Distributed Mobility Management: Current practices and gap analysis
draft-ietf-dmm-best-practices-gap-analysis-01
The information below is for an old version of the document.
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|
|---|---|---|---|
| Authors | Dapeng Liu , Juan-Carlos Zúñiga , Pierrick Seite , Anthony Chan , Carlos J. Bernardos | ||
| Last updated | 2013-07-24 (Latest revision 2013-06-17) | ||
| Replaces | draft-liu-dmm-best-practices-gap-analysis | ||
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draft-ietf-dmm-best-practices-gap-analysis-01
DMM D. Liu, Ed.
Internet-Draft China Mobile
Intended status: Informational JC. Zuniga, Ed.
Expires: December 19, 2013 InterDigital
P. Seite
Orange
H. Chan
Huawei Technologies
CJ. Bernardos
UC3M
June 17, 2013
Distributed Mobility Management: Current practices and gap analysis
draft-ietf-dmm-best-practices-gap-analysis-01
Abstract
The present document analyses deplyment practices of existing
mobility protocols in a distributed mobility management environment.
It also identifies some limitations compared to the expected
functionality of a fully distributed mobility management system. The
comparison is made taking into account the identified DMM
requirements.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on December 19, 2013.
Copyright Notice
Copyright (c) 2013 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
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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
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Functions of existing mobility protocols . . . . . . . . . . . 4
4. DMM practices . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. IP flat wireless network . . . . . . . . . . . . . . . . . 6
4.2.1. Host-based IP DMM practices . . . . . . . . . . . . . 8
4.2.2. Network-based IP DMM practices . . . . . . . . . . . . 11
4.3. 3GPP network flattening approaches . . . . . . . . . . . . 13
5. Gap analysis . . . . . . . . . . . . . . . . . . . . . . . . . 16
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
8. Informative References . . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 20
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1. Introduction
The distributed mobility management (DMM) WG has studied the problems
of centralized deployment of mobility management protocols and the
related requirements [I-D.ietf-dmm-requirements]. In order to guide
the deployment and before defining any new DMM protocol, the DMM WG
is chartered to investigate first whether it is feasible to deploy
current IP mobility protocols in a DMM scenario in a way that can
fullfil the requirements of DMM. This document discusses current
deployment practices of existing mobility protocols in a distributed
mobility management environment and identifies the limitations in
these practices with respect to the expected functionality.
The rest of this document is organized as follows. Section 3
analyzes existing IP mobility protocols by examining their functions
and how these functions can be reconfigured to work in a DMM
environment. Section 4 presents the current practices of IP flat
wireless networks and 3GPP architectures. Both network- and host-
based mobility protocols are considered. Section 5 presents the gap
analysis with respect to the current practices.
2. Terminology
All general mobility-related terms and their acronyms used in this
document are to be interpreted as defined in the Mobile IPv6 base
specification [RFC6275] and in the Proxy mobile IPv6 specification
[RFC5213]. These terms include mobile node (MN), correspondent node
(CN), home agent (HA), local mobility anchor (LMA), and mobile access
gateway (MAG).
In addition, this document uses the following terms:
Mobility routing (MR) is the logical function that intercepts
packets to/from the IP address/prefix delegated to the mobile node
and forwards them, based on internetwork location information,
either directly towards their destination or to some other network
element that knows how to forward the packets to their ultimate
destination.
Home address allocation is the logical function that allocates the
IP address/prefix (e.g., home address or home network prefix) to a
mobile node.
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Location management (LM) is the logical function that manages and
keeps track of the internetwork location information of a mobile
node, which includes the mapping of the IP address/prefix
delegated to the MN to the MN routing address or another network
element that knows where to forward packets destined for the MN.
Home network of an application session (or an HoA IP address) is the
network that has allocated the IP address used as the session
identifier (home address) by the application being run in an MN.
The MN may be attached to more than one home networks.
In the document, several references to a distributed mobility
management environment are made. By this term, we refer to an
scenario in which the IP mobility, access network and routing
solutions allow for setting up IP networks so that traffic is
distributed in an optimal way and does not rely on centrally deployed
anchors to manage IP mobility sessions.
3. Functions of existing mobility protocols
The host-based Mobile IPv6 [RFC6275] and its network-based extension,
PMIPv6 [RFC5213], are both logically centralized mobility management
approaches addressing primarily hierarchical mobile networks.
