Problem Statement for Fixed Mobile Convergence
draft-xue-intarea-fmc-ps-01
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| Authors | Li Xue , Behcet Sarikaya , Dirk Von Hugo | ||
| Last updated | 2012-03-09 | ||
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draft-xue-intarea-fmc-ps-01
Network Working Group L. Xue
Internet-Draft B. Sarikaya
Intended status: Informational Huawei
Expires: September 10, 2012 D. von Hugo
Telekom Innovation Laboratories
March 9, 2012
Problem Statement for Fixed Mobile Convergence
draft-xue-intarea-fmc-ps-01.txt
Abstract
The purpose of this document is to analyze the issues that have
arisen so far and then to propose a set of requirements for the Fixed
Mobile Convergence. The term Fixed Mobile Convergence spans several
scenarios from true integration of fixed and mobile terminals,
services, and network infrastructure on both technical and management
level down to pure interworking between fixed and mobile networks in
serving access for multi-interface terminals like todays'
smartphones. In the interworking scenario, the mobile network passes
on the mobile subscribers policies to the fixed broadband network in
order to maintain the end-to-end service level agreement and to
support remote terminal and access network management. Explicitly,
the fixed broadband network must have partnership with the mobile
network in Fixed Mobile Convergence interworking scenario. This
document gives a brief overview of the assumed Fixed Mobile
Convergence architecture and related works and then introduces
several requirements based on the partnership in Fixed Mobile
Convergence architecture, such as User Equipment identification and
authentication, Femto Access Point management, device type
identification and mobility considerations.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on September 10, 2012.
Copyright Notice
Copyright (c) 2012 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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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Conventions and Terminology . . . . . . . . . . . . . . . . . 7
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4. Key issues in Fixed Mobile Converged Interworking . . . . . . 8
4.1. UE identification and AAA management in fixed
broadband network . . . . . . . . . . . . . . . . . . . . 9
4.2. Femto Access Point Management . . . . . . . . . . . . . . 12
4.3. Device type identification . . . . . . . . . . . . . . . . 14
4.4. Carrier Grade NAT Related Issues . . . . . . . . . . . . . 14
4.5. UE Mobility in Fixed Broadband Network . . . . . . . . . . 15
4.6. Flow Mobility between different interface . . . . . . . . 17
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
6. Security Considerations . . . . . . . . . . . . . . . . . . . 18
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 18
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
8.1. Normative References . . . . . . . . . . . . . . . . . . . 18
8.2. Informative References . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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1. Introduction
Growing availability of intelligent mobile devices and mature
networks of operators providing both reliable carrier grade
connectivity and affordable high bandwidth access offer to the
customer a nice climate of mobile broadband. With widespread
availability and easy usability of mobile broadband, mobile broadband
applications become more ubiquitous. Subscribers demand for various
service applications, especially Internet applications, such as
mobile Internet video, mobile Internet real-time communication, etc.
The subscribers requirements lay the foundation of mobile broadband.
On the other hand, simultaneously, the subscribers' services promote
the evolution of mobile broadband, which will impact the network
architecture. The flourishing mobile applications demand more and
more bandwidth offered by the operators. Even with wireless networks
becoming mature, such as 3G and LTE, the average bandwidth offered is
not comparable to data rates offered by fixed networks. With data
services rapidly increasing, the traditional cellular network
operating at a shared medium and thus being limited in transmission
rate often becomes the bottle-neck of mobile broadband. In addition
radio network technology generally requires high capital investment
and operational expenditures. Cellular network operators are facing
the challenge of increasing traffic demand at decreasing revenue and
have to provide means of more cost efficient access technology in a
highly competitive environment. The trend of offloading the traffic
to fixed broadband network is emerging. Mobile industry has
specified functionalities to offload the data traffic to the fixed
broadband (FBB) network, via WLAN or a Home (e)NodeB (HNB or eNodeB,
aka. Femtocell) [TR23.829], which could alleviate traffic pressure
on the mobile network. That is to say, today, operators are able to
employ mechanisms to manage the subscriber service over both the
mobile and the fixed broadband network. We can say, FMC is emerging
on the basis of subscribers and operators requirements.
