Network Working Group G. Chen
Internet-Draft H. Deng
Intended status: Informational China Mobile
Expires: May 08, 2014 D. Michaud
Rogers
J. Korhonen
Renesas Mobile
M. Boucadair
France Telecom
A. Vizdal
Deutsche Telekom AG
C. Byrne
T-Mobile USA
November 04, 2013
IPv6 Roaming Behavior Analysis
draft-chen-v6ops-ipv6-roaming-analysis-02
Abstract
This document intends to enumerate failure cases when a IPv6
subscriber roams into visited network areas. The investigations on
those failed cases reveal the causes in order to notice improper
configurations, equipment's incomplete functions or inconsistent IPv6
strategy.
Status of This Memo
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This Internet-Draft will expire on May 08, 2014.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Roaming Architecture Descriptions . . . . . . . . . . . . . . 3
3. Roaming Scenario Overview . . . . . . . . . . . . . . . . . . 4
4. Failure Cases Descriptions . . . . . . . . . . . . . . . . . 5
4.1. Failure Case 1: Incompatible with Extended PDP/PDN Type . 5
4.2. Failure Case 2: Splitting Dual-stack Bearer . . . . . . . 6
4.3. Failure Case 3: Shortage of IPv6 support . . . . . . . . 7
4.4. Failure Case 4: Fallback Incapability . . . . . . . . . . 7
4.5. Failure Case 5: 464xlat Support . . . . . . . . . . . . . 7
5. Discussions . . . . . . . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
9.1. Normative References . . . . . . . . . . . . . . . . . . 9
9.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
IPv6 has been deployed globally to overcome the IPv4 depletion.
Operators likely start or plan to upgrade the networks that allow
IPv6 subscribers to access. As the dramatical uses of Internet
services with a mobile access, IPv6 is an essential part to be
considered in the mobile network evolution. 3rd Generation
Partnership Project (3GPP) published the IPv6 migration guidance
[TR23.975], which describes different technical evolution paths. In
general, operators may deploy dual-stack or IPv6 single-stack
depending on network's conditions. It has been observed that those
deployments are rolled out in multiple provisioning domains. In the
early IPv6 stage, a mobile subscriber roaming around the different
areas may experience service degradations or interruptions due to the
inconsistent configurations and incomplete functions in the networks
nodes. This memo intends to document the observed failed cases and
analyze the causes. It's expected that operators could notice the
issues and prevent potential risks.
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2. Roaming Architecture Descriptions
The roaming process could be triggered in the following scenarios:
o International roaming: a mobile subscriber may entry a visited
network, where different PLMN identity is used. The subscribers
could either in an automatic mode or a manual mode to attach a
PLMN cell.
o Intra-PLMN mobility: a subscriber moves to a visited network as
that of the Home Public Land Mobile Network (HPLMN). However, the
subscriber profiles may not be stored in the area. Once the
subscriber attaches to the network, the subscriber profile should
be extracted from the home network for the network registration.
When a mobile device is turned on or is transferred via a handover to
a visited network, the mobile device will scan all radio channels and
find available Public Land Mobile Networks (PLMNs) to attach.
Serving GPRS Support Node (SGSN) or Mobility Management Entity (MME)
in the visited networks must contact the home Home Location
Register(HLR) or Home Subscriber Server(HSS) and obtain the
subscriber profile. Once the authentication and registration process
is completed, the PDP activation and traffic flows may be operated
differently according to the subscriber data configuration. Two
modes have been shown at the figure to illustrate, that are "Home
routed traffic" and "Local breakout".
