draft-ietf-tuba-host-clnp-multicas-00.txt   draft-ietf-tuba-host-clnp-multicas-01.txt 
INTERNET-DRAFT Dave Marlow INTERNET-DRAFT Dave Marlow
March 9, 1994 NSWC-DD May 13, 1994 NSWC-DD
Host Group Extensions for CLNP Multicasting Host Group Extensions for CLNP Multicasting
draft-ietf-tuba-host-clnp-multicas-00.txt draft-ietf-tuba-host-clnp-multicas-01.txt
Status of this Memo Status of this Memo
This document is an Internet-Draft. Internet-Drafts are working This document is an Internet-Draft. Internet-Drafts are working
documents of the Internet Engineering Task Force (IETF), its areas, documents of the Internet Engineering Task Force (IETF), its areas,
and its working groups. Note that other groups may also distribute and its working groups. Note that other groups may also distribute
working documents as Internet-Drafts. working documents as Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six Internet-Drafts are draft documents valid for a maximum of six
months. Internet-Drafts may be updated, replaced, or obsoleted by months. Internet-Drafts may be updated, replaced, or obsoleted by
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group Network addresses which identify host groups. The multicast group Network addresses which identify host groups. The multicast
extensions to CLNP provides a means for identifying a CLNP packet and extensions to CLNP provides a means for identifying a CLNP packet and
provides scope control mechanisms for CLNP multicast packets. The provides scope control mechanisms for CLNP multicast packets. The
multicast extensions to the ES-IS protocol provide the mechanisms multicast extensions to the ES-IS protocol provide the mechanisms
needed for a host to exchange control information with multicast needed for a host to exchange control information with multicast
capable routers. These extensions to the ES-IS protocol provide for capable routers. These extensions to the ES-IS protocol provide for
a host to "announce" which multicast packets are of interest and for a host to "announce" which multicast packets are of interest and for
a multicast capable router to dynamically "map" group Network a multicast capable router to dynamically "map" group Network
addresses to subnetwork addresses. addresses to subnetwork addresses.
The primary change in this updated Internet Draft is the
incorporation of "direct origination of multicast packets" as
discussed at the March TUBA meeting and over the email. This change
to the behavior of hosts originating multicast packets enables hosts
announcing an interest in particular group Network addresses to
directly receive such multicast packets originated on a subnetwork to
which they are connected. This replaces the previous method which in
some cases required a multicast capable router to resend such
packets.
Contents Contents
Status of this Memo Status of this Memo
Abstract Abstract
1. Introduction 1. Introduction
2. Levels of Conformance 2. Levels of Conformance
3. Group Network Addresses 3. Group Network Addresses
4. Model of a CLNP End System Multicast Implementation 4. Model of a CLNP End System Multicast Implementation
5. Extensions to the CLNP Protocol 5. Extensions to the CLNP Protocol
6. Extensions to the ES-IS Routeing Protocol 6. Extensions to the ES-IS Routeing Protocol
Appendix A. Considerations for ESGH and MAM PDU destination Appendix A. Differences with RFC 1112
SNPA address parameters
Appendix B. Differences with RFC 1112
Appendix C. Issues Under Study Appendix B. Issues Under Study
References References
Author's Address Author's Address
1. Introduction 1. Introduction
This draft provides a specification for multicast extensions for CLNP This draft provides a specification for multicast extensions for CLNP
in order to provide a CLNP based Internet the capabilities provided in order to provide a CLNP based Internet the capabilities provided
for IP by RFC 1112 (Host Extensions for IP Multicasting) [RFC1112]. for IP by RFC 1112 (Host Extensions for IP Multicasting) [RFC1112].
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member of more than one group at a time. An End System need not be a member of more than one group at a time. An End System need not be a
member of a group to send datagrams to it. member of a group to send datagrams to it.
"A host group may be permanent or transient. A permanent group has an "A host group may be permanent or transient. A permanent group has an
administratively assigned GNA. It is the address, not the membership administratively assigned GNA. It is the address, not the membership
of the group, that is permanent; at any time a permanent group may of the group, that is permanent; at any time a permanent group may
have any number of members, even zero. have any number of members, even zero.
"Internetwork forwarding of CLNP multicast datagrams is handled by "Internetwork forwarding of CLNP multicast datagrams is handled by
"multicast capable" Intermediate Systems which may be co-resident "multicast capable" Intermediate Systems which may be co-resident
with, or separate from, unicast capable Intermediate Systems. with unicast capable Intermediate Systems.
This draft specifies the extensions required by an End System to make This draft specifies the extensions required by an End System to make
use of CLNP multicast. In addition the requirements placed upon use of CLNP multicast. In addition the requirements placed upon
multicast capable Intermediate Systems to exchange information with multicast capable Intermediate Systems to exchange information with
multicast capable End Systems is specified. No specifications are multicast capable End Systems is specified. No specifications are
provided related to the information exchanges between Intermediate provided related to the information exchanges between Intermediate
Systems to support multicast route selection or multicast Protocol Systems to support multicast route selection or multicast Protocol
Data Unit (PDU) forwarding. A discussion of multicast route selection Data Unit (PDU) forwarding. A discussion of multicast route selection
and PDU forwarding has been written by Steve Deering [Deering91]. and PDU forwarding has been written by Steve Deering [Deering91].
Note that for these multicast extensions to work there must exist an Note that for these multicast extensions to work there must exist an
uninterrupted path of multicast capable routers between the End uninterrupted path of multicast capable routers between the End
Systems comprising a host group (such paths may utilize tunneling Systems comprising a host group (such paths may utilize tunneling
(i.e. unicast CLNP encapsulated paths between multicast capable CLNP (i.e. unicast CLNP encapsulated paths between multicast capable CLNP
routers). In order to support multicast route selection and routers)). In order to support multicast route selection and
forwarding for a CLNP based internet additional specifications are forwarding for a CLNP based internet additional specifications are
needed. Specifications of this type could come in the form of new needed. Specifications of this type could come in the form of new
protocols, extensions to the current CLNP based routing protocols or protocols, extensions to the current CLNP based routing protocols or
use of a technique out of the IETF`s Inter-Domain Multicast Routing use of a technique out of the IETF`s Inter-Domain Multicast Routing
(IDMR) group. The IDMR group is currently investigating multicast (IDMR) group. The IDMR group is currently investigating multicast
protocols for routers which utilize a router's unicast routing protocols for routers which utilize a router's unicast routing
protocols, this approach may extend directly to CLNP routers. protocols, this approach may extend directly to CLNP routers.
While many of the techniques and assumptions of IP multicasting (as While many of the techniques and assumptions of IP multicasting (as
discussed in RFC 1112) are used in CLNP multicasting, there are discussed in RFC 1112) are used in CLNP multicasting, there are
number of differences. Appendix B describes the differences between number of differences. Appendix A describes the differences between
CLNP multicasting and IP multicasting. This draft describes CLNP multicasting and IP multicasting. This draft describes
techniques brought in directly from projects within ISO to techniques brought in directly from projects within ISO to
incorporate multicast transmission capabilities into CLNP [MULT- incorporate multicast transmission capabilities into CLNP [MULT-
AMDS]. This draft is consistent with the current draft specifications AMDS]. Coordination is being made to keep this draft consistent with
of these ISO projects. Key contributions to the techniques described the specifications of these ISO projects. Key contributions to the
in this draft have been made by a number of individuals within the techniques described in this draft have been made by a number of
ANSI X3S3.3 and ISO SC6 Working Group 2 committees. individuals within the TUBA, ANSI X3S3.3 and ISO SC6 Working Group 2
committees.
2. Levels of Conformance 2. Levels of Conformance
There are three levels of conformance for End Systems to this There are three levels of conformance for End Systems to this
specification: specification:
Level 0: no support for CLNP multicasting. Level 0: no support for CLNP multicasting.
There is no requirement for a CLNP End System (or Intermediate There is no requirement for a CLNP End System (or Intermediate
System) to support CLNP multicasting. Level 0 hosts should be System) to support CLNP multicasting. Level 0 hosts should be
unaffected by the presence of multicast activity. The destination unaffected by the presence of multicast activity. The destination
addresses used in support of multicast transfers, the GNA, should not addresses used in support of multicast transfers, the GNA, should not
be enabled by a non-multicast capable End System and the PDUs be enabled by a non-multicast capable End System and the PDUs
themselves are marked differently than unicast PDUs and thus should themselves are marked differently than unicast PDUs and thus should
be quietly discarded. be quietly discarded.
Level 1: support for sending but not receiving CLNP multicast PDUs. Level 1: support for sending but not receiving CLNP multicast PDUs.
At this point this level is not defined for CLNP multicast. An End An End System originating multicast PDUs is required to know whether
System sourcing multicast PDUs with the current specification at a multicast capable Intermediate System is attached to the
least needs to know whether a multicast Intermediate System is subnetwork(s) that it originates multicast PDUs (i.e. to determine
attached to the subnetwork that the multicast PDU is sourced on (i.e. the destination SNPA (subnet) address). An End System with Level 1
to determine the destination SNPA (subnet) address). Further work on conformance is required to implement all parts of this specification
this level of conformance may be undertaken if utility is identified. except for those supporting only Multicast Announcement. An End
System is not required to know the current Multicast Address Mapping
to start originating multicast PDUs.
Note: It is possible for End System not implementing Multicast
Address Mapping to successfully originate multicast PDUs (but with
the End System knowing of the existence of a multicast capable
Intermediate System). Such operation may lead to inefficient
subnetworks use. Thus when an End System continues (or may continue)
to originate multicast PDUs destined for the same group,
implementations are to provide Multicast Address Mapping support.
Level 2: full support for CLNP multicasting. Level 2: full support for CLNP multicasting.
Level 2 allows a host to join and leave host groups as well as send Level 2 allows a host to join and leave host groups as well as send
CLNP PDUs to host groups. It requires implementation by the End CLNP PDUs to host groups. It requires implementation by the End
System of all parts of this specification. System of all parts of this specification.
3. Group Network Addresses 3. Group Network Addresses
Individual Network addresses used by CLNP for End System addressing Individual Network addresses used by CLNP for End System addressing
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| 8A-8F | | 8A-8F |
| 9A-9F | | 9A-9F |
| FA-FE | | FA-FE |
-------------- --------------
4. Model of a CLNP End System Multicast Implementation 4. Model of a CLNP End System Multicast Implementation
The use of multicast transmission by a CLNP End System involves The use of multicast transmission by a CLNP End System involves
extensions to two protocols: CLNP and the ES-IS Routeing Protocol. To extensions to two protocols: CLNP and the ES-IS Routeing Protocol. To
provide level 0 service (no support for CLNP multicast), no provide level 0 service (no support for CLNP multicast), no
extensions to the two present protocols are required. In order to extensions to the two present protocols are required. To provide
level 1 service (support for sending but not receiving CLNP multicast
PDUs) all extensions contained in the following sections are required
except for those supporting only Multicast Announcement. In order to
support level 2 service (full support for CLNP multicasting), the support level 2 service (full support for CLNP multicasting), the
extensions contained in the following sections are required. extensions contained in the following sections are required.
Extensions identified for Intermediate Systems are not required (or Extensions identified for Intermediate Systems are not required (or
appropriate) for End Systems. Multicast transmission also requires appropriate) for End Systems. Multicast transmission also requires
the use of a group Network address (as previously described) as the the use of a group Network address (as previously described) as the
destination address parameter. destination address parameter.
5. Extensions to the CLNP protocol 5. Extensions to the CLNP protocol
This section provides extensions to the CLNP Protocol [CLNP] ISO This section provides extensions to the CLNP Protocol [CLNP] ISO
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This optional functionality is realized through a Network entity with This optional functionality is realized through a Network entity with
multicast capability identifying a PDU as using multicast transfer multicast capability identifying a PDU as using multicast transfer
via the PDU type and the PDU's destination address field. via the PDU type and the PDU's destination address field.
