Internet DRAFT - draft-ietf-teas-gmpls-resource-sharing-proc
draft-ietf-teas-gmpls-resource-sharing-proc
TEAS Working Group X. Zhang
Internet-Draft H. Zheng, Ed.
Intended Status: Informational Huawei Technologies
Expires: July 30, 2017 R. Gandhi, Ed.
Z. Ali
Cisco Systems, Inc.
P. Brzozowski
ADVA Optical
January 26, 2017
RSVP-TE Signaling Procedure for End-to-End GMPLS Restoration and
Resource Sharing
draft-ietf-teas-gmpls-resource-sharing-proc-08
Abstract
In non-packet transport networks, there are requirements where
Generalized Multi-Protocol Label Switching (GMPLS) end-to-end
recovery scheme needs to employ restoration Label Switched Path (LSP)
while keeping resources for the working and/or protecting LSPs
reserved in the network after the failure occurs.
This document reviews how the LSP association is to be provided using
Resource Reservation Protocol - Traffic Engineering (RSVP-TE)
signaling in the context of GMPLS end-to-end recovery scheme when
using restoration LSP where failed LSP is not torn down. In
addition, this document discusses resource sharing-based setup and
teardown of LSPs as well as LSP reversion procedures. No new
signaling extensions are defined by this document, and it is strictly
informative in nature.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Acronyms and Abbreviations . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Examples of Restoration Schemes . . . . . . . . . . . . . 5
3.1.1. 1+R Restoration . . . . . . . . . . . . . . . . . . . 5
3.1.2. 1+1+R Restoration . . . . . . . . . . . . . . . . . . 5
3.1.2.1. 1+1+R Restoration - Variants . . . . . . . . . . . 6
3.2. Resource Sharing by Restoration LSP . . . . . . . . . . . 7
4. RSVP-TE Signaling Procedure . . . . . . . . . . . . . . . . . 8
4.1. Restoration LSP Association . . . . . . . . . . . . . . . 8
4.2. Resource Sharing-based Restoration LSP Setup . . . . . . . 8
4.3. LSP Reversion . . . . . . . . . . . . . . . . . . . . . . 10
4.3.1. Make-while-break Reversion . . . . . . . . . . . . . . 10
4.3.2. Make-before-break Reversion . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7.1. Normative References . . . . . . . . . . . . . . . . . . . 13
7.2. Informative References . . . . . . . . . . . . . . . . . . 13
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 14
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] defines
a set of protocols, including Open Shortest Path First - Traffic
Engineering (OSPF-TE) [RFC4203] and Resource ReserVation Protocol -
Traffic Engineering (RSVP-TE) [RFC3473]. These protocols can be used
to set up Label Switched Paths (LSPs) in non-packet transport
networks. The GMPLS protocol extends MPLS to support interfaces
capable of Time Division Multiplexing (TDM), Lambda Switching and
Fiber Switching. These switching technologies provide several
protection schemes [RFC4426][RFC4427] (e.g., 1+1, 1:N and M:N).
Resource Reservation Protocol - Traffic Engineering (RSVP-TE)
signaling has been extended to support various GMPLS recovery
schemes, such as end-to-end recovery [RFC4872] and segment recovery
[RFC4873]. As described in [RFC6689], an ASSOCIATION object with
Association Type "Recovery" [RFC4872] can be signaled in the RSVP
Path message to identify the LSPs for restoration. Also, an
ASSOCIATION object with Association Type "Resource Sharing" [RFC4873]
can be signaled in the RSVP Path message to identify the LSPs for
resource sharing. [RFC6689] Section 2.2 reviews the procedure for
providing LSP associations for GMPLS end-to-end recovery and Section
2.4 reviews the procedure for providing LSP associations for sharing
resources.
Generally GMPLS end-to-end recovery schemes have the restoration LSP
set up after the failure has been detected and notified on the
working LSP. For recovery scheme with revertive behavior, a
restoration LSP is set up while working LSP and/or protecting LSP are
not torn down in control plane due to a failure. In non-packet
transport networks, as working LSPs are typically set up over
preferred paths, service providers would like to keep resources
associated with the working LSPs reserved. This is to make sure that
the service can be reverted to the preferred path (working LSP) when
the failure is repaired to provide deterministic behavior and
guaranteed Service Level Agreement (SLA).
