Network Working Group W. Cheng
Internet-Draft L. Wang
Intended status: Standards Track H. Li
Expires: December 19, 2014 China Mobile
K. Liu
Huawei Technologies
S. Davari
Broadcom Corporation
J. Dong
Huawei Technologies
July 01, 2014
Dual-Homing Protection for MPLS Transport Profile (MPLS-TP) Pseudowires
draft-cheng-pwe3-mpls-tp-dual-homing-protection-00
Abstract
In some scenarios, the MPLS Trasport Profile (MPLS-TP) Pseudowires
(PWs) are provisioned through either static configuration or
management plane, where a dynamic control plane is not available. A
fast protection mechanism for MPLS-TP PWs is needed to protect
against the failure of Attachment Circuit (AC), the failure of
Provider Edge (PE) and also the failure in the Packet Switched
Network (PSN). This document proposes a dual-homing protection
mechanism for MPLS-TP PWs, which can provide fast protection for
comprehensive failure scenarios including the failure of AC, the PE
node or the PSN network.
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/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
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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 December 19, 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 . . . . . . . . . . . . . . . . . . . . . . . . 2
2. MPLS-TP PW Dual-Homing Protection Scenarios . . . . . . . . . 3
2.1. One-side Dual-Homing Protection . . . . . . . . . . . . . 3
2.2. Two-side Dual-Homing Protection . . . . . . . . . . . . . 4
3. Overview of the Proposed Solution . . . . . . . . . . . . . . 5
4. Protocol Extensions for MPLS-TP PW Dual-Homing Protection . . 6
4.1. Information Exchange Between Dual-Homing PEs . . . . . . 6
4.2. Protection Procedures . . . . . . . . . . . . . . . . . . 9
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Security Considerations . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
[RFC6372] and [RFC6378] describe the framework and mechanism of MPLS-
TP Linear protection, which can provide protection for the MPLS LSP
or PW between the edge nodes. Such mechanism does not protect the
failure of the Attachement Circuit (AC) or the edge node. [RFC6718]
[RFC6870] describe the framework and mechanism for PW redundancy to
provide protection for AC or PE node failure. The PW redundancy
mechanism is based on the signaling of Label Distribution Protocol
(LDP), which is applicable to MPLS PWs or MPLS-TP PWs with a dynamic
control plane. [I-D.ietf-pwe3-endpoint-fast-protection] describes a
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fast local repair mechanism for PW egress endpoint failures, which is
based on PW redundancy, upstream label assignment and context
specific label switching. Such mechanism is applicable to PWs with a
dynamic control plane.
In some scenarios such as mobile backhauling, the MPLS-TP PWs are
provisioned through either static configuration or management plane,
where a dynamic control plane is not available. A fast protection
mechanism is needed for these MPLS-TP PWs to protect against the
failure of AC, the PE node or the PSN network.
In addition, if at least one side CE node is dual-homed to two PEs,
and a fault occurs in the primary AC, operators usually prefer to
perform switchover only in the AC side and keeps using the working
pseudowire if possible. The purpose is to avoid massive PW
switchover caused by AC failure in mobile backhaul networks and to
achieve efficient and balanced link bandwidth utilization in the PSN
network.
This document proposes a dual-homing protection mechanism for static
MPLS-TP PWs, which can provide fast protection for comprehensive
failure scenarios including failure of AC, the PE node or the PSN
network, and meet the requirement of avoiding PW switchover when
possible. The mechanism defined in this document is complementary to
the existing protection mechanisms.
The proposed mechanism has been deployed in several mobile backhaul
networks which use static MPLS-TP PWs for the backhauling of mobile
traffic from the RF sites to the core sites.
2. MPLS-TP PW Dual-Homing Protection Scenarios
The following sections describe the typical topology and application
scenarios of MPLS-TP PW dual-homing protection. The scenarios can be
classified into two categories: one-side dual-homing and two-side
dual-homing.
2.1. One-side Dual-Homing Protection
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|<--------------- Emulated Service --------------->|
| |
| |<------- Pseudo Wire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC +----+ +----+ V
+-----+ | | PE1| | | +-----+
| |----------|........PW1.(working).......| | |
| | | | | | | |
| | +----+ | | AC | |
| | || | | | | |
| CE1 | DNI PW |PE3 |----------| CE2 |
| | || | | | |
| | +----+ | | | |
| | | | | | | |
| |----------|......PW2.(protection)......| | |
+-----+ | | PE2| | | +-----+
AC +----+ +----+
Figure 1. One-side PW dual-homing protection
Figure 1 illustrates the network scenario of one-side CE dual-homing
protection. CE1 is dual-homed to PE1 and PE2, while CE2 is single-
homed to PE3. This topology protects the node failures of PE1 and
PE2 and the AC link failures between CE1 and PE1, PE2. This scheme
can be used in mobile backhauling application scenarios. For
example, NodeB serves as CE2 while RNC serves as CE1. PE3 works as
an access side MPLS-TP device while PE1 and PE2 works as a core side
MPLS-TP device.