If a Network entity supports multicast transmission, then the header If a Network entity supports multicast transmission, then the header
format analysis function shall provide checking to ensure that a PDU format analysis function shall provide checking to ensure that a PDU
does not contain a group Network address in the source address field. does not contain a group Network address in the source address field.
Any PDU header analyzed to have a group address in the source address Any PDU header analyzed to have a group address in the source address
field shall be discarded. field shall be discarded.
5.3.2 Route PDU functions 5.3.2 Route PDU function
The route PDU function optionally provides capabilities to Network The route PDU function optionally provides capabilities to Network
entities which support multicast transfer for determining multiple entities which support multicast transfer for determining multiple
Network entities to which a single PDU shall be forwarded to. This Network entities to which a single PDU shall be forwarded to. This
may result in multiple invocations of the forward PDU function and may result in multiple invocations of the forward PDU function and
hence the need to make multiple copies of the PDU. For PDUs that are hence the need to make multiple copies of the PDU. For PDUs that are
received from a different Network entity, the optional functionality received from a different Network entity, the optional functionality
for the route PDU function is realized as a result of the header for the route PDU function is realized as a result of the header
format analysis function's recognition of the PDU as being a format analysis function's recognition of the PDU as being a
multicast PDU. A Network entity originating a multicast PDU should multicast PDU. A Network entity attached to more than one subnetwork
invoke the forward PDU function on one and only one subnetwork to when originating a multicast PDU is permitted to originate the PDU on
which it is attached and on which it has learned of the existence of more than one subnetwork.
at least one multicast capable IS. A Network entity attached to
multiple subnetworks should select a subnetwork for which a multicast
capable Intermediate System is attached if one exists for the initial
sourcing of a PDU. A Network entity attached to multiple subnetworks
but has not learned of the existence of any multicast capable IS is
permitted to originate a multicast PDU on multiple subnetworks.
Editor's Note: The purpose in having an originating Network entity Note: The ES-IS function "Extensions to the ISO CLNP Route Function
source a multicast PDU on only one subnetwork to which a multicast by End Systems" discussed in section 6.10 identifies on which
capable IS is attached is to support the development of multicast subnetworks an End System attached to more than one subnetwork must
routing protocols which will need to determine on which subnetworks a originate multicast PDUs on.
multicast PDU has visited. This behavior is predicated on the
assumption that the Intermediate Systems performing multicast Note: The purpose in allowing an originating Network entity to
forwarding form a connected set. originate a multicast PDU on multiple subnetworks is to support the
development of multicast IS-IS protocols which will need to determine
on which subnetworks a multicast PDU has visited. This behavior is
predicated on the assumption that the Intermediate Systems in the OSI
environment performing multicast forwarding form a connected set.
5.3.3 Forward PDU function 5.3.3 Forward PDU function
This function issues an SN-UNITDATA request primitive, supplying the This function issues an SN-UNITDATA request primitive, supplying the
subnetwork or Subnetwork Dependent Convergence Function (SNDCF) subnetwork or Subnetwork Dependent Convergence Function (SNDCF)
identified by the route PDU function with the protocol data unit as identified by the route PDU function with the protocol data unit as
user data to be transmitted, the address information required by that user data to be transmitted, the address information required by that
subnetwork or SNDCF to identify the "next" system or systems within subnetwork or SNDCF to identify the "next" system or systems within
the subnetwork-specific addressing domain (this may be one or more the subnetwork-specific addressing domain (this may be one or more
Intermediate Systems and/or one or more destination End Systems), and Intermediate Systems and/or one or more destination End Systems), and
quality of service constraints (if any) to be considered in the quality of service constraints (if any) to be considered in the
processing of the user data. processing of the user data.
5.3.4 Discard PDU function 5.3.4 Discard PDU function
Add an additional reason for discard - a PDU is received with an Add an additional reason for discard - a PDU is received with an
unknown type code. unknown type code.
Editor's Note: Comments are requested as to whether this additional
reason for discard presents any problem with currently deployed CLNP
implementations.
5.3.5 Error reporting function 5.3.5 Error reporting function
It is important to carefully control the use of the error reporting It is important to carefully control the use of the error reporting
capability in the case of multicast transfers. The primary concern capability in the case of multicast transfers. The primary concern
is to avoid the occurrence of broadcast storms and thus a multicast is to avoid the occurrence of broadcast storms and thus a multicast
PDU may not cause the origination of another multicast PDU. This is PDU may not cause the origination of another multicast PDU. This is
the primary reason that the source address is not permitted to be a the primary reason that the source address is not permitted to be a
group address. In addition, a multicast PDU with error reporting group address. In addition, a multicast PDU with error reporting
permitted can result in flooding the source network-entity (as well permitted can result in flooding the source network-entity (as well
as the networks used) with Error Report PDUs. as the networks used) with Error Report PDUs.
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current functionality. Two basic functions are provided: multicast current functionality. Two basic functions are provided: multicast
announcement and multicast address mapping. announcement and multicast address mapping.
6.1 Overview of the protocol 6.1 Overview of the protocol
6.1.1 Operation of ESs receiving multicast PDUs 6.1.1 Operation of ESs receiving multicast PDUs
ESs, upon initialization and periodically thereafter, will construct ESs, upon initialization and periodically thereafter, will construct
End System Group Hello (ESGH) PDUs identifying, by particular group End System Group Hello (ESGH) PDUs identifying, by particular group
Network addresses, the multicast PDUs it wishes to receive. The ES Network addresses, the multicast PDUs it wishes to receive. The ES
will periodically source (announce) these ESGH PDUs on the subnetwork will periodically originate (announce) these ESGH PDUs on the subnet-
it wishes to receive these on. Reporting the same group Network work it wishes to receive these on. Reporting the same group Network
address on multiple subnetworks may result in the reception of dupli- address on multiple subnetworks may result in the reception of dupli-
cate PDUs. ES-IS operations related to requesting the same group Net- cate PDUs. ES-IS operations related to requesting the same group Net-
work address on multiple subnetworks are handled totally indepen- work address on multiple subnetworks are handled totally indepen-
dently (e.g. using different logical timers,...). It is permitted for dently (e.g. using different logical timers,...). It is permitted for
an ES to report a number of group Network addresses in the same ESGH an ES to report a number of group Network addresses in the same ESGH
PDU. The only restrictions placed on providing multiple group Net- PDU. The only restrictions placed on providing multiple group Net-
work addresses within the same ESGH PDU are that all packets work addresses within the same ESGH PDU are that all packets
requested are to be received on the same subnet, with the same hold- requested are to be received on the same subnet, with the same hold-
ing time and that the ESGH PDU be of length equal to or less that its ing time and that the ESGH PDU be of length equal to or less that its
maximum packet size constraint. Note each group Network address in maximum packet size constraint. Note each group Network address in
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address, in the case of a subnetwork which uses IEEE 802 addresses address, in the case of a subnetwork which uses IEEE 802 addresses
the SNPA address is a 48 bit IEEE 802 MAC (media access control) the SNPA address is a 48 bit IEEE 802 MAC (media access control)
address. Of particular interest is the address used to mark the des- address. Of particular interest is the address used to mark the des-
tination group. For a subnetwork using IEEE 802 addressing a group tination group. For a subnetwork using IEEE 802 addressing a group
SNPA address uses a particular bit position to "mark" group SNPA SNPA address uses a particular bit position to "mark" group SNPA
addresses. addresses.
Upon initialization the ES may have static SNPA address associations Upon initialization the ES may have static SNPA address associations
(Pre-configured SNPA addresses). For any group Network address (Pre-configured SNPA addresses). For any group Network address
without a Pre-configured SNPA address that the ES wishes to receive, without a Pre-configured SNPA address that the ES wishes to receive,
the ES will associate the "All Multicast End System Network Entities" the ES will associate the "All Multicast Capable End Systems" SNPA
SNPA address. Upon receiving a Multicast Address Mapping (MAM) PDU address. Upon receiving a Multicast Address Mapping (MAM) PDU con-
containing a group Network address that the ES is announcing, the ES taining a group Network address that the ES is announcing, the ES
will use the SNPA address pairing contained in the MAM PDU for that will use the SNPA address pairing contained in the MAM PDU for that
group Network address. Upon the expiration of the Mapping Holding group Network address. Upon the expiration of the Mapping Holding
Timer, the ES shall revert back to associating either the Pre- Timer, the ES shall revert back to associating either the Pre-
configured SNPA address if one exists or the "All Multicast End Sys- configured SNPA address if one exists or the "All Multicast Capable
tem Network Entities" SNPA address for the specific group Network End Systems" SNPA address for the specific group Network address.
address. While an ES is permitted to listen in on other ESs announce-
ments (needed for the damping option), an ES is not permitted to While an ES is permitted to listen in on other ESs announcements
change its group Network address to SNPA address mapping based on the (needed for the damping option), an ES is not permitted to change its
announcement of other ESs. group Network address to SNPA address mapping based on the announce-
ment of other ESs.
Optionally, the ES may perform damping (resetting a Multicast Optionally, the ES may perform damping (resetting a Multicast
Announcement Timer corresponding to a particular group Network Announcement Timer corresponding to a particular group Network
address) if the conditions necessary to withhold a particular address) if the conditions necessary to withhold a particular
announcement are met. In order to perform damping the following con- announcement are met. In order to perform damping the following con-
ditions must be met: (1)The ES must be processing other ES's ditions must be met: (1)The ES must be processing other ES's
announcements; (2)An ESGH PDU is received that identifies the exact announcements; (2)An ESGH PDU is received that identifies the exact
same group Network address and SNPA address pairing on a particular same group Network address and SNPA address pairing on a particular
subnetwork that this ES is announcing on; (3) The Multicast Holding subnetwork that this ES is announcing on; (3) The Multicast Holding
Timer parameter value in the ESGH PDU received is equal to or greater Timer parameter value in the ESGH PDU received is equal to or greater
than the Multicast Holding Timer value, for this subnetwork, that is than the Multicast Holding Timer value, for this subnetwork, that is
being used by the ES processing this ESGH PDU. being used by the ES processing this ESGH PDU.
ESs will utilize a local default value for their Multicast Announce- ESs will utilize a local default value for their Multicast Announce-
ment Timer to control the period for sending out their ESGH PDUs. The ment Timer to control the period for sending out their ESGH PDUs. The
Active Multicast IS, if one exists on a particular subnetwork, will Active Multicast IS, if one exists on a particular subnetwork, may
optionally suggest a value for ESs on the subnetwork to use for their suggest a value for ESs on the subnetwork to use for their Multicast
Multicast Announcement Timer for a specific group Network address. In Announcement Timer for a specific group Network address. In order to
order to support the optional damping function, ESs are required to support the optional damping function, ESs are required to incor-
incorporate a 25% jittering to the timer values that they are using. porate a 25% jittering to the timer values that they are using.
6.1.2 Operation of ESs sourcing multicast PDUs 6.1.2 Operation of ESs originating multicast PDUs
An ES which is attached to multiple subnetworks when sourcing multi- The ES originating multicast packets identified by a specific group
cast PDUs is required to source only one such PDUs on to a subnetwork Network address is not required to be a receiver of such packets (and
to which a multicast IS is attached. No restrictions are placed on a thus is not announcing that particular group Network address). The
multiply attached ES for which none of the subnetworks to which it is origination of multicast PDUs involves two differences to the origi-
attached to has a multicast capable IS. The ES sourcing multicast nation of unicast PDUs. The two differences are: (1)The mechanism
PDUs on a subnetwork that has a multicast IS attached always uses the for selecting a destination SNPA address and (2)For End Systems
"All Multicast Intermediate System Network entities" as the SNPA des- attached to more than one subnet, the decision on which subnet(s) to
tination address for all PDUs sourced. For an ES which is not originate the PDUs.
attached to a subnetwork with a multicast capable IS, the ES uses
pre-configured multicast address mapping information if available and
if there is no pre-configured information maps the "All Multicast End
System Network Entities" multi-destination address to the group Net-
work address. The ES sourcing multicast PDUs identified by a specific
group Network address is not required to be a receiver of such PDUs
(and thus is not announcing that particular group Network address).
