | |
| | | (MLD Query) | |
| | |<--------------+ |
| | | 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 their IPv4 stack enabled in a PMIPv6 domain.
PMIPv6 can provide IPv4 home address mobility support <xref
target="RFC5844"></xref>. IPv4 multicast is handled by an IGMP proxy
function at the MAG in an analogous way.</t>
<t>Following these deployment steps, multicast traffic distribution
transparently inter-operates with PMIPv6. It is worth noting that an
MN - while being attached to the same MAG as the mobile source, but
associated with a different LMA - cannot receive multicast traffic on
a shortest path. Instead, multicast streams flow up to the LMA of the
mobile source, are transferred to the LMA of the mobile listener and
tunneled downwards to the MAG again (see <xref
target="Extensions"></xref> for further optimizations).</t>
</section>
<section title="Base Solution for Source Mobility: Details">
<t>A support of multicast source mobility in PMIPv6 requires to deploy
general multicast functions at PMIPv6 routers and to define their
interaction with the PMIPv6 protocol in the following way.</t>
<section title="Operations of the Mobile Node">
<t>A Mobile Node willing to send multicast data will proceed as if
attached to the fixed Internet. No specific mobility or other
multicast related functionalities are required at the MN.</t>
</section>
<section title="Operations of the Mobile Access Gateway">
<t>A Mobile Access Gateway is required to have MLD proxy instances
deployed, one for each tunnel to an LMA, which serves as its unique
upstream link (cf., <xref target="RFC6224"></xref>). On the arrival
of an MN, the MAG decides on the mapping of downstream links to a
proxy instance and the upstream link to the LMA based on the regular
Binding Update List as maintained by PMIPv6 standard operations.
When multicast data is received from the MN, the MAG MUST identify
the corresponding proxy instance from the incoming interface and
forwards multicast data upstream according to <xref
target="RFC4605"></xref>.</t>
<t>The MAG MAY apply special admission control to enable multicast
data transition from an MN. It is advisable to take special care
that MLD proxy implementations do not redistribute multicast data to
downstream interfaces without appropriate subscriptions in
place.</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 upstream for the
corresponding MAG. It will manage and maintain a multicast
forwarding information base for all group traffic arriving from its
mobile sources. It SHOULD participate in multicast routing functions
that enable traffic redistribution to all adjacent LMAs within the
PMIPv6 domain and thereby ensure a continuous receptivity while the
source is in motion.</t>
<section anchor="PIM-Source"
title="Local Mobility Anchors Operating PIM">
<t>Local Mobility Anchors that operate the PIM-SM routing protocol
<xref target="RFC4601"></xref> will require sources to be directly
connected for sending PIM registers to the RP. This does not hold
in a PMIPv6 domain, as MAGs are routers intermediate to MN and the
LMA. In this sense, MNs are multicast sources external to the
PIM-SM domain.</t>
<t>To mitigate this incompatibility common to all subsidiary MLD
proxy domains, the LMA MUST act as a PIM Border Router and
activate the Border-bit. In this case, the DirectlyConnected(S) is
treated as being TRUE for mobile sources and the PIM-SM forwarding
rule "iif == RPF_interface(S)" is relaxed to be TRUE, as the
incoming tunnel interface from MAG to LMA is considered as not
part of the PIM-SM component of the LMA (see A.1 of <xref
target="RFC4601"></xref> ).</t>
<t>In addition, an LMA serving as PIM Designated Router is
connected to MLD proxies via individual IP-tunnel interfaces and
will experience changing PIM source states on handover. As the
incoming interface connects to a point-to-point link, PIM Assert
contention is not active, and incoming interface validation is
only performed by RPF checks. Consequently, a PIM DR SHOULD update
incoming source states, as soon as RPF inspection succeeds, i.e.,
after PMIPv6 forwarding state update. Consequently, PIM routers
SHOULD be able to manage these state changes, but some
implementations are expected to incorrectly refuse packets until
the previous state has timed out.</t>
<t>Notably, running BIDIR PIM <xref target="RFC5015"></xref> on
LMAs remains robust with respect to source location and does not
require special configurations or state management for
sources.</t>
</section>
</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="RFC5844"></xref>.
