DHC WG Y. Cui
Internet-Draft Q. Sun
Intended status: Standards Track Tsinghua University
Expires: October 6, 2014 I. Farrer
Deutsche Telekom AG
Y. Lee
Comcast
Q. Sun
China Telecom
M. Boucadair
France Telecom
April 4, 2014
Dynamic Allocation of Shared IPv4 Addresses
draft-ietf-dhc-dynamic-shared-v4allocation-00
Abstract
This memo describes the dynamic allocation of shared IPv4 addresses
to clients using DHCPv4. Address sharing allows a single IPv4
address to be allocated to multiple, active clients simultaneously,
each client being differentiated by a unique set of transport source
port numbers. The necessary changes to existing DHCPv4 client and
server behavior are described and a new DHCPv4 option for
provisioning clients with shared IPv4 addresses is included.
Due to the nature of IP addresses sharing, some limitations to their
applicability are necessary. This memo describes these limitations
and recommends suitable architectures and technologies where address
sharing may be utilized.
Requirements Language
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].
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
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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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."
This Internet-Draft will expire on October 6, 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
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. Functional Overview . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Client-Server Interaction . . . . . . . . . . . . . . . . . . 4
5. Server Behavior . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Leasing Shared and Non-Shared IPv4 Addresses from a
Single DHCP 4o6 Server . . . . . . . . . . . . . . . . . 6
6. Client Behavior . . . . . . . . . . . . . . . . . . . . . . . 6
6.1. Restrictions to Client Usage of a Shared IPv4 Address . . 7
7. DHCPv4 Port Parameters Option . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8.1. Denial-of-Service . . . . . . . . . . . . . . . . . . . . 9
8.2. Port Randomization . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
The shortage of available public IPv4 addresses means that it is not
always possible for operators to allocate a full IPv4 address to
every connected device. This problem is particularly acute whilst an
operator is migrating from their existing, native IPv4 network to a
native IPv6 network with IPv4 provided as an overlay service. During
this phase, public IPv4 addresses are needed to provide for both
existing and transition networks.
Two main types of solutions have emerged to address the problem (see
Appendix A of [RFC6269]):
1. Deploying Carrier Grade Network devices (CGNs, [RFC6888]).
2. Distributing the same public IPv4 address to multiple clients
using non-overlapping layer 4 port sets.
This memo focuses on the second category of solutions.
[I-D.ietf-dhc-dhcpv4-over-dhcpv6] introduces a "DHCP 4o6 Server",
which is capable of servicing both DHCPv6 [RFC3315] and DHCPv4-over-
DHCPv6 requests, and offers dynamic leasing for IPv4 addresses to
clients as in DHCPv4 [RFC2131]. This memo specifies a new DHCPv4
option, called OPTION_V4_PORTPARAMS, and describes how it can be used
to achieve dynamic leasing for shared IPv4 addresses.
This extension is only suitable for specific architectures based on
the Address plus Port model (A+P) [RFC6346].
Although DHCPv4 over DHCPv6 is used as the underlying DHCPv4
transport mechanism throughout this document, OPTION_V4_PORTPARAMS as
a DHCPv4 option may also be used in other solutions such as DHCPv4
over IPv6 [I-D.ietf-dhc-dhcpv4-over-ipv6]. The usage of
OPTION_V4_PORTPARAMS in these cases is out of scope of this document.
2. Functional Overview
Functionally, the dynamic allocation of shared IPv4 addresses by the
DHCP 4o6 Server is similar to the DHCPv4 server dynamic allocation
process for 'full' IPv4 addresses described in [RFC2131]. The
essential difference is that the DHCP 4o6 Server MAY allocate the
same IPv4 address to more than one DHCP 4o6 client simultaneously,
providing that each shared address allocation also includes a range
of layer 4 source ports unique to that address (i.e., the combined
tuple of IPv4 address and Port Set ID MUST be unique for each active
lease).
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The DHCP 4o6 client inlcudes OPTION_V4_PORTPARAMS (described below)
within the Parameter Request List option [RFC2132] in the
DHCPDISCOVER message to indicate to the DHCP 4o6 server that it
supports shared IPv4 addressing. OPTION_V4_PORTPARAMS is also used
by the server to convey the allocated PSID to the client.
OPTION_V4_PORTPARAMS is also implemented by the server to enable it
to identify clients which support shared, dynamic address leasing.
