PMIPv6 multicast handover optimization by the Subscription Information Acquisition through the LMA (SIAL)
draft-ietf-multimob-handover-optimization-00
The information below is for an old version of the document.
| Document | Type |
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|---|---|---|---|
| Authors | Luis M. Contreras , Carlos J. Bernardos , Ignacio Soto | ||
| Last updated | 2012-11-29 | ||
| Replaces | draft-ietf-multimob-fast-handover | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
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draft-ietf-multimob-handover-optimization-00
MULTIMOB Working Group LM. Contreras
Internet-Draft Telefonica I+D
Intended status: Experimental CJ. Bernardos
Expires: June 1, 2013 I. Soto
UC3M
November 28, 2012
PMIPv6 multicast handover optimization by the Subscription Information
Acquisition through the LMA (SIAL)
draft-ietf-multimob-handover-optimization-00
Abstract
This document specifies a multicast handover optimization mechanism
for Proxy Mobile IPv6 to accelerate the delivery of multicast traffic
to mobile nodes after handovers. The mechanism is based on speeding
up the acquisition of mobile nodes' multicast context by the mobile
access gateways. To do that, extensions to the current Proxy Mobile
IPv6 protocol are proposed. These extensions are not only applicable
to the base solution for multicast support in Proxy Mobile IPv6, but
they can also be applied to other solutions being developed to avoid
the tunnel convergence problem. Furthermore, they are also
independent of the role played by the mobile access gateway within
the multicast network (either acting as multicast listener discovery
proxy or multicast router).
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on June 1, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. PMIPv6 extensions . . . . . . . . . . . . . . . . . . . . . . 8
4.1. New mobility option . . . . . . . . . . . . . . . . . . . 8
4.1.1. Active Multicast Subscription mobility option . . . . 8
4.1.1.1. Option application rules . . . . . . . . . . . . . 8
4.1.1.2. Option format . . . . . . . . . . . . . . . . . . 8
4.2. New flags . . . . . . . . . . . . . . . . . . . . . . . . 9
4.2.1. Multicast Signaling flag on PBU/PBA message headers . 9
4.2.1.1. Flag application rules . . . . . . . . . . . . . . 9
4.2.1.1.1. Registration process . . . . . . . . . . . . . 9
4.2.1.1.2. De-registration process . . . . . . . . . . . 10
4.2.1.2. New format of conventional PBU/PBA messages . . . 11
4.2.1.2.1. Proxy Binding Update message . . . . . . . . . 11
4.2.1.2.2. Proxy Binding Acknowledgement Message . . . . 11
4.2.2. Multicast Active flag in the LMA Binding Cache and
(optionally) on the MN's policy store . . . . . . . . 11
4.2.2.1. Flag application rules . . . . . . . . . . . . . . 11
4.3. New messages . . . . . . . . . . . . . . . . . . . . . . . 12
4.3.1. Messages for active multicast subscription
interrogation . . . . . . . . . . . . . . . . . . . . 12
4.3.1.1. Subscription Query message . . . . . . . . . . . . 13
4.3.1.1.1. Message application rules . . . . . . . . . . 13
4.3.1.1.2. Message format . . . . . . . . . . . . . . . . 13
4.3.1.2. Subscription Response message . . . . . . . . . . 14
4.3.1.2.1. Message application rules . . . . . . . . . . 14
4.3.1.2.2. Message format . . . . . . . . . . . . . . . . 14
4.3.2. Messages for active multicast subscription
indication . . . . . . . . . . . . . . . . . . . . . . 15
4.3.2.1. Multicast Activity Indication message . . . . . . 15
4.3.2.1.1. Message application rules . . . . . . . . . . 16
4.3.2.1.2. Message format . . . . . . . . . . . . . . . . 16
4.3.2.2. Multicast Activity Indication Acknowledge
message . . . . . . . . . . . . . . . . . . . . . 17
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4.3.2.2.1. Message application rules . . . . . . . . . . 17
4.3.2.2.2. Message format . . . . . . . . . . . . . . . . 17
4.4. New PBA timer in the LMA . . . . . . . . . . . . . . . . . 18
5. Signaling processes description . . . . . . . . . . . . . . . 18
5.1. Multicast Activity signaling . . . . . . . . . . . . . . . 18
5.1.1. Multicast Activity set to ON (A=1) . . . . . . . . . . 19
5.1.2. Multicast Activity set to OFF (A=0) . . . . . . . . . 20
5.2. Handover signaling procedures . . . . . . . . . . . . . . 20
5.2.1. Handover of proactive type . . . . . . . . . . . . . . 21
5.2.1.1. Rationale . . . . . . . . . . . . . . . . . . . . 21
5.2.1.2. Message flow description . . . . . . . . . . . . . 21
5.2.2. Handover of reactive type . . . . . . . . . . . . . . 23
5.2.2.1. Rationale . . . . . . . . . . . . . . . . . . . . 23
5.2.2.2. Message flow description . . . . . . . . . . . . . 24
5.2.2.3. Further considerations for the reactive
handover signaling . . . . . . . . . . . . . . . . 27
5.2.3. LMA decision process . . . . . . . . . . . . . . . . . 28
5.2.3.1. LMA processing of S flag on reception of PBU
messages . . . . . . . . . . . . . . . . . . . . . 28
5.2.3.1.1. Proactive handover . . . . . . . . . . . . . . 28
5.2.3.1.2. Reactive handover . . . . . . . . . . . . . . 29
5.2.3.2. LMA set-up of S flag in PBA messages . . . . . . . 30
5.2.4. Prevention of large delays of the binding
acknowledgement for unicast traffic . . . . . . . . . 31
6. Co-existence with PMIPv6 multicast architectural evolutions . 34
7. Security Considerations . . . . . . . . . . . . . . . . . . . 34
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 36
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 36
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 36
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 37
11.1. Normative References . . . . . . . . . . . . . . . . . . . 37
11.2. Informative References . . . . . . . . . . . . . . . . . . 37
Appendix A. Performance comparison with base solution . . . . . . 38
A.1. Delay characterization of the base solution . . . . . . . 38
A.2. Delay characterization of the SIAL solution . . . . . . . 39
A.3. Performance comparison . . . . . . . . . . . . . . . . . . 40
Appendix B. Change Log . . . . . . . . . . . . . . . . . . . . . 41
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42
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1. Introduction
The base solution describing how continuous multicast service
delivery can be provided in Proxy Mobile IPv6 domains is described in
RFC 6224 [RFC6224]. This solution specifies the basic functionality
needed in the Proxy Mobile IPv6 [RFC5213] entities to provide a
multicast service, and supports the continuous delivery of multicast
traffic by obtaining, after a handover, the on-going multicast
subscription information directly from the mobile node. When a
mobile node attaches to a new mobile access gateway, the mobile node
is interrogated by the mobile access gateway through a multicast
listener discovery General Query, which is sent just after any new
link is set up, to get knowledge of any existing subscription, as
specified in [RFC2710].
However, as highlighted by [I-D.von-hugo-multimob-future-work], the
base solution needs to be improved to meet some performance
requirements, especially those referred to the user perceived service
quality, which is seriously affected by the disruption of multicast
content forwarding to the mobile node during handovers.
A mobile node with an active multicast subscription, moving from one
point of attachment to another within a Proxy Mobile IPv6 domain,
experiences a certain delay until it resumes receiving again the
multicast content that it was receiving at the previous location.
Such delay causes a gap in the content reception. Two different
actions can help to mitigate such reception gap. One of them is to
buffer at the previous mobile access gateway the traffic with
destination at the mobile node and forward it to the new mobile
access gateway, in order to deliver that traffic to the mobile node.
The other possible (complementary) action is to reduce the time
needed by the new mobile access gateway to get knowledge of the
active multicast subscription of the mobile node (i.e., the multicast
context), so the new mobile access gateway can subscribe to the
multicast group(s) on behalf of the mobile node as soon as possible.