For this purpose, an LMA can register an IPv4-Proxy-CoA in its
Binding Cache and the MAG can provide IPv4 support in its access
network. 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>
<t>A particular note is worth giving the scenario of <xref
target="RFC5845"></xref> in which overlapping private address spaces
of different operators can be hosted in a PMIP domain by using GRE
encapsulation with key identification. This scenario implies that
unicast communication in the MAG-LMA tunnel can be individually
identified per MN by the GRE keys. This scenario still does not
impose any special treatment of multicast communication for the
following reasons.</t>
<t>Multicast streams from and to MNs arrive at a MAG on
point-to-point links (identical to unicast). Multicast data
transmission from the MAG to the corresponding LMA is link-local
between the routers and routing/forwarding remains independent of
any individual MN. So the MAG-proxy and the LMA SHOULD NOT use GRE
key identifiers, but plain GRE encapsulation in multicast
communication (including MLD queries and reports). Multicast traffic
is transmitted as router-to-router forwarding via the MAG-to-LMA
tunnels and according to the multicast routing information base
(MRIB) of the MAG or the LMA. It remains independent of MN's unicast
addresses, while the MAG proxy instance re-distributes multicast
data down the point-to-point links (interfaces) according to its
local subscription states, independent of IP addresses of the
MN.</t>
</section>
<section title="Efficiency of the Distribution System">
<t>The distribution system of the base solution directly follows
PMIPv6 routing rules, and organizes multicast domains with respect
to LMAs. Thus, no coordination between address spaces or services is
required between the different instances, provided their associated
LMAs belong to disjoint multicast domains. Routing is optimal for
communication between MNs of the same domain, or stationary
subscribers.</t>
<t>In the following, efficiency-related issues remain.</t>
<t><list style="hanging">
<t hangText="Multicast reception at LMA">In the current
deployment scenario, the LMA will receive all multicast traffic
originating from its associated MNs. There is no mechanism to
suppress upstream forwarding in the absence of receivers.</t>
<t hangText="MNs on the same MAG using different LMAs">For a
mobile receiver and a source that use different LMAs, the
traffic has to go up to one LMA, cross over to the other LMA,
and then be tunneled back to the same MAG, causing redundant
flows in the access network and at the MAG.</t>
</list></t>
</section>
</section>
</section>
<section anchor="Direct-Routing" title="Direct Multicast Routing">
<t>There are deployment scenarios, where multicast services are
available throughout the access network independent of the PMIPv6
routing system <xref target="I-D.ietf-multimob-pmipv6-ropt"></xref>. In
these cases, the visited networks grant a local content distribution
service (in contrast to LMA-based home subscription) with locally
optimized traffic flows. It is also possible to deploy a mixed service
model of local and LMA-based subscriptions, provided a unique way of
service selection is implemented. For example, access routers (MAGs)
could decide on service access based on the multicast address G or the
SSM channel (S,G) under request (see <xref target="A-moup"></xref> for
further discussions).</t>
<section title="Overview">
<t>Direct multicast access can be supported by <list style="symbols">
<t>native multicast routing provided by one multicast router that
is neighboring MLD proxies deployed at MAGs within a flat access
network, or via tunnel uplinks,</t>
<t>a multicast routing protocol such as PIM-SM <xref
target="RFC4601"></xref> or BIDIR-PIM <xref
target="RFC5015"></xref> deployed at the MAGs.</t>
</list></t>
<figure anchor="fig2"
title="Reference Networks for (a) Proxy-assisted Direct Multicast Access and (b) Dynamic Multicast Routing at MAGs">
<artwork><![CDATA[
*** *** *** ***
* ** ** ** *
* *
* Multicast *
+----+ * Infrastructure * +----+
|LMA | * ** ** ** * |LMA |
+----+ *** *** *** *** +----+
| // \\ |
\\ // \\ PMIP (unicast) |
PMIP \\ // \\ // \\ ** *** *** ** //
(unicast) \\ // \\ // \\ * ** ** ** //
\\ // \\ // \\* Multicast *//
|| || || || * || Routing || *
+----+ +----+ * +----+ +----+ *
MLD Proxy |MAG1| |MAG2| * |MAG1| |MAG2| *
+----+ +----+ *+----+ ** ** +----+*
| | | | |*** *** ***|
| | | | | |
MN1 MN2 MN3 MN1 MN2 MN3
(a) Multicast Access at Proxy Uplink (b) Multicast Routing at MAG
]]></artwork>
</figure>
<t><xref target="fig2"></xref> displays the corresponding deployment
scenarios, which separate multicast from PMIPv6 unicast routing. It is
assumed throughout these scenarios that all MAGs (MLD proxies) are
linked to a single multicast routing domain. Notably, this scenario
requires coordination of multicast address utilization and service
bindings.</t>
<t>Multicast traffic distribution can be simplified in these
scenarios. A single proxy instance at MAGs with up-link into the
multicast domain will serve as a first hop multicast gateway and avoid
traffic duplication or detour routing. Multicast routing functions at
MAGs will seamlessly embed access gateways within a multicast cloud.
