Cross Stratum Optimization enabled Path Computation.
draft-dhody-pce-cso-enabled-path-computation-00
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draft-dhody-pce-cso-enabled-path-computation-00
Network Working Group D. Dhody
Internet-Draft Huawei Technologies India Pvt
Intended status: Informational Ltd
Expires: August 17, 2012 Y. Lee
Huawei Technologies
February 14, 2012
Cross Stratum Optimization enabled Path Computation.
draft-dhody-pce-cso-enabled-path-computation-00
Abstract
Applications like cloud computing, video gaming, HD Video streaming,
Live Concerts, Remote Medical Surgery, etc are offered by Data
Centers. These data centers are geographically distributed and
connected via a network. Many decisions are made in the Application
space without any concern of the underlying network. Cross stratum
application/network optimization focus on the challenges and
opportunities presented by data center based applications and
carriers networks together [CSO-DATACNTR].
Constraint-based path computation is a fundamental building block for
traffic engineering systems such as Multiprotocol Label Switching
(MPLS) and Generalized Multiprotocol Label Switching (GMPLS)
networks. [RFC4655] explains the architecture for a Path Computation
Element (PCE)-based model to address this problem space.
This document explains architecture for CSO enabled Path Computation.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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Task Force (IETF). Note that other groups may also distribute
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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."
This Internet-Draft will expire on August 17, 2012.
Copyright Notice
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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
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. CSO enabled PCE Architecture . . . . . . . . . . . . . . . . . 6
4. Path Computation and Setup Procedure . . . . . . . . . . . . . 9
4.1. Path Setup Using NMS . . . . . . . . . . . . . . . . . . . 10
4.2. Path Setup Using Centralized Control Plane . . . . . . . . 11
4.3. Path Setup using PCE . . . . . . . . . . . . . . . . . . . 12
5. Other Consideration . . . . . . . . . . . . . . . . . . . . . 13
5.1. Inter-domain . . . . . . . . . . . . . . . . . . . . . . . 13
5.1.1. One Application Domain with Multiple Network
Domains . . . . . . . . . . . . . . . . . . . . . . . 13
5.1.2. Multiple Application Domains with Multiple Network
Domains . . . . . . . . . . . . . . . . . . . . . . . 14
5.1.2.1. ACG talks to multiple NCGs . . . . . . . . . . . . 14
5.1.2.2. ACG talks to the primary NCG, which talks to
the other NCG of different domains . . . . . . . . 15
5.2. Bottleneck . . . . . . . . . . . . . . . . . . . . . . . . 16
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
7. Security Considerations . . . . . . . . . . . . . . . . . . . 17
8. Manageability Considerations . . . . . . . . . . . . . . . . . 17
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
9.1. Normative References . . . . . . . . . . . . . . . . . . . 17
9.2. Informative References . . . . . . . . . . . . . . . . . . 17
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1. Introduction
Many application services offered by Data Center to end-users make
significant use of the underlying networks resources in the form of
bandwidth consumption used to carry the actual traffic between a data
center & data center and data center & end-users. There is a need
for cross optimization for both network and application resources.
[CSO-PROBLEM] describes the problem space for cross stratum
optimization.
[NS-QUERY] describes the general problem of network stratum query in
Data Center environments. Network Stratum query is an ability to
query the network from application controller in Data Centers so that
decision would be jointly performed based on both the application and
the network status. Figure 1 shows typical data center architecture.
---------------
---------- | DC 1 |
| End-user |. . . . .>| o o o |
| | | \|/ |
---------- | O |
| ----- --|------
| |
| |
| -----------------|-----------
| / | \
| / ..........O PE1 \ --------------
| | . | | o o o DC 2 |
| | PE4 . PE2 | | \|/ |
----|---O.........................O---|---|---O |
| . | | |
| . PE3 | --------------
\ ..........O Carrier /
\ | Network /
---------------|-------------
|
--------|------
| O |
| /|\ |
| o o o |
| DC 3 |
---------------
Figure 1: Data Center Architecture
Figure 2 shows the context of NS Query within the overarching data
center architecture shown in Figure 1.
