DMM D. Liu, Ed.
Internet-Draft China Mobile
Intended status: Informational JC. Zuniga, Ed.
Expires: April 23, 2014 InterDigital
P. Seite
Orange
H. Chan
Huawei Technologies
CJ. Bernardos
UC3M
October 20, 2013
Distributed Mobility Management: Current practices and gap analysis
draft-ietf-dmm-best-practices-gap-analysis-02
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
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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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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Functions of existing mobility protocols . . . . . . . . . . . 4
4. DMM practices . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. IP flat wireless network . . . . . . . . . . . . . . . . . 6
4.2.1. Host-based IP DMM practices . . . . . . . . . . . . . 8
4.2.2. Network-based IP DMM practices . . . . . . . . . . . . 12
4.3. 3GPP network flattening approaches . . . . . . . . . . . . 14
5. Gap analysis . . . . . . . . . . . . . . . . . . . . . . . . . 17
5.1. Distributed processing - REQ1 . . . . . . . . . . . . . . 17
5.2. Transparency to Upper Layers - REQ2 . . . . . . . . . . . 19
5.3. IPv6 deployment - REQ3 . . . . . . . . . . . . . . . . . . 19
5.4. Existing mobility protocols - REQ4 . . . . . . . . . . . . 20
5.5. Co-existence - REQ5 . . . . . . . . . . . . . . . . . . . 20
5.6. Security considerations - REQ6 . . . . . . . . . . . . . . 20
5.7. Multicast - REQ7 . . . . . . . . . . . . . . . . . . . . . 21
5.8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 21
6. Security Considerations . . . . . . . . . . . . . . . . . . . 22
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 22
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
8.1. Normative References . . . . . . . . . . . . . . . . . . . 22
8.2. Informative References . . . . . . . . . . . . . . . . . . 23
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 25
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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
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].
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.
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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.
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).
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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;
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].
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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:
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. Typically, the a connection manager together
with the operating system configure the source address selection
mechanism of the IP stack. This might involve identifying
application capabilities and triggering the mobility support
accordingly. Further considerations on application management
and source address selection 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. We take WiFi an
exemplary wireless technology, as it is widely known and deployed
nowadays. 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.
Although we have adopted in this section the example of WiFi
networks, there are other IP flat wireless network architectures
specified, such as WiMAX [IEEE.802-16.2009], which integrates both
host and network-based IP mobility functionality.
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 by the IETF to enable an efficient dynamic discovery of
available anchors and the selection of the most suitable one. Note
that some of these mechanisms have been defined outside the IETF
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(e.g., 3GPP).
<- 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 because of
the security problems posed by extending return routability tests
for prefixes, although many different solutions have been
proposed.
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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].
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. Note that a mobile node can also use its CoA directly
[RFC5014] when communicating with CNs on the same link or anywhere in
the Internet, although no session continuity support would be
provided by the IP stack in this case.
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<- 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
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.,
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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.
There other host-based approaches standardized within the IETF that
can be used to provide mobility support. For example MOBIKE
[RFC4555] allows a mobile node encrypting traffic through IKEv2
[RFC5996] to change its point of attachment while maintaining a
Virtual Private Network (VPN) session. The MOBIKE protocol allows
updating the VPN Security Associations (SAs) in cases where the base
connection initially used is lost and needs to be re-established.
The use of the MOBIKE protocol avoids having to perform an IKEv2 re-
negotiation. Similar considerations to those made for Mobile IPv6
can be applied to MOBIKE; though MOBIKE is best suited for situations
where the address of at least one endpoint is relatively stable and
can be discovered using existing mechanisms such as DNS.
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
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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. 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
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resulting path would start to deviate from the optimal one.
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. Note that several possible dynamic
local mobility anchor discovery solutions can be used, as described
in [RFC6097].
