Network Working Group Kohei Shiomoto (NTT)
Internet-Draft Dimitri Papadimitriou (Alcatel)
Intended Status: Informational Jean-Louis Le Roux (France Telecom)
Martin Vigoureux (Alcatel)
Deborah Brungard (AT&T)
Expires: October 2007 April 2007
Requirements for GMPLS-based multi-region and
multi-layer networks (MRN/MLN)
draft-ietf-ccamp-gmpls-mln-reqs-03.txt
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Abstract
Most of the initial efforts to utilize Generalized MPLS (GMPLS)
have been related to environments hosting devices with a single
switching capability. The complexity raised by the control of such
data planes is similar to that seen in classical IP/MPLS networks.
By extending MPLS to support multiple switching technologies, GMPLS
provides a comprehensive framework for the control of a multi-
layered network of either a single switching technology or multiple
switching technologies.
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In GMPLS, a switching technology domain defines a region, and a
network of multiple switching types is referred to in this document
as a Multi-Region Network (MRN). When referring in general to a
layered network, which may consist of either a single or multiple
regions, this document uses the term, Multi-Layer Network (MLN).
This document defines a framework for GMPLS based multi-
region/multi-layer networks and lists a set of functional
requirements.
Table of Contents
1. Introduction...................................................3
2. Conventions Used in this Document..............................4
2.1. List of acronyms.............................................4
3. Positioning....................................................5
3.1. Data Plane Layers and Control Plane Regions..................5
3.2. Service layer networks.......................................6
3.3. Vertical and Horizontal interaction and integration..........6
4. Key Concepts of GMPLS-Based MLNs and MRNs......................7
4.1. Interface Switching Capability...............................7
4.2. Multiple Interface Switching Capabilities....................8
4.2.1. Networks with Multi-Switching-Type-Capable Hybrid Nodes....9
4.3. Integrated Traffic Engineering (TE) and Resource Control.....9
4.3.1. Triggered Signaling.......................................10
4.3.2. FA-LSPs...................................................10
4.3.3. Virtual Network Topology (VNT)............................11
5. Requirements..................................................12
5.1. Handling Single-Switching and Multi-Switching-Type-Capable
Nodes............................................................12
5.2. Advertisement of the Available Adaptation Resource..........13
5.3. Scalability.................................................13
5.4. Stability...................................................13
5.5. Disruption Minimization.....................................14
5.6. LSP Attribute Inheritance...................................14
5.7. Computing Paths With and Without Nested Signaling...........15
5.8. LSP Resource Utilization....................................16
5.8.1. FA-LSP Release and Setup..................................16
5.8.2. Virtual TE-Links..........................................17
5.9. Verification of the LSPs....................................18
6. Security Considerations.......................................18
7. IANA Considerations...........................................19
8. References....................................................19
8.1. Normative Reference.........................................19
8.2. Informative References......................................19
9. Authors' Addresses............................................20
10. Contributors' Addresses......................................21
11. Intellectual Property Considerations.........................21
12. Full Copyright Statement.....................................22
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1. Introduction
Generalized MPLS (GMPLS) extends MPLS to handle multiple switching
technologies: packet switching, layer-2 switching, TDM switching,
wavelength switching, and fiber switching (see [RFC3945]). The
Interface Switching Capability (ISC) concept is introduced for
these switching technologies and is designated as follows: PSC
(packet switch capable), L2SC (Layer-2 switch capable), TDM (Time
Division Multiplex capable), LSC (lambda switch capable), and FSC
(fiber switch capable).
Service providers may operate networks where multiple different
switching technologies exist. The representation, in a GMPLS
control plane, of a switching technology domain is referred to as a
region [RFC4206].
A switching type describes the ability of a node to forward data of
a particular data plane technology, and uniquely identifies a
network region. A layer describes a data plane switching
granularity level (e.g., VC4, VC-12). A data plane layer is
associated with a region in the control plane (e.g., VC4 is
associated with TDM, MPLS is associated with PSC). However, more
than one data plane layer can be associated with the same region
(e.g., both VC4 and VC12 are associated with TDM). Thus, a control
plane region, identified by its switching type value (e.g., TDM),
can be sub-divided into smaller granularity component networks
based on "data plane switching layers". The Interface Switching
Capability Descriptor (ISCD) [RFC4202], identifying the interface
switching capability (ISC), the encoding type, and the switching
bandwidth granularity, enables the characterization of the
associated layers.
A network comprising nodes with multiple data plane layers of
either the same ISC or different ISCs, controlled by a single GMPLS
control plane instance is called a Multi-Layer Network (MLN). To
differentiate a network supporting LSPs of different switching
types from a single region network, a network supporting more than
one switching technology and controlled by a single GMPLS control
plane instance is called a Multi-Region Network (MRN).
MLNs can be categorized according to the distribution of the ISCs
among the LSRs:
- Each LSR may support just one ISC. Such LSRs are known as
single-switching-type-capable LSRs. The MLN may comprise a set of
single-switching-type-capable LSRs that support different ISCs.
