One document matched: draft-waehlisch-sam-common-api-00.xml
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<rfc category="info" docName="draft-waehlisch-sam-common-api-00"
ipr="trust200811">
<front>
<title abbrev="Common Mcast API">A Common API for Transparent Hybrid
Multicast</title>
<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>
<uri>http://www.inf.fu-berlin.de/~waehl</uri>
</address>
</author>
<author fullname="Thomas C. Schmidt" initials="TC." 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>
<date day="19" month="October" year="2009" />
<abstract>
<t>Group communication services are most efficiently implemented on the
lowest layer available. This document describes a common multicast API
that serves the requirements of data distribution and maintenance for
multicast and broadcast on a middleware abstraction layer, suitable for
transparent underlay and overlay communication. Additionally, it
describes the application of this API in current Internet multicast
routing protocols.</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>Group communication is implemented on different layers. To allow for
a comprehensive development of applications and group services a common
API is required, which provides calls to transmit and receive multicast
data as well as a consistent view on multicast states. This document
describes an abstract group communication API. A specific implementation
description with respect to operating systems or programming languages
is out-of-scope of this document.</t>
<t>The aim of this API is twofold: An application programmer should be
able to implement group-oriented data distribution independent of the
underlying delivery mechanisms (e.g. native IP multicast or application
layer multicast). Receivers require an interface to subscribe and leave
a multicast group. Multicast sources send data to a group address. This
group address relies on a specific namespace. The API should reflect the
flexiblity in choosing an appropriate namespace.</t>
<t>Additionally, the multicast API should provide internal interfaces to
request current multicast states at the host. Multiple multicast
protocols may run in parallel on a single host. These protocols may
interact together.</t>
</section>
<section title="Terminology">
<t><list style="hanging">
<t hangText="Inter-domain Multicast Gateway:">An Inter-domain
Multicast Gateway (IMG) transparently forwards data between IP layer
and overlay multicast.</t>
</list></t>
</section>
<section title="Overview">
<t></t>
<t>The API consists of up and down calls. The down calls can be
implemented in a middleware that delegates those to overlay or
underlay:</t>
<t><figure>
<artwork><![CDATA[*-------* *-------*
| App 1 | | App 2 |
*-------* *-------*
| |
*---------------------*
| Middleware |
*---------------------*
| |
*---------* |
| Overlay | |
*---------* |
| |
| |
*---------------------*
| Underlay |
*---------------------*]]></artwork>
</figure></t>
</section>
<section title="Hybrid Multicast API">
<t></t>
<section title="Abstract Data Types">
<t><list style="hanging">
<t hangText="Namespace">describes the domain-specific context in
which the applications operate.</t>
<t hangText="Address">is any kind of address in underlay (e.g.
IPv4, IPv6) or overlay (e.g. SIP, hash-based ID).</t>
<t hangText="Mode">denotes the layer on which the corresponding
call will be effective. This may be unspecified to leave the
decicision at the group communication stack.</t>
</list></t>
</section>
<section title="Send/Receive Calls">
<t><list style="hanging">
<t hangText="init(in Namespace n)">This call is implemented</t>
<t hangText="join(in Address a, in Mode m)">This operation
initiates a group subscription. Depending on the mode, this may
result in an IGMP/MLD report.</t>
<t hangText="leave(in Address a, in Mode m)">This operation
results in an unsubscription for the given address.</t>
<t hangText="send(in Address a, in Mode m, out Message msg)"></t>
<t
hangText="receive(in Address a, in Mode m, out Message msg)"></t>
</list></t>
</section>
<section title="Service Calls">
<t><list style="hanging">
<t hangText="groupSet(out Address[] g, in Mode m)">This operation
returns all registered multicast groups. The information can be
provided by group management or routing protocols. The return
values distinguish between sender and listener states.</t>
<t hangText="neighborSet(out Address[] a, in Mode m)">This
function can be invoked to get the set of multicast routing
neighbors.</t>
<t hangText="designatedHost(out Bool b, in Address a)">This
function returns true, if the host has the role of a designated
forwarder or querier. Such an information is provided by almost
all multicast protocols to handle packet duplication, if multiple
multicast instances serve on the same subnet.</t>
<t hangText="updateListener(out Address g, in Mode m)">This upcall
is invoked to inform a group service about a change of listener
states for a group. This is the result of receiver new
subscriptions or leaves. The group service may call groupSet to
get updated information.</t>
<t hangText="updateSender(out Address g, in Mode m)">This upcall
should be implemented to inform the application about source state
changes. Analog to the updateListener case, the group service may
call thereupon groupSet.</t>
</list></t>
</section>
</section>
<section title="Deployment Use Cases">
<t>This section describes the application of the defined API to
implement an IMG.</t>
<section title="DVMRP">
<t>An arbitrary DVMRP <xref target="RFC1075"></xref> router will not
be informed about new receivers, but will learn about new sources
immediately. The concept of DVMRP does not provide any central
multicast instance. Thus, the IMG can be placed anywhere inside the
multicast region, but requires a DVMRP neighbor connectivity. The
group communication stack used by the IMG is enhanced by a DVMRP
implementation. New sources in the underlay will be advertised based
on the DVMRP flooding mechanism and received by the IMG. Based on this
the updateSender() call is triggered. The relay agent initiates a
corresponding join in the native network and forwards the received
source data towards the overlay routing protocol. Depending on the
group states, the data will be distributed to overlay peers.</t>
<t>DVMRP establishes source specific multicast trees. Therefore, a
graft message is only visible for DVMRP routers on the path from the
new receiver subnet to the source, but in general not for an IMG. To
overcome this problem, data of multicast senders will be flooded in
the overlay as well as in the underlay. Hence, an IMG has to initiate
an all-group join to the overlay using the namespace extension of the
API. Each IMG is initially required to forward the received overlay
data to the underlay, independent of native multicast receivers.
