draft-ietf-roll-efficient-npdao-05.txt   draft-ietf-roll-efficient-npdao-06.txt 
ROLL R. Jadhav, Ed. ROLL R. Jadhav, Ed.
Internet-Draft Huawei Internet-Draft Huawei
Intended status: Standards Track P. Thubert Intended status: Standards Track P. Thubert
Expires: February 25, 2019 Cisco Expires: March 30, 2019 Cisco
R. Sahoo R. Sahoo
Z. Cao Z. Cao
Huawei Huawei
August 24, 2018 September 26, 2018
Efficient Route Invalidation Efficient Route Invalidation
draft-ietf-roll-efficient-npdao-05 draft-ietf-roll-efficient-npdao-06
Abstract Abstract
This document describes the problems associated with the use of No- This document describes the problems associated with the use of NPDAO
Path DAO messaging in RPL and signaling changes to improve route messaging in RPL and signaling changes to improve route invalidation
invalidation efficiency. efficiency.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on February 25, 2019. This Internet-Draft will expire on March 30, 2019.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language and Terminology . . . . . . . . . . 3 1.1. Requirements Language and Terminology . . . . . . . . . . 3
1.2. Current No-Path DAO messaging . . . . . . . . . . . . . . 4 1.2. Current NPDAO messaging . . . . . . . . . . . . . . . . . 3
1.3. Cases when No-Path DAO may be used . . . . . . . . . . . 4 1.3. Why NPDAO is important? . . . . . . . . . . . . . . . . . 4
1.4. Why No-Path DAO is important? . . . . . . . . . . . . . . 5 2. Problems with current NPDAO messaging . . . . . . . . 5
2. Problems with current No-Path DAO messaging . . . . . 5
2.1. Lost NPDAO due to link break to the previous parent . . . 5 2.1. Lost NPDAO due to link break to the previous parent . . . 5
2.2. Invalidate routes to dependent nodes of the switching 2.2. Invalidate routes to dependent nodes . . . . . . . . . . 5
node . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.3. Possible route downtime caused by async operation of
2.3. Route downtime caused by asynchronous operation of NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 5
NPDAO and DAO . . . . . . . . . . . . . . . . . . . . . . 6 3. Requirements for the NPDAO Optimization . . . . . . . . . . . 5
3. Requirements for the No-Path DAO Optimization . . . . . . . . 6
3.1. Req#1: Tolerant to link failures to the previous 3.1. Req#1: Tolerant to link failures to the previous
parents . . . . . . . . . . . . . . . . . . . . . . . . . 6 parents . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Req#2: Dependent nodes route invalidation on parent 3.2. Req#2: Dependent nodes route invalidation on parent
switching . . . . . . . . . . . . . . . . . . . . . . . . 7 switching . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3. Req#3: No impact on traffic while NPDAO operation in 3.3. Req#3: Route invalidation should not impact data traffic 6
progress . . . . . . . . . . . . . . . . . . . . . . . . 7 4. Proposed changes to RPL signaling . . . . . . . . . . . . . . 6
4. Proposed changes to RPL signaling . . . . . . . . . . . . . . 7 4.1. Change in RPL route invalidation semantics . . . . . . . 6
4.1. Change in RPL route invalidation semantics . . . . . . . 7 4.2. Transit Information Option changes . . . . . . . . . . . 7
4.2. Transit Information Option format change . . . . . . . . 8 4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 8
4.3. Destination Cleanup Object (DCO) . . . . . . . . . . . . 9 4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 9
4.3.1. Secure DCO . . . . . . . . . . . . . . . . . . . . . 10 4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 9
4.3.2. DCO Options . . . . . . . . . . . . . . . . . . . . . 10 4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 9
4.3.3. Path Sequence number in the DCO . . . . . . . . . . . 10 4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 9
4.3.4. Destination Cleanup Option Acknowledgement (DCO-ACK) 10 4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 10
4.3.5. Secure DCO-ACK . . . . . . . . . . . . . . . . . . . 11 4.4. Other considerations . . . . . . . . . . . . . . . . . . 11
4.4. Other considerations . . . . . . . . . . . . . . . . . . 12 4.4.1. Dependent Nodes invalidation . . . . . . . . . . . . 11
