PCE Working Group Young Lee
Internet Draft Xian Zhang
Intended status: Informational Haomian Zheng
Huawei
Guoying Zhang
CATR
Expires: August 14, 2014 February 14, 2014
Application-oriented Stateful PCE Architecture and Use-cases for
Transport Networks
draft-lee-pce-app-oriented-arch-01.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)............................7
4.4. Time-based Scheduling....................................7
4.5. Multi-vendor Interoperation..............................8
5. References.....................................................9
5.1. Informative References....................................9
6. Authors' Addresses ............................................10
7. Acknowledgment................................................11
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
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supports the request for path computation issued by a Path
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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---------------
| 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
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
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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. It is worth noting
that the CVI can be an internal interface with respect to the TNC,
or be an external interface from the perspective of transport PCE,
according to the application. In this draft, it is assumed that VPI
is an external interface from the PCE. The VNC is considered as 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. There could be multiple recursive layered
client-server relationships in this architecture. For example,
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. In each relationship, client can be considered as PCC that
requesting service from server which can be considered as PCE. It is
worth noting that one client or PCC can be connected with multiple
servers and vice versa. Such layered relationship is important in
protocol definition work on 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. In this case there are multiple
client-server pairs. Each of the data center can be a client that
request resources from the data center network controller, which is
considered as a server for service provisioning. The data center
network controller is then a client that requesting services from
transport server. The two client pairs are slightly different in
this use case. The first pair is communicating on virtual resources,
while the second pair focuses on allocating physical resources. From
an extended PCE architecture point of view, client-server can be
regarded as PCC-PCE.
For each virtual resource request from client or application, the
VNC keeps the instance and creates an abstracted network topology
based on the network resources allocated to a particular request.
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 physical network resource information and is
needed to be filtered via the VNC's filtering mechanism based on
contract, policy and security. In this way, physical resources are
abstracted into virtual resources.
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
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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
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.
Synchronization is an important issue in layered path computation
procedure. As we assumed, the transport PCE is a stateful PCE with
TED and LSPD. Meanwhile the VNC also needs to maintain databases
that contain virtual topology information, including a virtual TED
and virtual LSPD. The information in these databases is obtained
from the transport PCE databases, with proper mapping scheme. The
mapping mechanism is out of scope for this draft.
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
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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.
4.5. Multi-vendor Interoperation
PCE orchestration is essential in multi-vendor scenario. VNC can be
connected with PCEs from more than one vendor to orchestrate the path
computation. For simplicity, in this case we assume a 'two domains with
two vendors', i.e., each vendor has a PCE within their respective
domain, as shown in Fig. 2.
+--------------+ +--------------+
| Client | | Client |
| Controller A | | Controller B |
+--------------+ +--------------+
/|\ /|\
| |
\|/ \|/
+--------------------------------------------+
| Virtual Network Controller |
| +---------------------+ |
| | Orchestrator | |
| +---------------------+ |
+--------------------------------------------+
/|\ /|\
| |
\|/ \|/
+-----------+ +-----------+
| Transport | | Transport |
| PCE A | | PCE B |
+-----------+ +-----------+
/|\ /|\
| |
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\|/ \|/
///------\\\ //-------\\
||| Vendor ||| ||| Vendor |||
|| A || || B ||
\\\------/// \\-------//
Fig. 2 Architecture for Interoperation
The original path computation request comes from one of the client
controllers, with multiple vendors involved. This request is sent to
VNC, which will then categorize the request into a 'multi-vendor' class.
Before allocating virtual resources, the VNC will determine the domain
path and decompose the path computation request from client controller,
and then send PCReq to two transport PCEs respectively. The path will
be replied to VNC after computation, and corresponding databases are
updated in VNC after establishing the path.
It is worth noting that the architecture in multi-vendor use case is
quite similar to the Hierarchical PCE [H-PCE] but slightly different.
The PCEs belong to different vendors and the VNC may play as a parent
PCE by a service provider, for example, operators.
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.
[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.
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[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.
[NCFV] 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.
[H-PCE] Zhang, F., Zhao, Q., Gonzalez de Dios, O., Casellas R.,
King D., Extensions to Path Computation Element
Communication Protocol (PCEP) for Hierarchical Path
Computation Elements (PCE), draft-zhang-pce-hierarchy-
extensions-04, 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
Huawei Technologies
Email: zhang.xian@huawei.com
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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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