Internet Engineering Task Force (IETF) LM. Contreras

Internet Engineering Task Force (IETF) LM. Contreras
Request for Comments: 7161 Telefonica I+D
Category: Experimental CJ. Bernardos
ISSN: 2070-1721 I. Soto
UC3M
March 2014

Proxy Mobile IPv6 (PMIPv6) Multicast Handover Optimization
by the Subscription Information Acquisition through the LMA (SIAL)

Abstract

This document specifies an experimental multicast handover
optimization mechanism for Proxy Mobile IPv6 (PMIPv6) to accelerate
the delivery of multicast traffic to mobile nodes after handovers.
The mechanism, called Subscription Information Acquisition through
the LMA (SIAL), is based on speeding up the acquisition of mobile
nodes' multicast context by the mobile access gateways. To do that,
extensions to the current PMIPv6 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 developed to avoid the tunnel convergence problem.
Furthermore, these extensions are also independent of the role played
by the mobile access gateway within the multicast network (acting as
either multicast listener discovery proxy or multicast router).

Status of This Memo

This document is not an Internet Standards Track specification; it is
published for examination, experimental implementation, and
evaluation.

This document defines an Experimental Protocol for the Internet
community. This document is a product of the Internet Engineering
Task Force (IETF). It represents the consensus of the IETF
community. It has received public review and has been approved for
publication by the Internet Engineering Steering Group (IESG). Not
all documents approved by the IESG are a candidate for any level of
Internet Standard; see Section 2 of RFC 5741.

Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7161.

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Copyright Notice

Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Handover Optimization
Requirements . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 6
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Proxy Mobile IPv6 Extensions . . . . . . . . . . . . . . . . 8
4.1. Active Multicast Subscription Mobility Option . . . . . . 8
4.1.1. Option Application Rules . . . . . . . . . . . . . . 8
4.1.2. Option Format . . . . . . . . . . . . . . . . . . . . 9
4.1.3. Backward Compatibility with MLDv1 . . . . . . . . . . 9
4.2. Multicast Signaling Flag on PBU/PBA Message Headers . . . 10
4.2.1. Flag Application Rules . . . . . . . . . . . . . . . 10
4.2.1.1. Registration Process . . . . . . . . . . . . . . 11
4.2.1.2. De-registration Process . . . . . . . . . . . . . 12
4.2.2. New Format of Conventional PBU/PBA Messages . . . . . 12
4.2.2.1. Proxy Binding Update Message . . . . . . . . . . 12
4.2.2.2. Proxy Binding Acknowledgement Message . . . . . . 13
4.3. Messages for Active Multicast Subscription Query . . . . 13
4.3.1. Subscription Query Message . . . . . . . . . . . . . 13
4.3.1.1. Message Application Rules . . . . . . . . . . . . 13
4.3.1.2. Message Format . . . . . . . . . . . . . . . . . 14
4.3.2. Subscription Response Message . . . . . . . . . . . . 15
4.3.2.1. Message Application Rules . . . . . . . . . . . . 15
4.3.2.2. Message Format . . . . . . . . . . . . . . . . . 15
4.4. New PBA Timer in the LMA . . . . . . . . . . . . . . . . 16
5. Handover Signaling Procedures . . . . . . . . . . . . . . . . 17
5.1. Handover of Proactive Type . . . . . . . . . . . . . . . 17
5.1.1. Rationale . . . . . . . . . . . . . . . . . . . . . . 17
5.1.2. Message Flow Description . . . . . . . . . . . . . . 18
5.2. Handover of Reactive Type . . . . . . . . . . . . . . . . 20