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--------------------------------------------
| Application Overlay |
| (Data Centers) |
| |
---------- | -------------- -------------- |
| End-User | | | Application |. . . .| Application | |
| |. . . >| | Control | | Processes | |
---------- | | Gateway (ACG)| -------------- |
| | | -------------- |
| ------------- . . . . | Application | |
| /\ | Related Data | |
| || -------------- |
----------||--------------------------------
||
|| Network Stratum Query (First Stage)
||
----------||--------------------------------
| \/ Network Underlay |
| |
| -------------- ---------------- |
| | Network |. . . | Network | |
| | Control | | Processes | |
| | Gateway (NCG)| ----------------
| | | ---------------- |
| ------------- | Network | |
| |------------->| Related Data | |
| (Second Stage) ---------------- |
-------------------------------------------
Figure 2: NS Query Architecture
NS Query is a two-stage query that consists of two stages:
o A vertical query capability where an external point (i.e., the
Application Control Gateway (ACG) in Data Center) will query the
network (i.e., the Network Control Gateway (NCG)).
o A horizontal query capability where the NCG to gather the
collective information of a variety of horizontal schemes
implemented in the network stratum.
This document describes how PCE Architecture as described in
[RFC4655] can help in the second stage of NS query.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in [RFC2119].
2. Terminology
The following terminology is used in this document.
ACG: Application Control Gateway.
Application Stratum: The application stratum is the functional block
which manages and controls application resources and provides
application resources to a variety of clients/end-users.
Application resources are non-network resources critical to
achieving the application service functionality. Examples
include: application specific servers, storage, content, large
data sets, and computing power. Data Centers are regarded as
tangible realization of the application stratum architecture.
CSO: Cross Stratum Optimization.
GMPLS: Generalized Multiprotocol Label Switching.
LSR: Label Switch Router.
MPLS: Multiprotocol Label Switching.
NCG: Network Control Gateway.
Network Stratum: The network stratum is the functional block which
manages and controls network resources and provides transport of
data between clients/end-users to and among application resources.
Network Resources are resources of any layer 3 or below (L1/L2/L3)
such as bandwidth, links, paths, path processing (creation,
deletion, and management), network databases, path computation,
admission control, and resource reservation capability.
NMS: Network Managemnt System
PCC: Path Computation Client: any client application requesting a
path computation to be performed by a Path Computation Element.
PCE: Path Computation Element. An entity (component, application,
or network node) that is capable of computing a network path or
route based on a network graph and applying computational
constraints.
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PCEP: Path Computation Element Communication Protocol.
TE: Traffic Engineering.
TED: Traffic Engineering Database.
UNI: User Network Interface.
3. CSO enabled PCE Architecture
In the network stratum, the Network Control Gateway (NCG) serves as
the proxy gateway to the network. The NCG receives the query request
from the ACG, probes the network to test the capabilities for data
flow to/from particular point in the network, and gather the
collective information of a variety of horizontal schemes implemented
in the network stratum. This is a horizontal query (Stage 2).
In this document we will describe how PCE fits in this horizontal
scheme.
A Path Computation Element (PCE) is an entity that is capable of
computing a network path or route based on a network graph, and of
applying computational constraints during the computation.
(1) NCG and PCE are co-located.
In this composite solution, the same node implements functionality of
both NCG and PCE. Network stratum query received from the ACG (stage
1), this query is broken into multiple Path computation requests and
handled by PCE functionality. There is no need for PCEP protocol
here.
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+--------------------------------------------------+
| -- -- -- -- -- -- -- -- -- |
| | | | | | | | | | | | | | | | | | | |
| -- -- -- -- -- -- -- -- -- |
| |
| Application Stratum |
| |
| +---------------------------------------+ |
| | | |
+----+ ACG +-----+
| |
+------*---*----------------------------+
| |
| |
| |
+------*---*----------------------------+
| +----------+ +----------+ |
+----+ + *----------* * +-----+
| | | NCG | | PCE | | |
| | | *----------* * | |
| | +----------+ +----------+ | |
| | | |
| +---------------------------------------+ |
| |
| Network Stratum |
| -- -- -- -- -- -- -- -- -- |
| | | | | | | | | | | | | | | | | | | |
| -- -- -- -- -- -- -- -- -- |
+--------------------------------------------------+
Figure 3: NCG and PCE Collocated
(2) NCG and external PCE
In this solution, the external node implements PCE functionality.
Network stratum query received from the ACG (stage 1) converted into
Path computation requests and relayed using the PCEP [RFC5440]
protocol.
