Network Working Group C. Bao
Internet-Draft X. Li
Intended status: Informational Y. Zhai
Expires: January 11, 2012 W. Shang
CERNET Center/Tsinghua
University
July 10, 2011
dIVI: Dual-Stateless IPv4/IPv6 Translation
draft-xli-behave-divi-03
Abstract
This document presents the concepts and the implementations of
address-sharing dual-stateless IPv4/IPv6 translation (dIVI).
The dIVI is an extension of 1:1 stateless IPv4/IPv6 translation with
features of IPv4 address sharing and dual translation. The major
benefits of those extensions are using public IPv4 addresses more
effectively and removing the requirements of DNS64 and ALG, without
loosing the stateless, end-to-end address transparency and
bidirectional-initiated communications.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on January 11, 2012.
Copyright Notice
Copyright (c) 2011 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Applicability . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminologies . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Port-set Algorithm . . . . . . . . . . . . . . . . . . . . . . 4
5. Suffix Coding . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Extended Address Format . . . . . . . . . . . . . . . . . 7
5.2. Suffix Table . . . . . . . . . . . . . . . . . . . . . . . 8
6. Dual Stateless Translation . . . . . . . . . . . . . . . . . . 8
6.1. Header Translation and MTU Handling . . . . . . . . . . . 9
6.2. Port Mapping Algorithm in CPE . . . . . . . . . . . . . . 9
6.3. Relations to Tunneling . . . . . . . . . . . . . . . . . . 9
7. Implementation Considerations . . . . . . . . . . . . . . . . 10
7.1. Host implementation . . . . . . . . . . . . . . . . . . . 10
7.2. Port Mapping in the Core Translator . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 11
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . . 12
Appendix A. Testing environment and workflow examples . . . . . . 12
A.1. The address-sharing host on an IPv6 network initiates
communication . . . . . . . . . . . . . . . . . . . . . . 13
A.2. A host in the IPv4 Internet initiates communication . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
The experiences for the IPv6 deployment in the past 10 years strongly
indicate that for a successful transition, the communication between
IPv4 and IPv6 address families should be supported.
Recently, the stateless and stateful IPv4/IPv6 translation methods
are developed and became the IETF standards. The original stateless
IPv4/IPv6 translation (stateless 1:1 IVI) is scalable, maintains the
end-to-end address transparency and support both IPv6 initiated and
IPv4 initiated communications [RFC6052], [RFC6144], [RFC6145],
[RFC6147], [RFC6219]. But it can not use the IPv4 addresses
effectively. The stateful IPv4/IPv6 translation can share the IPv4
addresses among IPv6 hosts, but it only supports IPv6 initiated
communication [RFC6052], [RFC6144], [RFC6145], [RFC6146], [RFC6147].
In addition, both stateless and stateful IPv4/IPv6 translation
technologies require the application layer gateway (ALG) for the
applications which embed IP address literals.
In this document, we present concepts and the implementations of the
dual-stateless IPv4/IPv6 translation (dIVI). The dIVI can solve the
IPv4 address sharing and the ALG problems mentioned above, though
still keeps the stateless, end-to-end address transparency and
supporting of both IPv6 initiated and IPv4 initiated communications.
The dIVI is in the family of stateless IPv4/IPv6 translation, along
with IVI and dIVI. These techniques are used for the following
scenarios defined in [RFC6144].
o Scenario 1: An IPv6 network to the IPv4 Internet.
o Scenario 2: The IPv4 Internet to an IPv6 network.
o Scenario 5: An IPv6 network to an IPv4 network.
o Scenario 6: An IPv4 network to an IPv6 network.
2. Applicability
The address sharing dual stateless IPv4/IPv6 translation (dIVI) is
shown in the following figure.
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----- ------
.-|CPE.0|---|Host.0|
/ ----- ------
------ ----- |
/ The \ ------ / An \ | ----- ------
| IPv4 |--| 1:N |---| IPv6 |------|CPE.1|---|Host.1|
\Internet/ | XLAT | \Network/ | ----- ------
------ ------ ----- |
|\ ----- ------
| -|CPE.2|---|Host.2|
| ----- ------
| ......
