Internet DRAFT - draft-takeda-l1vpn-framework
draft-takeda-l1vpn-framework
Network Working Group Tomonori Takeda (Editor)
Internet Draft NTT
Proposed Status: Informational
Expires: December 2005 June 2005
Framework and Requirements for Layer 1 Virtual Private Networks
draft-takeda-l1vpn-framework-04.txt
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Abstract
This document provides a framework and service level requirements
for Layer 1 Virtual Private Networks (L1VPNs). This framework is
intended to aid in developing and standardizing protocols and
mechanisms to support interoperable L1VPNs.
The document examines motivations for L1VPNs, high level (service
level) requirements, and outlines some of the architectural models
that might be used to build L1VPNs.
Contents
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1. Contributors ............................................... 2
2. Terminology ................................................ 3
3. Introduction ............................................... 4
3.1 Overview ................................................... 5
3.1.1 Network Topology ........................................... 5
3.1.2 Introducing Layer 1 VPNs ................................... 5
3.1.3 Current Technologies for Dynamic Layer 1 Provisioning ...... 5
3.2 Relationship with ITU-T .................................... 6
4. Motivations ................................................ 7
4.1 Basic Layer 1 Services ..................................... 7
4.1.1 L1VPN for Dynamic Layer 1 Provisioning ..................... 8
4.2 Merits of L1VPN ............................................ 8
4.2.1 Customer Merits ............................................ 8
4.2.2 Provider Merits ............................................ 9
4.3 L1VPN Deployment Scenarios ................................. 9
4.3.1 Multi-Service Backbone ..................................... 9
4.3.2 Carrier's Carrier .......................................... 10
4.3.3 Layer 1 Resource Trading .................................. 10
4.3.4 Inter-SP L1VPN ............................................. 11
4.3.5 Other Scenarios ............................................ 11
5. Reference Models ........................................... 11
5.1 Management Systems ......................................... 12
6. Generic Service Description ................................ 13
6.1 CE Construct ............................................... 13
6.2 Generic Service Features ................................... 13
7. Service Models ............................................. 13
7.1 Management-based Service Model ............................. 14
7.2 Signaling-based Service Model (Basic Mode) ................. 14
7.2.1 Overlay Service Model ...................................... 15
7.3 Signaling and Routing Service Model (Enhanced Mode) ........ 15
7.3.1 Overlay Extension Service Model ............................ 16
7.3.2 Virtual Node Service Model ................................. 16
7.3.3 Virtual Link Service Model ................................. 17
7.3.4 Per-VPN Peer Service Model ................................. 18
8. Service Models and Service Requirements .................... 18
8.1 Detailed Service Level Requirements ........................ 20
9. Security Considerations .................................... 21
9.1 Types of Information ....................................... 21
9.2 Security Features .......................................... 22
9.3 Scenarios .................................................. 22
10. Acknowledgements ........................................... 23
11. Normative References ....................................... 23
12. Informative References ..................................... 23
13. Authors' Addresses ......................................... 24
14. Intellectual Property Consideration ........................ 25
15. Full Copyright Statement ................................... 26
1. Contributors
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This document is based heavily on the work of ITU-T Study Group 13
Question 11. SG13/Q11 has been investigating the service requirements
and architecture for Layer 1 VPNs for some time, and this document
is a summary and development of the conclusions they have reached. As
such, ITU-T SG13 should be seen as a major contributor to this
document.
The details of this document are the result of contributions from
several authors who are listed here in alphabetic order. Contact
details for these authors can be found in a separate section near
the end of this document.
Raymond Aubin (Nortel)
Marco Carugi (Nortel)
Ichiro Inoue (NTT)
Hamid Ould-Brahim (Nortel)
Tomonori Takeda (NTT)
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].
The reader is assumed to be familiar with the terminology in
[RFC3031], [RFC3209], [RFC3471], [RFC3473], [GMPLS-ROUTING] and
[RFC4026].
In addition, following new terms are used within this document.
- Virtual link: A provider network TE link advertised to customers in
routing information for purposes which include path computation. A
data link may or may not exist between the two end points of a
virtual link.
- Virtual node: A provider network logical node advertised to
customers in routing information. A virtual node may represent a
single physical node, or multiple physical nodes and links.
- VPN end point: A CE's data plane interface, which is connected to a
PE device, and which is part of the VPN membership. Note that a
data plane interface is associated with a TE link end point. For
example, if a CE router's interface is a channelized interface
(defined in SONET/SDH), a channel in the channelized interface can
be a data plane interface.
- VPN connection (or connection in the L1VPN context): A connection
between a pair of VPN end points. Note that in some scenarios, a
connection may be established between a pair of Cs (customer
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devices), using this CE-CE VPN connection as a segment or
forwarding adjacency.
Note that following terms are aligned with PPVPN terminology
[RFC4026], and in this document, have a meaning in the context of
L1VPNs, unless otherwise specified.
- CE (Customer Edge) device: A CE device is a customer device that
receives L1VPN service from the provider. A CE device is connected
to at least one PE device. A CE device can be a variety of devices,
for example, TDM cross connect, router, and L2 switch. A CE device
does not have to have the capability to switch at layer 1, but it
must be capable of receiving a layer 1 signal and either switching
it or terminating it with adaptation. A CE device may also be
attached to one or more C devices on the customer site.