Although they are centralized approaches, they have important
mobility management functions resulting from years of extensive work
to develop and to extend these functions. It is therefore fruitful
to take these existing functions and examine them in a DMM scenario
in order to understand how to deploy the existing mobility protocols
in a distributed mobility management environment.
The existing mobility management functions of MIPv6, PMIPv6, and
HMIPv6 are the following:
1. Anchoring function (AF): allocation to a mobile node of an IP
addres/prefix (e.g., a HoA or HNP) topologically anchored by the
delegating node (i.e., the anchor node is able to advertise a
connected route into the routing infrastructure for the delegated
IP prefixes).
2. Mobility Routing (MR) function: packets interception and
forwarding to/from the IP address/prefix delegated to the MN,
based on the internetwork location information, either to the
destination or to some other network element that knows how to
forward the packets to their destination;
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3. Internetwork Location Management (LM) function: managing and
keeping track of the internetwork location of an MN, which
includes a mapping of the IP delegated address/prefix (e.g., HoA
or HNP) to the mobility anchoring point where the MN is anchored
to;
4. Location Update (LU): provisioning of MN location information to
the LM function;
In Mobile IPv6 [RFC6275], the home agent typically provides the
anchoring function (AF), Mobility Routing (MR), and Internetwork
Location Management (LM) functions, while the mobile node provides
the Location Update (LU) function. Proxy Mobile IPv6 [RFC5213]
relies on the function of the Local Mobility Anchor (LMA) to provide
mobile nodes with mobility support, without requiring the involvement
of the mobile nodes. The required functionality at the mobile node
is provided in a proxy manner by the Mobile Access Gateway (MAG).
With network-based IP mobility protocols, the local mobility anchor
typically provides the anchoring function (AF), Mobility Routing
(MR), and Internetwork Location Management (LM) functions, while the
mobile access gateway provides the Location Update (LU) function.
4. DMM practices
This section documents deployment practices of existing mobility
protocols in a distributed mobility management environment. This
description is divided into two main families of network
architectures: i) IP flat wireless networks (e.g., evolved WiFi
hotspots) and, ii) 3GPP network flattening approaches.
While describing the current DMM practices, references to the generic
mobility management functions described in Section 3 will be
provided, as well as some initial hints on the identified gaps with
respect to the DMM requirement documented in
[I-D.ietf-dmm-requirements].
4.1. Assumptions
There are many different approaches that can be considered to
implement and deploy a distributed anchoring and mobility solution.
Since this document cannot be too exhaustive, the focus is on current
mobile network architectures and standardized IP mobility solutions.
In order to limit the scope of our analysis of current DMM practices,
we consider the following list of technical assumptions:
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1. Both host- and network-based solutions should be covered.
2. Solution should allow selecting and using the most appropriate IP
anchor among a set of distributed ones.
3. Mobility management should be realized by the preservation of the
IP address across the different points of attachment during the
mobility (i.e., provision of IP address continuity). IP flows of
applications which do not need a constant IP address should not
be handled by DMM. It is typically the role of a connection
manager to distinguish application capabilities and trigger the
mobility support accordingly. Further considerations on
application management are out of the scope of this document.
4. Mobility management and traffic redirection should only be
triggered due to IP mobility reasons, that is when the MN moves
from the point of attachment where the IP flow was originally
initiated.
4.2. IP flat wireless network
This section focuses on common IP wireless network architectures and
how they can be flattened from an IP mobility and anchoring point of
view using common and standardized protocols. Since WiFi is the most
widely deployed wireless access technology nowadays, we take it as
example in the following. Some representative examples of WiFi
deployed architectures are depicted on Figure 1.
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+-------------+ _----_
+---+ | Access | _( )_
|AAA|. . . . . . | Aggregation |----------( Internet )
+---+ | Gateway | (_ _)
+-------------+ '----'
| | |
| | +-------------+
| | |
| | +-----+
+---------------+ | | AR |
| | +--+--+
+-----+ +-----+ *----+----*
| RG | | WLC | ( LAN )
+-----+ +-----+ *---------*
. / \ / \
/ \ +----+ +----+ +----+ +----+
MN MN |WiFi| |WiFi| |WiFi| |WiFi|
| AP | | AP | | AP | | AP |
+----+ +----+ +----+ +----+
. .
