One document matched: draft-chan-dmm-requirements-00.xml
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docName="draft-chan-dmm-requirements-00">
<front>
<title abbrev="DMM-Reqs">
Requirements of distributed mobility management
</title>
<author initials="H" surname="Chan (Ed.)" fullname="H Anthony Chan (editor)">
<organization>Huawei Technologies</organization>
<address>
<postal>
<street>5340 Legacy Dr. Building 3, Plano, TX 75024, USA</street>
<street>Email: h.a.chan@ieee.org</street>
<street>-</street>
<street>Dapeng Liu</street>
<street>China Mobile</street>
<street>Unit2, 28 Xuanwumenxi Ave, Xuanwu District, Beijing 100053, China</street>
<street>Email: liudapeng@chinamobile.com</street>
<street>-</street>
<street>Pierrick Seite</street>
<street>France Telecom - Orange</street>
<street>4, rue du Clos Courtel, BP 91226, Cesson-Sevigne 35512, France</street>
<street>Email: pierrick.seite@orange-ftgroup.com</street>
<street>-</street>
<street>Hidetoshi Yokota</street>
<street>KDDI Lab</street>
<street>2-1-15 Ohara, Fujimino, Saitama, 356-8502 Japan</street>
<street>Email: yokota@kddilabs.jp</street>
<street>-</street>
<street>Charles E. Perkins</street>
<street>Tellabs Inc.</street>
<street>4555 Great America Parkway, #S5-130</street>
<street>Email: charliep@computer.org</street>
<street>-</street>
<street>Melia Telemaco</street>
<street>Alcatel-Lucent Bell Labs</street>
<street>Email: telemaco.melia@alcatel-lucent.com</street>
<street>-</street>
<street>Wassim Michel Haddad</street>
<street>Ericsson</street>
<street>300 Holger Dr, San Jose, CA 95134, USA</street>
<street>Email: Wassam.Haddad@ericsson.com</street>
<street>-</street>
<street>Elena Demaria</street>
<street>Telecom Italia</street>
<street>via G. Reiss Romoli, 274, TORINO, 10148, Italy</street>
<street>Email: elena.demaria@telecomitalia.it</street>
<street>-</street>
<street>Seok Joo Koh</street>
<street>Kyungpook National University, Korea</street>
<street>Email: sjkoh@knu.ac.kr</street>
<street>-</street>
<street>Rute Sofia</street>
<street>University Lusofona, Portugal</street>
<street>Email: rute.sofia@ulusofona.pt</street>
<street>-</street>
</postal>
</address>
</author>
<date month="March" year="2012"></date>
<area></area>
<workgroup></workgroup>
<abstract>
<t>
The traditional hierarchical structure of cellular networks
has led to deployment models which are heavily centralized. Mobility management with centralized mobility anchoring
in existing hierarchical mobile networks
is quite prone to suboptimal routing
and issues related to scalability.
Centralized functions present a single point of failure,
and inevitably introduce longer delays
and higher signaling loads
for network operations related to mobility management.
To make matters worse,
there are numerous variants of Mobile IP
in addition to other protocols
standardized outside the IETF,
making it much more difficult
to create economical and interoperable solutions.
In this document we examine the problems
of centralized mobility management
and identify requirements
for distributed and dynamic mobility management.
</t>
</abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>
In the past decade a fair number of mobility protocols
have been standardized.
Although the protocols differ
in terms of functions and associated message format,
we can identify a few key common features:
<list>
<t>
presence of a centralized mobility anchor
providing global reachability and an always-on experience;
<vspace blankLines="1" />
</t>
<t>
extensions to optimize handover performance
while users roam across wireless cells;
<vspace blankLines="1" />
</t>
<t>
extensions to enable the use of heterogeneous wireless interfaces
for multi-mode terminals (e.g. cellular phones).
<vspace blankLines="1" />
</t>
</list>
The presence of the centralized mobility anchor
allows a mobile device to be reachable
when it is not connected to its home domain.
The anchor point, among other tasks,
ensures reachability
of forwarding of packets
destined to or sent from the mobile device.
Most of the deployed architectures today
have a small number of centralized anchors
managing the traffic of millions of mobile subscribers.
Compared with a distributed approach,
a centralized approach is likely to have several issues or limitations
affecting performance and scalability,
which require costly network dimensioning
and engineering to resolve.