+---------------------------------+ +------------------------+
|Visited Network | |Home Network |
| +----+ +--------+ | | +--------+ Traffic Flow
| | UE |==========>|SGSN/MME|======================>|GGSN/PGW|============>
| +----+ +--------+ | Signaling | +--------+ |
| |-------------------------->+--------+ |
| | | |HLR/HSS | |
| | | +--------+ |
+---------------------------------+ +------------------------+
Figure 1: Home Routed Traffic
+---------------------------------+ +------------------------+
|Visited Network | |Home Network |
| +----+ +--------+ | Signaling | +--------+ |
| | UE |==========>|SGSN/MME|---------------------->|HLR/HSS | |
| +----+ +--------+ | | +--------+ |
| || | | |
| +--------+ | | |
| |GGSN/PGW| | | |
| +--------+ | | |
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| Traffic Flow || | | |
+-----------------------||--------+ +------------------------+
\/
Figure2: Local Breadkout
In the home routed mode, subscribers will activate the PDP/PDN
context and get address from the home network. All traffic would be
routed back to the home networks. That is the default case for an
international roaming except for the IP Multimedia Subsystem (IMS)
scenario.
In the local breakout mode, the subscriber address will be assigned
from the visited network. The traffic flow would directly offloaded
locally at a network node close to that device's point of attachment
in the visited networks. Therefore, more efficient route would be
achieved. The following will describe the cases where there is local
breakout mode adopted.
o Operators may add the APN-OI-Replacement flag defined in 3GPP
[TS29.272] into user's subscription-data. The visited network
indicates a local domain name to replace the user requested Access
Point Name (APN). As the consequence, the traffic would be
steered to the visited network. Those functions are normally
deployed for the Intra-PLMN mobility cases.
o Operators could also configure VPLMN-Dynamic-Address-Allowed
flag[TS29.272] in the user profile to enable local breakout mode
in Visited Public Land Mobile Networks (VPLMNs).
o 3GPP specified Selected IP Traffic Offload (SIPTO)
function[TS23.401] since Release 10 in order to get efficient
route paths. It enables an operator to offload certain types of
traffic at a network node close to that device's point of
attachment to the access network.
o GSMA has defined RAVEL[IR.65] as IMS international roaming
architecture. Local breakout mode has been adopted for the
roaming architecture.
3. Roaming Scenario Overview
3GPP specified three types of Packet Data Protocol (PDP)/Packet Data
Networks (PDN) to describe each connection, i.e. PDP/PDN Type IPv4,
PDP/PDN Type IPv6 and PDP/PDN Type IPv4v6. User devices can be set
to request a particular PDP/PDN Type. Those PDP/PDN types should
also be restored in Home Subscriber Server (HSS) as a part of
subscriber profile, as defined in [TS29.272]. When a subscriber
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roams to a visited network, the new visited network notices that it
is not registered with its own system, and attempts to identify its
home network. Afterwards, the visited network will contact the home
network and request the subscriber profile from HSS. In this
process, service may be provided in a home routed or local breakout
mode. The IP address can be allocated from home network or visited
network accordingly. There may be a mismatch between the subscriber
request and network capability. The following table lists the
potential failure cases.
+-------------+-------------------+--------------+--------------+
| UE Request | Visited Network | Home routed |Local Breakout|
| | Capability | | |
+-------------+-------------------+--------------+--------------+
| Dual stack | IPv4-only |Failure case 1|Failure case 1|
+-------------+-------------------+--------------+--------------+
| Dual stack |IPv4-only/IPv6-only|Failure case 1|Failure case 2|
+-------------+-------------------+--------------+--------------+
| Dual stack | IPv6-only |Failure case 1|Failure case 3|
+-------------+-------------------+--------------+--------------+
| IPv6-only | IPv4-only | OK |Failure case 4|
+-------------+-------------------+--------------+--------------+
| IPv6-only | Dual stack | OK |Failure case 5|
| with 464xlat| | | |
+-------------+-------------------+--------------+--------------+
| IPv6-only | IPv6-only | OK | OK |
| with 464xlat| | | |
+-------------+-------------------+--------------+--------------+
| IPv4-only | Dual stack | OK | OK |
+-------------+-------------------+--------------+--------------+
Table 1: Roaming Scenario Descriptions
4. Failure Cases Descriptions
4.1. Failure Case 1: Incompatible with Extended PDP/PDN Type
A mobile device in a dual-stack network likely requests PDP/PDN type
IPv4v6 to allocate address. Such PDP/PDN type should be
understandable in the network nodes, including Serving GPRS Support
Node(SGSN), Gateway GPRS Support Node(GGSN), Mobility Management
Entity (MME), Serving Gateway(SGW), PDN Gateway(PGW), Home Location
Registrar(HLR) and Home Subscriber Server(HSS). When a subscriber
roams to the IPv4 network, the visited SGSN or MME has to communicate
with HLR/HSS in the home land to retrieve the subscriber profile.