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] [3GPP.29.281]
[3GPP.29.274] 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.23.401] 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
The 3GPP architecture specifications also provide mechanisms to allow
discovery and selection of gateways [3GPP.29.303]. These mechanisms
enable taking decisions taking into consideration topological
location and gateway collocation aspects, using heavily the DNS as a
"location database".
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, described in Section 4, with respect to the
expected DMM requirements listed in [I-D.ietf-dmm-requirements].
5.1. Distributed processing - REQ1
According to requirement #1 stated in [I-D.ietf-dmm-requirements], IP
mobility, network access and routing solutions provided by DMM MUST
enable distributed processing for mobility management so that traffic
does not need to traverse centrally deployed mobility anchors and
thereby avoid non-optimal routes.
From the analysis performed in Section 4, a DMM deployment can meet
the requirement "REQ#1 Distributed processing" usually relying on the
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following functions:
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.
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.
Dynamic anchor assignment may lead the MN to manage different
mobility sessions served by different mobility anchors. This is not
an issue with client based mobility management where the mobility
client natively knows each anchor associated to each mobility
sessions. However, it may raise issues with network based mobility
management. In this case, the mobile client, located in the network
(e.g., MAG), usually retrieves the MN's anchor from the MN's policy
profile (e.g., Section 6.2 of [RFC5213]). Currently, the MN's policy
profile implicitly assumes a single serving anchor and, thus, does
not maintain the association between home network prefix and anchor.
The consequence of the distribution of the mobility anchors is that
there might be more than one available anchor for a mobile node to
use, so leading to an anchor discovery and selection issue.
Currently, there is no efficient mechanism specified by the IETF 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. Note that there are 3GPP
mechanisms providing this functionality defined in [3GPP.29.303].
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5.2. Transparency to Upper Layers - REQ2
The need for "transparency to upper layer", introduced in
[I-D.ietf-dmm-requirements], requires dynamic mobility management,
which basically leverages the two following functions:
o Dynamically assign/relocate anchor: a mobility anchor is assigned
only to sessions which require IP continuity support. The MN may
thus manage more than one session; some of them may be associated
with anchored IP address(es), while the others may be associated
with local IP address(es).
o Multiple IP address management: this function is ensued from the
preceding and is about the 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.
The dynamic anchor assignment/relocation needs to ensure that IP
address continuity is guaranteed for sessions that need it and while
needed (in some scenarios, the provision of mobility locally within a
limited area might be enough from the mobile node or the application
point of view) 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 e.g., by its
connection manager). Therefore, (part of) this knowledge might need
to be transferred to/shared with the network.
Multiple IP address management requires the MN to pick-up the correct
address (with mobility support or not) depending on the application
requirements. When using client based mobility management, the
mobile node is natively aware about the anchoring capabilities of its
assigned IP addresses. This is not the case with network based IP
mobility management and current mechanisms does not allow the MN to
be aware of the IP addresses properties (i.e. the MN does not know
whether the allocated IP addresses are anchored). However, there are
ongoing IETF works that are proposing that the network could indicate
the different IP addresses properties during assignment procedures
[I-D.bhandari-dhc-class-based-prefix],
[I-D.korhonen-6man-prefix-properties].
5.3. IPv6 deployment - REQ3
This requirement states that DMM solutions SHOULD primariliy target
IPv6 as the primary deployment environment.. IPv4 support is not
considered mandatory and SHOULD NOT be tailored specifically to
support IPv4, in particular in situations where private IPv4
addresses and/or NATs are used.
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All analyzed DMM practices support IPv6. Some of them, such as
MIPv6/NEMO (including the support of dynamic HA selection), MOBIKE,
SIPTO have also IPv4 support. Additionally, there are also some
solutions that have some limited IPv4 support (e.g., PMIPv6). In
conclusion, this requirement is met by existing DMM practices.
5.4. Existing mobility protocols - REQ4
A DMM solution SHOULD first consider reusing and extending IETF-
standardized protocols before specifying new protocols.