/ \ / \
MN MN MN MN
Figure 1: IP WiFi network architectures
In the figure, three typical deployment options are shown
[I-D.gundavelli-v6ops-community-wifi-svcs]. On the left hand side of
the figure, mobile nodes directly connect to a Residential Gateway
(RG) which is a network device that is located in the customer
premises and provides both wireless layer-2 access connectivity
(i.e., it hosts the 802.11 Access Point function) with layer-3
routing functions. In the middle, mobile nodes connect to WiFi
Access Points (APs) that are managed by a WLAN Controller (WLC),
which performs radio resource management on the APs, system-wide
mobility policy enforcement and centralized forwarding function for
the user traffic. The WLC could also implement layer-3 routing
functions, or attach to an access router (AR). Last, on the right-
hand side of the figure, access points are directly connected to an
access router, which can also be used a generic connectivity model.
In some network architectures, such as the evolved Wi-Fi hotspot,
operators might make use of IP mobility protocols to provide mobility
support to users, for example to allow connecting the IP WiFi network
to a mobile operator core and support roaming between WLAN and 3GPP
accesses. Two main protocols can be used: Proxy Mobile IPv6
[RFC5213] or Mobile IPv6 [RFC6275], [RFC5555], with the anchor role
(e.g., local mobility anchor or home agent) typically being played by
the Access Aggregation Gateway or even by an entity placed on the
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mobile operator's core network.
Existing IP mobility protocols can also be deployed in a "flatter"
way, so the anchoring and access aggregation functions are
distributed. We next describe several practices for the deployment
of existing mobility protocols in a distributed mobility management
environment. We limit our analysis in this section to protocol
solutions based on existing IP mobility protocols, either host- or
network-based, such as Mobile IPv6 [RFC6275], [RFC5555], Proxy Mobile
IPv6 [RFC5213], [RFC5844] and NEMO [RFC3963]. Extensions to these
base protocol solutions are also considered. We pay special
attention to the management of the use of care-of-addresses versus
home addresses in an efficient manner for different types of
communications. Finally, and in order to simplify the analysis, we
divide it into two parts: host- and network-based practices.
4.2.1. Host-based IP DMM practices
Mobile IPv6 (MIPv6) [RFC6275] and its extension to support mobile
networks, the NEMO Basic Support protocol (hereafter, simply NEMO)
[RFC3963] are well-known host-based IP mobility protocols. They
heavily rely on the function of the Home Agent (HA), a centralized
anchor, to provide mobile nodes (hosts and routers) with mobility
support. In these approaches, the home agent typically provides the
anchoring function (AF), Mobility Routing (MR), and Internetwork
Location Management (LM) functions, while the mobile node provides
the Location Update (LU) function. We next describe some practices
on how Mobile IPv6/NEMO and several additional protocol extensions
can be deployed in a distributed mobility management environment.
One approach to distribute the anchors can be to deploy several HAs
(as shown in Figure 2), and assign to each MN the one closest to its
topological location [RFC4640], [RFC5026], [RFC6611]. In the example
shown in Figure 2, MN1 is assigned HA1 (and a home address anchored
by HA1), while MN2 is assigned HA2. Note that Mobile IPv6 / NEMO
specifications do not prevent the simultaneous use of multiple home
agents by a single mobile node. This deployment model could be
exploited by a mobile node to meet assumption #4 and use several
anchors at the same time, each of them anchoring IP flows initiated
at different point of attachment. However there is no mechanism
specified to enable an efficient dynamic discovery of available
anchors and the selection of the most suitable one.
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<- INTERNET -> <- HOME NETWORK -> <---- ACCESS NETWORK ---->
------- -------
| CN1 | ------- | AR1 |-(o) zzzz (o)
------- | HA1 | ------- |
------- (MN1 anchored at HA1) -------
------- | MN1 |
| AR2 |-(o) -------
-------
-------
| HA2 | -------
------- | AR3 |-(o) zzzz (o)
------- |
------- (MN2 anchored at HA2) -------
| CN2 | ------- | MN2 |
------- | AR4 |-(o) -------
-------
CN1 CN2 HA1 HA2 AR1 MN1 AR3 MN2
| | | | | | | |
|<------------>|<=================+=====>| | | BT mode
| | | | | | | |
| |<----------------------------------------+----->| RO mode
| | | | | | | |
Figure 2: Distributed operation of Mobile IPv6 (BT and RO) / NEMO
Since one of the goals of the deployment of mobility protocols in a
distributed mobility management environment is to avoid the
suboptimal routing caused by centralized anchoring, the Route
Optimization (RO) support provided by Mobile IPv6 can also be used to
achieve a flatter IP data forwarding. By default, Mobile IPv6 and
NEMO use the so-called Bidirectional Tunnel (BT) mode, in which data
traffic is always encapsulated between the MN and its HA before being
directed to any other destination. The Route Optimization (RO) mode
allows the MN to update its current location on the CNs, and then use
the direct path between them. Using the example shown in Figure 2,
MN1 is using BT mode with CN2 and MN2 is in RO mode with CN1.