In this document, we review procedures for GMPLS LSP associations,
resource sharing based LSP setup, teardown, and LSP reversion for
non-packet transport networks, including the following:
o Review the procedure for providing LSP associations for the GMPLS
end-to-end recovery using restoration LSP where working and
protecting LSPs are not torn down and resources are kept reserved
in the network after the failure.
o In [RFC3209], the make-before-break (MBB) method assumes the old
and new LSPs share the SESSION object and signal Shared Explicit
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(SE) flag in SESSION_ATTRIBUTE object for sharing resources.
According to [RFC6689], an ASSOCIATION object with Association
Type "Resource Sharing" in the Path message enables the sharing of
resources across LSPs with different SESSION objects. The
procedure for resource sharing using the SE flag in conjunction
with an ASSOCIATION object is discussed in this document.
o When using end-to-end recovery scheme with revertive behavior,
methods for LSP reversion and resource sharing are summarized in
this document.
This document is strictly informative in nature and does not define
any RSVP-TE signaling extensions.
2. Conventions Used in This Document
2.1. Terminology
The reader is assumed to be familiar with the terminology in
[RFC3209], [RFC3473], [RFC4872] and [RFC4873]. The terminology for
GMPLS recovery is defined in [RFC4427].
2.2. Acronyms and Abbreviations
GMPLS: Generalized Multi-Protocol Label Switching
LSP: An MPLS Label Switched Path
MBB: Make Before Break
MPLS: Multi-Protocol Label Switching
RSVP: Resource ReSerVation Protocol
SE: Shared Explicit flag
TDM: Time Division Multiplexing
TE: Traffic Engineering
3. Overview
The GMPLS end-to-end recovery scheme, as defined in [RFC4872] and
being considered in this document, switches normal traffic to an
alternate LSP that is not even partially established only after the
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working LSP failure occurs. The new alternate route is selected at
the LSP head-end node, it may reuse resources of the failed LSP at
intermediate nodes and may include additional intermediate nodes
and/or links.
3.1. Examples of Restoration Schemes
Two forms of end-to-end recovery schemes, 1+R restoration and 1+1+R
restoration are described in the following sections. Other forms of
end-to-end recovery schemes also exist and they can use these
signaling techniques.
3.1.1. 1+R Restoration
One example of the recovery scheme considered in this document is 1+R
recovery. The 1+R recovery scheme is exemplified in Figure 1. In
this example, a working LSP on path A-B-C-Z is pre-established.
Typically after a failure detection and notification on the working
LSP, a second LSP on path A-H-I-J-Z is established as a restoration
LSP. Unlike a protecting LSP which is set up before the failure, a
restoration LSP is set up when needed, after the failure.
+-----+ +-----+ +-----+ +-----+
| A +----+ B +-----+ C +-----+ Z |
+--+--+ +-----+ +-----+ +--+--+
\ /
\ /
+--+--+ +-----+ +--+--+
| H +-------+ I +--------+ J |
+-----+ +-----+ +-----+
Figure 1: An Example of 1+R Recovery Scheme
During failure switchover with 1+R recovery scheme, in general,
working LSP resources are not released so that working and
restoration LSPs coexist in the network. Nonetheless, working and
restoration LSPs can share network resources. Typically when the
failure has recovered on the working LSP, the restoration LSP is no
longer required and is torn down while the traffic is reverted to the
original working LSP.
3.1.2. 1+1+R Restoration
Another example of the recovery scheme considered in this document is
1+1+R. In 1+1+R, a restoration LSP is set up for the working LSP
and/or the protecting LSP after the failure has been detected, and
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this recovery scheme is exemplified in Figure 2.
+-----+ +-----+ +-----+
| D +-------+ E +--------+ F |
+--+--+ +-----+ +--+--+
/ \
/ \
+--+--+ +-----+ +-----+ +--+--+
| A +----+ B +-----+ C +-----+ Z |
+--+--+ +-----+ +-----+ +--+--+
\ /
\ /
+--+--+ +-----+ +--+--+
| H +-------+ I +--------+ J |
+-----+ +-----+ +-----+
Figure 2: An Example of 1+1+R Recovery Scheme
In this example, a working LSP on path A-B-C-Z and a protecting LSP
on path A-D-E-F-Z are pre-established. After a failure detection and
notification on the working LSP or protecting LSP, a third LSP on
path A-H-I-J-Z is established as a restoration LSP. The restoration
LSP in this case provides protection against failure of both the
working and protecting LSPs. During failure switchover with 1+1+R
recovery scheme, in general, failed LSP resources are not released so
that working, protecting and restoration LSPs coexist in the network.
The restoration LSP can share network resources with the working
LSP, and it can share network resources with the protecting LSP.
Typically, the restoration LSP is torn down when the traffic is
reverted to the original LSP and it is no longer needed.
