IP Multicast Use Case Analysis for PMIPv6.based Distributed Mobility Management
draft-sfigueiredo-multimob-use-case-dmm-02
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draft-sfigueiredo-multimob-use-case-dmm-02
MULTIMOB Group S. Figueiredo
Internet Draft Universidade de Aveiro
Intended status: Informational S. Jeon
Expires: January 16, 2013 Instituto de Telecomunicacoes
R. L. Aguiar
Universidade de Aveiro
July 16, 2012
IP Multicast Use Case Analysis for PMIPv6.based Distributed Mobility
Management
draft-sfigueiredo-multimob-use-case-dmm-02.txt
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Abstract
Mobile networks are changing towards distributed mobility management,
tackling inefficiencies in network management and packet routing.
Identifying IP multicast use cases applicable into DMM would be
meaningful before exploring solution spaces. This document describes
use cases when IP multicast is applied on DMM environment using Base
Solution approach specified in [RFC6224], and presents issues for
each use case.
Table of Contents
1. Introduction...................................................3
2. Conventions and Terminology....................................3
3. Use Cases Description..........................................4
3.1. Assumptions...............................................4
3.2. Multicast listener support................................4
3.2.1.1. Duplicated Traffic..............................5
3.2.1.2. Non-optimal routing.............................6
3.3. Multicast sender support..................................7
3.3.1.1. Triangular routing..............................8
3.3.1.2. Non-distributed anchoring......................10
4. IANA Considerations...........................................12
5. Security Considerations.......................................12
6. References....................................................13
6.1. Normative References.....................................13
6.2. Informative References...................................13
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1. Introduction
Centralized mobility management approach brings several drawbacks
such as single point of failure, non-optimal routing and severe
overloading on the anchor point. It is expected to be much severe as
data traffic consumed by mobile devices increases.
In order to tackle these problems, distributed mobility management
(DMM) is introduced, bringing the mobility anchor closer to the MN.
IP multicast provides an efficient method for distributing multimedia
contents, but it was mainly designed for fixed networks. [RFC6224]
specified the Base Solution applicable to network-based Proxy Mobile
IPv6 (PMIPv6) protocol, based on centralized mobility management. IP
multicast should be also specified in DMM, but the application of the
Base Solution for multicast support in PMIPv6 standardized in IETF
MULTIMOB WG needs to be identified first.
This document briefly describes use cases of IP multicast in a
PMIPv6-based DMM environment, following DMM Requirements [DMMREQ],
and introduces consequent problems. Both listener and sender cases
are studied.
2. Conventions and 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 RFC 2119 [RFC2119].
This document uses the terminology defined in [RFC5213], [RFC6275],
and [RFC3810], and [RFC4601]. Also, new entities are defined relying
on the PMIPv6 entities specified in [RFC5213]:
- Mobility Access Router (MAR): A router with the capability of
acting both as a mobility anchor and as an access router, in a per
flow basis.
- Previous Mobility Access Router (P-MAR): The MAR where the MN was
attached to previously to the network-layer mobility process, and
that may be acting as an anchor for one or multiple flows.
- New Mobility Access Gateway (N-MAR): The MAR to which the MN is
currently attached, providing the access functionality and thus
delivers all the flows destined to the MN.
- Multicast Listener Discovery Proxy (MLD-P): An entity providing
MLD based forwarding following the operation defined in [RFC4605].
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In the current document, only MLDv2-based signaling is considered,
targeting IPv6 networks (REQ3 from [DMMREQ]).
3. Use Cases Description
3.1. Assumptions
This draft refers to requirements of DMM as a base reference
architecture, with the major goal of showing multicast use cases
[DMMREQ]. Following the recommendation of reusing the existing
mobility protocols, the identified IP multicast model derives from
PMIPv6 Base multicast mobility solution [RFC6224]. As such, MAG and
LMA functionalities defined in [RFC5213] are assumed to be installed
in a mobility access router (MAR), defined in this document. A MAR
provides tunnel-based forwarding to provide a home network prefix
(HNP)-based flow with the necessary IP session continuity whenever
the MN moves to another MAR.