However, the RO mode has several drawbacks:
o The RO mode is only supported by Mobile IPv6. There is no route
optimization support standardized for the NEMO protocol, although
many different solutions have been proposed.
o The RO mode requires additional signaling, which adds some
protocol overhead.
o The signaling required to enable RO involves the home agent, and
it is repeated periodically because of security reasons [RFC4225].
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This basically means that the HA remains as single point of
failure, because the Mobile IPv6 RO mode does not mean HA-less
operation.
o The RO mode requires additional support on the correspondent node
(CN).
Notwithstanding these considerations, the RO mode does offer the
possibility of substantially reducing traffic through the Home Agent,
in cases when it can be supported on the relevant correspondent
nodes.
<- INTERNET -> <- HOME NETWORK -> <------- ACCESS NETWORK ------->
-----
/|AR1|-(o) zz (o)
-------- / ----- |
| MAP1 |< -------
-------- \ ----- | MN1 |
------- \|AR2| -------
| CN1 | ----- HoA anchored
------- ----- at HA1
------- /|AR3| RCoA anchored
| HA1 | -------- / ----- at MAP1
------- | MAP2 |< LCoA anchored
-------- \ ----- at AR1
\|AR4|
------- -----
| CN2 | -----
------- /|AR5|
-------- / -----
| MAP3 |<
-------- \ -----
\|AR6|
-----
CN1 CN2 HA1 MAP1 AR1 MN1
| | | | ________|__________ |
|<------------------>|<==============>|<________+__________>| HoA
| | | | | |
| |<-------------------------->|<===================>| RCoA
| | | | | |
Figure 3: Hierarchical Mobile IPv6
Hierarchical Mobile IPv6 (HMIPv6) [RFC5380] is another host-based IP
mobility extension that can be considered as a complement to provide
a less centralized mobility deployment. It allows reducing the
amount of mobility signaling as well as improving the overall
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handover performance of Mobile IPv6 by introducing a new hierarchy
level to handle local mobility. The Mobility Anchor Point (MAP)
entity is introduced as a local mobility handling node deployed
closer to the mobile node.
When HMIPv6 is used, the MN has two different temporal addresses: the
Regional Care-of Address (RCoA) and the Local Care-of Address (LCoA).
The RCoA is anchored at one MAP, that plays the role of local home
agent, while the LCoA is anchored at the access router level. The
mobile node uses the RCoA as the CoA signaled to its home agent.
Therefore, while roaming within a local domain handled by the same
MAP, the mobile node does not need to update its home agent (i.e.,
the mobile node does not change RCoA).
The use of HMIPv6 allows some route optimization, as a mobile node
may decide to directly use the RCoA as source address for a
communication with a given correspondent node, notably if the MN does
not expect to move outside the local domain during the lifetime of
the communication. This can be seen as a potential DMM mode of
operation. In the example shown in Figure 3, MN1 is using its global
HoA to communicate with CN1, while it is using its RCoA to
communicate with CN2.
Additionally, a local domain might have several MAPs deployed,
enabling hence different kind of HMIPv6 deployments (e.g., flat and
distributed). The HMIPv6 specification supports a flexible selection
of the MAP (e.g., based on the distance between the MN and the MAP,
taking into consideration the expected mobility pattern of the MN,
etc.).
An additional extension that can be used to help deploying a mobility
protocol in a distributed mobility management environment is the the
Home Agent switch specification [RFC5142], which defines a new
mobility header for signaling a mobile node that it should acquire a
new home agent. Even though the purposes of this specification do
not include the case of changing the mobile node's home address, as
that might imply loss of connectivity for ongoing persistent
connections, it could be used to force the change of home agent in
those situations where there are no active persistent data sessions
that cannot cope with a change of home address.