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5.2.1. Rationale . . . . . . . . . . . . . . . . . . . . . . 20
5.2.2. Message Flow Description . . . . . . . . . . . . . . 21
5.2.3. Further Considerations for the Reactive Handover
Signaling . . . . . . . . . . . . . . . . . . . . . . 22
5.3. Prevention of Large Delays of the Binding
Acknowledgement for Unicast Traffic . . . . . . . . . . . 23
6. IPv4 Support . . . . . . . . . . . . . . . . . . . . . . . . 26
6.1. Active Multicast Subscription for IPv4 . . . . . . . . . 26
6.2. Signaling Procedures for IPv4 Support . . . . . . . . . . 27
6.3. Binding Cache Extensions for IPv4 Support . . . . . . . . 28
7. Coexistence with PMIPv6 Multicast Architectural
Evolutions . . . . . . . . . . . . . . . . . . . . . . . . . 28
8. Security Considerations . . . . . . . . . . . . . . . . . . . 28
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 31
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 31
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 32
12.1. Normative References . . . . . . . . . . . . . . . . . . 32
12.2. Informative References . . . . . . . . . . . . . . . . . 32
Appendix A. Performance Comparison with Base Solution . . . . . 34
A.1. Delay Characterization of the Base Solution . . . . . . . 34
A.2. Delay Characterization of SIAL . . . . . . . . . . . . . 35
A.3. Performance Comparison . . . . . . . . . . . . . . . . . 35

1. Introduction

The base solution for providing continuous multicast service delivery
in Proxy Mobile IPv6 (PMIPv6) domains is described in [RFC6224]. It
specifies the basic functionality needed in the Proxy Mobile IPv6
[RFC5213] entities to provide a multicast service, so continuous
delivery of multicast traffic is supported by obtaining, after each
handover, the ongoing multicast subscription information directly
from the Mobile Node (MN). When a mobile node attaches to a new
Mobile Access Gateway (MAG), the mobile node is queried by the mobile
access gateway through a Multicast Listener Discovery (MLD) General
Query, which is sent just after any new link is set up, to learn of
any existing subscription, as specified in [RFC2710] and [RFC3810].

However, the base solution needs to be improved to meet some
performance requirements, especially those referring 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.

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Such delay causes a gap in the content reception. Two different
actions can help mitigate such reception gap. One of them is to
buffer at the previous mobile access gateway a copy of the multicast
traffic destined to 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 learn 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 (L2) triggers, thus requiring additional support on
the mobile node), there is no generic standard solution for the
accelerated acquisition of the ongoing multicast subscription of the
mobile node.

The approach followed by the base solution [RFC6224] to learn of an
existing multicast subscription relies on the behavior of the IGMP/
MLD protocols. Both protocols send multicast membership query
messages when a new link is up. The response to such a message
reports any existing multicast subscriptions by the mobile node.
While this is a straightforward approach, 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] and [RFC3810], 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). Furthermore, this specification does not
substitute the standard procedures defined in [RFC6224] (e.g., the
mobile access gateway continues sending an MLD Query to the entering
mobile node as soon as the point-to-point link is set up), but
complements them for accelerating the acquisition of the multicast
content by the mobile access gateway associated to the new point-of-
attachment.

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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 IGMP/MLD control messages. Issues
like radio framing, radio access contention, channel reliability,
MN's capabilities (i.e., L2 triggering support), IGMP/MLD timers
optimization for wireless environments, etc., will not impact the
observed multicast performance during handovers.

The mechanisms described in this document can also be applied to the
solutions defined in [RFC7028]. Furthermore, it is also independent
of the role played by the mobile access gateway within the multicast
network (acting as either MLD proxy or multicast router).

1.1. Handover Optimization Requirements

A basic solution for providing support of multicast in a network-
based mobility management environment has been specified in [RFC6224]
without introducing changes on the original PMIPv6 specification
[RFC5213]. The focus of the present document is on improving the
efficiency of the base solution regarding handover performance.

One of the critical aspects of the base solution is the expected
delay incurred by the mobile access gateway (where the mobile node is
being attached to) to be informed about the ongoing multicast
subscription of the entering MN, mainly due to the fact that the
mechanisms provided in the base solution relay on the original MLD
procedures, with long timing interactions not conceived for mobile
environments. Then, the requirements to be covered by a handover
optimization solution can be established in the following manner:

o The solution MUST be applicable to any kind of MN (that is, not
requiring any particular functionality such as, for example, L2
trigger capabilities), in such a way that any type of mobile node
in a PMIPv6 domain being served with multicast traffic can benefit
from the optimized solution.

o The solution MUST NOT impact existing multicast protocols.

o The solution MUST optimize the handover performance with respect
to the performance achieved with the base solution for any kind of
handover process (i.e., for proactive and reactive handovers).

