INTERNET-DRAFT Norihiro Ishikawa
Expires: January 1998 NTT
July, 1997
IP Multicast Routing over ATM
<draft-ishikawa-ion-mcatm-routing-00.txt>
Status of this Memo
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Abstract
This memo describes the specification for IP multicast routing
over ATM. This memo specifies the architecture and the protocol
for scalable IP multicast routing over ATM, based on the shared
tree architecture. Multicast shortcuts over ATM are possible in
an efficient and scalable manner. The same messages as specified
for IP multicasting over ATM MLIS [1] are applied for IP multicast
routing over ATM, with some extensions.
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1. Introduction
This memo describes the specification for IP multicast routing over
ATM. The requirements for the specification for IP multicast
routing over ATM are as follows:
- To interwork with the MBONE (an experimental multicasting network on
the Internet), the specification should be compatible with the basic
specifications for IP multicasting such as RFC 1112 [2] and the
multicast routing protocols such as RFC 1075 [3]. It should also
interwork with routers and hosts in which such specifications are
implemented.
- To accomplish IP multicasting over ATM efficiently, the specificaiton
should be able to effectively use the point-to-multipoint
connection that ATM provides.
- To be applicable to IP multicasting over ATM in different scales,
the specification should be able to achieve hierarchical and
scalable IP multicast routing.
- Functions for IP multicast shortcuts should be provided in an
efficient and scalable manner.
- It should be compatible with the specifications for IP over ATM
such as RFC 1577 [4] and RFC1755 [5] and be able to use those
protocols when necessary.
As a mechanism to satisfy above requirements, this memo describes the
specification for IP multicast routing over ATM, based on the
specification for IP multicast over ATM MLIS described in [1].
This memo assumes that "The ATM Forum UNI Specification, V 3.0/3.1" is
used as the interface with ATM.
2. Architecture
An architecture for IP multicast routing over ATM is described below.
The architecture for IP multicast routing over ATM specified in this
memo is an extension of the architecture of the specification for IP
multicast over ATM described in [1]. In this architecture, multiple ATM
multicast routers form a relationship that has a tree structure. Each
ATM multicast router may be connected with an ATM multicast router as
a parent. Such an ATM multicast router is called a parent router,
from the ATM multicast router's point of view. Each ATM multicast
router may be connected with multiple ATM multicast routers as a child.
Such an ATM multicast router is called a child router, from the ATM
multicast router's point of view. An ATM multicast router is connected
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with a parent router as well as child routers, using ATM VCCs. An ATM
multicast router that does not have a parent router is the highest
level router. An ATM multicast router that does not have a child is
the lowest level router.
A sending host may be connected with any level ATM multicast router,
and send multicast IP datagrams. A receiving host is usually connected
with the lowest level ATM multicast router, and receive multicast IP
datagrams, although a receiving host may be connected with other level
routers. An ATM multicast router views a receiving host directly
connected with it as its child. An ATM multicast router is connected
with a sending host and a receiving host, using ATM VCCs. For the
efficient use of ATM, an ATM multicast router is usually connected
with its child routers and/or receiving hosts, using ATM point-to-
multipoint connections.
For each host group that is identified by a class D IP address, a
multicast routing tree (MRT) is defined. A specific ATM multicast
router is designated as the root of an MRT. If the highest level
router is designated as the root of an MRT, large scale IP
multicasting is realized for the host group. If the lowest level
router is designated as the root of an MRT, small scale IP
multicasting is realized for the host group. Hence Hierarchical and
scalable IP multicast routing can be realized by adopting the
architecture that has a tree structure.
3. Mechanism
The mechanism for IP multicast routing over ATM specified in this memo
is explained below. The detailed procedures based on this mechanism
are described in section 4.
3.1 Sending Multicast IP Datagrams
If a sending host cat set up an ATM VCC with the root of an MRT, it
sends multicast IP datagrams to the root, using the ATM VCC. If a
sending host can not set up an ATM VCC with the root of an MRT, it
sends a multicast IP datagram as a unicast IP datagram whose
destination address is a unicast IP address of the root. In this
case, the class D IP address is inserted into a unicast IP datagram
using the loose source IP option. A unicast IP datagram travels
toward the root of an MRT, using unicast routing protocols.
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3.2 Start of Receiving Multicast IP Datagrams
A receiving host that requests to receive multicast IP datagrams sends
a Join message to an ATM multicast router.