- Each LSR may support more than one ISC at the same time.
Such LSRs are known as multi-switching-type-capable LSRs, and
can be further classified as either "simplex" or "hybrid" nodes
as defined in Section 4.2.
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- The MLN may be constructed from any combination of single-
switching-type-capable LSRs and multi-switching-type-capable
LSRs.
Since GMPLS provides a comprehensive framework for the control of
different switching capabilities, a single GMPLS instance may be
used to control the MLN enabling rapid service provisioning and
efficient traffic engineering across all switching capabilities. In
such networks, TE Links are consolidated into a single Traffic
Engineering Database (TED). Since this TED contains the information
relative to all the different regions and layers existing in the
network, a path across multiple regions or layers can be computed
using this TED. Thus optimization of network resources can be
achieved across the whole MLN.
Consider, for example, a MRN consisting of packet-switch capable
routers and TDM cross-connects. Assume that a packet LSP is routed
between source and destination packet-switch capable routers, and
that the LSP can be routed across the PSC-region (i.e., utilizing
only resources of the packet region topology). If the performance
objective for the LSP is not satisfied, new TE links may be created
between the packet-switch capable routers across the TDM-region
(for example, VC-12 links) and the LSP can be routed over those TE
links. Further, even if the LSP can be successfully established
across the PSC-region, TDM hierarchical LSPs across the TDM region
between the packet-switch capable routers may be established and
used if doing so is necessary to meet the operator's objectives for
network resources availability (e.g., link bandwidth, or adaptation
ports between regions) across the regions. The same considerations
hold when VC4 LSPs are provisioned to provide extra flexibility for
the VC12 and/or VC11 layers in an MLN.
This document describes the requirements to support multi-
region/multi-layer networks. There is no intention to specify
solution-specific elements in this document. The applicability of
existing GMPLS protocols and any protocol extensions to the MRN/MLN
is addressed in separate documents [MRN-EVAL].
2. Conventions Used in this Document
Although this is not a protocol specifcation, the key words "MUST",
"MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD
NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are used in this
document to highlight requirements, and are to be interpreted as
described in RFC 2119 [RFC2119].
2.1.List of acronyms
MLN: Multi-Layer Network
MRN: Multi-Region Network
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ISC: Interface Switching Capability
ISCD: Interface Switching Capability Descriptor
PSC: Packet Switching Capable
L2SC: Layer-2 Switching Capable
TDM: Time-Division Switch Capable
LSC: Lambda Switching Capable
FSC: Fiber Switching Capable
SRLG: Shared Risk Ling Group
VNT: Virtual Network Topology
FA: Forwarding Adjacency
FA-LSP: Forwarding Adjacency Label Switched Path
TE: Traffic Engineering
TED: Traffic Engineering Database
LSP: Label Switched Path
LSR: Label Switching Router
3. Positioning
A multi-region network (MRN) is always a multi-layer network (MLN)
since the network devices on region boundaries bring together
different ISCs. A MLN, however, is not necessarily a MRN since
multiple layers could be fully contained within a single region.
For example, VC12, VC4, and VC4-4c are different layers of the TDM
region.
3.1. Data Plane Layers and Control Plane Regions
A data plane layer is a collection of network resources capable of
terminating and/or switching data traffic of a particular
format[RFC4397]. These resources can be used for establishing LSPs
for traffic delivery. For example, VC-11 and VC4-64c represent two
different layers.
From the control plane viewpoint, an LSP region is defined as a set
of one or more data plane layers that share the same type of
switching technology, that is, the same switching type. For example,
VC-11 and VC-4 layers are part of the same TDM region. The regions
that are currently defined are: PSC, L2SC, TDM, LSC, and FSC. Hence,
an LSP region is a technology domain (identified by the ISC type)
for which data plane resources (i.e., data links) are represented
into the control plane as an aggregate of TE information associated
with a set of links (i.e., TE links). For example VC-11 and VC4-64c
capable TE links are part of the same TDM region. Multiple layers
can thus exist in a single region network.
Note also that the region may produce a distinction within the
control plane. Layers of the same region share the same switching
technology and, therefore, use the same set of technology-specific
signaling objects within the control plane, but layers from
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different regions may use different technology-specific objects or
encodings. This means that there is a control plane discontinuity
when crossing a region boundary even if a single control plane
instance is used to manage the whole MRN.
3.2. Service layer networks
A service provider's network may be divided into different service
layers. The customer's network is considered from the provider's
perspective as the highest service layer. It interfaces to the
highest service layer of the service provider's network.
Connectivity across the highest service layer of the service
provider's network may be provided with support from successively
lower service layers. Service layers are realized via a hierarchy
of network layers located generally in several regions and commonly
arranged according to the switching capabilities of network devices.
