Alternate Tunnel Encapsulation for Data Frames in CAPWAP
draft-ietf-opsawg-capwap-alt-tunnel-04
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 8350.
|
|
|---|---|---|---|
| Authors | Rong Zhang , Zehn Cao , DENG Hui , Rajesh Pazhyannur , Sri Gundavelli , Li Xue | ||
| Last updated | 2015-02-25 (Latest revision 2014-11-10) | ||
| Replaces | draft-zhang-opsawg-capwap-cds | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews |
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| Additional resources | Mailing list discussion | ||
| Stream | WG state | Submitted to IESG for Publication | |
| Document shepherd | Warren "Ace" Kumari | ||
| Shepherd write-up | Show Last changed 2014-09-09 | ||
| IESG | IESG state | Became RFC 8350 (Experimental) | |
| Consensus boilerplate | Unknown | ||
| Telechat date | (None) | ||
| Responsible AD | Benoît Claise | ||
| Send notices to | warren@kumari.net, opsawg-chairs@ietf.org |
draft-ietf-opsawg-capwap-alt-tunnel-04
Network Working Group R. Zhang
Internet-Draft China Telecom
Intended status: Standards Track Z. Cao
Expires: May 14, 2015 H. Deng
China Mobile
R. Pazhyannur
S. Gundavelli
Cisco
L. Xue
Huawei
November 10, 2014
Alternate Tunnel Encapsulation for Data Frames in CAPWAP
draft-ietf-opsawg-capwap-alt-tunnel-04
Abstract
Control And Provisioning of Wireless Access Points (CAPWAP) defines a
specification to encapsulate a station's data frames between the
Wireless Transmission Point (WTP) and Access Controller (AC).
Specifically, the station's IEEE 802.11 data frames can be either
locally bridged or tunneled to the AC. When tunneled, a CAPWAP data
channel is used for tunneling. In many deployments encapsulating
data frames to an entity other than the AC (for example to an Access
Router (AR)) is desirable. Further, it may also be desirable to use
different tunnel encapsulations to carry the stations' data frames.
This document provides a specification for this and refers to it as
Alternate tunnel encapsulation. The Alternate tunnel encapsulation
allows 1) the WTP to tunnel non-management data frames to an endpoint
different from the AC and 2) the WTP to tunnel using one of many
known encapsulation types such as IP-IP, IP-GRE, CAPWAP. The WTP may
advertise support for Alternate tunnel encapsulation during the
discovery or join process and AC may select one of the supported
Alternate Tunnel encapsulation types while configuring the WTP.
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 May 14, 2015.
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
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions used in this document . . . . . . . . . . . . 5
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Alternate Tunnel Encapsulation . . . . . . . . . . . . . . . 6
2.1. Description . . . . . . . . . . . . . . . . . . . . . . . 6
3. Protocol Considerations . . . . . . . . . . . . . . . . . . . 8
3.1. Supported Alternate Tunnel Encapsulations . . . . . . . . 8
3.2. Alternate Tunnel Encapsulations Type . . . . . . . . . . 9
3.3. IEEE 802.11 WTP Alternate Tunnel Failure Indication . . 10
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
7.1. Normative References . . . . . . . . . . . . . . . . . . 12
7.2. Informative References . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
Service Providers are deploying very large Wi-Fi deployments (ranging
from hundreds of thousands of Access Points, APs (referred to as WTPs
in CAPWAP terminology) to millions of APs. These networks are
designed to carry traffic generated from mobile users. The volume in
mobile user traffic is already very large (in the order of petabytes
per day) and expected to continue growing rapidly. As a result,
operators are looking for scalable solutions that can meet the
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increasing demand. The scalability requirement can be met by
splitting the control/management plane from the data plane. This
enables the data plane to scale independent of the control/management
plane. This specification provides a way to enable such separation.
CAPWAP ([RFC5415], [RFC5416]) defines a tunnel mode that describes
how the WTP handles the data plane (user traffic). The following
types are defined:
o Local Bridging: All data frames are locally bridged.
o 802.3 Tunnel: All data frames are tunneled to the AC in 802.3
format.
o 802.11 Tunnel: All data frames are tunneled to the AC in 802.11
format.