3.2. Multicast listener support
When a MN initially attaches to the P-MAR (as shown in Figure 1), it
receives a HNP address which will be associated with communications
started at that MAR. As the P-MAR detects the new logical link, it
transmits a general MLD Query message - to which the MN will not yet
reply, as it is not yet running any multicast session. The P-MAR then
adds the downstream logical link to the MLD Proxy instance [RFC4605].
In this case, i.e. when users subscribe to multicast content only
after associating with the MAR, the MLD Proxy will set its uplink to
the multicast infrastructure. When the MN intends to start receiving
the multicast session, it will send an unsolicited MLD Report,
triggered by its application. On receiving the latter message, the
MLD Proxy tries to join the multicast channel(s) by sending an
aggregated MLD Report through the MLD Proxy upstream interface. Note
that the same MLD Proxy instance will be assigned to all MNs which
initiated their multicast subscriptions in the current MAR (i.e. the
MNs having no multicast mobility session). When the joining procedure
ends, multicast data is transmitted through the same interfaces,
until reaching the MN.
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+----------------+
| Multicast |
| Infrastructure |
+----------------+
*
* (S,G)
*
+----------+ +----------+
| P-MAR |---------------| N-MAR |
| |***************| |
| (MLD-P) |---------------| (MLD-P) |
+----------+ +----------+
* *
* *
+------+ +------+
| MN | -----> | MN |
+------+ +------+
Figure 1 Multicasting architecture using distributed mobility
management
When the MN moves from P-MAR, the N-MAR is required to establish a
tunnel for IP session continuity of the flows being sent towards and
from the MN's HNP assigned by the P-MAR. This implies that N-MAR has
an appropriate method to know the P-MAR. Multiple ideas are supposed
to be made at the solution stage of DMM WG, therefore it is out of
scope of this document. Following the operation of the MLD Proxy
[RFC4605], after the bidirectional tunnel establishment, the
following process takes place. First, the N-MAR sends a General MLD
Query, and verifies whether the MN is admissible for multicast
sessions. Then, the MLD Proxy at the N-MAR adds the downstream
interface corresponding to the MN, and configures the upstream
interface towards the MN's P-MAR. This is simple and applicable as a
network-based multicast DMM approach. However, this approach leads to
a couple of relevant issues.
3.2.1.1. Duplicated Traffic
One of the problems is traffic duplication. This is a result of the
tunnel convergence problem occurring in [RFC6224]. As shown in Figure
2, MN1 and MN3, which moved from MAR1 and MAR3, respectively, are
currently located at the MAR2. Through their respective tunnels, they
receive multicast packets of the same channel through different
anchoring MARs. This causes duplicated traffic, converging to the
MAR2, with the magnitude of replicated traffic, which may be much
bigger than that of PMIPv6 when we assume that the number of MARs in
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future DMM domains is expected to be much larger than that of LMAs at
core level within a PMIPv6 domain.
+----------------+
| Multicast Tree | *
+----------------+ *
* * *
* * *
* * *
(S,G) * (S,G) * * (S,G)
* * *
+----------+ (-->) +----------+ (<--) +----------+
| MAR1 |---------| MAR2 |---------| MAR3 |
| |*********| |*********| |
| (MLD-P) |---------| (MLD-P) |---------| (MLD-P) |
+----------+ Tun.1 +----------+ Tun.2 +----------+
* * *
* * *
* * *
+---+ move +---+ +---+ +---+ move +---+
|MN1| ---> |MN1| |MN2| |MN3| <--- |MN3|
+---+ +---+ +---+ +---+ +---+
(<--/-->) : direction of the multicast packet flow
Figure 2 Data replication
3.2.1.2. Non-optimal routing
Another issue is non-optimal routing (Figure 3). If we consider a
significantly large domain, multicast packets MAY traverse a long
distance, depending on the setup direction of the upstream interface
of MLD Proxy instances. The issue is more obvious if we assume all
MARs are connected to the multicast infrastructure.
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+----------------+
| Multicast |
| Infrastructure |
+----------------+
*
* (S,G)
*
+----------+ +----------+
| P-MAR |------ ------| N-MAR |
| |****** ... ******| |
|(MLD-P) |------ ------| (MLD-P) |
+----------+ +----------+
* *
* *
+------+ +------+
| MN | -----> | MN |
+------+ +------+
Figure 3 Non-optimal routing problem
3.3. Multicast sender support
Mobile multicast sender using PMIPv6 base solution is being defined
in [SENDER]. Basically, MLD Proxies provide the ability for MAGs to
forward the multicast traffic to the MN's corresponding LMA.