While the first mechanism could potentially be accomplished by using
some adaptation of [RFC5949] to multicast traffic (despite being only
applicable in the case the underlying radio access technology
supports layer-2 triggers, thus requiring additional support on the
mobile node), there is no a generic standard solution for the
accelerated acquisition of the on-going multicast subscription of the
mobile node.
The approach followed by the base solution [RFC6224] to get knowledge
of an existing multicast subscription relies on the behavior of the
IGMP/MLD protocols. Both protocols send multicast membership
interrogation messages when a new link is up. The response to such a
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message reports any existing multicast subscription by the mobile
node. While this is a straightforward approach, it also causes that
the mobile access gateway can incur in a non-negligible delay in
receiving the corresponding MLD Report message. This delay is caused
by the time needed for the detection of the attachment in the new
link and the re-establishment of the data plane after the handover,
the radio transfer delays associated with the signaling to the mobile
node, and the MLD query response interval time required by this
procedure (whose default value is 10 seconds as defined in [RFC2710],
or between 5 and 10 seconds as considered in the best case wireless
link scenario in [RFC6636]).
This document extends the Proxy Mobile IPv6 signaling protocol
defined in the base protocol [RFC5213] by including a new multicast
information option to update Proxy Mobile IPv6 entities during the
registration and de-registration processes, and new messages to
trigger the transfer of multicast information. No extension is
required in any of the multicast-related protocols in use (IGMP/MLD
or PIM protocols). This document provides a signaling method
internal to the network to speed up the subscription information
acquisition by the mobile access gateway, in order to accelerate the
multicast delivery to the mobile node after having completed a
handover. By doing so, the knowledge by the mobile access gateway of
the currently active multicast subscription becomes independent of
the underlying radio technology dynamics and relaxes the requirement
of a rapid response from the mobile node in processing MLD control
messages. Issues like radio framing, radio access contention,
channel reliability, MN's capabilities (i.e., layer-2 triggering
support), IGMP/MLD timers optimization for wireless environments,
etc, will not impact on the observed multicast performance during
handovers.
The solution described in this document can also be applied to the
solutions described in [I-D.ietf-multimob-pmipv6-ropt]. Furthermore,
it is also independent of the role played by the mobile access
gateway within the multicast network (either acting as MLD proxy or
multicast router).
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119].
This document uses the terminology referring to PMIPv6 components as
defined in [RFC5213].
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Additionally, the following terms are defined.
pMAG: The previous MAG or pMAG is the MAG where the MN is initially
registered in a handover event.
nMAG: The new MAG or nMAG is the MAG where the MN is registered at
the end of the handover event.
Reactive Handover: A reactive handover is a handover event in which
the LMA receives the MN registration from the nMAG without having
previously received the MN de-registration from the pMAG.
Proactive handover: A proactive handover is a handover event where
the MN is firstly de-registered on the LMA by the pMAG, and later
on it is registered by the nMAG as consequence of changing the
point of attachment.
Multicast context: Along this document, multicast context makes
reference to the information relative to the currently active
multicast subscription of a MN in a handover event which is
transferred between the PMIPv6 entities to support the handover
optimization. The information comprising the multicast context is
transferred by using the Multicast Address record format as
defined in [RFC3810].
3. Overview
The LMA is a key element within the PMIPv6 infrastructure, which
traces the MN reachability along the PMIPv6 domain. Therefore the
LMA is the best element to maintain the MNs' multicast subscription
information updated and to forward it to the rest of PMIPv6 entities
(i.e., to the MAGs) as needed when MNs move within the domain. The
LMA has timely knowledge of the MNs' location, especially during
handover events, and it is therefore able to quickly provide
information to the new one point of attachment (querying the previous
one if required). Figure 1 shows this idea.
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+------+
| pMAG | |
+------+ |
/ |
/ |
/ |
/ |
-*-*-*-*- / (MN)
( ) / |
( ) +-----+ +------+ |
( Internet )--| LMA |------| nMAG | v
( ) +-----+ +------+
( )
-*-*-*-*- Registration
<--------------
Registration Ack
& Multicast Context
-------------->
Figure 1: High level solution description
The LMA only obtains the detailed subscription information or
multicast context during a handover event. There is no need of
continuously informing the LMA about MNs' multicast state while the
mobile nodes remain attached to the same mobile access gateway. Such
a continuous updating procedure would significantly increase the
signaling load within the PMIPv6 domain without a clear benefit. The
multicast context is only critical during handovers, neither after
nor before. Indicating the active subscription while the handover is
ongoing guarantees that such information will be up-to-date, ready to
be transferred to the new MAG where the MN has just attached.
However it should be noted that some signaling is needed to
differientate what MNs are maintaining active subscriptions in order
to restrict the optimization procedure to them in case of handover.
To be able to transfer the multicast subscription information between
PMIPv6 entities during a handover, this document extends the PMIPv6
protocol in several ways. First of all, a new mobility option is
defined to carry the multicast context of the current subscription.
Furthermore, additional messages are defined to manage the
interchange of the multicast information among PMIPv6 entities.
Finally, some flags are defined to govern the process.
Next sections provide the details of these Proxy Mobile IPv6 protocol
extensions.
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4. PMIPv6 extensions
This section outlines the extensions proposed to the PMIPv6 protocol
specified in [RFC5213].
4.1. New mobility option
4.1.1. Active Multicast Subscription mobility option
4.1.1.1. Option application rules
A new TLV-encoded mobility option, "Active Multicast Subscription"
option is defined for use with the PBU (Proxy Binding Update) and PBA
(Proxy Binding Acknowledge) messages exchanged between an LMA and a
MAG to transfer the multicast subscription information. This option
is used for exchanging the multicast context. This information is
carried by using directly the Multicast Address Record format defined
in [RFC3810]. There can be multiple "Active Multicast Subscription"
options present in the message, one for each active subscription
maintained by the MN when the handover is taking place (i.e., one per
Multicast Address Record).
This new option will be also used, with the same aim, by the new
message Subscription Response described later in this document.
4.1.1.2. Option format
The format of this new option is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Multicast Address Record +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type:
To be defined by IANA.
Length:
8-bit unsigned integer indicating the length of the option in
octects, excluding the type and length fields.
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Multicast Address Record:
Multicast subscription information corresponding to a single
subscribed multicast address as defined in [RFC3810].
4.2. New flags
Two new flags are defined and used to handle the forwarding of
multicast subscription information.
4.2.1. Multicast Signaling flag on PBU/PBA message headers
4.2.1.1. Flag application rules
A new flag S is added in both PBU and PBA message headers to advise
about the MAG and the LMA capabilities of processing multicast-
related signaling for the MN that caused the message.
This flag will govern the multicast-related signaling between the LMA
and the MAG. As a general rule, the value of the flag in the PBA
message SHOULD be a copy of the value received in the PBU message.
Specific rules are described in next sub-sections.
4.2.1.1.1. Registration process
During handover, the entities involved in this process are the nMAG
and the LMA. These rules also apply for the Initial Binding
registration process.
o PBU message
* S=0, it indicates that the MAG sending the PBU message does not
accept multicast-related signaling for the MN being attached.
This can be used to discriminate PMIPv6 nodes which are not
multicast enabled, for backward compatibility reasons.
* S=1, it indicates that the MAG sending the PBU message accepts
multicast-related signaling for the MN being attached.
Depending on the type of handover (reactive or proactive) the
LMA will take some actions, described later in this document.
o PBA message
* If S=0 in the corresponding PBU message, the value of the flag
in the PBA message SHOULD be a copy of the value received in
the PBU message (thus S=0), without any further meaning.
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* If S=1 in the corresponding PBU message, two sub-cases can
happen
+ S=1 and "Active Multicast Subscription" mobility option in
the PBA message. When the MN maintains an active multicast
session, if the LMA is able to provide the multicast
subscription information during registration, the PBA
message will include the "Active Multicast Subscription"
mobility option. If the LMA is not able to provide such
information during registration, the PBA message will not
include the "Active Multicast Subscription" mobility option.