</t>
<t>
To optimize handovers from the perspective of mobile nodes,
the base protocols have been extended
to efficiently handle packet forwarding
between the previous and new points of attachment.
These extensions are necessary
when applications impose stringent requirements in terms of delay.
Notions of localization and distribution of local agents
have been introduced to reduce signaling overhead.
Unfortunately today we witness difficulties
in getting such protocols deployed,
often leading to sub-optimal choices.
</t>
<t>
Moreover, the availability of multi-mode devices
and the possibility of using several network interfaces simultaneously
have motivated the development of more new protocol extensions.
Deployment is further complicated with so many extensions.
</t>
<t>
Mobile users are, more than ever, consuming Internet content;
such traffic imposes new requirements
on mobile core networks for data traffic delivery.
When the traffic demand exceeds available capacity,
service providers need to implement new strategies
such as selective traffic offload (e.g. 3GPP work items LIPA/SIPTO)
through alternative access networks (e.g. WLAN).
Moreover, the localization of content providers
closer to the Mobile/Fixed Internet Service Providers network
requires taking into account local Content Delivery Networks (CDNs)
while providing mobility services.
</t>
<t>
When demand exceeds capacity,
both offloading and CDN techniques
could benefit from the development of mobile architectures
with fewer levels of routing hierarchy
introduced into the data path by the mobility management system.
This trend in network flattening is reinforced
by a shift in users traffic behavior,
aimed at increasing direct communications among peers
in the same geographical area.
Distributed mobility management in a truly flat mobile architecture
would anchor the traffic closer to the point of attachment of the user
and overcome the suboptimal routing issues of a centralized mobility scheme.
</t>
<t>
While deploying
[Paper-Locating.User]
today's mobile networks,
service providers face new challenges.
More often than not,
mobile devices remain attached to the same point of attachment.
Specific IP mobility management support is not required for applications
that launch and complete while the mobile device is connected to the
same point of attachment.
However,
the mobility support has been designed to be always on
and to maintain the context for each mobile subscriber
as long as they are connected to the network.
This can result in a waste of resources
and ever-increasing costs for the service provider.
Infrequent mobility and intelligence of many applications
suggest that mobility can be provided dynamically,
thus simplifying the context maintained
in the different nodes of the mobile network.
</t>
<t>
The proposed charter will address two complementary aspects
of mobility management procedures:
the distribution of mobility anchors to achieve a more flat design
and the dynamic activation/deactivation of mobility protocol support
as an enabler to distributed mobility management.
The former has the goal of positioning mobility anchors (HA, LMA)
closer to the user;
ideally, these mobility agents could be collocated with the first hop router.
The latter, facilitated by the distribution of mobility anchors,
aims at identifying when mobility must be activated
and identifying sessions that do not impose mobility management
-- thus reducing the amount of state information
to be maintained in the various mobility agents of the mobile network.
The key idea is that dynamic mobility management relaxes some constraints
while also repositioning mobility anchors;
it avoids the establishment of non optimal tunnels
between two topologically distant anchors.
</t>
<t>
Considering the above,
the distributed mobility management working group will:
<list>
<t>
Define the problem statement and associated requirements
for distributed mobility management.
This work aims at defining the problem space
and identifies the key functional requirements.
<vspace blankLines="1" />
</t>
<t>
Produce a gap analysis mapping the above requirements
against existing solutions.
<vspace blankLines="1" />
</t>
<t>
Give best practices
for the deployment of existing mobility protocols
in a distributed mobility management
and describe limitations of each such approach.
<vspace blankLines="1" />
</t>
<t>
Describe extensions, if needed,
to current mobility protocols
for their applications in distributed mobility architectures.
<vspace blankLines="1" />
</t>
</list>
</t>
<t>
This document describes
the motivations of distributed mobility management
and the proposed work in Section 1.1.
Section 1.2 summarizes the problems
with centralized IP mobility management
compared with distributed and dynamic mobility management,
which is elaborated in Section 4.
The requirements to address these problems
are given in Section 5.
A companion document
[dmm-scenario]
discusses the use case scenarios.
</t>
<t>
Much of the contents this document together with those in
[dmm-scenario]
have been merged and elaborated into the following review
paper:
[Paper-Distributed.Mobility.Review].
</t>
</section>
<section title="Conventions used in this document">
<t>
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 <xref target="RFC2119" />.
</t>
</section>
<section title="Centralized versus distributed mobility management">
<t>
Mobility management functions
may be implemented at different layers
of the network protocol stack.