However, mobility of the multicast source in this scenario will
require some multicast routing protocols to rebuild distribution
trees. This can cause significant service disruptions or delays (see
<xref target="RFC5757"></xref> for further aspects). Deployment
details are specific to the multicast routing protocol in use, in the
following described for common protocols.</t>
</section>
<section title="MLD Proxies at MAGs">
<t>In a PMIPv6 domain, single MLD proxy instances can be deployed at
each MAG that enable multicast service at the access via an uplink to
a multicast service infrastructure (see <xref target="fig2"></xref>
(a) ). To avoid service disruptions on handovers, the uplinks of all
proxies SHOULD be adjacent to the same next-hop multicast router. This
can either be achieved by arranging proxies within a flat access
network, or by upstream tunnels that terminate at a common multicast
router.</t>
<t>Multicast data submitted by a mobile source will reach the MLD
proxy at the MAG that subsequently forwards flows to the upstream, and
all downstream interfaces with appropriate subscriptions. Traversing
the upstream will lead traffic into the multicast infrastructure
(e.g., to a PIM Designated Router) which will route packets to all
local MAGs that have joined the group, as well as further upstream
according to protocol procedures and forwarding states.</t>
<t>On handover, a mobile source will reattach to a new MAG and can
continue to send multicast packets as soon as PMIPv6 unicast
configurations have completed. Like at the previous MAG, the new MLD
proxy will forward data upstream and downstream to subscribers.
Listeners local to the previous MAG will continue to receive group
traffic via the local multicast distribution infrastructure following
aggregated listener reports of the previous proxy. In general, traffic
from the mobile source continues to be transmitted via the same
next-hop router using the same source address and thus remains
unchanged when seen from the wider multicast infrastructure.</t>
<section title="Considerations for PIM-SM on the Upstream">
<t>A mobile source that transmits data via an MLD proxy will not be
directly connected to a PIM Designated Router as discussed in <xref
target="PIM-Source"></xref>. Countermeasures apply
correspondingly.</t>
<t>A PIM Designated Router that is connected to MLD proxies via
individual IP-tunnel interfaces will experience invalid PIM source
states on handover. In some implementations of PIM-SM this could
lead to an interim packet loss (see Section <xref
target="PIM-Source"></xref>). This problem can be mitigated by
aggregating proxies on a lower layer.</t>
</section>
<section title="SSM Considerations">
<t>Source-specific subscriptions invalidate with routes, whenever
the source moves from or to the MAG/proxy of a subscriber. Multicast
forwarding states will rebuild with unicast route changes. However,
this may lead to noticeable service disruptions for locally
subscribed nodes.</t>
</section>
</section>
<section anchor="PIM-SM" title="PIM-SM at MAGs">
<t>The full-featured multicast routing protocol PIM-SM MAY be deployed
in the access network for providing multicast services in parallel to
unicast routes. Throughout this section, it is assumed that the PMIPv6
mobility domain is part of a single PIM-SM multicast routing domain
with PIM-SM routing functions present at all MAGs and all LMAs. The
PIM routing instance at a MAG SHALL then serve as the Designated
Router (DR) for all directly attached Mobile Nodes. For expediting
handover operations, it is advisable to position PIM Rendezvous Points
(RPs) in the core of the PMIPv6 network domain. However, regular IP
routing tables need not be present in a PMIPv6 deployment, and
additional effort is required to establish reverse path forwarding
rules as required by PIM-SM.</t>
<section anchor="PIM-MRIB" title="Routing Information Base for PIM-SM">
<t>In this scenario, PIM-SM will rely on a Multicast Routing
Information Base (MRIB) that is generated independently of the
policy-based routing rules of PMIPv6. The granularity of
mobility-related routing locators required in PIM depends on the
complexity (phases) of its deployment.</t>
<t>The following information is needed for all phases of PIM. <list
style="symbols">
<t>All routes to networks and nodes (including RPs) that are not
mobile members of the PMIPv6 domain MUST be defined consistently
among PIM routers and MUST remain uneffected by node mobility.