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o The solution SHOULD minimize the number and extent of additional
support (i.e., capabilities) required in the network, aiming at an
easier deployment.

o The solution MUST NOT impact deployments of legacy implementations
of [RFC5213] and [RFC6224].

The present specification addresses all these requirements, as
described in the following sections.

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].

This document uses the terminology referring to PMIPv6 components as
defined in [RFC5213].

Additionally, the following terms are defined and used in this
document.

pMAG: The previous MAG or pMAG is the mobile access gateway where
the MN was initially registered before a handover event.

nMAG: The new MAG or nMAG is the mobile access gateway where the MN
is registered at the end of the handover event.

Reactive Handover: A reactive handover is a handover event in which
the Local Mobility Anchor (LMA) receives the mobile node
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 mobile node is firstly de-registered on the local mobility
anchor by the pMAG, and later on it is registered by the nMAG as a
consequence of changing the point of attachment.

Multicast Membership Context: In this document, multicast membership
context makes reference to the information relative to the
currently active multicast subscription of an MN in a handover
event that is transferred between the PMIPv6 entities to support
the handover optimization.

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3. Overview

The local mobility anchor is a key element within the PMIPv6
infrastructure, which traces the mobile node reachability along the
PMIPv6 domain. Therefore, the LMA is the best element to keep the
MNs' multicast subscription information up-to-date and to forward it
to the rest of PMIPv6 entities (i.e., to the mobile access gateways)
as needed when MNs move within the domain. The LMA has timely
knowledge of the MNs' locations, especially during handover events,
and it is therefore able to quickly provide information to the new
point of attachment (e.g., by querying the previous one). Figure 1
summarizes the main idea of the optimization.

+------+
| pMAG | |
+------+ |
/ |
/ |
/ |
/ |
-*-*-*-*- / (MN)
( ) / |
( ) +-----+ +------+ |
( Internet )--| LMA |------| nMAG | v
( ) +-----+ +------+
( )
-*-*-*-*- Registration
<--------------

Registration Ack
& Multicast Context
-------------->

Figure 1: High-Level Description of the Solution

The local mobility anchor only obtains the detailed subscription
information or multicast context during a handover event. There is
no need for 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 and ready to be transferred to the new MAG where the mobile
node has just attached. Therefore, this solution defines the
Subscription Information Acquisition through the LMA (SIAL) as the

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procedure to inform the new MAG about the multicast subscriptions
maintained by the entering MN.

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.

4. Proxy Mobile IPv6 Extensions

This section outlines the extensions proposed to the PMIPv6 protocol
specified in [RFC5213].

4.1. Active Multicast Subscription Mobility Option

4.1.1. Option Application Rules

A new TLV-encoded mobility option, Active Multicast Subscription
option is defined for use with the Proxy Binding Update (PBU) and
Proxy Binding Acknowledgement (PBA) messages exchanged between a
local mobility anchor and a mobility access gateway to transfer the
multicast subscription information. This option is used for
exchanging the multicast membership context. This information is
carried by directly using the format defined in the original MLD
specifications. There can be multiple Active Multicast Subscription
options present in the message, one for each active subscription
maintained by the mobile node when the handover is taking place
(i.e., one per multicast membership context).

This new option is also used for the same purposes by the new
Subscription Response message defined later in this document.

MLDv2 [RFC3810] is the primary objective for the definition of the
option format. MLDv1 [RFC2710] is also considered for backward
compatibility.

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4.1.2. 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 | MLD Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Multicast Membership Context +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The alignment requirement of this option is 8n+1.

Type:

57, which indicates the Active Multicast Subscription IPv6 option.

Length:

8-bit unsigned integer indicating the length of the option in
octets, excluding the type and length fields.

MLD type:

Field used to identify the IPv6 multicast membership protocol in
use, and the corresponding format of the next Multicast Membership
Context information field. This field maps the type codification
used in the original MLD specifications for the Report message.
For MLDv2, the MLD Type value is 143, as specified in [RFC3810].

