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Differences from draft-waehlisch-sam-common-api-01.txt
SAM Research Group M. Waehlisch
Internet-Draft link-lab & FU Berlin
Intended status: Informational T C. Schmidt
Expires: September 9, 2010 HAW Hamburg
S. Venaas
cisco Systems
March 8, 2010
A Common API for Transparent Hybrid Multicast
draft-waehlisch-sam-common-api-02
Abstract
Group communication services are most efficiently implemented on the
lowest layer available. However, as the deployment status of
multicast technologies largely varies throughout the Internet,
globally operational group solutions are frequently forced to using a
stable, upper layer protocol controlled by the application itself.
This document describes a common multicast API that is suitable for
transparent underlay and overlay communication. It proposes abstract
naming and addressing by multicast URIs and discusses mapping
mechanisms between different namespaces and distribution
technologies. Additionally, it describes the application of this API
for building gateways that interconnect current multicast domains
throughout the Internet.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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This Internet-Draft will expire on September 9, 2010.
Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Objectives and Reference Scenarios . . . . . . . . . . . . 5
3.2. Group Communication Stack & API . . . . . . . . . . . . . 6
3.3. Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.4. Naming and Addressing . . . . . . . . . . . . . . . . . . 9
4. Hybrid Multicast API . . . . . . . . . . . . . . . . . . . . . 9
4.1. Abstract Data Types . . . . . . . . . . . . . . . . . . . 9
4.2. Send/Receive Calls . . . . . . . . . . . . . . . . . . . . 10
4.3. Socket Options . . . . . . . . . . . . . . . . . . . . . . 10
4.4. Service Calls . . . . . . . . . . . . . . . . . . . . . . 10
5. Functional Details . . . . . . . . . . . . . . . . . . . . . . 11
5.1. Mapping . . . . . . . . . . . . . . . . . . . . . . . . . 11
5.2. URI Scheme . . . . . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
9. Informative References . . . . . . . . . . . . . . . . . . . . 12
Appendix A. Practical Example of the API . . . . . . . . . . . . 13
Appendix B. Deployment Use Cases for Hybrid Multicast . . . . . . 15
B.1. DVMRP . . . . . . . . . . . . . . . . . . . . . . . . . . 15
B.2. PIM-SM . . . . . . . . . . . . . . . . . . . . . . . . . . 15
B.3. PIM-SSM . . . . . . . . . . . . . . . . . . . . . . . . . 16
B.4. BIDIR-PIM . . . . . . . . . . . . . . . . . . . . . . . . 17
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 17
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 17
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1. Introduction
Currently, group application programmers need to make a choice of the
distribution technology required at runtime. There is no common
communication interface that abstracts multicast subscriptions from
the underlying deployment. The standard multicast socket options
[RFC3493], [RFC3678] are bound to an IP version and do not
distinguish between naming and addressing of multicast identifiers.
Group communication, however, is commonly implemented in different
flavors and on different layers (e.g., IP vs. application layer
multicast), and may be based on different technologies on the same
tier (e.g., IPv4 vs. IPv6).
Multicast application development should be decoupled of
technological deployment throughout the infrastructure. It requires
a common multicast API that offers calls to transmit and receive
multicast data independent of the supporting layer and the underlying
technological details. For inter-technology transmissions, a
consistent view on multicast states is needed, as well. This
document describes an abstract group communication API and core
functions necessary for transparent operations. Specific
implementation guidelines with respect to operating systems or
programming languages are out-of-scope of this document.
In contrast to the standard multicast socket interface, the API
introduced in this document abstracts naming and addressing. Using a
multicast address in the current socket API predefines the
corresponding routing layer. In this memo, the multicast address
used for joining a group denotes an application layer data stream
that is identified by a multicast URI and without an association to
the underlying distribution technology. Group name can be mapped to
variable routing identifiers.
The aim of this common API is twofold:
o Enable any application programmer to implement group-oriented data
communication independent of the underlying delivery mechanisms.
In particular, allow for a late binding of group applications to
multicast technologies that makes applications efficient, but
robust with respect to deployment aspects.
o Allow for a flexible namespace support in group addressing, and
thereby separate naming and addressing/routing schemes from the
application design. This abstraction not only reduces the
dependency on specific apects of underlying protocols, but may
open application design to extend to specifically flavored group
services.
