DMM D. Liu, Ed.
Internet-Draft China Mobile
Intended status: Informational JC. Zuniga, Ed.
Expires: August 18, 2014 InterDigital
P. Seite
Orange
H. Chan
Huawei Technologies
CJ. Bernardos
UC3M
February 14, 2014
Distributed Mobility Management: Current practices and gap analysis
draft-ietf-dmm-best-practices-gap-analysis-03
Abstract
The present document analyzes deployment practices of existing IP
mobility protocols in a distributed mobility management environment.
It then identifies existing limitations when compared to the
requirements defined for a distributed mobility management solution.
Status of This Memo
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This Internet-Draft will expire on August 18, 2014.
Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Functions of existing mobility protocols . . . . . . . . . . 3
4. DMM practices . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Assumptions . . . . . . . . . . . . . . . . . . . . . . . 5
4.2. IP flat wireless network . . . . . . . . . . . . . . . . 5
4.2.1. Host-based IP DMM practices . . . . . . . . . . . . . 7
4.2.2. Network-based IP DMM practices . . . . . . . . . . . 11
4.3. 3GPP network flattening approaches . . . . . . . . . . . 13
5. Gap analysis . . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Distributed processing - REQ1 . . . . . . . . . . . . . . 16
5.2. Bypassable network-layer mobility support - REQ2 . . . . 18
5.3. IPv6 deployment - REQ3 . . . . . . . . . . . . . . . . . 19
5.4. Existing mobility protocols - REQ4 . . . . . . . . . . . 19
5.5. Co-existence - REQ5 . . . . . . . . . . . . . . . . . . . 19
5.6. Security considerations - REQ6 . . . . . . . . . . . . . 20
5.7. Multicast - REQ7 . . . . . . . . . . . . . . . . . . . . 20
5.8. Summary . . . . . . . . . . . . . . . . . . . . . . . . . 21
6. Security Considerations . . . . . . . . . . . . . . . . . . . 21
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
8.1. Normative References . . . . . . . . . . . . . . . . . . 22
8.2. Informative References . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 25
1. Introduction
The distributed mobility management (DMM) WG has studied the problems
of centralized deployment of mobility management protocols and
specified the DMM requirements [I-D.ietf-dmm-requirements]. This
document investigates whether it is feasible to deploy current IP
mobility protocols in a DMM scenario in a way that can fulfill the
requirements. It discusses current deployment practices of existing
mobility protocols in a distributed mobility management environment
and identifies the limitations (gaps) in these practices with respect
to the DMM functionality, as defined in [I-D.ietf-dmm-requirements].
The rest of this document is organized as follows. Section 3
analyzes existing IP mobility protocols by examining their functions
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and how these functions can be configured and used 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 also introduces some definitions of IP
mobility functions in Section 3.
In this document there are also references to a "distributed mobility
management environment". By this term, we refer to a 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, without relying 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 useful 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 main mobility management functions of MIPv6, PMIPv6, and HMIPv6
are the following:
1. Anchoring function (AF): allocation to a mobile node of an IP
address/prefix (e.g., a Home Address or Home Network Prefix)
topologically anchored by the delegating node (i.e., the anchor
node is able to advertise a connected route into the routing
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infrastructure for the delegated IP prefixes). It is a control
plane function.
2. Internetwork Location Management (LM) function: managing and
keeping track of the internetwork location of an MN. The
location information may be a mapping of the IP delegated address
/prefix (e.g., HoA or HNP) to the IP routing address of the MN or
of a node that can forward packets destined to the MN. It is a
control plane function.
In a client-server model of the system, location query and update
messages may be exchanged between the client (LMc) and the server
(LMs).
Optionally, one (or more) proxy may exist between the LMs and the
LMc, i.e., LMs-proxy-LMc. Then, to the LMs, the proxy behaves
like the LMc; to the LMc, the proxy behaves like the LMs.
3. Routing management (RM) function: packet 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.
RM may optionally be split into the control plane (RM-CP) and
data plane (RM-DP).
In Mobile IPv6 [RFC6275], the home agent (HA) typically provides the
anchoring function (AF); the location management server (LMs) is at
the HA while the location management client (LMc) is at the MN; the
routing management (RM) function is both ends of tunneling at the HA
and the MN.
In Proxy Mobile IPv6 [RFC5213], the Local Mobility Anchor (LMA)
provides the anchoring function (AF); the location management server
(LMs) is at the LMA while the location management client (LMc) is at
the mobile access gateway (MAG); the routing management (RM) function
is both ends of tunneling at the HA and the MAG.
