RTGWG C. Villamizar, Ed.
Internet-Draft OCCNC, LLC
Intended status: Informational D. McDysan, Ed.
Expires: August 2, 2012 S. Ning
A. Malis
Verizon
L. Yong
Huawei USA
January 30, 2012
Requirements for MPLS Over a Composite Link
draft-ietf-rtgwg-cl-requirement-05
Abstract
There is often a need to provide large aggregates of bandwidth that
are best provided using parallel links between routers or MPLS LSR.
In core networks there is often no alternative since the aggregate
capacities of core networks today far exceed the capacity of a single
physical link or single packet processing element.
The presence of parallel links, with each link potentially comprised
of multiple layers has resulted in additional requirements. Certain
services may benefit from being restricted to a subset of the
component links or a specific component link, where component link
characteristics, such as latency, differ. Certain services require
that an LSP be treated as atomic and avoid reordering. Other
services will continue to require only that reordering not occur
within a microflow as is current practice.
Current practice related to multipath is described briefly in an
appendix.
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
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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This Internet-Draft will expire on August 2, 2012.
Copyright Notice
Copyright (c) 2012 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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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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Network Operator Functional Requirements . . . . . . . . . . . 5
4.1. Availability, Stability and Transient Response . . . . . . 5
4.2. Component Links Provided by Lower Layer Networks . . . . . 6
4.3. Parallel Component Links with Different Characteristics . 7
5. Derived Requirements . . . . . . . . . . . . . . . . . . . . . 9
6. Management Requirements . . . . . . . . . . . . . . . . . . . 10
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
9. Security Considerations . . . . . . . . . . . . . . . . . . . 11
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
10.1. Normative References . . . . . . . . . . . . . . . . . . . 11
10.2. Informative References . . . . . . . . . . . . . . . . . . 12
10.3. Appendix References . . . . . . . . . . . . . . . . . . . 13
Appendix A. Existing Network Operator Practices and Protocol
Usage . . . . . . . . . . . . . . . . . . . . . . . . 14
Appendix B. Existing Multipath Standards and Techniques . . . . . 14
Appendix C. ITU-T G.800 Composite Link Definitions and
Terminology . . . . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15
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1. Introduction
The purpose of this document is to describe why network operators
require certain functions in order to solve certain business problems
(Section 2). The intent is to first describe why things need to be
done in terms of functional requirements that are as independent as
possible of protocol specifications (Section 4). For certain
functional requirements this document describes a set of derived
protocol requirements (Section 5). Three appendices provide
supporting details as a summary of existing/prior operator approaches
(Appendix A), a summary of implementation techniques and relevant
protocol standards (Appendix B), and a summary of G.800 terminology
used to define a composite link (Appendix C).
1.1. 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].
2. Assumptions
The services supported include L3VPN RFC 4364 [RFC4364], RFC 4797
[RFC4797]L2VPN RFC 4664 [RFC4664] (VPWS, VPLS (RFC 4761 [RFC4761],
RFC 4762 [RFC4762]) and VPMS VPMS Framework
[I-D.ietf-l2vpn-vpms-frmwk-requirements]), Internet traffic
encapsulated by at least one MPLS label, and dynamically signaled
MPLS or MPLS-TP LSPs and pseudowires. The MPLS LSPs supporting these
services may be pt-pt, pt-mpt, or mpt-mpt.
The locations in a network where these requirements apply are a Label
Edge Router (LER) or a Label Switch Router (LSR) as defined in RFC
3031 [RFC3031].
The IP DSCP cannot be used for flow identification since L3VPN
requires Diffserv transparency (see RFC 4031 5.5.2 [RFC4031]), and in
general network operators do not rely on the DSCP of Internet
packets.
3. Definitions
ITU-T G.800 Based Composite and Component Link Definitions:
Section 6.9.2 of ITU-T-G.800 [ITU-T.G.800] defines composite and
component links as summarized in Appendix C. The following
definitions for composite and component links are derived from
and intended to be consistent with the cited ITU-T G.800
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terminology.
Composite Link: A composite link is a logical link composed of a
set of parallel point-to-point component links, where all
links in the set share the same endpoints. A composite link
may itself be a component of another composite link, but only
a strict hierarchy of links is allowed.