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+--------------------------------------------------+
| -- -- -- -- -- -- -- -- -- |
| | | | | | | | | | | | | | | | | | | |
| -- -- -- -- -- -- -- -- -- |
| |
| Application Stratum |
| |
| +---------------------------------------+ |
| | | |
+----+ ACG +-----+
| |
+------*---*----------------------------+
| |
| |
| |
+------*---*-------+
| +----------+ | +----------+
+----+ | | *------* *--------+
| | | NCG | | | PCE | |
| | | | *------* * |
| | +----------+ | +----------+ |
| | | |
| +------------------+ |
| |
| Network Stratum |
| -- -- -- -- -- -- -- -- -- |
| | | | | | | | | | | | | | | | | | | |
| -- -- -- -- -- -- -- -- -- |
+--------------------------------------------------+
Figure 4: NCG and external PCE
PCE has the capability to compute constrained paths on source and
destination(s). Thus it can fit very well in the horizontal query
stage of CSO. PCE has further capability to do multi-layer, inter-
domain path computation which can be further utilized. NCG which
understands the vertical query and the presence of applications can
break the application request into suitable path computation request
which PCE understands. PCE MAY have no knowledge of applications and
thus we can use PCE architecture to achieve the CSO objective.
With this architecture, NCG can request PCE different sets of
computation mode that are not currently supported by PCE. For
instance, NCG may request PCE a multi-destination and multi-source
path computation request. This scenario arises when there are many
possible Data Center choices for a given application request and
there could be multiple sources for this request. Multi-destination
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with a single source (aka., anycast) is a default case for multi-
destination and multi-source path computation.
In addition, with this architecture, NCG may have different sets of
objectives and constraints than typical path computation requests.
For instance, multi-criteria objective functions that combine the
bandwidth requirement and latency may be very useful for some
applications.
In a Statefull PCE, there is a strict synchronization of the network
states (in term of topology and resource information), and the set of
computed paths and reserved resources in use in the network. In
other words, the PCE utilizes information from the TED as well as
information about existing paths (for example, TE LSPs) in the
network when processing new requests. Statefull PCE will be very
important tool to achieve the goals of cross stratum optimization as
maintains the status of final path selected after cross (application
and network) optimization.
As Statefull PCE would keep both LSP ID and the application ID
associated with the LSP, it will make path computation more efficient
in terms of resource usage and computation time. Moreover, Statefull
PCE would have an accurate snapshot of network resource information
and as such it can increase adaptability to the changes. This may be
important for some application that requires a stringent performance
objective.
In conclusion -
o NCG can use the PCE to do path computation based on constrains
from multiple sources and destinations.
o Statefull PCE can help in maintaining the status of the final
cross optimized path. It can also help NCG in maintaining the
relationship of application request and setup path. In case of
any change of the path, the Statefull PCE and NCG and cooperate
and take suitable action.
4. Path Computation and Setup Procedure
Path computation flow is shown in Figure 5.
1. User for application would contact the application gateway ACG
with its requirements.
2. ACG would further query the NCG to obtain the underlying network
status.
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3. NCG would break the vertical request into suitable horizontal
path computation request(s).
4. PCE would provide the result to NCG.
5. NCG would abstract the computation result and provide to ACG.
6. NCG and ACG would cooperate to finalize the path that needs to be
setup.
+----------+ 1 +---------------------------------------+
| |-------->| |
| User | | ACG |
| |<--------| |
+----------+ 6 +---------------------------------------+
^ |
| 2|
| | +----------+ 3 +----------+
| +->| |--------->| |
| | NCG | | PCE |
+-----| |<---------| |
5 +----------+ 4 +----------+
Figure 5: Path Computation Flow
In this section we would analyze the mechanism to finally setup the
cross stratum optimized path.
4.1. Path Setup Using NMS
After ACG and NCG have decided the path that needs to be set, it can
send a request to NMS asking it relay the message to the head end LSR
(also a PCC) to setup the pre computed path. Once the path signaling
is completed and the LSP is setup, PCC should relay the status of the
LSP to the Statefull PCE.
In this mechanism we can reuse the existing NMS to establish the
path. Any updates or deletion of such path would be made via the
NMS.
Head end LSR (PCC) 'H' is always the owner of the path.
See Figure 6 for this scenario.
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+----------+ +---------------------------------------+
| |-------->| |
| User | | ACG |
| |<--------| |
+----------+ +---------------------------------------+
^ |
+-----------------+--+------------------------------------+
|+----------+ | | +----------+ +----------+|
|| | | +->| |--------->| ||
|| NMS | | | NCG | | PCE ||
|| |<----+-----| |<---------| ||
|+----------+ +----------+ +----------+|
| | ^ |
| | +------------------------------------+ |
| | | Network Stratum |
| | -- -- -- -- -- -- -- -- -- |
| +----->|H | | | | | | | | | | | | | | | | | |
| -- -- -- -- -- -- -- -- -- |
+---------------------------------------------------------+
Figure 6: Path Setup Using NMS
4.2. Path Setup Using Centralized Control Plane
A centralized control plane MAY be developed to communicate the cross
optimized path to the head end LSR. This centralized control maybe
achieved via -
o NCG to Control Plane: GMPLS UNI or Open-flow
o Control Plane to Head end Router: GMPLS Control Channel Interface
(CCI)
Suitable Protocol extensions are needed to achieve this.