Fixed Mobile Convergence is a technology trend which aims to provide
the subscribers access to services regardless of the access network
type they are connecting to and provide the operators with the
flexibility to ensure transparency of services to the end user. For
a mobile subscriber to access services over both mobile and fixed
broadband networks seamlessly, additionally, the subscriber's end-to-
end service level agreement (SLA) must be maintained. This is
achieved by interworking the control planes of the fixed broadband
network and the mobile network.
In the FMC interworking scenario addressed here, the fixed broadband
network must partner with the mobile network to perform
authorisation, authentication, and accounting (AAA) and acquire the
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policies for the mobile subscriber. Please note, a single converged
control plane, used for both the fixed broadband and the mobile
network, may be used in a truely converged, i.e. integrated
convergence scenario. This document only focuses on the interworking
scenario in this version. The convergence scenario is for further
study.
Figure 1 shows the assumed reference architecture of Fixed Mobile
Convergence Interworking for a Mobile (3GPP) Network and a fixed non-
3GPP access network as proposed by 3GPP and BroadBand Forum (BBF) as
an example in document [WT203].
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+---------------------------------------+
| Mobile Network |
| ---- |
| +------+ / \|
| +----+ PCRF | |Operator|
| | +---+--+ | Service|
| | | \ /|
| | | --+- |
+------+ +------+ | +------+ +---+--+ | | |
| UE | | eNB +-----+ SGW +---+ PGW +-----|---------+----------+
+------+ +------+ | +------+ +--+---+---+ | +------+| |
| +--+---+ +-|-----+M AAA || --+-
| | ePDG +---+ | +---+--+| / \
+------------+------+-----|---------|---+ |Internet
| | | | Service
+---------------|---------|---------|---+ \ /
| Fixed Network | +---+--+ +---+--+| --+-
| | +---+ BPCF | |F AAA || |
| +--+-+-+ +------+ +---+--+| |
+------+ | | BNG +---------------+ | |
| Femto+-----------+ +--+-+-+ | |
+------+ | | | +----------------------------+
+------+ | | +--+---+ |
| UE | | +----+ AN | |
+------+ +------+ | +--+---+ |
|WiFiAP|-------------------+ |
| RG | | |
+------+ | |
+---------------------------------------+
Legend:
M AAA Authentication Authorization Accounting in Mobile Network
F AAA Authentication Authorization Accounting in Fixed Network
BPCF Broadband Policy Control Function
BNG Broadband Network Gateway
ePDG evolved Packet Data Gateway
PCRF Policy Charging Rule Function
PGW Packet Data Network Gateway
SGW Serving Gateway
UE User Equipment
RG Residential Gateway
Figure 1: Reference Architecture of Fixed Mobile Convergence
The policy and charging control (PCC) system is an important element
in FMC architecture. PCC system of FMC consists of policy decision
point (PCRF in the mobile network and BPCF in the fixed broadband
network) and the policy enforcement point (PGW and BNG,
respectively), shown in Figure 1. PCC should support for controlling
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the QoS (e.g., QoS class and bit rates) authorized for service, and
IP flow based charging. In FMC interworking scenario, these services
can be divided into four types.
1. Service via macrocell wireless network
2. Service via WiFi/Femtocell access routed back to 3GPP Evolved
Packet Core (EPC), where the fixed broadband network is used as
the access network,
* The service from a mobile UE is connected to WiFi or to
Femtocell Access Point (FAP) at the residential gateway (RG),
routed back to 3GPP Evolved Packet Core (EPC).
3. Services via WiFi access only fixed broadband routed
* The service from a mobile UE is connected to WiFi without
traversing the mobile network.
* In this scenario, the UE service may be guaranteed based on
subscriber's policy from the mobile network.
4. LIPA/SIPTO traffic
* Support of Local IP access (LIPA) and of Selected IP traffic
offload (SIPTO) for the Home (e)NodeB Subsystem and for the
macro layer network include a more integrated FMC scenario and
thus are for further study.
As for the services stated above, only the second and the third type
are related to FMC, where both the fixed broadband and the mobile
network are involved. The FMC architecture shall be capable to set
operator policies to support simultaneous access to these service.
In the network today, deploying FMC is a worthy way for operators to
satisfy subscriber's requirement and ease pressure from bandwidth.