Component Link: A point-to-point physical or logical link that
preserves ordering in the steady state. A component link may
have transient out of order events, but such events must not
exceed the network's specific NPO. Examples of a physical
link are: Lambda, Ethernet PHY, and OTN. Examples of a
logical link are: MPLS LSP, Ethernet VLAN, and MPLS-TP LSP.
Flow: A sequence of packets that must be transferred in order on one
component link.
Flow identification: The label stack and other information that
uniquely identifies a flow. Other information in flow
identification may include an IP header, PW control word,
Ethernet MAC address, etc. Note that an LSP may contain one or
more Flows or an LSP may be equivalent to a Flow. Flow
identification is used to locally select a component link, or a
path through the network toward the destination.
Network Performance Objective (NPO): Numerical values for
performance measures, principally availability, latency, and
delay variation. See Appendix A for more details.
4. Network Operator Functional Requirements
The Functional Requirements in this section are grouped in
subsections starting with the highest priority.
4.1. Availability, Stability and Transient Response
Limiting the period of unavailability in response to failures or
transient events is extremely important as well as maintaining
stability. The transient period between some service disrupting
event and the convergence of the routing and/or signaling protocols
MUST occur within a time frame specified by NPO values. Appendix A
provides references and a summary of service types requiring a range
of restoration times.
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FR#1 The solution SHALL provide a means to summarize some routing
advertisements regarding the characteristics of a composite
link such that the routing protocol converges within the
timeframe needed to meet the network performance objective. A
composite link CAN be announced in conjunction with detailed
parameters about its component links, such as bandwidth and
latency. The composite link SHALL behave as a single IGP
adjacency.
FR#2 The solution SHALL ensure that all possible restoration
operations happen within the timeframe needed to meet the NPO.
The solution may need to specify a means for aggregating
signaling to meet this requirement.
FR#3 The solution SHALL provide a mechanism to select a path for a
flow across a network that contains a number of paths comprised
of pairs of nodes connected by composite links in such a way as
to automatically distribute the load over the network nodes
connected by composite links while meeting all of the other
mandatory requirements stated above. The solution SHOULD work
in a manner similar to that of current networks without any
composite link protocol enhancements when the characteristics
of the individual component links are advertised.
FR#4 If extensions to existing protocols are specified and/or new
protocols are defined, then the solution SHOULD provide a means
for a network operator to migrate an existing deployment in a
minimally disruptive manner.
FR#5 Any automatic LSP routing and/or load balancing solutions MUST
not oscillate such that performance observed by users changes
such that an NPO is violated. Since oscillation may cause
reordering, there MUST be means to control the frequency of
changing the component link over which a flow is placed.
FR#6 Management and diagnostic protocols MUST be able to operate
over composite links.
4.2. Component Links Provided by Lower Layer Networks
Case 3 as defined in [ITU-T.G.800] involves a component link
supporting an MPLS layer network over another lower layer network
(e.g., circuit switched or another MPLS network (e.g., MPLS-TP)).
The lower layer network may change the latency (and/or other
performance parameters) seen by the MPLS layer network. Network
Operators have NPOs of which some components are based on performance
parameters. Currently, there is no protocol for the lower layer
network to inform the higher layer network of a change in a
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performance parameter. Communication of the latency performance
parameter is a very important requirement. Communication of other
performance parameters (e.g., delay variation) is desirable.
FR#7 In order to support network NPOs and provide acceptable user
experience, the solution SHALL specify a protocol means to
allow a lower layer server network to communicate latency to
the higher layer client network.
FR#8 The precision of latency reporting SHOULD be at least 10% of
the one way latencies for latency of 1 ms or more.
FR#9 The solution SHALL provide a means to limit the latency on a
per LSP basis between nodes within a network to meet an NPO
target when the path between these nodes contains one or more
pairs of nodes connected via a composite link.
The NPOs differ across the services, and some services have
different NPOs for different QoS classes, for example, one QoS
class may have a much larger latency bound than another.
Overload can occur which would violate an NPO parameter (e.g.,
loss) and some remedy to handle this case for a composite link
is required.
FR#10 If the total demand offered by traffic flows exceeds the
capacity of the composite link, the solution SHOULD define a
means to cause the LSPs for some traffic flows to move to some
other point in the network that is not congested. These
"preempted LSPs" may not be restored if there is no
uncongested path in the network.
