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Internet Engineering Task Force (IETF) M. Mawatari
Request for Comments: 6877 Japan Internet Exchange
Category: Informational M. Kawashima
ISSN: 2070-1721 NEC AccessTechnica, Ltd.
C. Byrne
T-Mobile USA
April 2013
464XLAT: Combination of Stateful and Stateless Translation
Abstract
This document describes an architecture (464XLAT) for providing
limited IPv4 connectivity across an IPv6-only network by combining
existing and well-known stateful protocol translation (as described
in RFC 6146) in the core and stateless protocol translation (as
described in RFC 6145) at the edge. 464XLAT is a simple and scalable
technique to quickly deploy limited IPv4 access service to IPv6-only
edge networks without encapsulation.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6877.
Mawatari, et al. Informational [Page 1]
RFC 6877 464XLAT April 2013
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation and Uniqueness of 464XLAT . . . . . . . . . . . . . 4
4. Network Architecture . . . . . . . . . . . . . . . . . . . . . 4
4.1. Wireline Network Architecture . . . . . . . . . . . . . . 4
4.2. Wireless 3GPP Network Architecture . . . . . . . . . . . . 5
5. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Wireline Network Applicability . . . . . . . . . . . . . . 6
5.2. Wireless 3GPP Network Applicability . . . . . . . . . . . 7
6. Implementation Considerations . . . . . . . . . . . . . . . . 7
6.1. IPv6 Address Format . . . . . . . . . . . . . . . . . . . 7
6.2. IPv4/IPv6 Address Translation Chart . . . . . . . . . . . 7
6.3. IPv6 Prefix Handling . . . . . . . . . . . . . . . . . . . 9
6.4. DNS Proxy Implementation . . . . . . . . . . . . . . . . . 9
6.5. CLAT in a Gateway . . . . . . . . . . . . . . . . . . . . 9
6.6. CLAT-to-CLAT Communications . . . . . . . . . . . . . . . 10
7. Deployment Considerations . . . . . . . . . . . . . . . . . . 10
7.1. Traffic Engineering . . . . . . . . . . . . . . . . . . . 10
7.2. Traffic Treatment Scenarios . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . . 11
10.2. Informative References . . . . . . . . . . . . . . . . . . 12
Appendix A. Examples of IPv4/IPv6 Address Translation . . . . . . 13
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1. Introduction
With the exhaustion of the unallocated IPv4 address pools, it will be
difficult for many networks to assign IPv4 addresses to end users.
This document describes an IPv4-over-IPv6 solution as one of the
techniques for IPv4 service extension and encouragement of IPv6
deployment. 464XLAT is not a one-for-one replacement of full IPv4
functionality. The 464XLAT architecture only supports IPv4 in the
client-server model, where the server has a global IPv4 address.
This means it is not fit for IPv4 peer-to-peer communication or
inbound IPv4 connections. 464XLAT builds on IPv6 transport and
includes full any-to-any IPv6 communication.
The 464XLAT architecture described in this document uses IPv4/IPv6
translation standardized in [RFC6145] and [RFC6146]. It does not
require DNS64 [RFC6147] since an IPv4 host may simply send IPv4
packets, including packets to an IPv4 DNS server, that will be
translated to IPv6 on the customer-side translator (CLAT) and back to
IPv4 on the provider-side translator (PLAT). 464XLAT networks may
use DNS64 [RFC6147] to enable single stateful translation [RFC6146]
instead of 464XLAT double translation where possible. The 464XLAT
architecture encourages the IPv6 transition by making IPv4 services
reachable across IPv6-only networks and providing IPv6 and IPv4
connectivity to single-stack IPv4 or IPv6 servers and peers.
2. Terminology
PLAT: PLAT is provider-side translator (XLAT) that complies with
[RFC6146]. It translates N:1 global IPv6 addresses to global
IPv4 addresses, and vice versa.
CLAT: CLAT is customer-side translator (XLAT) that complies with
[RFC6145]. It algorithmically translates 1:1 private IPv4
addresses to global IPv6 addresses, and vice versa. The CLAT
function is applicable to a router or an end-node such as a
mobile phone. The CLAT should perform IP routing and
forwarding to facilitate packets forwarding through the
stateless translation even if it is an end-node. The CLAT as
a common home router or wireless Third Generation Partnership
Project (3GPP) router is expected to perform gateway
functions such as being a DHCP server and DNS proxy for local
clients. The CLAT uses different IPv6 prefixes for CLAT-side
and PLAT-side IPv4 addresses and therefore does not comply
with the sentence "Both IPv4-translatable IPv6 addresses and
IPv4-converted IPv6 addresses SHOULD use the same prefix." in
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RFC 6877 464XLAT April 2013
Section 3.3 of [RFC6052]. The CLAT does not facilitate
communications between a local IPv4-only node and an IPv6-
only node on the Internet.