2.2. Two-side Dual-Homing Protection
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|<---------------- Emulated Service -------------->|
| |
| |<-------- Pseudowire ------>| |
| | | |
| | |<-- PSN Tunnels-->| | |
| V V V V |
V AC +----+ +----+ AC V
+-----+ | |....|.......PW1........|....| | +-----+
| |----------| PE1| | PE3|----------| |
| | +----+ +----+ | |
| | || || | |
| CE1 | DNI PW DNI PW | CE2 |
| | || || | |
| | +----+ +----+ | |
| | | | | | | |
| |----------| PE2| | PE4|--------- | |
+-----+ | |....|.......PW2........|....| | +-----+
AC +----+ +----+ AC
Figure 2. Two-side PW dual-homing protection
Figure 2 illustrates the network scenario of two-side CE dual-homing.
CE1 is dual-homed to PE1 and PE2, and CE2 is dual-homed to PE3 and
PE4. This topology can protect the node failure of the dual-homing
PEs on both sides, and also protects the AC link failures between the
CEs and their dual-homing PEs. Meanwhile, dual-homing PW protection
can protect the failure occured in the PSN network. This scenario is
mainly used for services providing for important business customers.
In this case, CE1 and CE2 can be regarded as service access points.
3. Overview of the Proposed Solution
The linear protection mechanisms for MPLS-TP network are defined in
[RFC6378] [I-D.ietf-mpls-tp-psc-itu]. When such mechanisms are
applied to PW linear protection, both the working PW and the
protection PW need to terminate on the same PE nodes. This section
extends these mechanisms to provide dual-homing protection for MPLS-
TP PWs.
With MPLS-TP PW dual-homing protection mechanism, the linear
protection mechanisms on the Single-homing PE (e.g. PE3 in figure 3)
are not changed, while on the dual-homing side the working PW and
protection PW are terminated on two dual-homing PEs (e.g. PE1 and
PE2 in figure 3) respectively, to provide protection for the dual-
homing PEs and the connected ACs. A dedicated Dual-Node
Interconnection (DNI) PW is established between the two dual-homing
PE nodes, which is used to bridge the PW traffic when failure happens
in the working PW or the primary AC. In order to make the linear
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protection mechanism work under the dual-homing PEs scenario, some
coordination between the dual-homing PE nodes is necessary. The
protection switching mechanism is detailed in following sections.
+----------------+
/ | +--------+
AC1 /| PE1 | Working PW | |
/ | ++-----------------------| |
/ | || | Service PW1 | |
+---/+ +--------||------+ | | +----+
| | DNI PW | PE3 | | |
| CE1| || | |---| CE2|
+---\+ +--------||------+ | | +----+
\ | || | Protection PW | |
\ | ++-----------------------| |
AC2 \| | Service PW2 | |
\ PE2 | +--------+
+----------------+
Figure 3. Dual-homing Proctection with DNI PW
The following failure scenarios can be protected by MPLS-TP PW dual-
homing protection:
o Failure of the working PW (PW1)
o Failure of the working AC (AC1)
o Failure of the working PE (PE1)
4. Protocol Extensions for MPLS-TP PW Dual-Homing Protection
In order to achieve the MPLS-TP PW dual-homing protection,
coordination is needed between the dual-homing PE nodes to
communicate the service PW status and protection coordination
requests. The forwarding state of dual-homing PEs is also specified.
4.1. Information Exchange Between Dual-Homing PEs
A new Channel Type is defined for the coordination between the dual-
homing PEs of MPLS-TP PWs. Such channel type can be used for the
exchange of different kinds of information. This document uses this
channel type for the PW status exchange and protection coordination
between the dual-homing PEs. Other use cases of this channel type
are for further study and are out of the scope of this document.
The MPLS-TP Dual-Homing Coordination (DHC) message is sent on the DNI
PW between the dual-homing PEs.
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The format of an MPLS-TP DHC message is shown below:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Flags | DHC Code Point |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Dual-Homing Group ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TLVs ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4. MPLS-TP Dual-Homing Coordination Message
The Dual-Homing Group ID is a 4-octet unsigned integer to identify
the dual-homing PEs in the same dual-homing group.
