Network Control Function Virtualization for Transport SDN
draft-lee-network-control-function-virtualization-00
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| Authors | Young Lee , Greg M. Bernstein | ||
| Last updated | 2013-10-14 | ||
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draft-lee-network-control-function-virtualization-00
Network Working Group Young Lee
Internet Draft Huawei Technologies
Intended status: Informational Greg Bernstein
Expires: April 2014 Grotto Networking
Ning So
Tata Communications
October 14, 2013
Network Control Function Virtualization for Transport SDN
draft-lee-network-control-function-virtualization-00.txt
Abstract
This presentation explores the concept of network control function
virtualization for transport SDN to help evolve transport networks
to provide programmable virtual network services with infrastructure
changes to the traditional control plane architecture.
Status of this Memo
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Table of Contents
1. Terminology....................................................2
2. Requirements Language..........................................2
3. Introduction...................................................3
4. Transport SDN Control Architecture.............................4
5. Transport SDN Virtual Network Service..........................6
6. Summary and Conclusion........................................11
7. Acknowledgments...............................................11
8. References....................................................11
8.1. Informative References...................................11
9. Contributors..................................................12
Authors' Addresses...............................................12
Intellectual Property Statement..................................12
Disclaimer of Validity...........................................13
1. Terminology
This document uses the terminology defined in [RFC4655], and
[RFC5440].
2. 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 [RFC2119].
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3. Introduction
One of the main drivers for SDN has been a separation of network
control plane from forwarding plane. This separation alone, however,
would not provide much benefit for transport SDN as this separation
has been already achieved by control plane technology such as
GMPLS/ASON for transport networks. In fact, in transport networks
such separation of data and control plane was dictated at the onset
due to the very different natures of the data plane (circuit
switched TDM or wavelength) and a packet switched control plane.
Another attraction of SDN technology is its logically centralized
control regime which allows a global view of the underlying networks
under its control. The centralized control of SDN helps improve
network resource utilization from a distributed network control.
Transport networks have long used this centralized model via network
management systems and currently supplement it with topology and
resource status information gathered dynamically via GMPLS routing.
For transport network control, PCE technology is essentially
equivalent to a logically centralized control for path computation
function. By combining the strength of GMPLS/ASON [GMPLS] and PCE
[PCE], transport network control plane technology has already been
in a position to take advantage of these SDN concepts.
However, the current transport network control plane technology is
not suitable for virtualization and client programmability, which
are the two of the main drivers for SDN in recent years.
Virtualization refers to allowing the clients to utilize a certain
amount of network resources as if they own them and thus control
their allocated resources in a way most optimal with higher layer or
application processes. This empowerment of client control
facilitates introduction of new services and applications as the
clients are given to create, modify, and delete their virtual
network services. The level of virtual control given to the clients
can vary from a tunnel connecting two end-points to virtual network
elements that consist of a set of virtual nodes and virtual links in
a mesh network topology. As part of the VNS, a client control
concept is added to the traditional VPN along with a client specific
virtual network view. Client control is operated on the view of
virtual network resources allocated to the client. This view is
called abstracted network topology. Such a view may be specific to
the set of client services as well as the particular client. As the
client control is envisioned to support a plethora of applications,
there is another level of virtualization from the client to
individual applications.
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4. Transport SDN Control Architecture
To allow virtualization, the network has to provide open,
programmable interfaces in which clients/applications can create,
replace, modify virtual network services in an interactive manner
while having no impact on other network clients. Traditional
transport network infrastructure is not suitable for providing
programmable interfaces to clients. Direct client control of
transport network elements over existing programmable interfaces
(control or management plane) is not perceived as a viable
proposition for transport network providers due to security and
policy concerns among other reasons.
Hence, the need for network control function virtualization where
there is a "virtualizer" that interfaces directly with client
control and translates/allocates resources (from physical to virtual
and vice versa) and creates abstracted network topology for each
client and interacts with physical network connection control
functions (e.g., GMPLS/ASON for provisioning, PCE for path
computation). The Network control function virtualizer maintains two
interfaces: one interface with physical network control functions
assumed by GMPLS/ASON and PCE, which is termed as VNC-PNC Interface
(VPI); another interface with client control of virtual network,
which is termed as Client-VNC Interface (CVI). Figure 1 depicts the
overall architecture for transport SDN control in which the virtual
network control entity provides network control function
virtualization.