In the following sections, we first describe the motivation and then
discuss the key issues in FMC interworking scenario.
2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
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3. Motivation
The motivation is to highlight and discuss the issues when
facilitating FMC. We systematically analyze the issues that have
been proposed so far and briefly assess the possible extensions which
could solve the problems. In the network architecture, we target and
limit the scope to the interworking architecture for FMC. The
convergence architecture is out of scope.
Regarding the traffic management and control requirements in FMC
interworking scenario, there are five essential issues from an IETF
Internet Area and fixed broadband network point of view, as follows.
1. UE identification in fixed broadband network
2. Femto Access Point management
3. Device type identification
4. UE Mobility in fixed broadband network
5. Flow Mobility
In Section 4 below, we discuss the key issues and some problems based
on the FMC architecture. There are many standardization issues
related to FMC and protocol extension work needed are stated in this
document.
If these issues are fixed, the advantages brought out will be:
1. Optimize traffic management (per-UE granularity in the fixed
broadband network)
2. Enhance device management (via IP address synchronization between
fixed broadband network and mobile network)
3. Reduce operators load on Deep Packet Inspection (DPI) (bypass the
unnecessary traffic)
4. Quick Responsiveness based on UE status
4. Key issues in Fixed Mobile Converged Interworking
This section provides some key issues related to FMC when deployed.
These issues, which motivate the FMC, must be resolved. It is
difficult to foresee the most suitable solutions to resolve these
issues now, but in any event, some possibilities need to be analysed
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based on the scenarios. Mobile network solutions of these issues are
out of scope.
4.1. UE identification and AAA management in fixed broadband network
A user accessing a network point of attachment has to be authorised
and authenticated by the network as well as vice versa to assure
reliability of service as well as proper exchange of accounting
information. That is the identity of the user and the AAA
credentials have to be transferred and acknowledged. In addition a
unique identity has to be assigned to the customer and/or his
terminal, i.e. to maintain a session, a routable IP address has to be
provided. Detailed consideration of AAA issues is out of sccope of
this document.
Nowadays, a subscriber is always provided with a single private IPv4
address at their home or small business, which should reduce the
pressure on the available public IPv4 addresses which are now
exhausted. For instance, in the fixed broadband network, each host
within the local network will be assigned a private IPv4 address,
then NA(P)T function is responsible for translating the private IPv4
address to the public IPv4 address assigned to the CPE (Customer
Premises Equipment) by operators, and vice versa.
As a result of maintaining growth of IPv4 service, private addressing
plan will require address sharing, which will cause issues for
operators, such as traffic management, QoS enforcement, etc. in the
FMC scenarios, where the policy control must be based on the
fundamental concept of per-UE granularity. Note that ultimately,
deploying IPv6 is the only perennial way to ease pressure on the
public IPv4 address without the need for address sharing mechanisms
that give rise to the issues identified herein. But in the interim,
however, IPv4 services are also very important for end-users, and
service providers, which can not be ignored.
The FMC architecture shall be capable to set operator policies to
support simultaneous access to mobile services and traffic offloading
to the fixed broadband network. Accordingly, regarding policy and
QoS interworking between the fixed broadband and mobile
architectures, we consider the following scenarios:
1. Mobile UE with mobile-routed traffic and no NAT in Residential
Gateway (RG)
2. Mobile UE with mobile-routed traffic with NAT in RG
3. Mobile UE with offloaded traffic and no NAT in RG
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4. Mobile UE with offloaded traffic with NAT in RG
+---------------------------------------+
| Mobile Network |
| ---- |
| / \|
| |Operator|
| +-----------------> | Service|
| |+--------------->> /|
| || ---- |
| +-----+ ||+------+ |
| | SGW +--||+ PGW +--------------------------+
| +-----+ ||+--+---+ | |
| || | | --+-
| || | | / \
+----------||---+-----------------------+ |Internet
|| | | Service
+----------||---+-----------------------+ \ /
| || | +------------------>>> --+-
| || | |+----------------->>>> |
| ||+--+---+ || | |
| ||| BNG +-||----------------+------+
+------+ +------+<----case1-- -+|+------+ || |
| UE | | RG | | | || |
+------+ +------|<<---case3-----++------+ || |
| | AN | || |
+------+ +------+<<---case2---+ +------+ || |
| UE | |RG NAT| | +-----------+| |
+------+ +------+<<<<-case4----------------+ |
Private IP | +---------------------------------------+
Public IP + UDP
Currently PCC can support case 1 and 3, but issues will be introduced
in cases 2 and 4 because of address sharing via NA(P)T. The important
consideration is that today's PCC (including QoS control and IP flow
based charging) must be based on the fundamental concept of IP
Connectivity Access Network (IP-CAN) in per-UE granularity. IP-CAN
session [TS23.203] is the association between a UE and an IP network.