For instance some customers purchase Layer 1 (i.e., transport)
services from the service provider, some Layer 2 (e.g., ATM), while
others purchase Layer 3 (IP/MPLS) services. The service provider
realizes the services by a stack of network layers located within
one or more network regions. The network layers are commonly
arranged according to the switching capabilities of the devices in
the networks. Thus, a customer network may be provided on top of
the GMPLS-based multi-region/multi-layer network. For example, a
Layer 1 service (realized via the network layers of TDM, and/or LSC,
and/or FSC regions) may support a Layer 2 network (realized via ATM
VP/VC) which may itself support a Layer 3 network (IP/MPLS region).
The supported data plane relationship is a data plane client-server
relationship where the lower layer provides a service for the
higher layer using the data links realized in the lower layer.
Services provided by a GMPLS-based multi-region/multi-layer network
are referred to as "Multi-region/Multi-layer network services". For
example, legacy IP and IP/MPLS networks can be supported on top of
multi-region/multi-layer networks. It has to be emphasized that
delivery of such diverse services is a strong motivator for the
deployment of multi-region/multi-layer networks.
A customer network may be provided on top of a server GMPLS-based
MRN/MLN which is operated by a service provider. For example, a
pure IP and/or an IP/MPLS network can be provided on top of GMPLS-
based packet over optical networks [MPLS-GMPLS]. The relationship
between the networks is a client/server relationship and, such
services are referred to as "MRN/MLN services". In this case, the
customer network may form part of the MRN/MLN, or may be partially
separated, for example to maintain separate routing information but
retain common signaling.
3.3. Vertical and Horizontal interaction and integration
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Vertical interaction is defined as the collaborative mechanisms
within a network element that is capable of supporting more than
one layer and of realizing the client/server relationships between
the layers. Protocol exchanges between two network controllers
managing different regions or layers are also a vertical
interaction. Integration of these interactions as part of the
control plane is referred to as vertical integration. Thus, this
refers to the collaborative mechanisms within a single control
plane instance driving multiple network layers. Such a concept is
useful in order to construct a framework that facilitates efficient
network resource usage and rapid service provisioning in carrier
networks that are based on multiple layers, switching technologies,
or ISCs.
Horizontal interaction is defined as the protocol exchange between
network controllers that manage transport nodes within a given
layer or region (i.e., nodes with the same switching capability).
For instance, the control plane interaction between two TDM network
elements switching at OC-48 is an example of horizontal interaction.
GMPLS protocol operations handle horizontal interactions within the
same routing area. The case where the interaction takes place
across a domain boundary, such as between two routing areas within
the same network layer, is evaluated as part of the inter-domain
work [RFC4726], and is referred to as horizontal integration. Thus,
horizontal integration refers to the collaborative mechanisms
between network partitions and/or administrative divisions such as
routing areas or autonomous systems.
This distinction needs further clarification when administrative
domains match layer boundaries. Horizontal interaction is extended
to cover such cases. For example, the collaborative mechanisms in
place between two lambda switching capable areas relate to
horizontal integration. On the other hand, the collaborative
mechanisms in place in a network that supports IP/MPLS over TDM
switching could be described as vertical and horizontal integration
in the case where each network belongs to a separate routing area.
4. Key Concepts of GMPLS-Based MLNs and MRNs
A network comprising transport nodes with multiple data plane
layers of either the same ISC or different ISCs, controlled by a
single GMPLS control plane instance, is called a Multi-Layer
Network (MLN). A sub-set of MLNs consists of networks supporting
LSPs of different switching technologies (ISCs). A network
supporting more than one switching technology is called a Multi-
Region Network (MRN).
4.1. Interface Switching Capability
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The Interface Switching Capability (ISC) is introduced in GMPLS to
support various kinds of switching technology in a unified way
[RFC4202]. An ISC is identified via a switching type.
A switching type (also referred to as the switching capability
type) describes the ability of a node to forward data of a
particular data plane technology, and uniquely identifies a network
region. The following ISC types (and, hence, regions) are defined:
PSC, L2SC, TDM, LSC, and FSC. Each end of a data link (more
precisely, each interface connecting a data link to a node) in a
GMPLS network is associated with an ISC.
The ISC value is advertised as a part of the Interface Switching
Capability Descriptor (ISCD) attribute (sub-TLV) of a TE link end
associated with a particular link interface [RFC4202]. Apart from
the ISC, the ISCD contains information including the encoding type,
the bandwidth granularity, and the unreserved bandwidth on each of
eight priorities at which LSPs can be established. The ISCD does
not "identify" network layers, it uniquely characterizes
information associated to one or more network layers.
TE link end advertisements may contain multiple ISCDs. This can be
interpreted as advertising a multi-layer (or multi-switching-
capable) TE link end. That is, the TE link end (and therefore the
TE link) is present in multiple layers.
4.2. Multiple Interface Switching Capabilities
In an MLN, network elements may be single-switching-type-capable or
multi-switching-type-capable nodes. Single-switching-type-capable
nodes advertise the same ISC value as part of their ISCD sub-TLV(s)
to describe the termination capabilities of each of their TE
Link(s). This case is described in [RFC4202].