This case is useful to decouple unicast and multicast
signaling for an MN being registered at nMAG. A way for
obtaining later active multicast-subscription information is
described later in this document.
+ S=0 in the PBA message if the MN does not maintain an active
multicast subscription (note that for backward compatibility
reasons an LMA not supporting multicast related signaling
would always send S=0).
4.2.1.1.2. De-registration process
During handover, the entities involved in this process are the pMAG
and the LMA. These rules apply for the Binding De-registration
process
o PBU message
* S=0, it indicates that the MN has no active multicast session
(note that for backward compatibility reasons a pMAG not
supporting multicast related signaling would always send S=0).
* S=1, it indicates that the MN has an active multicast session,
and the multicast context is transported in the "Active
Multicast Subscription" mobility option.
o PBA message
* The value of the flag in the PBA message SHOULD be 0, without
any further meaning (note that for backward compatibility
reasons an LMA not supporting multicast related signaling would
always send S=0).
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4.2.1.2. New format of conventional PBU/PBA messages
4.2.1.2.1. Proxy Binding Update message
As result of the new defined flag, the PBU message results as
follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|A|H|L|K|M|R|P|S| Reserved | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.2.1.2.2. Proxy Binding Acknowledgement Message
As result of the new defined flag, the PBA message results as
follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Status |K|R|P|S| Rsrvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # | Lifetime |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4.2.2. Multicast Active flag in the LMA Binding Cache and (optionally)
on the MN's policy store
4.2.2.1. Flag application rules
A new flag A is added in the LMA Binding Cache to retain the
knowledge that the registered MN maintains or not an active multicast
subscription. The basic use of this flag is to restrict the
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interrogation of the pMAG only to the cases in which the MN certainly
is maintaining an active subscription. The algorithm which is
followed by the LMA to interrogate or not the pMAG (after receiving a
PBU message from the nMAG) is as follows:
o Flag S=0 & flag A=0: this situation represents the case where the
nMAG does not support multicast-related signaling for the MN being
registered, and, additionally, the LMA is not aware of any active
multicast subscription on-going. Then, the LMA does not
interrogate the pMAG, and registers the MN as attached to the nMAG
as usual.
o Flag S=0 & flag A=1: this situation represents the case where the
nMAG does not support multicast-related signaling for the MN being
registered, but the LMA is aware of one or more on-going MN's
active multicast subscriptions. Due to the fact that multicast
signaling is not supported by the nMAG for that MN, the LMA does
not interrogate the pMAG, and registers the MN as attached to the
nMAG as usual.
o Flag S=1 & flag A=0: this situation represents the case where the
nMAG supports multicast-related signaling for the MN being
registered, but the LMA is not aware of any active multicast
subscription. Then, the LMA does not interrogate the pMAG, and
registers the MN as attached to the nMAG as usual.
o Flag S=1 & flag A=1: this situation represents the case where the
nMAG supports multicast-related signaling for the MN being
registered, and, additionally, the LMA is aware of one or more on-
going MN's active multicast subscriptions. Then, the LMA
interrogates the pMAG to obtain the multicast context details
previously to complete the registration of the MN attached to the
nMAG.
The flag A SHOULD be initialized to the value 0.
Optionally, this flag can be also added to the MN's policy store, and
dynamically updated by the LMA to signal that the MN has (or not) an
active multicast subscription. By introducing this flag in the MN's
policy profile, the nMAG can know in advance the existence of an
active multicast session by the incoming MN.
4.3. New messages
4.3.1. Messages for active multicast subscription interrogation
A new pair of messages is defined for interrogating entities about
the active multicast subscription of the MN when the handover is of
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reactive type.
These messages are sent using the Mobility Header as defined in
[RFC6275].
4.3.1.1. Subscription Query message
4.3.1.1.1. Message application rules
The Subscription Query message is sent by the LMA towards the pMAG to
interrogate it about any existing multicast subscription of the MN
which is being registered by the nMAG. This message is generated in
case that the handover is of reactive type.
Additionally, this message is sent by the nMAG towards the LMA to
interrogate it about the existing multicast subscription of the MN
when the LMA acknowledges the PBU sent by the nMAG but the multicast
context is not provided (in detail, when the PBU messages has set the
flag S to 1, and the PBA message has set the flag S to 1 but the
multicast context is missing).
4.3.1.1.2. Message format
The Subscription Query message has the following format.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sequence Number:
The Sequence Number field establishes the order of the messages
sent in the Subscription Query / Subscription Response dialogue
between the LMA and the MAG for a certain MN. The initial
Sequence Number will be determined by the entity which creates the
message (either LMA or MAG, depending on the scenario), which will
be responsible of managing this counter.
Reserved:
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This field is unused for now. The value MUST be initialized to 0.
Mobility options:
This message will carry one or more TLV-encoded mobility options.
The valid mobility options for this message are the following:
* Mobile Node Identifier option (mandatory)
* Home Network Prefix option (optional)
There can be one or more instances of the Home Network Prefix
option, but only one instance of the Mobile Node Identifier
option.
4.3.1.2. Subscription Response message
4.3.1.2.1. Message application rules
The Subscription Response message is sent by the pMAG towards the
LMA, or by the LMA towards the nMAG, to answer a previously received
Subscription Query message, as described above.
4.3.1.2.2. Message format
The Subscription Response message has the following format.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |I| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sequence Number:
The value of the Sequence Number field in the Subscriber Response
message MUST be a copy of the Sequence Number received in the
Subscription Query message.
Multicast Information (I):
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The multicast Information flag I specifies if there is multicast
subscription information available for the MN or not. The meaning
is the following:
I=0: there is no multicast subscription information available
for the MN identified by the Mobile Node Identifier option in
this message.
I=1: there is multicast subscription information available for
the MN identified by the Mobile Node Identifier option in this
message. The multicast subscription information is carried on
one or more instances of the Active Multicast Subscription
option in this message (one instance for each active
subscription).
Reserved:
This field is unused for now. The value MUST be initialized to 0.
Mobility options:
This message will carry one or more TLV-encoded mobility options.
The valid mobility options for this message are the following:
* Mobile Node Identifier option (mandatory)
* Active Multicast Subscription option (mandatory) only when flag
I=1, not present in any other case
* Home Network Prefix option (optional)
There can be one or more instances of the Home Network Prefix
option (in all cases) and the Active Multicast Subscription option
(only when I=1), but only one instance of the Mobile Node
Identifier option.
4.3.2. Messages for active multicast subscription indication
A new pair of messages is defined for setting up and down the
optional A flag defined above.
These messages are sent using the Mobility Header as defined in
[RFC6275].
4.3.2.1. Multicast Activity Indication message
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4.3.2.1.1. Message application rules
The Multicast Activity Indication message is sent by a MAG towards
the LMA to set to 1 or 0 the A flag either to indicate the start or
the complete cease of any multicast subscription by the MN. Through
the use of this message, the LMA becomes aware that one or more
multicast flows are being forwarded to a MN. This information is
useful for the LMA during a handover to discriminate if the pMAG
needs to be asked or not about multicast information corresponding to
the MN being registered at the nMAG, in case that the handover is of
reactive type.
4.3.2.1.2. Message format
The Multicast Activity Indication message has the following format.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # |A| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sequence Number:
The Sequence Number field establishes the order of the messages
sent in the Activity Indication / Activity Indication Ack dialogue
between the MAG and the LMA for a certain MN. The initial
Sequence Number will be determined by the MAG, which will be
responsible of managing this counter.
Activity indicator (A):
The Activity indicator flag A specifies if the MN multicast
activity is on, that is, if the MN maintains one or more active
multicast subscriptions at the MAG. The meaning is the following:
A=0: the multicast activity of the MN (identified by the Mobile
Node Identifier option in this message) is OFF.