So in FMC network, it is assumed that fixed broadband network could
manage the traffic in per-UE granularity.
Obviously, the fixed broadband network and mobile network must
support inter-operator subscribers policy exchange, this introduces a
major challenge on how to coordinate UE identification across the
operators' domains so that the mobile network can inform the suitable
policy to the serving fixed broadband access network that its mobile
user equipment (UE) is attached to. So that the fixed broadband
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network can provide the appropriate FMC interworking policy and
bearer control on UE's traffic.
There may be limitations with BNG implementations with respect to the
level of granularity (per-UE) of the enforcement. Take case 4 for an
example, a key problem is to identify offloaded traffic from a
special UE, i.e. UE identification substantively, behind the NA(P)T
embedded into RG, there is no longer a unique IP address per UE, in
addition, the UDP port behind NA(P)T is not bound to the special UE.
Another factor that contributes to UE identification is efficient
packet inspection. Operators expect the fixed broadband network
could be configured in such a way that the traffic subject to packet
inspection is routed via the Traffic Detection Function (TDF)
[TS29.212], otherwise, the traffic that is not subject to packet
inspection may bypass the TDF. This assumption only holds if it is
possible to identify individual UEs behind NA(P)T embedded into the
RG in fixed broadband network, shown in Figure 2. Issues may arise
if there is a NA(P)T in or beyond the RG, even a NA(P)T in or beyond
the BNG. As a result, additional mechanisms are needed to enable
this.
+--------+
| |
+-------+ PCRF |
| | |
| +--------+
+--------+ +--------+ +--------+ +----+----+
| | | | | +-----+ |
| ------------------------------------------------------------------
| | | | | | | TDF | / \
| ******************************************************************
| | | +-------+ | | | Service
| | | | | | | \ /
| | | | | | | +--------+
| | |Resident| | | +--------+ |
| ********---------**********--------************------------******* |
| UE | |Gateway | | BNG +------------------+ PGW |
+--------+ +--------+ +--------+ +--------+
Legends:
--------- 3GPP UE User Plane Traffic Offloaded subject to packet inspection
********* 3GPP UE User Plane Traffic Offloaded not subject to packet inspection
*****---- 3GPP UE User Plane Traffic Home Routed
Figure 2: UE's Traffic Route with TDF
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As discussed before, there are many drivers for the UE identification
in the broadband network. They include efficient packet inspection,
QoS enforcement, charging. We can note that all these functions in
FMC depend on being able to identify UEs behind the NA(P)T.
There are several possibilities which provide solutions. One
recommendation from fixed broadband, defined in [WT146], is to bind
the UDP port (after NA(P)T) to the special UE. This solution has
limitations because it may not be feasible due to static
configuration in RG, to provide unique UDP port numbers to all the
devices on user side. This is the overload scenario for operators.
Beside 3GPP-defined algorithms to derive unique identities for use
within a fixed access network from 3GPP-specified SIM (Subscriber
Identity Module) such as in [EAP-SIM, RFC 4186] or [EAP-AKA, RFC 4187
or EAP-AKA', RFC 5448] there are several possible IP or TCP protocol
extensions, discussed in [I-D.ietf-intarea-nat-reveal-analysis]. In
that draft, TCP host identifier option is also discussed.
Additionally, there may be other possibilities, such as some other
new identifier to be defined, etc. It is difficult to foresee which
is the suitable solution, more work needs to be done.