The reason for sourcing packets on a subnetwork with a multicast The destination SNPA address used for originating each multicast
capable IS attached by multicasting to all multicast capable ISs packet depends on whether there is a multicast capable IS attached to
versus unicasting to one of the multicast capable ISs is to limit the the subnetworks. When a multicast capabale IS is attached, the deci-
maximum number of transmissions required on any subnetwork to two. sion depends on whether there is multicast address mapping informa-
In the case of sourcing a packet, one transmission would be used for tion corresponding to the group Network address used as the destina-
sourcing the packet to all ISs that might need it and the second, if tion address parameter of the multicast packet available for that
needed, to multicast the packet to ESs on the subnetwork which belong subnetwork. When there is a multicast capable IS attached to a sub-
to the group. If this packet were sourced via a unicast to an IS, network and there is multicast address mapping information available
then the packet may need to passed on to other ISs on the subnet corresponding to the group Network address, then the SNPA address
(depending upon the particular multicast tree) and the same packet obtained from the multicast address mapping information is used. Ori-
may need to be transmitted again to the ESs on the subnetwork which ginating multicast packets using the destination SNPA address used
belong to the group. for receiving such multicast packets ensures that the multicast pack-
ets will not require additional forwarding on the originating
subnetwork(s). When there is a multicast capable IS attached to a
subnetwork but for which there is no multicast address mapping infor-
mation available corresponding to the the group Network address, then
the SNPA address used is the "All Multicast Capable Intermediate Sys-
tems" address.
When there is no multicast capable IS attached to a subnetwork then
the ES originating a multicast PDU uses pre-configured information if
it is available or the "All Multicast Capable End Systems" SNPA
address when no pre-configured information is available.
ES's attached to more than one subnetwork forward each multicast
packet that they originate onto every attached subnetwork for which
the NSAP address being used as the source address of the multicast
packet is actively being reported through the unicast ES-IS Report
Configuration function.
6.1.3 Operation of the Active Multicast IS 6.1.3 Operation of the Active Multicast IS
The Active Multicast IS listens in on all ESGH PDUs sourced on the The Active Multicast IS listens in on all ESGH PDUs originated on the
subnetwork for which it is serving as the Active Multicast IS. All subnetwork for which it is serving as the Active Multicast IS. All
subnetworks are handled independently (even if multiple subnetworks subnetworks are handled independently (even if multiple subnetworks
have the same ESs attached and the IS is serving as the Active Multi- have the same ESs attached and the IS is serving as the Active Multi-
cast IS for these multiple subnetworks). cast IS for these subnetworks).
The Active Multicast IS sources MAM PDUs, for all group Network The Active Multicast IS originates MAM PDUs, for all group Network
addresses for which it has received ESGH PDUs, on the subnetwork due addresses for which it has received ESGH PDUs, on the subnetwork due
to the following operational conditions: (1)The IS initializes either to the following operational conditions:
as the Active Multicast IS after an election with other multicast
capable ISs or initializes believing it is the only multicast capable
IS (the determination of such conditions are outside of the scope of
this specification); (2)The IS receives an ESGH PDU with a group Net-
work address paired to an incorrect SNPA address; (3)The expiration
of the IS's Multicast Address Mapping Timer for that group Network
address (this is to prevent the expiration of Mapping Holding Timers
in ESs and to ensure that ESs which source specific multicast PDUs
but are not receivers of such PDUs are using the correct SNPA desti-
nation address in such PDUs that they source) or (4)The IS receives a
multicast PDU sourced on the subnetwork which used an incorrect des-
tination SNPA address (note: this specification does not place any
requirement on an IS to listen in on any multicast PDU, with the
exception of multicast PDUs addressed to "the All Multicast Inter-
mediate System Network Entities" group SNPA address but an IS may
receive a PDU with an incorrect destination SNPA address due to other
operational actions).
Actual relaying of any multicast PDUs sourced on a subnetwork will be 1) The IS initializes either as the Active Multicast IS after an
the responsibility of the multicast routing protocol used and is out- election with other multicast capable ISs or initializes believ-
side the scope of this specification. ing it is the only multicast capable IS;
Note: The determination of such conditions is outside of the scope of
this specification;
2) The IS receives an ESGH PDU with a group Network address paired
to an incorrect SNPA address;
3) The expiration of the IS's Multicast Address Mapping Timer for
that group Network address; or
Note: This is to prevent the expiration of Mapping Holding Timers in
ESs.
4) The IS receives a multicast PDU originated on the subnetwork
which used an incorrect destination SNPA address.
Note: Of particular concern are those multicast packets using the
"All Multicast Capable Intermediate Systems" SNPA address when
another SNPA address should have been used. In addition the multi-
cast capable ISs are responsible for listening in on all multicast
packets using destination SNPA addresses that are contained within
the current multicast address mapping information.
As a result of the event driven conditions (i.e. conditions 2 or 4
above), the Active Multicast IS sends a MAM PDU with direct informa-
tion (i.e. not needing analysis of the Mask parameters). The Active
Multicast IS limits the number of MAM PDUs that are sent out per unit
of time. Particular MAM PDUs with direct information will not be
sent more than once per second. MAM PDU will be sent in response to
continuing event driven conditions such that events occurring greater
than 10 seconds after the issuance of such a MAM PDU will result in
the issuance of another MAM PDU. .
The Active Multicast IS is responsible for forwarding a multicast
packet back on the subnetwork it was originated when a multicast
packet used the "All Multicast Capable Intermediate System" SNPA
address when another SNPA address should have been used. A packet
forwarded back onto the subnetwork the multicast packet was ori-
ginated on will be given a CLNP Lifetime of "1" to prevent the con-
tinued relaying of duplicate packets by the multicast ISs.
The further relaying of any multicast packet originated on a subnet-
work is the responsibility of the multicast routing protocol used and
is outside the scope of this specification.
6.2 Definitions 6.2 Definitions
Active Multicast IS: The one multicast capable IS selected (via means Active Multicast IS: The one multicast capable IS selected (via means
outside of this specification) to source Multicast Address Mapping outside of this specification) to originate Multicast Address Mapping
information on a particular subnetwork. information on a particular subnetwork.
Paired SNPA Address: The SNPA address associated with a particular Paired SNPA Address: The SNPA address associated with a particular
group Network address on a specific subnetwork. group Network address on a specific subnetwork.
6.3 Routing information supporting multicast transmission 6.3 Routing information supporting multicast transmission
6.3.1 Multicast Announcement Information 6.3.1 Multicast Announcement Information
An IS should forward a multicast PDU containing a particular destina- An IS should forward a multicast PDU containing a particular destina-
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On a point-to-point subnetwork the multicast announcement information On a point-to-point subnetwork the multicast announcement information
informs the Network entity, in the case where it is attached to an informs the Network entity, in the case where it is attached to an
End System, of the group Network addresses for which that End System End System, of the group Network addresses for which that End System
expects to receive multicast PDUs. expects to receive multicast PDUs.
On a broadcast subnetwork the multicast announcement information On a broadcast subnetwork the multicast announcement information
informs the multicast capable Intermediate Systems, of the group Net- informs the multicast capable Intermediate Systems, of the group Net-
work addresses for which ESs attached to that subnetwork expect to work addresses for which ESs attached to that subnetwork expect to
receive multicast PDUs. receive multicast PDUs.
Editor's Note: Intermediate Systems with the optional OSI multicast Note: Intermediate Systems with the optional OSI multicast capabili-
capabilities do receive information identifying the SNPA address of ties do receive information identifying the SNPA address of ESs on
ESs on the broadcast network that want PDUs with particular group the broadcast network that want PDUs with particular group Network
Network addresses as their destination address; however, the critical addresses as their destination address; however, the critical
information is which multicast PDUs are needed, not which ESs need information is which multicast PDUs are needed, not which ESs need
them. them.
6.3.2 Multicast Address Mapping Information 6.3.2 Multicast Address Mapping Information
In order to receive multicast PDUs destined for a particular group In order to receive multicast packets destined for a particular group
Network address, an ES may be able to take advantage of an associa- Network address, an ES may need to associate with the group Network
tion of the group Network address with a specific SNPA address. Mul- address a specific SNPA address. Multicast address mapping informa-
ticast address mapping information enables an IS to inform ESs that tion enables an IS to inform ESs that they can receive multicast
they can receive multicast PDUs destined for a particular group Net- packets destined for a particular group Network address on a
work address on a corresponding specific SNPA address. corresponding specific SNPA address. In addition, multicast address
mapping information may provide the specific destination SNPA
addresses needed by an ES for originating multicast packets.
Multicast address mapping information is not employed on point-to- Multicast address mapping information is not employed on point-to-
point subnetworks. point subnetworks.
Multicast address mapping information is employed on broadcast sub- Multicast address mapping information is employed on broadcast sub-
networks to enable multicast capable Intermediate Systems to inform networks to enable multicast capable Intermediate Systems to inform
the multicast capable End Systems that they can receive, on a the multicast capable End Systems that they can receive, on a
specific broadcast subnetwork, multicast PDUs destined for a particu- specific broadcast subnetwork, multicast packets destined for a par-
lar group network address on a corresponding specific SNPA address. ticular group Network address on a corresponding specific SNPA
address. In addition multicast address mapping information provides
the specific destination SNPA address, that corresponds to a particu-
lar group Network address, for each multicast packet that it ori-
ginates on a specific broadcast subnetwork.
6.4 Addresses 6.4 Addresses
All exchanges using this protocol are accomplished over a single sub- All exchanges using this protocol are accomplished over a single sub-
network. While the control PDU's contain Network addresses (i.e. network. While the control PDU's contain Network addresses (i.e.
group Network addresses) actual control PDU transfer is accomplished group Network addresses) actual control PDU transfer is accomplished
via Subnetwork based group addresses (i.e. group SNPA addresses). The via Subnetwork based group addresses (i.e. group SNPA addresses). The
following group SNPA addresses are used: (1)All Multicast End System following group SNPA addresses are used: (1)All Multicast Capable End
Network entities; (2)All Multicast Intermediate System Network enti- Systems; (2)All Multicast Announcements; (3)All Multicast Capable
ties and (3)a group SNPA address corresponding to a group Network Intermediate Systems and (4)a group SNPA address corresponding to a
address group Network address
6.5 Timers 6.5 Timers
Two additional timers are employed: (1)the Multicast Announcement Two additional timers are employed: (1)the Multicast Announcement
Timer (MAT) and (2)Multicast Address Mapping Timer (MAMT). Old Timer (MAT) and (2)Multicast Address Mapping Timer (MAMT). Old multi-
multicast announcement or multicast address mapping information shall cast announcement or multicast address mapping information shall be
be discarded after the Holding Timer expires to ensure the correct discarded after the Holding Timer expires to ensure the correct
operation of the protocol. operation of the protocol.
6.5.1 Multicast Announcement Timer 6.5.1 Multicast Announcement Timer
The Multicast Announcement Timer is a local timer (i.e. maintained The Multicast Announcement Timer is a local timer (i.e. maintained
independently by each End System, one timer per group Network independently by each End System, one timer per group Network
address) which assists in performing the Report Multicast Announce- address) which assists in performing the Report Multicast Announce-
ment function. The timer determines how often an End System reports ment function. The timer determines how often an End System reports
its desire to receive multicast PDUs with that group Network address its desire to receive multicast PDUs with that group Network address
as its destination address parameter. Considerations in setting this as its destination address parameter. Considerations in setting this
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in the End Systems. in the End Systems.
6.6 Extensions to the current protocol functions 6.6 Extensions to the current protocol functions
In order to support multicast transmissions the following optional In order to support multicast transmissions the following optional
ES-IS protocol functions will be implemented: ES-IS protocol functions will be implemented:
6.6.1 Report Configuration by Intermediate Systems 6.6.1 Report Configuration by Intermediate Systems
All multicast capable Intermediate Systems on a subnetwork will use All multicast capable Intermediate Systems on a subnetwork will use
the Multicast Capable option in all ISH PDUs that they source. This the Multicast Capable option in all ISH PDUs that they originate.
will provide multicast capable End Systems with a way to determine This will provide multicast capable End Systems with a way to deter-
that a multicast capable Intermediate System is operating on a par- mine that a multicast capable Intermediate System is operating on a
ticular subnetwork. particular subnetwork.