At the IP (network) layer,
they may reside in the network or in the mobile node.
In particular,
a network-based solution resides in the network only.
It therefore enables mobility for existing hosts
and network applications
which are already in deployment but lack mobility support.
</t>
<t>
At the IP layer,
a mobility management protocol to achieve session continuity
is typically based on the principle
of distinguishing between identifier and routing address
and maintaining a mapping between them.
With Mobile IP, the home address serves as an identifier of the device
whereas the care-of-address takes the role of routing address,
and the binding between them is maintained at the mobility anchor,
i.e., the home agent.
If packets can be continuously delivered
to a mobile device at its home address,
then all sessions using that home address can be preserved
even though the routing or care-of address changes.
</t>
<t>
The next two subsections explain centralized and distributed
mobility management functions in the network.
</t>
<section title="Centralized mobility management">
<t>
With centralized mobility management,
the mapping information between the stable node identifier
and the changing IP address of an MN
is kept at a centralized mobility anchor.
Packets destined to an MN are routed via this anchor.
In other words,
such mobility management systems are centralized
in both the control plane and the data plane.
</t>
<t>
Many existing mobility management deployments
make use of centralized mobility anchoring
in a hierarchical network architecture,
as shown in Figure 1.
Examples of such centralized mobility anchors
are the home agent (HA) and local mobility anchor (LMA)
in Mobile IP <xref target="RFC3775"/>
and Proxy Mobile IP <xref target="RFC5213"/>, respectively.
Current mobile networks
such as the Third Generation Partnership Project (3GPP)
UMTS networks, CDMA networks,
and 3GPP Evolved Packet System (EPS) networks
also employ centralized mobility management,
with Gateway GPRS Support Node (GGSN)
and Serving GPRS Support Node (SGSN)
in the 3GPP UMTS hierarchical network
and with Packet data network Gateway (P-GW)
and Serving Gateway (S-GW) in the 3GPP EPS network.
</t>
<figure>
<preamble></preamble>
<artwork><![CDATA[
UMTS 3GPP SAE MIP/PMIP
+------+ +------+ +------+
| GGSN | | P-GW | |HA/LMA|
+------+ +------+ +------+
/\ /\ /\
/ \ / \ / \
/ \ / \ / \
/ \ / \ / \
/ \ / \ / \
+------+ +------+ +------+ +------+ +------+ +------+
| SGSN | | SGSN | | S-GW | | S-GW | |FA/MAG| |FA/MAG|
+------+ +------+ +------+ +------+ +------+ +------+
]]></artwork>
<postamble></postamble>
</figure>
<t>Figure 1. Centralized mobility management.
</t>
</section>
<section title="Distributed mobility management">
<t>Mobility management functions may also be distributed
to multiple locations in different networks
as shown in Figure 2,
so that a mobile node in any of these networks
may be served by a closeby mobility function (MF).
</t>
<figure>
<preamble></preamble>
<artwork><![CDATA[
+------+ +------+ +------+ +------+
| MF | | MF | | MF | | MF |
+------+ +------+ +------+ +------+
|
----
| MN |
----
]]></artwork>
<postamble></postamble>
</figure>
<t>Figure 2. Distributed mobility management.
</t>
<t>
Mobility management may be partially distributed,
i.e., only the data plane is distributed,
or fully distributed
where both the data plane and control plane are distributed.
These different approaches are described in detail in
[I-D.dmm-scenario].
</t>
<t>
[Paper-New.Perspective] discusses
some initial steps towards a clear definition
of what mobility management may be,
to assist in better developing distributed architecture.
[Paper-Characterization.Mobility.Management]
analyses current mobility solutions
and propses an initial decoupling of mobility management
into well-defined functional blocks,
identifying their interactions,
as well as a potential grouping,
which later can assist
in deriving more flexible mobility management architectures.
According to the split functional blocks,
this paper proposes three ways
into which mobility management functional blocks
can be groups, as an initial way
to consider a better distribution:
location and handover management,
control and data plane,
user and access perspective.
</t>
<t>
A distributed mobility management scheme is proposed in
[Paper-Distributed.Dynamic.Mobility]
for future flat IP architecture consisting of access nodes.
The benefits of this design
over centralized mobility management
are also verified through simulations in
[Paper-Distributed.Centralized.Mobility].