- PE (Provider Edge) device: A PE device is a provider device that
provides L1VPN service to the customer. A PE device is connected to
at least one CE device. A layer 1 PE device is a Time Division
Multiplex (TDM) switch, an Optical Cross-Connect (OXC), a Fiber
Switch (FXC), or a PE device may be an EPL (Ethernet Private Line)
type of device, that maps Ethernet frames onto layer 1 connections.
- P (Provider) device: A P device is a provider device, which is
connected only to other provider devices (P or PE devices). A layer
1 P is a TDM switch, OXC, or FXC.
- Customer: A Customer has authority over a set of CE devices within
the same VPN (e.g., the owner of CE devices). Note that a customer
may outsource the management of CE devices to other organizations,
including to the provider itself.
- Provider: A Provider has authority over the management of the
provider network.
3. Introduction
The document examines motivations for Layer 1 Virtual Private
Networks (L1VPNs), provides high level (service level) requirements,
and outlines some of the architectural models that might be used to
build L1VPNs.
The objective of the document is mainly to present the requirements
and architecture work in this field that has been undertaken within
the ITU-T.
L1VPNs provide services over layer 1 networks. This document provides
a framework for L1VPNs and the realization of the framework by those
networks being controlled by GMPLS protocols.
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3.1 Overview
3.1.1 Network Topology
The layer 1 network, made of Optical Cross-Connects (OXCs), Time
Division Multiplex (TDM) capable switches, or Fiber Switches (FXCs)
may be seen as consisting of provider edge (PE) devices that give
access from outside of the network, and provider (P) devices that
operate only within the core of the network. Similarly, outside the
layer 1 network is the customer network consisting of customer (C)
devices with access to the layer 1 network made through customer edge
(CE) devices.
A CE and PE are connected by one or more links. A CE may also be
connected to more than one PE, and a PE may have more than one CE
connected to it.
3.1.2 Introducing Layer 1 VPNs
The concept of a provider provisioned VPN (PPVPN) has been
established through many previous documents such as [L2VPN-FRAME] and
[L3VPN-FRAME]. Terminology for PPVPNs is set out in [RFC4026] with
special reference to layer 2 and layer 3 VPNs.
The realization of Layer 1 VPNs (L1VPNs) can be based on extensions
of the concepts of the PPVPN to the layer 1 network. It must be
understood that meeting the requirements set out in this document may
necessitate modifications to the existing mechanisms both for the
control plane within the layer 1 network and for service provisioning
at the edge of the network (CE and PE devices). It is at the
interface between CE and PE devices that the L1VPN service is
provided.
Note that one of the fundamental differences between L1VPNs and L2/L3
VPNs is that in L1VPNs data plane connectivity does not guarantee
control plane connectivity (and vice versa). CE-PE control plane
connectivity is essential, and CE-CE data plane connectivity is
maintained by signaling mechanisms based on this control plane
connectivity. The provision of CE-CE control plane connectivity over
the provider network is also a unique aspect of the L1VPN services,
by which control packets can be exchanged between CEs over the
control plane of the provider network.
3.1.3 Current Technologies for Dynamic Layer 1 Provisioning
Pre-existing efforts at standardization have focused on the provision
of dynamic connections within the layer 1 network (signaling and
routing), and the interfaces for requesting services between the CE
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and PE, or between PEs at network boundaries (UNI and E-NNI
respectively).
Current UNIs include features to facilitate requests for end-to-end
(that is, CE to CE) services that include the specification
of constraints such as explicit paths, bandwidth requirements,
protection needs, and (of course) destinations.
Current E-NNIs include features to exchange routing information, as
well as to facilitate requests for end-to-end services.
The UNIs and E-NNIs, however, do not provide a sufficiently high
level of service to support VPNs without some additions. For example,
there is no way to distinguish between control messages received over
a shared control link (i.e., a control link shared by multiple VPNs)
at a UNI/E-NNI, and these messages must be disambiguated to determine
the L1VPN to which they apply.
Furthermore, there is no clear defined way to restrict connectivity
among CEs (or over a UNI/E-NNI). In addition, E-NNIs allow routing
information exchange, but there is no clear defined way to allow
limited routing information exchange (i.e., a specific set of routing
information is distributed to a specific set of CEs).
In order that L1VPNs can be supported in a fully functional manner,
these deficiencies and other requirements set out later in this
document must be addressed.
3.2 Relationship with ITU-T
This document is based on the work of the ITU-T Study Group 13
Question 11. This group has been researching and specifying both the
requirements and the architecture of L1VPNs for some time. In this
context, this document is a representation of the findings of the
ITU-T, and a presentation of those findings in terms and format that
are familiar to the IETF.
In particular, this document is limited to the areas of concern of
the IETF. That is, it is limited to layer 1 networks that utilize
IP as the underlying support for their control plane.
This document presents the requirements and architectures developed
within the ITU-T for better understanding within the IETF and to
further cooperation between the two bodies.