4.2.2. Network-based IP DMM practices
Proxy Mobile IPv6 (PMIPv6) [RFC5213] is the main network-based IP
mobility protocol specified for IPv6 ([RFC5844] defines some IPv4
extensions). Architecturally, PMIPv6 is similar to MIPv6, as it
relies on the function of the Local Mobility Anchor (LMA) to provide
mobile nodes with mobility support, without requiring the involvement
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of the mobile nodes. The required functionality at the mobile node
is provided in a proxy manner by the Mobile Access Gateway (MAG).
With network-based IP mobility protocols, the local mobility anchor
typically provides the anchoring function (AF), Mobility Routing
(MR), and Internetwork Location Management (LM) functions, while the
mobile access gateway provides the Location Update (LU) function. We
next describe some practices on how network-based mobility protocols
and several additional protocol extensions can be deployed in a
distributed mobility management environment.
<- INTERNET -><- HOME NET -><----------- ACCESS NETWORK ------------>
-------
| CN1 | -------- -------- --------
------- -------- | MAG1 | | MAG2 | | MAG3 |
| LMA1 | ---+---- ---+---- ---+----
------- -------- | | |
| CN2 | (o) (o) (o)
------- -------- x x
| LMA2 | x x
------- -------- (o) (o)
| CN3 | | |
------- ---+--- ---+---
Anchored | MN1 | Anchored | MN2 |
at LMA1 -> ------- at LMA2 -> -------
CN1 CN2 LMA1 LMA2 MAG1 MN1 MAG3 MN2
| | | | | | | |
|<------------>|<================>|<---->| | |
| | | | | | | |
| |<------------>|<========================>|<----->|
| | | | | | | |
Figure 4: Distributed operation of Proxy Mobile IPv6
As with Mobile IPv6, plain Proxy Mobile IPv6 operation cannot be
easily decentralized, as in this case there also exists a single
network anchor point. One simple but still suboptimal approach, can
be to deploy several local mobility anchors and use some selection
criteria to assign LMAs to attaching mobile nodes (an example of this
type of assignment is shown in Figure 4). As per the client based
approach, a mobile node may use several anchors at the same time,
each of them anchoring IP flows initiated at different point of
attachment. This assignment can be static or dynamic (as described
later in this document). The main advantage of this simple approach
is that the IP address anchor (i.e., the LMA) could be placed closer
to the mobile node, and therefore resulting paths are close-to-
optimal. On the other hand, as soon as the mobile node moves, the
resulting path would start to deviate from the optimal one.
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As for host-based IP mobility, there are some extensions defined to
mitigate the sub-optimal routing issues that might arise due to the
use of a centralized anchor. The Local Routing extensions [RFC6705]
enable optimal routing in Proxy Mobile IPv6 in three cases: i) when
two communicating MNs are attached to the same MAG and LMA, ii) when
two communicating MNs are attached to different MAGs but to the same
LMA, and iii) when two communicating MNs are attached to the same MAG
but have different LMAs. In these three cases, data traffic between
the two mobile nodes does not traverse the LMA(s), thus providing
some form of path optimization since the traffic is locally routed at
the edge. The main disadvantage of this approach is that it only
tackles the MN-to-MN communication scenario, and only under certain
circumstances.
An interesting extension that can also be used to facilitate the
deployment of network-based mobility protocols in a distributes
mobility management environment is the LMA runtime assignment
[RFC6463]. This extension specifies a runtime local mobility anchor
assignment functionality and corresponding mobility options for Proxy
Mobile IPv6. This runtime local mobility anchor assignment takes
place during the Proxy Binding Update / Proxy Binding Acknowledgment
message exchange between a mobile access gateway and a local mobility
anchor. While this mechanism is mainly aimed for load-balancing
purposes, it can also be used to select an optimal LMA from the
routing point of view. A runtime LMA assignment can be used to
change the assigned LMA of an MN, for example in case when the mobile
node does not have any session active, or when running sessions can
survive an IP address change.
4.3. 3GPP network flattening approaches
The 3rd Generation Partnership Project (3GPP) is the standard
development organization that specifies the 3rd generation mobile
network and LTE (Long Term Evolution).