2 TLVs are defined in MPLS-TP Dual-Homing Coordination message for
MPLS-TP PW dual-homing protection:
Type Description Length
1 PW Status 20 Bytes
2 Dual-Node Switching 16 Bytes
The PW Status TLV is used by a dual-homing PE to report its Service
PW status to the other dual-homing PE in the same dual-homing group.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=1 (PW Status) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Node_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Node_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DNI PW-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service PW Request |D|F|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5. PW Status TLV
- The Destination Node_ID is the 32-bit Node_ID of the receiving PE.
- The Source Node_ID is the 32-bit Node_ID of the sending PE.
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- The DNI PW-ID field contains PW-ID of the DNI PW.
- The P (Protection) bit indicates whether the message is sent by the
working PE (P=0) or by the protection PE (P=1).
- The Service PW Request field indicates the protection request
generated on the Service PW between the sending PE and the remote PE.
Two bits are defined in the Service PW Request field:
o F bit: Indicates Signal Fail (SF) request is generated on the
service PW. It can be either a local request or a remote request
received from the remote PE.
o D bit: Indicates Signal Degrade (SD) request is generated on the
service PW. It can be either a local request or a remote request
received from the remote PE.
o Other bits are reserved and MUST be set to 0 and SHOULD be ignored
upon receipt.
The Dual-Node Switching TLV is used by the protection dual-homing PE
to send protection state coordination to the working dual-homing PE.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=2 (Dual-Node Switching) | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Node_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Node_ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DNI PW-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |S|P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6. Dual-node Switching TLV
- The Destination Node_ID is the 32-bit Node_ID of the receiving PE.
- The Source Node_ID is the 32-bit Node_ID of the sending PE.
- The DNI PW-ID field contains PW-ID of the DNI PW.
- The P (Protection) bit indicates whether the message is sent by the
working PE (P=0) or by the protection PE (P=1). With the mechanism
described in this document, only the protection PE could send out the
DHC message with the Dual-node Switching TLV.
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- The S (PW Switching) bit indicates which service PW is used for
transporting user traffic. It is set to 0 when traffic is
transported on the working PW, and is set to 1 if traffic will be
transported on the protection PW. The value of the S bit is
determined by the protection coordination mechanism between the dual-
homing protection PE and the remote PE.
4.2. Protection Procedures
MPLS-TP PW dual-homing protection mechanism can work with the
existing AC side redundancy mechanisms, e.g. MC-LAG. On PSN network
side, PSN tunnel protection mechanism is not required, as the dual-
homing PW protection can also protect the failure happened in the PSN
network.
For the single-homing PE, it just treats the working PW and
protection PW as if they terminate on the same remote PE node, thus
normal protection coordination mechanisms still apply to the single-
homing PE.
The protection behavior of the dual-homing PEs is determined by the
components shown in the figure below:
+------------+ +------------------+
| PE3 | | PE1 |
| +---+| service PW1 |+---+ +---+|
| |PW1|---------------|PW1| |AC1|\
| +---+| working PW |+---+ +---+|\
| | | +------+ | \
| | | |DNI PW| | \ AC1
| | | +------+ | \(active)
| | +--------||--------+ \
+-----+ AC3 | | || +--\---+
| CE2 |------| | || DNI PW | CE1 |
+-----| | | || +--/---+
| | +--------||--------+ /
| | | +------+ | /
| | | |DNI PW| | / AC2
| | | +------+ | /(standby)
| | | |/
| +---+| service PW2 |+---+ +---+/
| |PW2|---------------|PW2| |AC2||
| +---+|protection PW|+---+ PE2 +---+|
+------------+ +------------------+
Figure 7. Components of PW Dual-Homing protection
In figure 7, for a dual-homing PE, Service PW is the PW which carries
service between dual-homing PE and the remote PE. The status of
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Service PW is determined by the OAM and protection switching
coordination mechanisms between the dual-homing PEs and the remote
PE.
DNI PW is the PW between the two dual-homing PE nodes. It is used to
bridge traffic when failure occurs in PSN network or in the AC side.
The status of DNI PW is determined by OAM protocol running between
the dual-homing PEs.
AC is the link which connects the dual-homing PEs to the dual-homed
CE. The AC status is determined by MC-LAG or other AC redundancy
mechanisms.
The PW status and protection coordination requests are exchanged
between the dual-homing PEs using the DHC message defined in section
4.1.
After the exchange of PW status information using the MPLS-TP DHC
Message, both dual-homing PEs obtain the status of working and
protection service PWs, the AC and the DNI PW. The forwarding
behavoir of dual-homing PE nodes are determined by the forwarding
state machine shown in the following table:
+-----------+---------+--------+---------------------+
|Service PW | AC | DNI PW | Forwarding Behavior |
+-----------+---------+--------+---------------------+
| Active | Active | Up |Service PW <-> AC |
+-----------+---------+--------+---------------------+
| Active | Standby | Up |Service PW <-> DNI PW|
+-----------+---------+--------+---------------------+
| Standby | Active | Up | DNI PW <-> AC |
+-----------+---------+--------+---------------------+
| Standby | Standby | Up | Drop all packets |
+-----------+---------+--------+---------------------+
Table 1. Dual-homing PE Forwarding State Machine
In normal state, the working PW is in active state, and the primary
AC is active state, according to Table 1, PW traffic will be
forwarded between the working service PW and the primary AC (AC1).