There are two possible models when using a restoration LSP with 1+1+R
recovery scheme:
o A restoration LSP is set up after either a working or protecting
LSP fails. Only one restoration LSP is present at a time.
o A restoration LSP is set up after both working and protecting LSPs
fail. Only one restoration LSP is present at a time.
3.1.2.1. 1+1+R Restoration - Variants
Two other possible variants exist when using a restoration LSP with
1+1+R recovery scheme:
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o A restoration LSP is set up after either a working or protecting
LSP fails. Two different restoration LSPs may be present, one for
the working LSP and one for the protecting LSP.
o Two different restoration LSPs are set up after both working and
protecting LSPs fail, one for the working LSP and one for the
protecting LSP.
In all these models, if a restoration LSP also fails, it is torn down
and a new restoration LSP is set up.
3.2. Resource Sharing by Restoration LSP
+-----+ +-----+
| F +------+ G +--------+
+--+--+ +-----+ |
| |
| |
+-----+ +-----+ +--+--+ +-----+ +--+--+
| A +----+ B +-----+ C +--X---+ D +-----+ E |
+-----+ +-----+ +-----+ +-----+ +-----+
Figure 3: Resource Sharing in 1+R Recovery Scheme
Using the network shown in Figure 3 as an example using 1+R recovery
scheme, LSP1 (A-B-C-D-E) is the working LSP, and assume it allows for
resource sharing when the LSP traffic is dynamically restored. Upon
detecting the failure of a link along the LSP1, e.g. Link C-D, node A
needs to decide which alternative path it will use to signal
restoration LSP and reroute traffic. In this case, A-B-C-F-G-E is
chosen as the restoration LSP path and the resources on the path
segment A-B-C are re-used by this LSP. The working LSP is not torn
down and co-exists with the restoration LSP. When the head-end node
A signals the restoration LSP, nodes C, F, G and E reconfigure the
resources (as listed in Table 1 of this document) to set up the LSP
by sending cross-connection command to the data plane.
In the recovery scheme employing revertive behavior, after the
failure is repaired, the resources on nodes C and E need to be
reconfigured to set up the working LSP (using a procedure described
in Section 4.3 of this document) by sending cross-connection command
to the data plane. The traffic is then reverted back to the original
working LSP.
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4. RSVP-TE Signaling Procedure
4.1. Restoration LSP Association
Where GMPLS end-to-end recovery scheme needs to employ a restoration
LSP while keeping resources for the working and/or protecting LSPs
reserved in the network after the failure, the restoration LSP is set
up with an ASSOCIATION object that has Association Type set to
"Recovery" [RFC4872], the Association ID and the Association Source
set to the corresponding Association ID and the Association Source
signaled in the Path message of the LSP it is restoring. For
example, when a restoration LSP is signaled for a failed working LSP,
the ASSOCIATION object in the Path message of the restoration LSP
contains the Association ID and Association Source set to the
Association ID and Association Source signaled in the working LSP for
the "Recovery" Association Type. Similarly, when a restoration LSP
is set up for a failed protecting LSP, the ASSOCIATION object in the
Path message of the restoration LSP contains the Association ID and
Association Source set to the Association ID and Association Source
signaled in the protecting LSP for the "Recovery" Association Type.
The procedure for signaling the PROTECTION object is specified in
[RFC4872]. Specifically, the restoration LSP used for a working LSP
is set up with P bit cleared in the PROTECTION object in the Path
message of the restoration LSP and the restoration LSP used for a
protecting LSP is set up with P bit set in the PROTECTION object in
the Path message of the restoration LSP.
4.2. Resource Sharing-based Restoration LSP Setup
GMPLS LSPs can share resources during LSP setup if they have Shared
Explicit (SE) flag set in the SESSION_ATTRIBUTE objects [RFC3209] in
the Path messages that create them and:
o As defined in [RFC3209], LSPs have identical SESSION objects
and/or
o As defined in [RFC6689], LSPs have matching ASSOCIATION object
with Association Type set to "Resource Sharing" signaled in their
Path messages. LSPs in this case can have different SESSION
objects i.e. different Tunnel ID, Source and/or Destination
signaled in their Path messages.
As described in [RFC3209], Section 2.5, the purpose of make-before-
break is not to disrupt traffic, or adversely impact network
operations while TE tunnel rerouting is in progress. In non-packet
transport networks during the RSVP-TE signaling procedure, the nodes
set up cross-connections along the LSP accordingly. Because the
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cross-connection cannot simultaneously connect a shared resource to
different resources in two alternative LSPs, nodes may not be able to
fulfill this request when LSPs share resources.