The setup of these general routes is expected to follow the
topology of the operator network and is beyond the scope of this
document.</t>
</list> The following route entries are required at a
PIM-operating MAG when phases two or three of PIM, or PIM-SSM are in
operation.<list style="symbols">
<t>Local routes to the Home Network Prefixes (HNPs) of all MNs
associated with their corresponding point-to-point attachments
that MUST be included in the local MRIB.</t>
<t>All routes to MNs that are attached to distant MAGs of the
PMIPv6 domain point towards their corresponding LMAs. These
routes MUST be made available in the MRIB of all PIM routers
(except for the local MAG of attachment), but MAY be eventually
expressed by an appropriate default entry.</t>
</list></t>
</section>
<section anchor="PIM-One" title="Operations of PIM in Phase One">
<t>A new mobile source S will transmit multicast data of group G
towards its MAG of attachment. Acting as a PIM DR, the access
gateway will unicast-encapsulate the multicast packets and forward
the data to the Virtual Interface (VI) with encapsulation target
RP(G), a process known as PIM source registering. The RP will
decapsulate and natively forward the packets down the RP-based
distribution tree towards (mobile and stationary) subscribers.</t>
<t>On handover, the point-to-point link connecting the mobile source
to the old MAG will go down and all (S,*) flows terminate. In
response, the previous DR (MAG) deactivates the data encapsulation
channels for the transient source (i.e., all
DownstreamJPState(S,*,VI) are set to NoInfo state). After
reattaching and completing unicast handover negotiations, the mobile
source can continue to transmit multicast packets, while being
treated as a new source at its new DR (MAG). Source register
encapsulation will be immediately initiated, and (S,G) data continue
to flow natively down the (*,G) RP-based tree.</t>
<t>Source handover management in PIM phase one admits low complexity
and remains transparent to receivers. In addition, the source
register tunnel management of PIM is a fast protocol operation and
little overhead ís induced thereof. In a PMIPv6 deployment,
PIM RPs MAY be configured to not initiated (S,G) shortest path tress
for mobile sources, and thus remain in phase one of the protocol.
The price to pay for such simplified deployment lies in possible
routing detours by an overall RP-based packet distribution.</t>
</section>
<section anchor="PIM-Two" title="Operations of PIM in Phase Two">
<t>After receiving source register packets, a PIM RP eventually will
initiate a source-specific Join for creating a shortest path tree to
the (mobile) source S, and issue a source register stop at the
native arrival of data from S. For initiating an (S,G) tree, the RP,
as well as all intermediate routers, require route entries for the
HNP of the MN that - unless the RP coincides with the MAG of S -
point towards the corresponding LMA of S. Consequently, the (S,G)
tree will proceed from the RP via the (stable) LMA, down the LMA-MAG
tunnel to the mobile source. This tree can be of lesser routing
efficiency than the PIM source register tunnel established in phase
one, but provides the advantage of immediate data delivery to
receivers that share a MAG with S.</t>
<t>On handover, the mobile source reattaches to a new MAG (DR), and
PMIPv6 unicast management will transfer the LMA-MAG tunnel to the
new point of attachment. However, in the absence of a corresponding
multicast forwarding state, the new DR will treat S as a new source
and initiate a source registering of PIM phase one with the RP. In
response, the PIM RP will recognize the known source at a new
(tunnel) interface immediately responds with a register stop. As the
RP had joined the shortest path tree to receive from the source via
the LMA, it will see an RPF change when data arrives at a new
interface. Implementation-dependent, this can trigger an update of
the PIM MRIB and trigger a new PIM Join message. Otherwise, the tree
is periodically updated by Joins transmitted towards the new MAG on
a path via the LMA. In proceeding this way, a quick recovery of PIM
transition from phase one to two will be performed per handover.</t>
</section>
<section anchor="PIM-Three" title="Operations of PIM in Phase Three">
<t>In response to an exceeded threshold of packet transmission, DRs
of receivers eventually will initiated a source-specific Join for
creating a shortest path tree to the (mobile) source S, thereby
transitioning PIM into the final short-cut phase three. For all
receivers not sharing a MAG with S, this (S,G) tree will range from
the receiving DR via the (stable) LMA, the LMA-MAG tunnel to the
mobile source. This tree is of higher routing efficiency than