Multicast Membership Context:

Multicast subscription information corresponding to a single
subscribed multicast address. For MLDv2, the format of this field
follows the Multicast Address Record format as defined in
[RFC3810].

4.1.3. Backward Compatibility with MLDv1

The following values are adopted when MLDv1 is used.

MLD type:

For MLDv1, the MLD Type value is 131, as specified in [RFC2710].

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Multicast Membership Context:

For MLDv1, the relevant information for multicast context is
simply given, according to [RFC2710], by the multicast address of
the subscribed content.

In consequence, the Multicast Membership Context is defined as a
4-octet reserved field and the Multicast Address of the subscribed
content as in [RFC2710], as shown next.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
* *
| |
* Multicast Address *
| |
* *
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.2. Multicast Signaling Flag on PBU/PBA Message Headers

4.2.1. Flag Application Rules

A new flag S has been added in both the PBU and PBA message headers
to advertise the mobile access gateway and the local mobility anchor
capabilities of processing multicast-related signaling for the MN
that caused the message.

This flag governs the multicast-related signaling between the LMA and
the MAG. As a general rule, the value of the flag in the PBA message
is a copy of the value received in the PBU message. Specific rules
are described in next subsections.

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4.2.1.1. 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 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 that are not
multicast enabled, for backward compatibility reasons.

* S=1 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 takes 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 MUST be a copy of the value received in the
PBU message (thus S=0), without any further meaning.

* If S=1 in the corresponding PBU message, two subcases are
possible:

+ 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 MUST include the Active Multicast Subscription
mobility option. If the LMA is not able to provide such
information during registration, the PBA message MUST 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).

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4.2.1.2. 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 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 indicates that the MN has an active multicast session, and
the multicast context MUST be 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).

4.2.2. New Format of Conventional PBU/PBA Messages

4.2.2.1. Proxy Binding Update Message

As result of the new defined flag, the PBU message format is updated
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 .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

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4.2.2.2. Proxy Binding Acknowledgement Message

As result of the new defined flag, the PBA message format is updated
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 .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

4.3. Messages for Active Multicast Subscription Query

A new pair of messages is defined for querying entities about the
active multicast subscription of the MN when the handover is of
reactive type.

These messages are sent using the Mobility Header as defined in
[RFC6275].

4.3.1. Subscription Query Message

4.3.1.1. Message Application Rules

The Subscription Query message (value 22) is sent by the LMA towards
the pMAG to query it about any existing multicast subscriptions of
the MN that is being registered by the nMAG. This message is
generated in case the handover is of reactive type.

Additionally, this message is sent by the nMAG towards the LMA to
query it about the existing multicast subscriptions of the MN when
the LMA acknowledges the PBU sent by the nMAG but the multicast
context is not provided (namely, when the PBU message has set the
flag S to 1, and the PBA message has set the flag S to 1 but the
multicast context is missing).

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4.3.1.2. 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 MUST be determined by the entity that creates the
message (either LMA or MAG, depending on the scenario), which is
responsible for managing this counter.

This Sequence Number comparison MUST be performed modulo 2**8,
i.e., the number is a free-running counter represented modulo 256.
A Sequence Number in a received Subscription Query message is
considered less than or equal to the last received number if its
value lies in the range of the last received number and the
preceding 128 values, inclusive. For example, if the last
received sequence number was 15, then messages with sequence
numbers 0 through 15, as well as 143 through 255, would be
considered less than or equal.

Reserved:

This field is unused for now. The value MUST be initialized to 0.

Mobility options:

This message carries one or more TLV-encoded mobility options.
The valid mobility options for this message are the following:

* Mobile Node Identifier option [RFC4283] (mandatory).

* Home Network Prefix option [RFC5213] (optional).

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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. Subscription Response Message

4.3.2.1. Message Application Rules

The Subscription Response message (value 23) 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.

4.3.2.2. 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):

The multicast Information flag I specifies whether or not there is
multicast subscription information available for the MN. 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 MUST be

Contreras, et al. Experimental [Page 15]

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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 carries one or more TLV-encoded mobility options.
The valid mobility options for this message are the following:

* Mobile Node Identifier option [RFC4283] (mandatory).

