Internet DRAFT - draft-shiomoto-ccamp-gmpls-mrn-reqs
draft-shiomoto-ccamp-gmpls-mrn-reqs
Network Working Group Kohei Shiomoto (NTT)
Internet Draft Dimitri Papadimitriou (Alcatel)
Jean-Louis Le Roux (France Telecom)
Martin Vigoureux (Alcatel)
Deborah Brungard (AT&T)
Expires: April 2006 October 2005
Requirements for GMPLS-based multi-region and
multi-layer networks (MRN/MLN)
draft-shiomoto-ccamp-gmpls-mrn-reqs-03.txt
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Copyright (C) The Internet Society (2005).
Abstract
Most of the initial efforts on 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-
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layered network of either a single switching technology or multiple
switching technologies. In GMPLS, a switching technology domain
defines a region, and a network of multiple switching types is
referenced 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 draft defines a framework for GMPLS
based multi-region/multi-layer networks and lists a set of
functional requirements.
Table of Contents
1. Introduction...................................................2
2. Conventions used in this document..............................4
3. Positioning....................................................4
3.1. Data plane layers and control plane regions..................5
3.2. Services.....................................................5
3.3. Vertical and Horizontal interaction and integration..........6
4. Key concepts of GMPLS-based MLNs and MRNs......................6
4.1. Interface Switching Capability...............................7
4.2. Multiple Interface Switching Capabilities....................7
4.2.1. Networks with multi-switching capable hybrid nodes.........8
4.3. Integrated Traffic Engineering (TE) and Resource Control.....9
4.3.1. Triggered signaling........................................9
4.3.2. FA-LSP....................................................10
4.3.3. Virtual network topology (VNT)............................10
5. Service networks provided over MRN/MLN........................11
6. Requirements..................................................11
6.1. Scalability.................................................11
6.2. LSP resource utilization....................................12
6.2.1. FA-LSP release and setup..................................12
6.2.2. Virtual TE-Link...........................................12
6.3. LSP Attribute inheritance...................................14
6.4. Verification of the LSP.....................................14
6.5. Disruption minimization.....................................14
6.6. Stability...................................................14
6.7. Computing paths with and without nested signaling...........15
6.8. Handling single-switching and multi-switching type capable
nodes............................................................16
6.9. Advertisement of the available adaptation resource..........16
7. Security Considerations.......................................17
8. References....................................................17
8.1. Normative Reference.........................................17
8.2. Informative References......................................18
9. Author's Addresses............................................18
10. Intellectual Property Considerations.........................19
11. Full Copyright Statement.....................................20
1. Introduction
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Generalized MPLS (GMPLS) extends MPLS to handle multiple switching
technologies: packet switching, layer-two 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 [HIER].
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 associated
to TDM, IP associated to PSC). However, more than one data plane
layer can be associated to the same region (e.g. both VC4 and VC12
are associated to TDM). Thus, a control plane region, identified by
its switching type value (e.g. TDM), can itself be sub-divided into
smaller granularity based on the bandwidth that defines the "data
plane switching layers" e.g. from VC-11 to VC4-256c. The Interface
Switching Capability Descriptor (ISCD) [GMPLS-RTG], identifying the
interface switching type, the encoding type and the switching
bandwidth granularity, enable the characterization of the
associated layers.
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). To differentiate a network supporting LSPs of
different switching technologies (ISCs) from a single region
network, a network supporting more than one switching technology is
called a Multi-Region Network (MRN).
MRNs can be categorized according to the distribution of the
switching type values amongst the LSRs:
- Network elements are single switching capable LSRs and
different types of LSRs form the network.
- Network elements are multi-switching capable LSRs i.e. nodes
hosting at least more than one switching capability. Multi-
switching capable LSRs are further
classified as "simplex" and "hybrid" nodes (see Section 4.2).
- Any combination of the above two elements. A network composed
of both single and multi-switching capable LSRs.
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Since GMPLS provides a comprehensive framework for the control of
different switching capabilities, a single GMPLS instance may be
used to control the MRNs/MLNs 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/layers existing in the
network, a path across multiple regions/layers can be computed
using this TED. Thus optimization of network resources can be
achieved across multiple regions/layers.
Consider, for example, a MRN consisting of IP/MPLS routers and TDM
cross-connects. Assume that a packet LSP is routed between source
and destination IP/MPLS routers, and that the LSP can be routed
across the PSC-region (i.e. utilizing only resources of the IP/MPLS
level topology). If the performance objective for the LSP is not
satisfied, new TE links may be created between the IP/MPLS routers
across the TDM-region (for example, VC-12 links) and the LSP can be
routed over those links. Further, even if the LSP can be
successfully established across the PSC-region, TDM hierarchical
LSPs across the TDM region between the IP/MPLS routers may be
established and used if doing so enables meeting an operator's
objectives on network resources available (e.g. link bandwidth, and
adaptation port between regions) across the multiple regions. The
same considerations hold when VC4 LSPs are provisioned to provide
extra flexibility for the VC12 and/or VC11 layers in a 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
will be addressed in separate documents [MRN-EVAL].
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119
[RFC2119].
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.
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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.
These resources can be used for establishing LSPs or connectionless
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 several data plane layers that share the same type of
switching technology, that is, the same switching type. The
currently defined regions are: PSC, L2SC, TDM, LSC, and FSC regions.