Some work related to the L1VPN solution space has already been done
within the IETF. This document sets a framework of requirements and
architecture into which solutions can fit.
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4. Motivations
In this discussion many merits and motivations may be taken for
granted.
The general benefits and desirability of VPNs has been described
many times and in many places. This document does not dwell on the
merits of VPNs as such, but focuses entirely on the applicability
of the VPN concept to layer 1 networks.
Similarly, the utility and value of a control plane for the
configuration, management and operation of a layer 1 network is
well-rehearsed.
4.1 Basic Layer 1 Services
Basic layer 1 services may be characterized in terms that include:
- Connectivity: Between a pair of CEs.
- Capacity: For example, the bit rate for a TDM service or the
capacity of a lambda.
- Transparency: For example, for an SDH network, overhead
transparency.
- Availability: The percentage of time that the offered service
meets the agreed criteria. To achieve the required level of
availability for the customer connections the service provider's
network may use restoration or protected resources.
- Performance: The quality of the service delivered to customers,
e.g., the number of error-seconds per month.
The layer 1 services may be categorized based on the combination of
connectivity features (data plane) and service control capability
features (control plane) available to the customer. A CE is
associated with the service interface between a customer site and the
provider network, and the categorization can be seen in the context
of this service interface as follows.
1. A single connection between a pair of CEs.
- Static Service
The classic private line service achieved through a permanent
connection.
- Dynamic Service
Either a switched connection service, or a customer-controlled
soft permanent connection service
2. Multiple connections among a set of CEs.
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- Static Service
A private network service consisting of a mesh of permanent
connections.
- Dynamic Service
A dynamic private network service consisting of any combination
of switched connection services and customer-controlled soft
permanent connection services.
For both service types, connections are point-to-point, and can be
permanent, soft-permanent, or switched. For a static service, the
management plane of the provider network is responsible for the
management of both the network infrastructure and the end-user
connections. For dynamic services, the management plane of the
provider network is only responsible for the configuration of the
infrastructure; end-user connections are established dynamically via
the control plane of the provider network upon customer request.
Note that the ITU-T allows the second categorization of service type
to embrace a variety of control plane types.
4.1.1 L1VPN for Dynamic Layer 1 Provisioning
Private network services in the second category (above) can be
enhanced so that multiple private networks are supported across the
layer 1 network as virtual private networks. These are Layer 1
Virtual Private Networks (L1VPNs). Note the first category (above)
would include L1VPNs with only two CEs as a special case.
Compared to the first category of service, the L1VPN service has
features such as connectivity restriction, a separate policy per VPN,
and distribution of membership information.
4.2 Merits of L1VPN
4.2.1 Customer Merits
From the customer's perspective, there are two main benefits to a
L1VPN. These benefits apply over and above the advantages of access
to a dynamically provisioned network.
- The customer can outsource the direct management of an optical
network by placing the VPN management in the control of a third
party. This frees the customer from the need to configure and
manage the connectivity information for the CEs that participate
in the VPN.
- The customer can make small-scale use of an optical network. So,
for example, by sharing access to the optical network with many
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other users, the customer sites can be connected together across
the optical network without bearing the full cost of deploying
and managing the optical network.
To some extent, the customer may also gain from the provider's
benefits (see below). That is, if the provider is able to extract
more value from the layer 1 network, and provide better
differentiated services, the customer will benefit from lower
priced services that are better tailored to the customer's needs.
4.2.2 Provider Merits
The provider benefits from the customer's perception of benefits.
In particular, the provider can build on dynamic, on-demand services
by offering new VPN services and off-loading the CE-to-CE
configuration requirements from the customers.
Additionally, a more flexible VPN structure applied to the optical
network allows the provider to make more comprehensive use of the
spare (that is, previously unused) resources within the network. In
particular, since the PE could be responsible for routing the
connection through the optical network, the optical network can
reclaim control of how resources are used and adjust the paths so
that optimal use is made of all available resources.
4.3 L1VPN Deployment Scenarios
In large carrier networks providing various kinds of service, it is
often the case that multiple service networks are supported over a
shared transport network. L1VPNs are expected to support this type of
network architecture. Namely, by applying L1VPNs, multiple internal
service networks (which may be managed and operated separately) can
be supported over a shared layer 1 transport network controlled and
managed by GMPLS. In addition, L1VPNs can support capabilities to
offer innovative services to external clients.
Some more specific deployment scenarios are as follows.
4.3.1 Multi-Service Backbone
A multi-service backbone is characterized in terms such that each
service department of a carrier that receives the carrier's L1VPN
service provides a different kind of higher-layer service. The
customer receiving the L1VPN service (i.e., each service department)
can offer its own services whose payloads can be any layer (e.g.,
ATM, IP, TDM). From the L1VPN service provider's point of view, these
services are not visible and are not part of the L1VPN service. That
is, the type of service being carried within the layer 1 payload is
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not known by the service provider.
The benefit is that the same layer 1 core network resources are
shared by multiple services. A large capacity backbone network (data
plane) can be built economically by having the resources shared by
multiple services usually with flexibility to modify topologies,
while separating the control functions. Thus, each customer can
select a specific set of features that are needed to provide their
own service.