* Active Multicast Subscription option (mandatory) only when flag
I=1; it MUST NOT be present in any other case.

* Home Network Prefix option [RFC5213] (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.

4.4. 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 in the SIAL solution.

This timer SHOULD be upper bounded by the constant defined in
[RFC6275] INITIAL_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 be set to a
value that ensures that the nMAG does not enter the retry mode.
Operational experience is needed on how to set up the PBA timer, and
therefore it is RECOMMENDED to set the "PBA timer" to zero, except
for experimental purposes.

Contreras, et al. Experimental [Page 16]

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5. 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; 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.

5.1. Handover of Proactive Type

5.1.1. Rationale

In the proactive case, the MN is firstly de-registered by the pMAG,
and later on it is registered by the nMAG as a consequence of
changing the point of attachment.

Only for those MNs that maintain an active multicast subscription,
the pMAG includes the Active Multicast Subscription mobility option
carrying the multicast context of the MN at that moment as part of
the PBU message (with flag S set to 1).

The local mobility anchor stores that information in the
corresponding binding cache. If later on the MN attaches to an nMAG,
this information is sent (using the same TLV option) to the nMAG as
part of the PBA confirmation of the registration process (if the PBU
message sent by the nMAG has the flag S set to 1). On the other
hand, if no further registration happens, the multicast information
is 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 in case there is no other MN
already receiving it at the nMAG. The multicast status can also be
set in advance for the point-to-point link towards the MN.

Note that the SIAL 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 L2 capabilities.

Contreras, et al. Experimental [Page 17]

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5.1.2. Message Flow Description

Figure 2 summarizes this process.

+-----+ +----+ +-----+ +----+
| 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 2: Proactive Handover

Contreras, et al. Experimental [Page 18]

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The message flow is as follows:

1. A registered MN is receiving a multicast content that has been
previously subscribed to by sending a standard MLD report from
the mobile node to the currently serving mobile access gateway,
pMAG. The pMAG keeps the multicast state of the point-to-point
link with the MN.

2. The MN initiates a handover process (e.g., because of better
radio conditions) over a radio access controlled by a new MAG.
As a consequence, pMAG determines a detachment event
corresponding to this mobile node, and updates the attachment
status of this MN to the local mobility anchor by sending an
extended Proxy Binding Update message, including the 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 ongoing
multicast subscription(s) when the detachment is initiated. This
information is kept until a new registration of the MN is
completed by another MAG, or until the binding cache expiration,
according to [RFC5213].

4. The local mobility anchor acknowledges to the pMAG the previous
PBU message.

5. As a result of the handover process, the mobile node attaches to
another mobility access gateway, called nMAG.

6. The nMAG triggers a registration process by sending a PBU message
(with flag S set to 1) to the local mobility anchor.

7. After the analysis of the PBU message, the LMA sends an extended
PBA including the 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 sets up
the multicast status of the point-to-point link between the nMAG
and the MN, and joins 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.

Contreras, et al. Experimental [Page 19]

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5.2. Handover of Reactive Type

5.2.1. Rationale

In the reactive case, the LMA receives the mobile node 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
mobile node, the nMAG starts a conventional registration process, by
sending a normal PBU message (with flag S set to 1) towards the local
mobility anchor.

In the reactive handover case, after MN registration at the nMAG, the
local mobility anchor SHOULD generically query the pMAG to retrieve
the multicast context of the ongoing multicast subscription of the
mobile node. However, the LMA may know in advance if the pMAG
supports multicast signaling based on the value of the flag S
received during the MN registration in pMAG. Specifically, in case
the pMAG does not support multicast signaling (e.g., the S flag value
received from pMAG at the time of registering the mobile node was 0),
the LMA MAY decide not to query pMAG even in the case of receiving an
nMAG indication of supporting multicast signaling.

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 mobile node receiving it already at
the nMAG. The multicast status can be also set in advance for the
point-to-point link towards the mobile node.