\ ----- ------
-|CPE.K|---|Host.K|
----- ------
......
Figure 1: dIVI
Where the 1:N XLAT (first translator) is the IPv4/IPv6 translator
perform stateless 1:N translation between the IPv4 Internet and an
IPv6 network; The CPE.0 to CPE.K (second translators) are 1:1 IPv6/
IPv4 translators/IPv6 routers which also perform port mapping
function for Host.x when it is communicating with the IPv4 Internet
with IPv4 address sharing; the Host.1 to Host.N are the dual-stack
hosts.
The IPv6 network routes the IPv6 more specific routes of the IPv4-
translatable addresses (longer than /64) defined in Section 5 of this
document to corresponding CPEs. In the case of prefix delegation
(shorter than /64), the dual stateless IPv4/IPv6 translation with
prefix delegation (dIVI-pd) defined in [I-D.xli-behave-divi-pd] can
be used.
3. Terminologies
This document uses the terminologies defined in [RFC6144].
The key words MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
document, are to be interpreted as described in [RFC2119].
4. Port-set Algorithm
The address-sharing scheme is shown in the following figure.
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---------------------------------
-----|IPv4-translatable.0#port-range.0 |
/ ---------------------------------
/ ---------------------------------
|--------|IPv4-translatable.1#port-range.1 |
| ---------------------------------
-------------------- | ---------------------------------
| IPv4-addr#any ports|-----------|IPv4-translatable.2#port-range.2 |
-------------------- | ---------------------------------
| ---------------------------------
|--------|IPv4-translatable.3#port-range.3 |
| ---------------------------------
\ ...
\ ---------------------------------
-----|IPv4-translatable.K#port-range.K |
---------------------------------
...
Figure 2: Address Sharing Scheme
In the above figure, the IPv4-translatable.0, IPv4-translatable.1,
IPv4-translatable.2, ..., IPv4-translatable.K are sharing the same
IPv4 address IPv4-addr, but port number range for different IPv4-
translatable addresses (i.e. port-range.0, port-range.1, port-
range.2, port-range.K) are not overlapped. When an IPv6 node using
IPv4-translatable addresses communicates with the IPv4 Internet via a
translator, it looks like a single host using IPv4 address (IPv4-
addr) communicating with the IPv4 Internet.
There exist many port-range coding schemes and each one may have its
advantages and disadvantages, as well as has its best application
scenario. In this document, we will introduce a simple one, which we
believe is suitable for the IPv4/IPv6 stateless translation. This
encoding scheme uses the modulus operator to define the port number
range for each host to use.
o For given multiplexing ratio N, the port-set numbers of a IPv4-
translatable address with port-set-id K is composed of P=j*N + K +
1024, for all the values of j=0, 1, ..., (65536-N)/N.
o For a destination port number (P), the port-set-id of a given
IPv4-tanslatable address with port-set-id K is determined by the
modulo operation: K=((P-1024)%N) (% is the Modulus Operator).
For example, If N=128, then IPv6 node K=5 is only allowed to use port
numbers 5, 133, 261, 389, 517, 645, 773, 901, ... 65,413 as the
source port, while the packets with these port numbers as the
destination port number will be send to IPv6 node K=5.
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The modulus operator has several features:
1. The port ranges are not overlapped for different IPv6 nodes.
2. The individual ports for each IPv6 node are not continues and the
whole 65536 port range is equally shared by IPv6 nodes.
3. The port number range can be uniquely determined by given sharing
ratio (N) and the IPv6 node index (K).
Based on the modulus operator, We need to encode N and K in the
suffix as discussed in [RFC6052].