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Multicast technologies may be various P2P-based, IPv4 or IPv6 network
layer multicast, or implemented by some other application service.
Corresponding namespaces may be IP addresses, overlay hashes, other
application layer group identifiers, e.g., <sip:*@peanuts.org>, or
names defined by the applications.
This document also proposes and discusses mapping mechanisms between
different namespaces and forwarding technologies. Additionally, the
multicast API provides internal interfaces to access current
multicast states at the host. Multiple multicast protocols may run
in parallel on a single host. These protocols may interact to
provide a gateway function that bridges data between different
domains. The application of this API at gateways operating between
current multicast instances throughout the Internet is described, as
well.
2. Terminology
This document uses the terminology as defined for the multicast
protocols [RFC2710],[RFC3376],[RFC3810],[RFC4601],[RFC4604]. In
addition, the following terms will be used.
Group Address: A Group Address is a routing identifier. It
represents a technological identifier and thus reflects the
distribution technology in use. Multicast packet forwarding is
based on this ID.
Group Name: A Group Name is an application identifier that is used
by applications to manage (e.g., join/leave and send/receive) a
multicast group. The Group Name does not imply any distribution
technologies but represents a logical identifier.
Multicast Namespace: A Multicast Namespace is a collection of
designators (i.e., names or addresses) for groups that share a
common syntax. Typical instances of namespaces are IPv4 or IPv6
multicast addresses, overlay group ids, group names defined on the
application layer (e.g., SIP or Email), or some human readable
strings.
Multicast Domain: A Multicast Domain accommodates nodes and routers
of a common, single multicast forwarding technology and is bound
to a single namespace.
Interface An Interface is a forwarding instance of a distribution
technology on a given node. For example, the IP interface
192.168.1.1 at an IPv4 host.
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Inter-domain Multicast Gateway: An Inter-domain Multicast Gateway
(IMG) is an entity that interconnects different multicast domains.
Its objective is to forward data between these domains, e.g.,
between IP layer and overlay multicast.
3. Overview
3.1. Objectives and Reference Scenarios
The default use case addressed in this memo targets at applications
that participate in a group by using a common identifier taken from
some common namespace. Programmers should be able to transparently
use this identifier in their program without the need to consider a
deployment status in target domains. Aided by gateways and, where
available, by a node-specific multicast middleware, applications
shall be enabled to establish group communication, even if resident
in domains that are not connected by a common multicast service
technology.
This document covers the following two general scenarios:
1. Multicast domains running the same multicast technology but
remaining isolated, possibly only connected by network layer
unicast.
2. Multicast domains running different multicast technologies, but
hosting nodes that are members of the same multicast group.
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+-------+ +-------+
| Member| | Member|
| Foo | | G |
+-------+ +-------+
\ /
*** *** *** ***
* ** ** ** *
* *
* MCast Tec A *
* *
* ** ** ** *
*** *** *** ***
+-------+ +-------+ |
| Member| | Member| +-------+
| G | | Foo | | IMG |
+-------+ +-------+ +-------+
| | |
*** *** *** *** *** *** *** ***
* ** ** ** * * ** ** ** *
* * +-------+ * *
* MCast Tec A * --| IMG |-- * MCast Tec B * +-------+
* * +-------+ * * - | Member|
* ** ** ** * * ** ** ** * | G |
*** *** *** *** *** *** *** *** +-------+
Figure 1: Reference scenarios for hybrid multicast, interconnecting
group members from isolated homogeneous and heterogeneous domains.
It is assumed throughout the document that the domain composition, as
well as the node attachement to a specific technology remain
unchanged during a multicast session.
3.2. Group Communication Stack & API
Multicast applications may use a group communication stack to deliver
and receive multicast data. This group communication stack exhibits
two tasks:
o It provides an extended API that supports a common multicast
interface with namespace support.
o It bridges data between different multicast technologies.
