PCE Working Group Young Lee
Internet Draft Xian Zhang
Intended status: Informational Haomian Zheng
Huawei
Guoying Zhang
CATR
Expires: April 21 2014 October 18, 2013
Application-oriented Stateful PCE Architecture and Use-cases for
Transport Networks
draft-lee-pce-app-oriented-arch-00.txt
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Abstract
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This draft presents an application-oriented stateful PCE
architecture for transport networks. Under this architecture,
several use cases are described.
Conventions used in this document
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].
Table of Contents
1. Introduction...................................................2
2. Terminology....................................................3
3. Architecture and Key Features..................................3
4. Use-cases......................................................5
4.1. Dynamic Data Center Network Interconnection..............6
4.2. Packet-Optical Integration (POI).........................6
4.3. Virtual Network Service (VNS)............................6
4.4. Time-based Scheduling....................................7
5. References.....................................................7
5.1. Informative References....................................7
6. Authors' Addresses .............................................8
7. Acknowledgment.................................................9
1. Introduction
With the emerging applications requiring large bandwidth and dynamic
provisioning, such as Data Center Interconnection(DCI), cloud
bursting and so on, the traditional transport network architecture
is limited as it only provides "dumb pipe" services. These services
lack the flexibility for operation and management. In order to
support the demands, including large bandwidth, low service latency
as well as dynamic and flexible resource allocation, transport
networks may need to be enhanced architecturally such that it could
be aware of application requirements in a dynamic fashion. The Path
Computation Elements (PCE) architecture and the corresponding
protocol extensions provide a mechanism that enables path
computation for transport network. As specified in [RFC4655], a PCE
supports the request for path computation issued by a Path
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Computation Client (PCC). When the PCC is external to the PCE, a
communication protocol, i.e., PCE Protocol (PCEP), is required to
support the path computation request/reply process. Furthermore,
extensions to PCEP are proposed in [PCE-S] , [PCE-I], and [PCE-S-
GMPLS] to enable stateful control over networks including transport
networks.
This draft provides an application-oriented stateful PCE
architecture for transport networks. In particular, this
architecture introduces transport network controller (TNC) component
in which transport PCE plays a central role. Given the high demands
from applications, an interface between the transport network
controller and the application client controller is also introduced
to enable the communication function between these entities. The
application client controller is a special type of PCC with respect
to PCE capability within the transport network controller. This
interface and its communication mechanism between the application
client controller and the transport network controller enables
operation of the transport network with more flexibility.
Specifically, in a larger-scale transport network with multiple
layers or multiple domains, the communication mechanism between
different PCEs and the application client controllers is very
important to satisfy the request from the application stratum.
Current PCEP can provide communication between PCE and PCCs, and
further extensions to PCEP may be desirable to cooperate with new
types of PCCs such as application client controllers.
2. Terminology
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].
3. Architecture and Key Features
In this draft, a PCE-centric architecture which supports
application-oriented transport network is defined. The architecture
is illustrated in Figure 1. The functions of each architectural
component are described. And then interfaces between the stateful
PCE and the other functional blocks in the transport network are
defined.
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------------------------------------------
| Application Stratum |
------------------------------------------
/|\ /|\ /|\
| | \|/ North Bound API
| | ---------------
| \|/ | Client |
| -------------- Control |
\|/ | Client |--------
-------------- Control | /|\
| Client |------- |
| Control | /|\ |
-------------- | |
/|\ | | Client-VNC Interface
| | | (CVI)
\|/ \|/ \|/
----------------------------------
/ | Virtual Network Control (VNC) |
Transport | ----------------------------------
Network | /|\
Controller | | VNC-PCE Interface (VPI)
(TNC) | \|/
| ----------------------------------
\ | Transport PCE |
----------------------------------
/|\
| PCEP
\|/
Physical Network Infrastructure
Figure 1: Application-oriented PCE Architecture for Transport
Network
Transport Network Controller (TNC) in Figure 1 is the core of the
application-oriented PCE architecture for transport network. It is
built around the Transport PCE and provides additional functions
that facilitate multi-layer control, virtual network service control
and other functionalities such as topology abstraction via the
Virtual Network Control (VNC) block. The VNC interfaces can be
different types of client controllers, such as packet network
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controllers, data center provider controllers, enterprise network
controllers, virtual service provider controllers, etc. The VNC
provides network control function virtualization to the PCE and to
the clients via the VNC-PCE Interface (VPI) and the Client-VNC
Interface (CVI), respectively. The VNC allows the clients (via their
client controllers) to program their client-defined virtual network
services (VNS) over the CVI. The VNC also provides abstract network
topology for each client based on the network resources allocated to
the client. In order to facilitate this capability, the VNC needs to
communicate with the PCE via the VPI interface. The VPI can be an
internal interface from an implementation standpoint. In this draft,
it is assumed an external entity from the PCE. The VNC is a PCC to
the PCE.