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------------------------------------------
| Application Stratum |
------------------------------------------
/|\ /|\ /|\
| | \|/ North Bound API
| | ---------------
| \|/ | Client |
| -------------- Control |
\|/ | Client |--------
-------------- Control | /|\
| Client |------- |
| Control | /|\ |
-------------- | |
/|\ | | Client-VNC Interface
| | | (CVI)
\|/ \|/ \|/
----------------------------------
| Virtual Network Control (VNC) |
----------------------------------
/|\
| VNC-PNC Interface (VPI)
\|/
----------------------------------
| Physical Network Control (PNC) |
----------------------------------
/|\
| Control Interface to NEs
\|/
Physical Network Infrastructure
Figure 1: Transport SDN control architecture
Figure 1 shows that there are multiple client controls which are
independent to each other and that each client supports various
business applications over its NB API. There are layered client-
server relationships in this architecture. As various applications
are clients to client control, client control itself is also a
client to virtual network control; likewise, virtual network control
is also a client to physical network control. This layered
relationship is important in protocol definition work on NB API, CVI
and VPI interfaces as this allows third-party software developers to
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program client control and virtual network control functions in such
a way to create, modify and delete virtual network services.
5. Transport SDN Virtual Network Service
Virtual Network Service is instantiated by the client control via
the CVI. As client control directly interfaces the application
stratum, it understands multiple application requirements and their
service needs. It is assumed that client control and VNC have the
common knowledge on the end-point interfaces based on their business
negotiation prior to service instantiation. End-point interfaces
refer to client-network physical interfaces that connect client
premise equipment to network provider equipment. Figure 2 shows an
example physical network topology that supports multiple clients. In
this example, client A has three end-points A.1, A.2 and A.3. The
interfaces between clients and transport networks are assumed to be
40G OTU links. For simplicity's sake, all network interfaces are
assumed to be 40G OTU links and all network ports support ODU
switching and grooming on the level of ODU1 and ODU2. Client control
for A provides its traffic demand matrix that describes bandwidth
requirements and other optional QoS parameters (e.g., latency,
diversity requirement, etc.) for each pair of end-point connections.
Figure 2 shows that three independent clients A, B and C provide its
respective traffic demand matrices to the VNC. The physical network
topology shown in Figure 2 is the provider's network topology
created by the PNC's topology creation engine such as the link state
database (LSDB) and Traffic Engineering DB (TEDB) based on control
plane discovery function. This topology is internal to PNC and not
available to the client. What is available to the client is
abstracted network topology (aka, virtual network topology) based on
the negotiated level of abstraction. This is a part of VNS
instantiation between a client control and VNC.
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+------+ +------+ +------+
A.1 ------o o-----------o o----------o o------- A.2
B.1 ------o 1 | | 2 | | 3 |
C.1 ------o o-----------o o----------o o------- B.2
+-o--o-+ +-o--o-+ +-o--o-+
| | | | | |
| | | | | |
| | | | | |
| | +-o--o-+ +-o--o-+
| `-------------o o----------o o------- B.3
| | 4 | | 5 |
`----------------o o----------o o------- C.3
+-o--o-+ +------+
| |
| |
| |
C.2 A.3
Traffic Matrix Traffic Matrix Traffic Matrix
for Client A for Client B for Client C
A.1 A.2 A.3 B.1 B.2 B.3 C.1 C.2 C.3
------------------- ------------------ -----------------
A.1 - 20G 20G B.1 - 40G 40G C.1 - 20G 20G
A.2 20G - 10G B.2 40G - 20G C.2 20G - 10G
A.3 20G 10G - B.3 40G 20G - C.3 20G 10G -
Figure 2: Physical network topology shared with multiple clients
Figure 3 depicts illustrative examples of different level of
topology abstractions that can be provided by the VNC topology
abstraction engine based on physical topology base maintained by the
PNC. The level of topology abstraction is expressed in terms of the
number of virtual network elements (VNEs) and virtual links (VLs).
For example, the abstracted topology for client A shows there are 5
VNEs and 10 VLs. This is by far the most detail topology abstraction
with a minimal link hiding compared to other abstracted topologies
in Figure 3.
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Abstracted Topology for Client A (5 VNEs and 10 VLs)
+------+ +------+ +------+
A.1 ------o o-----------o o----------o o------- A.2
| 1 | | 2 | | 3 |
| | | | | |
+-o----+ +-o----+ +-o----+
| | |
| | |
| | |
| +-o----+ +-o--o-+
| | | | |
| | 4 | | 5 |
`----------------o o----------o |
+----o-+ +------+
|
|
|
A.3
Abstracted Topology for Client B (3 VNEs and 6 VLs)
+------+ +------+
B.1 ------o o-----------------------------o o------ B.2
| 1 | | 3 |
| | | |
+-o----+ +-o----+
\ |
\ |
\ |
`------------------- |
` +-o----+
\ | o------ B.3
\ | 5 |
`-------o |
+------+
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Abstracted Topology for Client B (1 VNE and 3 VLs)
+-------------------------------------------+
| |
| |
C.1 ------o |
| |
| |
| |
| o--------C.3
| |
+--------------------o----------------------+
|
|
|
|
C.2
Figure 3: Topology Abstraction Examples for Clients
As different client has different control/application needs,
abstracted topologies for client B and C, respectively show much
less degree of abstraction. The level of topology abstraction is
determined by the policy (e.g., the granularity level) placed for
the client and/or the path computation results by the PNC's PCE. The
more granular the abstraction topology is, the more control is given
to the client control. If the client controller has applications
that require more granular control of virtual network resources,
then abstracted topology for client A may be the right abstraction
level for such client controller. For instance, if the client is a
third-party virtual service broker/provider, then it would desire
much more sophisticated control of virtual network resources to
support differing application needs. On the other hand, if the
client were only to support simple tunnel services to its
application, then abstracted topology for client C that consists of
one VNE and three VLs would suffice.