To allow the sender to deliver multicast content to the multicast
tree, the MLD Proxy should configure its upstream interface towards a
multicast router [PM-HOME]. Depending on the network topology, it may
also be configured towards a MLD Proxy placed on a neighbor MAR. On
the multicast source's mobility (Figure 4), an identical operation to
the listener mobility case is expected from the MLD Proxy behavior.
In this case, the source uploads multicast traffic through one of MLD
Proxy's downstream interfaces, and the traffic is forwarded through
the uplink interface towards the P-MAR.
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+------+ +----------------+
| RP |---------| Multicast |
+------+ | Infrastructure |
* +----------------+
* (S,G) |
* |
+----------+ +----------+
| P-MAR |----------| N-MAR |
| |**********| |
| (MLD-P) |----------| (MLD-P) |
+----------+ +----------+
* *
* *
+------+ +------+
| S | ----> | S |
+------+ +------+
Figure 4 Multicast sender mobility
3.3.1.1. Triangular routing
When a source moves to N-MAR from P-MAR, multicast data will be sent
through the mobility tunnel between N-MAR and P-MAR (Figure 5). If a
listener (L1) attaches to the same MAR (N-MAR), it will receive the
multicast data through multicast infrastructure, following the
regular configuration of MLD Proxy. Hence, the multicast data is
routed non-optimally between the source and the listener, going from
N-MAR to P-MAR, to the multicast routing tree, and then back to N-MAR
again before reaching the listener.
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+------+ +----------------+
| RP |*********| Multicast |
+------+ | Infrastructure |
* +----------------+
* (S,G) *
* *
+----------+ +----------+
| P-MAR |-------| N-MAR |
| |*******| |
| (MLD-P) |-------| (MLD-P) |
+----------+ +----------+
* * *
* * *
+------+ move +------+ +-----+
| S | ---> | S | | L1 |
+------+ +------+ +-----+
Figure 5 Triangular routing after source mobility
A similar problem occurs in the opposite process, i.e. if a multicast
source starts transmitting multicast content at a MAR, and a listener
moves to the same MAR while receiving the source's content (Figure
6).
+------+ +----------------+
| RP |*********| Multicast |
+------+ | Infrastructure |
* +----------------+
* (S,G) *
* *
+----------+ +----------+
| N-MAR |-------| P-MAR |
| |*******| |
| (MLD-P) |-------| (MLD-P) |
+----------+ +----------+
* * *
* * *
+------+ +----+ move +----+
| S | | L1 | <--- | L1 |
+------+ +----+ +----+
Figure 6 Triangular routing after listener mobility
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When the source and the listener are within a same MAR (MAR2), if
both the source and listener try to send the session and receive it,
respectively, the traffic will be optimally sent to the listener
without going through native multicast infrastructure. As the traffic
reaches the MLD Proxy via the downstream interface to which the
source is attached, it will be sent through the downstream interface
to which the listener sent the MLD Report. However, if the source and
the listener move to different MARs, the traffic will traverse the
following non-optimal path, even though they share a common anchor:
Source -> MAR1 -> MAR2 -> Multicast Tree -> MAR2 -> MAR3
This problem is depicted in Figure 7.
+----------------+
| Multicast Tree |
+----------------+
* *
* *
* *
* *
* *
+----------+ (-->) +----------+ (-->) +----------+
| MAR1 |---------| MAR2 |---------| MAR3 |
| |*********| |*********| |
| (MLD-P) |---------| (MLD-P) |---------| (MLD-P) |
+----------+ Tun.1 +----------+ Tun.2 +----------+
* * * *
* * * *
* * * *
+---+ move +---+ +---+ move +---+
| S | <--- | S | | L | --> | L |
+---+ +---+ +---+ +---+
(<--/-->) : direction of the multicast packet flow
Figure 7 Multicast traffic non-optimal routing due to both mobile
sender and listener
3.3.1.2. Non-distributed anchoring
REQ1 from [DMMREQ] refers that "DMM MUST enable a distributed
deployment of mobility management of IP sessions so that the traffic
can be routed in an optimal manner without traversing centrally
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deployed mobility anchors". When a MN subscribes to a new multicast
session with existing multicast mobility session, the Aggregated MLD
Report containing all the MN's multicast subscriptions will be sent
from the current MLD Proxy through the same uplink interface, i.e.