See Figure 7 for this scenario.
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+----------+ +---------------------------------------+
| |-------->| |
| User | | ACG |
| |<--------| |
+----------+ +---------------------------------------+
^ |
+-----------------+--+------------------------------------+
|+----------+ | | +----------+ +----------+|
|| Central | | +->| |--------->| ||
|| Control | | | NCG | | PCE ||
|| plane |<----+-----| |<---------| ||
|+----------+ +----------+ +----------+|
| | ^ |
| | +------------------------------------+ |
| | | Network Stratum |
| | -- -- -- -- -- -- -- -- -- |
| +----->|H | | | | | | | | | | | | | | | | | |
| -- -- -- -- -- -- -- -- -- |
+---------------------------------------------------------+
Figure 7: Path Setup Using Centralized Control Plane
After cross optimization, ACG and NCG will select the suitable end
points, (the path is already calculated by PCE), this path is
conveyed to the head end LSR which signals the path and notify the
status to the Statefull PCE. Later NCG can send suitable message to
tear down the path.
Using centralized control plane can make the NCG responsible for of
the LSP. Head end LSR signals and maintain the status but the
establishment and tear-down are initiated by the control plane. This
would have an obvious advantage in managing the setup paths. The
Statefull PCE will maintain the TED as well as the status of setup
LSP. NCG through centralized control plan can further setup/
teardown/modify/re-optimize those paths.
4.3. Path Setup using PCE
A Statefull PCE extension MAY be developed to communicate the cross
optimized path to the head end LSR. Current PCEP protocol requires
PCC to trigger Path request and PCE to provide reply. Even in
Statefull PCE, PCC must delegate the LSP to a PCE, a PCE never
initiate path setup. An extension to PCEP protocol MAY let PCE
notify to PCC (Head end LSR) to establish the path.
NCG via PCE and PCEP protocol can establish and tear-down LSP as
shown in Figure 8.
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+----------+ +---------------------------------------+
| |-------->| |
| User | | ACG |
| |<--------| |
+----------+ +---------------------------------------+
^ |
+-----------------+--+------------------------------------+
| | | +----------+ +----------+|
| | +->| |--------->| ||
| | | NCG | | PCE ||
| +-----| |<---------| ||
| +----------+ +----------+|
| +---------------------------------------+ ^ |
| | +------------------------------------+ |
| | | Network Stratum |
| | -- -- -- -- -- -- -- -- -- |
| +->|H | | | | | | | | | | | | | | | | | |
| -- -- -- -- -- -- -- -- -- |
+---------------------------------------------------------+
Figure 8: Path Setup using PCE
5. Other Consideration
5.1. Inter-domain
5.1.1. One Application Domain with Multiple Network Domains
Underlying network connecting the datacenters MAYBE made up of
multiple domains (AS and Area). In this case an inter-domain path
computation is required.
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+----------+ +---------------------------------------+
| |-------->| |
| User | | ACG |
| |<--------| |
+----------+ +---------------------------------------+
^ |
| |
+--------------+ +--+--+------------------------------------+
| +----------+| | | | +----------+ +----------+|
| | || | | +->| |--------->| ||
| | PCE || | | | NCG | | PCE ||
| | || | +-----| |<---------| ||
| +----+-----+| | +----------+ +----+-----+|
| | | | | |
+-------+------+ +-----------------------------------+------+
| |
| |
|<---------------pcep session----------------->|
| |
Figure 9: Multi-domain Scenario
[RFC5441] describes an inter-domain path computation with cooperating
PCEs which can be enhanced and utilized in CSO enabled path
computation.
5.1.2. Multiple Application Domains with Multiple Network Domains
Underlying network connecting the datacenters MAYBE made up of
multiple domains (AS and Area) as well as applications domains and
ACG MAYBE distributed. In such case multiple ACG and NCG will be
involved in cross optimizing. This needs to be analyzed further.
5.1.2.1. ACG talks to multiple NCGs
As shown in Figure 10, ACG where the request originates may
communicate with multiple NCG to get the network information from
multiple domains to be cross optimized.