</t>
<t>
Before designing new mobility management protocols
for a future flat IP architecture,
one should first ask
whether the existing mobility management protocols
that have already been deployed
for the hierarchical mobile networks
can be extended to serve the flat IP architecture.
MIPv4 has already been deployed in 3GPP2 networks,
and PMIPv6 has already been adopted in WiMAX Forum
and in 3GPP standards.
Using MIP or PMIP
for both centralized and distributed architectures
would ease the migration of the current mobile networks
towards a flat architecture.
It has therefore been proposed to adapt MIP or PMIPv6
to achieve distributed mobility management
by using a distributed mobility anchor architecture.
</t>
<t>
In
[Paper-Migrating.Home.Agents],
the HA functionality is copied to many locations.
The HoA of all MNs are anycast addresses,
so that a packet destined to a HoA from any CN from any network
can be routed via the nearest copy of the HA.
In addition,
distributing the function of HA
using a distributed hash table structure is proposed in
[Paper-Distributed.Mobility.SAE].
A lookup query to the hash table
will retrieve the location information of an MN is stored.
</t>
<t>
In
[Paper-Distributed.Mobility.PMIP],
only the mobility routing (MR) function
is duplicated and distributed in many locations.
The location information for any MN
that has moved to a visited network
is still centralized
and kept at a location management (LM) function
in the home network of the MN.
The LM function at different networks
constitutes a distributed database system
of all the MNs
that belong to any of these networks
and have moved to a visited network.
The location information is maintained
in the form of a hierarchy:
the LM at the home network,
the CoA of the MR of the visited network,
and then the CoA to reach the MN in the visited network.
The LM in the home network
keeps a binding of the HoA of the MN
to the CoA of the MR of the visited network.
The MR keeps the binding of the HoA of the MN
to the CoA of the MN in the case of MIP,
or the proxy-CoA of the Mobile Access Gateway (MAG)
serving the MN in the case of PMIP.
</t>
<t>
[I-D.PMIP-DMC] discusses two distributed mobility control schemes
using the PMIP protocol:
Signal-driven PMIP (S-PMIP)
and Signal-driven Distributed PMIP (SD-PMIP).
S-PMIP is a partially distributed scheme,
in which the control plane
(using a Proxy Binding Query to get the Proxy-CoA of the MN)
is separate from the data plane,
and the optimized data path
is directly between the CN and the MN.
SD-PMIP is a fully distributed scheme,
in which the Proxy Binding Update is not performed,
and instead each MAG will multicast a Proxy Binding Query message
to all of the MAGs in its local PMIP domain
to retrieve the Proxy-CoA of the MN.
</t>
</section>
</section>
<section title="Problem statement">
<t>
This section identifies problems and limitations
of centralized mobility approaches,
and compares against possible distributed approaches.
</t>
<section title="Non-optimal routes">
<t>Routing via a centralized anchor often results in a longer route.
Figure 3 shows two cases of non-optimized routes.
</t>
<figure>
<preamble></preamble>
<artwork><![CDATA[
MIP/PMIP
+------+
|HA/LMA|
+------+
/\ \ \ +---+
/ \ \ \ |CDN|
/ \ \ \ +---+
/ \ \ \ |
/ \ \ \ |
+------+ +------+ +------+ +------+
|FA/MAG| |FA/MAG| |FA/MAG| |FA/MAG|
+------+ +------+ +------+ +------+
| |
---- ----
| CN | | MN |
---- ----
]]></artwork>
<postamble></postamble>
</figure>
<t>Figure 3. Non-optimized route when communicating with CN
and when accessing local content.
</t>
<t>
In the first case, the mobile node and the correspondent node
are close to each other but are both far from the mobility anchor.
Packets destined to the mobile node
need to be routed via the mobility anchor,
which is not on the shortest path.
<!-- CEP: stopped here for now... -->
The second case involves a content delivery network (CDN).
A user may obtain content from a server,
such as when watching a video.
As such usage becomes more popular,
resulting in an increase in the core network traffic,
service providers may relieve the core network traffic
by placing these contents closer to the users
in the access network in the form of cache or local CDN servers.
Yet as the MN is getting content
from a local or cache server of a CDN,
even though the server is close to the MN,
packets still need to go through the core network
to route via the mobility anchor in the home network of the MN,
if the MN uses the HoA as its identifier.