No traffic will go through the protection PE or the DNI PW, as both
the protection service PW and the AC connecting to the protection PE
are in standby state.
If AC1 goes down due to some fault, the AC side redundancy mechanism
would switchover to the backup AC (AC2), the state of AC2 changes to
active. There is no change in the status of working and protection
PW. According to Table 1, PE1 starts to forward traffic between the
working PW and the DNI PW, while PE2 starts to forward traffic
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between DNI PW and AC2. Note that in this case only AC switchover
takes place, in PSN network traffic keeps transporting on the working
PW and PW switchover is no needed.
If the working PW is down due to some fault in the PSN network, both
the remote PE (PE3) and the working PE (PE1) would detect the failure
using MPLS-TP OAM mechanisms, then PE3 would send a normal protection
coordination message on the protection path to inform its peer node
(PE2) to switchover to the protection PW. PE1 would also inform PE2
the working PW status (down) using the MPLS-TP DHC message. Then
according to Table 1, PE2 starts to forward traffic between the
protection PW and the DNI PW, and PE1 starts to forward traffic
between the DNI PW and AC1.
If the working PE (PE1) goes down, both the remote PE(PE3) and the
protection PE(PE2) would detect the failure using MPLS-TP OAM
mechanisms, the state of AC1 would change to down, and the state of
AC2 will change to active according to AC side redundancy mechansim.
Then PE3 would send a normal protection coordination message on the
protection path to inform its peer node (PE2) to switchover to the
protection PW. Then according to table 1, PE2 starts to forward
traffic between the protection PW and AC2.
5. IANA Considerations
IANA needs to assign one new channel type for "MPLS-TP Dual-Homing
Coordination messgae" from the "Pseudowire Associated Channel Types"
registry.
This document creates a new registry called "MPLS-TP DHC TLVs"
registry. 2 new TLVs are defined in this document:
Type Description Length
1 PW Status 20 Bytes
2 Dual-Node Switching 16 Bytes
6. Security Considerations
Procedures and protocol extensions defined in this document do not
affect the security model of MPLS-TP linear protection as defined in
[RFC6378]. Please refer to [RFC5920] for MPLS security issues and
generic methods for securing traffic privacy and integrity.
7. References
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7.1. Normative References
[I-D.ietf-mpls-tp-psc-itu]
Ryoo, J., Gray, E., Helvoort, H., D'Alessandro, A.,
Cheung, T., and E. Osborne, "MPLS Transport Profile (MPLS-
TP) Linear Protection to Match the Operational
Expectations of SDH, OTN and Ethernet Transport Network
Operators", draft-ietf-mpls-tp-psc-itu-04 (work in
progress), March 2014.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6372] Sprecher, N. and A. Farrel, "MPLS Transport Profile (MPLS-
TP) Survivability Framework", RFC 6372, September 2011.
[RFC6378] Weingarten, Y., Bryant, S., Osborne, E., Sprecher, N., and
A. Fulignoli, "MPLS Transport Profile (MPLS-TP) Linear
Protection", RFC 6378, October 2011.
7.2. Informative References
[I-D.ietf-pwe3-endpoint-fast-protection]
Shen, Y., Aggarwal, R., Henderickx, W., and Y. Jiang, "PW
Endpoint Fast Failure Protection", draft-ietf-pwe3-
endpoint-fast-protection-00 (work in progress), December
2013.
[RFC5920] Fang, L., "Security Framework for MPLS and GMPLS
Networks", RFC 5920, July 2010.
[RFC6718] Muley, P., Aissaoui, M., and M. Bocci, "Pseudowire
Redundancy", RFC 6718, August 2012.
[RFC6870] Muley, P. and M. Aissaoui, "Pseudowire Preferential
Forwarding Status Bit", RFC 6870, February 2013.
Authors' Addresses
Weiqiang Cheng
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: chengweiqiang@chinamobile.com
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Lei Wang
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: Wangleiyj@chinamobile.com
Han Li
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: Lihan@chinamobile.com
Kai Liu
Huawei Technologies
Huawei Base, Bantian, Longgang District
Shenzhen 518129
China
Email: alex.liukai@huawei.com
Shahram Davari
Broadcom Corporation
3151 Zanker Road
San Jose 95134-1933
United States
Email: davari@broadcom.com
Jie Dong
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: jie.dong@huawei.com
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