As stated in [I-D.ietf-dmm-requirements], a DMM solution could reuse
existing IETF and standardized protocols before specifying new
protocols. Besides, Section 4 of this document discusses various
ways to flatten and distribute current mobility solutions. Actually,
nothing prevent the distribution of mobility functions with vanilla
IP mobility protocols. However, as discussed in Section 5.1 and
Section 5.2, limitations exist. The 3GPP data plane anchoring
function, i.e., the PGW, can be also be distributed, but with
limitations; e.g., no anchoring relocation, no context transfer
between anchors, centralized control plane . The 3GPP architecture
is also going into the direction of flattening with SIPTO and LIPA
where IP anchoring function, however these solutions are supposed to
be deployed do and, thus, do not provide mobility support. In
conclusion this requirement can be met, DMM can reuse existing
mobility solutions, however some limitations exist.
5.5. Co-existence - REQ5
According to [I-D.ietf-dmm-requirements], DMM solution should be able
to co-exist with existing network deployments and end hosts. All of
current mobility protocols can co-exist with existing network
deployments and end hosts. There is no gap between existing mobility
protocols and this requirement.
5.6. Security considerations - REQ6
As stated in [I-D.ietf-dmm-requirements], a DMM solution MUST NOT
introduce new security risks or amplify existing security risks
against which the existing security mechanisms/protocols cannot offer
sufficient protection. Current mobility protocols all have security
mechanisms. For example, Mobile IPv6 defines security features to
protect binding updates both to home agents and correspondent nodes.
It also defines mechanisms to protect the data packets transmission
for Mobile IPv6 users. Proxy Mobile IPv6 and other variation of
mobile IP also have similar security considerations.
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5.7. Multicast - REQ7
It is stated in [I-D.ietf-dmm-requirements] that DMM solutions SHOULD
consider multicast traffic delivery so that network inefficiency
issues, such as duplicate multicast subscriptions towards the
downstream tunnel entities, can be avoided.
Current IP mobility solutions address mainly the mobility problem for
unicast traffic. Solutions relying on the use of an anchor point for
tunneling multicast traffic down to the access router, or to the MN,
introduce the so-called "tunnel convergence problem". This means
that multiple instances of the same multicast traffic can converge to
the same node, defeating hence the advantage of using multicast
protocols.
The MULTIMOB WG in IETF has studied the issue, for the specific case
of PMIPv6, and has produced a baseline solution [RFC6224] as well as
a routing optimization solution [RFC7028] to address the problem.
The baseline solution suggests deploying an MLD proxy function at the
MAG, and either a multicast router or another MLD proxy function at
the LMA. The routing optimization solution describes an architecture
where a dedicated multicast tree mobility anchor (MTMA) or a direct
routing option can be used to avoid the tunnel convergence problem.
Besides the solutions proposed in MULTIMOB for PMIPv6, there are no
solutions for other mobility protocols to address the multicast
tunnel convergence problem.
5.8. Summary
We next list the main gaps identified from the analysis performed
above.
o 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.
o The mobile node needs to simultaneously use multiple IP addresses,
which requires additional support which might not be available on
the mobile node's stack, especially for the case of network-based
solutions.
o Currently, there is no efficient mechanism specified by the IETF
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.
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o While existing network-based DMM practices may allow to deploy
multiple LMAs and dynamically select the best one, this requires
to still keep some centralization in the control plane, to access
on the policy store (as defined in RFC5213).
The following table summarizes the previous analysis, indicating the
gaps existing DMM solutions have when compared to the requirements
listed in [I-D.ietf-dmm-requirements].