In Hirarchical mobile IPv6 (HMIPv6) [RFC5380], a location management
proxy is at the mobility anchor point (MAP) to proxy between the LMs
at the LMA and the LMc at the MN. The MAP also has RM funtion to
enable tunneling between LMA and itself as well as tunneling between
MN and itself.
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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 Wi-Fi
hotspots) and, ii) 3GPP network flattening approaches.
While describing the current DMM practices, references to the generic
mobility management functions described in Section 3 are provided, as
well as some initial hints on the identified gaps with respect to the
DMM requirements 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.
The focus of the gap analysis is on current mobile network
architectures and standardized IP mobility solutions, considering any
kind of deployment options which do not violate the original protocol
specifications. 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 considered.
2. Solutions SHOULD allow selecting and using the most appropriate
IP anchor among a set of available ones.
3. Mobility management SHOULD be realized by the preservation of the
IP address across the different points of attachment (i.e.,
provision of IP address continuity).
Applications which can cope with changes in the MN's IP address do
not depend on IP mobility management protocols such as DMM.
Typically, a connection manager together with the operating system
will 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.
4.2. 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 Wi-Fi as an
exemplary wireless technology, since it is widely known and deployed
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nowadays. Some representative examples of Wi-Fi deployment
architectures are depicted in Figure 1.
+-------------+ _----_
+---+ | Access | _( )_
|AAA|. . . . . . | Aggregation |----------( Internet )
+---+ | Gateway | (_ _)
+-------------+ '----'
| | |
| | +-------------+
| | |
| | +-----+
+---------------+ | | AR |
| | +--+--+
+-----+ +-----+ *----+----*
| RG | | WLC | ( LAN )
+-----+ +-----+ *---------*
. / \ / \
/ \ +-----+ +-----+ +-----+ +-----+
MN MN |Wi-Fi| |Wi-Fi| |Wi-Fi| |Wi-Fi|
| AP | | AP | | AP | | AP |
+-----+ +-----+ +-----+ +-----+
. .
/ \ / \
MN MN MN MN
Figure 1: IP Wi-Fi 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 at the customer premises and provides
both wireless layer-2 access connectivity (i.e., it hosts the 802.11
Access Point function) and layer-3 routing functions. In the middle
of the figure, mobile nodes connect to Wi-Fi 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. This can also be
used as 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 Wi-Fi
network to a mobile operator core and support roaming between WLAN
and 3GPP accesses. Two main protocols can be used: Proxy Mobile IPv6
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[RFC5213] or Mobile IPv6 [RFC6275], [RFC5555], with the anchor (e.g.,
local mobility anchor or home agent) role typically being played by
the Access Aggregation Gateway or even by an entity placed in the
mobile operator's core network.
Although this section has adopted the example of Wi-Fi 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 more
flattened manner, so that 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. The analysis in this section is
limited 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 how to efficiently select
the source address (care-of-addresses versus home addresses) for
different types of communications. The analysis is divided 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 referred
to as 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), Routing management (RM), and
Internetwork Location Management server (LMs) functions. The mobile
node possesses the Location management client (LMc) function and the
RM function to enable tunneling between HA and itself. We next
describe some practices on how MIPv6/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 the topologically closest anchor
to each MN [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 MIPv6/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 of Section 4.1 and use several anchors at
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the same time, each of them anchoring IP flows initiated at a
different point of attachment. However there is no mechanism
specified by 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 IETF (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 CN1 and MN2 is in RO mode with CN2.
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
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the security problems posed by extending return routability tests
for prefixes, although many different solutions have been proposed
[RFC4889].
o The RO mode requires additional signaling, which adds some
protocol overhead.
o The signaling required to enable RO involves the home agent and is
repeated periodically for security reasons [RFC4225]. This
basically means that the HA remains a single point of failure,
because the Mobile IPv6 RO mode does not mean HA-less operation.
o The RO mode requires additional support from 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 by 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.
Hierarchical Mobile IPv6 (HMIPv6) [RFC5380] (as shown in Figure 3),
is another host-based IP mobility extension which 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. It provides LM
proxy function between the LM server (LMs) at the HA and the LM
client (LMc) at the MN. It also possess RM function to tunnel with
the HA and also to tunnel with the MN.
<- 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
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\|AR4|
------- -----
| CN2 | -----
------- /|AR5|
-------- / -----
| MAP3 |<
-------- \ -----
\|AR6|
-----
CN1 CN2 HA1 MAP1 AR1 MN1
| | | | ________|__________ |
|<------------------>|<==============>|<________+__________>| HoA
| | | | | |
| |<-------------------------->|<===================>| RCoA
| | | | | |
Figure 3: Hierarchical Mobile IPv6
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 its RCoA).