A=1: the multicast activity of the MN (identified by the Mobile
Node Identifier option in this message) is ON.
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Reserved:
This field is unused for now. The value MUST be initialized to 0.
Mobility options:
This message will carry one or more TLV-encoded mobility options.
The valid mobility options for this message are the following:
* Mobile Node Identifier option (mandatory)
* Home Network Prefix option (optional)
There can be one or more instances of the Home Network Prefix
option, but only one instance of the Mobile Node Identifier
option.
4.3.2.2. Multicast Activity Indication Acknowledge message
4.3.2.2.1. Message application rules
The Multicast Activity Indication Acknowledge message is sent by the
LMA towards a MAG to confirm the reception of a previously sent
Multicast Activity Indication message.
4.3.2.2.2. Message format
The Multicast Activity Indication message has the following format.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence # | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Mobility options .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Sequence Number:
The value of the Sequence Number field in the Activity Indication
Ack message MUST be a copy of the Sequence Number received in the
Activity Indication message.
Reserved:
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This field is unused for now. The value MUST be initialized to 0.
Mobility options:
This message will carry one or more TLV-encoded mobility options.
The valid mobility options for this message are the following:
* Mobile Node Identifier option (mandatory)
* Home Network Prefix option (optional)
There can be one or more instances of the Home Network Prefix
option, but only one instance of the Mobile Node Identifier
option.
4.4. New PBA timer in the LMA
A new timer named "PBA timer" is used in the LMA to define the
maximum waiting time before the PBA message is sent to the nMAG in
case the multicast subscription information relative to the MN is not
yet available. The aim of this timer is to prevent potential large
delays in the forwarding of unicast traffic towards the MN being
registered at the nMAG. This timer allows decoupling the unicast
signaling from the multicast one.
This timer SHOULD be upper bounded by the constant defined in
[RFC6275] INIT_BINDACK_TIMEOUT, whose default value is 1 s. This
constant sets the time when the nMAG will retry the MN registration
by sending again the PBU message. The "PBA timer" has to ensure that
the nMAG does not enter the retry mode.
5. Signaling processes description
A number of new signaling processes are introduced with this
solution. Next sections describe these new processes in detail.
5.1. Multicast Activity signaling
This solution makes use of the flag A to keep track of existing
multicast activity in a certain MN. The idea behind this is to
define a mechanism which helps the LMA to decide whether to
interrogate or not the pMAG about potential subscription information.
This signaling message is used to allow the LMA to distinguish among
MNs with on-going multicast subscription, and MN without active
multicast status. This differentiation further allows to apply the
optimization procedure only to those MNs with active multicast
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subscription (no actions are taken for MN without active multicast
subscription).
5.1.1. Multicast Activity set to ON (A=1)
Figure 2 summarizes this process.
+-----+ +-----+ +-----+
| MN1 | | MAG | | LMA |
+-----+ +-----+ +-----+
| | |
1) | |==Bi-Dir Tunnel=|
| | |
| unicast data | |
|<-v-v-v-v-v-v-v-| |
| | |
| MLD Rep(S,G) | |
|--------------->| Act Ind(start) |
2) | |--------------->|
| (S,G) Data | (flag A = 1)
|<---------------| Act Ind Ack |
| |<---------------|
| | |
Figure 2: Multicast Activity set to ON
The sequence of messages is the following:
1. An MN, named MN1, is attached to the MAG. The MN is a multicast-
enabled node, and it is only receiving unicast traffic as usual
in PMIPv6 domains, with no multicast subscription yet. At some
point in time, the MN1 requests to the MAG to be subscribed to
the content identified by the IP addresses (S,G), by sending a
standard MLD report from the MN to the MAG. The MAG will keep
the multicast status state of the point-to-point link with the
MN. In case the MAG has not already subscribed to the multicast
flow (S,G) it joins the content on behalf of MN. Multicast flow
(S,G) is subsequently forwarded by the MAG to the MN1.
2. Due to this initial multicast subscription for the MN1, the MAG
triggers the multicast Activity Indication message towards the
LMA, to indicate that the MN1 multicast activity is ON. The LMA
will set the flag A to 1. Afterwards, the LMA sends an Activity
Indication Ack message to the MAG to acknowledge the previous
indication.
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5.1.2. Multicast Activity set to OFF (A=0)
Figure 3 presents the corresponding flow.
+-----+ +-----+ +-----+
| MN1 | | MAG | | LMA |
+-----+ +-----+ +-----+
| | |
| MLD Done(S,G) | |
1) |---------------->X stops fwrding |
| | |
| | Act Ind(stop) |
2) | |--------------->|
| | (flag A = 0)
| | Act Ind Ack |
| |<---------------|
| | |
Figure 3: Multicast Activity set to OFF
The message flow is as follows:
1. Some time later, the MN1 decides to totally stop all the active
multicast subscriptions that it maintains. The MN1 will send an
MLD Done message to the MAG to request the cease of the multicast
traffic delivery. As a consequence, the MAG will stop all the
multicast traffic forwarding to the MN1.
2. After removing the active subscriptions for the MN1, the MAG
sends a multicast Activity Indication message to the LMA
indicating that the MN1 multicast activity is OFF. The LMA will
set the flag A to 0, its default value. Afterwards, the LMA
sends an Activity Indication Ack message to the MAG to
acknowledge the previous indication.
5.2. Handover signaling procedures
As the MN moves from one access gateway to another, the mobility-
related signaling due to the handover event is carried out
independently by the pMAG and the nMAG. That signaling process is
not synchronized and, thus, two scenarios need to be considered
depending on the order in which the LMA receives notification of the
MN registration and de-registration in the nMAG and the pMAG
respectively.
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5.2.1. Handover of proactive type
5.2.1.1. Rationale
In the proactive case, the MN is firstly de-registered by the pMAG,
and later on it is registered by the nMAG as consequence of changing
the point of attachment.
Only for those MNs which maintain an active multicast subscription,
the pMAG will include, as part of the PBU message (with flag S set to
1), the new TLV-encoded mobility option "Active Multicast
Subscription" carrying the multicast context of the MN at that
moment.
The LMA will store that information in the corresponding binding
cache. If, later on, the MN attaches to a nMAG, this information
will be sent (using the same TLV option) to the nMAG as part of the
PBA confirmation of the registration process (the PBU message sent by
the nMAG SHOULD set the flag S to 1). On the other hand, if no
further registration happens, the multicast information will be
removed together with the rest of binding database for that MN.
After receiving the multicast context, the nMAG can subscribe to the
multicast flow(s) on behalf of the MN if there is no other MN
receiving it already at the nMAG. The multicast status can be also
set in advance for the point-to-point link towards the MN.
Note that the solution described here does not prevent benefiting
from extended support in the mobile node/network that facilitates the
proactive mode operation of the solution, e.g., based on layer-2
capabilities.
5.2.1.2. Message flow description
Figure 4 summarizes this process.
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+-----+ +----+ +-----+ +----+
| MN | |pMAG| | LMA | |nMAG|
+-----+ +----+ +-----+ +----+
| | | |
| |==Bi-Dir Tunnel=| |
| Multicast Data | | |
|<---------------| | |
| | | |
1) MN Detached | | |
| MN Detached Event | |
| | | |
| |Ext'd DeReg PBU | |
2) | |--------------->| |
| | | |
3) | | Accept PBU |
| |(Multicast Subscription info stored)
| | | |
| | PBA | |
4) | |<---------------| |
| | | |
5) MN Attached | | |
| | | MN Attached Event
| | | |
| | | PBU |
6) | | |<---------------|
| | | |
| | | Ext'd PBA |
7) | | |--------------->|
| | | |
8) | | | Accept PBA,
| | | Multicast Group join
| | | and P-t-P status setup
| | | |
| | |==Bi-Dir Tunnel=|
| | | |
| | | Multicast Data |
|<-------------------------------------------------|
| | | |
| | | |
Figure 4: Proactive handover
The message flow is as follows:
1. A registered MN is receiving a multicast content which has been
previously subscribed to by sending a standard MLD report from
the MN to the currently serving MAG, pMAG. The pMAG keeps the
multicast status state of the point-to-point link with the MN.