The group communication API consists of three parts: (1) Send/Receive
Calls, (2) Socket Options, and (3) Service Calls. (1) provides a
minimal API to initiate a multicast socket, send and receive
multicast data in a technology-transparent fashion. (2) allows for
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the configuration of the multicast socket, i.e., setting path length
and associate interfaces explicitly. (3) returns internal multicast
states per interface such as the multicast groups under subscription.
The general procedure to initiate multicast communication is the
following:
1. An application opens a multicast socket.
2. An application subscribes/leaves/sends to a logical group
identifier.
3. A function maps the logical group ID (Group Name) to a technical
group ID (Group Address).
4. The technical group ID is allocated or revised if already in use.
The multicast socket describes a group communication channel composed
of one or multiple interfaces. A socket may be created without
explicit interface association by the application, which leaves the
choice of the underlying forwarding technology to the group
communication stack. However, an application may also bind the
socket to one or multiple dedicated interfaces, which predefines the
forwarding technology and the namespace(s) of the Group Address(es).
Applications are not required to maintain states for Group Addresses.
The group communication stack accounts for the mapping of the Group
Name to the Group Address(es) and vice versa. Multicast data passed
to the application will be augmented by the corresponding Group Name.
Multiple multicast subscriptions thus can be conducted on a single
multicast socket without the need for Group Name encoding at the
application side.
Hosts may support several multicast protocols. The group
communication stack discovers available multicast-enabled
communication interfaces. It provides a minimal hybrid function that
bridges data between different interfaces and multicast domains.
Details of service discovery are out-of-scope of this document.
The extended multicast functions can be implemented by a middleware,
for example.
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*-------* *-------*
| App 1 | | App 2 |
*-------* *-------*
| |
*---------------------* ---|
| Middleware | |
*---------------------* |
| | |
*---------* | |
| Overlay | | \ Group Communication
*---------* | / Stack
| | |
| | |
*---------------------* |
| Underlay | |
*---------------------* ---|
Figure 2: The middleware covers underlay and overlay for the
application
3.3. Mapping
A mapping is required between a Group Name and the Group Address
space, as well as between Group Addresses in different namespaces.
Two (or more) identifiers in different namespaces may belong to
a. the same multicast channel (i.e., same technical ID).
b. different multicast channels (i.e., different technical IDs).
This decision can be solved based on invertible mappings. However,
the application of such functions depends on the cardinality of the
namespaces and thus does not hold in general. A large identifier
space (e.g., IPv6) cannot obviously be mapped to a smaller set (e.g.,
IPv4).
A mapping can be realized by embedding smaller in larger namespaces
or selecting an arbitrary, unused ID in the target space. The
relation between logical and technical ID is stored based on a
mapping service (e.g., DHT). The middleware thus queries the mapping
service first, and creates an new technical group ID only if there is
no identifier available for the namespace in use. The Group Name is
associated with one or more Group Addresses, which belong to
different namespaces. Depending on the scope of the mapping service,
it ensures a consistent use of the technical ID in a local or global
domain.
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All group members subscribe to the same Group Name within the same
namespace.
3.4. Naming and Addressing
The Group Name is used by applications to identify groups. It hides
the deployed technology employed to distribute data. In contrast to
this, multicast forwarding operates on Group Addresses. Although
both identifiers may be identical in symbols, they carry different
meaning. They may also belong to different namespaces. The
namespace of the Group Address reflects the routing technology, and
the namespace of the Group Name represents the context in which the
application operates.
A multicast socket (IPv4/v6 interface) can be used by multiple
logical multicast IDs from different namespaces (IPv4-group address,
IPv6-group address). In practice, a library that implements the
defined API would provide high-level data types to the application
similar to the current socket API (e.g., InetAddress in Java). Using
this data type would implicitly determine the namespace.
To reflect namespace specific treatment for applications, identifiers
in API calls are represented by URIs. An implementation of the API
may provide convenience functions that detect the namespace of a
Group Name (e.g., InetAddress instead of Inet6Address and
Inet4Address). Details of automatic identifcation is out-of-scope of
this document.
4. Hybrid Multicast API
4.1. Abstract Data Types
URI is any kind of Group Address or Group Name that follows the
syntax defined in Section 5.2. For example, ipv4://224.1.2.3:5000
and sip://news@cnn.com.