The issue we observe is that multiple SGSN/MME will be unable to
correctly process a subscriber profile received in the Insert
Subscriber Data procedure if it contains an Ext-PDP-Type defined in
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3GPP [TS29.002]. Therefore, it will likely refuse the subscriber
registration.
Operators may have to remove the PDP/PDN type IPv4v6 from HLR/HSS in
home networks, that will restrict UEs only initiates IPv4 PDP or IPv6
PDP activation. In order to avoid this situation, operators should
make a comprehensive roaming agreement to support IPv6 and ensure
that aligns with GSMA document, e.g [IR.33], [IR.88] and [IR.21].
Since the agreement requires visited operators to upgrade all SGSN
nodes, some short- or medium-term solutions have been implemented to
fix the issue. There are some specific configurations in HLS/HSS of
home network. Multiple PDP/PDN subscription information will be
added in the subscriber profiles, for example it may include both PDP
/PDN type IPv4 and PDP/PDN type IPv4v6 for a user profile. Once the
HLR/HSS receives an Update Location message from visited SGSN/MME,
only the subscription data with PDP/PDN type IPv4 will be sent to
SGSN/MME in the Insert Subscriber Data procedure. It guarantee the
user profile could compatible with visited SGSN/MME capability.
4.2. Failure Case 2: Splitting Dual-stack Bearer
Dual-stack capability can also be provided in a early mobile
network(i.e. Pre-Release 8 network) using separate PDP/PDN
activations. That means only a single IPv4 and IPv6 PDP/PDN can be
initiated to allocate IPv4 and IPv6 address separately. Once a UE
with PDP/PDN type IPv4v6 request roams to those networks, same issue
described in failure case 1 will be occurred if the UE initiate a
network attachment process.
If networks could allow UE to make a success attachment, a roaming
subscriber with IPv4v6 PDP/PDN type should change the request to two
separated PDP/PDN request with single IP version in order to achieve
equivalent results. This restriction may be occurred in the below
two cases.
o The GGSN/PGW preferences dictate the use of IPv4 addressing only
or IPv6 prefix only for a specific APN.
o The SGSN/MME does not set the Dual Address Bearer Flag due to the
operator using single addressing per bearer to support
interworking with nodes of earlier releases
Above process would likely double PDP/PDN allocation costs. Some
operators may only allow one PDP/PDN is alive for each subscriber.
For example, IPv6 PDP/PDN would be rejected if the subscriber has an
active IPv4 PDP/PDN. Therefore, the subscriber will lost IPv6
connection in the visited network. Even the two parallel PDP/PDN
activations are allowed, it will require additional correlation of
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those two sessions of single IP version on the charging system. If
there are Policy and Charging Rules Function(PCRF)/Policy and
Charging Enforcement Function (PCEF) deployed, the system would treat
IPv4 and IPv6 session as independent and perform different Quality of
Service(QoS) policies. The subscriber may have unstable experiences
due to different behaviors on each IP version connection.
4.3. Failure Case 3: Shortage of IPv6 support
Some operators may adopt IPv6-only configuration for the IMS service,
e.g. Voice over LTE(VoLTE) or Rich Communication Suite (RCS). Since
IMS roaming architecture will offload all traffic in the visited
network, a dual-stack subscriber can only be assigned with IPv6
address. There is no IPv4 address returned. It requires all the IMS
based applications should be IPv6 enable. A translation-based
method, for example Bump-in-the-host (BIH)[RFC6535] and
464xlat[RFC6877] , may help to address the issue if there is IPv6
compatibility problems. Operators may could automatically enable the
function in a IPv6-only network and disable in a dual-stack or IPv4
network.