Multi-switching-type-capable LSRs are classified as "simplex" or
"hybrid" nodes. Simplex and hybrid nodes are categorized according
to the way they advertise these multiple ISCs:
- A simplex node can terminate data links with different switching
capabilities where each data link is connected to the node by a
separate link interface. So, it advertises several TE Links each
with a single ISC value carried in its ISCD sub-TLV. For example,
an LSR with PSC and TDM links each of which is connected to the LSR
via a separate interface.
- A hybrid node can terminate data links with different switching
capabilities where the data links are connected to the node by the
same interface. So, it advertises a single TE Link containing more
than one ISCD each with a different ISC value. For example, a node
may terminate PSC and TDM data links and interconnect those
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external data links via internal links. The external interfaces
connected to the node have both PSC and TDM capabilities.
Additionally, TE link advertisements issued by a simplex or a
hybrid node may need to provide information about the node's
internal adaptation capabilities between the switching technologies
supported. That is, the node's capability to perform layer border
node functions.
4.2.1. Networks with Multi-Switching-Type-Capable Hybrid Nodes
This type of network contains at least one hybrid node, zero or
more simplex nodes, and a set of single-switching-type-capable
nodes.
Figure 1 shows an example hybrid node. The hybrid node has two
switching elements (matrices), which support, for instance, TDM and
PSC switching respectively. The node terminates a PSC and a TDM
link (Link1 and Link2 respectively). It also has an internal link
connecting the two switching elements.
The two switching elements are internally interconnected in such a
way that it is possible to terminate some of the resources of, say,
Link2 and provide adaptation for PSC traffic received/sent over the
PSC interface (#b). This situation is modeled in GMPLS by
connecting the local end of Link2 to the TDM switching element via
an additional interface realizing the termination/adaptation
function. There are two possible ways to set up PSC LSPs through
the hybrid node. Available resource advertisement (i.e., Unreserved
and Min/Max LSP Bandwidth) should cover both of these methods.
Network element
.............................
: -------- :
: | PSC | :
Link1 -------------<->--|#a | :
: +--<->---|#b | :
: | -------- :
TDM : | ---------- :
+PSC : +--<->--|#c TDM | :
Link2 ------------<->--|#d | :
: ---------- :
:............................
Figure 1. Hybrid node.
4.3. Integrated Traffic Engineering (TE) and Resource Control
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In GMPLS-based multi-region/multi-layer networks, TE Links may be
consolidated into a single Traffic Engineering Database (TED) for
use by the single control plane instance. Since this TED contains
the information relative to all the layers of all regions in the
network, a path across multiple layers (possibly crossing multiple
regions) can be computed using the information in this TED. Thus,
optimization of network resources across the multiple layers of the
same region and across multiple regions can be achieved.
These concepts allow for the operation of one network layer over
the topology (that is, TE links) provided by other network layers
(for example, the use of a lower layer LSC LSP carrying PSC LSPs).
In turn, a greater degree of control and inter-working can be
achieved, including (but not limited too):
- Dynamic establishment of Forwarding Adjacency (FA) LSPs
[RFC4206] (see Sections 4.3.2 and 4.3.3).
- Provisioning of end-to-end LSPs with dynamic triggering of FA
LSPs.
Note that in a multi-layer/multi-region network that includes
multi-switching-type-capable nodes, an explicit route used to
establish an end-to-end LSP can specify nodes that belong to
different layers or regions. In this case, a mechanism to control
the dynamic creation of FA LSPs may be required (see Sections 4.3.2
and 4.3.3).
There is a full spectrum of options to control how FA LSPs are
dynamically established. The process can be subject to the control
of a policy, which may be set by a management component, and which
may require that the management plane is consulted at the time that
the FA LSP is established. Alternatively, the FA LSP can be
established at the request of the control plane without any
management control.
4.3.1. Triggered Signaling
When an LSP crosses the boundary from an upper to a lower layer, it
may be nested into a lower layer FA LSP that crosses the lower
layer. From a signaling perspective, there are two alternatives to
establish the lower layer FA LSP: static (pre-provisioned) and
dynamic (triggered). A pre-provisioned FA-LSP may be initiated
either by the operator or automatically using features like TE
auto-mesh [AUTO-MESH]. If such a lower layer LSP does not already
exist, the LSP may be established dynamically. Such a mechanism is
referred to as "triggered signaling".
4.3.2. FA-LSPs
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Once an LSP is created across a layer from one layer border node to
another, it can be used as a data link in an upper layer.