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2. The MN perceives a better radio link and decides to initiate a
handover process over a radio access controlled by a new MAG,
nMAG. As a consequence, pMAG determines a detach event
corresponding to this MN, and updates the attachment status of
this MN to the LMA by sending an extended Proxy Binding Update
message, including a new TLV-encoded option, named "Active
Multicast Subscription", which contains the multicast context of
the active multicast subscriptions in the moment of handover.
3. The LMA processes the PBU message. Additionally, the LMA stores
in the Binding Cache the information regarding the on-going
multicast subscription(s) when the detachment is initiated. This
information will be kept until a new registration of the MN is
completed by another MAG, or till the Binding Cache expiration,
according to [RFC5213].
4. The LMA acknowledges to the pMAG the previous PBU message.
5. As a result of the handover process, the MN attaches to another
MAG, called nMAG.
6. The nMAG triggers a registration process by sending a PBU message
(with flag S set to 1) to the LMA.
7. After the analysis of the PBU message, the LMA sends an extended
PBA including the new "Active Multicast Subscription" option,
which contains the multicast context of the active subscriptions
in the moment of handover.
8. The nMAG processes the PBA message following all the standard
procedures described in [RFC5213]. Additionally, with the new
information relative to multicast subscription, the nMAG will set
up the multicast status of the point-to-point link between the
nMAG and the MN, and will join the content identified by (S,G) on
behalf of the MN in case the nMAG is not receiving already such
content due to a previous subscription ordered by another MN
attached to it. From that instant, the multicast content is
served to the MN.
5.2.2. Handover of reactive type
5.2.2.1. Rationale
In the reactive case, the LMA receives the MN registration from the
nMAG without having previously received the MN de-registration from
the pMAG.
As the nMAG is not aware of any active multicast subscription of the
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MN, the nMAG will start a conventional registration process, by
sending a normal PBU message (with flag S set to 1) towards the LMA.
After receiving the PBU message from the nMAG, the LMA will take the
decision of interrogating or not the pMAG regarding any existing
multicast subscription for that MN. This decision is taken following
a procedure that is described later in section Section 5.2.3.
Once the multicast subscription information is retrieved from the
pMAG, the LMA encapsulates it in the PBA message by using the TLV
option "Active Multicast Subscription", and forwards the PBA message
to the nMAG. Then, the nMAG can subscribe the multicast flow on
behalf of the MN, if there is no other MN receiving it already at the
nMAG. The multicast status can be also set in advance for the point-
to-point link towards the MN.
5.2.2.2. Message flow description
Figure 5 and Figure 6 summarize this process.
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+-----+ +-----+ +----+ +-----+ +----+
| MN1 | | MN2 | |pMAG| | LMA | |nMAG|
+-----+ +-----+ +----+ +-----+ +----+
| | | | |
| | | | MN1 Attached Event
| | | | |
| | | | PBU |
1) | | | |<---------------|
| | | LMA decision |
| | | | |
| | | Subscr Query | |
2) | | |<---------------| |
| | | | |
| | | Subscr Resp | |
3) | | |--------------->| |
| | | | |
| | | (Multicast Subscription |
| | | info forwarding) |
| | | | |
| | | | Ext'd PBA |
4) | | | |--------------->|
| | | | |
5) | | | | Accept PBA,
| | | | Multicast Group join
| | | | and P-t-P status setup
| | | | |
| | | |==Bi-Dir Tunnel=|
| | | | |
| | | | (S,G) Data |
|<-------------------------------------------------|
| | | | |
~ ~ ~ ~ ~
~ ~ ~ ~ ~
Figure 5: Reactive handover (steps 1 to 5)
Consider as starting point the situation where a couple of MNs, named
MN1 and MN2, are attached to the pMAG, both MNs being multicast-
enabled nodes, but only MN1 maintains an active multicast
subscription at this moment. As consequence, the value of the A flag
in the LMA is set to 1 for MN1, and set to 0 for MN2.
The sequence of messages for the handover of MN1 and MN2 is the
following (as depicted in Figure 5):
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1. At certain time, the MN1 perceives a better radio link and
decides to attach at a new MAG, nMAG, in a handover process (as
it is a reactive case, the pMAG is not aware of the detachment
process). Then, the nMAG triggers a registration process by
sending a PBU message (with flag S set to 1) to the LMA.
2. Prior to acknowledge the received PBU message, the LMA checks the
status of the A flag for this MN. Due that the flag A=1, the LMA
interrogates the pMAG about if there is any active multicast
subscription for the MN1, by sending a Subscription Query
message.
3. The pMAG answers the LMA with a Subscription Response message
including the multicast context of the existing subscriptions.
4. After processing the pMAG answer, the LMA acknowledges (with flag
S set to 1) the PBU message, including the multicast subscription
information within the new TLV-encoded option "Active Multicast
Subscription". The nMAG then processes the extended PBA message.
5. The nMAG processes the PBA message, and it proceeds to set up the
multicast status of the point-to-point link between the nMAG and
the MN1, and to join the content identified by (S,G) on behalf of
the MN1 in case the nMAG is not receiving already such content.
(The bidirectional tunnel is also set up between the nMAG and the
LMA if it has not been established before by another MN
connection). At this moment, the multicast content can be served
to the MN1. The unicast traffic for the MN1 can be forwarded as
well.
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+-----+ +-----+ +----+ +-----+ +----+
| MN1 | | MN2 | |pMAG| | LMA | |nMAG|
+-----+ +-----+ +----+ +-----+ +----+
| | | | |
~ ~ ~ ~ ~
~ ~ ~ ~ ~
| | | | |
| | | | MN2 Attached Event
| | | | |
| | | | PBU |
6) | | | |<---------------|
| | | LMA decision |
| | | | PBA |
7) | | | |--------------->|
| | | | |
8) | | | | Accept PBA
| | | | |
Figure 6: Reactive handover (steps 6 to 8)
6. In parallel, the MN2 perceives a better radio link and decides to
attach also to the nMAG in a reactive handover process as well
(the pMAG is not aware of this detachment process either). Then,
the nMAG triggers a registration process by sending a PBU message
(with flag S set to 1) to the LMA.
7. Prior to acknowledge the received PBU message, the LMA checks the
status of the A flag for this MN. Due that the flag A=0, the LMA
does not interrogate the pMAG, and acknowledges the PBU message
(with flag S set to 0). The nMAG then processes PBA message.
8. The nMAG is now ready to forward the unicast traffic to the MN2.
5.2.2.3. Further considerations for the reactive handover signaling
A handover event is managed independently by the pMAG and nMAG. It
is not a synchronized process. In a reactive handover, the LMA will
receive a registration PBU from nMAG before a de-registration PBU
from pMAG, if any.
In the message flows detailed above, it could be the case that the
LMA receives a de-registration PBU from pMAG just after sending the
Subscription Query message, but before receiving the Subscription
Response message. That de-registration PBU message from pMAG will
carry the multicast subscription information required to assist the
MN in the handover, so such valuable information SHOULD be kept by
the LMA. Furthermore, it is possible that once the Subscription
Query message arrives to pMAG, the pMAG could have already removed
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the multicast related information for the MN.
In order to avoid losing the multicast subscription information sent
in the de-registration PBU message, the LMA SHOULD store it, and
include it in the PBA message towards the nMAG in case the
Subscription Response message from the pMAG does not contain
multicast subscription information for the MN.
5.2.3. LMA decision process
A key point of the solution proposed in this document resides on the
LMA decision of interrogating the pMAG about a potential active
subscription of the MN entering the nMAG. Several variables take
place, and it is required to define a mechanism for assisting the LMA
in its decision process.