The VNC provides 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. See [NCFV]
for details of control function virtualization concept. With this
evolutionary architecture built on top of transport PCE, a number of
challenging use-cases can be supported. Transport PCE is a stateful
PCE and supports all the generic stateful PCE functions as described
in [PCE-S] and [PCE-S-GMPLS].
The CVI is an external interface with respect to the transport
network controller (TNC). Client controller is an external client.
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
program client control and virtual network control functions in such
a way to create, modify and delete virtual network services.
4. Use-cases
This section provides a number of use-cases to which the
architecture discussed in Section 3 is applied.
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4.1. Dynamic Data Center Network Interconnection
In the context of multiple data center networks where there is a
need to move large data dynamically from one location to other
location(s), data center network controller is a type of client
controller that coordinates with the virtual network controller
(VNC). This coordination across data center client controller and
the VNC allows multiple instances of inter data center connections
need for different applications.
For each application, the VNC keeps the instance and creates an
abstracted network topology based on the network resources allocated
to a particular application. The data center client controller has
the view of this abstracted network topology and is given a full
control of how to use the allocated virtual resources.
The topology abstraction created by the VNC for the client is based
on the transport PCE's real network resource information and is
needed to be filtered via the VNC's filtering mechanism based on
contract, policy and security.
The VNC interlays client control's request for inter data center
connection and converts into a PC request to the PCE. Then a PCE
instantiates a network path via its provisioning mechanism described
in [PCE-I].
4.2. Packet-Optical Integration (POI)
Client controller can also be a router network controller that needs
transport network interconnections. The router network controller
can request different connection services from the transport network
based on different QoS needs.
Note that this POI use-case is different from multi-layer PCE work
[RFC5623] in that it allows more flexible interactions and more
granular level of abstracted network topologies than tunnel-based
virtual network topology.
4.3. Virtual Network Service (VNS)
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
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premise equipment to network provider equipment. The different level
of topology abstractions 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).
As different client has different control/application needs,
abstracted topologies for a certain client can 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 finer
granularity the abstraction topology is, the more control is given
to the client control. 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 such client is a simple abstracted topology
with a set of end-point tunnels.
4.4. Time-based Scheduling
Transport services with time constraints are another highly-demanded
task in the network. In this scenario, a client controller can
request to reserve some bandwidth for future use. This 'time-based'
service needs to be considered together with the traffic Engineering
Database (TED) and Label Switched Path Database (LSPD). PCE will
compute the scheduled network resource for this 'time-based' service,
and reserve such resources for future use.
In this scenario, the LSPD contains two categories of LSP information,
current LSP in use and scheduled LSP. These two groups of LSP can be
included in a single LSPD or two separate ones, with internal interface
to PCE. PCEP should also be extended to include the scheduled
information for service requests, such as proposed in [Time-based].
With these extensions, the PCC (for example, application stratum) can
generate the path computation request.
5. References
5.1. Informative References
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
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[RFC5440] Vasseur, J. P. and J. L. Le Roux, "Path Computation
Element (PCE) Communication Protocol (PCEP)", RFC 5440,
March 2009.
[RFC5623] Oki, E., Takeda, T., et al, "Framework for PCE-Based
Inter-Layer MPLS and GMPLS Traffic Engineering", RFC 5623,
September 2009.
[PCE-S] Crabbe, E., Medved, J., Minei, I., and R. Varga, "PCEP
Extensions for Stateful PCE", draft-ietf-pce-stateful-pce,
work in progress. [PCE-I] Crabbe, E., Minei, I.,
Sivabalan, S., and Varga, R., "PCEP Extensions for PCE-
initiated LSP Setup in a Stateful PCE Model", draft-
crabbe-pce-pce-initiated-lsp, work in progress.
[PCE-S-GMPLS] Zhang, X., Lee, Y., Casellas, R., Gonzalez de Dios,
O., "Path Computation Element (PCE) Protocol Extensions
for Stateful PCE Usage in GMPLS-controlled Networks",
draft-zhang-pce-pcep-stateful-pce-gmpls-03.txt, work in
progress.
[NCVF] Lee, Y. Bernstein, G., So, N., Fang L., and Ceccarelli, D.
"Network Control Function Virtualization for Transport
SDN", draft-lee-network-control-function-virtualization,
work in progress.
[Time-based] Zhang, X., Lee, Y., Casellas, R., Ganzalez, O.,
"Stateful Path Computation Element (PCE) for Time-based
Scheduling", draft-zhang-pce-stateful-time-based-
scheduling-00, work in progress.
6. Authors' Addresses
Young Lee
Huawei Technologies
5340 Legacy Dr.
Plano, TX 75023, USA
Phone: (469)277-5838
Email: leeyoung@huawei.com
Xian Zhang
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Huawei Technologies
Email: zhang.xian@huawei.com
Haomian Zheng
Huawei Technologies
Email: Zhenghaomian@huawei.com
Guoying Zhang
China Academy of Telecommunication Research of MII
11 Yue Tan Nan Jie Beijing, P.R.China
Phone: +86-10-68094272
Email: zhangguoying@mail.ritt.com.cn
7. Acknowledgment
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