established in the previous phase two, but need not outperform the
PIM source register tunnel established in phase one. It provides the
advantage of immediate data delivery to receivers that share a MAG
with S.</t>
<t>On handover, the mobile source reattaches to a new MAG (DR), and
PMIPv6 unicast management will transfer the LMA-MAG tunnel to the
new point of attachment. However, in the absence of a corresponding
multicast forwarding state, the new DR will treat S as a new source
and initiate a source registering of PIM phase one. A PIM
implementation compliant with this change can recover phase three
states in the following way. First, the RP recovers to phase two as
described in the previous section, and will not forward data
arriving via the source register tunnel. Tree mainenance eventually
triggered by the RPF change (see <xref target="PIM-Two"></xref>)
will generate proper states for a native forwarding from the new MAG
via the LMA. Thereafter, packets arriving at the LMA without source
register encapsulation are forwarded natively along the shortest
path tree towards receivers.</t>
<t>In consequence, the PIM transition from phase one to two and
three will be quickly recovered per handover, but still leads to an
enhanced signaling load and intermediate packet loss.</t>
</section>
<section title="PIM-SSM Considerations">
<t>Source-specific Joins of receivers will guide PIM to operate in
SSM mode and lead to an immediate establishment of source-specific
shortest path trees. Such (S,G) trees will equal the distribution
system of PIM's final phase three (see <xref
target="PIM-Three"></xref>). However, on handover and in the absence
of RP-based data distribution, SSM data delivery cannot be resumed
via source registering as in PIM phase one. Consequently, data
packets transmitted after a handover will be discarded at the MAG
until regular tree maintenance has re-established the (S,G)
forwarding state at the new MAG.</t>
</section>
<section title="Handover Optimizations for PIM">
<t>Source-specific shortest path trees are constructed in PIM-SM
(phase two and three), and in PIM-SSM that follow LMA-MAG tunnels
towards a source. As PIM remains unaware of source mobility
management, these trees invalidate under handovers with each tunnel
re-establishment at a new MAG. Regular tree maintenance of PIM will
recover the states, but remains unsynchronized and too slow to
seamlessly preserve PIM data dissemination.</t>
<t>A method to quickly recover PIM (S,G) trees under handover SHOULD
synchronize multicast state maintenance with unicast handover
operations and MAY proceed as follows. On handover, an LMA reads all
(S,G) Join states from its corresponding tunnel interface and
identifies those source addresses S_i that match moving HNPs. After
re-establishing the new tunnel, it SHOULD associate the (S_i,*) Join
states with the new tunnel endpoint and immediately trigger a state
maintenance (PIM Join) message. In proceeding this way, the
source-specific PIM states are transferred to the new tunnel end
point and propagated to the new MAG in synchrony with unicast
handover procedures.</t>
</section>
</section>
<section anchor="BIDIR-PIM" title="BIDIR-PIM">
<t>BIDIR-PIM MAY be deployed in the access network for providing
multicast services in parallel to unicast routes. Throughout this
section, it is assumed that the PMIPv6 mobility domain is part of a
single BIDIR-PIM multicast routing domain with BIDIR-PIM routing
functions present at all MAGs and all LMAs. The PIM routing instance
at a MAG SHALL then serve as the Designated Forwarder (DF) for all
directly attached Mobile Nodes. For expediting handover operations, it
is advisable to position BIDIR-PIM Rendezvous Point Addresses (RPAs)
in the core of the PMIPv6 network domain. As regular IP routing tables
need not be present in a PMIPv6 deployment, reverse path forwarding
rules as required by BIDIR-PIM need to be established.</t>
<section anchor="BIDIR-MRIB"
title="Routing Information Base for BIDIR-PIM">
<t>In this scenario, BIDIR-PIM will rely on a Multicast Routing
Information Base (MRIB) that is generated independently of the
policy-based routing rules of PMIPv6. The following information is
needed.</t>
<t><list style="symbols">
<t>All routes to networks and nodes (including RPAs) that are
not mobile members of the PMIPv6 domain MUST be defined
consistently among BIDIR-PIM routers and remain uneffected by
node mobility. The setup of these general routes is expected to
follow the topology of the operator network and is beyond the
scope of this document.</t>
</list></t>
</section>
<section title="Operations of BIDIR-PIM">
<t>BIDIR-PIM will establish spanning trees across its network domain