Basically two flags will be used. One flag, the named "multicast
Signaling" or S flag, is used to signal the multicast capabilities of
the MAGs and the transport of the multicast subscription information
within the PBU/PBA messages. The other one, the named "multicast
Activity" or A flag, is used to register on the LMA whether the MN is
maintaining an active multicast subscription or not.
The following sections summarize the use of these flags on the LMA
decision process.
5.2.3.1. LMA processing of S flag on reception of PBU messages
5.2.3.1.1. Proactive handover
In the event of proactive handover, the pMAG has previously informed
the LMA about any potential subscription information currently active
in the MN. The actions to be carried out by the LMA once it receives
the PBU message from the nMAG are summarized in the table below.
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+---------+---------+------------------------+----------------------+
|multicast|multicast| | |
|signaling|activity | Meaning | LMA action |
| flag S | flag A | | |
| in PBU | in LMA | | |
+---------+---------+------------------------+----------------------+
| | |- Multicast not | |
| | A=0 | supported by nMAG |- MN registration as |
| | |- No active subscription| in RFC 5213 |
| | | by MN | (S=0 in PBA) |
| S=0 +---------+------------------------+----------------------+
| | |- Multicast not |- LMA stores multicast|
| | A=1 | supported by nMAG | subscription info |
| | |- Active subscription |- MN registration as |
| | | by MN | in RFC 5213 |
| | | | (S=0 in PBA) |
+---------+---------+------------------------+----------------------+
| | |- Multicast supported by| |
| | A=0 | nMAG |- MN registration as |
| | |- No active subscription| in RFC 5213 |
| | | by MN | (S=0 in PBA) |
| S=1 +---------+------------------------+----------------------+
| | | |- LMA stores multicast|
| | |- Multicast supported by| subscription info |
| | A=1 | nMAG |- MN registration |
| | |- Active subscription | conveys multicast |
| | | by MN | subscription info |
| | | | (S=1 in PBA) |
+---------+---------+------------------------+----------------------+
Figure 7: Flag processing on LMA for proactive handover
5.2.3.1.2. Reactive handover
In the event of reactive handover, the LMA is not aware about any
potential subscription information currently active in the MN. The
actions to be carried out by the LMA once it receives the PBU message
from the nMAG are summarized in the table below.
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+---------+---------+------------------------+----------------------+
|multicast|multicast| | |
|signaling|activity | Meaning | LMA action |
| flag S | flag A | | |
| in PBU | in LMA | | |
+---------+---------+------------------------+----------------------+
| | |- Multicast not supported| |
| | A=0 | by nMAG |- MN registration as |
| | |- No active subscription | in RFC 5213 |
| | | by MN | (S=0 in PBA) |
| S=0 +---------+-------------------------+---------------------+
| | |- Multicast not supported|- LMA does not |
| | A=1 | by nMAG | interrogate pMAG |
| | |- Active subscription |- MN registration as |
| | | by MN | in RFC 5213 |
| | | | (S=0 in PBA) |
+---------+---------+-------------------------+---------------------+
| | |- Multicast supported by |- LMA does not |
| | A=0 | nMAG | interrogate pMAG |
| | |- No active subscription |- MN registration as |
| | | by MN | in RFC 5213 |
| | | | (S=0 in PBA) |
| +---------+-------------------------+---------------------+
| | | |- LMA interrogates |
| S=1 | | | pMAG to obtain |
| | |- Multicast supported by | multicast |
| | A=1 | nMAG | subscription |
| | |- Active subscription |- MN registration |
| | | by MN | conveys multicast |
| | | | subscription info |
| | | | (S=1 in PBA) |
+---------+---------+-------------------------+---------------------+
Figure 8: Flag processing on LMA for reactive handover
5.2.3.2. LMA set-up of S flag in PBA messages
Once the LMA decision process is finished, the LMA builds the PBA
message to complete the registration process triggered by the nMAG.
The value of the S flag in the PBA message will be set according to
the data specified in the table below.
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+---------------+-------------+-------------------------------+
| S flag | S flag | |
| received in | sent in | Meaning |
| PBU message | PBA message | |
+---------------+-------------+-------------------------------+
| | | |
| S=0 | S=0 | No further meaning |
| | | |
| (multicast +-------------+-------------------------------+
| not supported | | |
| by nMAG) | S=1 | N/A |
| | | |
+-------------- +-------------+-------------------------------+
| | | |
| | S=0 | No active subscription on MN |
| | | |
| +-------------+-------------------------------+
| S=1 | | - Mcast context available: |
| (multicast is | | Multicast subscription info |
| supported by | | is conveyed in the PBA |
| nMAG) | | message |
| | S=1 | - Mcast context not available:|
| | | It has to be requested by |
| | | using the Subscription Query|
| | | message. |
+---------------+-------------+-------------------------------+
Figure 9: S flag configuration in PBA messages
5.2.4. Prevention of large delays of the binding acknowledgement for
unicast traffic
According to the message sequences described for the reactive
handover case, in case the LMA has to request the multicast
subscription information from the pMAG, the binding request sent by
the nMAG is maintained on-hold till the LMA receives, processes and
includes the multicast subscription information into the extended PBA
message. As consequence, the unicast traffic may then suffer an
extra delay motivated by the multicast-related signaling. During
that time, the unicast traffic with destination the MN being
registered by the nMAG MUST be buffered or discarded by the LMA.
In order to avoid any potential large delay in the forwarding of
unicast traffic arriving at the LMA towards the MN, a mechanism
SHOULD be implemented to decouple multicast from unicast traffic
reception by the MN.
Figure 10 shows this mechanism:
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+-----+ +----+ +-----+ +----+
| MN | |pMAG| | LMA | |nMAG|
+-----+ +----+ +-----+ +----+
1) | |==Bi-Dir Tunnel=| |
| unicast data | | |
|<-v-v-v-v-v-v-v-| | |
| | | |
| Multicast Data | | |
|<---------------| | |
| | | MN1 Attached Event
| | | PBU |
2) | | |<---------------|
| | Subscr Query | |
3) | |<---------------| |
| | | |
4) | | <PBA timer starts> |
| | /// |
| | /// |
5) | | <PBA timer expires> |
| | | |
| | | Ext'd PBA |
| | |--------------->|
| | | |
| | | Accept PBA
| | | |
| | |==Bi-Dir Tunnel=|
| | | |
| | | Unicast Data |
|<-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-v-|
| | | |
| | | Subscr Query |
6) | | |<---------------|
| | Subscr Resp | |
7) | |--------------->| |
| | | |
| | (Multicast Subscription |
| | info forwarding) |
| | | |
| | | Subscr Resp |
8) | | |--------------->|
| | | |
| | | Multicast Group join
| | | and P-t-P status setup
| | Multicast Data | |
|<-------------------------------------------------|
| | | |
Figure 10: Decoupling of unicast and multicast signaling
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The sequence of messages is the following:
1. An MN is attached to the pMAG. The MN is a multicast-enabled
node, and it is receiving both unicast and multicast traffic
simultaneously.
2. Some time later, the MN perceives a better radio link and decides
to attach at a new MAG, nMAG, in a handover process (as a
reactive case, the pMAG is not aware of the detachment process).
Then, the nMAG triggers a registration process by sending a PBU
message (with flag S set to 1) to the LMA.
3. Prior to acknowledge the received PBU message, the LMA decides to
interrogate the pMAG about if there is any active multicast
subscription for the MN, by sending a Subscription Query message.
The LMA decision is based on the checking of flag A when the
reactive handover manages the multicast activity indication.
4. Immediately after sending the Subscription Query message, the LMA
starts the timer "PBA timer", which determines the maximum
waiting time before the PBA is sent to avoid any potential large
delay in the forwarding of unicast traffic towards the MN.
5. In case the "PBA timer" expires, the LMA acknowledges the PBU
message, by sending the PBA message with flag S=1, without the
multicast context information. The nMAG then processes the
extended PBA message. Such acknowledgement will allow the MN to
receive the unicast traffic from that time on. The bidirectional
tunnel is also set up between the nMAG and the LMA if it has not
been established before.