The use of HMIPv6 allows achieving some form of route optimization,
since 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 therefore a 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 Home
Agent switch specification [RFC5142], which defines a new mobility
header for signaling a mobile node that it should acquire a new home
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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 are other host-based approaches standardized within 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). With network-based IP mobility protocols, the local
mobility anchor (LMA) typically provides the anchoring function (AF),
Routing management (RM) function, Internetwork Location Management
server (LMs) function and RM function. The mobile access gateway
(MAG) provides the Location Management client (LMc) function and
Routing management (RM) function to tunnel with LMA. PMIPv6 is
architecturally similar to MIPv6, as the mobility signaling and
routing between LMA and MAG in PMIPv6 is similar to those between HA
and MN in MIPv6. The required mobility functionality at the MN is
provided by the MAG so that the involvement in mobility support by
the MN is not required.
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.
One simple but still suboptimal approach to decentralize Proxy Mobile
IPv6 operation 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 a
different point of attachment. This assignment can be static or
dynamic (as described later in this document). The main advantage of
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this simple approach is that the IP address anchor (i.e., the LMA)
could be placed closer to the mobile node. Therefore the resulting
paths are close-to-optimal. On the other hand, as soon as the mobile
node moves, the resulting path will start deviating from the optimal
one.
<- 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
Similar to the host-based IP mobility case, network-based IP mobility
has some extensions defined to mitigate the suboptimal routing issues
that may 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 distributed
mobility management environment is the LMA runtime assignment
[RFC6463]. This extension specifies a runtime local mobility anchor
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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 cases when the
mobile node does not have any active session, or when the 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 standards
development organization that specifies the 3rd generation mobile
network and the Evolved Packet System (EPS), which mainly comprises
the Evolved Packet Core (EPC) and a new radio access network,
sometimes referred to as 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 will be analyzed together. We next describe how 3GPP
mobility protocols and several additional completed or ongoing
extensions can be deployed to meet some of the DMM requirements
[I-D.ietf-dmm-requirements].
+---------------------------------------------------------+
| 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 | | | |
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| | +------------------------+ | | 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
The GPRS Tunnelling Protocol (GTP) [SDO-3GPP.29.060]
[SDO-3GPP.29.281] [SDO-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 User Equipment (UE) implements
the mobile node functionality, while the home agent role is played by
the PGW.
A Local IP Access (LIPA) and Selected IP Traffic Offload (SIPTO)
enabled network [SDO-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 |
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|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 are
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 traversing the mobile
operator's network core in the user plane. 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.
+---------------+-------+ +----------+ +-------------+ =====
|Residential | |H(e)NB | | Backhaul | |Mobile | ( IP )
|Enterprise |..|-------|..| |..|Operator |..(Network)
|Network | |L-GW | | | |Core network | =======
+---------------+-------+ +----------+ +-------------+
/
|
/
+-----+
| UE |
+-----+
Figure 8: LIPA architecture
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The 3GPP architecture specifications also provide mechanisms to allow
discovery and selection of gateways [SDO-3GPP.29.303]. These
mechanisms enable 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-12. 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 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
can avoid traversing single mobility anchor far from the optimal
route.
From the analysis performed in Section 4, a DMM deployment can meet
the requirement "REQ#1 Distributed processing" usually relying on the
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 allow deploying multiple anchors (i.e., home
agents and localized mobility anchors), therefore providing the
multiple anchoring function. However, existing solutions only
provide an optimal initial anchor assignment, thus the lack of
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dynamic anchor change/new anchor assignment is a gap. 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 to transfer 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, there is one gap, as the MN should be capable of
handling IP addresses in a DMM-friendly way, meaning that the MN can
perform smart source address selection (i.e., deprecating IP
addresses from previous mobility anchors, so they are not used for
new sessions). Besides, managing different mobility sessions served
by different mobility anchors 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, which leads to an anchor discovery and selection issue.
Currently, there is no efficient mechanism specified by IETF to allow
dynamically discovering the presence of nodes that can play the
anchor role, discovering their capabilities and selecting the most
suitable one. There is also no mechanism to allow selecting a node
that is currently anchoring a given home address/prefix (capability
sometimes required to meet REQ#2). There are though some mechanisms
that could help discovering anchors, such as the Dynamic Home Agent
Address Discovery (DHAAD), the use of the Home Agent (H) flag in
Router Advertisements (which indicates that the router sending the
Router Advertisement is also functioning as a Mobile IPv6 home agent
on the link) or the MAP option in Router Advertisements defined by
HMIPv6. Note that there are 3GPP mechanisms providing that
functionality defined in [SDO-3GPP.29.303].