If the ATM multicast router that has received a Join message from the
receiving host is the root of the MRT that is identified by the class
D IP address, it will send a Join Ack message to the receiving host,
and start sending multicast IP datagrams.
The procedure is as follows in the case where the ATM multicast router
that has received a Join message from the receiving host is not the
root of the MRT that is identified by the class D IP address:
(1) If the ATM multicast router has already sent a Join message to the
parent router and received a Join Ack message as its response, it
will send a Join Ack message to the receiving host and start
sending multicast IP datagrams.
(2) If the ATM multicast router has already sent a Join message to the
parent router but has not received a Join Ack/Join Nak message
from the parent router, it will wait for the response of the
parent router.
(3) If the ATM multicast router has not sent a Join message to the
parent router, it will send a Join message to the parent router.
(4) If there is no parent router, the ATM multicast router will send
a Join Nak message to the receiving host.
If the ATM multicast router receives a Join Ack message from the
parent router later, in the case of (2) and (3), it will send a Join
Ack message to the receiving host and start sending of multicast IP
datagrams. If a Join Nak message is received, the ATM multicast router
will send a Join Nak message to the receiving host.
The operation of an ATM multicast router that has received a Join
message from a child router is the same as that of the ATM multicast
router that has received a Join message from a receiving host.
3.3 Stop of Receiving Multicast IP Datagrams
A receiving host that requests to end receiving multicast IP datagrams
sends a Leave message to the ATM multicast router.
The ATM multicast router that has received a Leave message from the
receiving host ends sending multicast IP datagrams to the receiving
host.
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The ATM multicast router that has received a Leave message from the
receiving host sends a Leave message to its parent router when the
following conditions are satisfied:
(1) The ATM multicast router is not the root of the MRT that is
identified by the class D IP address.
(2) There exists no receiving host that is receiving multicast IP
datagrams for the host group that is identified by the class D
IP address as a result.
The operation of an ATM multicast router that has received a Leave
message from a child router is the same as that of the ATM
multicast router that has received a Leave message from a receiving
host.
4. Protocol Procedures
The protocol procedures based on the mechanism specified in Section
3 are described below.
The specification for IP multicast routing over ATM described in
this memo is an extension of the specification for IP multicast
over ATM MLIS described in [1]. Therefore, the operation of sending
hosts, receicing hosts and ATM multicast routers that is not
described in this memo is the same as described in [1].
4.1 Operation of Sending Hosts
A sending host must send multicast IP datagrams toward the root
of an MRT which is defined for the host group identified by its
destination address.
If a sender can set up an ATM VCC directly with the root, the
same procedures described in [1] are applied. If a sending host
can not set up an ATM VCC with the root, it sends a multicast IP
datagram as a unicast IP datagram whose destination address is an
IP address of the root. In this case, the destination address of
a multicast IP datagram (i.e. class D address) is inserted into
a unicast IP datagram, using the Loose Source Route option. A
unicast IP datagram travels toward the root of an MRT, using
unicast IP routing protocols.
4.2 Operation of ATM Multicast Routers
4.2.1 Receiving Multicast IP Datagrams
The operation of an ATM multicast router is described below, in the
case where it has received a multicast IP datagram.
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4.2.1.1 When Loose Source Route Option is Designated
The operation of an ATM multicast router is described below, in the
case where the Loose Source Route option is designated:
An ATM multicast router executes the procedures below, if the
following condition is satisfied:
- The ATM multicast router is the root of the MRT designated in
the Loose Source option.
(1) The ATM multicast router processes the Loose Source Route
option of the received unicast IP datagram. In other words, the
received unicast IP datagram is replaced with a multicast IP
datagram with the multicast IP address of the host group as its
destination IP address.
(2) the ATM multicast router retrieves the conversion table of the
destination IP address of the multicast IP datagram and the VCC
for data transfer, in order to check whether the VCC for data
transfer that forwards the received multicast IP datagram has
been set up.
NOTE: This conversion table is used when forwarding multicast
IP datagrams to child routers and/or receiving hosts.
(3) If the VCC for data transfer has been set up, the multicast IP
datagram will be sent by using the VCC. If the VCC for data
transfer has not been set up, the multicast IP datagram will
be discarded.
4.2.1.2 When Loose Source Route Option is not Designated
The operation of an ATM multicast router is the same as described
in [1], in the case where the Loose Source Option is not designated.
NOTE: In this case, an ATM multicast router does not need to
distinguish whether it has received a multicast IP datagram
from either a sending host or a parent router.