Architecturally, the 3GPP Evolved Packet Core (EPC) network is
similar to an IP wireless network running PMIPv6 or MIPv6, as it
relies on the Packet Data Gateway (PGW) anchoring services to provide
mobile nodes with mobility support (see Figure 5). There are client-
based and network-based mobility solutions in 3GPP, which for
simplicity we will analyze together. We next describe how 3GPP
mobility protocols and several additional completed or on-going
extensions can be deployed to meet some of the DMM requirements
[I-D.ietf-dmm-requirements].
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+---------------------------------------------------------+
| PCRF |
+-----------+--------------------------+----------------+-+
| | |
+----+ +-----------+------------+ +--------+-----------+ +-+-+
| | | +-+ | | Core Network | | |
| | | +------+ |S|__ | | +--------+ +---+ | | |
| | | |GERAN/|_|G| \ | | | HSS | | | | | |
| +-----+ UTRAN| |S| \ | | +---+----+ | | | | E |
| | | +------+ |N| +-+-+ | | | | | | | x |
| | | +-+ /|MME| | | +---+----+ | | | | t |
| | | +---------+ / +---+ | | | 3GPP | | | | | e |
| +-----+ E-UTRAN |/ | | | AAA | | | | | r |
| | | +---------+\ | | | SERVER | | | | | n |
| | | \ +---+ | | +--------+ | | | | a |
| | | 3GPP AN \|SGW+----- S5---------------+ P | | | l |
| | | +---+ | | | G | | | |
| | +------------------------+ | | W | | | I |
| UE | | | | | | P |
| | +------------------------+ | | +-----+ |
| | |+-------------+ +------+| | | | | | n |
| | || Untrusted +-+ ePDG +-S2b---------------+ | | | e |
| +---+| non-3GPP AN | +------+| | | | | | t |
| | |+-------------+ | | | | | | w |
| | +------------------------+ | | | | | o |
| | | | | | | r |
| | +------------------------+ | | | | | k |
| +---+ Trusted non-3GPP AN +-S2a--------------+ | | | s |
| | +------------------------+ | | | | | |
| | | +-+-+ | | |
| +--------------------------S2c--------------------| | | |
| | | | | |
+----+ +--------------------+ +---+
Figure 5: EPS (non-roaming) architecture overview
GPRS Tunnelling Protocol (GTP) [3GPP.29.060] is a network-based
mobility protocol specified for 3GPP networks (S2a, S2b, S5 and S8
interfaces). Similar to PMIPv6, it can handle mobility without
requiring the involvement of the mobile nodes. In this case, the
mobile node functionality is provided in a proxy manner by the
Serving Data Gateway (SGW), Evolved Packet Data Gateway (ePDG), or
Trusted Wireless Access Gateway (TWAG).
3GPP specifications also include client-based mobility support, based
on adopting the use of Dual-Stack Mobile IPv6 (DSMIPv6) [RFC5555] for
the S2c interface. In this case, the UE implements the mobile node
functionality, while the home agent role is played by the PGW.
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A Local IP Access (LIPA) and Selected IP Traffic Offload (SIPTO)
enabled network [3GPP.23.829] allows offloading some IP services at
the local access network, above the Radio Access Network (RAN) or at
the macro, without the need to traverse back to the PGW (see
Figure 6.
+---------+ IP traffic to mobile operator's CN
| User |....................................(Operator's CN)
| Equipm. |..................
+---------+ . Local IP traffic
.
+-----------+
|Residential|
|enterprise |
|IP network |
+-----------+
Figure 6: LIPA scenario
SIPTO enables an operator to offload certain types of traffic at a
network node close to the UE's point of attachment to the access
network, by selecting a set of GWs (SGW and PGW) that is
geographically/topologically close to the UE's point of attachment.
SIPTO Traffic
|
.
.
+------+ +------+
|L-PGW | ---- | MME |
+------+ / +------+
| /
+-------+ +------+ +------+/ +------+
| UE |.....|eNB |....| S-GW |........| P-GW |...> CN Traffic
+-------+ +------+ +------+ +------+
Figure 7: SIPTO architecture
LIPA, on the other hand, enables an IP capable UE connected via a
Home eNB (HeNB) to access other IP capable entities in the same
residential/enterprise IP network without the user plane traversing
the mobile operator's network core. In order to achieve this, a
Local GW (L-GW) collocated with the HeNB is used. LIPA is
established by the UE requesting a new PDN connection to an access
point name for which LIPA is permitted, and the network selecting the
Local GW associated with the HeNB and enabling a direct user plane
path between the Local GW and the HeNB.