6.6.2 Query Configuration 6.6.2 Query Configuration
Note: The Query Configuration function cannot be performed to find Note: The Query Configuration function cannot be performed to find
the corresponding SNPA address of a group Network address since the the corresponding SNPA address of a group Network address since the
addressing information needed is the corresponding group SNPA address addressing information needed is the corresponding group SNPA address
and not the SNPA address of a particular End System responding. On a and not the SNPA address of a particular End System responding. On a
large broadcast subnetwork, many different Configuration Responses large broadcast subnetwork, many different Configuration Responses
could result each incorporating a different End System Address. While could result each incorporating a different End System Address. While
it is possible to design a Query Configuration for use with multi- it is possible to design a Query Configuration for use with multi-
cast, this function does not appear to be required given the use of cast, this function does not appear to be required given the use of
the "All Multicast End System Network Entities" address for supplying the "All Multicast Capable End Systems" address for supplying a SNPA
a SNPA address when the group SNPA address is not known. address when the group SNPA address is not known.
6.7 Multicast Announcement 6.7 Multicast Announcement
6.7.1 Report Multicast Announcement Function by End Systems 6.7.1 Report Multicast Announcement Function by End Systems
An End System which needs to receive or continue to receive any mul- An End System which needs to receive or continue to receive any mul-
ticast PDUs (i.e. PDUs with group Network addresses as their destina- ticast PDUs (i.e. PDUs with group Network addresses as their destina-
tion address), constructs and transmits ESGH PDUs to inform multicast tion address), constructs and transmits ESGH PDUs to inform multicast
capable Intermediate Systems of the set of group Network address des- capable Intermediate Systems of the set of group Network address des-
tinations for which it wishes to receive PDUs. This may be done by tinations for which it wishes to receive PDUs. This may be done by
constructing ESGH PDUs for each group Network address. Alternatively, constructing ESGH PDUs for each group Network address. Alternatively,
ESGH PDUs may be constructed which convey information about more than ESGH PDUs may be constructed which convey information about more than
one group Network address at a time, up to the limits imposed by the one group Network address at a time, up to the limits imposed by the
permitted SNSDU size and the maximum header size of the ESGH PDU. permitted SNSDU size and the maximum header size of the ESGH PDU.
Each ESGH PDU is transmitted by issuing an SN-UNITDATA.Request with Each ESGH PDU is transmitted by issuing an SN-UNITDATA.Request with
the following parameters: the following parameters:
SN_Userdata (SNSDU) <- ESGH PDU SN_Userdata (SNSDU) <- ESGH PDU
SN_Destination _Address <- multi-destination address that indicates SN_Destination _Address <- multi-destination address that indicates
"All Multicast Intermediate System Network Entities" "All Multicast Announcements"
If an End System supports more than one SNPA, the information about If an End System is attached to more than one subnetwork, the infor-
each group Network address desired for receiving on a particular SNPA mation about each group Network address desired for receiving on a
serving the End System shall be transmitted via that SNPA. It is per- particular subnetwork serving the End System shall be transmitted via
missible for an End System to report group Network addresses on mul- that subnetwork. It is permissible for an End System to report group
tiple SNPAs; however, duplicate multicast PDUs should be anticipated. Network addresses on multiple subnetworks; however, duplicate multi-
cast PDUs should be anticipated.
The Group Address Pair parameter carries a list of Group Network The Group Address Pair parameter carries a list of Group Network
Addresses, each paired with its associated SNPA address. This infor- Addresses, each paired with its associated SNPA address. This infor-
mation is used by the Active Multicast IS to determine whether a Mul- mation is used by the Active Multicast IS to determine whether a Mul-
ticast Address Mapping PDU should be emitted to update the associa- ticast Address Mapping PDU should be emitted to update the associa-
tion between Group Network Addresses and SNPA addresses. tion between Group Network Addresses and SNPA addresses.
The Holding Time (HT) field is set to approximately twice the ES's The Holding Time (HT) field is set to approximately twice the ES's
Multicast Announcement Timer (MAT) parameter. The value shall be Multicast Announcement Timer (MAT) parameter. The value shall be
large enough so that even if every other ESGH PDU is discarded (due large enough so that even if every other ESGH PDU is discarded (due
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(Note: -- Applying jitter to the MAT parameter is required in order (Note: -- Applying jitter to the MAT parameter is required in order
to support the optional Damping function. If no jitter is applied on to support the optional Damping function. If no jitter is applied on
a subnetwork where many ESs are requesting a particular multicast PDU a subnetwork where many ESs are requesting a particular multicast PDU
it is likely that they will have the same value for their MAT and it is likely that they will have the same value for their MAT and
these timers may all become synchronised. Such synchronisation will these timers may all become synchronised. Such synchronisation will
result in peaks in the distribution of traffic as described above. result in peaks in the distribution of traffic as described above.
The resulting overloading of the transmission medium and the systems The resulting overloading of the transmission medium and the systems
receiving the PDUs will negate any beneficial use of the Damping receiving the PDUs will negate any beneficial use of the Damping
function (since systems may be attempting to transmit their own ESGH function (since systems may be attempting to transmit their own ESGH
PDUs at the time they receive ESGH PDUs sourced by other ESs with the PDUs at the time they receive ESGH PDUs originated by other ESs with
same group Network address). the same group Network address).
6.7.2 Record Multicast Announcement Function 6.7.2 Record Multicast Announcement Function
The Record Multicast Announcement function receives ESGH PDUs, The Record Multicast Announcement function receives ESGH PDUs,
extracts the multicast announcement information and updates the extracts the multicast announcement information and updates the
information in its routing information base. information in its routing information base.
The receiving system is not required to process any option fields in The receiving system is not required to process any option fields in
a received ESGH PDU. a received ESGH PDU.
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address does not match, the Report Multicast Address Mapping function address does not match, the Report Multicast Address Mapping function
is performed. is performed.
6.7.2.2 Optional Damping Function 6.7.2.2 Optional Damping Function
An ES with the optional capabilities to support multicast transfer An ES with the optional capabilities to support multicast transfer
may decide to process ESGH PDUs multicast by other End Systems. There may decide to process ESGH PDUs multicast by other End Systems. There
is potentially some reduction in network traffic by doing this. An ES is potentially some reduction in network traffic by doing this. An ES
requesting to receive multicast PDUs is permitted to reset its Multi- requesting to receive multicast PDUs is permitted to reset its Multi-
cast Announcement Timer corresponding to one group Network address on cast Announcement Timer corresponding to one group Network address on
one SNPA upon receiving an ESGH PDU from another ES under the follow- one subnetwork upon receiving an ESGH PDU from another ES under the
ing circumstances: following circumstances:
a) The {group Network address, paired SNPA address} received on a a) The {group Network address, paired SNPA address} received on a
particular subnetwork matches that of the ES processing the ESGH particular subnetwork matches that of the ES processing the ESGH
PDU for that subnetwork. PDU for that subnetwork.
b) The Holding Timer parameter value in the ESGH PDU received is b) The Holding Timer parameter value in the ESGH PDU received is
equal to or greater than the Holding Timer value for the, group equal to or greater than the Holding Timer value for the, group
Network address, being used by the ES processing this PDU. Network address, being used by the ES processing this PDU.
6.7.3 Flush Old Multicast Announcement Function 6.7.3 Flush Old Multicast Announcement Function
The Flush Old Multicast Announcement function is executed to remove The Flush Old Multicast Announcement function is executed to remove
multicast announcement entries in its routing information base whose multicast announcement entries in its routing information base whose
Holding Timer has expired. When the Holding Timer for a group Network Holding Timer has expired. When the Holding Timer for a group Network
address expires, this function removes the corresponding entry from address expires, this function removes the corresponding entry from
the routing information base of the local IS for the corresponding the routing information base of the local IS for the corresponding
SNPA. subnetwork.
The Flush Old Multicast Announcement function is also executed when-
ever a subnetwork service provider re-initializes a local SNPA. When
the SNPA is either disabled or re-initialized, all multicast
announcement information for any group Network address associated
with that SNPA is removed.
6.8 Multicast Address Mapping 6.8 Multicast Address Mapping
6.8.1 Report Multicast Address Mapping Function by Intermediate Systems 6.8.1 Report Multicast Address Mapping Function by Intermediate Systems
The Active Multicast Intermediate System constructs a MAM PDU, The Active Multicast Intermediate System constructs a MAM PDU,
corresponding to a group Network address for which it received via corresponding to a group Network address for which it received via
the Record Multicast Announcement function, and issues these PDUs the Record Multicast Announcement function, and issues these PDUs
under the following circumstances: under the following circumstances:
a) The IS initializes either as the Active Multicast IS after an a) The IS initializes either as the Active Multicast IS after an
election with other multicast capable ISs or initializes after election with other multicast capable ISs or initializes after
determining it is the only multicast capable IS (the determina- determining it is the only multicast capable IS (the determina-
tion of such conditions are outside of the scope of this stan- tion of such conditions are outside of the scope of this stan-
dard), or dard), or
b) The IS receives an ESGH PDU with a group Network address paired b) The IS receives an ESGH PDU with a group Network address paired
to an SNPA address other than the one to which the IS is for- to an SNPA address other than the SNPA address contained in the
warding multicast PDUs, or Active Multicast IS's multicast address mapping information for
that group Network address, or
Note: -- The Active Multicast IS determines which mappings are Note: -- The Active Multicast IS determines which mappings are
correct. Pre-configured mappings which are used prior to the initial- correct. Pre-configured mappings which are used prior to the initial-
ization of the Active Multicast IS may be determined incorrect by the ization of the Active Multicast IS may be determined to be incorrect
Active Multicast IS. by the Active Multicast IS.
c) The expiration of the IS's Multicast Address Mapping Timer for c) The expiration of the IS's Multicast Address Mapping Timer for
that group Network address. that group Network address.
Note: -- This is to prevent the expiration of Holding Timers in ESs Note: -- This is to prevent the expiration of Holding Timers in ESs.
and to ensure that ESs which source specific multicast PDUs but are
not receivers of such PDUs use the correct SNPA destination address. d) The IS receives a multicast PDU originated on the subnetwork
which used an incorrect destination SNPA address.
Note: Of particular concern are those multicast packets using the
"All Multicast Capable Intermediate Systems" SNPA address when
another SNPA address should have been used. The Originating Subnet-
work Forwarding function is performed if this event occurs (see sec-
tion 6.11).
Note: The multicast capable ISs need to receive multicast packets on
all SNPA addresses that are contained in the current multicast
address mapping information for the subnetwork. The multicast capa-
ble ISs are not required to receive multicast packets on any SNPA
addresses other than those contained in the current multicast address
mapping information and the "All Multicast Capable Intermediate Sys-
tems" SNPA address.
Circumstances b) and d) are the event driven conditions for the
Active Multicast IS to construct and issue a MAM PDU. The Active
Multicast IS shall limit the number of MAM PDUs issued per unit of
time. MAM PDUs with identical information shall not be issued more
than once per second. Event conditions occurring 10 seconds after
the last issue of an appropriate MAM PDU shall result in the issuance
of another such MAM PDU.