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5.2.2. Message Flow Description

Figure 3 summarizes this process.

+-----+ +----+ +-----+ +----+
| MN | |pMAG| | LMA | |nMAG|
+-----+ +----+ +-----+ +----+
| | | |
| | | MN Attached Event
| | | |
| | | PBU |
1) | | |<---------------|
| | | |
| | 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 3: Reactive Handover

We next take as starting point the situation where an MN is attached
to the pMAG, being multicast enabled and maintaining an active
multicast subscription at this moment.

The sequence of messages for the handover of the mobile node is the
following (as depicted in Figure 3):

1. At a certain time, the MN initiates a handover process (e.g.,
because of better radio conditions) over a radio access
controlled by a new MAG. Then, the nMAG triggers a registration

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process by sending a PBU message (with flag S set to 1) to the
local mobility anchor. As it is a reactive case, the pMAG is not
aware of the detachment process.

2. Prior to acknowledging the received PBU message, the LMA queries
the pMAG about if there is any active multicast subscription for
the MN, 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 Active Multicast Subscription option. 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 mobile node, 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 local mobility anchor if it has not been established
before by another MN connection. At this moment, the multicast
content can be served to the MN. The unicast traffic for the
mobile node can be forwarded as well.

5.2.3. 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
receives a registration PBU from nMAG before a de-registration PBU is
received from pMAG.

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 carries
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 the multicast
related information for the MN.

In order to avoid losing the multicast subscription information sent
in the de-registration PBU message, the local mobility anchor SHOULD
store it, and SHOULD 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 mobile node.

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5.3. 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 until the local mobility anchor
receives, processes and includes the multicast subscription
information into the extended PBA message. As a 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 MAY be buffered
by the local mobility anchor.

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 4 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 | | |
|<---------------| | |
| | | MN 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 4: 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 initiates a handover process (e.g.,
because of better radio conditions) over a radio access
controlled by a new mobile access gateway. Then, the nMAG
triggers a registration process by sending a PBU message (with
flag S set to 1) to the local mobility anchor. As it is a
reactive case, the pMAG is not aware of the detachment process.

3. Prior to acknowledging the received PBU message, the LMA decides
to query the pMAG about if there is any active multicast
subscription for the mobile node, by sending a Subscription Query
message.

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 allows the mobile
node 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 mobile node.

7. The pMAG answers the Subscription Query message originally sent
by the local mobility anchor, 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 Active Multicast Subscription
option. 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 mobile node, 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

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between the nMAG and the LMA if it has not been established
before. At this moment, the multicast content can also be served
to the mobile node.

The "PBA timer" in the LMA determines if the signaling flow follows
Figure 3 or Figure 4 in a reactive handover. A value of 0 for the
"PBA timer" guarantees that the unicast traffic does not suffer any
delay (according to the Figure 4 signaling flow), because the PBA is
sent immediately after the LMA receives the PBU from the nMAG. A
small non-zero "PBA timer" value MAY be used to reduce the signaling
load in the LMA and MAGs (as shown in the signaling flow of Figure 3
if the Subscription Response message from the pMAG is received at the
LMA before the "PBA timer" expires), but this has to be carefully
balanced against added delay to the unicast traffic.

6. IPv4 Support

IPv4-based mobile nodes (being either IPv4/IPv6 dual-stack or
IPv4-only enabled) can be supported in a PMIPv6 domain according to
[RFC5844]. When referring to multicast membership protocols and
procedures, this means that IGMP functionality has to be also
supported between the PMIPv6 entities, as documented in [RFC6224], to
allow the mobile access gateway requesting multicast contents to the
mobility anchor on behalf of the mobile nodes attached to it.

6.1. Active Multicast Subscription for IPv4

The Active Multicast Subscription option defined in Section 4.1,
which transports the multicast membership context of the mobile node
during handover, should be compatible with IGMP-based formats.
Specifically, the option format is defined for IPv4-based MNs 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 | IGMP Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ Multicast Membership Context +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

IGMPv3 is the primary objective for the definition of the option
format. IGMPv1 and IGMPv2 are also considered for backward
compatibility. The alignment requirement of this option is 4n+1.