3. Motivation and Uniqueness of 464XLAT
The list below describes the motivation for 464XLAT and its unique
characteristics.
o 464XLAT has minimal IPv4 resource requirements and maximum IPv4
efficiency through statistical multiplexing.
o No new protocols are required; there is quick deployment.
o IPv6-only networks are simpler and therefore less expensive to
operate than dual-stack networks.
o 464XLAT has consistent native IP-based monitoring and traffic
engineering. Capacity-planning techniques can be applied without
the indirection or obfuscation of a tunnel.
4. Network Architecture
Examples of 464XLAT architectures are shown in the figures in the
following sections.
Wireline Network Architecture can be used in situations where there
are clients behind the CLAT, regardless of the type of access service
-- for example, fiber to the home (FTTH), Data Over Cable Service
Interface Specification (DOCSIS), or WiFi.
Wireless 3GPP Network Architecture can be used in situations where a
client terminates the wireless access network and possibly acts as a
router with tethered clients.
4.1. Wireline Network Architecture
The private IPv4 host in this diagram can reach global IPv4 hosts via
translation on both the CLAT and PLAT. On the other hand, the IPv6
host can reach other IPv6 hosts on the Internet directly without
translation. This means that the Customer Premises Equipment (CPE) /
CLAT can not only have the function of a CLAT but also the function
of an IPv6 native router for native IPv6 traffic. In this diagram,
the v4p host behind the CLAT has [RFC1918] addresses.
Mawatari, et al. Informational [Page 4]
RFC 6877 464XLAT April 2013
+------+
| v6 |
| host |
+--+---+
|
.---+---.
/ \
/ IPv6 \
| Internet |
\ /
`----+----'
|
+------+ | .---+---. .------.
| v6 +---+ +------+ / \ +------+ / \
| host | | | | / IPv6 \ | | / IPv4 \
+------+ +---+ CLAT +---+ Network +---+ PLAT +---+ Internet |
+--------+ | | | \ / | | \ /
| v4p/v6 +-+ +------+ `---------' +------+ `----+----'
| host | | |
+--------+ | +--+---+
+------+ | | v4g |
| v4p +---+ | host |
| host | | +------+
+------+ |
<- v4p -> XLAT <--------- v6 --------> XLAT <- v4g ->
v6 : Global IPv6
v4p : Private IPv4
v4g : Global IPv4
Figure 1: Wireline Network Topology
4.2. Wireless 3GPP Network Architecture
The CLAT function on the User Equipment (UE) provides an [RFC1918]
address and IPv4 default route to the local node's network stack.
The applications on the UE can use the private IPv4 address for
reaching global IPv4 hosts via translation on both the CLAT and the
PLAT. On the other hand, reaching IPv6 hosts (including hosts
presented via DNS64 [RFC6147]) does not require the CLAT function on
the UE.
Presenting a private IPv4 network for tethering via NAT44 and
stateless translation on the UE is also an application of the CLAT.
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RFC 6877 464XLAT April 2013
+------+
| v6 |
| host |
+--+---+
|
.---+---.
/ \
/ IPv6 \
| Internet |
\ /
UE / Mobile Phone `---------'
+----------------------+ |
| +----+ | | .---+---. .------.
| | v6 +----+ +------+ / \ +------+ / \
| +----+ | | | / IPv6 PDP \ | | / IPv4 \
| +---+ CLAT +---+ Mobile Core +---+ PLAT +--+ Internet |
| | | | \ GGSN / | | \ /
| | +------+ \ ' +------+ `----+---'
| +-----+ | | `-------' |
| | v4p +---+ | +--+---+
| +-----+ | | | v4g |
+----------------------+ | host |
+------+
<- v4p -> XLAT <--------- v6 --------> XLAT <- v4g ->
v6 : Global IPv6
v4p : Private IPv4
v4g : Global IPv4
PDP : Packet Data Protocol
GGSN : Gateway GPRS Support Node
Figure 2: Wireless 3GPP Network Topology
5. Applicability
5.1. Wireline Network Applicability
When an Internet Service Provider (ISP) has IPv6 access service and
provides 464XLAT, the ISP can provide outgoing IPv4 service to end
users across an IPv6 access network. The result is that edge network
growth is no longer tightly coupled to the availability of scarce
IPv4 addresses.