</t>
<t>
In a distributed mobility management design,
one possibility is to have
mobility anchors distributed in different access networks
so that packets may be routed
via a nearby mobility anchor function,
as shown in Figure 4.
</t>
<figure>
<preamble></preamble>
<artwork><![CDATA[
+---+
|CDN|
+---+
|
|
+------+ +------+ +------+ +------+
| MF | | MF | | MF | | MF |
+------+ +------+ +------+ +------+
| |
---- ----
| CN | | MN |
---- ----
]]></artwork>
<postamble></postamble>
</figure>
<t>Figure 4.
Mobile node in any network is served by a close by mobility function.
</t>
<t>
Due to the above limitation,
with the centralized mobility anchor design,
route optimization extensions to mobility protocols
are therefore needed.
Whereas the location privacy of each MN may be compromised
when the CoA of an MN is given to the CN,
those mobility protocol deployments
that lack such optimization extensions
will encounter non-optimal routes,
which affect the performance.
</t>
<t>
In contrast,
route optimization may be naturally
an integral part of a distributed mobility management design.
With the help of such intrinsic route optimization,
the data transmission delay will be reduced,
by which the data transmission throughputs can be enhanced.
Furthermore, the data traffic overhead at the mobility agents
such as the HA and the LMA in the core network can be alleviated significantly.
</t>
</section>
<section title="Non-optimality in Evolved Network Architecture">
<t>
Centralized mobility management
is currently deployed
to support the existing hierarchical mobile data networks.
It leverages on the hierarchical architecture.
However,
the volume of wireless data traffic
continues to increase exponentially.
The data traffic increase
would require costly capacity upgrade
of centralized architectures.
It is thus predictable
that the data traffic increase will soon overload
the centralized data anchor point,
e.g., the P-GW in 3GPP EPS.
In order to address this issue,
a trend in the evolution of mobile networks
is to distribute network functions
close to access networks.
These network functions can be the content servers
in a CDN,
and also the data anchor point.
</t>
<t>
Mobile networks have been evolving
from a hierarchical architecture to a more flattened architecture.
In the 3GPP standards,
the GPRS network has the hierarchy GGSN 每 SGSN 每 RNC 每 NB (Node B).
In 3GPP EPS networks,
the hierarchy is reduced to P-GW 每 S-GW 每 eNB (Evolved NB).
In some deployments,
the P-GW and the S-GW are collocated to further reduce the hierarchy.
Reducing the hierarchy this way
reduces the number of different physical network elements in the network,
contributing to easier system maintenance and lower cost.
As mobile networks become more flattened,
the centralized mobility management can become non-optimal.
Mobility management deployment
with distributed architecture
is then needed to support the more flattened network and the CDN networks.
</t>
</section>
<section title="Lack of user-centricity">
<t>
The mobility anchor point,
as the main element of a mobility management system,
has been object of intensive studies
in order to create more distributed and decentralized systems.
Accordingly, its role, its functionalities,
and the location it should take in the network
(e.g. router, server, etc) are not a consensus.
Depending on the architecture,
on the network characteristics, and on the functionalities
we have in the mobility anchor element,
its location may vary,
and its function in the whole system may change.
Considering that user-centric networks
present particular characteristics
(e.g. there is no clear splitting
between network elements and end-devices),
the current centralized standards may not be suitable.
Thus, a novel mobility management approach should be designed
for such networks,
considering all its particularities
and following this trend
of rethinking the mobility anchor point element.
</t>
<t>
These aspects reinforce the need
for distributed and dynamic mobility mechanisms.
Positioning the anchor-point in network elements
closer to the end user
provides the capability
to have a more flexible mobility management service,
with (potentially) more control
in terms of users expectations;
it also assists the access operation
by lowering the operation complexity.
For instance, traffic locality can be more easily achieved
by having mobility management functionality
deployed in elements that are closer to customer premises,
or on the edges of the access network.
</t>
</section>
<section title="Low scalability of centralized route and mobility context maintenance">
<t>
Special routes are set up
to enable session continuity when a handover occurs.
Packets sent from the CN
need to be tunneled between the HA and FA in MIP
and between the LMA and MAG in PMIP.
However,
these network elements at the ends of the tunnel
are also routers
performing the regular routing tasks
for ordinary packets not involving a mobile node.
These ordinary packets need to be directly routed
according to the routing table in the routers without tunneling.
Therefore,
the network must be able to distinguish
those packets requiring tunneling from the regular packets.