6. In parallel, the nMAG sends a Subscription Query message to the
LMA requesting the multicast-subscription details yet unknown for
the MN.
7. The pMAG answers the Subscription Query message originally sent
by the LMA, including the multicast context.
8. After processing the pMAG answer, the LMA sends a Subscription
Response message to the nMAG, including the multicast
subscription information within the new TLV-encoded option
"Active Multicast Subscription". The nMAG processes the PBA
message, and it proceeds to set up the multicast status of the
point-to-point link between the nMAG and the MN, and to join the
content identified by (S,G) on behalf of the MN in case the nMAG
is not receiving already such content. The bidirectional tunnel
is also set up between the nMAG and the LMA if it has not been
established before. At this moment, the multicast content can
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also be served to the MN.
6. Co-existence with PMIPv6 multicast architectural evolutions
Along this document, it has been considered that the LMA entity is in
charge of delivering both unicast and multicast traffic to a certain
MN through the bi-directional tunnels connecting to the MAG where the
MN is attached, as specified in the base solution defined in
[RFC6224]. However, the solution described in this memo is not only
applicable to the base solution, but it can also be applied to the
solutions described in [I-D.ietf-multimob-pmipv6-ropt] to solve the
tunnel convergence problem.
The Multicast Tree Mobility Anchor (MTMA) solution in
[I-D.ietf-multimob-pmipv6-ropt] makes use of a separate entity to
serve multicast traffic through distinct tunnels connected to the
MAGs. The tunnels for multicast traffic could not be set up in
advance if they are dynamical in nature.
When the "multicast activity" flag is also present in the MN's policy
store, the nMAG knows in advance the multicast activity of the
incoming MN. Consequently, the nMAG can trigger the multicast tunnel
set up in parallel to the registration process, including the
acquisition of the active multicast subscription details (the
multicast context), saving time on serving the multicast flow to the
incoming MN. The concrete procedure for multicast tunnel
establishment is out of the scope of this document.
7. Security Considerations
This proposal does not pose any additional security threats to those
already identified in [RFC5213]. All the security considerations in
[RFC5213] are directly applicable to this protocol. The signaling
messages, Proxy Binding Update, and Proxy Binding Acknowledgement
(extended with the new options defined in this document), the
Subscription Query Message, the Subscription Response Message, the
Multicast Activity Indication and the Multicast Activity Indication
Acknowledge, exchanged between the mobile access gateway and the
local mobility anchor, MUST be protected using end-to-end security
association(s) offering integrity and data origin authentication.
The mobile access gateway and the local mobility anchor MUST
implement the IPsec security mechanism mandated by Proxy Mobile IPv6
[RFC5213] to secure the signaling described in this document. In the
following, we describe the Security Policy Database (SPD) and
Security Association Database (SAD) entries necessary to protect the
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new signaling introduced by this specification (Subscription Query
Message, Subscription Response Message, Multicast Activity Indication
and Multicast Activity Indication Acknowledge). We use the same
format used by [RFC4877]. The SPD and SAD entries are only example
configurations. A particular mobile access gateway implementation
and a local mobility anchor home agent implementation could configure
different SPD and SAD entries as long as they provide the required
security of the signaling messages.
For the examples described in this document, a mobile access gateway
with address "mag_address_1", and a local mobility anchor with
address "lma_address_1" are assumed.
mobile access gateway SPD-S:
- IF local_address = mag_address_1 &
remote_address = lma_address_1 &
proto = MH & (remote_mh_type = Subscription Query |
local_mh_type = Subscription Response |
remote_mh_type = Multicast Activity Indication Ack.|
local_mh_type = Multicast Activity Indication)
Then use SA1 (OUT) and SA2 (IN)
mobile access gateway SAD:
- SA1(OUT, spi_a, lma_address_1, ESP, TRANSPORT):
local_address = mag_address_1 &
remote_address = lma_address_1 &
proto = MH
- SA2(IN, spi_b, mag_address_1, ESP, TRANSPORT):
local_address = lma_address_1 &
remote_address = mag_address_1 &
proto = MH
local mobility anchor SPD-S:
- IF local_address = lma_address_1 &
remote_address =mag_address_1 &
proto = MH & (remote_mh_type = Subscription Response |
local_mh_type = Subscription Query |
remote_mh_type = Multicast Activity Indication |
local_mh_type = Multicast Activity Indication Ack.)
Then use SA2 (OUT) and SA1 (IN)
local mobility anchor SAD:
- SA2(OUT, spi_b, mag_address_1, ESP, TRANSPORT):
local_address = lma_address_1 &
remote_address = mag_address_1 &
proto = MH
- SA1(IN, spi_a, lma_address_1, ESP, TRANSPORT):
local_address = mag_address_1 &
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remote_address = lma_address_1 &
proto = MH
8. IANA Considerations
This document defines the new following elements which values to be
allocated by IANA:
o Mobility Header types: the Subscription Query and Subscription
Response, and the Multicast Activity Indication and Multicast
Activity Indication Acknowledge mobility header types.
o Mobility options: the Active Multicast Subscription mobility
option.
o Flags: the multicast Signaling (S), the multicast Information (I),
and the multicast Active (A) flags.
9. Contributors
Dirk Von Hugo (Telekom Innovation Laboratories,
Dirk.von-Hugo@telekom.de) extensively contributed to this document.
10. Acknowledgments
The authors would like to thank (in alphabetical order) Hitoshi
Asaeda, Marco Liebsch, Behcet Sarikaya, Thomas C. Schmidt and Stig
Venaas for their valuable comments and discussions on the Multimob
mailing list. The authors are also grateful with Hitoshi Asaeda,
Akbar Rahman and Behcet Sarikaya for their review of this document.
The research of Carlos J. Bernardos leading to these results has
received funding from the European Community's Seventh Framework
Programme (FP7-ICT-2009-5) under grant agreement n. 258053 (MEDIEVAL
project), being also partially supported by the Ministry of Science
and Innovation (MICINN) of Spain under the QUARTET project (TIN2009-
13992-C02-01).
The research of Ignacio Soto has also received funding from the
Spanish MICINN through the I-MOVING project (TEC2010-18907).
11. References
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11.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710,
October 1999.
[RFC4877] Devarapalli, V. and F. Dupont, "Mobile IPv6 Operation with
IKEv2 and the Revised IPsec Architecture", RFC 4877,
April 2007.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
[RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
in IPv6", RFC 6275, July 2011.
11.2. Informative References
[I-D.ietf-multimob-pmipv6-ropt]
Zuniga, J., Contreras, L., Bernardos, C., Jeon, S., and Y.
Kim, "Multicast Mobility Routing Optimizations for Proxy
Mobile IPv6", draft-ietf-multimob-pmipv6-ropt-02 (work in
progress), October 2012.
[I-D.von-hugo-multimob-future-work]
Hugo, D., Asaeda, H., Sarikaya, B., and P. Seite,
"Evaluation of further issues on Multicast Mobility:
Potential future work for WG MultiMob",
draft-von-hugo-multimob-future-work-02 (work in progress),
June 2010.
[Papagiannaki, et al.]
Papagiannaki, K., Moon, S., Fraliegh, C., Thiran, P., and
C. Diot, "Measurement and Analysis of Single-Hop Delay on
an IP Backbone Network", IEEE Journal on Selected Areas in
Communications, vol.21, no.6 , August 2003.
[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.
[RFC5949] Yokota, H., Chowdhury, K., Koodli, R., Patil, B., and F.
Xia, "Fast Handovers for Proxy Mobile IPv6", RFC 5949,
September 2010.
[RFC6224] Schmidt, T., Waehlisch, M., and S. Krishnan, "Base
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Deployment for Multicast Listener Support in Proxy Mobile
IPv6 (PMIPv6) Domains", RFC 6224, April 2011.