For LSP restoration upon failure, as explained in Section 11 of
[RFC4872], the reroute procedure may re-use existing resources. The
action of the intermediate nodes during the rerouting process to
reconfigure cross-connections does not further impact the traffic
since it has been interrupted due to the already failed LSP.
The node actions for setting up the restoration LSP can be
categorized into the following:
-----------------------------------+---------------------------------
| Category | Action |
-----------------------------------+---------------------------------
| Reusing existing resource on | This type of node needs to |
| both input and output interfaces | reserve the existing resources |
| (nodes A & B in Figure 3). | and no cross-connection |
| | command is needed. |
-----------------------------------+---------------------------------
| Reusing existing resource only | This type of node needs to |
| on one of the interfaces, either | reserve the resources and send |
| input or output interfaces and | the re-configuration |
| using new resource on the | cross-connection command to its|
| other interfaces. | corresponding data plane |
| (nodes C & E in Figure 3). | node on the interfaces where |
| | new resources are needed and |
| | it needs to re-use the existing|
| | resources on the other |
| | interfaces. |
-----------------------------------+---------------------------------
| Using new resources on both | This type of node needs to |
| interfaces. | reserve the new resources |
| (nodes F & G in Figure 3). | and send the cross-connection |
| | command on both interfaces. |
-----------------------------------+---------------------------------
Table 1: Node Actions During Restoration LSP Setup
Depending on whether the resource is re-used or not, the node actions
differ. This deviates from normal LSP setup since some nodes do not
need to re-configure the cross-connection. Also, the judgment
whether the control plane node needs to send a cross-connection setup
or modification command to its corresponding data plane node(s)
relies on the check whether the LSPs are sharing resources.
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4.3. LSP Reversion
If the end-to-end LSP recovery scheme employs the revertive behavior,
as described in Section 3 of this document, traffic can be reverted
from the restoration LSP to the working or protecting LSP after its
failure is recovered. The LSP reversion can be achieved using two
methods:
1. Make-while-break Reversion, where resources associated with a
working or protecting LSP are reconfigured while removing
reservations for the restoration LSP.
2. Make-before-break Reversion, where resources associated with a
working or protecting LSP are reconfigured before removing
reservations for the restoration LSP.
In non-packet transport networks, both of the above reversion methods
will result in some traffic disruption when the restoration LSP and
the LSP being restored are sharing resources and the
cross-connections need to be reconfigured on intermediate nodes.
4.3.1. Make-while-break Reversion
In this reversion method, restoration LSP is simply requested to be
deleted by the head-end. Removing reservations for restoration LSP
triggers reconfiguration of resources associated with a working or
protecting LSP on every node where resources are shared. The working
or protecting LSP state was not removed from the nodes when the
failure occurred. Whenever reservation for restoration LSP is
removed from a node, data plane configuration changes to reflect
reservations of working or protecting LSP as signaling progresses.
Eventually, after the whole restoration LSP is deleted, data plane
configuration will fully match working or protecting LSP reservations
on the whole path. Thus reversion is complete.
Make-while-break, while being relatively simple in its logic, has a
few limitations as follows which may not be acceptable in some
networks:
o No rollback
If for some reason reconfiguration of data plane on one of the nodes
to match working or protecting LSP reservations fails, falling back
to restoration LSP is no longer an option, as its state might have
already been removed from other nodes.
o No completion guarantee
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Deletion of an LSP provides no guarantees of completion. In
particular, if RSVP packets are lost due to a node or link failure it
is possible for an LSP to be only partially deleted. To mitigate
this, RSVP could maintain soft state reservations and hence
eventually remove remaining reservations due to refresh timeouts.
This approach is not feasible in non-packet transport networks
however, where control and data channels are often separated and
hence soft state reservations are not useful.
Finally, one could argue that graceful LSP deletion [RFC3473] would
provide guarantee of completion. While this is true for most cases,
many implementations will time out graceful deletion if LSP is not
removed within certain amount of time, e.g. due to a transit node
fault. After that, deletion procedures which provide no completion
guarantees will be attempted. Hence, in corner cases a completion
guarantee cannot be provided.
o No explicit notification of completion to head-end node
In some cases, it may be useful for a head-end node to know when the
data plane has been reconfigured to match working or protecting LSP
reservations. This knowledge could be used for initiating operations
like enabling alarm monitoring, power equalization and others.
Unfortunately, for the reasons mentioned above, make-while-break
reversion lacks such explicit notification.