If another ISP operates the PLAT, the edge ISP is only required to
deploy an IPv6 access network. All ISPs do not need IPv4 access
networks. They can migrate their access network to a simple and
highly scalable IPv6-only environment.
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5.2. Wireless 3GPP Network Applicability
At the time of writing, in April 2013, the vast majority of mobile
networks are compliant to Pre-Release 9 3GPP standards. In Pre-
Release 9 3GPP networks, Global System for Mobile Communications
(GSM) and Universal Mobile Telecommunications System (UMTS) networks
must signal and support both IPv4 and IPv6 Packet Data Protocol (PDP)
attachments to access IPv4 and IPv6 network destinations [RFC6459].
Since there are two PDPs required to support two address families,
this is double the number of PDPs required to support the status quo
of one address family, which is IPv4.
For the cases of connecting to an IPv4 literal or IPv4 socket that
require IPv4 connectivity, the CLAT function on the UE provides a
private IPv4 address and IPv4 default route on the host for the
applications to reference and bind to. Connections sourced from the
IPv4 interface are immediately routed to the CLAT function and passed
to the IPv6-only mobile network, destined for the PLAT. In summary,
the UE performs the CLAT function that does a stateless translation
[RFC6145], but only when required by an IPv4-only scenario such as
IPv4 literals or IPv4-only sockets. The mobile network has a PLAT
that does stateful translation [RFC6146].
464XLAT works with today's existing systems as much as possible.
464XLAT is compatible with existing solutions for network-based deep
packet inspection like 3GPP standardized Policy and Charging Control
(PCC) [TS.23203].
6. Implementation Considerations
6.1. IPv6 Address Format
The IPv6 address format in 464XLAT is defined in Section 2.2 of
[RFC6052].
6.2. IPv4/IPv6 Address Translation Chart
This chart offers an explanation about address translation
architecture using a combination of stateful translation at the PLAT
and stateless translation at the CLAT. The client on this chart is
delegated an IPv6 prefix from a prefix delegation mechanism such as
DHCPv6 Prefix Delegation (DHCPv6-PD) [RFC3633]; therefore, it has a
dedicated IPv6 prefix for translation.
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Destination IPv4 address
+----------------------------+
| Global IPv4 address |
| assigned to IPv4 server |
+--------+ +----------------------------+
| IPv4 | Source IPv4 address
| server | +----------------------------+
+--------+ | Global IPv4 address |
^ | assigned to IPv4 PLAT pool |
| +----------------------------+
+--------+
| PLAT | Stateful XLATE(IPv4:IPv6=1:n)
+--------+
^
|
(IPv6 cloud)
Destination IPv6 address
+--------------------------------------------------------------+
| IPv4-embedded IPv6 address |
| defined in Section 2.2 of RFC 6052 |
+--------------------------------------------------------------+
Source IPv6 address
+--------------------------------------------------------------+
| IPv4-embedded IPv6 address |
| defined in Section 2.2 of RFC 6052 |
+--------------------------------------------------------------+
(IPv6 cloud)
^
|
+--------+
| CLAT | Stateless XLATE(IPv4:IPv6=1:1)
+--------+
^ Destination IPv4 address
| +----------------------------+
+--------+ | Global IPv4 address |
| IPv4 | | assigned to IPv4 server |
| client | +----------------------------+
+--------+ Source IPv4 address
+----------------------------+
| Private IPv4 address |
| assigned to IPv4 client |
+----------------------------+
Figure 3: Case of Enabling Only Stateless XLATE on CLAT
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6.3. IPv6 Prefix Handling
There are two relevant IPv6 prefixes that the CLAT must be aware of.
First, CLAT must know its own IPv6 prefixes. The CLAT should acquire
a /64 for the uplink interface, a /64 for all downlink interfaces,
and a dedicated /64 prefix for the purpose of sending and receiving
statelessly translated packets. When a dedicated /64 prefix is not
available for translation from DHCPv6-PD [RFC3633], the CLAT may
perform NAT44 for all IPv4 LAN packets so that all the LAN-originated
IPv4 packets appear from a single IPv4 address and are then
statelessly translated to one interface IPv6 address that is claimed
by the CLAT via the Neighbor Discovery Protocol (NDP) and defended
with Duplicate Address Detection (DAD).