Also note that REQ1 is such that the data plane traffic can avoid
suboptimal route. Distributed processing of the traffic is then
needed only in the data plane. The needed capability in distributed
processing therefore should not contradict with centralized control
plane. Other control plane solutions such as charging, lawful
interception, etc. should not be limited. Yet combining the control
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plane and data plane routing management (RM) function may limit the
choice to distributing boht data plane and control plane together.
In order to enable distributing only the data plane without
distributing the control plane, a gap is to split the routing
management function into the control plane (RM-CP) and data plane
(RM-DP).
5.2. Bypassable network-layer mobility support - REQ2
The need for "bypassable network-layer mobility support" introduced
in [I-D.ietf-dmm-requirements] will enable dynamic mobility
management. Note that this requirement is not on dynamic mobilitly
itself but only enables it. It therefore leaves flexibility on the
determination of whether network-layer mobility support is needed and
the role to use of not use network-layer mobility support. The
requirement only enables one to use or not use network-layer mobility
support. It only enables the which basically leverages the two
following functions:
o Dynamically assign/relocate anchor: a mobility anchor is assigned
only to sessions which uses the network-layer mobility 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 related to 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 uses such mobility
support (e.g., 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. Implicitly, when
no applications are using the network-layer mobility support, DMM may
releave the needed resources. This may imply having the knowledge of
which sessions at the mobile node are active and are using the
mobility support. This 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 provides the MN with the choice to
pick-up the correct address (provided 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
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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, such as
[I-D.bhandari-dhc-class-based-prefix],
[I-D.korhonen-6man-prefix-properties] and [I-D.anipko-mif-mpvd-arch].
However, although there exist these individual efforts that could be
be considered as attempts to fix the gap, there is no solution close
to be adopted and standardized in IETF.
5.3. IPv6 deployment - REQ3
This requirement states that DMM solutions SHOULD primarily target
IPv6 as the primary deployment environment. IPv4 support is not
considered mandatory and solutions SHOULD NOT be tailored
specifically to support IPv4, in particular in situations where
private IPv4 addresses and/or NATs are used.
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 MUST 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,
though they do not provide mobility support.
5.5. Co-existence - REQ5
According to [I-D.ietf-dmm-requirements], DMM solution MUST be able
to co-exist with existing network deployments, end hosts and routers.
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All 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 NOT
introduce new security risks, or amplify existing security risks,
that cannot be mitigated by existing security mechanisms or
protocols. Current mobility protocols have all security mechanisms
in place. 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.
5.7. Multicast - REQ7
It is stated in [I-D.ietf-dmm-requirements] that DMM solutions SHOULD
enable multicast solutions to be developed to avoid network
inefficiency in multicast traffic delivery.
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
mobile node, 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 this 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.
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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.
While MOBIKE could be used to switch from a gateway to another in
the middle of a session from MN side, there is no protocol support
for the network side.
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. There are though some
mechanisms that could help discovering anchors, such as the
Dynamic Home Agent Address Discovery (DHAAD), the use of the Home
Agent (H) flag in Router Advertisements (which indicates that the
router sending the Router Advertisement is also functioning as a
Mobile IPv6 home agent on the link) or the MAP option in Router
Advertisements defined by HMIPv6.
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). Currently, there is
a lack of solutions/extensions that support a clear control and
data plane separation for IETF IP mobility protocols.
6. Security Considerations
This document does not define any protocol, so it does not introduce
any new security concern.
7. IANA Considerations
None.
8. References
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8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
8.2. Informative References
[I-D.anipko-mif-mpvd-arch]
Anipko, D., "Multiple Provisioning Domain Architecture",
draft-anipko-mif-mpvd-arch-05 (work in progress), November
2013.
[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", draft-
ietf-dmm-requirements-12 (work in progress), December
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.
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[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.
[RFC4889] Ng, C., Zhao, F., Watari, M., and P. Thubert, "Network
Mobility Route Optimization Solution Space Analysis", RFC
4889, July 2007.
[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.
[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.
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[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.
[SDO-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.
[SDO-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.
[SDO-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.
[SDO-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.
[SDO-3GPP.29.281]
3GPP, "General Packet Radio System (GPRS) Tunnelling
Protocol User Plane (GTPv1-U)", 3GPP TS 29.281 10.3.0,
September 2011.
[SDO-3GPP.29.303]
3GPP, "Domain Name System Procedures; Stage 3", 3GPP TS
29.303 10.4.0, September 2012.
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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
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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