The IS serving as the Active Multicast Intermediate System may con- The IS serving as the Active Multicast Intermediate System may con-
struct a MAM PDU for each group Network address. Alternatively, MAM struct a MAM PDU for each group Network address. Alternatively, MAM
PDUs may be constructed which convey information about more than one PDUs may be constructed which convey information about more than one
group Network address at a time, up to the limits imposed by the per- group Network address at a time, up to the limits imposed by the per-
mitted SNSDU size and the maximum header size of the MAM PDU. The IS mitted SNSDU size and the maximum header size of the MAM PDU. The IS
performs all multicast address mapping functions independently for performs all multicast address mapping functions independently for
each of its SNPAs even if this IS is the Active Multicast IS on mul- each of its subnetworks even if this IS is the Active Multicast IS on
tiple subnetworks. Each MAM PDU is transmitted by issuing an SN- multiple subnetworks. Each MAM PDU is transmitted by issuing an SN-
UNITDATA.Request with the following parameters: UNITDATA.Request with the following parameters:
SN_Userdata (SNSDU) <- MAM PDU SN_Userdata (SNSDU) <- MAM PDU
SN_Destination _Address <- multi-destination address that indicates SN_Destination _Address <- multi-destination address that indicates
"All Multicast End System Network Entities" "All Multicast Capable End Systems"
The Holding Time (HT) field is set to approximately twice the Inter- The Holding Time (HT) field is set to approximately twice the
mediate System's Multicast Address Mapping Timer (MAMT) parameter. Intermediate System's Multicast Address Mapping Timer (MAMT) parame-
This variable shall be set to a value large enough so that even if ter. This variable shall be set to a value large enough so that even
every other MAM PDU, for a particular group Network address, is dis- if every other MAM PDU, for a particular group Network address, is
carded (due to lack of resources), or otherwise lost in the subnet- discarded (due to lack of resources), or otherwise lost in the sub-
work, the multicast address mapping information will still be main- network, the multicast address mapping information will still be
tained. The value should be set small enough so that End Systems will maintained. The value should be set small enough so that End Systems
quickly cease to use the multicast address mappings supplied by ISs will quickly cease to use the multicast address mappings supplied by
that have failed. ISs that have failed.
Note: -- The Holding Timer parameter value applies to all group Net- Note: -- The Holding Timer parameter value applies to all group Net-
work addresses called out in the MAM PDU. work addresses called out in the MAM PDU.
The Group Address Pair parameter is used to convey the association The Group Address Pair parameter is used to convey the association
between Group Network Addresses and SNPA addresses. between Group Network Addresses and SNPA addresses.
Optionally, the Active Multicast IS may include information in the Optionally, the Active Multicast IS may include information in the
MAM PDU indicating a larger population of group Network addresses to MAM PDU indicating a larger population of group Network addresses to
which the same multicast address mapping information applies. There which the same multicast address mapping information applies. There
are two optional fields for this purpose: the Group Network Address are two optional fields for this purpose: the Group Network Address
Mask option and the Paired SNPA Address Mask option. Their usage Mask option and the Paired SNPA Address Mask option.
depends on the fact that group Network addresses are represented
using the preferred binary encoding, as specified in 7.3.2.
There are three permitted cases for including or excluding the masks. There are three permitted cases for including or excluding the masks.
In the first case, both masks are absent. In this case the MAM PDU In the first case, both masks are absent. In this case the MAM PDU
conveys information about one set of enumerated group Network conveys information about one set of enumerated group Network
addresses only. addresses only.
Note: -- Multiple group address pairs may be contained in a single Note: -- Multiple group address pairs may be contained in a single
MAM PDU. MAM PDU.
In the second case, the MAM PDU contains a Group Network Address Mask In the second case, the MAM PDU contains a Group Network Address Mask
but no Paired SNPA Address Mask. In this case, the MAM PDU conveys but no Paired SNPA Address Mask. In this case, the MAM PDU conveys
information about an equivalence class of group Network addresses. information about an equivalence class of group Network addresses.
The information reveals that multiple group Network addresses are The information reveals that multiple group Network addresses are
mapped to the same SNPA address. mapped to the same SNPA address.
In the third case, the MAM PDU contains both masks. As in the second In the third case, the MAM PDU contains both masks. As in the second
case, the MAM PDU conveys information about an equivalence class of case, the MAM PDU conveys information about an equivalence class of
group Network addresses. But in this case, the information reveals group Network addresses. But in this case, the information reveals
that the SNPAs for the equivalence class of group Network address are that the SNPA addresses for the equivalence class of group Network
embedded in the group Network address. In particular the Paired SNPA address are embedded in the group Network address. In particular the
Address Mask indicates the location of the SNPA address in the group Paired SNPA Address Mask indicates the location of the SNPA address
Network Address(es). in the group Network Address(es).
An IS may optionally suggest a value for End Systems on the local The Active Multicast IS shall construct a MAM PDU with direct infor-
subnetwork to use as their Multicast Announcement Timers, for a mation, not needing analysis of the Mask parameters, in response to
specific group Network address, by including the Suggested ES Multi- the occurrence of an event driven condition. The Active Multicast IS
cast Announcement Timer (ESMAT) option in the transmitted MAM PDU. may provide additional information in such a MAM PDU via the use of
Setting this option permits the Active Multicast IS to influence the Mask parameters.
frequency with which ESs transmit ESGH PDUs.
Note: -- If the ESMAT option is used, the one value permitted in the An IS may suggest a value for End Systems on the local subnetwork to
MAM PDU is suggested for all group Network addresses called out in use as their Multicast Announcement Timers, for a specific group Net-
the MAM PDU. work address, by including the Suggested ES Multicast Announcement
Timer (ESMAT) parameter in the transmitted MAM PDU. Setting this
parameter permits the Active Multicast IS to influence the frequency
with which ESs transmit ESGH PDUs.
Note: -- If the ESMAT parameter is used, the one value permitted in
the MAM PDU is suggested for all group Network addresses called out
in the MAM PDU.
6.8.2 Record Multicast Address Mapping Function by End Systems 6.8.2 Record Multicast Address Mapping Function by End Systems
The Record Multicast Address Mapping function receives MAM PDUs, The Record Multicast Address Mapping function receives MAM PDUs,
extracts the multicast address mapping information and updates the extracts the multicast address mapping information and updates the
information in its routing information base. The receiving system is information in its routing information base. The receiving system is
not required to process any option fields in a received MAM PDU. not required to process any option fields in a received MAM PDU with
the exception of the Suggested ES Multicast Announcement Timer
(ESMAT) parameter.
Note: -- When a system chooses to process these optional fields, the Note: -- When a system chooses to process these optional fields, the
precise actions are not specified by this International Standard. precise actions are not specified by this International Standard.
On receipt of a MAM PDU an ES with the optional multicast capabili- On receipt of a MAM PDU an ES with the optional multicast capabili-
ties extracts the multicast address mapping information and stores ties extracts the multicast address mapping information and stores
the {group Network address, paired SNPA address} for a particular the {group Network address, paired SNPA address} for a particular
subnetwork in its routing information base replacing any other infor- subnetwork in its routing information base replacing any other infor-
mation for the same group Network address and subnetwork. mation for the same group Network address and subnetwork.
In addition, an ES may also set its Multicast Announcement Timer In addition, an ES shall set its Multicast Announcement Timer,
corresponding to the group Network address for which it is performing corresponding to the group Network address for which it is performing
the Record Multicast Address Mapping function based on receipt of a the Record Multicast Address Mapping function, based on receipt of a
MAM PDU containing the ESMAT optional field. MAM PDU, corresponding to that group Network address, containing an
ESMAT parameter.
Note: -- While an ES may process ESGH PDUs multicast by other ESs to Note: -- While an ES may process ESGH PDUs multicast by other ESs to
support the optional Damping function, an ES is not permitted to support the optional Damping function, an ES is not permitted to
change its own mapping due to the mapping found in other ES's ESGH change its own mapping due to the mapping found in other ES's ESGH
PDUs. PDUs.
6.8.3 Flush Old Multicast Address Mapping Function by End Systems 6.8.3 Flush Old Multicast Address Mapping Function by End Systems
The Flush Old Multicast Address Mapping function is executed to The Flush Old Multicast Address Mapping function is executed to
remove multicast address mapping entries in its routing information remove multicast address mapping entries in its routing information
base whose corresponding Holding Timer has expired. When such a Hold- base whose corresponding Holding Timer has expired. When such a Hold-
ing Timer for a multicast address mapping expires, this function ing Timer for a multicast address mapping expires, this function
removes the corresponding entry from its routing information base for removes the corresponding entry from its routing information base for
the corresponding SNPA. the corresponding SNPA.
The Flush Old Multicast Address Mapping function is also executed 6.9 Paired SNPA Address Selection Function by End Systems
whenever a subnetwork service provider re-initializes a local SNPA.
When the SNPA is either disabled or re-initialized, all multicast
address mapping information for any multicast address mapping associ-
ated with that SNPA is removed.
6.9 Paired SNPA Address Selection
6.9.1 Paired SNPA Address Selection Function by End Systems
An End System must pair each group Network address with an associated An End System shall pair each group Network address with an associ-
SNPA address to support receiving (e.g. performing the Report Multi- ated SNPA address to support receiving (e.g. performing the Report
cast Announcement function) and sourcing Multicast PDUs. Multicast Announcement function) and originating multicast PDUs.
6.9.1.1 Paired SNPA Address Selection for Receiving Multicast PDUs 6.9.1 Paired SNPA Address Selection for Receiving Multicast PDUs
An End System always has a paired SNPA address for every active group An End System always has a paired SNPA address for every active group
Network address on a particular subnetwork. This mapping is obtained Network address on a particular subnetwork. This mapping is obtained
by: by:
a) recording a multicast address mapping which is maintaining an a) recording a multicast address mapping which is maintaining an
active holding timer, or if there has been no dynamic informa- active holding timer, or if there has been no dynamic informa-
tion received, by tion received, by
b) having pre-configured multicast address mapping information, or b) having pre-configured multicast address mapping information, or
if neither dynamic nor pre-configured information is available, if neither dynamic nor pre-configured information is available,
by by
c) mapping the "All Multicast End System Network Entities" multi- c) mapping the "All Multicast Capable End Systems" multi-
destination address to the group Network address. destination address to the group Network address.
6.9.1.2 Paired SNPA Address Selection for Sourcing Multicast PDUs 6.9.2 Paired SNPA Address Selection for Originating Multicast PDUs
An End System sourcing a multicast PDU pairs a SNPA address to the An End System, originating a multicast PDU, pairs a SNPA address to
group Network address. This mapping is obtained in the following the group Network address. This mapping is obtained in the following
manner: manner:
a) If there is a multicast capable IS reachable on the subnetwork, a) If there is a multicast capable IS reachable on the subnetwork
(i.e. an ISH PDU containing a Multicast Capable optional parame- then the SNPA address used by an End System originating a multi-
ter has been received and the Holding Timer associated with this cast PDU is either the paired SNPA address obtained from the
routing information received is still active), then the SNPA multicast address mapping information associated with the group
address used by an End System sourcing a multicast PDU on the Network address in the multicast PDU's Destination address
subnetwork is the "All Multicast Intermediate System Network parameter or if there is no valid entry for the group Network
Entities" multi-destination address, or if there is no multicast address by using the "All Multicast Capable Intermediate Sys-
tems" multi-destination address, or if there is no multicast
capable Intermediate System on the subnetwork, by capable Intermediate System on the subnetwork, by
Note: Multicast address mapping information is valid if the Holding
Timer associated with it has not expired.
Note: An ES can determine if a multicast capable IS is reachable on
the subnetwork by having for that subnetwork either (1)multicast
address mapping information or (2)routing information received via an
ISH PDU containing a Multicast Capable optional parameter. In either
case the information must be valid (i.e. the Holding Timer for the
information must not have expired).
b) having pre-configured multicast address mapping information, or b) having pre-configured multicast address mapping information, or
if neither a multicast capable Intermediate System is present on if neither a multicast capable Intermediate System is present on
the subnetwork nor pre-configured information is available, by the subnetwork nor pre-configured information is available, by
c) mapping the "All Multicast End System Network Entities" multi- c) mapping the "All Multicast Capable End Systems" multi-
destination address to the group Network address. destination address to the group Network address.
6.10 Structure and Encoding of PDUs 6.10 Extensions to the ISO CLNP Route Function by End Systems
An End System attached to more than one subnetwork shall determine
when originating a multicast PDU whether to forward this multicast
PDU to more than one subnetwork or not. End Systems shall originate
each multicast PDU on all subnetworks for which the ISO ES-IS Confi-
guration function is actively reporting the NSAP address contained in
the Source Address parameter of the multicast PDU. As a result of
this function multiple invocations of the ISO CLNP Forwarding func-
tion may result when such an ES originates a multicast PDU.