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Type:

56, which indicates the Active Multicast Subscription IPv4 option.

Length:

8-bit unsigned integer indicating the length of the option in
octets, excluding the type and length fields.

IGMP type:

Field used to identify the IPv4 multicast membership protocol in
use, and the corresponding format of the next Multicast Membership
Context information field. This field maps the type codification
used in the original IGMP specifications for the Report message.

0x12: Use of IGMPv1 multicast membership protocol.

0x16: Use of IGMPv2 multicast membership protocol.

0x22: Use of IGMPv3 multicast membership protocol.

Multicast Membership Context:

Multicast subscription information corresponding to a single
subscribed multicast address. Depending on the IGMP version being
used by the mobile node, the format of the Multicast Membership
Context could follow the following formats:

* For IGMPv1, the Group Address format as defined in [RFC1112].

* For IGMPv2, the Group Address format as defined in [RFC2236].

* For IGMPv3, the Group Record format as defined in [RFC3376].

6.2. Signaling Procedures for IPv4 Support

Generic signaling procedures for the support of IPv4 in PMIPv6
domains have been already specified in [RFC5844]. In order to
prevent errors while signaling the ongoing multicast subscription for
a mobile node during the handover process, the following extensions
have to be considered in SIAL.

o If the registration/de-registration process in a handover is for
an IPv6-only MN, and the type of the received Active Multicast
Subscription option indicates IPv4, then the multicast membership
context received MUST be silently discarded.

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o If the registration/de-registration process in a handover is for
an IPv4-only MN, and the type of the received Active Multicast
Subscription option indicates IPv6, then the multicast membership
context received MUST be silently discarded.

o If the registration/de-registration process in a handover is for a
dual stack MN, the received Active Multicast Subscription option
(or options) MUST be accepted independently of the type
indication.

6.3. Binding Cache Extensions for IPv4 Support

Additionally, since the multicast membership information is
temporally stored in the mobility anchor under some circumstances
(e.g., proactive handover), the binding cache entry for an IPv4-based
multicast-enabled MN should be extended for storing the IGMP-based
context formats mentioned above, including the IGMP version
indicator.

7. Coexistence with PMIPv6 Multicast Architectural Evolutions

Throughout this document, the base solution for multicast support in
Proxy Mobile IPv6, described in [RFC6224], has been implicitly
considered, i.e., both unicast and multicast traffic addressing a
mobile node is delivered via the standard PMIPv6 bidirectional tunnel
between LMA and MAG. While here all multicast traffic is assumed to
be delivered via the local mobility anchor, the SIAL approach
described in this document can be also applied to other solutions in
which the multicast content is served from other entities in the
PMIPv6 domain, as described in [RFC7028] to solve the tunnel
convergence problem.

In this case, the transfer of the multicast context would also pass
through the local mobility anchor, as described here. However, the
nMAG subscribes to the multicast content through the node in charge
of distributing multicast according to the adopted solution for
multicast distribution in the PMIPv6 domain.

8. 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, and the Subscription Response Message

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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
new signaling introduced by this specification (Subscription Query
Message and Subscription Response Message). 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.

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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 &
remote_address = lma_address_1 &
proto = MH

While in the base solution the LMA has learned of the subscribed
multicast groups per MAG, in this specification the LMA is aware
(during a handover process) of the multicast groups to which an MN
visiting the PMIP domain is subscribed.

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9. IANA Considerations

This document establishes new assignments to the IANA mobility
parameters registry.

o Mobility Header types: the Subscription Query (22) and
Subscription Response (23) mobility header types. The Type value
for these Headers has been assigned from the "Mobility Header
Types - for the MH Type field in the Mobility Header" registry
defined in <http://www.iana.org/assignments/mobility-parameters>.

o Mobility options: the Active Multicast Subscription mobility
option for both IPv4 (56) and IPv6 (57) modes of operation. The
Type value for these Mobility options has been assigned from the
"Mobility Options" registry defined in <http://www.iana.org/
assignments/mobility-parameters>.

o Flags: this document reserves a new multicast Signaling flag (S).
This flag has been reserved as value 0x0020 in the "Binding Update
Flags" registry and value 0x04 in the "Binding Acknowledgment
Flags" registry. These registries appear on <http://www.iana.org/
assignments/mobility-parameters>.