[RFC6636] Asaeda, H., Liu, H., and Q. Wu, "Tuning the Behavior of
the Internet Group Management Protocol (IGMP) and
Multicast Listener Discovery (MLD) for Routers in Mobile
and Wireless Networks", RFC 6636, May 2012.
[Verizon] "LTE: The Future of Mobile Broadband Technology", Verizon
White Paper (http://opennetwork.verizonwireless.com/pdfs/
VZW_LTE_White_Paper_12-10.pdf) , 2010.
[Y.1541] "Network performance objectives for IP-based services",
ITU-T Recommendation Y.1541 , December 2011.
Appendix A. Performance comparison with base solution
This appendix briefly analyzes and compares the performance
improvement provided by the fast handover extensions specified in
this document with the base multicast solution defined in [RFC6224].
The main aim is to determine the potential delay reduction in the
acquisition of the multicast subscription information by the nMAG
during the MN handover. To do that, the analysis will focus on the
delay additional to the unicast handover due to the multicast
operation in both cases.
Different delay components have to be taken into account for this
comparison. Since the interaction between the actors during the
handover process (MN, pMAG, nMAG, LMA) is different for each of the
solutions, then different sources of delay can be expected for each
of them.
A.1. Delay characterization of the base solution
The base solution relies on the standard MLD procedures to obtain the
multicast subscription information directly from the MN. Once the
nMAG completes the configuration of point-to-point link to the
attaching MN (the configuration of this link as downstream interface
of an MLD proxy instance can run in parallel), it immediately sends
an MLD General Query towards the MN for getting knowledge of any
active multicast subscription by the MN. When the MN receives the
MLD Query, the MN provides information about the active memberships
it maintains in the form of an MLD Report message. After successful
transmission of this information via the wireless point of attachment
to nMAG the corresponding MLD proxy instance at the nMAG will set up
the multicast status of the downstream interface. According to this
process, the delay is originated on the MAG-MN communication.
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The delay components to be considered for the base solution are the
following:
o D_bh, which is the unidirectional (one way) delay encountered in
the transmission path between the nMAG and the wireless point of
attachment
o D_radio, which is the unidirectional delay due to the transfer of
MLD control messages over the radio channel (user plane) between
the wireless point of attachment and the MN, for the MLD Query and
Report messages.
o D_mld, which is the delay incurred by the MN to answer the MLD
Query.
The total observed delay can be then formulated as:
D_base = 2 x (D_bh + D_radio) + D_mld
A.2. Delay characterization of the SIAL solution
As described in this document, it is possible to distinguish two
scenarios depending on the order in which the LMA receives the
notifications of the MN registration and de-registration in the nMAG
and the pMAG respectively.
In the proactive case, the MN is firstly de-registered by the pMAG,
and later on it is registered by the nMAG. As specified in this
document, the LMA will store the multicast subscription information,
which will be provided to the nMAG during the MN registration
process. Since the registration process necessarily happens before
the MLD Query and Report process described in the base solution, the
proactive case is inherently faster than the base solution. In fact,
since the multicast subscription information is acquired properly
during the registration process, the delay incurred is null.
In the reactive case, the LMA receives the MN registration from the
nMAG without having previously received the MN de-registration from
the pMAG. In case the MN maintains an active subscription, the LMA
will interrogate the pMAG to retrieve the multicast subscription
information, which is forwarded to the nMAG. According to this
process, the delay is originated on the MAG-LMA communication.
The delay components to be considered for the base solution are the
following:
o D_net, which is the unidirectional delay found in the network path
between the LMA and the MAG.
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The total observed delay can be then formulated as:
D_sial = 2 x D_net
A.3. Performance comparison
The performance of the base solution is highly dependent on the radio
technology used by the MN to attach to the PMIPv6-Domain. Different
radio technologies have distinct properties in terms of radio
framing, radio access contention or collision avoidance, channel
reliability, etc.
New radio access technologies, such as the one specified in new Long
Term Evolution (LTE) standards intend to reduce the latency in order
to provide high speed communications. Even though, typical one-way
latencies in the LTE radio access will stay around 15 ms [Verizon].
The backhaul delay characterization becomes problematic. In a real
network there are several solutions for the backhaul connection in
terms of network topology (ring, star, point-to-point, etc) and
technology (optical fiber, microwave transmission, xDSL-based
accesses, etc), all of them having distinct properties in terms of
performance, reliability and delay. These solutions commonly coexist
in a real mobile network, in such a way that an MN changing the point
of attachment can pass smoothly from one solution to another. A
value of D_bh=5 ms can be established as typical value for the
backhaul latency in modern networks.
Finally, the MLD induced delay is intrinsic to the MLD protocol
specification. A host receiving an MLD Query message will wait a
random time in the range (0, Maximum Response Delay) to send the MLD
Report message. The default value of the Maximum Response Delay
(configurable through the Query Response Interval in MLD) is 10 s in
[RFC2710], or 5 s in the best case described in [RFC6636]. Then, in
average, it can be expected a potential delay of 5 or 2,5 s,
respectively.
As we have seen, D_base is, on average, greater than 2,5 sec with the
best case of the values of Query Response Interval in MLD that are
recommended in [RFC6636]. That means that the handover delay of the
base solution is on the order of seconds while in the solution
presented in this specification it is on the order of milliseconds
(as it is shown below). To improve the performance of the base
solution we could further reduce the value of Query Response Interval
but the implications of doing so would need to be carefully analyzed.
Even if we assume that Query Response Interval is 0 sec, D_base would
be of around 2 x (5 ms + 15 ms) = 40 ms for last generation systems.
Note that this calculation does not take into account the necessary
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time to re-establish the data plane after the handover to make
possible the MLD Query reception. The expected delay will get much
worse for older generation systems (e.g., 3G-based radio systems can
suffer radio delays in the order of hundreds of ms).
For the SIAL case, the delay in the MAG-LMA communication will be
derived from the network diameter (i.e., the number of hops found
between the MAG and the LMA in the PMIPv6-Domain). This is largely
influenced by the internal network planning. An administrative
domain can typically have in the order of 5 hops from access to the
interconnection gateway providing connectivity to other networks.
Even if the LMA plays a central role topologically in the PMIPv6
domain, such number of hops seems reasonable in a common nation-wide
network. Each hop in the path between MAG and LMA will add a certain
delay, which can be estimated to be around 1 ms in the best case
[Papagiannaki, et al.] and 3 ms in the worst case [Y.1541]. With
this in mind, a total delay D_sial of around 2 x 5 x 3 ms = 30 ms can
be expected in the worst case.
Then, as conclusion, in a typical deployment, it can be stated that
SIAL proposal, even for the worst-case consideration, will perform
better than the best case situation for the base solution, which
consists of the last generation radio technology, LTE. For any other
radio technology the base solution will show even larger deviation
from the delay achievable with the SIAL proposal.
Appendix B. Change Log
The following changes has been made from -00 version.
1. Multicast Address Record format defined in [RFC3810] has been
adopted for transfering multicast subscrition information in the
Active Multicast Subscription mobility option.
The following changes has been made from -01 version.
1. A new appendix has been created to include a performance
comparison between this proposal and the base solution.
2. Comments from Akbar Rahman review has been addressed.
The following changes has been made from -02 version.
1. Minor editorial corrections.
The following changes has been made from
draft-ietf-multimob-fast-handover-03 version.
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1. The name of the draft file has been changed to
draft-ietf-multimob-handover-optimization as requested by the
chairs.
Authors' Addresses
Luis M. Contreras
Telefonica I+D
Distrito Telefonica, Sur-3 building, 3rd floor
Madrid 28050
Spain
Email: lmcm@tid.es
Carlos J. Bernardos
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain
Phone: +34 91624 6236
Email: cjbc@it.uc3m.es
URI: http://www.it.uc3m.es/cjbc/
Ignacio Soto
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain
Email: isoto@it.uc3m.es
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