6.11 Originating Subnetwork Forwarding Function by Intermediate Sys-
tems
The Active Multicast IS upon receiving a multicast PDU originated on
a subnetwork which used the "All Multicast Capable Intermediate Sys-
tems" SNPA address when another SNPA address should have been used,
performs the Originating Subnetwork Forwarding function. The multi-
cast address mapping information defines the correct SNPA address
pairings for a given subnetwork. The Originating Subnetwork Forward-
ing function forwards the multicast PDU back on subnetwork it was
originated on. In the case that the ES was attached to more than one
subnetwork and originated the multicast PDU on more than one subnet-
work, the Active Multicast IS for each subnetwork performs the Ori-
ginating Subnetwork Forwarding function for the subnetwork that they
are responsible for.
The Active Multicast IS obtains the contents for the multicast PDU
for the Originating Subnetwork Forwarding function by using the con-
tents of the multicast PDU received with the incorrect destination
SNPA address and replacing the original PDU Lifetime field with the
value one (0000 0001). The Active Multicast IS performs the ISO 8473
PDU Composition function and forwards the PDU to the subnetwork that
the PDU was originated on using the ISO 8473 Forwarding function with
the correct destination SNPA address.
Note: The PDU Lifetime field is set to "one" to ensure that ISs
attached to the originating subnetwork do not forward this PDU on.
Such ISs should have received the PDU when it was originated since
this function is only performed in the event of receiving a multicast
PDU incorrectly addressed to the "All Multicast Capable Intermediate
Systems" SNPA address.
6.12 Structure and Encoding of PDUs
The ES-IS multicast control functions are supported via the exchange The ES-IS multicast control functions are supported via the exchange
of ESGH and MAM PDUs. The one exception to this is that a new of ESGH and MAM PDUs. The one exception to this is that a new
optional parameter, the Multicast Capable parameter, is provided for optional parameter, the Multicast Capable parameter, is provided for
use within the ISH PDU. use within the ISH PDU.
6.10.1 PDU Type Codes 6.12.1 PDU Type Codes
The Multicast Announcement is accomplished via the transfer of End The Multicast Announcement is accomplished via the transfer of End
System Group Hello (ESGH) PDUs. The PDU type code for an ESGH PDU is System Group Hello (ESGH) PDUs. The PDU type code for an ESGH PDU is
"0 0 1 0 1". The Multicast Address Mapping (MAM) is accomplished via "0 0 1 0 1". The Multicast Address Mapping (MAM) is accomplished via
the transfer of Multicast Address Mapping PDUs. The PDU type code for the transfer of Multicast Address Mapping PDUs. The PDU type code for
a MAM PDU is "0 0 1 1 1". a MAM PDU is "0 0 1 1 1".
6.10.2 Hold Time field 6.12.2 Hold Time field
The Holding Time field specifies the maximum time for the receiving The Holding Time field specifies the maximum time for the receiving
Network entity to retain the multicast announcement or multicast Network entity to retain the multicast announcement or multicast
address mapping information contained in the PDU. address mapping information contained in the PDU.
6.10.3 Structure of Addressing Parameters 6.12.3 Structure of Addressing Parameters
The ESGH and MAM PDUs carry one or more group Network addresses The ESGH and MAM PDUs carry one or more group Network addresses
(GNAs) each with their associated Paired SNPA Address (PSA). (GNAs) each with their associated Paired SNPA Address (PSA).
6.10.4 Group Address Pair Parameter for ESGH and MAM PDUs 6.12.4 Group Address Pair Parameter for ESGH and MAM PDUs
The Group Address Pair parameter is a list of one or more group Net- The Group Address Pair parameter is a list of one or more group Net-
work addresses each with their associated Paired SNPA address. The work addresses each with their associated Paired SNPA address. The
group Network address identifies specific multicast PDUs and the group Network address identifies specific multicast PDUs and the
Paired SNPA address is the SNPA address on which the ES expects to Paired SNPA address is the SNPA address on which the ES expects to
receive such multicast PDUs on that subnetwork. It is encoded in the receive such multicast PDUs on that subnetwork. It is encoded in the
ESGH and MAM PDUs as shown in Figure 1. ESGH and MAM PDUs as shown in Figure 1.
Octet Octet
,----------------------------------------------------, ,----------------------------------------------------,
skipping to change at page 28, line 45 skipping to change at page 30, line 45
|----------------------------------------------------| |----------------------------------------------------|
| PSAL | | PSAL |
|----------------------------------------------------| |----------------------------------------------------|
| | | |
: PSA : : PSA :
| | m-1 | | m-1
'----------------------------------------------------' '----------------------------------------------------'
Figure 1 - ESGH and MAM PDUs - - Group Address Pair Parameter Figure 1 - ESGH and MAM PDUs - - Group Address Pair Parameter
6.10.5 Extensions to the current Option Parameters 6.12.5 Extensions to the current Option Parameters
The Security and Priority optional parameters may be carried in a The Security and Priority optional parameters may be carried in a
ESGH PDU. There is no Security or Priority option for the MAM PDU. ESGH PDU. There is no Security or Priority option for the MAM PDU.
6.10.6 Suggested ES Multicast Announcement Timer 6.12.6 Suggested ES Multicast Announcement Timer
The ESMAT option may appear only in the MAM PDU The ESMAT parameter may appear only in the MAM PDU
The ESMAT parameter conveys the value that an IS would like the The ESMAT parameter conveys the value that an IS requests the
receiving ESs to use as their local Multicast Announcement Timer. receiving ESs to use as their local Multicast Announcement Timer.
Parameter Code: 1100 0111 Parameter Code: 1100 0111
Parameter Length: two octets Parameter Length: two octets
Parameter Value: ESMAT in units of seconds. Parameter Value: ESMAT in units of seconds.
6.10.7 Multicast Capable 6.12.7 Multicast Capable
The Multicast Capable option may appear only in the ISH PDU The Multicast Capable option may appear only in the ISH PDU
The Multicast Capable options consists only of a one octet code and a The Multicast Capable options consists only of a one octet code and a
one octet parameter length field, there is no parameter field. one octet parameter length field, there is no parameter field.
Parameter Code: 1100 1000 Parameter Code: 1100 1000
Parameter Length: zero octets Parameter Length: zero octets
Parameter Value: none (parameter does not exist). Parameter Value: none (parameter does not exist).
6.10.8 Group Network Address Mask 6.12.8 Group Network Address Mask
The Group Network Address Mask option may only appear in the MAM PDU. The Group Network Address Mask option may only appear in the MAM PDU.
The Group Network Address Mask parameter indicates that the multicast The Group Network Address Mask parameter indicates that the multicast
address mapping information applies to a larger population of group address mapping information applies to a larger population of group
Network Addresses than the group Network address(es) contained in the Network Addresses than the group Network address(es) contained in the
MAM PDU indicates. When this option is provided in a MAM PDU, the MAM PDU indicates. When this option is provided in a MAM PDU, the
masking relationship contained must be valid for all group Network masking relationship contained must be valid for all group Network
addresses contained in this PDU. An End System may ignore this param- addresses contained in this PDU. An End System may ignore this param-
eter. eter.
skipping to change at page 30, line 5 skipping to change at page 32, line 5
when considered with the Paired SNPA Address Mask parameter. when considered with the Paired SNPA Address Mask parameter.
Parameter Code: 1110 0011 Parameter Code: 1110 0011
Parameter Length: variable, up to 20 octets Parameter Length: variable, up to 20 octets
Parameter Value: a comparison mask of octets to be aligned with the Parameter Value: a comparison mask of octets to be aligned with the
Group Network Address field of the Group Address Pair parameter of Group Network Address field of the Group Address Pair parameter of
the MAM PDU. the MAM PDU.
6.10.9 Paired SNPA Address Mask 6.12.9 Paired SNPA Address Mask
The Paired SNPA Address Mask option may only appear in the MAM PDU. The Paired SNPA Address Mask option may only appear in the MAM PDU.
When the Paired SNPA Address Mask is present, the equivalence class When the Paired SNPA Address Mask is present, the equivalence class
defined by the Group Network Address Mask also has common structure defined by the Group Network Address Mask also has common structure
below the Group Network Address Mask; i.e. in the portion of the below the Group Network Address Mask; i.e. in the portion of the
group Network address where the Group Network Address Mask is logi- group Network address where the Group Network Address Mask is logi-
cally "0". The Paired SNPA Address Mask supplies additional informa- cally "0". The Paired SNPA Address Mask supplies additional informa-
tion about the structure, by indicating certain bit positions within tion about the structure, by indicating certain bit positions within
the space "below" the Group Network Address Mask. Specifically, the the space "below" the Group Network Address Mask. Specifically, the
skipping to change at page 30, line 36 skipping to change at page 32, line 36
masks while heeding the other. masks while heeding the other.
Parameter Code: 1110 0100 Parameter Code: 1110 0100
Parameter Length: variable Parameter Length: variable
Parameter Value: a comparison mask of octets to be aligned with the Parameter Value: a comparison mask of octets to be aligned with the
Group Network Address field(s) of the Group Address Pair parameter of Group Network Address field(s) of the Group Address Pair parameter of
the MAM PDU. the MAM PDU.
6.10.9.1 Mask Parameters Example 6.12.9.1 Mask Parameters Example
This section provides examples of using the Group Network Address This section provides examples of using the Group Network Address
Mask and the Paired SNPA Address Mask. The examples given are for an Mask and the Paired SNPA Address Mask. The examples given are for an
Internet usage of CLNP Multicasting across subnetworks using IEEE 802 Internet usage of CLNP Multicasting across subnetworks using IEEE 802
addressing. For these examples the Group Network address format is: addressing. For these examples the Group Network address format is:
+-----+----------------------------------------+ +-----+----------------------------------------+
| IDP | Upper DSP | Embedded SNPA address | SEL| | IDP | Upper DSP | Embedded SNPA address | SEL|
+-----+-----------+-----------------------+----+ +-----+-----------+-----------------------+----+
octets: | 3 | 10 | 6 | 1 | octets: | 3 | 10 | 6 | 1 |
skipping to change at page 31, line 6 skipping to change at page 33, line 6
Thus the group Network address used is 20 octets. For these exam- Thus the group Network address used is 20 octets. For these exam-
ples, the only field considered is the Embedded SNPA address field ples, the only field considered is the Embedded SNPA address field
and its placement within the group Network address. and its placement within the group Network address.
In the first example it is the policy in "this part of the Internet" In the first example it is the policy in "this part of the Internet"
to map the Embedded SNPA address into the IEEE 802 address space to map the Embedded SNPA address into the IEEE 802 address space
reserved by IEEE 802 for group addressing using LOCAL assignment, reserved by IEEE 802 for group addressing using LOCAL assignment,
this corresponds to all 48 bit values with the two low order bits of this corresponds to all 48 bit values with the two low order bits of
the first octet set to "11". the first octet set to "11".
The Active Multicast Intermediate System on this subnet may construct The Active Multicast Intermediate System on this subnetwork may con-
a MAM PDU to map, for this example, a group Network address of {13 struct a MAM PDU to map, for this example, a group Network address of
octets, 03-00-DA-DA-DA-DA, 1 octet} and a paired SNPA address of 03- {13 octets, 03-00-DA-DA-DA-DA, 1 octet} and a paired SNPA address of
00-DA-DA-DA-DA. In addition the Active Multicast Intermediate System 03-00-DA-DA-DA-DA. In addition the Active Multicast Intermediate
can include in the MAM PDU a Group Network Address Mask of FF-FF-FF- System can include in the MAM PDU a Group Network Address Mask of
FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-03-00-00-00-00-00-00. FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-FF-03-00-00-00-00-00-00.