4.2.2 Receiving a Join Message
The operation of an ATM multicast router is described below, in the
case where it has received a Join message from either a receiving
host or a child router.
NOTE: In this case, an ATM multicast router does not need to
distinguish whether it has received a Join message from either
a receiving host or a child router.
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4.2.2.1 When an ATM multicast router is the root of an MRT
The operation of an ATM multicast router is the same as described
in [1].
4.2.2.2 When an ATM multicast router is not the root of an MRT
The procedures are as follows, in the case where the ATM multicast
router has already sent a Join message to its parent router and
then received Join Ack message as its response:
(1) An ATM multicast router sets up a leaf to the VCC for data
transfer, by using the ATM address of the receiving host or
the child router.
(2) If the setup of the leaf to the VCC succeeds, the ATM multicast
router sends a Join Ack message to it.
(3) If the setup of the leaf to the VCC fails, the ATM multicast
router sends a Join Nak message to it.
The procedures are as follows, in the case where the ATM multicast
has already sent a Join message to its parent router, but has not
received a Join Ack message or a Join Nak message from it.
(1) The ATM multicast router will wait for a Join Ack message or
a Join Nak message from its parent router.
The procedures are as follows, in the case where the ATM multicast
router has not sent a Join message to its parent router.
(1) The ATM multicast router sends a Join message to its parent
router.
The procedures are as follows, in the case where there exists no
parent router for the ATM multicast router.
(1) The ATM multicast router sends a Join Nak message to the
receiving host or the child router.
4.2.3 Receiving a Join Ack message
The operation of an ATM multicast router is described below, in
the case where it has received a Join Ack message from its parent
router.
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The operation of an ATM multicast router is as follows if the
following condition is satisfied:
- The ATM multicast has sent a Join message to its parent router,
regarding the received group address
(1) The ATM multicast router sets up (a leaf of) a VCC for data
transfer, by using the ATM address of the receiving host or
the child router, from which it has received a Join message.
NOTE: When the ATM multicast router has received a Join message
from more than one receiving hosts and/or child routers,
it sets up (a leaf of) the VCC to each of them. The VCC
shall be a point-to-multipoint connection.
(2) If the setup of (the leaf of) the VCC to the receiving host
or the child router succeeds, the ATM multicast router sends
a Join Ack message to it.
(3) If the setup of (the leaf of) the VCC to the receiving host
or the child router fails, the ATM multicast router sends
a Join Nak message to it.
NOTE: When the ATM multicast router has received a Join message
from more than one receiving hosts and/or child routers,
it sends a Join Ack message or a Join Nak message to
each of them.
An ATM multicast router discards the received Join Ack message if
the following condition is satisfied:
- The ATM multicast router has not sent a Join message to its
parent router, regarding the received group address.
4.2.4 Receiving a Join Nak message
The operation of an ATM multicast router is described below, in
the case where it has received a Join Nak message from its parent
router.
The operation of an ATM multicast router is as follows if the
following condition is satisfied:
- The ATM multicast has sent a Join message to its parent router,
regarding the received group address.
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(1) The ATM multicast router sends a Join Nak message to the
receiving host or the child router, from which it has received a
Join message.
NOTE: When the ATM multicast router has received a Join message
from more than one receiving hosts and/or child routers,
it sends a Join Nak message to each of them.
An ATM multicast router discards the received Join Nak message if
the following condition is satisfied:
- The ATM multicast router has not sent a Join message to its
parent router, regarding the received group address.
4.2.5 Receiving a Leave Message
The operation of an ATM multicast router is described below, in the
case where it has received a Leave message from either a receiving
host or a child router.
NOTE: In this case, an ATM multicast router does not need to
distinguish whether it has received a Leave message from either
a receiving host or a child router.
The operation of an ATM multicast router is as follows if the
following conditions are satisfied:
- The number of members becomes zero in the list of the IP
addresses of receiving hosts and/or child routers that have
joined the host group identified by the received group address.
- The ATM multicast router is not the root of the MRT defined for
the host group identified by the received group address.
(1) The ATM multicast router sends a Leave message to its parent
router.
4.2.6 Sending a Shortcut message
An ATM multicast router may order Shortcut to receiving hosts
and/or child routers that have joined the host group identified by
the group address. It is a local decision by an ATM multicast
router, whether it orders Shortcut or not.