4.3. Parallel Component Links with Different Characteristics
Corresponding to Case 1 of [ITU-T.G.800], as one means to provide
high availability, network operators deploy a topology in the MPLS
network using lower layer networks that have a certain degree of
diversity at the lower layer(s). Many techniques have been developed
to balance the distribution of flows across component links that
connect the same pair of nodes. When the path for a flow can be
chosen from a set of candidate nodes connected via composite links,
other techniques have been developed.
FR#11 The solution SHALL measure traffic on a labeled traffic flow
and dynamically select the component link on which to place
this flow in order to balance the load so that no component
link in the composite link between a pair of nodes is
overloaded.
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FR#12 When a traffic flow is moved from one component link to
another in the same composite link between a set of nodes (or
sites), it MUST be done so in a minimally disruptive manner.
When a flow is moved from a current link to a target link with
different latency, reordering can occur if the target link
latency is less than that of the current or clumping can occur
if target link latency is greater than that of the current.
Therefore, some flows (e.g., timing distribution, PW circuit
emulation) are quite sensitive to these effects, which may be
specified in an NPO or are needed to meet a user experience
objective (e.g. jitter buffer under/overrun).
FR#13 The solution SHALL provide a means to identify flows whose
rearrangement frequency needs to be bounded by a configured
value.
FR#14 The solution SHALL provide a means that communicates whether
the flows within an LSP can be split across multiple component
links. The solution SHOULD provide a means to indicate the
flow identification field(s) which can be used along the flow
path which can be used to perform this function.
FR#15 The solution SHALL provide a means to indicate that a traffic
flow shall select a component link with the minimum latency
value.
FR#16 The solution SHALL provide a means to indicate that a traffic
flow shall select a component link with a maximum acceptable
latency value as specified by protocol.
FR#17 The solution SHALL provide a means to indicate that a traffic
flow shall select a component link with a maximum acceptable
delay variation value as specified by protocol.
FR#18 The solution SHALL provide a means local to a node that
automatically distributes flows across the component links in
the composite link such that NPOs are met.
FR#19 The solution SHALL provide a means to distribute flows from a
single LSP across multiple component links to handle at least
the case where the traffic carried in an LSP exceeds that of
any component link in the composite link. As defined in
section 3, a flow is a sequence of packets that must be
transferred on one component link.
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FR#20 The solution SHOULD support the use case where a composite
link itself is a component link for a higher order composite
link. For example, a composite link comprised of MPLS-TP bi-
directional tunnels viewed as logical links could then be used
as a component link in yet another composite link that
connects MPLS routers.
FR#21 The solution MUST support an optional means for LSP signaling
to bind an LSP to a particular component link within a
composite link. If this option is not exercised, then an LSP
that is bound to a composite link may be bound to any
component link matching all other signaled requirements, and
different directions of a bidirectional LSP can be bound to
different component links.
FR#22 The solution MUST support a means to indicate that both
directions of co-routed bidirectional LSP MUST be bound to the
same component link.
5. Derived Requirements
This section takes the next step and derives high-level requirements
on protocol specification from the functional requirements.
DR#1 The solution SHOULD attempt to extend existing protocols
wherever possible, developing a new protocol only if this adds
a significant set of capabilities.
DR#2 A solution SHOULD extend LDP capabilities to meet functional
requirements (without using TE methods as decided in
[RFC3468]).
DR#3 Coexistence of LDP and RSVP-TE signaled LSPs MUST be supported
on a composite link. Other functional requirements should be
supported as independently of signaling protocol as possible.
DR#4 When the nodes connected via a composite link are in the same
MPLS network topology, the solution MAY define extensions to
the IGP.
DR#5 When the nodes are connected via a composite link are in
different MPLS network topologies, the solution SHALL NOT rely
on extensions to the IGP.
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DR#6 The Solution SHOULD support composite link IGP advertisement
that results in convergence time better than that of
advertising the individual component links. The solution SHALL
be designed so that it represents the range of capabilities of
the individual component links such that functional
requirements are met, and also minimizes the frequency of
advertisement updates which may cause IGP convergence to occur.
Examples of advertisement update triggering events to be
considered include: LSP establishment/release, changes in
component link characteristics (e.g., latency, up/down state),
and/or bandwidth utilization.
DR#7 When a worst case failure scenario occurs, the number of
RSVP-TE LSPs to be resignaled will cause a period of
unavailability as perceived by users. The resignaling time of
the solution MUST meet the NPO objective for the duration of
unavailability. The resignaling time of the solution MUST not
increase significantly as compared with current methods.