Note that it is also possible to control and manage these service
networks and the layer 1 core network by using GMPLS as a unified
control plane, instead of using L1VPNs. However, using L1VPNs is
beneficial in the following points.
- Independent address space for each of the service networks.
- Network isolation (topology information isolation, fault isolation
among service networks).
- Independent layer 1 resource view for each of the service networks.
- Independent policies that could be applied for each of the service
networks.
4.3.2 Carrier's Carrier
A carrier's carrier is characterized in terms such that one carrier
that receives another carrier's L1VPN service provides its own
services. In this scenario, two carriers may be in different
organizations (or may be separately managed within the same
organization). It is, therefore, expected that the information
provided at the service demarcation points is more limited than in
the multi-service backbone case. Similarly, less control of the
L1VPN service is given at the service demarcation points. For
example, customers of an L1VPN service receive:
- A more limited view of the L1VPN service provider network.
- More limited control over the L1VPN service provider network.
One of the merits is that each carrier can concentrate on a specific
service. For example, the customer of the L1VPN service may focus on
L3 services, e.g., providing secure access to the Internet, leaving
the L1VPN provider to focus on the layer 1 service, e.g., providing a
long haul bandwidth between cities. The L1VPN customer can construct
its own network using layer 1 resources supplied by the L1VPN
provider, usually with flexibility to modify topologies, and utilize
dedicated control plane functionalities.
4.3.3 Layer 1 Resource Trading
In addition to the scenarios where the second tier service provider
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is using a single core service provider as mentioned above, it is
possible for the second tier provider to receive services from more
than one core service provider. In this scenario, there are some
benefits for the second tier service provider such as route
redundancy and dynamic carrier selection based on the price.
The second tier service provider can support a function that enables
a layer 1 resource trading service. Using resource information
published by its core service providers, a second tier service
provider can decide how to best use the core providers. For example,
if one core service provider is no longer able to satisfy requests
for service, an alternate service provider can be used. Or the second
tier service provider could choose to respond to price changes over
time.
Another example of second tier service provider use is to reduce
exposure to failures in each provider (i.e., to improve
availability).
4.3.4 Inter-SP L1VPN
In addition to the scenarios where a single connection between two
CEs is routed over a single service provider, it is possible that a
connection is routed over multiple service providers. This service
scenario is called Inter-SP L1VPN.
This scenario can be used to construct a single L1VPN from services
provided by multiple regional providers. There could be a variety
of business relationships among providers and customers.
4.3.5 Other Scenarios
There could be more complex L1VPN scenarios such as the case where
one or both CE-PE links of a L1VPN connection are not static, but are
based on L1VPN connections in their own right provided by the same or
different L1VPN service provider.
5. Reference Models
Figure 5.1 describes the L1VPN reference model.
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+--------------------------------+
| |
| +------------+ | : +------+
| | Management | | : | CE |
| | system(s) | | : |device|
| +------------+ +------+ : | of |
| | |==:=|VPN A|
| | | : +------+
+------+ : | L1 +------+ | PE | : +------+
| CE | : | connection | | |device| : | CE |
|device| : +------+ +------+ | P |==| | : |device|
| of |=:==| |=======| |===|device| | |--:-| of |
|VPN A| : | | | | | | +------+ : |VPN B|
+------+ : | PE | | P | +------+ | : +------+
+------+ : |device| |device| +------+ | : +------+
| CE | : | | | | | | +------+ : | CE |
|device|=:==| |=======| |===| P | | |--:-|device|
| of | : +------+ +------+ |device|==| | : | of |
|VPN B| : | | | | PE | : |VPN A|
+------+ : | +------+ |device| : +------+
: | | | : +------+
: | | |==:=| CE |
: | +------+ : |device|
: | | : | of |
: | | : |VPN B|
: | | : +------+
Customer | | Customer
interface | | interface
+--------------------------------+
|<------ Provider network ------>|
| |
Figure 5.1: L1VPN reference model
In a L1VPN, layer 1 connections are provided between CEs' data plane
interfaces within the same VPN. In Figure 5.1, a connection is
provided between the left-hand CE of VPN A and the upper right-hand
CE of VPN A, and another connection is provided between the left-hand
CE of VPN B and lower right-hand CE of VPN B (shown as "=" mark).
These layer 1 connections are called VPN connections.
5.1 Management Systems
As shown in the reference model, a provider network may contain one
or more management systems. A management system may support functions
including provisioning, monitoring, billing and recording. Provider
management systems may also communicate with customer management
systems in order to provide services.
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6. Generic Service Description
This section describes generic L1VPN services. More detailed service
descriptions are provided through specific service models in section
7.
6.1 CE Construct
- The CE device may support more than one customer VPN.
- CE-PE data plane links (between data plane interfaces) may be
shared by multiple VPNs.
Note that it is necessary to disambiguate control plane messages
exchanged between CE and PE if the CE-PE relationship is applicable
to more than one VPN. This makes it possible to determine to which
VPN such control plane messages apply. Such disambiguation might be
achieved by allocating a separate control channel to each VPN (either
using a separate physical channel, a separate logical channel (e.g.,
IP tunnel), or using separate addressing) or by extending the
signaling and routing protocols to allow them to identify the correct
VPN.