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Application stratum
+---------------------------+ +---------------------------+
| | | |
| | | |
| | | |
| | | |
| | | |
| +----------------------+ | | +----------------------+ |
| | | | | | | |
+--+ ACG +-+ +--+ ACG +-+
| | | |
+-+-+-------------+-+--+ +-------+-+------------+
| | | +------------+ | |
| | +------------+ | | |
+-+-+--------+ +-----+ +-+-----+-+--+ +-----+
+--+ +---+ +-+ +--+ +----+ ++
| | NCG |---| | | | | NCG |----| ||
| | |---| | | | | |----| ||
| +------------+ | PCE | | | +------------+ | PCE ||
| | | | | | ||
| | |<+--+------------------->| ||
| +-----+ | | +-----+|
|Domain 1 | |Domain 2 |
+---------------------------+ +---------------------------+
Network Stratum
Figure 10: ACG talks to multiple NCG
5.1.2.2. ACG talks to the primary NCG, which talks to the other NCG of
different domains
As shown in Figure 11, ACG communicated only to the primary NCG,
which may gather network information from multiple NCG and then
communicate consolidated information to ACG.
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Application stratum
+---------------------------+ +---------------------------+
| | | |
| | | |
| | | |
| | | |
| | | |
| +----------------------+ | | +----------------------+ |
| | | | | | | |
+--+ ACG +-+ +--+ ACG +-+
| | | |
+-+-+------------------+ +-------+-+------------+
| | | |
| | | |
+-+-+--------+ +-----+ +-------+-+--+ +-----+
+--+ +---+ +-+ +--+ +----+ ++
| | NCG |---| | | | | NCG |----| ||
| | |---| | | | | |----| ||
| +------+-----+ | PCE | | | +---+--------+ | PCE ||
| | | | | | | | ||
| | | |<+--+------+------------>| ||
| | +-----+ | | | +-----+|
|Domain 1 | | |Domain|2 |
+---------+-----------------+ +------+--------------------+
| | Network Stratum
| |
|<------------------------->|
| |
Figure 11: Primary NCG talks to other NCG
5.2. Bottleneck
In optical networks all PCE messages are sent over control channel,
in Statefull PCE cases its observed that in case of a major link or
node failure lot of PCEP messages are sent from all PCC to PCE. This
use lot of bandwidth of the control channel.
PCE MAY become a common point of failure and bottleneck. PCE/NCG/ACG
failure as well as the link-failure disrupting connectivity could be
highly disruptive to the system.
The solution should focus on reducing such bottleneck.
6. IANA Considerations
TBD
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7. Security Considerations
TBD
8. Manageability Considerations
TBD
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
9.2. Informative References
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture",
RFC 4655, August 2006.
[RFC5440] Vasseur, JP. and JL. Le Roux, "Path Computation
Element (PCE) Communication Protocol (PCEP)",
RFC 5440, March 2009.
[RFC5441] Vasseur, JP., Zhang, R., Bitar, N., and JL. Le Roux,
"A Backward-Recursive PCE-Based Computation (BRPC)
Procedure to Compute Shortest Constrained Inter-
Domain Traffic Engineering Label Switched Paths",
RFC 5441, April 2009.
[CSO-DATACNTR] Lee, Y., Bernstein, G., So, N., Kim, T., Shiomoto,
K., and O. Gonzalez-de-Dios, "Research Proposal for
Cross Stratum Optimization (CSO) between Data Centers
and Networks.
(draft-lee-cross-stratum-optimization-datacenter-
00)", March 2011.
[CSO-PROBLEM] Lee, Y., Bernstein, G., So, N., Hares, S., Xia, F.,
Shiomoto, K., and O. Gonzalez-de-Dios, "Problem
Statement for Cross-Layer Optimization.
(draft-lee-cross-layer-optimization-problem-02)",
January 2011.
[NS-QUERY] Lee, Y., Bernstein, G., So, N., McDysan, D., Kim, T.,
Shiomoto, K., and O. Gonzalez-de-Dios, "Problem
Statement for Network Stratum Query.
(draft-lee-network-stratum-query-problem-02)",
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January 2011.
Authors' Addresses
Dhruv Dhody
Huawei Technologies India Pvt Ltd
Leela Palace
Bangalore, Karnataka 560008
INDIA
EMail: dhruv.dhody@huawei.com
Young Lee
Huawei Technologies
1700 Alma Drive, Suite 500
Plano, TX 75075
USA
EMail: leeyoung@huawei.com
Dhody & Lee Expires August 17, 2012 [Page 18]