With this option, the server can dynamically maintain shared IPv4
address leases. The server must also manage unique client leases
based on both the IPv4 address and PSID tuple, instead of using only
the IPv4 address.
3. Terminology
This document makes use of the following terms:
Shared IPv4 address: An IPv4 address with a restricted layer 4 port
set. Connections sourced from the shared address
must use source ports within the assigned port
set.
Port Set ID (PSID): Identifier for a range of ports assigned to a
DHCP client.
4. Client-Server Interaction
Using DHCPv4 over DHCPv6, the following DHCPv4 message flow is
transported within the DHCPv4-query and DHCPv4-response messages (the
DHCPv6 messages used for carrying DHCPv4 messages).
1. When the client constructs its DHCPv4 DHCPDISCOVER message to be
transported within the DHCPv4-query message, the DHCPDISCOVER
message MUST include the following options: A client identifier
(constructed as per [RFC4361] and OPTION_V4_PORTPARAMS (described
below). The client MAY insert a non-zero value in the PSID-Len
field within OPTION_V4_PORTPARAMS to indicate the preferred size
of the restricted port set to the DHCP 4o6 Server.
2. Each DHCP 4o6 Server that receives the DHCPDISCOVER message
within the DHCPv4-query message and supports shared IPv4
addresses responds with a DHCPOFFER message containing an
available IPv4 address in the 'yiaddr' field. The response MUST
also include OPTION_V4_PORTPARAMS containing a restricted port
set. If the received OPTION_V4_PORTPARAMS field contains a non-
zero PSID-Len field, the DHCP 4o6 Server MAY allocate a port set
of the requested size to the client (depending on policy). The
DHCPOFFER message is included in the DHCPv4-response message and
sent to the client.
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3. The client evaluates all received DHCPOFFER messages and selects
one (e.g. based on the configuration parameters received, such as
the size of the offered port set). The client then sends a
DHCPREQUEST encapsulated in the DHCPv4-query message, containing
the selected DHCP server's server identifier and the
corresponding OPTION_V4_PORTPARAMS received in the DHCPOFFER
message.
4. The server identified in the DHCPREQUEST message (via the siaddr
field) creates a binding for the client. The binding includes
the client identifier, the IPv4 address and the PSID. These
parameters are used by both the server and the client to identify
a lease in any DHCP messages. The server responds with a DHCPACK
message containing the configuration parameters for the
requesting client. Optionally, the server MAY also store the
IPv6 address that the client has bound the received IPv4
parameters to.
5. On receipt of the DHCPACK message with the configuration
parameters, the client MUST NOT perform a final check on the
address, such as ARPing for a duplicate allocated address.
6. If the client chooses to relinquish its lease by sending a
DHCPRELEASE message, the client MUST include the original client
identifier, the leased network address and the allocated
restricted port set in OPTION_V4_PORTPARAMS.
In the case that the client has stored the previously allocated
address and restricted port set, the process described in section 3.2
of [RFC2131] must be followed to reuse the previously allocated
shared IPv4 address. OPTION_V4_PORTPARAMS MUST be included in the
message flow, with the client's requested port set being included in
the DHCPDISCOVER message.
5. Server Behavior
The DHCP 4o6 Server MUST NOT reply with the OPTION_V4_PORTPARAMS
until the client has explicitly listed the option code in the
Parameter Request List (Option 55) [RFC2132].
The DHCP 4o6 Server SHOULD reply with OPTION_V4_PORTPARAMS if the
client includes the OPTION_V4_PORTPARAMS in its Parameter Request
List. In order to achieve the dynamic management the shared IPv4
address, the server MUST run an address and port-set pool that
provides the same function as the address pool in a regular DHCP
server. The server MUST use the combination of address and PSID as
the key for maintaining the state of a lease, and for searching for
an available lease for assignment. The leasing database MUST include
the IPv4 address, PSID and client identifier of the requesting
client.
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When a server receives a DHCPDISCOVER message with
OPTION_V4_PORTPARAMS in the Parameter Request List, the server
determines an IPv4 address with a port-set for the requesting client.
The logic for selection is similar to that in Section 4.3.1 of
[RFC2131].
When the server receives a DHCPREQUEST message with
OPTION_V4_PORTPARAMS, the server MUST determine the client's state
according to related parameters (Section 4.3.2 of [RFC2131]) and the
value of OPTION_V4_PORTPARAMS.