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+---------------+-------+ +----------+ +-------------+ =====
|Residential | |H(e)NB | | Backhaul | |Mobile | ( IP )
|Enterprise |..|-------|..| |..|Operator |..(Network)
|Network | |L-GW | | | |Core network | =======
+---------------+-------+ +----------+ +-------------+
/
|
/
+-----+
| UE |
+-----+
Figure 8: LIPA architecture
Both SIPTO and LIPA have a very limited mobility support, specially
in 3GPP specifications up to Rel-10. In Rel-11, there is currently a
work item on LIPA Mobility and SIPTO at the Local Network (LIMONET)
[3GPP.23.859] that is studying how to provide SIPTO and LIPA
mechanisms with some additional, but still limited, mobility support.
In a glimpse, LIPA mobility support is limited to handovers between
HeNBs that are managed by the same L-GW (i.e., mobility within the
local domain), while seamless SIPTO mobility is still limited to the
case where the SGW/PGW is at or above Radio Access Network (RAN)
level.
5. Gap analysis
The goal of this section is to identify the limitations in the
current practices with respect to providing the expected DMM
functionality.
From the analysis performed in Section 4, we can first identify a
basic set of functions that a DMM solution needs to provide:
o Multiple (distributed) anchoring: ability to anchor different
sessions of a single mobile node at different anchors. In order
to make this feature "DMM-friendly", some anchors might need to be
placed closer to the mobile node.
o Dynamic anchor assignment/re-location: ability to i) optimally
assign initial anchor, and ii) dynamically change the initially
assigned anchor and/or assign a new one (this may also require to
transfer mobility context between anchors). This can be achieved
either by changing anchor for all ongoing sessions, or by
assigning new anchors just for new sessions.
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o Multiple IP address management: ability of the mobile node to
simultaneously use multiple IP addresses and select the best one
(from an anchoring point of view) to use on a per-session/
application/service basis. Depending on the mobile node support,
this functionality might require more or less support from the
network side. This is typically the role of a connection manager.
In order to summarize the previously listed functions, Figure 9 shows
an example of a conceptual DMM solution deployment.
( )
+------------------------------------------------+
/ | \
/ * Internet | x Internet \ Internet
/ * / access | x / access \ / access
/ * / (IP a) | x / (IP b) \ /
--+------+----- ----+-----+---- ------+---+----
| distributed | * * *| distributed | | distributed |
| anchor 1 | | anchor i | | anchor n |
---+----------- ---+----------- ---+-----------
| | |
(o) (o) (o)
session X * x session Y
anchored * x anchored
at 1 * x at i
(IP a) (o) (IP b)
|
+--+--+
| MN1 |
+-----+
Figure 9: DMM functions
Based on the analysis performed in Section 4, the following list of
gaps can be identified:
o Both the main client- and network-based IP mobility protocols,
namely (DS)MIPv6 and PMIPv6 allows to deploy multiple anchors
(i.e., home agents and localized mobility anchors), therefore
providing the multiple anchoring function. However, existing
solutions do only provide an optimal initial anchor assignment, a
gap being the lack of dynamic anchor change/new anchor assignment.
Neither the HA switch nor the LMA runtime assignment allow
changing the anchor during an ongoing session. This actually
comprises several gaps: ability to perform anchor assignment at
any time (not only at the initial MN's attachment), ability of the
current anchor to initiate/trigger the relocation, and ability of
transferring registration context between anchors.
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o The dynamic anchor relocation needs to ensure that IP address
continuity is guaranteed for sessions that need it at the
relocated anchor. This for example implies having the knowledge
of which sessions are active at the mobile node, which is
something typically known only by the MN (namely, by its
connection manager). Therefore, (part of) this knowledge might
need to be transferred to/shared with the network.
o Dynamic discovery and selection of anchors. There might be more
than one available anchor for a mobile node to use. Currently,
there is no efficient mechanism that allows to dynamically
discover the presence of nodes that can play the role of anchor,
discover their capabilities and allow the selection of the most
suitable one.
o NOTE: This section is in progress. More gaps are still to be
identified and more text added to these bullets (perhaps even
assigning one subsection to each one). More discussion/feedback
from the group is still needed.