Figure 1 describes a system with Local Bridging. The AC is in a
centralized location. The data plane is locally bridged by the WTPs
leading to a system with centralized control plane with distributed
data plane. This system has two benefits: 1) reduces the scale
requirement on data traffic handling capability of the AC and 2)
leads to more efficient/optimal routing of data traffic while
maintaining centralized control/management.
Locally Bridged
+-----+ Data Frames +----------------+
| WTP |===============| Access Router |
+-----+ +----------------+
\\
\\ CAPWAP Control Channel +----------+
++=========================| AC |
// CAPWAP Data Channel: | |
// IEEE 802.11 Mgmt traffic +----------+
//
+-----+ +----------------+
| WTP |============== | Access Router |
+=====+ +----------------+
Locally Bridged
Data Frames
Figure 1: Centralized Control with Distributed Data
The AC handles control of WTPs. In addition, the AC also handles the
IEEE 802.11 management traffic to/ from the stations. There is
CAPWAP Control and Data Channel between the WTP and the AC. Note
that even though there is no user traffic transported between the WTP
and AC, there is still a CAPWAP Data Channel. The CAPWAP Data
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channel carries the IEEE 802.11 management traffic (like IEEE 802.11
Action Frames).
Figure 2 shows a system where the tunnel mode is configured to tunnel
data frames between the WTP and the AC either using 802.3 Tunnel or
802.11 Tunnel configurations. Operators deploy this configuration
when they need to tunnel the user traffic. The tunneling requirement
may be driven by the need to apply policy at the Access Router or a
legal requirement to support lawful intercept of user traffic. This
requirement could be met in the locally bridged system (Figure 1) if
the access router implemented the required policy. However, in many
deployments the operator managing the WTP is different than the
operator managing the Access Router. When the operators are
different, the policy has to be enforced in a tunnel termination
point in the WTP operator's network.
+-----+
| WTP |
+-----+
\\
\\ CAPWAP Control Channel +----------+
++=========================| AC |
// CAPWAP Data Channel: | |
// IEEE 802.11 Mgmt traffic | |
// Data Frames +----------+
//
+-----+
| WTP |
+=====+
Figure 2: Centralized Control and Centralized Data
The key difference with the locally bridged system is that the data
frames are tunneled to the AC instead of being locally bridged.
There are two shortcomings with system in Figure 2. 1) They do not
allow the WTP to tunnel data frames to an endpoint different from the
AC and 2) They do not allow the WTP to tunnel data frames using any
encapsulation other than CAPWAP (as specified in Section 4.4.2 of
[RFC5415]).
Figure 3 shows a system where the WTP tunnels data frames to an
alternate entity different from the AC. The WTP also uses an
alternate tunnel encapsulation such as such as L2TP, L2TPv3, IP-in-
IP, IP/GRE, etc. This enables 1) independent scaling of data plane
and 2) leveraging of commonly used tunnel encapsulations such as
L2TP, GRE, etc
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Alternate Tunnel to AR (L2TPv3, IP-IP, CAPWAP, etc)
_________
+-----+ ( ) +-----------------+
| WTP |======+Internet +==============|Access Router(AR)|
+-----+ (_________} +-----------------+
\\ ________ CAPWAP Control
\\ ( ) Channel +--------+
++==Internet+========================| AC |
// ( )CAPWAP Data Channel: +--------+
// IEEE 802.11 Mgmt traffic
// ---------
+-----+ ( ) +----------------+
| WTP |====+Internet +================| Access Router |
+=====+ (_________} +----------------+
Alternate Tunnel to AR (L2TPv3, IP-IP, CAPWAP, etc)
Figure 3: Centralized Control with Alternate Tunnel for Data
The WTP may support widely used encapsulation types such as L2TP,
L2TPv3, IP-in-IP, IP/GRE, etc. The WTP advertises the different
alternate tunnel encapsulation types it can support. The AC
configures one of the advertised types. As shown in the figure there
is a CAPWAP control and data channel between the WTP and AC. The
CAPWAP data channel carries the stations' management traffic as in
the case of the locally bridged system. The main reason to maintain
a CAPWAP data channel is to maintain similarity with the locally
bridged system. The WTP maintains three tunnels: CAPWAP Control,
CAPWAP Data, and another alternate tunnel for the data frame. The
data frames are transported by an alternate tunnel between the WTP
and a tunnel termination point such as an Access Router. This
specification describes how the alternate tunnel can be established.