5. Suffix Coding
In Section 2.2 of [RFC6052] IPv4-embedded IPv6 address format is
defined which composed of a variable length prefix, the embedded IPv4
address, and a variable length suffix, as presented in the following
diagram, in which PL designates the prefix length:
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|PL| 0-------------32--40--48--56--64--72--80--88--96--104-112-120-|
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|32| prefix |v4(32) | u | suffix |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|40| prefix |v4(24) | u |(8)| suffix |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|48| prefix |v4(16) | u | (16) | suffix |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|56| prefix |(8)| u | v4(24) | suffix |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|64| prefix | u | v4(32) | suffix |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|96| prefix | v4(32) |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 3: Address Format
In Section 3.5 of [RFC6052], it states:
"There have been proposals to complement stateless translation
with a port-range feature. Instead of mapping an IPv4 address to
exactly one IPv6 prefix, the options would allow several IPv6
nodes to share an IPv4 address, with each node managing a
different range of ports. If a port range extension is needed, it
could be defined later, using bits currently reserved as null in
the suffix."
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This document defines such a suffix encoding scheme with the
corresponding port-range algorithm.
5.1. Extended Address Format
It is clear that only Prefix lengths (PL) with 32, 40, 48, 56 and 64
have suffix portions, with maximum suffix lengths of 56, 48, 40, 32,
24, respectively. In order to use different prefix length and unify
the port range encoding method, the suffix should be 24 bits or less.
Since the transport port number is a 16 bit integer, the sharing
ratio (N) and the port-set index (K) can both have the value from 0
to 65535, which requires 32 bits. In order to fit into 24 bit suffix
range, we need to do compression.
First, we can use number of bits to represent the sharing ratio when
the sharing ratio is bit-wise, hence 4 bits is enough for N.
Secondly, if sharing ratio N is very high, each IPv6 node can only
use a small number of concurrent sessions. For example, if N=4096,
each IPv6 node will have 16 concurrent sessions, which may be too
small for most of the applications. That may limit the use of some
applications, therefore, we set the maximum sharing ratio N=4096,
then 12 bits are enough for the IPv6 node index. In this case, we
can design suffix which consists of 16 bits for encoding the port
range as in the following figures. Note that for different PL, zero
padding is needed.
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|PL| 0-------------32--40--48--56--64--72--80--88--96--104-112-120-|
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|32| prefix |v4(32) | u | suffix| zero |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|40| prefix |v4(24) | u |(8)| suffix| zero |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|48| prefix |v4(16) | u | (16) | suffix| zero |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|56| prefix |(8)| u | v4(24) | suffix| zero |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|64| prefix | u | v4(32) | suffix|zer|
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 4: Extended Address Format
The port range is therefore embedded in the extended IPv4-
translatable IPv6 addresses and bound to the IPv6 node index (K), the
packets containing extended IPv4-translatable IPv6 addresses as the
destination can be routed to different IPv6 nodes.
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5.2. Suffix Table
The suffix table is shown in the following figures, where the most
significant 4 bits define the multiplexing ratio and the least
significant 12 bits define the port-set index.
ratio | suffix range | # of Ports
--------------------------------------
1 0000 - 0000 65,536
2 1000 - 1001 32,768
4 2000 - 2003 16,384
8 3000 - 3007 8,192
16 4000 - 400f 4,096
32 5000 - 501f 2,048
64 6000 - 603f 1,024
128 7000 - 707f 512
256 8000 - 80ff 256
512 9000 - 91ff 128
1,024 a000 - a3ff 64
2,048 b000 - b7ff 32
4,096 c000 - cfff 16
--------------------------------------
Figure 5: Suffix for Port Range Encoding
6. Dual Stateless Translation
In general dual stateful IPv4/IPv6 translations (IPv4-IPv6-IPv4) are
considered harmful, since the two translators cannot synchronize the
parameter to translate the IPv4 address to its original format.
However, the dual stateless IPv4/IPv6 translation (IPv4-IPv6-IPv4)
can translate the IPv4 address to its original format based on
algorithm. There are several reasons for using dual stateless IPv4/
IPv6 translation.
o The second translator (CPE) performs the port-set mapping
algorithm defined in Section 4, therefore, there is no need to
modify the host with IPv4 address sharing.
o ALG cannot be developed for some applications, or has not been
developed during the early transition stage.
o DNS64 is not allowed (due to DNSSec, etc.).
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6.1. Header Translation and MTU Handling
The general header and ICMP translation specifications are defined in
[RFC6145].