Upon receipt of a DHCPRELEASE message with OPTION_V4_PORTPARAMS, the
server searches for the lease using the address in the 'ciaddr' field
and the PSID information in the OPTION_V4_PORTPARAMS, and marks the
lease as unallocated.
The port-set assignment MUST be coupled with the address assignment
process. Therefore server MUST assign the address and port set in
the same DHCP messages. The lease information for the address is
applicable to the port-set as well.
When defining the pools of IPv4 addresses and PSIDs which are
available to lease to clients, the server SHOULD implement a
mechanism to reserve some port ranges (e.g. 'well-known-ports'
0-1023) from allocation to clients.
5.1. Leasing Shared and Non-Shared IPv4 Addresses from a Single DHCP
4o6 Server
A single DHCP 4o6 server may serve clients that do not support
OPTION_PORTPARAMS as well as those that do. As the rules for the
allocation of shared addresses differ from the rules for full IPv4
address assignment, the DHCP 4o6 server MUST implement a mechanism to
ensure that clients which do not support OPTION_PORTPARAMS do not
receive shared addresses. For example, two separate IPv4 addressing
pools could be used, one of which allocates IPv4 addresses and PSIDs
only to clients that have requested them.
If the server is only configured one address pool for shared address
allocation, it MUST discard requests that do not contain
OPTION_V4_PORTPARAMS in the Parameter Request List option.
6. Client Behavior
The DHCP 4o6 client applying for a shared IPv4 address MUST include
the OPTION_V4_PORTPARAMS code in the Parameter Request List (Option
55). The client retrieves a port set using the value contained in
OPTION_V4_PORTPARAMS.
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The client MAY use a non-zero value for the PSID-len field within
OPTION_PORTPARMAS in the DHCPDISCOVER message. This is used to
request a specific size of port-set (i.e., the number of source ports
that it will be allocated).
The client MUST NOT probe a newly received IPv4 address (e.g., with
ARP) to see if it is in use by another host.
When the client renews or releases the DHCP lease, it MUST put the
values of offset, PSID length and PSID into the OPTION_V4_PORTPARAMS,
and send to the server within corresponding DHCPv4 messages that are
conveyed through DHCPv4-query message.
6.1. Restrictions to Client Usage of a Shared IPv4 Address
As a single IPv4 address is being shared between a number of
different clients, the allocated shared address is only suitable for
certain uses. The client MUST implement a function to ensure that
only the allocated layer 4 ports of the shared IPv4 address are used
for sourcing new connections, or accepting inbound connections.
The client MUST apply the following rules for any traffic to or from
the shared IPv4 address:
o Only port-aware protocols or ICMP implementing [RFC5508] MUST be
used.
o All connections originating from the shared IPv4 address MUST use
a source port taken from the allocated restricted port set.
o The client MUST NOT accept inbound connections on ports outside of
the allocated restricted port set.
In order to prevent addressing conflicts which could arise from the
allocation of the same IPv4 address, the client MUST NOT configure
the received restricted IPv4 address on-link.
The mechanism by which a client implements the above rules is outside
of the scope of this document.
In the event that the DHCPv4 over DHCPv6 configuration mechanism
fails for any reason, the client MUST NOT configure an IPv4 link-
local address [RFC3927](taken from the 169.254.0.0/16 range).
7. DHCPv4 Port Parameters Option
The Port Parameters Option for DHCPv4 is specified to convey the
restricted set of layer 4 source ports that are necessary to
dynamically allocate a shared address. The option uses the same
fields as the Port Parameters Option described in Section 4.5 of
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[I-D.ietf-softwire-map-dhcp], implemented as a DHCPv4 option. This
is to maintain compatibility with existing port set implementations.
The format of OPTION_V4_PORTPARAMS is shown in Figure 1.