The specification defines message elements for the WTP to advertise
support for alternate tunnel encapsulation, the AC to configure
alternate tunnel encapsulation, and for the WTP to report failure of
the alternate tunnel.
1.1. Conventions used in this document
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 [RFC2119]
1.2. Terminology
Station (STA): A device that contains an IEEE 802.11 conformant
medium access control (MAC) and physical layer (PHY) interface to the
wireless medium (WM).
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Access Controller (AC): The network entity that provides WTP access
to the network infrastructure in the data plane, control plane,
management plane, or a combination therein.
Wireless Termination Point (WTP), The physical or network entity that
contains an RF antenna and wireless Physical Layer (PHY) to transmit
and receive station traffic for wireless access networks.
CAPWAP Control Channel: A bi-directional flow defined by the AC IP
Address, WTP IP Address, AC control port, WTP control port, and the
transport-layer protocol (UDP or UDP-Lite) over which CAPWAP Control
packets are sent and received.
CAPWAP Data Channel: A bi-directional flow defined by the AC IP
Address, WTP IP Address, AC data port, WTP data port, and the
transport-layer protocol (UDP or UDP-Lite) over which CAPWAP Data
packets are sent and received. In certain WTP modes, the CAPWAP Data
Channel only transports IEEE 802.11 management frames and not the
data plane (user traffic).
2. Alternate Tunnel Encapsulation
2.1. Description
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+-+-+-+-+-+-+ +-+-+-+-+-+-+
| WTP | | AC |
+-+-+-+-+-+-+ +-+-+-+-+-+-+
|Join Request[Supported Alternate Tunnel |
| Encapsulations ] |
|---------------------------------------->|
| |
|Join Response |
|<----------------------------------------|
| |
|IEEE 802.11 WLAN Config. Request [ |
| IEEE 802.11 Add WLAN, |
| Alternate Tunnel Encapsulation ( |
| Tunnel Type, Tunnel Info Element) |
| ] |
|<----------------------------------------|
| |
| |
+-+-+-+-+-+-+ |
| Setup | |
| Alternate | |
| Tunnel | |
+-+-+-+-+-+-+ |
| |
|IEEE 802.11 WLAN Config. Response |
|---------------------------------------->|
| |
| |
+-+-+-+-+-+-+ |
| Tunnel | |
| Failure | |
+-+-+-+-+-+-+ |
|WTP Alternate Tunnel Failure Indication |
|(report failure) |
|---------------------------------------->|
| |
+-+-+-+-+-+-+-+ |
| Tunnel | |
| Established | |
+-+-+-+-+-+-+-+ |
|WTP Alternate Tunnel Failure Indication |
|(report clearing failure) |
|---------------------------------------->|
| |
Figure 4: Setup of Alternate Tunnel
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The above example describes how the alternate tunnel encapsulation
may be established. When the WTP joins the AC, it should indicate
its alternate tunnel encapsulation capability. The AC determines
whether an alternate tunnel configuration is required. If an
appropriate alternate tunnel type is selected, then the AC provides
the alternate tunnel encapsulation message element containing the
tunnel type and a tunnel-specific information element. (The tunnel-
specific information element, for example, may contain information
like the IP address of the tunnel termination point.) The WTP sets
up the alternate tunnel using the alternate tunnel encapsulation
message element.
On detecting a tunnel failure, WTP shall forward data frames to the
AC and discard the frames. In addition, WTP may dissociate existing
clients and refuse association requests from new clients. Depending
on the implementation and deployment scenario, the AC may choose to
reconfigure the WLAN (on the WTP) to a local bridging mode or to
tunnel frames to the AC. When the WTP detects an alternate tunnel
failure, the WTP informs the AC using a message element, WTP
Alternate Tunnel Fail Indication (defined in this specification).
The message element has a status field that indicates whether the
message denotes reporting a failure or the clearing of the previously
reported failure.