4.4. Failure Case 4: Fallback Incapability
3GPP specified the PDP/PDN type IPv6 as early as PDP/PDN type IPv4.
Therefore, the IPv6 single PDP/PDN type has been well supported and
interpretable in the 3GPP network nodes. When a subscriber requests
PDP/PDN type IPv6, the network should only return the expected IPv6
address. Otherwise, the request should be dropped and the error code
should be sent to the user. Roaming to IPv4-only networks with IPv6
PDP/PDN request would fail to get addresses. A proper fallback is
desirable however the behavior is implementation specific. There are
some UE have the ability to provide a different configuration for
home network and visited network respectively. It guarantees UE will
always initiate PDP/PDN type IPv4 in the roaming area. Android
system solves the issue by setting the roaming Access Point
Name(APN). The mobile terminal is allowed to ignore the original
requested protocol and always adhere to IPv4 when roaming. Those
fallback mechanisms are deserved to be implemented timely.
4.5. Failure Case 5: 464xlat Support
464xlat[RFC6877] is proposed to address IPv4 compability issue in a
IPv6 single-stack environment. The function on a mobile terminal
likely gets along with PDP/PDN IPv6 type request to cooperate with a
remote NAT64[RFC6146] gateway. 464xlat may use the mechanism defined
in [I-D.ietf-behave-nat64-discovery-heuristic] to automatically
discover NAT64 prefixes. Those behaviors depend on the network
deployment. If the DNS64 or NAT64 is not deployed in the visited
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networks, 464xlat may be failed to perform. Considering the various
network's situations, operators may adopt 464xlat in the home
networks and use IPv4-only in the roaming networks with different
roaming profile configurations.
As an alternative solution, an AAA Server could be deployed to
connect with GGSN/PGW. Once the GGSN/PGW receive the session
creation requests, it will initiate an Access-Request to an AAA
server via Radius protocol. The Access-Request contains subscriber
and visited network information, e.g. PDP/PDN Type, International
Mobile Equipment Id (IMEI), Software Version(SV) and visited SGSN/MME
location code, etc. The AAA server could take IMEI and SV components
to verify if device has 464XLAT support. Combining with the visited
network information, the AAA server will ultimately decide to enable
464xlat in an IPv6-only roaming or fallback to IPv4.
5. Discussions
The dual-stack deployment is recommended in most cases. However, it
may take some times in a mobile environment. 3GPP didn't specify PDP/
PDN type IPv4v6 in the early release. Such PDP/PDN type is supported
in new-built Long Term Evolution(LTE)/System Architecture
Evolution(SAE) network, but didn't support well in the third
generation network. The situations may cause the roaming issues
dropping the attachment from dual-stack subscribers in the case of
LTE to 3G and IPv6-enabled 3G to IPv4 3G. Operators may have to adopt
temporary solution unless all the interworking nodes(i.e. SSGN and
SGW) in the visited network have been upgraded to support Ext-PDP-
Type feature.
As an alternative solution for dual-stack, operators may change a
unified PDP/PDN request into two separated single IP version
requests. However, this approach is problematic in the Charging
records and QoS policy enforcement. In addition, it doubles the PDP
resource uses. It may be unappealing for the deployment.
Conversely, some operators may choose PDP/PDN Type IPv6 to start the
communications in home networks and use different profile in the
roaming area. Since PDP/PDN Type IPv6 has been introduced in 3GPP
early release, it didn't require upgrading on the interworking nodes
to make compatibility. The proper IPv4 fallback mechanism should be
supported either on the mobile terminal or network equipment.