in conformance to its preconfigured RPAs and the routing information
provided. Multicast data transmitted by a mobile source will
immediately be forwarded by its DF (MAG) onto the spanning group
tree without further protocol operations.</t>
<t>On handover, the mobile source re-attaches to a new MAG (DF),
which completes unicast network configurations. Thereafter, the
source can immediately proceed with multicast packet transmission
onto the pre-established distribution tree. BIDIR-PIM does neither
require protocol signaling nor additional reconfiguration delays to
adapt to source mobility and can be considered the protocol of
choice for mobile multicast operations in the access. As multicast
streams always flow up to the Rendezvous Point Link, some care
should be taken to configure RPAs compliant with network
capacities.</t>
</section>
</section>
</section>
<section anchor="Extensions"
title="Extended MLD Proxy Function for Optimized Source Mobility in PMIPv6">
<t>A deployment of MLD Proxies (see <xref target="RFC4605"></xref>) at
MAGs has proven a useful and appropriate approach to multicast in
PMIPv6, see <xref target="RFC6224"></xref>, <xref
target="I-D.ietf-multimob-pmipv6-ropt"></xref>. However, deploying
unmodified standard proxies can go along with significant performance
degradation for mobile senders as discussed along the lines of this
document. To overcome these deficits, an optimized approach to multicast
source mobility based on extended peering functions among proxies is
introduced in this section. Prior to presenting the solution, we will
sketch the relevant requirements.</t>
<t>Solutions that extend MLD Proxies by additional uplinking functions
need to comply to the following requirements.</t>
<t><list style="hanging">
<t hangText="Prevention of Routing Loops">In the absence of a
full-featured routing logic at an MLD Proxy, simple and locally
decidable rules need to prevent source traffic from traversing the
network in loops as potentially enabled by multiple uplinks.</t>
<t hangText="Unique coverage of receivers">Listener functions at
Proxies require simple, locally decidable rules to initiate a unique
delivery of multicast packets to all receivers.</t>
</list>Following different techniques, these requirements are met in
the following solutions.</t>
<section title="Peering Function for MLD Proxies">
<t>In this section, we define a peering interface for MLD proxies that
allows for a direct data exchange of locally attached multicast
sources. Such peering interfaces can be configured - as a direct link
or a bidirectional tunnel - between any two proxy instances (locally
deployed as in <xref target="RFC6224"></xref> or remotely) and remain
as silent virtual links in regular proxy operations. Data on such link
is exchanged only in cases, where one peering proxy directly connects
on the downstream to a source of multicast traffic, which the other
peering proxy actively subscribes to. Operations are defined for ASM
and SSM, but provide superior performance in the presence of
source-specific signaling (IGMPv3/MLDv2).</t>
<section title="Operations at the Multicast Sender">
<t>An MLD Proxy in the perspective of a sender will see peering
interfaces as restricted downstream interfaces. It will install and
maintain source filters at its peering links that will restrict data
transmission to those packets that originate from a locally attached
source at the downstream. In detail, a proxy will extract from its
configuration the network prefixes attached to its downstream
interfaces and MUST implement a source filter base at its peering
interfaces that restricts data transmission to IP source addresses
from its local prefixes. This filter base Must be updated, if and
only if the downstream configuration changes. In this way, a
multihop forwarding on peering links is prevented. Multicast packets
that arrive from the upstream interface of the proxy are thus only
forwarded to regular downstream interfaces with appropriate
subscription states.</t>
<t>Multicast traffic arriving from a locally attached source will be
forwarded to the regular upstream interface and all downstreams with
appropriate subscription states (i.e., regular Proxy operations). In
addition, local multicast packets are transferred to those peering
interfaces with appropriate subscription states.</t>
</section>
<section title="Operations at the Multicast Listener">
<t>From the listener side, peering interfaces appear as preferred
upstream links. Thus an MLD proxy with peering interconnects will
offer several interfaces for pulling remote traffic: the regular
upstream and the peerings. Traffic arriving from any of the peering
links will be mutually disjoint, but normally also available from