4.2. Femto Access Point Management
Femtocells (FAPs), whose architecture is specified in the mobile
standards (e.g., 3GPP, Femto Forum, etc.), are an exemplary feature
of an FMC network. The access network to which Femtocells are
attached is the fixed broadband network as depicted in Figure 3. As
mentioned before, in order to achieve PCC, there is a need for the
fixed broadband network to have partnership with mobile network to
maintain the service level agreement (SLA). Here, the private IPv4
addressing plan in fixed broadband network introduces the
limitations, which was described in the draft
[I-D.so-ipsecme-ikev2-cpext]. In today's generic FAP architecture,
it is difficult to guarantee a unique mapping, shown as follows:
1. Determine the UE attached FAP's public IPv4 address together with
the translated port number of the UDP header of the encapsulated
IPsec tunnel between the FAP and the Security Gateway (SeGW)
which are assigned by the fixed broadband network. The FAP's
public IPv4 address is:
* used for identifying the location of the FAP,
* used for identifying the UE's traffic at the fixed broadband
network.
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2. Determine the corresponding FAP's public IPv4 address's
association with the UE's inner-IPv4 address which is assigned by
the mobile network. The association is:
* used for identifying the mobile UE that is attached to the FAP
in order to allow the PCRF to retrieve the UE's policy to be
passed onto the BPCF at the fixed broadband network.
+-------------+ +------------------------+
(Mobile network | | | |
assigned Inner | | | |
IP) | | | |
| | +------+ | | +------+ +---------+ |
| | | BPCF +---------+ PCRF +--+MME/SGW | |
| | +--+---+ | | +------+ +----+----+ |
| | | | | | |
| | +--+---+ | | +------+ +----+----+ |
+---+ | +---+ | | | | | | | | | |
+----+ | <---|----------+--+------+---+---+-> | | | |
| UE | |FAP| v |RG | | | BNG | | | | SeGW +--+ FAP-GW | |
+----+ | <--------------+--+------+---+---+-> | | | |
+---+^ +---+^ | | | | | | | | | |
| | | +------+ | | +------+ +----+----+ |
| | | | | | |
| | | | | | |
| | | Fixed | | +----+----+ |
Private | | Broadband | | | | |
IP | | Network | | | PGW | |
| | | | | | |
Public-------------+ | +----+----+ |
IP+Port | Mobile | |
(NAPT) | Network | |
| | |
+----------------+-------+
--+-
Legends: / \
|Internet|
<---> | Service|
<---> IPsec Tunnel \ /
MME Mobility Management Entity ----
Figure 3: FMC Femto Access Architecture
Due to the requirement for inter-operators subscribers policy
exchange, the private and public addressing which rely on NA(P)T,
must be coordinated cross the operators domains. Additionally, FAP
location must be identified for management. These major factors
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drive the solutions in interworking architecture with Femtocell
scenario such as extending IKEv2 [RFC5996], so that the overall
service performance and the user experience could be enhanced.
4.3. Device type identification
As there are multiple types of user terminal devices, e.g. PDA,
mobile phone, personal computer, etc. with different characteristic
capabilities (portability, screen size, audio output etc.) for some
service applications and corresponding QoS and management
requirements, it is important for operators to capture the service-
specific terminal device type, especially in FMC interworking
scenario. In such cases, different rules for policy control and
traffic routing are needed to be provided by the operators to ensure
acceptable SLA to the device.
When WiFi is deployed for traffic offload, the terminal devices, such
as mobile phone and personal computer could be used for service. In
this case, only the traffic from the 3GPP service, such as mobile
voice may need policy control and management. The best effort
traffic will not be routed via the mobile core (EPC) and thus has no
impact to the FMC at all. With this method, the traffic management
optimization generally occurs based on selecting suitable types of
device which need special policy control and management.
In the current WiFi network, the device type information is
transparent to the fixed broadband network, because only IP and port
information is used for identification. It is difficult for BNG to
distinguish the traffic from UE device, and then route it specially.
So a solution is needed to identify the device type, especially at
the BNG.
4.4. Carrier Grade NAT Related Issues
Referring to Figure 3, FAP is usually behind a Carrier Grade NAT
(CGN) box. CGN may be used as part of architecting the support of
NAT44 or NAT444 [RFC6264]. CGN could be colocated with BNG in
Figure 3. In such a configuration, UE maintains long lived IPsec or
TLS connection across the CGN.