Special MTU and fragmentation actions must be taken in the case of
dual translation.
6.2. Port Mapping Algorithm in CPE
The port mapping algorithm is straightforward. The port mapping
device maintains a database of allowed port numbers defined by the
extended IPv4-translatable address format. If the packets from the
host contains the source port number which do not match the port
number range defined by the extended IPv4-translatable address
format, the CPE will map the source port number to an allowed one and
keep the record in the database for mapping back the returning
packets and all the packets in the same session.
The port number database can be refreshed via the corresponding
transport layer flags for TCP or via timeout for UDP sessions.
6.3. Relations to Tunneling
When dual stateless IPv4/IPv6 translation is deployed, its behavior
is similar to tunneling. Tunneling do not require DNS64 and ALG.,
because the communication occurs in same address family. Dual
translation don't need DNS64 and ALG as well, even in each translator
the communication occurs between different address families.
However, there are following differences:
o Scalability. Dual stateless translation is based on routing,
there is nothing needed to maintain in the translator, operator's
management loads are minimum compared with tunneling scheme, which
has to maintain tunnel states.
o Low OPEX. Dual stateless translation can do traffic engineering
and flow analysis without decapsulation which is a must in tunnel
case.
o Header Compression. The dual stateless IPv4/IPv6 translation does
not need to do encapsulation and at least 20 octets header
overhead are reduced.
o No performance bottlenecks. The dual stateless translation
handles the fragmented packets by hosts, while the tunneling
handles the fragmented packets in the tunnel end points.
Therefore, there is no performance bottlenecks.
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o Transparent transition to IPv6. The dual stateless translation
can be treated as a special case of single stateless translation,
the first XLAT performances exactly the same function, no matter
there is a XLAT.x or not. Hence it is a unified approach, rather
than special setup for the coexistence and transition. This is to
say that the ISP can deploy IPv6-only network with XLAT, so the
IPv6-only hosts can communicate with both the IPv6 Internet and
the IPv4 Internet. However, if for some reason a specific ALG
cannot be supported, and for users, who need that specific
application, can deploy XLAT.x. When the application is updated,
the XLAT.x can be removed. There is nothing to change to XLAT.
with more and more contents and users move to IPv6, the working
load of XLAT will be less and less, and eventually can be removed.
The whole process is transparent, smooth and incremental.
7. Implementation Considerations
7.1. Host implementation
For the wireless mobile Internet environment, it is not difficult to
modify the operating system of the mobile device, therefore it
possible to integrate the port mapping algorithm and the second IPv4/
IPv6 translation function in the mobile device, which is an IPv6-only
host to the network and has a dual-stack socket API for the
applications running on this host.
7.2. Port Mapping in the Core Translator
The port mapping can be performed in the core translator, in this
case, in this case, there is no need to have the second translator
(CPE.x) and no need to modify the IPv6 host for the port restriction
requirements.
8. Security Considerations
There are no security considerations in this document.
9. IANA Considerations
This memo adds no new IANA considerations.
Note to RFC Editor: This section will have served its purpose if it
correctly tells IANA that no new assignments or registries are
required, or if those assignments or registries are created during
the RFC publication process. From the author's perspective, it may
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therefore be removed upon publication as an RFC at the RFC Editor's
discretion.
10. Acknowledgments
The authors would like to acknowledge the following contributors in
the different phases of the address-sharing IVI and dIVI development:
Maoke Chen, Hong Zhang, Weifeng Jiang, Yuncehng Zhu and Guoliang Han.
The authors would like to acknowledge the following contributors who
provided helpful inputs: Dan Wing, Fred Baker, Dave Thaler, Randy
Bush, Kevin Yin, Wojciech Dec and Rajiv Asati.
11. References
11.1. Normative References
[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.
[RFC6144] Baker, F., Li, X., Bao, C., and K. Yin, "Framework for
IPv4/IPv6 Translation", RFC 6144, April 2011.
[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.
[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.
[RFC6219] Li, X., Bao, C., Chen, M., Zhang, H., and J. Wu, "The
China Education and Research Network (CERNET) IVI
Translation Design and Deployment for the IPv4/IPv6
Coexistence and Transition", RFC 6219, May 2011.