Subsequent prunes may limit unwanted data distribution thereafter.</t>
</section>
<section title="PIM-SM">
<t>The Protocol Independent Multicast Sparse Mode (PIM-SM) <xref
target="RFC4601"></xref> establishes rendezvous points (RP). These
entities receive listener and source subscriptions of a domain. To be
continuously updated, an IMG has to be co-located with a RP. Whenever
PIM register messages are received, the IMG must signal internally a
new multicast source using updateSender(). Subsequently, the IMG joins
the group and a shared tree between the RP and the sources will be
established, which may change to a source specific tree after a
sufficient number of data has been delivered. Source traffic will be
forwarded to the RP based on the IMG join, even if there are no
further receivers in the native multicast domain. Designated routers
of a PIM-domain send receiver subscriptions towards the PIM-SM RP. The
reception of such messages invokes the updateListener() call at the
IMG, which initiates a join towards the overlay routing protocol.
Overlay multicast data arriving at the IMG will then transparently be
forwarded in the underlay network and distributed through the RP
instance.</t>
</section>
<section title="PIM-SSM">
<t>PIM Source Specific Multicast (PIM-SSM) is defined as part of
PIM-SM and admits source specific joins (S,G) according to the source
specific host group model <xref target="RFC4604"></xref>. A multicast
distribution tree can be established without the assistance of a
rendezvous point.</t>
<t>Sources are not advertised within a PIM-SSM domain. Consequently,
an IMG cannot anticipate the local join inside a sender domain and
deliver a priori the multicast data to the overlay instance. If an IMG
of a receiver domain initiates a group subscription via the overlay
routing protocol, relaying multicast data fails, as data are not
available at the overlay instance. The IMG instance of the receiver
domain, thus, has to locate the IMG instance of the source domain to
trigger the corresponding join. In the sense of PIM-SSM, the signaling
should not be flooded in underlay and overlay.</t>
<t>One solution could be to intercept the subscription at both, source
and receiver sites: To monitor multicast receiver subscriptions
(updateListener()) in the underlay, the IMG is placed on path towards
the source, e.g., at a domain border router. This router intercepts
join messages and extracts the unicast source address S, initializing
an IMG specific join to S via regular unicast. Multicast data arriving
at the IMG of the sender domain can be distributed via the overlay.
Discovering the IMG of a multicast sender domain may be implemented
analogously to AMT <xref
target="I-D.ietf-mboned-auto-multicast"></xref> by anycast.
Consequently, the source address S of the group (S,G) should be built
based on an anycast prefix. The corresponding IMG anycast address for
a source domain is then derived from the prefix of S.</t>
</section>
<section title="BIDIR-PIM">
<t>Bidirectional PIM <xref target="RFC5015"></xref> is a variant of
PIM-SM. In contrast to PIM-SM, the protocol pre-establishes
bidirectional shared trees per group, connecting multicast sources and
receivers. The rendezvous points are virtualized in BIDIR-PIM as an
address to identify on-tree directions (up and down). However, routers
with the best link towards the (virtualized) rendezvous point address
are selected as designated forwarders for a link-local domain and
represent the actual distribution tree. The IMG is to be placed at the
RP-link, where the rendezvous point address is located. As source data
in either cases will be transmitted to the rendezvous point address,
the BIDIR-PIM instance of the IMG receives the data and can internally
signal new senders towards the stack via updateSender(). The first
receiver subscription for a new group within a BIDIR-PIM domain needs
to be transmitted to the RP to establish the first branching point.
Using the updateListener() invocation, an IMG will thereby be informed
about group requests from its domain, which are then delegated to the
overlay.</t>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This document makes no request of IANA.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>This draft does neither introduce additional messages nor novel
protocol operations. TODO</t>
</section>
<section anchor="Acknowledgements" title="Acknowledgements">
<t>TODO</t>
</section>
</middle>
<back>
<references title="Normative References">
<?rfc include="reference.RFC.2119"?>
<?rfc include="reference.RFC.1075"?>
<?rfc include="reference.RFC.5015"?>
<?rfc include="reference.RFC.3810"?>
<?rfc include="reference.RFC.4604"?>
<?rfc include="reference.RFC.2710"?>
<?rfc include="reference.RFC.4601"?>
<?rfc include="reference.RFC.3376"?>
</references>
<references title="Informative References">
<?rfc include="reference.I-D.ietf-mboned-auto-multicast"?>
</references>
</back>
</rfc>
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