4.4.1. Dependent Nodes invalidation . . . . . . . . . . . . 12 4.4.2. NPDAO and DCO in the same network . . . . . . . . . . 11
4.4.2. NPDAO and DCO in the same network . . . . . . . . . . 12 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 12 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12 7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.1. Normative References . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . 13 Appendix A. Example DCO Messaging . . . . . . . . . . . . . . . 12
Appendix A. Example DCO Messaging . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 14
1. Introduction 1. Introduction
RPL [RFC6550] specifies a proactive distance-vector based routing RPL [RFC6550] specifies a proactive distance-vector based routing
scheme. The specification has an optional messaging in the form of scheme. RPL has an optional messaging in the form of DAO messages
DAO messages using which the 6LBR can learn route towards any of the using which the 6LBR can learn route towards the nodes. In storing
nodes. In storing mode, DAO messages would result in routing entries mode, DAO messages would result in routing entries been created on
been created on all intermediate hops from the node's parent all the all intermediate hops from the node's parent all the way towards the
way towards the 6LBR. 6LBR.
RPL allows use of No-Path DAO (NPDAO) messaging to invalidate a RPL allows use of No-Path DAO (NPDAO) messaging to invalidate a
routing path corresponding to the given target, thus releasing routing path corresponding to the given target, thus releasing
resources utilized on that path. A No-Path DAO is a DAO message with resources utilized on that path. A NPDAO is a DAO message with route
route lifetime of zero, originates at the target node and always lifetime of zero, originates at the target node and always flows
flows upstream towards the 6LBR, signaling route invalidation for the upstream towards the 6LBR. This document explains the problems
given target. This document explains the problems associated with associated with the current use of NPDAO messaging and also discusses
the current use of NPDAO messaging and also discusses the the requirements for an optimized route invalidation messaging
requirements for an optimized No-Path DAO messaging scheme. Further scheme. Further a new pro-active route invalidation message called
a new pro-active route invalidation message called as "Destination as "Destination Cleanup Object (DCO)" is specified which fulfills
Cleanup Object (DCO)" is specified which fulfills all mentioned
requirements of an optimized route invalidation messaging. requirements of an optimized route invalidation messaging.
6TiSCH architecture [I-D.ietf-6tisch-architecture] leverages RPL and
specifies use of non-storing and storing MOP for its routing
operation. Thus an improvement in route invalidation will help
optimize 6TiSCH based networks.
1.1. Requirements Language and Terminology 1.1. Requirements Language and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119]. document are to be interpreted as described in RFC 2119 [RFC2119].
The document only caters to the RPL's storing mode of operation The document only caters to the RPL's storing mode of operation
(MOP). The non-storing MOP does not require use of NPDAO for route (MOP). The non-storing MOP does not require use of NPDAO for route
invalidation since routing entries are not maintained on 6LRs. invalidation since routing entries are not maintained on 6LRs.
Common Ancestor node: 6LR node which is the first common node on the Common Ancestor node: 6LR node which is the first common node on the
old and new path for the child node. old and new path for the child node.
NPDAO: No-Path DAO. A DAO message which has target with lifetime 0. NPDAO: No-Path DAO. A DAO message which has target with lifetime 0.
DCO: Destination Cleanup Object, A new RPL control message type DCO: Destination Cleanup Object, A new RPL control message type
defined by this draft. defined by this draft.
Regular DAO: A DAO message with non-zero lifetime. Regular DAO: A DAO message with non-zero lifetime.
LLN: Low Power and Lossy Networks.