For the case where AC is unreachable but the tunnel end point is
still reachable, the WTP behavior is up to the implementation. For
example, the WTP could either choose to tear down the alternate
tunnel or let the existing user's traffic continue to be tunneled.
3. Protocol Considerations
3.1. Supported Alternate Tunnel Encapsulations
This message element is sent by a WTP to communicate its capability
to support alternate tunnel encapsulations. The message element
contains the following fields:
0 1 2 3
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7 0
+=+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Num_Tunnels | Tunnel-Type 1 | Tunnel-Type [2..N]
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Supported Alternate Tunnel Encapsulations
o Type: <IANA-1> for Supported Alternate Tunnel Encapsulations
o Length: The length in bytes is 1 + Num_Tunnels
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o Num_Tunnels: This refers to number of tunnel types present in the
message element. At least one tunnel type must be present.
o Tunnel-Type: This is identified by value defined in Section 3.2
3.2. Alternate Tunnel Encapsulations Type
This message element is sent by the AC. This message element allows
the AC to select the alternate tunnel encapsulation. This message
element may be provided along with the IEEE 802.11 Add WLAN message
element. When the message element is present the following fields of
the IEEE 802.11 Add WLAN element shall be set as follows: MAC mode is
set to 0 (Local MAC) and Tunnel Mode is set to 0 (Local Bridging).
The message element contains the following fields
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tunnel-Type | Info Element Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Info Element
+-+-+-+-+-+-+-+-+-+
Figure 6: Alternate Tunnel Encapsulations Type
o Type: <IANA-2> for Alternate Tunnel Encapsulation Type
o Length: > 4
o Tunnel-Type: The tunnel type is specified by a 2 byte value. This
specification defines the values from zero (0) to five (5) as
given below. The remaining values are reserved for future use.
* 0: CAPWAP. This refers to a CAPWAP data channel described in
[RFC5415][RFC5416].
* 1: L2TP. This refers to tunnel encapsulation described in
[RFC2661].
* 2: L2TPv3. This refers to tunnel encapsulation described in
[RFC3931].
* 3: IP-in-IP. This refers to tunnel encapsulation described in
[RFC2003].
* 4: PMIPv6. This refers to the tunneling encapsulation
described in [RFC5213]
* 5: GRE-IPv4. This refers to GRE encapsulation with IPv4 as the
delivery protocol as described in [RFC2784]
* 6: GRE-IPv6. This refers to GRE encapsulation with IPv6 as the
delivery protocol as described in [RFC2784]
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o Info Element: This field contains tunnel specific configuration
parameters to enable the WTP to setup the alternate tunnel. For
example if the tunnel type is CAPWAP then this field may contain
the following (non-exhaustive) list of parameters
* Access Router IPv4 address
* Access Router IPv6 address
* Tunnel DTLS Policy
* IEEE 802.11 Tagging Policy
This specification only defines a generic container for such
message elements. We anticipate that these message elements (for
the different protocols) will be defined in separate documents,
potentially one for each tunneling protocols.
3.3. IEEE 802.11 WTP Alternate Tunnel Failure Indication
The Alternate Tunnel Encapsulation message element is sent by the WTP
to inform the AC about the status of the Alternate Tunnel. The
message element contains the following fields
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Radio ID | WLAN ID | Status | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: IEEE 802.11 WTP Alternate Tunnel Failure Indication
o Type: <IANA-3> for IEEE 802.11 WTP Alternate Tunnel Failure
Indication
o Length: == 4
o Radio ID: The Radio Identifier, whose value is between one (1) and
31, typically refers to some interface index on the WTP.
o WLAN ID: An 8-bit value specifying the WLAN Identifier. The value
MUST be between one (1) and 16.
o Status: An 8-bit boolean indicating whether the radio failure is
being reported or cleared. A value of zero is used to clear the
event, while a value of one is used to report the event.
4. IANA Considerations
This document requires the following IANA considerations.