Furthermore, it can be advertised as a TE-link, allowing other
nodes to consider the LSP as a TE link for their path computation
[RFC4206]. An LSP created either statically or dynamically by one
instance of the control plane and advertised as a TE link into the
same instance of the control plane is called a Forwarding Adjacency
LSP (FA-LSP). The FA-LSP is advertised as a TE link, and that TE
link is called a Forwarding Adjacency (FA). An FA has the special
characteristic of not requiring a routing adjacency (peering)
between its end points yet still guaranteeing control plane
connectivity between the FA-LSP end points based on a signaling
adjacency. An FA is a useful and powerful tool for improving the
scalability of GMPLS Traffic Engineering (TE) capable networks
since multiple higher layer LSPs may be nested (aggregated) over a
single FA-LSP.
The aggregation of LSPs enables the creation of a vertical (nested)
LSP Hierarchy. A set of FA-LSPs across or within a lower layer can
be used during path selection by a higher layer LSP. Likewise, the
higher layer LSPs may be carried over dynamic data links realized
via LSPs (just as they are carried over any "regular" static data
links). This process requires the nesting of LSPs through a
hierarchical process [RFC4206]. The TED contains a set of LSP
advertisements from different layers that are identified by the
ISCD contained within the TE link advertisement associated with the
LSP [RFC4202].
If a lower layer LSP is not advertised as an FA, it can still be
used to carry higher layer LSPs across the lower layer. For example,
if the LSP is set up using triggered signaling, it will be used to
carry the higher layer LSP that caused the trigger. Further, the
lower layer remains available for use by other higher layer LSPs
arriving at the boundary.
Under some circumstances it may be useful to control the
advertisement of LSPs as FAs during the signaling establishment of
the LSPs [DYN-HIER].
4.3.3. Virtual Network Topology (VNT)
A set of one or more of lower-layer LSPs provides information for
efficient path handling in upper-layer(s) of the MLN, or, in other
words, provides a virtual network topology (VNT) to the upper-
layers. For instance, a set of LSPs, each of which is supported by
an LSC LSP, provides a virtual network topology to the layers of a
PSC region, assuming that the PSC region is connected to the LSC
region. Note that a single lower-layer LSP is a special case of the
VNT. The virtual network topology is configured by setting up or
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tearing down the lower layer LSPs. By using GMPLS signaling and
routing protocols, the virtual network topology can be adapted to
traffic demands.
A lower-layer LSP appears as a TE-link in the VNT. Whether the
diversely-routed lower-layer LSPs are used or not, the routes of
lower-layer LSPs are hidden from the upper layer in the VNT. Thus,
the VNT simplifies the upper-layer routing and traffic engineering
decisions by hiding the routes taken by the lower-layer LSPs.
However hiding the routes of the lower-layer LSPs may lose
important information that is needed to make the higher-layer LSPs
reliable. For instance, the routing and traffic engineering in the
IP/MPLS layer does not usually consider how the IP/MPLS TE links
are formed from optical paths that are routed in the fiber layer.
Two optical paths may share the same fiber link in the lower-layer
and therefore they may both fail if the fiber link is cut. Thus the
shared risk properties of the TE links in the VNT must be made
available to the higher layer during path computation. Further, the
topology of the VNT should be designed so that any single fiber cut
does not bisect the VNT. These issues are addressed later in this
document.
Reconfiguration of the virtual network topology may be triggered by
traffic demand changes, topology configuration changes, signaling
requests from the upper layer, and network failures. For instance,
by reconfiguring the virtual network topology according to the
traffic demand between source and destination node pairs, network
performance factors, such as maximum link utilization and residual
capacity of the network, can be optimized. Reconfiguration is
performed by computing the new VNT from the traffic demand matrix
and optionally from the current VNT. Exact details are outside the
scope of this document. However, this method may be tailored
according to the service provider's policy regarding network
performance and quality of service (delay, loss/disruption,
utilization, residual capacity, reliability).
5.Requirements
5.1.Handling Single-Switching and Multi-Switching-Type-Capable Nodes
The MRN/MLN can consist of single-switching-type-capable and multi-
switching-type-capable nodes. The path computation mechanism in the
MLN SHOULD be able to compute paths consisting of any combination
of such nodes.
Both single-switching-type-capable and multi-switching-type-capable
(simplex or hybrid) nodes could play the role of layer boundary.
MRN/MLN Path computation SHOULD handle TE topologies built of any
combination of nodes
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5.2. Advertisement of the Available Adaptation Resource
A hybrid node SHOULD maintain resources on its internal links (the
links required for vertical (layer) integration) and SHOULD
advertise the resource information for those links. Likewise, path
computation elements SHOULD be prepared to use the availability of
termination/adaptation resources as a constraint in MRN/MLN path
computations to reduce the higher layer LSP setup blocking
probability caused by the lack of necessary termination/ adaptation
resources in the lower layer(s).
The advertisement of the adaptation capability to terminate LSPs of
lower-region and forward traffic in the upper-region is REQUIRED,
as it provides critical information when performing multi-region
path computation.
The mechanism SHOULD cover the case where the upper-layer links
which are directly connected to upper-layer switching element and
the ones which are connected through internal links between upper-
layer element and lower-layer element coexist (See section 4.2.1).