Target Node: The node switching its parent whose routing adjacencies
are updated (created/removed).
This document also uses terminology described in [RFC6550]. This document also uses terminology described in [RFC6550].
1.2. Current No-Path DAO messaging 1.2. Current NPDAO messaging
RPL introduced No-Path DAO messaging in the storing mode so that the RPL uses NPDAO messaging in the storing mode so that the node
node switching its current parent can inform its parents and changing it routing adjacencies can invalidate the previous route.
ancestors to invalidate the existing route. Subsequently parents or This is needed so that nodes along previous path can release any
ancestors would release any resources (such as the routing entry) it resources (such as the routing entry) it maintains on behalf of
maintains on behalf of target node. The NPDAO message always target node.
traverses the RPL tree in upward direction, originating at the target
node itself.
For the rest of this document consider the following topology: For the rest of this document consider the following topology:
(6LBR) (6LBR)
| |
| |
| |
(A) (A)
/ \ / \
/ \ / \
skipping to change at page 4, line 44 skipping to change at page 4, line 34
/ \ / \
/ \ / \
/ \ / \
(E) (F) (E) (F)
Figure 1: Sample topology Figure 1: Sample topology
Node (D) is connected via preferred parent (B). (D) has an alternate Node (D) is connected via preferred parent (B). (D) has an alternate
path via (C) towards the BR. Node (A) is the common ancestor for (D) path via (C) towards the BR. Node (A) is the common ancestor for (D)
for paths through (B)-(G) and (C)-(H). When (D) switches from (B) to for paths through (B)-(G) and (C)-(H). When (D) switches from (B) to
(C), [RFC6550] suggests sending No-Path DAO to (B) and regular DAO to (C), RPL allows sending NPDAO to (B) and regular DAO to (C).
(C).
1.3. Cases when No-Path DAO may be used
There are following cases in which a node switches its parent and may
employ No-Path DAO messaging:
Case I: Current parent becomes unavailable because of transient or
permanent link or parent node failure.
Case II: The node finds a better parent node i.e. the metrics of
another parent is better than its current parent.
Case III: The node switches to a new parent whom it "thinks" has a
better metric but does not in reality.
The usual steps of operation when the node switches the parent is
that the node sends a No-Path DAO message via its current parent to
invalidate its current route and subsequently it tries to establish a
new routing path by sending a new DAO via its new parent.
1.4. Why No-Path DAO is important? 1.3. Why NPDAO is important?
Nodes in LLNs may be resource constrained. There is limited memory Nodes in LLNs may be resource constrained. There is limited memory
available and routing entry records are the one of the primary available and routing entry records are one of the primary elements
elements occupying dynamic memory in the nodes. Route invalidation occupying dynamic memory in the nodes. Route invalidation helps 6LR
helps 6LR nodes to decide which entries could be discarded to better nodes to decide which entries could be discarded to better achieve
achieve resource utilization in case of contention. Thus it becomes resource utilization. Thus it becomes necessary to have efficient
necessary to have efficient route invalidation mechanism. Also note route invalidation mechanism. Also note that a single parent switch
that a single parent switch may result in a "sub-tree" switching from may result in a "sub-tree" switching from one parent to another.
one parent to another. Thus the route invalidation needs to be done Thus the route invalidation needs to be done on behalf of the sub-
on behalf of the sub-tree and not the switching node alone. In the tree and not the switching node alone. In the above example, when
above example, when Node (D) switches parent, the route invalidation Node (D) switches parent, the route invalidation needs to be done for
needs to be done for (D), (E) and (F). Thus without efficient route (D), (E) and (F). Thus without efficient route invalidation, a 6LR
invalidation, a 6LR may have to hold a lot of unwanted route entries. may have to hold a lot of stale route entries.