6.2 Generic Service Features
L1VPN has the following two generic service features.
- Connectivity restriction: Layer 1 connectivity is provided to a
limited set of CEs' data plane interfaces, called VPN end points.
(This set forms the L1VPN membership.)
- Per VPN control and management: Some level of control and
management capability is provided to the customer. Details differ
depending on service models described in section 7.
7. Service Models
This section describes Layer 1 VPN service models that can be
supported by Generalized MPLS (GMPLS) protocols enabled networks.
These models are derived from the generic service description
presented above.
Such layer 1 networks are managed and controlled using GMPLS
signaling as described in [RFC3471] and [RFC3473], and GMPLS routing
as described in [GMPLS-ROUTING]. It must be understood that meeting
the requirements set out in this document may necessitate
modifications to the existing GMPLS protocols both for the control
plane within the layer 1 network and for service provisioning at the
edge of the network (CE and PE devices). Such modifications are
discussed in [L1VPN-APP]. A CE and a PE are connected by one or more
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data links. The ends of each link are usually represented as
GMPLS-capable interfaces.
Note that in this document, service models are classified by the
semantics of information exchanged over the customer interface.
7.1 Management-based Service Model
Figure 7.1 describes the management-based service model.
+--------------------+
| |
+----------+ | +----------+ |
| Customer | | | Provider | |
|Management| : | |Management| |
| system(s)|-:-----|----| system(s)| |
+----------+ : | +----------+ |
: | |
: | |
+----+ : +----+ +----+ +----+ : +----+
| CE |-------:---| PE |----| P |----| PE |---:-------| CE |
+----+ : +----+ +----+ +----+ : +----+
: | | :
: +--------------------+ :
: |<-Provider network->| :
Customer Customer
interface interface
Figure 7.1: Management-based service model
In this service model, customer management systems and provider
management systems communicate with each other. Customer
management systems access provider management systems to request
layer 1 connection setup/deletion between a pair of CEs. Customer
management systems may obtain additional information, such as
resource availability information and monitoring information, from
provider management systems. There is no control message exchange
between a CE and PE.
The provider network may be based on GMPLS. In this case, existing
protocols to meet this service model may need to be extended (e.g.,
to support soft permanent connections). However, interfaces between
management systems are not within the scope of this document.
Interfaces between management systems and network devices controlled
by GMPLS may need to be studied further in [L1VPN-APP].
7.2 Signaling-based Service Model (Basic Mode)
In this service model, the CE-PE interface's functional repertoire is
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limited to path setup signalling only. The provider's network is not
involved in distribution of customer network's routing information.
7.2.1 Overlay Service Model
Figure 7.2 describes the Overlay service model.
+--------------------+
| |
+----+ : +----+ +----+ : +----+
| CE |-------:---| PE | | PE |---:-------| CE |
+----+ : +----+ +----+ : +----+
: | | :
: +--------------------+ :
: |<-Provider network->| :
Customer Customer
interface interface
Figure 7.2: Overlay service model
In this service model, the customer interface is based on the GMPLS
UNI Overlay [GMPLS-UNI]. The CE requests layer 1 connection
setup/deletion to a remote CE. There is no routing between a CE and
PE. The CE does not receive routing information from remote customer
sites, nor routing information about the provider network. The CE's
interface may be assigned a public or private address, that
designates VPN end points.
There are various ways that customers perceive the provider network.
In one example, the whole provider network may be considered as one
node - the path specified and recorded in signaling messages reflects
this. Note that this is distinct from the Virtual Node service model
described in section 7.3.2 because such a model requires that the
network is represented to the VPN sites as a virtual node - that is,
some form of routing advertisement is implied, and this is not in
scope for the Signaling-based service model.
Note that in addition, there may be communication between customer
management system(s) and provider management system(s) in order to
provide detailed monitoring, fault information etc. to customers.
7.3 Signaling and Routing Service Model (Enhanced Mode)
In this service model, the CE-PE interface provides the signaling
capabilities as in the Basic Mode, plus permits limited exchange of
information between the control planes of the provider and the
customer to help such functions as discovery of reachability
information in remote sites, or parameters of the part of the
provider's network dedicated to the customer.
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By allowing CEs to obtain reachability information, a so-called
N-square routing problem could be solved [GVPN].
In addition, by using the received traffic engineering-based routing
information, a customer can use traffic engineering capabilities
within his portion of the provider network. For example, a customer
can set up two disjoint connections between a pair of CEs. Another
example is that a customer can request a connection between a pair of
devices within customer sites, and not necessarily between CEs, with
more effective traffic engineering.
As such, the customer interface is based on GMPLS signaling and
mechanisms to exchange reachability/TE information. Typically, a
routing protocol is used between a CE and PE, or more precisely
between a CE and the VPN routing context instantiated on the PE. Link
state routing information would be needed to implement the above two
example scenarios. Some scenarios may be satisfied with reachability
routing information only.