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Figure 4 shows workflows across client control, VNC and PNC for the
VNS instantiation, topology exchange, and VNS setup. Client control
"owns" a VNS and initiates by providing the instantiation identifier
with the traffic demand matrix with path selection constraints for
that instance. This VNS instantiation request from Client Control
triggers a path computation request by the virtual PCE (vPCE) agent
in the VNC after VNC's proxy's interlay of this request to the vPCE.
vPCE requests a concurrent path computation request that is
converted based on the traffic demand matrix as part of the VNS
instantiation request from Client Control. Upon receipt of this path
computation request, the PCE in the PNC block computes paths and
updates network topology DB and informs the vPCE agent of the VNC of
the paths and topology updates.
------------------------------------------------------------------
| Client ----------------------------------------------- |
| Control | VNS Control | |
| ----------------------------------------------- |
------------------------------------------------------------------
1.VNS | /|\ 4. Abstracted | /|\
Instantiation | | Topology | |
(instance id, | | | |
Traffic Matr.) | | | | 8. VNS
| | 5. VNS | | Set-up
\|/ | Set-up \|/ | Confirm
------------------------------------------------------------------
| Virtual ------------------------------------------ |
| Network | VNS Proxy | |
| Control ------------------------------------------ |
| ----------------------- ----------------------- |
| | vPCE Agent | | vConnection Ageet | |
| ----------------------- ----------------------- |
------------------------------------------------------------------
2. Path | /|\ 3. PC Reply | /|\
Computation | | with updated | |
Request | | topology | |
| | 6. Network | |8.Network
| | Provisioning | |Provisioning
\|/ | Request \|/ |Confirm
------------------------------------------------------------------
| Physical ------------- -------------------------- |
| Network | PCE | | Network Provisioning ||
| Control ------------- -------------------------- |
------------------------------------------------------------------
Figure 4. Workflows across Client control, VNC and PNC
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It is assumed that the PCE in PNC is a stateful PCE [PCE-S]. vPCE
agent abstracts the network topology into an abstracted topology for
the client based on the agree-upon granularity level. The abstracted
topology is then passed to the VNS control of the Client Control
block. The Client Control's VNS control computes and assigns virtual
network resources for its applications based on the abstracted
topology and creates VNS setup command to the VNC. The VNC's
vConnection module turns this VN setup command into network
provisioning requests over the network elements using control plane
messages such as GMPLS, etc.
6. Summary and Conclusion
This presentation explores the concept of network control function
virtualization for transport SDN to help evolve transport networks
to provide programmable virtual network services with infrastructure
changes to the traditional control plane architecture. The VNC and
its interfaces with the Client Control and the PNC provide control
plane function virtualization over programmable interfaces such as
virtual network path computation and optimization, topology
abstraction hiding details of physical topology while supporting
service-specific objectives the clients demand, maintaining virtual
network service instances and the states, policy enforcement for
virtual network services. With this evolutionary architecture,
virtual network services can be readily introduced while re-using
physical network control plane functions.
7. Acknowledgments
The authors would like to thank Adrian Farrel for many helpful
comments that greatly improved the contents of this draft.
This document was prepared using 2-Word-v2.0.template.dot.
8. References
8.1. Informative References
[PCE] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", IETF RFC
4655, August 2006.
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[PCE-S] Crabbe, E, et. al., "PCEP extension for stateful
PCE",draft-ietf-pce-stateful-pce, work in progress.
[GMPLS] Manning, E., et al., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture, RFC 3945, October 2004.
9. Contributors
Authors' Addresses
Young Lee
Huawei Technologies
1700 Alma Drive, Suite 100
Plano, TX 75075, USA
Phone: (972) 509-5599 (x2240)
Email: leeyoung@huawei.com
Greg Bernstein
Grotto Networking
Fremont, CA, USA
Phone: (510) 573-2237
Email: gregb@grotto-networking.com
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