4.3.2. Make-before-break Reversion
This reversion method can be used to overcome limitations of
make-while-break reversion. It is similar in spirit to MBB concept
used for re-optimization. Instead of relying on deletion of the
restoration LSP, the head-end chooses to establish a new reversion
LSP that duplicates the configuration of the resources on the working
or protecting LSP, and uses identical ASSOCIATION and PROTECTION
objects in the Path message of that LSP. Only if setup of this LSP
is successful will other (restoration and working or protecting) LSPs
be deleted by the head-end. MBB reversion consists of two parts:
A) Make part:
Creating a new reversion LSP following working or protecting LSP's
path. The reversion LSP shares all of the resources of the working
or protecting LSP and may share resources with the restoration LSP.
As reversion LSP is created, resources are reconfigured to match its
reservations. Hence, after reversion LSP is created, data plane
configuration reflects working or protecting LSP reservations.
B) Break part:
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After "make" part is finished, the original working or protecting and
restoration LSPs are torn down, and the reversion LSP becomes the new
working or protecting LSP. Removing reservations for working or
restoration LSPs does not cause any resource reconfiguration on
reversion LSP's path - nodes follow same procedures as for "break"
part of any MBB operation. Hence, after working or protecting and
restoration LSPs are removed, data plane configuration is exactly the
same as before starting restoration. Thus, reversion is complete.
MBB reversion uses make-before-break characteristics to overcome
challenges related to make-while-break reversion as follow:
o Rollback
If "make" part fails, (existing) restoration LSP will still be used
to carry existing traffic as the restoration LSP state was not
removed. Same logic applies here as for any MBB operation failure.
o Completion guarantee
LSP setup is resilient against RSVP message loss, as Path and Resv
messages are refreshed periodically. Hence, given that network
recovers from node and link failures eventually, reversion LSP setup
is guaranteed to finish with either success or failure.
o Explicit notification of completion to head-end node
Head-end knows that data plane has been reconfigured to match working
or protecting LSP reservations on intermediate nodes when it receives
Resv for the reversion LSP.
5. Security Considerations
This document reviews procedures defined in [RFC3209] [RFC4872]
[RFC4873] and [RFC6689] and does not define any new procedure. This
document does not introduce any new security issues other than those
already covered in [RFC3209] [RFC4872] [RFC4873] and [RFC6689].
6. IANA Considerations
This informational document does not make any request for IANA
action.
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7. References
7.1. Normative References
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001.
[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003.
[RFC4872] Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
Ed., "RSVP-TE Extensions in Support of End-to-End
Generalized Multi-Protocol Label Switching (GMPLS)
Recovery", RFC 4872, May 2007.
[RFC4873] Berger, L., Bryskin, I., Papadimitriou, D., and A.
Farrel, "GMPLS Segment Recovery", RFC 4873, May 2007.
[RFC6689] L. Berger, "Usage of the RSVP ASSOCIATION Object", RFC
6689, July 2012.
7.2. Informative References
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4203] Kompella, K., and Rekhter, Y., "OSPF Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.
[RFC4426] Lang, J., Rajagopalan, B., and Papadimitriou, D.,
"Generalized Multiprotocol Label Switching (GMPLS)
Recovery Functional Specification", RFC 4426, March 2006.
[RFC4427] Mannie, E., and Papadimitriou, D., "Recovery (Protection
and Restoration) Terminology for Generalized
Multi-Protocol Label Switching", RFC 4427, March 2006.
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Acknowledgements
The authors would like to thank George Swallow for the discussions on
the GMPLS restoration. The authors would like to thank Lou Berger
for the guidance on this work. The authors would also like to thank
Lou Berger, Vishnu Pavan Beeram and Christian Hopps for reviewing
this document and providing valuable comments. A special thanks to
Dale Worley for his thorough review of this document.
Contributors
Gabriele Maria Galimberti
Cisco Systems, Inc.
EMail: ggalimbe@cisco.com
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Authors' Addresses
Xian Zhang
Huawei Technologies
F3-1-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
EMail: zhang.xian@huawei.com
Haomian Zheng (editor)
Huawei Technologies
F3-1-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
EMail: zhenghaomian@huawei.com
Rakesh Gandhi (editor)
Cisco Systems, Inc.
EMail: rgandhi@cisco.com
Zafar Ali
Cisco Systems, Inc.
EMail: zali@cisco.com
Pawel Brzozowski
ADVA Optical
EMail: PBrzozowski@advaoptical.com
Zhang, et al Expires July 30, 2017 [Page 15]