2. Problems with current No-Path DAO messaging 2. Problems with current NPDAO messaging
2.1. Lost NPDAO due to link break to the previous parent 2.1. Lost NPDAO due to link break to the previous parent
When a node switches its parent, the NPDAO is to be sent via its When a node switches its parent, the NPDAO is to be sent to its
previous parent and a regular DAO via its new parent. In cases where previous parent and a regular DAO to its new parent. In cases where
the node switches its parent because of transient or permanent parent the node switches its parent because of transient or permanent parent
link/node failure then the NPDAO message is bound to fail. RPL link/node failure then the NPDAO message is bound to fail.
assumes communication link with the previous parent for No-Path DAO
messaging.
RPL allows use of route lifetime to remove unwanted routes in case
the routes could not be refreshed. But route lifetimes in case of
LLNs could be substantially high and thus the route entries would be
stuck for longer times.
2.2. Invalidate routes to dependent nodes of the switching node 2.2. Invalidate routes to dependent nodes
No-path DAO is sent by the node who has switched the parent but it RPL does not specify how route invalidation will work for dependent
does not work for the dependent child nodes below it. The nodes rooted at switching node, resulting in stale routing entries of
specification does not specify how route invalidation will work for the dependent nodes. The only way for 6LR to invalidate the route
sub-childs, resulting in stale routing entries on behalf of the sub- entries for dependent nodes would be to use route lifetime expiry
childs on the previous route. The only way for 6LR to invalidate the which could be substantially high for LLNs.
route entries for dependent nodes would be to use route lifetime
expiry which could be substantially high for LLNs.
In the example topology, when Node (D) switches its parent, Node (D) In the example topology, when Node (D) switches its parent, Node (D)
generates an NPDAO on its behalf. Post switching, Node (D) transmits generates an NPDAO on its behalf. There is no NPDAO generated by
a DIO with incremented DTSN so that child nodes, node (E) and (F), these child nodes through the previous path resulting in stale
generate DAOs to trigger route update on the new path for themselves. entries on nodes (B) and (G) for nodes (E) and (F).
There is no NPDAO generated by these child nodes through the previous
path resulting in stale entries on nodes (B) and (G) for nodes (E)
and (F).
2.3. Route downtime caused by asynchronous operation of NPDAO and DAO 2.3. Possible route downtime caused by async operation of NPDAO and DAO
A switching node may generate both an NPDAO and DAO via two different A switching node may generate both an NPDAO and DAO via two different
paths at almost the same time. There is a possibility that an NPDAO paths at almost the same time. There is a possibility that an NPDAO
generated may invalidate the previous route and the regular DAO sent generated may invalidate the previous route and the regular DAO sent
via the new path gets lost on the way. This may result in route via the new path gets lost on the way. This may result in route
downtime thus impacting downward traffic for the switching node. In downtime impacting downward traffic for the switching node.
the example topology, consider Node (D) switches from parent (B) to
(C) because the metrics of the path via (C) are better. Note that
the previous path via (B) may still be available (albeit at
relatively bad metrics). An NPDAO sent from previous route may
invalidate the existing route whereas there is no way to determine
whether the new DAO has successfully updated the route entries on the
new path.
3. Requirements for the No-Path DAO Optimization In the example topology, consider Node (D) switches from parent (B)
to (C). An NPDAO sent from previous route may invalidate the
existing route whereas there is no way to determine whether the new
DAO has successfully updated the route entries on the new path.
3. Requirements for the NPDAO Optimization
3.1. Req#1: Tolerant to link failures to the previous parents 3.1. Req#1: Tolerant to link failures to the previous parents
When the switching node sends the NPDAO message to the previous When the switching node sends the NPDAO message to the previous
parent, it is normal that the link to the previous parent is prone to parent, it is normal that the link to the previous parent is prone to
failure. Therefore, it is required that the NPDAO message MUST be failure. Therefore, it is required that the NPDAO message must be
tolerant to the link failure during the switching. The link referred tolerant to the link failure. The link referred here represents the
here represents the link between the node and its previous parent link between the node and its previous parent (from whom the node is
(from whom the node is now disassociating). now disassociating).