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o <IANA-1>. This specification defines the Supported Alternate
Tunnel Encapsulations Type message element in Section 3.1. This
elements needs to be registered in the existing CAPWAP Message
Element Type registry, defined in [RFC5415]. The Type value for
this element needs to be between 1 and 1023 (see Section 15.7 in
[RFC5415]).
o <IANA-2>. This specification defines the Alternate Tunnel
Encapsulations Type message element in Section 3.2. This element
needs to be registered in the existing CAPWAP Message Element Type
registry, defined in [RFC5415]. The Type value for this element
needs to be between 1 and 1023.
o <IANA-3>. This specification defines the IEEE 802.11 WTP
Alternate Tunnel Failure Indication message element in
Section 3.3. This element needs to be registered in the existing
CAPWAP Message Element Type registry, defined in [RFC5415]. The
Type value for this element needs to be between 1024 and 2047.
o Tunnel-Type: This specification defines the Alternate Tunnel
Encapsulations Type message element. This element contains a
field Tunnel-Type. The namespace for the field is 16 bits
(0-65535)). This specification defines values, zero (0) through
six (6) and can be found in Section 3.2. Future allocations of
values in this name space are to be assigned by IANA using the
"Specification Required" policy. IANA needs to create a registry
called CAPWAP Alternate Tunnel-Types. The registry format is
given below.
Tunnel-Type Type Value Reference
CAPWAP 0 [RFC5415],[RFC5416]
L2TP 1 [RFC2661]
L2TPv3 2 [RFC3931]
IP-IP 3 [RFC2003]
PMIPv6 4 [RFC5213]
GRE-IPv4 5 [RFC2784]
GRE-IPv6 6 [RFC2784]
5. Security Considerations
This document introduces three new CAPWAP WTP message elements.
These elements are transported within CAPWAP Control messages as the
existing message elements. Therefore, this document does not
introduce any new security risks compared to [RFC5415] and [RFC5416].
In CAPWAP, security for CAPWAP Data Channel is optional and security
policy is determined by AC. Similarly, the AC determines the
security for the Alternate Tunnel between WTP and Alternate Tunnel
Encapsulation Gateway. The security considerations described in
[RFC5415] and [RFC5416] apply here as well.
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6. Contributors
This document stems from the joint work of Hong Liu, Yifan Chen,
Chunju Shao from China Mobile Research.
7. References
7.1. Normative References
[RFC2003] Perkins, C., "IP Encapsulation within IP", RFC 2003,
October 1996.
[RFC2661] Townsley, W., Valencia, A., Rubens, A., Pall, G., Zorn,
G., and B. Palter, "Layer Two Tunneling Protocol "L2TP"",
RFC 2661, August 1999.
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC3931] Lau, J., Townsley, M., and I. Goyret, "Layer Two Tunneling
Protocol - Version 3 (L2TPv3)", RFC 3931, March 2005.
[RFC5213] Gundavelli, S., Leung, K., Devarapalli, V., Chowdhury, K.,
and B. Patil, "Proxy Mobile IPv6", RFC 5213, August 2008.
[RFC5415] Calhoun, P., Montemurro, M., and D. Stanley, "Control And
Provisioning of Wireless Access Points (CAPWAP) Protocol
Specification", RFC 5415, March 2009.
[RFC5416] Calhoun, P., Montemurro, M., and D. Stanley, "Control and
Provisioning of Wireless Access Points (CAPWAP) Protocol
Binding for IEEE 802.11", RFC 5416, March 2009.
7.2. Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
Authors' Addresses
Rong Zhang
China Telecom
No.109 Zhongshandadao avenue
Guangzhou 510630
China
Email: zhangr@gsta.com
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Zhen Cao
China Mobile
Xuanwumenxi Ave. No. 32
Beijing 100871
China
Phone: +86-10-52686688
Email: zehn.cao@gmail.com, caozhen@chinamobile.com
Hui Deng
China Mobile
No.32 Xuanwumen West Street
Beijing 100053
China
Email: denghui@chinamobile.com
Rajesh S. Pazhyannur
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
Email: rpazhyan@cisco.com
Sri Gundavelli
Cisco
170 West Tasman Drive
San Jose, CA 95134
USA
Email: sgundave@cisco.com
Li Xue
Huawei
No.156 Beiqing Rd. Z-park, HaiDian District
Beijing
China
Email: xueli@huawei.com
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