Second, the CLAT must discover the PLAT-side translation IPv6 prefix
used as a destination of the PLAT. The CLAT will use this prefix as
the destination of all translation packets that require stateful
translation to the IPv4 Internet. It may discover the PLAT-side
translation prefix using [Discovery-Heuristic]. In the future, some
other mechanisms, such as a new DHCPv6 option, will possibly be
defined to communicate the PLAT-side translation prefix.
6.4. DNS Proxy Implementation
The CLAT should implement a DNS proxy as defined in [RFC5625]. The
case of an IPv4-only node behind the CLAT querying an IPv4 DNS server
is undesirable since it requires both stateful and stateless
translation for each DNS lookup. The CLAT should set itself as the
DNS server via DHCP or other means and should proxy DNS queries for
IPv4 and IPv6 LAN clients. Using the CLAT-enabled home router or UE
as a DNS proxy is a normal consumer gateway function and simplifies
the traffic flow so that only IPv6 native queries are made across the
access network. DNS queries from the client that are not sent to the
DNS proxy on the CLAT must be allowed and are translated and
forwarded just like any other IP traffic.
6.5. CLAT in a Gateway
The CLAT feature can be implemented in a common home router or mobile
phone that has a tethering feature. Routers with a CLAT feature
should also provide common router services such as DHCP of [RFC1918]
addresses, DHCPv6, NDP with Router Advertisement, and DNS service.
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RFC 6877 464XLAT April 2013
6.6. CLAT-to-CLAT Communications
464XLAT is a hub and spoke architecture focused on enabling IPv4-only
services over IPv6-only networks. Interactive Connectivity
Establishment (ICE) [RFC5245] may be used to support peer-to-peer
communication within a 464XLAT network.
7. Deployment Considerations
7.1. Traffic Engineering
Even if the ISP for end users is different from the PLAT provider
(e.g., another ISP), it can implement traffic engineering
independently from the PLAT provider. Detailed reasons are below:
1. The ISP for end users can figure out the IPv4 destination address
from the translated IPv6 packet header, so it can implement
traffic engineering based on the IPv4 destination address (e.g.,
traffic monitoring for each IPv4 destination address, packet
filtering for each IPv4 destination address, etc.). The
tunneling methods do not have such an advantage, without any deep
packet inspection for processing the inner IPv4 packet of the
tunnel packet.
2. If the ISP for end users can assign an IPv6 prefix greater than
/64 to each subscriber, this 464XLAT architecture can separate
the IPv6 prefix for native IPv6 packets and the XLAT prefixes for
IPv4/IPv6 translation packets. Accordingly, it can identify the
type of packets ("native IPv6 packets" and "IPv4/IPv6 translation
packets") and implement traffic engineering based on the IPv6
prefix.
7.2. Traffic Treatment Scenarios
The below table outlines how different permutations of connectivity
are treated in the 464XLAT architecture.
Note: 464XLAT double translation treatment will be stateless when a
dedicated /64 is available for translation on the CLAT. Otherwise,
the CLAT will have both stateful and stateless since it requires
NAT44 from the LAN to a single IPv4 address and then stateless
translation to a single IPv6 address.
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RFC 6877 464XLAT April 2013
+--------+-------------+-----------------------+-------------+
| Server | Application | Traffic Treatment | Location of |
| | and Host | | Translation |
+--------+-------------+-----------------------+-------------+
| IPv6 | IPv6 | End-to-End IPv6 | None |
+--------+-------------+-----------------------+-------------+
| IPv4 | IPv6 | Stateful Translation | PLAT |
+--------+-------------+-----------------------+-------------+
| IPv4 | IPv4 | 464XLAT | PLAT/CLAT |
+--------+-------------+-----------------------+-------------+
Traffic Treatment Scenarios
8. Security Considerations
To implement a PLAT, see the security considerations presented in
Section 5 of [RFC6146].
To implement a CLAT, see the security considerations presented in
Section 7 of [RFC6145]. The CLAT may comply with [RFC6092].
9. Acknowledgements
The authors would like to thank JPIX NOC members, JPIX 464XLAT trial
service members, Seiichi Kawamura, Dan Drown, Brian Carpenter, Rajiv
Asati, Washam Fan, Behcet Sarikaya, Jan Zorz, Tatsuya Oishi, Lorenzo
Colitti, Erik Kline, Ole Troan, Maoke Chen, Gang Chen, Tom Petch,
Jouni Korhonen, Bjoern A. Zeeb, Hemant Singh, Vizdal Ales, Mark ZZZ
Smith, Mikael Abrahamsson, Tore Anderson, Teemu Savolainen, Alexandru
Petrescu, Gert Doering, Victor Kuarsingh, Ray Hunter, James Woodyatt,
Tom Taylor, and Remi Despres for their helpful comments. We also
would like to thank Fred Baker and Joel Jaeggli for their support.