+------------+------+------+------+------+------+------+------+
| | REQ1 | REQ2 | REQ3 | REQ4 | REQ5 | REQ6 | REQ7 |
+------------+------+------+------+------+------+------+------+
| MIPv6/NEMO | X | X | | | | | X |
| MIPv6 RO | X | | | | | | X |
| HMIPv6 | X | | | | | | X |
| HA sel | X | X | | | | | X |
| MOBIKE | X | X | | | | | X |
| PMIPv6 | X | X | | | | | * |
| LMA sel | X | X | | | | | X |
| LIPA | X | X | | | | | X |
| SIPTO | X | X | | | | | X |
| LIMONET | X | X | | | | | X |
+------------+------+------+------+------+------+------+------+
* MULTIMOB optimizations for PMIPv6 can be used to handle multicast
traffic.
6. Security Considerations
This document does not define any protocol, there is no security
considerations.
7. IANA Considerations
None.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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8.2. Informative References
[3GPP.23.401]
3GPP, "General Packet Radio Service (GPRS) enhancements
for Evolved Universal Terrestrial Radio Access Network
(E-UTRAN) access", 3GPP TS 23.401 10.10.0, March 2013.
[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.
[3GPP.29.274]
3GPP, "3GPP Evolved Packet System (EPS); Evolved General
Packet Radio Service (GPRS) Tunnelling Protocol for
Control plane (GTPv2-C); Stage 3", 3GPP TS 29.274 10.11.0,
June 2013.
[3GPP.29.281]
3GPP, "General Packet Radio System (GPRS) Tunnelling
Protocol User Plane (GTPv1-U)", 3GPP TS 29.281 10.3.0,
September 2011.
[3GPP.29.303]
3GPP, "Domain Name System Procedures; Stage 3", 3GPP
TS 29.303 10.4.0, September 2012.
[I-D.bhandari-dhc-class-based-prefix]
Systems, C., Halwasia, G., Gundavelli, S., Deng, H.,
Thiebaut, L., Korhonen, J., and I. Farrer, "DHCPv6 class
based prefix", draft-bhandari-dhc-class-based-prefix-05
(work in progress), July 2013.
[]
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",
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draft-ietf-dmm-requirements-09 (work in progress),
September 2013.
[I-D.korhonen-6man-prefix-properties]
Korhonen, J., Patil, B., Gundavelli, S., Seite, P., and D.
Liu, "IPv6 Prefix Properties",
draft-korhonen-6man-prefix-properties-02 (work in
progress), July 2013.
[IEEE.802-16.2009]
"IEEE Standard for Local and metropolitan area networks
Part 16: Air Interface for Broadband Wireless Access
Systems", IEEE Standard 802.16, 2009, <http://
standards.ieee.org/getieee802/download/802.16-2009.pdf>.
[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.
[RFC4555] Eronen, P., "IKEv2 Mobility and Multihoming Protocol
(MOBIKE)", RFC 4555, June 2006.
[RFC4640] Patel, A. and G. Giaretta, "Problem Statement for
bootstrapping Mobile IPv6 (MIPv6)", RFC 4640,
September 2006.
[RFC5014] Nordmark, E., Chakrabarti, S., and J. Laganier, "IPv6
Socket API for Source Address Selection", RFC 5014,
September 2007.
[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.
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[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.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
[RFC6097] Korhonen, J. and V. Devarapalli, "Local Mobility Anchor
(LMA) Discovery for Proxy Mobile IPv6", RFC 6097,
February 2011.
[RFC6224] Schmidt, T., Waehlisch, M., and S. Krishnan, "Base
Deployment for Multicast Listener Support in Proxy Mobile
IPv6 (PMIPv6) Domains", RFC 6224, April 2011.
[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,
"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.
[RFC7028] Zuniga, JC., Contreras, LM., Bernardos, CJ., Jeon, S., and
Y. Kim, "Multicast Mobility Routing Optimizations for
Proxy Mobile IPv6", RFC 7028, September 2013.
Authors' Addresses
Dapeng Liu (editor)
China Mobile
Unit2, 28 Xuanwumenxi Ave, Xuanwu District
Beijing 100053
China
Email: liudapeng@chinamobile.com
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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
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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