5.3. Scalability
The MRN/MLN relies on a unified traffic engineering and routing
model. The TED in each LSR is populated with TE-links from all
layers of all regions. This may lead to a huge amount of
information that has to be flooded and stored within the network.
Furthermore, path computation times, which may be of great
importance during restoration, will depend on the size of the TED.
Thus MRN/MLN routing mechanisms MUST be designed to scale well with
an increase of any of the following:
- Number of nodes
- Number of TE-links (including FA-LSPs)
- Number of LSPs
- Number of regions and layers
- Number of ISCDs per TE-link.
Further, design of the routing protocols MUST NOT prevent TE
information filtering based on ISCDs. The path computation
mechanism and the signaling protocol SHOULD be able to operate on
partial TE information.
5.4.Stability
Path computation is dependent on the network topology and
associated link state. The path computation stability of an upper
layer may be impaired if the VNT changes frequently and/or if the
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status and TE parameters (the TE metric, for instance) of links in
the VNT changes frequently.
In this context, robustness of the VNT is defined as the capability
to smooth changes that may occur and avoid their propagation into
higher layers. Changes to the VNT may be caused by the creation,
deletion, or modification of LSPs.
Creation, deletion, and modification of LSPs MAY be triggered by
adjacent layers or through operational actions to meet traffic
demand changes, topology changes, signaling requests from the upper
layer, and network failures. Routing robustness SHOULD be traded
with adaptability with respect to the change of incoming traffic
requests.
5.5.Disruption Minimization
When reconfiguring the VNT according to a change in traffic demand,
the upper-layer LSP might be disrupted. Such disruption to the
upper layers MUST be minimized.
When residual resource decreases to a certain level, some lower
layer LSPs MAY be released according to local or network policies.
There is a trade-off between minimizing the amount of resource
reserved in the lower layer and disrupting higher layer traffic
(i.e. moving the traffic to other TE-LSPs so that some LSPs can be
released). Such traffic disruption MAY be allowed, but MUST be
under the control of policy that can be configured by the operator.
Any repositioning of traffic MUST be as non-disruptive as possible
(for example, using make-before-break).
5.6.LSP Attribute Inheritance
TE-Link parameters SHOULD be inherited from the parameters of the
LSP that provides the TE-link, and so from the TE-links in the
lower layer that are traversed by the LSP.
These include:
- Interface Switching Capability
- TE metric
- Maximum LSP bandwidth per priority level
- Unreserved bandwidth for all priority levels
- Maximum Reservable bandwidth
- Protection attribute
- Minimum LSP bandwidth (depending on the Switching Capability)
- SRLG
Inheritance rules MUST be applied based on specific policies.
Particular attention should be given to the inheritance of TE
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metric (which may be other than a strict sum of the metrics of the
component TE links at the lower layer), protection attributes, and
SRLG.
As described earlier, hiding the routes of the lower-layer LSPs may
lose important information necessary to make LSPs in the higher
layer network reliable. SRLGs may be used to identify which lower-
layer LSPs share the same failure risk so that the potential risk
of the VNT becoming disjoint can be minimized, and so that resource
disjoint protection paths can be set up in the higher layer. How to
inherit the SRLG information from the lower layer to the upper
layer needs more discussion and is out of scope of this document.
5.7.Computing Paths With and Without Nested Signaling
Path computation MAY take into account LSP region and layer
boundaries when computing a path for an LSP. For example, path
computation MAY restrict the path taken by an LSP to only the links
whose interface switching capability is PSC.
Interface switching capability is used as a constraint in path
computation. For example, a TDM-LSP is routed over the topology
composed of TE links of the same TDM layer. In calculating the path
for the LSP, the TED MAY be filtered to include only links where
both end include requested LSP switching type. In this way
hierarchical routing is done by using a TED filtered with respect
to switching capability (that is, with respect to particular layer).
If triggered signaling is allowed, the path computation mechanism
MAY produce a route containing multiple layers/regions. The path is
computed over the multiple layers/regions even if the path is not
"connected" in the same layer as the endpoints of the path exist.
Note that here we assume that triggered signaling will be invoked
to make the path "connected", when the upper-layer signaling
request arrives at the boundary node.
The upper-layer signaling request may contain an ERO that includes
only hops in the upper layer, in which case the boundary node is
responsible for triggered creation of the lower-layer FA-LSP using
a path of its choice, or for the selection of any available lower
layer LSP as a data link for the higher layer. This mechanism is
appropriate for environments where the TED is filtered in the
higher layer, where separate routing instances are used per layer,
or where administrative policies prevent the higher layer from
specifying paths through the lower layer.
Obviously, if the lower layer LSP has been advertised as a TE link
(virtual or real) into the higher layer, then the higher layer
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signaling request may contain the TE link identifier and so
indicate the lower layer resources to be used. But in this case,
the path of the lower layer LSP can be dynamically changed by the
lower layer at any time.