6. Management Requirements
MR#1 Management Plane MUST support polling of the status and
configuration of a composite link and its individual composite
link and support notification of status change.
MR#2 Management Plane MUST be able to activate or de-activate any
component link in a composite link in order to facilitate
operation maintenance tasks. The routers at each end of a
composite link MUST redistribute traffic to move traffic from a
de-activated link to other component links based on the traffic
flow TE criteria.
MR#3 Management Plane MUST be able to configure a LSP over a
composite link and be able to select a component link for the
LSP.
MR#4 Management Plane MUST be able to trace which component link a
LSP is assigned to and monitor individual component link and
composite link performance.
MR#5 Management Plane MUST be able to verify connectivity over each
individual component link within a composite link.
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MR#6 Management Plane SHOULD provide the means for an operator to
initiate an optimization process.
7. Acknowledgements
Frederic Jounay of France Telecom and Yuji Kamite of NTT
Communications Corporation co-authored a version of this document.
A rewrite of this document occurred after the IETF77 meeting.
Dimitri Papadimitriou, Lou Berger, Tony Li, the WG chairs John Scuder
and Alex Zinin, and others provided valuable guidance prior to and at
the IETF77 RTGWG meeting.
Tony Li and John Drake have made numerous valuable comments on the
RTGWG mailing list that are reflected in versions following the
IETF77 meeting.
8. IANA Considerations
This memo includes no request to IANA.
9. Security Considerations
This document specifies a set of requirements. The requirements
themselves do not pose a security threat. If these requirements are
met using MPLS signaling as commonly practiced today with
authenticated but unencrypted OSPF-TE, ISIS-TE, and RSVP-TE or LDP,
then the requirement to provide additional information in this
communication presents additional information that could conceivably
be gathered in a man-in-the-middle confidentiality breach. Such an
attack would require a capability to monitor this signaling either
through a provider breach or access to provider physical transmission
infrastructure. A provider breach already poses a threat of numerous
tpes of attacks which are of far more serious consequence. Encrption
of the signaling can prevent or render more difficult any
confidentiality breach that otherwise might occur by means of access
to provider physical transmission infrastructure.
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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10.2. Informative References
[I-D.ietf-l2vpn-vpms-frmwk-requirements]
Kamite, Y., JOUNAY, F., Niven-Jenkins, B., Brungard, D.,
and L. Jin, "Framework and Requirements for Virtual
Private Multicast Service (VPMS)",
draft-ietf-l2vpn-vpms-frmwk-requirements-03 (work in
progress), July 2010.
[ITU-T.G.800]
ITU-T, "Unified functional architecture of transport
networks", 2007, <http://www.itu.int/rec/T-REC-G/
recommendation.asp?parent=T-REC-G.800>.
[RFC2702] Awduche, D., Malcolm, J., Agogbua, J., O'Dell, M., and J.
McManus, "Requirements for Traffic Engineering Over MPLS",
RFC 2702, September 1999.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3468] Andersson, L. and G. Swallow, "The Multiprotocol Label
Switching (MPLS) Working Group decision on MPLS signaling
protocols", RFC 3468, February 2003.
[RFC3809] Nagarajan, A., "Generic Requirements for Provider
Provisioned Virtual Private Networks (PPVPN)", RFC 3809,
June 2004.
[RFC4031] Carugi, M. and D. McDysan, "Service Requirements for Layer
3 Provider Provisioned Virtual Private Networks (PPVPNs)",
RFC 4031, April 2005.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, February 2006.
[RFC4664] Andersson, L. and E. Rosen, "Framework for Layer 2 Virtual
Private Networks (L2VPNs)", RFC 4664, September 2006.
[RFC4665] Augustyn, W. and Y. Serbest, "Service Requirements for
Layer 2 Provider-Provisioned Virtual Private Networks",
RFC 4665, September 2006.
[RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
(VPLS) Using BGP for Auto-Discovery and Signaling",
RFC 4761, January 2007.
[RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service
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(VPLS) Using Label Distribution Protocol (LDP) Signaling",
RFC 4762, January 2007.
[RFC4797] Rekhter, Y., Bonica, R., and E. Rosen, "Use of Provider
Edge to Provider Edge (PE-PE) Generic Routing
Encapsulation (GRE) or IP in BGP/MPLS IP Virtual Private
Networks", RFC 4797, January 2007.