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11.2. Informative References
[I-D.xli-behave-divi-pd]
Li, X., Bao, C., Dec, W., and R. Asati, "dIVI-pd: Dual-
Stateless IPv4/IPv6 Translation with Prefix Delegation",
draft-xli-behave-divi-pd-00 (work in progress), July 2011.
Appendix A. Testing environment and workflow examples
The prefix we selected is 2001:da8:a4a6::/48. The IPv4-converted
address and the IPv4-translatable address are:
IPv4-converted address
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|PL| 0-------------32--40--48--56--64--72--80--88--96--104-112-120-|
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|48| prefix |v4(16) | u | (16) | zero |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
IPv4-translatable address
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|PL| 0-------------32--40--48--56--64--72--80--88--96--104-112-120-|
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
|48| prefix |v4(16) | u | (16) | suffix| zero |
+--+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
Figure 6: Address format
The IPv4 address sharing ratio is 16. So the port-set index is
ratio | suffix range | # of Ports
--------------------------------------
16 4000 - 400f 4,096
--------------------------------------
Figure 7: Address format
The public IPv4 address is 202.38.117.0/24.
The host in the IPv4 Internet is 202.112.35.254 and the corresponding
IPv4-converted address is 2001:da8:b4b6:ca:7023:fe00::.
The shared IPv4 address is 202.38.117.1 with sharing ratio 16, the
corresponding IPv4-translatable addresses are 2001:da8:b4b6:ca:2675:
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0140:100::, 2001:da8:b4b6:ca:2675:0140:200::, 2001:da8:b4b6:ca:2675:
0140:300::, 2001:da8:b4b6:ca:2675:0140:400::, 2001:da8:b4b6:ca:2675:
0140:500::, ..., 2001:da8:b4b6:ca:2675:0140:f00::.
A.1. The address-sharing host on an IPv6 network initiates
communication
An address-sharing Host.0 (202.38.117.1) in an IPv6 network behind
CPE initiates communication with Host 202.112.35.254:80 in the IPv4
Internet
On the Host.0
Src#p= 202.38.117.1#1881 (random port)
Dst#p= 202.112.35.254#80 (server port)
On an IPv6 network
Src#p= [2001:da8:b4b6:ca:2675:0140:100::]#8192 (CPE mapped port)
Dst#p= [2001:da8:b4b6:ca:7023:fe00::]#80 (server port)
On the IPv4 Internet
Src#p= 202.38.117.1#8192 (CPE mapped port)
Dst#p= 202.112.35.254#80 (server port)
Figure 8: Example 1
The returning packets reverse the Src and Dst, the CPE maps the "CPE
mapped port (8192)" back to the original "random port (1881)".
A.2. A host in the IPv4 Internet initiates communication
A host 202.112.35.254 in the IPv4 Internet initiates communication to
the address-sharing Host.0 (202.38.117.1#2000)
On the IPv4 Internet
Src#p= 202.112.35.254#36567 (random port)
Dst#p= 202.38.117.1#2000 (server port)
On an IPv6 network
Src#p= [2001:da8:b4b6:ca:7023:fe00::]#36567 (random port)
Dst#p= [2001:da8:b4b6:ca:2675:0140:100::]#2000 (server port)
On the Host.0
Src#p= 202.112.35.254#36567 (random port)
Dst#p= 202.38.117.1#2000 (server port)
Figure 9: Example 2
The returning packets reverse the Src and Dst.
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Internet-Draft Address-sharing dIVI July 2011
Authors' Addresses
Congxiao Bao
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 10-62785983
Email: congxiao@cernet.edu.cn
Xing Li
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 10-62785983
Email: xing@cernet.edu.cn
Yu Zhai
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 10-62785983
Email: jacky.zhai@gmail.com
Wentao Shang
CERNET Center/Tsinghua University
Room 225, Main Building, Tsinghua University
Beijing 100084
CN
Phone: +86 10-62785983
Email: wentaoshang@gmail.com
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