Alternatively, the upper-layer signaling request may contain an ERO
specifying the lower layer FA-LSP route. In this case, the boundary
node is responsible for decision as to which it should use the path
contained in the strict ERO or it should re-compute the path within
in the lower-layer.
Even in case the lower-layer FA-LSPs are already established, a
signaling request may also be encoded as loose ERO. In this
situation, it is up to the boundary node to decide whether it
should a new lower-layer FA-LSP or it should use the existing
lower-layer FA-LSPs.
The lower-layer FA-LSP can be advertised just as an FA-LSP in the
upper-layer or an IGP adjacency can be brought up on the lower-
layer FA-LSP.
5.8. LSP Resource Utilization
It MUST be possible to utilize network resources efficiently.
Particularly, resource usage in all layers SHOULD be optimized as a
whole (i.e., across all layers), in a coordinated manner, (i.e.,
taking all layers into account). The number of lower-layer LSPs
carrying upper-layer LSPs SHOULD be minimized (Note that multiple
LSPs MAY be used for load balancing). Lower-layer LSPs that could
have their traffic re-routed onto other LSPs are unnecessary and
SHOULD be avoided.
5.8.1. FA-LSP Release and Setup
Statistical multiplexing can only be employed in PSC and L2SC
regions. A PSC or L2SC LSP may or may not consume the maximum
reservable bandwidth of the TE link (FA LSP) that carries it. On
the other hand, a TDM, or LSC LSP always consumes a fixed amount of
bandwidth as long as it exists (and is fully instantiated) because
statistical multiplexing is not available.
If there is low traffic demand, some FA LSPs that do not carry any
higher-layer LSP MAY be released so that lower-layer resources are
released and can be assigned to other uses. Note that if a small
fraction of the available bandwidth of an FA-LSP is still in use,
the nested LSPs can also be re-routed to other FA-LSPs (optionally
using the make-before-break technique) to completely free up the
FA-LSP. Alternatively, unused FA LSPs MAY be retained for future
use. Release or retention of underutilized FA LSPs is a policy
decision.
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As part of the re-optimization process, the solution MUST allow
rerouting of an FA LSP while keeping interface identifiers of
corresponding TE links unchanged. Further, this process MUST be
possible while the FA LSP is carrying traffic (higher layer LSPs)
with minimal disruption to the traffic.
Additional FA LSPs MAY also be created based on policy, which might
consider residual resources and the change of traffic demand across
the region. By creating the new FA LSPs, the network performance
such as maximum residual capacity may increase.
As the number of FA LSPs grows, the residual resource may decrease.
In this case, re-optimization of FA LSPs MAY be invoked according
to policy.
Any solution MUST include measures to protect against network
destabilization caused by the rapid setup and teardown of LSPs as
traffic demand varies near a threshold.
Signaling of lower-layer LSPs SHOULD include a mechanism to rapidly
advertise the LSP as a TE link and to coordinate into which routing
instances the TE link should be advertised.
5.8.2. Virtual TE-Links
It may be considered disadvantageous to fully instantiate (i.e.
pre-provision) the set of lower layer LSPs that provide the VNT
since this might reserve bandwidth that could be used for other
LSPs in the absence of upper-layer traffic.
However, in order to allow path computation of upper-layer LSPs
across the lower-layer, the lower-layer LSPs MAY be advertised into
the upper-layer as though they had been fully established, but
without actually establishing them. Such TE links that represent
the possibility of an underlying LSP are termed "virtual TE-links."
It is an implementation choice at a layer boundary node whether to
create real or virtual TE-links, and the choice if available in an
implementation MUST be under the control of operator policy. Note
that there is no requirement to support the creation of virtual TE-
links, since real TE-links (with established LSPs) may be used, and
even if there are no TE-links (virtual or real) advertised to the
higher layer, it is possible to route a higher layer LSP into a
lower layer on the assumptions that proper hierarchical LSPs in the
lower layer will be dynamically created (triggered) as needed.
If an upper-layer LSP that makes use of a virtual TE-Link is set up,
the underlying LSP MUST be immediately signaled in the lower layer.
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If virtual TE-Links are used in place of pre-established LSPs, the
TE-links across the upper-layer can remain stable using pre-
computed paths while wastage of bandwidth within the lower-layer
and unnecessary reservation of adaptation ports at the border nodes
can be avoided.
The concept of the VNT can be extended to allow the virtual TE-
links to form part of the VNT. The combination of the fully
provisioned TE-links and the virtual TE-links defines the VNT
provided by the lower layer.
The solution SHOULD provide operations to facilitate the build-up
of such virtual TE-links, taking into account the (forecast)
traffic demand and available resource in the lower-layer.
Virtual TE-links MAY be modified dynamically (by adding or removing
virtual TE links, or changing their capacity) according to the
change of the (forecast) traffic demand and the available resource
in the lower-layer.
Any solution MUST include measures to protect against network
destabilization caused by the rapid changes in the virtual network
topology as traffic demand varies near a threshold.