3.2. Req#2: Dependent nodes route invalidation on parent switching 3.2. Req#2: Dependent nodes route invalidation on parent switching
While switching the parent node and sending NPDAO message, it is It should be possible to do route invalidation for dependent nodes
required that the routing entries to the dependent nodes of the rooted at the switching node.
switching node will be updated accordingly on the previous parents
and other relevant upstream nodes.
3.3. Req#3: No impact on traffic while NPDAO operation in progress 3.3. Req#3: Route invalidation should not impact data traffic
While sending the NPDAO and DAO messages, it is possible that the While sending the NPDAO and DAO messages, it is possible that the
NPDAO successfully invalidates the previous path, while the newly NPDAO successfully invalidates the previous path, while the newly
sent DAO gets lost (new path not set up successfully). This will sent DAO gets lost (new path not set up successfully). This will
result into downstream unreachability to the current switching node. result in downstream unreachability to the node switching paths.
Therefore, it is desirable that the NPDAO is synchronized with the Therefore, it is desirable that the route invalidation is
DAO to avoid the risk of route downtime. synchronized with the DAO to avoid the risk of route downtime.
4. Proposed changes to RPL signaling 4. Proposed changes to RPL signaling
4.1. Change in RPL route invalidation semantics 4.1. Change in RPL route invalidation semantics
As described in Section 1.2, the NPDAO originates at the node As described in Section 1.2, the NPDAO originates at the node
switching the parent and traverses upstream towards the root. In switching the parent and traverses upstream towards the root. In
order to solve the problems as mentioned in Section 2, the draft adds order to solve the problems as mentioned in Section 2, the draft adds
new pro-active route invalidation message called as "Destination new pro-active route invalidation message called as "Destination
Cleanup Object" (DCO) that originates at a common ancestor node Cleanup Object" (DCO) that originates at a common ancestor node
skipping to change at page 8, line 5 skipping to change at page 7, line 5
node A receives the regular DAO, it finds that it already has a node A receives the regular DAO, it finds that it already has a
routing table entry on behalf of the target address of node D. It routing table entry on behalf of the target address of node D. It
finds however that the next hop information for reaching node D has finds however that the next hop information for reaching node D has
changed i.e. the node D has decided to change the paths. In this changed i.e. the node D has decided to change the paths. In this
case, Node A which is the common ancestor node for node D along the case, Node A which is the common ancestor node for node D along the
two paths (previous and new), may generate a DCO which traverses two paths (previous and new), may generate a DCO which traverses
downwards in the network. The document in the subsequent section downwards in the network. The document in the subsequent section
will explain the message format changes to handle this downward flow will explain the message format changes to handle this downward flow
of NPDAO. of NPDAO.
4.2. Transit Information Option format change 4.2. Transit Information Option changes
Every RPL message is divided into base message fields and additional Every RPL message is divided into base message fields and additional
Options. The base fields apply to the message as a whole and options Options. The base fields apply to the message as a whole and options
are appended to add message/use-case specific attributes. As an are appended to add message/use-case specific attributes. As an
example, a DAO message may be attributed by one or more "RPL Target" example, a DAO message may be attributed by one or more "RPL Target"
options which specifies the reachability information for the given options which specifies the reachability information for the given
targets. Similarly, a Transit Information option may be associated targets. Similarly, a Transit Information option may be associated
with a set of RPL Target options. with a set of RPL Target options.
The draft proposes a change in Transit Information option to contain The draft proposes a change in Transit Information option to contain
skipping to change at page 9, line 42 skipping to change at page 8, line 42
RPLInstanceID: 8-bit field indicating the topology instance RPLInstanceID: 8-bit field indicating the topology instance
associated with the DODAG, as learned from the DIO. associated with the DODAG, as learned from the DIO.