towards a single multicast mobility anchor. This results in some of
previously identified issues (e.g. non-optimality in the path that
both the subscription and multicast traffic traverse). It can be
stated that the MLD Proxy nature doesn't comply with the
aforementioned requirement, leading to the subscription of any
multicast flow using the same multicast mobility data path.
This problem is depicted in Figure 8, where both multicast flow 1 and
flow 2 reach MAR2 from MAR1, being flow 2's optimal routing path
affected by the mobility status of the MN, and in particular by the
order in which the multicast flows were subscribed. While this issue
is not exclusively related to mobile multicast sources, it is better
depicted and its' impact in the routing is more obvious when
considering one.
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+----------------+
| Multicast Tree |
* +----------------+#
* #
* #
* #
* #
+----------+ (-->) +----------+
| MAR1 |--------- -------| MAR2 |
| |#*#*#*#*#............#*#*#*#| |
| (MLD-P) |--------- -------| (MLD-P) |
+----------+ Tun. +----------+
* * #
* downstream) # # (upstream)
* * #
* # #
+---+ move +---+ +---+
| L | ----------> | L | | S |
+---+ +---+ +---+
* : Multicast flow 1
# : Multicast flow 2 (subscribed after some time in MAR2)
Figure 8 Non-optimal routing due to single MLD Proxy uplink
4. IANA Considerations
This document makes no request of IANA.
5. Security Considerations
TBD
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6. References
6.1. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[RFC6275] Johnson, D., Perkins, C., and J. Arkko, "Mobility Support
in IPv6", RFC 6275, July 2011.
[RFC3810] R. Vida, and L. Costa, "Multicast Listener Discovery
Version 2 (MLDv2) for IPv6," IETF RFC 3810, June 2004.
[RFC5213] S. Gundavelli, K. Leung, V. Devarapalli, K. Chowdhury, and
B. Patil, "Proxy Mobile IPv6", IETF RFC 5213, August 2008.
[RFC4605] B. Fenner, H. He, B. Haberman, and H. Sandick, "Internet
Group Management Protocol (IGMP) / Multicast Listener
Discovery (MLD) Based Multicast Forwarding ("IGMP/MLD
Proxying")", IETF RFC 4605, August 2006.
[RFC4601] B. Fenner, M. Handley, H. Holbrook, and I. Kouvelas,
"Protocol Independent Multicast - Sparse Mode (PIM-SM):
Protocol Specification (Revised)", RFC 4601, August 2006.
6.2. Informative References
[RFC6224] T. Schmidt, M. Waehlisch, S. Krishnan, "Base Deployment for
Multicast Listener Support in PMIPv6 Domain,", RFC 6224,
April 2011.
[DMMREQ] H. Chan, "Requirements of distributed mobility management",
draft-ietf-dmm-requirements-01 (work in progress), July
2012.
[SENDER] T C. Schmidt et al, "Mobile Multicast Sender Support in
Proxy Mobile IPv6 (PMIPv6) Domains", draft-ietf-multimob-
pmipv6-source-00 (work expired), January 2012.
[PM-HOME] S. Jeon, N. Kang, and Y. Kim, "Mobility Management based on
Proxy Mobile IPv6 for Multicasting Services in Home
Networks," IEEE Transactions on Consumer Electronics (TCE),
vol. 55, no. 3, pp. 1227-1232, August 2009.
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Authors' Addresses
Sergio Figueiredo
Universidade de Aveiro
3810-193 Aveiro, Portugal
E-mail: sfigueiredo@av.it.pt
Seil Jeon
Instituto de Telecomunicacoes
Campus Universitario de Santiago
3810-193 Aveiro, Portugal
E-mail: seiljeon@av.it.pt
Rui L. Aguiar
Universidade de Aveiro
3810-193 Aveiro, Portugal
E-mail: ruilaa@ua.pt
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