the upstream. To prevent duplicate traffic from arriving at the
listener side, the proxy <list style="symbols">
<t>MAY delay aggregated reports to the upstream, and</t>
<t>MUST apply appropriate filters to exclude duplicate
streams.</t>
</list></t>
<t>In detail, it first issues listener reports (in parallel) to its
peering links, which only span one (virtual) hop. Whenever the
expected traffic (e.g., SSM channels) does not completely arrive
from the peerings after a waiting time (default: 10 ms), additional
(complementary, in the case of SSM) reports are sent to the standard
upstream interface.</t>
<t>After the arrival of traffic from peering links, an MLD proxy
MUST install source filters at the upstream in the following
way.</t>
<t><list style="hanging">
<t hangText="ASM with IGMPv2/MLDv1">In the presence of Any
Source Multicast using IGMPv2/MLDv1, only, the proxy cannot
signal source filtering to its upstream. Correspondingly, it
applies (S,*) ingress filters at its upstream interface for all
sources S seen in traffic of the peering links. It is noteworthy
that unwanted traffic is still replicated to the proxy via the
access network.</t>
<t hangText="ASM with IGMPv3/MLDv2">In the presence of
source-specific signaling (IGMPv3/MLDv2), the upstream interface
is set to (S,*) exclude mode for all sources S seen in traffic
of the peering links. The corresponding source-specific
signaling will prevent duplicate traffic forwarding throughout
the access network.</t>
<t hangText="SSM">In the presence of Source Specific Multicast,
the proxy will subscribe on its uplink interface to those (S,G)
channels, only, that do not arrive via the peering links.</t>
</list>In proceeding this way, multicast group data arrive from
peering interfaces first, while only peer-wise unavailable traffic
is retrieved from the regular upstream interface.</t>
</section>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>TODO.</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>TODO</t>
<t>Consequently, no new threats are introduced by this document in
addition to those identified as security concerns of <xref
target="RFC3810"></xref>, <xref target="RFC4605"></xref>, <xref
target="RFC5213"></xref>, and <xref target="RFC5844"></xref>.</t>
<t>However, particular attention should be paid to implications of
combining multicast and mobility management at network entities. As this
specification allows mobile nodes to initiate the creation of multicast
forwarding states at MAGs and LMAs while changing attachments, threats
of resource exhaustion at PMIP routers and access networks arrive from
rapid state changes, as well as from high volume data streams routed
into access networks of limited capacities. In addition to proper
authorization checks of MNs, rate controls at replicators MAY be
required to protect the agents and the downstream networks. In
particular, MLD proxy implementations at MAGs SHOULD carefully procure
for automatic multicast state extinction on the departure of MNs, as
mobile multicast listeners in the PMIPv6 domain will not actively
terminate group membership prior to departure.</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>The authors would like to thank (in alphabetical order) Luis M.
Contreras, Muhamma Omer Farooq, Bohao Feng, Dirk von Hugo, Ning Kong,
Jouni Korhonen, He-Wu Li, Akbar Rahman, Stig Venaas, Li-Li Wang, Qian
Wu, Zhi-Wei Yan for advice, help and reviews of the document. Funding by
the German Federal Ministry of Education and Research within the G-LAB
Initiative (projects HAMcast, Mindstone and SAFEST) is gratefully
acknowledged.</t>
<t></t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.6275"?>
<?rfc include="reference.RFC.5213"?>
<?rfc include="reference.RFC.3810"?>
<?rfc include="reference.RFC.4601"?>
<?rfc include="reference.RFC.4605"?>
<?rfc include="reference.RFC.5015"?>
<?rfc include="reference.RFC.2710"?>
<?rfc include="reference.RFC.5844"?>
<?rfc include="reference.RFC.3376"?>
</references>
<references title="Informative References">
<?rfc include="reference.RFC.5757"?>
<?rfc include="reference.RFC.6224"?>
<?rfc include="reference.RFC.5845"?>
<?rfc include="reference.RFC.2236"?>
<?rfc include="reference.I-D.ietf-multimob-pmipv6-ropt"?>
</references>
<section anchor="A-moup" title="Multiple Upstream Interface Proxy">
<t>In this section, we document upstream extensions for an MLD proxy
that were originally developed during the work on this document.
Multiple proxy instances deployed at a single MAG (see <xref
target="Base"></xref>) can be avoided by adding multiple upstream
interfaces to a single MLD Proxy. In a typical PMIPv6 deployment, each
upstream of a single proxy instance can interconnect to one of the LMAs.