10. References
10.1. Normative References
[RFC6052] Bao, C., Huitema, C., Bagnulo, M., Boucadair, M., and X.
Li, "IPv6 Addressing of IPv4/IPv6 Translators", RFC 6052,
October 2010.
[RFC6145] Li, X., Bao, C., and F. Baker, "IP/ICMP Translation
Algorithm", RFC 6145, April 2011.
[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.
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RFC 6877 464XLAT April 2013
10.2. Informative References
[Discovery-Heuristic]
Savolainen, T., Korhonen, J., and D. Wing, "Discovery of
the IPv6 Prefix Used for IPv6 Address Synthesis", Work
in Progress, March 2013.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC3633] Troan, O. and R. Droms, "IPv6 Prefix Options for Dynamic
Host Configuration Protocol (DHCP) version 6", RFC 3633,
December 2003.
[RFC5245] Rosenberg, J., "Interactive Connectivity Establishment
(ICE): A Protocol for Network Address Translator (NAT)
Traversal for Offer/Answer Protocols", RFC 5245,
April 2010.
[RFC5625] Bellis, R., "DNS Proxy Implementation Guidelines",
BCP 152, RFC 5625, August 2009.
[RFC6092] Woodyatt, J., "Recommended Simple Security Capabilities in
Customer Premises Equipment (CPE) for Providing
Residential IPv6 Internet Service", RFC 6092,
January 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.
[RFC6459] Korhonen, J., Soininen, J., Patil, B., Savolainen, T.,
Bajko, G., and K. Iisakkila, "IPv6 in 3rd Generation
Partnership Project (3GPP) Evolved Packet System (EPS)",
RFC 6459, January 2012.
[TS.23203] 3GPP, "Policy and charging control architecture", 3GPP
TS 23.203 10.7.0, June 2012.
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Appendix A. Examples of IPv4/IPv6 Address Translation
The following is an example of IPv4/IPv6 address translation on the
464XLAT architecture.
In the case that an IPv6 prefix greater than /64 is assigned to an
end user by such as DHCPv6-PD [RFC3633], the CLAT can use a dedicated
/64 from the assigned IPv6 prefix.
Host & configuration value
+------------------------------+
| IPv4 server |
| [198.51.100.1] | IP packet header
+------------------------------+ +--------------------------------+
^ | Destination IP address |
| | [198.51.100.1] |
| | Source IP address |
| | [192.0.2.1] |
+------------------------------+ +--------------------------------+
| PLAT | ^
| IPv4 pool address | |
| [192.0.2.1 - 192.0.2.100] | |
| PLAT-side XLATE IPv6 prefix | |
| [2001:db8:1234::/96] | |
+------------------------------+ +--------------------------------+
^ | Destination IP address |
| | [2001:db8:1234::198.51.100.1] |
| | Source IP address |
| | [2001:db8:aaaa::192.168.1.2] |
+------------------------------+ +--------------------------------+
| CLAT | ^
| PLAT-side XLATE IPv6 prefix | |
| [2001:db8:1234::/96] | |
| CLAT-side XLATE IPv6 prefix | |
| [2001:db8:aaaa::/96] | |
+------------------------------+ +--------------------------------+
^ | Destination IP address |
| | [198.51.100.1] |
| | Source IP address |
| | [192.168.1.2] |
+------------------------------+ +--------------------------------+
| IPv4 client |
| [192.168.1.2/24] |
+------------------------------+
Delegated IPv6 prefix for client: 2001:db8:aaaa::/56
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Authors' Addresses
Masataka Mawatari
Japan Internet Exchange Co., Ltd.
KDDI Otemachi Building 19F, 1-8-1 Otemachi,
Chiyoda-ku, Tokyo 100-0004
JAPAN
Phone: +81 3 3243 9579
EMail: mawatari@jpix.ad.jp
Masanobu Kawashima
NEC AccessTechnica, Ltd.
800, Shimomata
Kakegawa-shi, Shizuoka 436-8501
JAPAN
Phone: +81 537 22 8274
EMail: kawashimam@vx.jp.nec.com
Cameron Byrne
T-Mobile USA
Bellevue, Washington 98006
USA
EMail: cameron.byrne@t-mobile.com
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