Carrier Grade NAT may flush the long lived session after a certain
timeout period. Currently most NAT implementations would flush all
sessions after they reach 24 hours, regardless of the state of the
session.
CGN terminating all existing sessions of a UE does present a number
of problems. One problem is that this will cause more attachment
signaling to be introduced in order to reestablish UE's sessions.
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More serious problem may occur though. UEs all active phone calls
are possibly disrupted. UE may even be involved in calls to
emergency services like 911 which would be disrupted as well.
4.5. UE Mobility in Fixed Broadband Network
The users are the mobile subscribers in FMC. Note that all the
services depend on the substantive character of subscriber's
mobility. It is important for operators to capture the user device
when it is moving into or outside the network, even in WiFi access.
Besides, the application and service from the subscriber must be
guaranteed based on the policy of operators.
In mobile network today, there are many mature solutions offered for
user's mobility already. Herein, only mobility in fixed access,
i.e., WiFi access, will be considered. For example, the user device
is attached to the home LAN (e.g., WiFi ) network, and establishes a
connection back to the subscriber's mobile service provider network
via the fixed broadband network. The mobile operator should
cooperate with the broadband access operator to deliver proper policy
for the service from UE.
The mobility considered in the fixed access is a little different.
In this section, we divide the mobility capability into two cases:
1. UE is moving into or outside the coverage area of WiFi AP
2. UE's WiFi access is dormant or not.
The following figure shows an example of the scenario where mobile
UEs are served in WiFi deployment over the fixed broadband network.
RG embeds WiFi AP and NA(P)T function. Each UE is provided with a
single private IPv4 address assigned within the local network.
NA(P)T in RG is responsible for translating the private IPv4 address
to the public IPv4 address assigned by the fixed operator.
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Policy for UE
identified by IP + Port
+-------------+| +------------------------+
| || | |
| || | |
| || | |
| +------+ || | +------+ +---------+ |
| | BPCF +---+V--+-+ PCRF +--+ MME | |
| +--+---+ | | +---+--+ +----+----+ |
+----+ | | | | | | |
|UE1 |Private IP1 | +--+---+ | | +---+--+ +----+----+ |
+----+ +---+ | | | | | | | | | |
| <----------+--+------+---+---+-> | | | |
|RG | | | BNG | | | | ePDG +--+ SGW | |
+----+ | <-^--------+--+------+---+---+-> | | | |
|UE2 | +---+ | | | | | | | | | | |
+----+Private IP2 | | +------+ | | +------+ +----+----+ |
| | | | | |
| | | | | |
| | Fixed | | +----+----+ |
| | Broadband | | | | |
Public IP | Network | | | PGW | |
NA(P)T | | | | | |
+-------------+ | +----+----+ |
| Mobile | |
| Network | |
| | |
Legends: +----------------+-------+
--+-
<---> / \
<---> IPsec Tunnel |Internet|
| Service|
\ /
----
Figure 4: Mobility in the Fixed Broadband Network
As described previously, BPCF in fixed broadband network must have
partnership with PCRF in mobile network in order to maintain the
service level agreement (SLA). In order to allow the PCRF to
retrieve the UE's policy to be passed onto the BPCF in the fixed
broadband network, it is mainly concerned about the traffic and UE
identification binding used to achieve the actual traffic control.
The BPCF/BNG will perform the policy control based on the binding.
Based on the UE's mobility, issues will arise. For example, the PCRF
will retrieve the wrong policy to the BPCF, if the UE identification
can not be updated in time. For instance, there are two UEs, shown
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in Figure 4. UE1 and UE2 are assigned different private IP addresses
within the local network, IP1 and IP2 accordingly. After NAPT, BPCF/
BNG will be based on the public IPv4 address and the different UDP
port numbers assigned by NAPT to perform the admission control and
policy enforcement on the UE's traffic.
Since plenty of UEs may move into the coverage of WiFi AP, it is
possible that the same UDP port will be used for both UE1 and UE2 at
the different time period. For example, UE1 moved out of the WiFi
coverage and later the UE2 moved in. The same UDP port used by UE1
before is assigned to UE2 again. As mentioned, the identification
must be consistent between fixed broadband network and the mobile
network for policy exchange. So the UDP port used as part of UE
identification must be updated in time based on the status of UE,
otherwise the PCRF will confused about which policy is used.