For each packet that requires tunneling owing to mobility,
the network will encapsulate it
with a proper outer IP header
with the proper source and destination IP addresses.
The network therefore
needs to maintain and manage the mobility context of each MN,
which is the relevant information
needed to characterize the mobility situation of that MN
to allow the network to distinguish
their packets from other packets
and to perform the required tunneling.
</t>
<t>
Setting up such special routes
and maintaining the mobility context for each MN
is more difficult to scale
in a centralized design with a large number of MNs.
Distributing the route maintenance function
and the mobility context maintenance function
among different networks can be more scalable.
</t>
</section>
<section title="Wasting resources to support mobile nodes not needing mobility support">
<t>
The problem of centralized route and mobility context maintenance
is aggravated
when the via routes are set up
for many more MNs
that are not requiring IP mobility support.
On the one hand,
the network needs to provide mobility support
for the increasing number of mobile devices
because the existing mobility management
has been designed to always provide such support
as long as a mobile device is attached to the network.
On the other hand,
many nomadic users connected to a network in an office
or meeting room. Such users will not move
for the entire network session.
It has been measured that over two-thirds of a
user mobility is local
[Paper-Locating.User].
In addition,
it is possible to have the intelligence
for applications to manage mobility
without needing help from the network.
Network resources are therefore wasted
to provide mobility support for the devices
that do not really need it at the moment.
</t>
<t>
It is necessary to dynamically set up the via routes
only for MNs that actually undergo handovers
and lack higher-layer mobility support.
With distributed mobility anchors,
such dynamic mobility management mechanism
may then also be distributed.
Therefore, dynamic mobility
and distributed mobility may complement each other
and may be integrated.
</t>
</section>
<section title="Complicated deployment with too many variants and extensions of MIP">
<t>
Mobile IP,
which has primarily been deployed in a centralized manner
for the hierarchical mobile networks,
already has numerous variants and extensions
including PMIP, Fast MIP (FMIP)
<xref target="RFC4068"/>
<xref target="RFC4988"/>
, Proxy-based FMIP (PFMIP)
<xref target="RFC5949"/>
, hierarchical MIP (HMIP)
<xref target="RFC5380"/>
, Dual-Stack Mobile IP (DSMIP)
<xref target="RFC5454"/>
<xref target="RFC5555"/>
and there may be more to come.
These different modifications or extensions of MIP
have been developed over the years
owing to the different needs that are found afterwards.
Deployment can then become complicated,
especially if interoperability with different deployments
is an issue.
</t>
<t>
A desirable feature of mobility management
is to be able to work with network architectures
of both hierarchical networks and flattened networks,
so that the mobility management protocol
possesses enough flexibility to support different networks.
In addition, one goal of dynamic mobility management
is the capability to selectively turn on and off mobility support
and certain different mobility signaling.
Such flexibility in the design
is compatible with the goal
to integrate different mobility variants as options.
Some additional extensions to the base protocols
may then be needed to improve the integration.
</t>
</section>
<section title="Mobility signaling overhead with peer-to-peer communication">
<t>
In peer-to-peer communications,
end users communicate by sending packets
directly addressed to each other's IP address.
However, they need to find each other's IP address first
through signaling in the network.
While different schemes for this purpose may be used,
MIP already has a mechanism to locate an MN
and may be used in this way.
In particular,
MIPv6 Route Optimization (RO) mode
enables a more efficient data packets exchange
than the bidirectional tunneling (BT) mode,
as shown in Figure 5.
</t>
<figure>
<preamble></preamble>
<artwork><![CDATA[
MIP/PMIP
+------+
|HA/LMA|
+------+
/\ \ \
/ \ \ \
/ \ \ \
/ \ \ \
/ \ \ \
+------+ +------+ +------+ +------+
|FA/MAG| |FA/MAG| |FA/MAG| |FA/MAG|
+------+ +------+ +------+ +------+
| |
---- ----
| MN |<--->| CN |
---- ----
]]></artwork>
<postamble></postamble>
</figure>
<t>Figure 5. Non-optimized route when communicating with CN
and when accessing local content.
</t>
<t>
This RO mode is expected to be used whenever possible
unless the MN is not interested
in disclosing its topological location,
i.e., the CoA, to the CN (e.g., for privacy reasons)
or some other network constraints are put in place.
However,
MIPv6 RO mode requires
exchanging a significant amount of signaling messages
in order to establish
and periodically refresh
a bidirectional security association (BSA)
between an MN and its CN.