K: The 'K' flag indicates that the recipient is expected to send a K: The 'K' flag indicates that the recipient is expected to send a
DCO-ACK back. DCO-ACK back.
D: The 'D' flag indicates that the DODAGID field is present. This D: The 'D' flag indicates that the DODAGID field is present. This
flag MUST be set when a local RPLInstanceID is used. flag MUST be set when a local RPLInstanceID is used.
Flags: The 6 bits remaining unused in the Flags field are reserved Flags: The 6 bits remaining unused in the Flags field are reserved
for flags. The field MUST be initialized to zero by the sender and for future use. These bits MUST be initialized to zero by the sender
MUST be ignored by the receiver. and MUST be ignored by the receiver.
Reserved: 8-bit unused field. The field MUST be initialized to zero Reserved: 8-bit unused field. The field MUST be initialized to zero
by the sender and MUST be ignored by the receiver. by the sender and MUST be ignored by the receiver.
DCOSequence: Incremented at each unique DCO message from a node and DCOSequence: Incremented at each unique DCO message from a node and
echoed in the DCO-ACK message. echoed in the DCO-ACK message.
DODAGID (optional): 128-bit unsigned integer set by a DODAG root that DODAGID (optional): 128-bit unsigned integer set by a DODAG root that
uniquely identifies a DODAG. This field is only present when the 'D' uniquely identifies a DODAG. This field is only present when the 'D'
flag is set. This field is typically only present when a local flag is set. This field is typically only present when a local
skipping to change at page 12, line 30 skipping to change at page 11, line 30
Even with the changed semantics, the current NPDAO mechanism in Even with the changed semantics, the current NPDAO mechanism in
[RFC6550] can still be used. There are certain scenarios where [RFC6550] can still be used. There are certain scenarios where
current NPDAO signalling may still be used, for example, when the current NPDAO signalling may still be used, for example, when the
route lifetime expiry of the target happens or when the node simply route lifetime expiry of the target happens or when the node simply
decides to gracefully terminate the RPL session on graceful node decides to gracefully terminate the RPL session on graceful node
shutdown. Moreover a deployment can have a mix of nodes supporting shutdown. Moreover a deployment can have a mix of nodes supporting
the proposed DCO and the existing NPDAO mechanism. the proposed DCO and the existing NPDAO mechanism.
5. Acknowledgements 5. Acknowledgements
Many thanks to Cenk Gundogan, Simon Duquennoy, and Georgios Many thanks to Cenk Gundogan, Simon Duquennoy, Georgios
Papadopoulous for their review and comments. Papadopoulous, Peter Van Der Stok for their review and comments.
6. IANA Considerations 6. IANA Considerations
IANA is requested to allocate new ICMPv6 RPL control codes in RPL IANA is requested to allocate new ICMPv6 RPL control codes in RPL
[RFC6550] for DCO and DCO-ACK messages. [RFC6550] for DCO and DCO-ACK messages.
+------+---------------------------------------------+--------------+ +------+---------------------------------------------+--------------+
| Code | Description | Reference | | Code | Description | Reference |
+------+---------------------------------------------+--------------+ +------+---------------------------------------------+--------------+
| 0x04 | Destination Cleanup Object | This | | 0x04 | Destination Cleanup Object | This |
skipping to change at page 15, line 16 skipping to change at page 14, line 16
Kundalahalli Village, Whitefield, Kundalahalli Village, Whitefield,
Bangalore, Karnataka 560037 Bangalore, Karnataka 560037
India India
Phone: +91-080-49160700 Phone: +91-080-49160700
Email: rabinarayans@huawei.com Email: rabinarayans@huawei.com
Zhen Cao Zhen Cao
Huawei Huawei
W Chang'an Ave W Chang'an Ave
Beijing 560037 Beijing
China China
Email: zhencao.ietf@gmail.com Email: zhencao.ietf@gmail.com
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