With this paramete, all group Network addresses which share the With this parameter, all group Network addresses which share the
identical first 13 octet and with "11" in the two low order bits of identical first 13 octet and with "11" in the two low order bits of
the 14th octet are put in an equivalence class and share the same the 14th octet are put in an equivalence class and share the same
mapping information. If this were the only option present then all of mapping information. If this were the only option present then all of
these group Network addresses would all have a paired SNPA of 03-00- these group Network addresses would all have a paired SNPA address of
DA-DA-DA-DA. 03-00-DA-DA-DA-DA.
In order to map the group Network addresses to the range of IEEE In order to map the group Network addresses to the range of IEEE
addresses of this example, the MAM PDU must also contain a Paired addresses of this example, the MAM PDU must also contain a Paired
SNPA Address Mask. The Paired SNPA Address Mask identifies where the SNPA Address Mask. The Paired SNPA Address Mask identifies where the
SNPA Address is contained within the group Network addresses (defined SNPA Address is contained within the group Network addresses (defined
by the equivalence class formed by the Group Network Address Mask by the equivalence class formed by the Group Network Address Mask
within the same PDU). For this example the Paired SNPA Address Mask within the same PDU). For this example the Paired SNPA Address Mask
is 00-00-00-00-00-00-00-00-00-00-00-00-00-FF-FF-FF-FF-FF-FF-00. is 00-00-00-00-00-00-00-00-00-00-00-00-00-FF-FF-FF-FF-FF-FF-00.
As a second example, all group Network addresses with a specific OUI As a second example, all group Network addresses with a specific OUI
skipping to change at page 31, line 45 skipping to change at page 33, line 45
1. A group Network address contained within the MAM PDU with the 1. A group Network address contained within the MAM PDU with the
OUI of interest. OUI of interest.
2. A group Network address Mask of FF-FF-FF-FF-FF-FF-FF-FF-FF- 2. A group Network address Mask of FF-FF-FF-FF-FF-FF-FF-FF-FF-
FF-FF-FF-FF-FF-FF-FF-00-00-00-00. FF-FF-FF-FF-FF-FF-FF-00-00-00-00.
3. A Paired SNPA Address of 00-00-00-00-00-00-00-00-00- 3. A Paired SNPA Address of 00-00-00-00-00-00-00-00-00-
00-00-00-00-FF-FF-FF-FF-FF-FF-00. 00-00-00-00-FF-FF-FF-FF-FF-FF-00.
6.10.10 End System Group Hello (ESGH) PDU 6.12.10 End System Group Hello (ESGH) PDU
The ESGH PDU has the format shown in figure 2: The ESGH PDU has the format shown in figure 2:
Octet Octet
,----------------------------------------------------, ,----------------------------------------------------,
| Network Layer Protocol Identifier | 1 | Network Layer Protocol Identifier | 1
|----------------------------------------------------| |----------------------------------------------------|
| Length Indicator | 2 | Length Indicator | 2
|----------------------------------------------------| |----------------------------------------------------|
| Version/Protocol ID Extension | 3 | Version/Protocol ID Extension | 3
skipping to change at page 32, line 53 skipping to change at page 34, line 53
| | | |
: PSA : : PSA :
| | m-1 | | m-1
|----------------------------------------------------| |----------------------------------------------------|
| | m | | m
: Options : : Options :
| | p-1 | | p-1
'----------------------------------------------------' '----------------------------------------------------'
Figure 2 - ESGH PDU Format Figure 2 - ESGH PDU Format
6.10.11 Multicast Address Mapping (MAM) PDU 6.12.11 Multicast Address Mapping (MAM) PDU
The MAM PDU has the format shown in figure 3. The MAM PDU has the format shown in figure 3.
Octet Octet
,----------------------------------------------------, ,----------------------------------------------------,
| Network Layer Protocol Identifier | 1 | Network Layer Protocol Identifier | 1
|----------------------------------------------------| |----------------------------------------------------|
| Length Indicator | 2 | Length Indicator | 2
|----------------------------------------------------| |----------------------------------------------------|
| Version/Protocol ID Extension | 3 | Version/Protocol ID Extension | 3
skipping to change at page 33, line 53 skipping to change at page 35, line 53
| | | |
: PSA : : PSA :
| | m-1 | | m-1
|----------------------------------------------------| |----------------------------------------------------|
| | m | | m
: Options : : Options :
| | p-1 | | p-1
'----------------------------------------------------' '----------------------------------------------------'
Figure 3 - MAM PDU Format Figure 3 - MAM PDU Format
6.11 Conformance 6.13 Conformance
All of the extensions provided to the functions to support multicast All of the extensions provided to the functions to support multicast
capability are optional. For an End System or Intermediate System capability are optional. For an End System or Intermediate System
which is not multicast capable these extensions are not applicable. A which is not multicast capable these extensions are not applicable. A
Network entity may choose to be multicast capable, a multicast capa- Network entity may choose to be multicast capable, a multicast capa-
ble Network entity is required to support both multicast announcement ble Network entity is required to support both multicast announcement
information and multicast address mapping information. information and multicast address mapping information.
An implementation claiming conformance as a multicast capable End An implementation claiming conformance as a multicast capable End
System shall meet all of the requirements for an End System which is System shall meet all of the requirements for an End System which is
skipping to change at page 34, line 42 skipping to change at page 37, line 19
Clause -------------- Clause --------------
Label Function Reference AI MI AI MI Label Function Reference AI MI AI MI
------------------------------------------------------------------ ------------------------------------------------------------------
RpMAn Report Multicast Announcement 6.7.1 M - - - RpMAn Report Multicast Announcement 6.7.1 M - - -
RcMAn Record Multicast Announcement 6.7.2.1 - - M - RcMAn Record Multicast Announcement 6.7.2.1 - - M -
RcDamp Record Damping 6.7.2.2 O - - - RcDamp Record Damping 6.7.2.2 O - - -
FlMAn Flush Old Multicast Announcement 6.7.3 O - M - FlMAn Flush Old Multicast Announcement 6.7.3 O - M -
RpMAdMa Report Multicast Address Mapping 6.8.1 - - - M RpMAdMa Report Multicast Address Mapping 6.8.1 - - - M
MATGn ESMAT Generation 6.8.1 - - - O MATGn ESMAT Generation 6.8.1 - - - M
RcMAdMa Record Multicast Address Mapping 6.8.2 - M - - RcMAdMa Record Multicast Address Mapping 6.8.2 - M - -
MATPr ESMAT Processing 6.8.2 - O - - MATPr ESMAT Processing 6.8.2 - M - -
FlMAdMa Flush Old Multicast Address Map 6.8.3 - M - - FlMAdMa Flush Old Multicast Address Map 6.8.3 - M - -
PSAdSel Paired SNPA Address Selection 6.9.1 - M - - PSAdSel Paired SNPA Address Selection 6.9.1 - M - -
ExtForw Extensions to CLNP Route Function 6.10 - M - -
OSuForw Originating Subnetwork Forwarding 6.11 - - - M
Key: Key:
AI = Multicast Announcement information supported AI = Multicast Announcement information supported
MI = Multicast Address Mapping information supported MI = Multicast Address Mapping information supported
M = Mandatory; O = Optional; - = not applicable M = Mandatory; O = Optional; - = not applicable
Appendix A. Considerations for ESGH and MAM destination SNPA address Appendix A. Differences with RFC 1112
parameters
One of the design decisions needed for this specification is what desti-
nation SNPA addresses to use for the control PDUs. One multicast
transfer to all entities needing these control PDUs provides great effi-
ciency; however the reception and processing of such PDUs by entities
not participating in the transfer of specific multicast PDUs wastes such
entities resources.
The MAM PDU is sent using the "All Multicast End System Network enti-
ties" SNPA address in the destination parameter field of its subnetwork
protocol. Such PDUs are intended to correct SNPA address problems and
need to be received by all End Systems receiving a specific multicast
PDU (identified by its group Network address) especially to those End
Systems which are presently utilizing an incorrect SNPA address. While
it appears feasible to send MAM PDUs utilizing the unicast SNPA address
of ESs which has sourced an ESGH with an incorrect mapping (identified
via receiving an ESGH with the incorrect mapping), there appears to be a
valid concern that if one ES has an incorrect mapping that others may
also have this problem. Further limiting the scope to only ESs which
receive particular multicast PDUs appears possible, this is left for
further study. Actual reception of a particular MAM mapping is only
required by those ESs which are announcing the associated group Network
address; however given the capability to use the optional damping func-
tion and the capability to place multiple mappings within a MAM PDU,
this further limiting of scope is not recommended at this time.
The ESGH PDU is sent using the "All Multicast Intermediate System Net-
work entities" SNPA address in the destination parameter field of its
subnetwork protocol. The support of the damping option requires that all
systems supporting a specific multicast PDU transfer monitor ESGHs sent
for a specific group Network address and thus this requires these ESGH
PDUs to be sent on a multicast address. The other possible SNPA address
to use is that which is paired to that group Network address; however,
this address may be pre-configured and may not be known to the Active
Multicast IS. This will lead to the Active Multicast IS missing the ESGH
PDUs announcing these addresses. Another concern with using the paired
SNPA address is that multiple group Network addresses can be announced
in the same ESGH PDU and these other group Network addresses would be
expected to use different paired SNPA addresses.
Appendix B. Differences with RFC 1112
This appendix is intended to identify differences between the mechanisms This appendix is intended to identify differences between the mechanisms
defined for CLNP Multicast in this specification and those for IP multi- defined for CLNP Multicast in this specification and those for IP multi-
cast defined in RFC 1112. The work on CLNP Multicast followed the work cast defined in RFC 1112. The work on CLNP Multicast followed the work
on IP multicast and was explicitly aimed at bringing the capabilities on IP multicast and was explicitly aimed at bringing the capabilities
described in RFC 1112 into a CLNP context. This appendix is intended to described in RFC 1112 into a CLNP context. This appendix is intended to
provide some background information on the difference; however, it is provide some background information on the difference; however, it is
not intended to justify the mechanisms selected for CLNP multicast use. not intended to justify the mechanisms selected for CLNP multicast use.
Static/Dynamic Address Binding of Multicast Datagrams Static/Dynamic Address Binding of Multicast Datagrams
skipping to change at page 36, line 33 skipping to change at page 38, line 33
scheme is very simple and efficient. Given the use of a 32 bit IP scheme is very simple and efficient. Given the use of a 32 bit IP
address, the lower 23 bits of the Class D address are mapped into the address, the lower 23 bits of the Class D address are mapped into the
lower 23 bits of a 48 bit IEEE 802 address where the upper 25 bits are lower 23 bits of a 48 bit IEEE 802 address where the upper 25 bits are
fixed. Static binding of this form is global in scope (all members of a fixed. Static binding of this form is global in scope (all members of a
group use the same IEEE 802 address on all subnets (at least all that group use the same IEEE 802 address on all subnets (at least all that
use IEEE 802 addressing). use IEEE 802 addressing).
CLNP multicast uses a dynamic binding of a group Network address (up to CLNP multicast uses a dynamic binding of a group Network address (up to
20 bytes) to any subnetwork address. In cases where no multicast capable 20 bytes) to any subnetwork address. In cases where no multicast capable
Intermediate Systems are attached to a subnetwork then a binding using Intermediate Systems are attached to a subnetwork then a binding using
preconfigured information or the "All Multicast End System Network enti- preconfigured information or the "All Multicast Capable End Systems"
ties" subnetwork addresses is used. The large GNA provides the room to subnetwork addresses is used. The large GNA provides the room to contain
contain a full 48 bit IEEE 802 address if desired. Mask capabilities a full 48 bit IEEE 802 address if desired. Mask capabilities are
are optionally provided which allow a multicast capable Intermediate optionally provided which allow a multicast capable Intermediate System
System to specify a "static" binding for a particular subnetwork. One of to specify a "static" binding for a particular subnetwork. One of the
the major purposes of providing a dynamic binding is to customize a major purposes of providing a dynamic binding is to customize a host's
host's subnetwork address usage to the capabilities of the attached sys- subnetwork address usage to the capabilities of the attached systems.
tems. There is considerable differences in the numbers of group subnet- There is considerable differences in the numbers of group subnetwork
work addresses that a system can recognize using hardware hooks built addresses that a system can recognize using hardware hooks built into
into the integrated circuits used. For example the number of addresses the integrated circuits used. For example the number of addresses that
that can be recognized by hardware may differ by an attached system can be recognized by hardware may differ by an attached system depending
depending upon the interface it uses (e.g. Ethernet interface and FDDI upon the interface it uses (e.g. Ethernet interface and FDDI within the
within the same system may have quite different capabilities). Dynamic same system may have quite different capabilities). Dynamic binding of
binding of this form is local in scope (members of a group may use dif- this form is local in scope (members of a group may use different sub-
ferent subnet addresses (e.g. IEEE 802 addresses) on different subnets). network addresses (e.g. IEEE 802 addresses) on different subnets).