The VNT can be changed by setting up and/or tearing down virtual TE
links as well as by modifying real links (i.e. the fully
provisioned LSPs).
The maximum number of virtual TE links that can be defined SHOULD
be configurable.
How to design the VNT and how to manage it are out of scope of this
document.
5.9. Verification of the LSPs
When a lower layer LSP is established for use as a data link by a
higher layer, the LSP MAY be verified for correct connectivity and
data integrity. Such mechanisms are data technology-specific and
are beyond the scope of this document, but may be coordinated
through the GMPLS control plane.
6. Security Considerations
The current version of this document does not introduce any new
security considerations as it only lists a set of requirements.
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It is expected that solution documents will include a full analysis
of the security issues that any protocol extensions introduce.
7. IANA Considerations
This informational document makes no requests to IANA for action.
8. References
8.1. Normative Reference
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997.
[RFC4202] K.Kompella and Y.Rekhter, "Routing Extensions in
Support of Generalized Multi-Protocol Label
Switching (GMPLS)," RFC4202, October 2005.
[RFC4726] A.Farrel, J-P. Vasseur, and A.Ayyangar, "A Framework
for Inter-Domain Multiprotocol Label Switching
Traffic Engineering", RFC 4726, November 2006.
[RFC4206] K.Kompella and Y.Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label
Switching (GMPLS) Traffic Engineering (TE),"
RFC4206, Oct. 2005.
[RFC3945] E.Mannie (Ed.), "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October
2004.
[RFC4397] I.Bryskin and A. Farrel, "A Lexicography for the
Interpretation of Generalized Multiprotocol
Label Switching (GMPLS) Terminology within the
Context of the ITU-T's Automatically Switched
Optical Network (ASON) Architecture", RFC 4397,
February 2006.
8.2. Informative References
[MRN-EVAL] Le Roux, J.L., Brungard, D., Oki, E., Papadimitriou, D.,
Shiomoto, K., Vigoureux, M.,"Evaluation of existing
GMPLS Protocols against Multi Layer and Multi Region
Networks (MLN/MRN)", draft-ietf-ccamp-gmpls-mrn-eval,
work in progress.
[MPLS-GMPLS] K. Kumaki (Editor), "Interworking Requirements to
Support operation of MPLS-TE over GMPLS networks",
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draft-ietf-ccamp-mpls-gmpls-interwork-reqts, work in
progress.
[DYN-HIER] Shiomoto, K., Rabbat, R., Ayyangar, A., Farrel, A. and
Ali, Z., "Procedures for Dynamically Signaled
Hierarchical Label Switched Paths", draft-ietf-
ccamp-lsp-hierarchy-bis, work in progress.
[AUTO-MESH] Vasseur, JP., Le Roux, JL., et al., "Routing
extensions for discovery of Multiprotocol (MPLS)
Label Switch Router (LSR) Traffic Engineering (TE)
mesh membership", draft-ietf-ccamp-automesh, work in
progress.
9. Authors' Addresses
Kohei Shiomoto
NTT Network Service Systems Laboratories
3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan
Email: shiomoto.kohei@lab.ntt.co.jp
Dimitri Papadimitriou
Alcatel-Lucent
Francis Wellensplein 1,
B-2018 Antwerpen, Belgium
Phone : +32 3 240 8491
Email: dimitri.papadimitriou@alcatel-lucent.be
Jean-Louis Le Roux
France Telecom R&D,
Av Pierre Marzin,
22300 Lannion, France
Email: jeanlouis.leroux@orange-ft.com
Martin Vigoureux
Alcatel-Lucent
Route de Nozay, 91461 Marcoussis cedex, France
Phone: +33 (0)1 69 63 18 52
Email: martin.vigoureux@alcatel-lucent.fr
Deborah Brungard
AT&T
Rm. D1-3C22 - 200
S. Laurel Ave., Middletown, NJ 07748, USA
Phone: +1 732 420 1573
Email: dbrungard@att.com
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10.Contributors' Addresses
Eiji Oki
NTT Network Service Systems Laboratories
3-9-11 Midori-cho,
Musashino-shi,
Tokyo 180-8585,
Japan
Phone: +81 422 59 3441
Email: oki.eiji@lab.ntt.co.jp
Ichiro Inoue
NTT Network Service Systems Laboratories
3-9-11 Midori-cho,
Musashino-shi,
Tokyo 180-8585,
Japan
Phone: +81 422 59 3441
Email: ichiro.inoue@lab.ntt.co.jp
Emmanuel Dotaro
Alcatel-Lucent
Route de Nozay,
91461 Marcoussis cedex,
France
Phone : +33 1 6963 4723
Email: emmanuel.dotaro@alcatel-lucent.fr
11. Intellectual Property Considerations
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed
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
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
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this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
12. Full Copyright Statement
Copyright (C) The IETF Trust (2007). 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, THE
IETF TRUST, 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.
Expires October 2007 [Page 22]