Note that this service model does not preclude the use of mechanisms
other than routing protocols to exchange reachability/TE information.
Details need to be studied in [L1VPN-APP].
Note that in addition, there may be communication between customer
management system(s) and provider management system(s) in order to
provide detailed monitoring, fault information etc. to customers.
Four specific types of the Signaling and Routing service model are
the Overlay Extension service model, the Virtual Node service model,
the Virtual Link service model and the Per-VPN Peer service model,
depending on how customers perceive the provider network in routing
and signaling.
7.3.1 Overlay Extension Service Model
This service model is a slight extension from the Overlay service
model. In this service model, a CE receives a list of TE link
addresses to which it can request a VPN connection (a list of
addresses within the same VPN). This may include additional
information concerning these TE links (e.g., switching type). Note,
in the Overlay Extension service model, information a CE can receive
is limited to information about the CE-PE TE link. Mechanisms other
than routing could be used to exchange reachability/TE information
between the CE and the PE.
7.3.2 Virtual Node Service Model
Figure 7.3 describes the Virtual Node service model.
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+--------------------+
| |
+----+ : | | : +----+
| CE |-------:-----| Virtual Node |-----:-------| CE |
+----+ : | | : +----+
: | | :
: +--------------------+ :
: |<-Provider network->| :
Customer Customer
interface interface
Figure 7.3: Virtual Node service model
In this type of service model, the whole provider network is
represented as a virtual node (defined in section 2). The customer
perceives the provider network as one single node, i.e., a
Generalized Virtual Private Cross-Connect (GVPXC) [GVPN]. The CE
receives routing information about CE-PE links and remote customer
sites.
Note that in this service model, there must be one single virtual
node, and this virtual node must be connected with every CE in the
VPN.
7.3.3 Virtual Link Service Model
Figure 7.4 describes the Virtual Link service model.
+--------------------+
| Virtual |
+----+ : +----+ link +----+ : +----+
| CE |-------:---| PE |**************| PE |---:-------| CE |
+----+ : +----+ +----+ : +----+
: | | :
: +--------------------+ :
: |<-Provider network->| :
Customer Customer
interface interface
Figure 7.4: Virtual Link service model
In this service model, a virtual link is constructed between PEs.
For the definition of a virtual link, please refer to terminology in
section 2. The CE receives routing information about CE-PE links,
remote customer sites, as well as virtual links. A special property
of the virtual links used in this service model is that the provider
network allocates data plane link resources for the exclusive use of
each virtual link. The TE attributes of a virtual link are determined
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according to data plane link resources allocated to this virtual
link. Virtual links are an abstraction of the provider network to
customers for administrative purposes as well as to exclude
"unnecessary information".
Note that in this service model, both end points of each virtual link
must be a PE device.
7.3.4 Per-VPN Peer Service Model
Figure 7.5 describes the Per-VPN Peer service model.
+--------------------+
| |
+----+ : +----+ +----+ +----+ : +----+
| CE |-------:---| PE |----| P |----| PE |---:-------| CE |
+----+ : +----+ +----+ +----+ : +----+
: | | :
: +--------------------+ :
: |<-Provider network->| :
Customer Customer
interface interface
Figure 7.5: Per-VPN Peer service model
In this service model, the provider partitions the TE links within
the provider network per VPN, and discloses per-VPN TE link
information to corresponding CEs. As such, a CE receives routing
information about CE-PE links, remote customer sites, as well as
partitioned portions of the provider network.
Note that PEs may advertise abstracted routing information about the
provider network to CEs for administrative purpose as well as to
exclude "unnecessary information". In other words, virtual links
may be constructed between two nodes where direct data links do
not exist, or virtual nodes may be constructed to represent multiple
physical nodes and links.
In the Per-VPN Peer service model, at least one virtual node
corresponding to P devices (one single P or a set of Ps) must be
visible to customers.
8. Service Models and Service Requirements
The service models mentioned in section 7 are related to which
information is exchanged between CE and PE. In addition, service
models differ in how data plane resources are allocated for each VPN.
Note that in the ITU-T documents, the term "U-Plane" is used instead
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of "data plane".
o Data plane resource allocation
- Shared or dedicated:
Shared means that provider network data plane links are shared by
multiple (i.e., any or a specific set of) VPNs. (Data plane links
are dynamically allocated to a VPN when a VPN connection is
requested, and data plane links allocated to one VPN at one time
can be allocated to another VPN at another time.)
Dedicated means that provider network data plane links are
partitioned per VPN. (Data plane links are statically allocated
to one VPN and can not be used by other VPNs.)
o Information exchanged between CE and PE
- Signaling
- Membership information : A list of TE link addresses within the
same VPN (associated with VPN end points)
- Customer network routing information
- Provider network routing information
Table 1 shows combination of service requirements and service models.
| Data plane | Data plane
| shared | dedicated
---------------------------+------------------+-------------------
Signaling | Overlay | Overlay
---------------------------+------------------+-------------------
Signaling + | Overlay | Overlay
Membership information | Extension | Extension
---------------------------+------------------+-------------------
Signaling + | |
Membership information + | Virtual Node | Virtual Node
Customer network routing | |
information | |
---------------------------+------------------+-------------------
Signaling + | |
Membership information + | | Virtual Link
Customer network routing | Not applicable |
information + | | Per-VPN Peer
Provider network routing | |
information | |
Table 1: Combination of service requirements and service models
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As described in previous sections, the difference between the Virtual
Link service model and the Per-VPN Peer service model is whether
customers have visibility of P devices. In the Virtual Link service
model, the end points of virtual links must be PE devices, thus P
devices are not visible to customers. In the Per-VPN Peer service
model, at least one virtual node corresponding to P devices (one
single P, or a set of Ps) is visible to customers.