While the mobility signaling exchange
impacts the overall handover latency,
the BSA is needed to authenticate the binding update
and acknowledgment messages
(note that the latter is not mandatory).
In addition,
the amount of mobility signaling messages increases further
when both endpoints are mobile.
</t>
<t>
A dynamic mobility management capability
to turn off these signaling when they are not needed
will enable the RO mode between two mobile endpoints
at minimum or no cost.
It will also reduce the handover latency
owing to the removal of the extra signaling.
These benefits for peer-to-peer communications
will encourage the adoption
and large-scale deployment of dynamic mobility management.
</t>
</section>
<section title="Single point of failure and attack">
<t>
A centralized anchoring architecture
is generally more vulnerable
to a single point of failure or attack,
requiring duplication and backups of the support functions.
</t>
<t>
On the other hand,
a distributed mobility management architecture
has intrinsically mitigated the problem
to a local network which is then of a smaller scope.
In addition,
the availability of such functions in neighboring networks
has already provided the needed architecture to support protection.
</t>
</section>
</section>
<section title="Requirements">
<t>
After reviewing the problems and limitations
of centralized deployment in Section 4,
this section states
the requirements as follows:
<list style="numbers">
<t>
Distributed mobility requirement:
The mobility management functions
in interconnecting networks
be available in multiple locations
and therefore are always close to any node
so that the node may perform handover with session continuity
without routing the data-plane traffic
via a centralized anchor.
<vspace blankLines="1" />
It is noted that
centralized functions in the control plane
are not excluded
and should still be possible.
<vspace blankLines="1" />
This requirement
enables mobility management deployment
in a distributed architure
to avoid the non-optimal routes
described in Section 4.1.
It enables placing the mobility anchor
closer to the access network
to which the mobile node is attached,
thereby supporting the more flattened network
and the CDN networks
described in Section 4.2.
Such a distributed architecture
is more scalable
than a centralized one
as described in Section 4.4,
and avoids the single point of failure and attack
as described in Section 4.8.
<vspace blankLines="1" />
</t>
<t>
Dynamic mobility requirement:
A network supporting a mix of mobile nodes
some of which may be stationary for extended time
while others may be actively mobile
may minimize traffic overhead
and avoid unnecessary mobility support.
<vspace blankLines="1" />
This requirement addresses the problems of
unnecessary mobility support
described in Section 4.5
and of the mobility signaling overhead
with peer-to-peer communication
described in Section 4.7.
<vspace blankLines="1" />
</t>
<t>
To further ease the deployment
it is desirable that the mobility management
can be deployed in a mix of hierarchical architecture
and distributed architecture
and the different variants and extensions of MIP
are compatible and integrated.
</t>
</list>
</t>
</section>
<section anchor="security" title="Security Considerations">
<t>TBD</t>
</section>
<section title="IANA Considerations">
<t>None</t>
</section>
<section title="Co-authors and Contributors">
<t>This problem statement document is a joint effort
among the following participants.
Each individual has made significant contributions to this work.
</t>
<t>Dapeng Liu: liudapeng@chinamobile.com</t>
<t>Pierrick Seite: pierrick.seite@orange-ftgroup.com</t>
<t>Hidetoshi Yokota: yokota@kddilabs.jp</t>
<t>Charles E. Perkins: charliep@computer.org</t>
<t>Melia Telemaco: telemaco.melia@alcatel-lucent.com</t>
<t>Elena Demaria: elena.demaria@telecomitalia.it</t>
<t>Wassim Michel Haddad: Wassam.Haddad@ericsson.com</t>
<t>Hui Deng: denghui@chinamobile.com</t>
<t>Seok Joo Koh: sjkoh@knu.ac.kr</t>
<t>Rute Sofia
(in collaboration with
Tiago Condeixa, Andrea Nascimento, and Susana Sargento): rute.sofia@ulusofona.pt</t>
</section>
</middle>
<back>
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&rfc2119;
</references>
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<?rfc include="reference.RFC.3775" ?>
<?rfc include="reference.RFC.5213" ?>
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<?rfc include="reference.RFC.4068" ?>
<?rfc include="reference.RFC.4988" ?>
<?rfc include="reference.RFC.5454" ?>
<?rfc include="reference.RFC.5555" ?>
<?rfc include="reference.RFC.5949" ?>
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</rfc>
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