NOTE: An ATM multicast router may order Shortcut in the following
cases.
- An ATM multicast router is receiving large amount of
multicast IP datagrams (e.g. file or video) toward the host
group identified by the group address.
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The operation of an ATM multicast router is as follows if the
following condition is satisfied:
- The ATM multicast router is not the root of an MRT defined for
the host group identified by the group address.
(1) An ATM multicast router may send a Shortcut message to the
receiving host or the child router that has joined the host
group identified by the group address.
NOTE: When more than one receiving hosts and/or child routers
have joined the host group, An ATM multicast router sends
a Shortcut message to each of them.
4.2.7 Receiving a Shortcut message
When an ATM multicast router has received a Shortcut message, it
may execute Shortcut. It is a local decision by an ATM multicast
router, whether it executes Shortcut or not.
The operation of an ATM multicast router is as follows if the
following condition is satisfied:
- The ATM multicast router can set up a VCC toward the ATM
multicast router designated by the Shortcut Address field
of the received Shortcut message.
(1) An ATM multicast router may send a Join message to the ATM
multicast router designated by the Shortcut Address field of
the received Shortcut message.
(2) When the ATM multicast router receives a Join Ack message, it
sends a Leave message to its parent router.
(3) When the ATM multicast router receives a Join Nak message, it
does nothing.
NOTE: The ATM multicast router may send a Join message to the
same router again.
4.3 Operation of Receiving Hosts
4.3.1 Receiving an Shortcut message
When a receiving host has received a Shortcut message, it may execute
Shortcut. It is a local decision by a receiving host, whether it
executes Shortcut or not.
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The operation of a receiving host is as follows if the following
condition is satisfied:
- The receiving host can set up a VCC toward the ATM multicast
router designated by the Shortcut Address field of the received
Shortcut message.
(1) A receiving host may send a Join message to the ATM multicast
router designated by the Shortcut Address field of the received
Shortcut message.
(2) When the receiving host receives a Join Ack message, it sends
a Leave message to its parent router.
(3) When the receiving host receives a Join Nack message, it does
nothing.
NOTE: The receiving host may send a Join message to the same
router again.
5. Protocol Specification
The same messages as specified in IGMP-ATM [1] are applied for
IP multicast routing over ATM, with the following extension.
NOTE: The Join message (2) is called the Host Membership Join message
in IGMP-ATM [1]. The Leave message (5) is called the Host
Membership Leave message in IGMP-ATM [1].
The Shortcut message is added to IGMP-ATM, for IP multicast
routing over ATM specified in this memo.
The format of the Shortcut message is as follows.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Type | Unused | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Shortcut Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(1) Version
The version of this specification shall be ?.
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(2) Type
The type of the Shortcut message is as follows:
6 = Shortcut
(3) Unused
Unused field, zeroed when sent, ignored when received.
(4) Checksum
The Checksum is the 16-bit one's complement sum of the Shortcut
message. For computing the checksum, the checksum field is
zeroed.
(5) Shortcut Address
An IP address of the ATM multicast router to which a receiving
host or a child router will set up a VCC for Shortcut. When
an ATM multicast router sends a Shortcut message to a receiving
host or a child router, it usually sets an IP address of its
parent router in this field.
6. Security Considerations
The authentication parameter is added to the Join message, so that
unauthorized receiving hosts and child routers can not join the host
group.
However, the definition of the format of the authentication
parameter for the specific authentication mechanism is for
further study.
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References
[1] N. Ishikawa, "IP Multicast over ATM MLIS using ATM
Multicast Routers", Internet Draft, July 1997.
[2] S. Deering, "Host Extensions for IP Multicasting", RFC 1112,
Stanford University, August 1989.
[3] D. Waitzman, C. Partridge, S. Deering, "Distance Vector
Multicast Routing Protocol", RFC 1075, November 1988.
[4] M. Laubach, "Classical IP and ARP over ATM", RFC 1577,
Hewlett-Packard Laboratories, December 1993.
[5] M. Perez, F. Liaw, D. Grossman, A. Mankin, E. Hoffman,
A. Malis, "ATM Signalling Support for IP over ATM", RFC 1755
February 1995.
Authors' Address:
Norihiro Ishikawa
NTT Information and Communication Systems Laboratory
1-1 Hikarino-oka Yokosuka-Shi
Kanagawa 239 Japan
isic@isl.ntt.co.jp
+81 468 59 2434 (tel)
+81 468 59 3796 (fax)
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