[RFC5254] Bitar, N., Bocci, M., and L. Martini, "Requirements for
Multi-Segment Pseudowire Emulation Edge-to-Edge (PWE3)",
RFC 5254, October 2008.
10.3. Appendix References
[I-D.ietf-pwe3-fat-pw]
Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,
J., and S. Amante, "Flow Aware Transport of Pseudowires
over an MPLS PSN", draft-ietf-pwe3-fat-pw-03 (work in
progress), January 2010.
[RFC1717] Sklower, K., Lloyd, B., McGregor, G., and D. Carr, "The
PPP Multilink Protocol (MP)", RFC 1717, November 1994.
[RFC2475] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[RFC2615] Malis, A. and W. Simpson, "PPP over SONET/SDH", RFC 2615,
June 1999.
[RFC2991] Thaler, D. and C. Hopps, "Multipath Issues in Unicast and
Multicast Next-Hop Selection", RFC 2991, November 2000.
[RFC2992] Hopps, C., "Analysis of an Equal-Cost Multi-Path
Algorithm", RFC 2992, November 2000.
[RFC3260] Grossman, D., "New Terminology and Clarifications for
Diffserv", RFC 3260, April 2002.
[RFC4201] Kompella, K., Rekhter, Y., and L. Berger, "Link Bundling
in MPLS Traffic Engineering (TE)", RFC 4201, October 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC4385] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for
Use over an MPLS PSN", RFC 4385, February 2006.
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[RFC4928] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal
Cost Multipath Treatment in MPLS Networks", BCP 128,
RFC 4928, June 2007.
Appendix A. Existing Network Operator Practices and Protocol Usage
The network operator practices appendix has been moved to a separate
document. When that document has an XML I-D tag the references to
this appendix will be changed to that document and this appendix will
be deleted.
Appendix B. Existing Multipath Standards and Techniques
The multipath standards and techniques appendix has been moved to a
separate document. When that document has an XML I-D tag the
references to this appendix will be changed to that document and this
appendix will be deleted.
Appendix C. ITU-T G.800 Composite Link Definitions and Terminology
Composite Link:
Section 6.9.2 of ITU-T-G.800 [ITU-T.G.800] defines composite link
in terms of three cases, of which the following two are relevant
(the one describing inverse (TDM) multiplexing does not apply).
Note that these case definitions are taken verbatim from section
6.9, "Layer Relationships".
Case 1: "Multiple parallel links between the same subnetworks
can be bundled together into a single composite link. Each
component of the composite link is independent in the sense
that each component link is supported by a separate server
layer trail. The composite link conveys communication
information using different server layer trails thus the
sequence of symbols crossing this link may not be preserved.
This is illustrated in Figure 14."
Case 3: "A link can also be constructed by a concatenation of
component links and configured channel forwarding
relationships. The forwarding relationships must have a 1:1
correspondence to the link connections that will be provided
by the client link. In this case, it is not possible to
fully infer the status of the link by observing the server
layer trails visible at the ends of the link. This is
illustrated in Figure 16."
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Subnetwork: A set of one or more nodes (i.e., LER or LSR) and links.
As a special case it can represent a site comprised of multiple
nodes.
Forwarding Relationship: Configured forwarding between ports on a
subnetwork. It may be connectionless (e.g., IP, not considered
in this draft), or connection oriented (e.g., MPLS signaled or
configured).
Component Link: A topolological relationship between subnetworks
(i.e., a connection between nodes), which may be a wavelength,
circuit, virtual circuit or an MPLS LSP.
Authors' Addresses
Curtis Villamizar (editor)
OCCNC, LLC
Email: curtis@occnc.com
Dave McDysan (editor)
Verizon
22001 Loudoun County PKWY
Ashburn, VA 20147
Email: dave.mcdysan@verizon.com
So Ning
Verizon
2400 N. Glenville Ave.
Richardson, TX 75082
Phone: +1 972-729-7905
Email: ning.so@verizonbusiness.com
Andrew Malis
Verizon
117 West St.
Waltham, MA 02451
Phone: +1 781-466-2362
Email: andrew.g.malis@verizon.com
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Lucy Yong
Huawei USA
1700 Alma Dr. Suite 500
Plano, TX 75075
Phone: +1 469-229-5387
Email: lucyyong@huawei.com
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