With such ambiguous upstream options, appropriate forwarding rules MUST
be supplied to</t>
<t><list style="symbols">
<t>unambiguously guide traffic forwarding from directly attached
mobile sources, and</t>
<t>lead listener reports to initiating unique traffic
subscriptions.</t>
</list>This can be achieved by a complete set of source- and
group-specific filter rules (e.g., (S,*), (*,G)) installed at proxy
interfaces. These filters MAY be derived in parts from PMIPv6 routing
policies, and can include a default behavior (e.g., (*,*)).</t>
<section title="Operations for Local Multicast Sources">
<t>Packets from a locally attached multicast source will be forwarded
to all downstream interfaces with appropriate subscriptions, as well
as up the interface with the matching source-specific filter.</t>
<t>Typically, the upstream interface for a mobile multicast source is
chosen based on the policy routing (e.g., the MAG-LMA tunnel interface
for LMA-based routing or the interface towards the multicast router
for direct routing), but alternate configuriations MAY be applied.
Packets from a locally attached multicast source will be forwarded to
the corresponding upstream interface with the matching source-specific
filter, as well as all the downstream interfaces with appropriate
subscriptions.</t>
</section>
<section title="Operations for Local Multicast Subscribers">
<t>Multicast listener reports are group-wise aggregated by the MLD
proxy. The aggregated report is issued to the upstream interface with
matching group/channel-specific filter. The choice of the
corresponding upstream interface for aggregated group membership
reports MAY be additionally based on some administrative scoping rules
for scoped multicast group addresses.</t>
<t>In detail, a Multiple Upstream Interface Proxy will provide and
maintain a Multicast Subscription Filter Table that maps source- and
group-specific filters to upstream interfaces. The forwarding decision
for an aggregated MLD listener report is based on the first matching
entry from this table, with the understanding that for IGMPv3/MLDv2
the MLD Proxy performs a state decomposition , if needed (i.e., a
(*,G) subscription is split into (S,G) and (* \ S,G) in the presence
of (*,G) after (S,G) interface entries), and that (S,*)-filters are
always false in the absence of source-specific signaling, i.e. in
IGMPv2/MLDv1 only domains.</t>
<t>In typical deployment scenarios, specific group services (channels)
could be either associated with selected uplinks to remote LMAs, while
a (*,*) default subscription entry (in the last table line) is bound
to a local routing interface, or selected groups are configured as
local services first, while a (*,*) default entry (in the last table
line) points to a remote uplink that provides the general multicast
support.</t>
</section>
</section>
<section title="Change Log ">
<t>The following changes have been made from version
draft-ietf-multimob-pmipv6-source-03:</t>
<t><list style="numbers">
<t>Fixed issues in Section <xref target="PIM-SM"></xref> (PIM phase
two and three transistion) according to WG feedback.</t>
<t>Editorial improvements, resolved nits.</t>
<t>Updated references.</t>
</list></t>
<t>The following changes have been made from version
draft-ietf-multimob-pmipv6-source-02:</t>
<t><list style="numbers">
<t>Added clarifications and details as requested by the working
group, resolved nits.</t>
<t>Moved Multiple Upstream MLD Proxy to Appendix in response to WG
desire.</t>
<t>Updated references.</t>
</list></t>
<t>The following changes have been made from version
draft-ietf-multimob-pmipv6-source-01:</t>
<t><list style="numbers">
<t>Added clarifications and details as requested by the working
group, resolved nits.</t>
<t>Detailed out operations of Multiple Upstream MLD Proxies.</t>
<t>Clarified operations of MLD proxies with peering links.</t>
<t>Many editorial improvements.</t>
<t>Updated references.</t>
</list></t>
<t>The following changes have been made from version
draft-ietf-multimob-pmipv6-source-00:</t>
<t><list style="numbers">
<t>Direct routing with PIM-SM and PIM-SSM has been added.</t>
<t>PMIP synchronization with PIM added for improved handover.</t>
<t>Direct routing with BIDIR-PIM has been added.</t>
<t>MLD Proxy extensions requirements added.</t>
<t>Peering of MLD Proxies added.</t>
<t>First sketch of multiple upstream proxy added.</t>
<t>Editorial improvements.</t>
<t>Updated references.</t>
</list></t>
</section>
</back>
</rfc>
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