Interface denotes the interface and thus the layer and instance on
which the corresponding call will be effective. This may be
unspecified to leave the decicision to the group communication
stack.
SocketHandle references on an instance of a multicast socket.
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4.2. Send/Receive Calls
init(out SocketHandle h, [in enum Interface i] This call initiates a
multicast socket and provides the application programmer with a
corresponding handle. If no interfaces will be assigned based on
the call, the default interface will be selected and associated
with the socket. The call may return an error code in the case of
failures, e.g., due to a non-operational middleware.
join(in SocketHandle h, in URI g, [in Interface i]) This operation
initiates a group subscription. Depending on the interfaces that
are associated with the socket , this may result in an IGMP/MLD
report or overlay subscriptions.
leave(in SocketHandle h, in URI g, [in Interface i]) This operation
results in an unsubscription for the given address.
send(in SocketHandle h, in URI g, in Message msg) This call passes
multicast data for a Multicast Name g from the application to the
multicast socket.
receive(in SocketHandle h, out URI g, out Message msg) This call
passes multicast data and the corresponding Group Name g to the
application.
4.3. Socket Options
getInterfaces(out enum Interface i) This call returns a list of all
available multicast communication interfaces at the current host.
addInterface(in SocketHandle h, in Interface i) This call adds a
distribution channel to the socket. This may be an overlay or
underlay interface, e.g., IPv6 or DHT. Multiple interfaces of the
same technology may be associated with the socket.
delInterface(in SocketHandle h, in Interface i) This call removes an
interface from the socket.
setTTL(in SocketHandle h) This function configures the maximum hop
count for the socket h a multicast message is allowed to traverse.
4.4. Service Calls
groupSet(out enum URI g, in Interface i) 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.
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neighborSet(out enum URI g, in Interface i) This function can be
invoked to get the set of multicast routing neighbors.
designatedHost(out Bool b, in URI g) 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.
updateListener(out URI g, in Interface i) 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.
5. Functional Details
In this section, we describe the functional details of the API and
the middleware.
TODO
5.1. Mapping
Group Name to Group Address, SSM/ASM TODO
5.2. URI Scheme
Multicast Names and Multicast Addresses are described based on a URI
scheme. The scheme defines a subset of the URI specified in
[RFC3986] and follows the guidelines in [RFC4395].
The multicast URI is defined as follows:
scheme "://" group "@" instantiation ":" port "/" sec-credentials
The parts of the URI are defined as follows:
scheme referes to the specification of the assigned identifier
[RFC3986].
group identifies the group.
instantiation identifies the entitiy that generates the instance of
the group (e.g., a SIP domain or a source in SSM).
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port identifies a specific application at an instance of a group.
sec-credentials used to implement security credentials (e.g., to
authorize a multicast group access).
TODO
6. IANA Considerations
This document makes no request of IANA.
7. Security Considerations
This draft does neither introduce additional messages nor novel
protocol operations. TODO
8. Acknowledgements
We would like to thank the HAMcast-team (Dominik Charousset, Gabriel
Hege, Fabian Holler, Alexander Knauf, Sebastian Meiling, and
Sebastian Woelke) at the HAW Hamburg for fruitful discussions.
This work is partially supported by the German Federal Ministry of
Education and Research within the HAMcast project, which is part of
G-Lab.
9. Informative References
[I-D.ietf-mboned-auto-multicast]
Thaler, D., Talwar, M., Aggarwal, A., Vicisano, L., and T.
Pusateri, "Automatic IP Multicast Without Explicit Tunnels
(AMT)", draft-ietf-mboned-auto-multicast-10 (work in
progress), March 2010.
[RFC1075] Waitzman, D., Partridge, C., and S. Deering, "Distance
Vector Multicast Routing Protocol", RFC 1075,
November 1988.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
October 1999.
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[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.
[RFC3493] Gilligan, R., Thomson, S., Bound, J., McCann, J., and W.
Stevens, "Basic Socket Interface Extensions for IPv6",
RFC 3493, February 2003.