Note that when provider network routing information is provided to
customers, customers must be able to specify explicit links for a VPN
connection over the provider network.
8.1 Detailed Service Level Requirements
More detailed service requirements are provided below. They are
generally common to the various service models, except where
indicated.
- Selection of layer 1 class of service: Customers MAY be allowed to
specify a layer 1 class of service (e.g., availability level) for a
VPN connection.
- Reception of performance information: Customers MAY be allowed to
receive performance information for their VPN connections (e.g.,
performance monitoring data). When data plane links are dedicated,
customers MAY be allowed to receive performance information for
links dedicated to them.
- Reception of fault information: Customers MAY be allowed to receive
fault information for their VPN connections (e.g., failures, data
plane alarms, rejections). When data plane links are dedicated,
customers MAY be allowed to receive fault information for links
dedicated to them.
- Reception of connection information: Customers MAY be allowed to
receive information for current VPN connections.
- Reception of accounting information: Customers MUST be able to
receive accounting information for each VPN.
- Specification of policy: Customers MAY be allowed to specify
policies (e.g., path computation policies, recovery policies
including parameters) for each VPN.
- Security: The communication between the customer and the provider
MUST be secure. Further details are described in section 9.
- Filtering: Unnecessary information (e.g., information concerning
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other VPNs) MUST NOT be provided to each customer. This applies
particularly to Signaling and Routing service models, but is also
relevant to Signaling-based service models and to Management-based
service models. Further details are described in section 9.
- Requests/indications for arbitrary CE-CE control plane information
delivery. All models that support routing exchanges MAY support the
exchange of arbitrary CE-CE control plane information passed from
CE to PE within routing protocol messages and delivered from PE to
CE at the other side of the core network. In addition, some
signaling models MAY allow directed signaling message exchange
between CEs for hierarchical or stitched LSPs over CE-CE LSP.
9. Security Considerations
Security is clearly one of the essential requirements in L1VPNs. In
this section, key security requirements are highlighted. Security
considerations for L3VPNs and L2VPNs are described in existing
documents, such as [L3VPN-FRAME] and [L2VPN-FRAME]. These security
considerations should also be applied in L1VPNs, and these aspects
are described in this section. In addition, there are some specific
security considerations for L1VPNs, such as connectivity restriction
and shared control links.
This section first describes types of information to be secured.
Then, security features or aspects are described. Finally, some
considerations concerning scenarios where security mechanisms are
applied is described.
9.1 Types of Information
It MUST be possible to secure the information exchanged between the
customer and the provider. This includes data plane information,
control plane information and management plane information. At layer
1, data plane information is normally assumed to be secured once
connections are established, since those connections are dedicated to
each VPN. In L1VPNs, VPN connections MUST be restricted to be used
only within the same VPN, as described in section 6.2. Note that a
customer may wish to assure data plane information security against
not only other customers, but also the provider. In such case, the
customer may wish to apply their own security mechanisms for data
plane information (CE-CE security), as later described.
In addition, information contained in the provider network MUST be
secured. This includes VPN service contract information, current VPN
connection information, VPN membership information, and system
information. Note these types of information MAY be accessible to
authorized entities.
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9.2 Security Features
Security features include the following:
o Data integrity
The information exchanged between the customer and the provider
MUST be delivered unchanged.
o Confidentiality
The information exchanged between the customer and the provider
MUST NOT be retrieved by the third party.
o Authentication
The entity requesting the service to the provider MUST be
identified.
o Access control
Access to the information contained in the provider network MUST be
restricted to the authorized entity.
9.3 Scenarios
There are two scenarios (or occasions) in which security mechanisms
are applied. One is the service contract phase, where security
mechanisms are applied once. The other is the service access phase,
where security mechanisms are applied every time the service is
requested.
o Service contract scenario (static)
This scenario includes the addition of new physical devices, such
as CE devices, data links and control links. It MUST be guaranteed
that these physical devices are connected to the right entity. In
addition, authority to access specific information MAY be given to
each customer as a part of service contract.
o Service access scenario (dynamic)
This scenario includes the reception of connection requests,
routing information exchange requests, and management information
retrieval requests. If a communication channel between the customer
and the provider (control channel, management interface) is
physically separate per customer, and the entity connected over
this communication channel is identified in the service contract
phase, the provider can ensure who is requesting the service. Also,
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the communication channel could be considered as secure. However,
when communication channel is physically shared among customers,
security mechanisms MUST be available and SHOULD be enforced. Note
that even in the case of physically separate communication
channels, customers may wish to apply security mechanisms, such as
IPsec, to assure higher security, and such mechanisms MUST be
available.