6. Security Considerations
TBD.
7. IANA Considerations
None.
8. Informative References
[3GPP.23.829]
3GPP, "Local IP Access and Selected IP Traffic Offload
(LIPA-SIPTO)", 3GPP TR 23.829 10.0.1, October 2011.
[3GPP.23.859]
3GPP, "Local IP access (LIPA) mobility and Selected IP
Traffic Offload (SIPTO) at the local network", 3GPP
TR 23.859 12.0.1, April 2013.
[3GPP.29.060]
3GPP, "General Packet Radio Service (GPRS); GPRS
Tunnelling Protocol (GTP) across the Gn and Gp interface",
3GPP TS 29.060 3.19.0, March 2004.
[I-D.gundavelli-v6ops-community-wifi-svcs]
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Gundavelli, S., Grayson, M., Seite, P., and Y. Lee,
"Service Provider Wi-Fi Services Over Residential
Architectures",
draft-gundavelli-v6ops-community-wifi-svcs-06 (work in
progress), April 2013.
[I-D.ietf-dmm-requirements]
Chan, A., Liu, D., Seite, P., Yokota, H., and J. Korhonen,
"Requirements for Distributed Mobility Management",
draft-ietf-dmm-requirements-05 (work in progress),
June 2013.
[RFC3963] Devarapalli, V., Wakikawa, R., Petrescu, A., and P.
Thubert, "Network Mobility (NEMO) Basic Support Protocol",
RFC 3963, January 2005.
[RFC4225] Nikander, P., Arkko, J., Aura, T., Montenegro, G., and E.
Nordmark, "Mobile IP Version 6 Route Optimization Security
Design Background", RFC 4225, December 2005.
[RFC4640] Patel, A. and G. Giaretta, "Problem Statement for
bootstrapping Mobile IPv6 (MIPv6)", RFC 4640,
September 2006.
[RFC5026] Giaretta, G., Kempf, J., and V. Devarapalli, "Mobile IPv6
Bootstrapping in Split Scenario", RFC 5026, October 2007.
[RFC5142] Haley, B., Devarapalli, V., Deng, H., and J. Kempf,
"Mobility Header Home Agent Switch Message", RFC 5142,
January 2008.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
[RFC5380] Soliman, H., Castelluccia, C., ElMalki, K., and L.
Bellier, "Hierarchical Mobile IPv6 (HMIPv6) Mobility
Management", RFC 5380, October 2008.
[RFC5555] Soliman, H., "Mobile IPv6 Support for Dual Stack Hosts and
Routers", RFC 5555, June 2009.
[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.
[RFC6463] Korhonen, J., Gundavelli, S., Yokota, H., and X. Cui,
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"Runtime Local Mobility Anchor (LMA) Assignment Support
for Proxy Mobile IPv6", RFC 6463, February 2012.
[RFC6611] Chowdhury, K. and A. Yegin, "Mobile IPv6 (MIPv6)
Bootstrapping for the Integrated Scenario", RFC 6611,
May 2012.
[RFC6705] Krishnan, S., Koodli, R., Loureiro, P., Wu, Q., and A.
Dutta, "Localized Routing for Proxy Mobile IPv6",
RFC 6705, September 2012.
Authors' Addresses
Dapeng Liu (editor)
China Mobile
Unit2, 28 Xuanwumenxi Ave, Xuanwu District
Beijing 100053
China
Email: liudapeng@chinamobile.com
Juan Carlos Zuniga (editor)
InterDigital Communications, LLC
1000 Sherbrooke Street West, 10th floor
Montreal, Quebec H3A 3G4
Canada
Email: JuanCarlos.Zuniga@InterDigital.com
URI: http://www.InterDigital.com/
Pierrick Seite
Orange
4, rue du Clos Courtel, BP 91226
Cesson-Sevigne 35512
France
Email: pierrick.seite@orange.com
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H Anthony Chan
Huawei Technologies
5340 Legacy Dr. Building 3
Plano, TX 75024
USA
Email: h.a.chan@ieee.org
Carlos J. Bernardos
Universidad Carlos III de Madrid
Av. Universidad, 30
Leganes, Madrid 28911
Spain
Phone: +34 91624 6236
Email: cjbc@it.uc3m.es
URI: http://www.it.uc3m.es/cjbc/
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