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| option-code | Length |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| offset | PSID-Len |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
| PSID |
+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+
Figure 1: DHCPv4 Port Parameters Option
o option-code: OPTION_V4_PORTPARAMS (TBA)
o option-length: 4
o offset: (PSID offset) 8 bits long field that specifies the numeric
value for the excluded port range/offset bits (A-bits), as per
section 5.1 of [I-D.ietf-softwire-map]. Allowed values are
between 0 and 15, with the default value being 6 for MAP based
implementations. This parameter is unused by a Lightweight 4over6
client and should be set to 0.
o PSID-Len: Bit length value of the number of significant bits in
the PSID field (also known as 'k'). When set to 0, the PSID field
is to be ignored. After the first 'a' bits, there are k bits in
the port number representing valid of PSID. Subsequently, the
address sharing ratio would be 2^k.
o PSID: Explicit 16-bit (unsigned word) PSID value. The PSID value
algorithmically identifies a set of ports assigned to a CE. The
first k-bits on the left of this 2-octets field is the PSID value.
The remaining (16-k) bits on the right are padding zeros.
[I-D.ietf-softwire-map] Section 5.1 provides a full description of
how the PSID is interpreted by the client.
In order to exclude the system ports ([RFC6335]) or ports saved by
ISPs, the former port-sets that contain well-known ports SHOULD NOT
be assigned.
When receiving the Port Parameters option with an explicit PSID, the
client MUST use this explicit PSID in configuring its DHCPv4 over
DHCPv6 interface.
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8. Security Considerations
The security considerations in [RFC2131] and
[I-D.ietf-dhc-dhcpv4-over-dhcpv6] are to be considered. Additional
considerations are elaborated in the following sub-sections.
8.1. Denial-of-Service
The solution is vulnerable to DoS attacks when used on a shared
medium or when access network authentication is not a prerequisite to
IP address assignment. The solution SHOULD only be used on point-to-
point links, tunnels, and/or in environments where authentication at
the link layer is performed before IP address assignment. It is not
suitable for network access over shared mediums.
8.2. Port Randomization
Preserving port randomization [RFC6056] may be more or less difficult
depending on the address sharing ratio (i.e., the size of the port
space assigned to a CPE). The host can only randomize the ports
inside a fixed port range [RFC6269].
More discussion to improve the robustness of TCP against Blind In-
Window Attacks can be found at [RFC5961]. Other means than the
(IPv4) source port randomization to provide protection against
attacks should be used (e.g., use [I-D.vixie-dnsext-dns0x20] to
protect against DNS attacks, [RFC5961] to improve the robustness of
TCP against Blind In-Window Attacks, use IPv6).
A proposal to preserve the entropy when selecting port is discussed
in [I-D.bajko-pripaddrassign].
9. IANA Considerations
IANA is requested to assign the following new DHCPv4 Option Code in
the registry maintained in http://www.iana.org/assignments/bootp-
dhcp-parameters/:
Option Name Value Data Meaning
length
-------------------- ----- ------ -----------------------------------
OPTION_V4_PORTPARAMS TBA 4 This option is used to configure a
set of ports bound to a shared IPv4
address.
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10. Acknowledgements
This document is merged from [I-D.sun-dhc-port-set-option] and
[I-D.farrer-dhc-shared-address-lease].
The authors would like to thank Peng Wu, Gabor Bajko, Teemu
Savolainen, Ted Lemon, Tina Tsou, Pierre Levis, Cong Liu for Marcin
Siodelski, for their contribution to this work.
11. References
11.1. Normative References
[I-D.ietf-dhc-dhcpv4-over-dhcpv6]
Sun, Q., Cui, Y., Siodelski, M., Krishnan, S., and I.
Farrer, "DHCPv4 over DHCPv6 Transport", draft-ietf-dhc-
dhcpv4-over-dhcpv6-06 (work in progress), February 2014.
[I-D.ietf-softwire-map]
Troan, O., Dec, W., Li, X., Bao, C., Matsushima, S.,
Murakami, T., and T. Taylor, "Mapping of Address and Port
with Encapsulation (MAP)", draft-ietf-softwire-map-10
(work in progress), January 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC
2131, March 1997.
[RFC2132] Alexander, S. and R. Droms, "DHCP Options and BOOTP Vendor
Extensions", RFC 2132, March 1997.
[RFC4361] Lemon, T. and B. Sommerfeld, "Node-specific Client
Identifiers for Dynamic Host Configuration Protocol
Version Four (DHCPv4)", RFC 4361, February 2006.
[RFC5961] Ramaiah, A., Stewart, R., and M. Dalal, "Improving TCP's
Robustness to Blind In-Window Attacks", RFC 5961, August
2010.