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A roaming to IPv6-only network occurs when operators deploy roaming
function for IMS service. A dual-stack capable device could
implement translation-based function to support the IPv4
applications. Those inserted translation function can be turned off
properly when the terminals roam back to dual-stack or IPv4 networks.
Operators can also deploy AAA servers to make final decision
6. IANA Considerations
This document makes no request of IANA.
7. Security Considerations
The draft didn't introduce additional security concerns to the
networks.
8. Acknowledgements
The authors would like to thank V6ops chairs(Fred Baker and John
Brzozowski) to encourage us to continue the work. This document is
the result of the IETF V6ops IPv6-Roaming design team effort.
9. References
9.1. Normative References
[I-D.ietf-behave-nat64-discovery-heuristic]
Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
the IPv6 Prefix Used for IPv6 Address Synthesis", draft-
ietf-behave-nat64-discovery-heuristic-17 (work in
progress), April 2013.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[RFC6146] Bagnulo, M., Matthews, P., and I. van Beijnum, "Stateful
NAT64: Network Address and Protocol Translation from IPv6
Clients to IPv4 Servers", RFC 6146, April 2011.
[RFC6147] Bagnulo, M., Sullivan, A., Matthews, P., and I. van
Beijnum, "DNS64: DNS Extensions for Network Address
Translation from IPv6 Clients to IPv4 Servers", RFC 6147,
April 2011.
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[RFC6535] Huang, B., Deng, H., and T. Savolainen, "Dual-Stack Hosts
Using "Bump-in-the-Host" (BIH)", RFC 6535, February 2012.
[RFC6877] Mawatari, M., Kawashima, M., and C. Byrne, "464XLAT:
Combination of Stateful and Stateless Translation", RFC
6877, April 2013.
9.2. Informative References
[IR.21] Global System for Mobile Communications Association,
GSMA., "Roaming Database, Structure and Updating
Procedures", July 2012.
[IR.33] Global System for Mobile Communications Association,
GSMA., "GPRS Roaming Guidelines", July 2012.
[IR.65] Global System for Mobile Communications Association,
GSMA., "IMS Roaming & Interworking Guidelines", May 2012.
[IR.88] Global System for Mobile Communications Association,
GSMA., "LTE Roaming Guidelines", January 2012.
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[RFC6586] Arkko, J. and A. Keranen, "Experiences from an IPv6-Only
Network", RFC 6586, April 2012.
[TR23.975]
3rd Generation Partnership Project, 3GPP., "IPv6 migration
guidelines", June 2011.
[TS23.401]
3rd Generation Partnership Project, 3GPP., "General Packet
Radio Service (GPRS) enhancements for Evolved Universal
Terrestrial Radio Access Network (E-UTRAN) access v9.00",
March 2009.
[TS29.002]
3rd Generation Partnership Project, 3GPP., "Mobile
Application Part (MAP) specification v9.00", December
2009.
[TS29.272]
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3rd Generation Partnership Project, 3GPP., "Mobility
Management Entity (MME) and Serving GPRS Support Node
(SGSN) related interfaces based on Diameter protocol
v9.00", September 2009.
Authors' Addresses
Gang Chen
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: phdgang@gmail.com
Hui Deng
China Mobile
53A,Xibianmennei Ave.,
Xuanwu District,
Beijing 100053
China
Email: denghui@chinamobile.com
Dave Michaud
Rogers
Email: Michaud@rci.rogers.com
Jouni Korhonen
Renesas Mobile
Porkkalankatu 24
FIN-00180 Helsinki, Finland
Email: jouni.nospam@gmail.com
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Mohamed Boucadair
France Telecom
No.32 Xuanwumen West Street
Rennes,
35000
France
Email: mohamed.boucadair@orange.com
Vizdal Ales
Deutsche Telekom AG
Tomickova 2144/1
Prague 4, 149 00
Czech Republic
Email: ales.vizdal@t-mobile.cz
Cameron Byrne
T-Mobile USA
Bellevue
Washington 98105
USA
Email: cameron.byrne@t-mobile.com
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