Sourcing of Multicast Datagrams Originating of Multicast Datagrams
IP multicast sources multicast datagrams directly, where the host sourc- IP multicast originates multicast datagrams directly, where the host
ing a datagram sends it with the group Subnetwork address as its desti- originating a datagram sends it with the group Subnetwork address as its
nation. Hosts attached to the network where the datagram is sourced destination. Hosts attached to the network where the datagram is ori-
receive the datagram directly. ginated receive the datagram directly.
CLNP multicast sources multicast datagrams to the "All Multicast Inter- CLNP multicast originates multicast datagrams directly using the group's
mediate System Network entities" address if there is a multicast capable subnetwork address as its destination when multicast address mapping
Intermediate System attached to a subnetwork that the End System information is available. This case occurs when a multicast capable
sourcing the datagram is attached to. This requires an extra hop over Intermediate System is attached to the subnetwork and a host on the sub-
the IP multicast case when there are End Systems on the same subnetwork network is announcing an interest in multicast packets identified by a
which have requested to receive datagrams being sourced using a particu- particular group Network address. The Active Multicast IS may use MAM
lar GNA. When a multicast capable Intermediate System is not attached PDU mask parameters to provide multicast address mapping information for
to a subnetwork, the End System may utilize either preconfigured infor- a large number of group Network addresses. When there is no multicast
mation (which might be a direct mapping from a portion of the group Net- address mapping information for the particular group Network address on
work address) or use the "All Multicast End System Network entities" a subnetwork with a multicast capable IS attached to it, hosts originate
address. packets using such addresses sends to the "All Multicast Capable Inter-
mediate Systems" SNPA address. This case occurs when there are no
receivers of such multicast packets on the originating subnetwork. When
a multicast capable Intermediate System is not attached to a subnetwork,
the End System may utilize either preconfigured information (which might
be a direct mapping from a portion of the group Network address) or use
the "All Multicast Capable End Systems" address.
Address Binding of Control Packets Address Binding of Control Packets
IP multicast sends the control packets related to the IGMP protocol on IP multicast sends the control packets related to the IGMP protocol on
the same subnetwork address that is used by the multicast data traffic. the same subnetwork address that is used by the multicast data traffic.
CLNP multicast sends the control packets related to the ES-IS protocol CLNP multicast sends the control packets related to the ES-IS protocol
extensions on specific group subnetwork addresses (i.e. "All Multicast extensions on specific group subnetwork addresses (i.e. "All Multicast
End System Network entities" and "All Multicast Intermediate System Net- Capable End Systems" and "All Multicast Announcements" addresses).
work entities" addresses).
Router Requirements for relaying Multicast Datagrams Router Requirements for relaying Multicast Datagrams
IP multicast requires that a multicast router run in "promiscuous" mode IP multicast requires that a multicast router run in "promiscuous" mode
where it must receive all multicast datagrams sourced on a subnetwork where it must receive all multicast datagrams originated on a subnetwork
regardless of the destination. This is a result of the choices selected regardless of the destination. This is a result of the choices selected
in the "Sourcing of Multicast Datagrams" and "Address Binding of Control in the "Originating of Multicast Datagrams" and "Address Binding of Con-
Packets" discussed above. trol Packets" discussed above.
CLNP multicast allows a multicast router to only receive datagrams sent CLNP multicast allows a multicast router to limit multicast packet
to the "All Multicast Intermediate System Network entities" address. reception to only those datagrams sent to the SNPA addresses where there
This is a result of the choices selected in the "Sourcing of Multicast is current multicast address mapping information or to the "All Multi-
Datagrams" and "Address Binding of Control Packets" discussed above. cast Capable Intermediate Systems" address. The intention is to allow
the multicast routers to be in control of the SNPA addresses for multi-
cast packets that they need to receive. This is a result of the
choices selected in the "Originating of Multicast Datagrams" and
"Address Binding of Control Packets" discussed above.
Aggregation of Control Information Aggregation of Control Information
In IP multicast, a host is required to withhold an announcement report In IP multicast, a host is required to withhold an announcement report
upon hearing another host reporting a similar interest in a particular upon hearing another host reporting a similar interest in a particular
Class D address on a particular subnetwork. This is an option for CLNP Class D address on a particular subnetwork. This is an option for CLNP
multicast (upon hearing interest in a particular group Network address multicast (upon hearing interest in a particular group Network address
on a particular subnetwork). Such reports are not combined in IP multi- on a particular subnetwork). Such reports are not combined in IP multi-
cast while CLNP multicast supports providing multiple announcements (and cast while CLNP multicast supports providing multiple announcements (and
address mappings) within a single packet. A mask feature for address address mappings) within a single packet. A mask feature for address
skipping to change at page 38, line 22 skipping to change at page 40, line 30
IP multicast marks a multicast PDU via the use of an IP Class D address IP multicast marks a multicast PDU via the use of an IP Class D address
as its destination address parameter. CLNP multicast marks both the PDU as its destination address parameter. CLNP multicast marks both the PDU
(a different PDU type) and the destination address (i.e. group Network (a different PDU type) and the destination address (i.e. group Network
address) parameter. address) parameter.
Unicast Addressing Differences Unicast Addressing Differences
An IP address identifies a specific host interface while a CLNP indivi- An IP address identifies a specific host interface while a CLNP indivi-
dual Network address (i.e. NSAP address) identifies a particular Network dual Network address (i.e. NSAP address) identifies a particular Network
entity. This difference has not impacted a difference with RFC 1112; entity. This difference has lead to a difference with RFC 1112. IP
however, this may impact using the techniques developed for IP multicast multicast requires a host which is attached to more than one subnetwork
in a CLNP multicast context. to originate a multicast packet on only one subnetwork. CLNP multicast
requires a host which is attached to more than one subnetwork to ori-
ginate a multicast packet on every subnetwork that the ISO ES-IS Confi-
guration function is reporting the NSAP address contained in the source
address parameter of the multicast PDU.
Error Reports Error Reports
Error reports sent in response to receiving a multicast PDU are not per- Error reports sent in response to receiving a multicast PDU are not per-
mitted in IP multicast while they are permitted in CLNP multicast. mitted in IP multicast while they are permitted in CLNP multicast.
Source Routing Source Routing
Source routing of multicast PDUs are permitted in IP multicast (but at Source routing of multicast PDUs are permitted in IP multicast (but at
the present time this is discouraged) while they are not permitted in the present time this is discouraged) while they are not permitted in
CLNP multicast. CLNP multicast.
Appendix C. Issues Under Study Appendix B. Issues Under Study
1. Packets Traversing a Subnet Twice
The multicast extensions to CLNP were developed to be as free from con-
siderations of multicast routing as possible. A certain number of
assumptions concerning multicast routing were made in the developments
of the extensions to the ES-IS routing protocol (these extensions are
described in section 6.). A key assumption was that PDU transmissions
on a subnet involving hosts would be separated from PDU forwarding.
This is in-line with the present ISO unicast routing architecture. Thus
PDU sourcing, in the presence of a multicast capable router would be
separate from PDU forwarding to other hosts even if they are on the same
subnet. This results in the same Data PDU being sent twice when: (1)a
subnet has members of a group attached and (2)a packet needs to be for-
warded to one or more routers via that subnet.
Concern has been expressed since the immediate application for multicast
involves sending real time data in support of multi media applications.
Such exchanges may already using a significant proportion of a subnet's
bandwidth and doubling the bandwidth used in this case may not be
acceptable.
Note that the only piece of this problem that this Internet Draft covers This appendix is intended to record the current issues (as discussed at
is the sourcing of a packet in the presense of multicast capable the March 1994 TUBA meeting).
routers. The other issues are involved in multicast routing which is
not addressed by this Internet Draft.
2. Local versus Global address bindings 1. Local versus Global address bindings
The extensions to the ES-IS protocol provide a multicast address mapping The extensions to the ES-IS protocol provide a multicast address mapping
function which supports dynamically binding a group Network address to a function which supports dynamically binding a group Network address to a
subnetwork address. Concern has been expressed that this is an unneces- subnetwork address. Concern has been expressed that this is an unneces-
sary feature which complicates the job of network administrators without sary feature which complicates the job of network administrators without
suitable benefit. A static, global binding of group Network addresses suitable benefit. A static, global binding of group Network addresses
to IEEE 802 subnet addresses has been suggested. to IEEE 802 subnetwork addresses, as is used by IP multicast has been
suggested.
The two main reasons that the group Network address to subnet (IEEE 802) The two main reasons that the group Network address to subnetwork (IEEE
address was made locally configurable were to support multicast on sub- 802) address was made locally configurable were to support multicast on
nets with hosts having a mixture of capabilities (as to how many multi- subnets with hosts having a mixture of capabilities (as to how many mul-
cast subnet addresses a host could register to receive at a time) and to ticast subnetwork addresses a host could register to receive at a time)
support multicast on subnets that do not use 48 bit IEEE 802 addresses. and to support multicast on subnets that do not use 48 bit IEEE 802
Thus it was felt that this should be done per subnet versus globally. addresses. Thus it was felt that this should be done per subnetwork
Even multi-homed hosts with subnets that use 802 addresses may have versus globally. Even multi-homed hosts with subnets that use 802
varying capabilities (looking at typical Ethernet, FDDI and 802.5 imple- addresses may have varying capabilities (looking at typical Ethernet,
mentations). FDDI and 802.5 implementations).
One possible solution is to recommend a direct mapping in any Internet One possible solution is to recommend a direct mapping in any Internet
use of CLNP multicast on subnets which use IEEE 802 addressing. This use of CLNP multicast on subnets which use IEEE 802 addressing. This
could be a default for all Internet hosts. A policy would be needed to could be a default for all Internet hosts. A policy would be needed to
identify the Internet's group Network address format. Given such a map- identify the Internet's group Network address format. Given such a map-
ping the only operational overhead that would occur is that in the pres- ping the only operational overhead that would occur is that in the pres-
ence of a mapping server (the Active Multicast IS), which was supporting ence of a mapping server (the Active Multicast IS), which was supporting
this mapping, a MAM PDU would periodically be sent with a Group Network this mapping, a MAM PDU would periodically be sent with a Group Network
Address Mask which would identify the direct mapping. Address Mask which would identify the direct mapping.
2. "Real Time" Scope Control Features
The scope control features are provided via optional parameters. Use of
multicast transfer of audio and video streams may require scope control
mechanisms which operate very quickly.
One possible solution is to embed scope control mechanisms into the
group Network address itself. For example, a group Network address
using the "Local" AFI is automatically limited to not cross inter-domain
borders. Further, more flexible, address formats may be developed.
References References
[Deering91] S.E. Deering. Multicast Routing in a Datagram Internetwork. [Deering91] S.E. Deering. Multicast Routing in a Datagram Internetwork.
PhD thesis, Electrical Engineering Dept., Stanford University, December PhD thesis, Electrical Engineering Dept., Stanford University, December
1991. 1991.
[RFC1112] Host Extensions for IP Multicasting, Network Working Group, [RFC1112] Host Extensions for IP Multicasting, Network Working Group,
RFC 1112, S. Deering, August 1989. RFC 1112, S. Deering, August 1989.
[RFC1237] Guidelines for OSI NSAP Allocation in the Internet, Network [RFC1237] Guidelines for OSI NSAP Allocation in the Internet, Network
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