[RFC6056] Larsen, M. and F. Gont, "Recommendations for Transport-
Protocol Port Randomization", BCP 156, RFC 6056, January
2011.
[RFC6269] Ford, M., Boucadair, M., Durand, A., Levis, P., and P.
Roberts, "Issues with IP Address Sharing", RFC 6269, June
2011.
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11.2. Informative References
[I-D.bajko-pripaddrassign]
Bajko, G., Savolainen, T., Boucadair, M., and P. Levis,
"Port Restricted IP Address Assignment", draft-bajko-
pripaddrassign-04 (work in progress), April 2012.
[I-D.farrer-dhc-shared-address-lease]
Farrer, I., "Dynamic Allocation of Shared IPv4 Addresses
using DHCPv4 over DHCPv6", draft-farrer-dhc-shared-
address-lease-00 (work in progress), June 2013.
[I-D.ietf-dhc-dhcpv4-over-ipv6]
Cui, Y., Wu, P., Wu, J., Lemon, T., and Q. Sun, "DHCPv4
over IPv6 Transport", draft-ietf-dhc-dhcpv4-over-ipv6-08
(work in progress), October 2013.
[I-D.ietf-softwire-lw4over6]
Cui, Y., Qiong, Q., Boucadair, M., Tsou, T., Lee, Y., and
I. Farrer, "Lightweight 4over6: An Extension to the DS-
Lite Architecture", draft-ietf-softwire-lw4over6-08 (work
in progress), March 2014.
[I-D.ietf-softwire-map-dhcp]
Mrugalski, T., Troan, O., Farrer, I., Perreault, S., Dec,
W., Bao, C., leaf.yeh.sdo@gmail.com, l., and X. Deng,
"DHCPv6 Options for configuration of Softwire Address and
Port Mapped Clients", draft-ietf-softwire-map-dhcp-07
(work in progress), March 2014.
[I-D.sun-dhc-port-set-option]
Qiong, Q., Lee, Y., Sun, Q., Bajko, G., and M. Boucadair,
"Dynamic Host Configuration Protocol (DHCP) Option for
Port Set Assignment", draft-sun-dhc-port-set-option-02
(work in progress), October 2013.
[I-D.vixie-dnsext-dns0x20]
Vixie, P. and D. Dagon, "Use of Bit 0x20 in DNS Labels to
Improve Transaction Identity", draft-vixie-dnsext-
dns0x20-00 (work in progress), March 2008.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
[RFC3927] Cheshire, S., Aboba, B., and E. Guttman, "Dynamic
Configuration of IPv4 Link-Local Addresses", RFC 3927, May
2005.
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[RFC5508] Srisuresh, P., Ford, B., Sivakumar, S., and S. Guha, "NAT
Behavioral Requirements for ICMP", BCP 148, RFC 5508,
April 2009.
[RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S.
Cheshire, "Internet Assigned Numbers Authority (IANA)
Procedures for the Management of the Service Name and
Transport Protocol Port Number Registry", BCP 165, RFC
6335, August 2011.
[RFC6346] Bush, R., "The Address plus Port (A+P) Approach to the
IPv4 Address Shortage", RFC 6346, August 2011.
[RFC6888] Perreault, S., Yamagata, I., Miyakawa, S., Nakagawa, A.,
and H. Ashida, "Common Requirements for Carrier-Grade NATs
(CGNs)", BCP 127, RFC 6888, April 2013.
Authors' Addresses
Yong Cui
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6260-3059
Email: yong@csnet1.cs.tsinghua.edu.cn
Qi Sun
Tsinghua University
Beijing 100084
P.R.China
Phone: +86-10-6278-5822
Email: sunqi@csnet1.cs.tsinghua.edu.cn
Ian Farrer
Deutsche Telekom AG
CTO-ATI, Landgrabenweg 151
Bonn, NRW 53227
Germany
Email: ian.farrer@telekom.de
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Yiu L. Lee
Comcast
One Comcast Center
Philadelphia PA 19103
USA
Email: yiu_lee@cable.comcast.com
Qiong Sun
China Telecom
Room 708, No.118, Xizhimennei Street
Beijing 100035
P.R.China
Phone: +86-10-58552936
Email: sunqiong@ctbri.com.cn
Mohamed Boucadair
France Telecom
2330 Central Expressway
Rennes 35000
France
Email: mohamed.boucadair@orange.com
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