[RFC3678] Thaler, D., Fenner, B., and B. Quinn, "Socket Interface
Extensions for Multicast Source Filters", RFC 3678,
January 2004.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[RFC4395] Hansen, T., Hardie, T., and L. Masinter, "Guidelines and
Registration Procedures for New URI Schemes", BCP 35,
RFC 4395, February 2006.
[RFC4601] Fenner, B., Handley, M., Holbrook, H., and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
[RFC4604] Holbrook, H., Cain, B., and B. Haberman, "Using Internet
Group Management Protocol Version 3 (IGMPv3) and Multicast
Listener Discovery Protocol Version 2 (MLDv2) for Source-
Specific Multicast", RFC 4604, August 2006.
[RFC5015] Handley, M., Kouvelas, I., Speakman, T., and L. Vicisano,
"Bidirectional Protocol Independent Multicast (BIDIR-
PIM)", RFC 5015, October 2007.
Appendix A. Practical Example of the API
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-- Application above middleware:
//Initialize multicast socket; the middleware selects all available
//interfaces
MulticastSocket m = new MulticastSocket();
URI mcAddressv4 = new URI("ipv4://224.1.2.3:5000");
m.join(mcAddressv4);
URI mcAddressv6 = new URI("ipv6://[FF02:0:0:0:0:0:0:3]:6000");
m.join(mcAddressv6)
URI mcAddressSIP = new URI("sip://news@cnn.com");
m.join(mcAddressSIP)
-- Middleware:
join(URI mcAddress) {
//Select interfaces in use
for all this.interfaces {
switch (interface.type) {
case "ipv6":
//... map logical ID to routing address
Inet6Address rtAddressIPv6 = new Inet6Address()
mapNametoAddress(mcAddress,rtAddressIPv6)
interface.join(rtAddressIPv6)
case "ipv4":
//... map logical ID to routing address
Inet4Address rtAddressIPv4 = new Inet4Address()
mapNametoAddress(mcAddress,rtAddressIPv4)
interface.join(rtAddressIPv4)
case "sip":
//... map logical ID to routing address
SIPAddress rtAddressSIP = new SIPAddress()
mapNametoAddress(mcAddress,rtAddressSIP)
interface.join(rtAddressSIP)
case "dht":
//... map logical ID to routing address
DHTAddress rtAddressDHT = new DHTAddress()
mapNametoAddress(mcAddress,rtAddressDHT)
interface.join(rtAddressDHT)
//...
}
}
}
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Appendix B. Deployment Use Cases for Hybrid Multicast
This section describes the application of the defined API to
implement an IMG.
B.1. DVMRP
The following procedure describes a transparent mapping of a DVMRP-
based any source multicast service to another many-to-many multicast
technology.
An arbitrary DVMRP [RFC1075] 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.
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.
B.2. PIM-SM
The following procedure describes a transparent mapping of a PIM-SM-
based any source multicast service to another many-to-many multicast
technology.
The Protocol Independent Multicast Sparse Mode (PIM-SM) [RFC4601]
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
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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.
B.3. PIM-SSM
The following procedure describes a transparent mapping of a PIM-SSM-
based source specific multicast service to another one-to-many
multicast technology.
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 [RFC4604]. A multicast distribution tree
can be established without the assistance of a rendezvous point.
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.
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 [I-D.ietf-mboned-auto-multicast] 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.
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B.4. BIDIR-PIM
The following procedure describes a transparent mapping of a BIDIR-
PIM-based any source multicast service to another many-to-many
multicast technology.
Bidirectional PIM [RFC5015] 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.
Appendix C. Change Log
Changes since draft-waehlisch-sam-common-api-01
1. TODO
Authors' Addresses
Matthias Waehlisch
link-lab & FU Berlin
Hoenower Str. 35
Berlin 10318
Germany
Email: mw@link-lab.net
URI: http://www.inf.fu-berlin.de/~waehl
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Thomas C. Schmidt
HAW Hamburg
Berliner Tor 7
Hamburg 20099
Germany
Email: schmidt@informatik.haw-hamburg.de
URI: http://inet.cpt.haw-hamburg.de/members/schmidt
Stig Venaas
cisco Systems
Tasman Drive
San Jose, CA 95134
USA
Email: stig@cisco.com
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