When the entity requesting the service is identified, the provider
MUST ensure that the request is authorized for that entity. This
includes assuring that connection request is between VPN end points
belonging to the same VPN.
Also note that customers may wish to apply their own security
mechanisms for data plane information (CE-CE security). This
includes IPsec for IP traffic.
10. Acknowledgements
The material in this document is based on the work of the ITU-T Study
Group 13.
We would like to thank Dimitri Papadimitriou, Deborah Brungard,
Yakov Rekhter, Alex Zinin, Igor Bryskin and Adrian Farrel for their
useful comments and suggestions.
11. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
12. Informative References
For information on the availability of this document, please see
http://www.itu.int.
[Y.1312] Y.1312 - Layer 1 Virtual Private Network Generic
requirements and architecture elements, ITU-T
Recommendation, September 2003.
For information on the availability of this document, please see
http://www.itu.int.
[Y.1313] Y.1313 - Layer 1 Virtual Private Network service and
network architectures, ITU-T Recommendation, July
2004.
[RFC3031] Rosen, E., Viswanathan, A. and R. Callon,
"Multiprotocol label switching Architecture", RFC
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3031, January 2001.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T.,
Srinivasan, V. and G. Swallow, "RSVP-TE: Extensions
to RSVP for LSP Tunnels", RFC 3209, December 2001.
[RFC3471] Berger, L., Editor, "Generalized Multi-Protocol
Label Switching (GMPLS) Signaling Functional
Description", RFC 3471, January 2003.
[RFC3473] Berger, L., Editor "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling - Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions",
RFC 3473, January 2003.
[RFC4026] Anderssion, L., and Madsen, T., "Provider Provisioned
Virtual Private Network (VPN) Terminology", RFC 4026,
March 2005.
[GMPLS-UNI] Swallow, G., et al., "GMPLS UNI: RSVP Support for the
Overlay Model", draft-ietf-ccamp-gmpls-overlay, work
in progress.
[GMPLS-ROUTING] Kompella, K., and Rekhter, Y. (editors), "Routing
Extensions in Support of Generalized MPLS", draft-
ietf-ccamp-gmpls-routing, work in progress.
[L2VPN-FRAME] Andersson, L., and Rosen, E. (editors), "Framework
for Layer 2 Virtual Private Networks (L2VPNs)",
draft-ietf-l2vpn-l2-framework, work in progress.
[L3VPN-FRAME] Callon, R., and Suzuki, M. (editors), "A Framework
for Layer 3 Provider Provisioned Virtual Private
Networks", draft-ietf-l3vpn-framework, work in
progress.
[GVPN] Ould-Brahim, H., and Rekhter, Y. (editors), "GVPN
Services: Generalized VPN Services using BGP and
GMPLS Toolkit", draft-ouldbrahim-ppvpn-gvpn-bgpgmpls,
work in progress.
[L1VPN-APP] T. Takeda (Ed.), "Applicability analysis of GMPLS
protocols to Layer 1 Virtual Private Networks",
draft-takeda-l1vpn-applicability, work in progress.
13. Authors' Addresses
Raymond Aubin
Nortel Networks
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P O Box 3511 Station C
Ottawa, ON K1Y 4H7 Canada
Phone: +1 (613) 763 2208
Email: aubin@nortelnetworks.com
Marco Carugi
Nortel Networks S.A.
Parc d'activites de Magny-Chateaufort
Les Jeunes Bois - MS CTF 32B5 - Chateaufort
78928 YVELINES Cedex 9 - FRANCE
Phone: +33 1 6955 7027
Email: marco.carugi@nortelnetworks.com
Ichiro Inoue
NTT Network Service Systems Laboratories, NTT Corporation
3-9-11, Midori-Cho
Musashino-Shi, Tokyo 180-8585 Japan
Phone: +81 422 59 6076
Email: inoue.ichiro@lab.ntt.co.jp
Hamid Ould-Brahim
Nortel Networks
P O Box 3511 Station C
Ottawa, ON K1Y 4H7 Canada
Phone: +1 (613) 765 3418
Email: hbrahim@nortelnetworks.com
Tomonori Takeda
NTT Network Service Systems Laboratories, NTT Corporation
3-9-11, Midori-Cho
Musashino-Shi, Tokyo 180-8585 Japan
Phone: +81 422 59 7434
Email : takeda.tomonori@lab.ntt.co.jp
14. Intellectual Property Consideration
The IETF takes no position regarding the validity or scope of any
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to pertain to the implementation or use of the technology
described in this document or the extent to which any license
under such rights might or might not be available; nor does it
represent that it has made any independent effort to identify any
such rights. Information on the procedures with respect to
rights in RFC documents can be found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use
of such proprietary rights by implementers or users of this
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specification can be obtained from the IETF on-line IPR repository
at http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention
any copyrights, patents or patent applications, or other
proprietary rights that may cover technology that may be required
to implement this standard. Please address the information to the
IETF at ietf-ipr@ietf.org.
15. Full Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE
REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE
INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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