10. Contributors

Dirk Von Hugo (Telekom Innovation Laboratories,
[email protected]) extensively contributed to this document.

11. Acknowledgments

The authors would like to thank (in alphabetical order) Hitoshi
Asaeda, Sergio Figueiredo, Georgios Karagiannis, 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, Behcet
Sarikaya, and Stig Venaas for their reviews 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).

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12. References

12.1. Normative References

[RFC1112] Deering, S., "Host extensions for IP multicasting", STD 5,
RFC 1112, August 1989.

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC2236] Fenner, W., "Internet Group Management Protocol, Version
2", RFC 2236, November 1997.

[RFC2710] Deering, S., Fenner, W., and B. Haberman, "Multicast
Listener Discovery (MLD) for IPv6", RFC 2710, October
1999.

[RFC3376] Cain, B., Deering, S., Kouvelas, I., Fenner, B., and A.
Thyagarajan, "Internet Group Management Protocol, Version
3", RFC 3376, October 2002.

[RFC3810] Vida, R. and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6", RFC 3810, June 2004.

[RFC4283] Patel, A., Leung, K., Khalil, M., Akhtar, H., and K.
Chowdhury, "Mobile Node Identifier Option for Mobile IPv6
(MIPv6)", RFC 4283, November 2005.

[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.

[RFC5844] Wakikawa, R. and S. Gundavelli, "IPv4 Support for Proxy
Mobile IPv6", RFC 5844, May 2010.

[RFC6275] Perkins, C., Johnson, D., and J. Arkko, "Mobility Support
in IPv6", RFC 6275, July 2011.

12.2. Informative References

[Papagiannaki]
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.

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RFC 7161 PMIPv6 Multicast Handover Optimization March 2014

[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
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.

[RFC7028] Zuniga, JC., Contreras, LM., Bernardos, CJ., Jeon, S., and
Y. Kim, "Multicast Mobility Routing Optimizations for
Proxy Mobile IPv6", RFC 7028, September 2013.

[Verizon] Verizon, "LTE: The Future of Mobile Broadband Technology",
Verizon White Paper, 2010,
<http://opennetwork.verizonwireless.com/pdfs/
VZW_LTE_White_Paper_12-10.pdf>.

[Y.1541] ITU-T, "Network performance objectives for IP-based
services", ITU-T Recommendation Y.1541, December 2011.

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Appendix A. Performance Comparison with Base Solution

This informative annex 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 focuses 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, 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 learning 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 sets up the
multicast status of the downstream interface. According to this
process, the delay is originated on the MAG-MN communication.

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.

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The total observed delay can be then formulated as:

D_base = 2 x (D_bh + D_radio) + D_mld

A.2. Delay Characterization of SIAL

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 stores the multicast subscription information,
which is 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
queries 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.

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.

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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 the 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 waits 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] and [RFC3810]. In [RFC6636] the effect of tuning the value
of the Query Response Interval is analyzed and 5 s is the smallest
value recommended (best case). Then, on average, a potential delay
of 5 s or 2.5 s, default and best case respectively, can be expected.

As we have seen, D_base is, on average, greater than 2.5 s 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 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 s, D_base would be
around 2 x (5 ms + 15 ms) = 40 ms for last-generation systems. Note
that this calculation does not take into account the necessary 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 five hops from access to
the interconnection gateway providing connectivity to other networks.

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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] 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, in conclusion, in a typical deployment, it can be stated that
the 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
deviations from the delay achievable with the SIAL solution.

Authors' Addresses

Luis M. Contreras
Telefonica I+D
Ronda de la Comunicacion, s/n
Sur-3 building, 3rd floor
Madrid 28050
Spain

EMail: [email protected]

Carlos J. Bernardos
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain

Phone: +34 91624 6236
EMail: [email protected]
URI: http://www.it.uc3m.es/cjbc/

Ignacio Soto
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain

EMail: [email protected]

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