Especially, there may be a requirement to binding the UDP port to a
special UE described in Section 4. The UDP ports must be cleared if
the UEs corresponding to prior port binding are out of coverage of
the WiFi AP. That is to say the configuration must be updated
regularly to satisfy that the WiFi AP can serve thousands of UEs.
Other solutions to solve the issue in Section 4 may also fix this
challenge introduced by the mobility of UE.
Based on the discussion, for UE's mobility in WiFi network, we can
recognize that the important requirement for the fixed broadband
network is to update the UE identification based on UE mobility. In
this scenario, the fixed broadband network must be able to update the
record for UE during the UE mobility.
4.6. Flow Mobility between different interface
Traffic offloading requires the ability to move the traffic flows
from one interface to the other interface of the UE. The type of
flows to be moved depends on the policy and should be dictated by the
mobile operator.
Several IP flow mobility protocol approaches are under discussion
some of which have been already adopted for use in mobile networks,
e.g. by 3GPP, but currently no such flow mobility protocol has been
applied for use in an fixed broadband network, e.g. by BBF. Without
an overarching commonly agreed on flow mobility protocol, offloading
traffic from mobile network to fixed broadband network can simply not
be achieved.
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5. IANA Considerations
This document makes no request to IANA.
6. Security Considerations
Serious concern of mobile operators towards FMC approaches has been
the customer access via networks not under control of the operator.
Operators would like to keep their own high security measures to
prevent various kinds of fraud or attack to the operators services
and network entities. Well known risks and vulnerabilities which are
common to any NA(P)T application are documented in the NAT
specification [RFC2663]. Any additional security considerations
arising from FMC are TBD.
7. Acknowledgements
Many people provided comments that have been incorporated into this
document including Mohamed Boucadair, David Binet, Pierrick Seite.
Special thanks to Cameron Byrne for providing the text in Section
4.4.
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.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)",
RFC 5996, September 2010.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269,
June 2011.
[TR23.829]
"3GPP TR23.829, Local IP Access and Selected IP Traffic
Offload (LIPA-SIPTO)", October 2010.
[TS23.203]
"3GPP TS23.203, Policy and Charging control architecture",
December 2011.
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[TS29.212]
"3GPP TS29.212, Policy and Charging Control (PCC) over
Gx/Sd reference point", December 2011.
8.2. Informative References
[I-D.ietf-intarea-nat-reveal-analysis]
Boucadair, M., Touch, J., Levis, P., and R. Penno,
"Analysis of Solution Candidates to Reveal a Host
Identifier in Shared Address Deployments",
draft-ietf-intarea-nat-reveal-analysis-01 (work in
progress), March 2012.
[I-D.so-ipsecme-ikev2-cpext]
So, T., "IKEv2 Configuration Payload Extension for Private
IPv4 Support for Fixed Mobile Convergence",
draft-so-ipsecme-ikev2-cpext-01 (work in progress),
February 2012.
[RFC2663] Srisuresh, P. and M. Holdrege, "IP Network Address
Translator (NAT) Terminology and Considerations",
RFC 2663, August 1999.
[RFC6264] Jiang, S., Guo, D., and B. Carpenter, "An Incremental
Carrier-Grade NAT (CGN) for IPv6 Transition", RFC 6264,
June 2011.
[WT146] "Broadband Forum Working Text WT-146, Subscriber
Sessions", June 2011.
[WT203] "Broadband Forum Working Text WT-203, Interworking between
Next Generation Fixed and 3GPP Wireless Access",
December 2011.
Authors' Addresses
Li Xue
Huawei
NO.156 Beiqing Rd. Z-park, Shi-Chuang-Ke-Ji-Shi-Fan-Yuan,
Beijing, HaiDian District 100095
China
Email: xueli@huawei.com
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Behcet Sarikaya
Huawei
5340 Legacy Dr.
Plano, TX 75074
Email: sarikaya@ieee.org
Dirk von Hugo
Telekom Innovation Laboratories
Deutsche-Telekom-Allee 7
D-64295 Darmstadt
Germany
Phone:
Email: Dirk.von-Hugo@telekom.de
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