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 is a control plane only concept. That is,
layers of the same region share the same switching technology and,
therefore, need the same set of technology specific signaling
objects.
3.2. Services
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 One service (realized via the network layers of TDM, and/or
LSC, and/or FSC regions) may support a Layer Two network (realized
via ATM VP/VC) which may itself support a Layer Three network
(IP/MPLS region). The supported data plane relationship is a data-
plane client-server relationship where the lower layer provides a
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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.
3.3. Vertical and Horizontal interaction and integration
Vertical interaction is defined as the collaborative mechanisms
within a network element that is capable of supporting more than
one switching capability and of realizing the client/server
relationships between them. Protocol exchanges between two network
controllers managing different regions are also a vertical
interaction. Integration of these interactions as part of the
control plane is referred to as vertical integration. The latter
refers thus to the collaborative mechanisms within a single control
plane instance driving multiple switching capabilities. Such a
concept is useful in order to construct a framework that
facilitates efficient network resource usage and rapid service
provisioning in carrier's networks that are based on multiple
switching technologies.
In a strict sense, horizontal interaction is defined as the
protocol exchange between network controllers that manage transport
nodes within a given region (i.e. nodes with the same switching
capability). For instance, the control plane interaction between
two LSC network elements 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 currently being evaluated as part of the
inter-domain work [Inter-domain], 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 gets blurred when administrative domains
match layer boundaries. Horizontal interaction is extended to cover
such case. 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 area.
4. Key concepts of GMPLS-based MLNs and MRNs
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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
The Interface Switching Capability (ISC) is introduced in GMPLS to
support various kinds of switching technology in a unified way
[GMPLS-ROUTING]. An ISC is identified via a switching type.
A switching type (also referred to as the switching capability
types) 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. Apart from the ISC,
the ISCD contains information, such as 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) TE
link end.
4.2. Multiple Interface Switching Capabilities
In a MLN, network elements may be single-switching 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 their TE Link(s). This
case is described in [GMPLS-ROUTING].
Multi-switching capable LSRs are classified as "simplex" and
"hybrid" nodes. Simplex and Hybrid nodes are categorized according
to the way they advertise these multiple ISCs:
- A simplex node can terminate links with different switching
capabilities each of them connected to the node by a single link
interface. So, it advertises several TE Links each with a single
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ISC value as part of its ISCD sub-TLVs. For example, an LSR with
PSC and TDM links each of which is connected to the LSR via single
interface.
- A hybrid node can terminate links with different switching
capabilities terminating on the same interface. So, it advertises
at least one TE Link containing more than one ISCDs with different
ISC values. For example, a node comprising of PSC and TDM links,
which are interconnected via internal links. The external
interfaces connected to the node have both PSC and TDM capability.
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 capable hybrid nodes
The network contains at least one hybrid node, zero or more simplex
nodes, and a set of single switching capable nodes.
Figure 5a 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 two PSC and TDM
links (Link1 and Link2 respectively). It also has internal link
connecting the two swtching 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 through them 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. Two ways are possible to set up
PSC LSPs. Available resource advertisement e.g. Unreserved and
Min/Max LSP Bandwidth should cover both two ways.
Network element
.............................
: -------- :
: | PSC | :
Link1 -------------<->--|#a | :
: +--<->---|#b | :
: | -------- :
TDM : | ---------- :
+PSC : +--<->--|#c TDM | :
Link2 ------------<->--|#d | :
: ---------- :
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:............................
Figure 5a. Hybrid node.
4.3. Integrated Traffic Engineering (TE) and Resource Control
In GMPLS-based multi-region/multi-layer networks, TE Links are
consolidated into a single Traffic Engineering Database (TED).
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 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 layer(s)
(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 LSPs (see Section
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.
There is a full spectrum of options to control how FA LSPs are
dynamically established. It 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 signaling perspective, there are two alternatives to
establish lower layer FA LSP: static and dynamic. Decision will be
made either by the operator or automatically using features like
TE auto-mesh, for instance. 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".
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4.3.2. FA-LSP
Once an LSP is created across a layer, 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
[HIER]. 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 FA-LSP. The TE-link
associated to an FA-LSP is called an FA. An FA has the special
characteristic of not requiring a routing adjacency (peering)
between its ends yet still guaranteeing control plane connectivity
between the FA-LSP ends based on a signaling adjacency. A FA is a
useful and powerful tool for improving the scalability of GMPLS
Traffic Engineering (TE) capable networks.
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 [HIER]. 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 [GMPLS-ROUTING].
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 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 VNT. The virtual
network topology is configured by setting up or tearing down the
LSC LSPs. By using GMPLS signaling and routing protocols, the
virtual network topology can be adapted to traffic demands.
Reconfiguration of the virtual network topology may be triggered by
traffic demand change, topology configuration change, signaling
request from the upper layer, and network failure. 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 [MAMLTE]. Reconfiguration
is performed by computing the new VNT from the traffic demand
matrix and optionally from the current VNT. Exact details are
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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. Service networks provided over MRN/MLN
A customer network may be provided on top of a server MRN/MLN
network (such as a transport network) which is operated by a
service provider. For example legacy IP or IP/MPLS networks can be
provided on top of GMPLS packet or optical networks [IW-MIG-FW].
The relationship between the networks is a client/server
relationship and, such services are referred to as "MRN/MLN
services".
The customer network may be provided either as part of the MRN/MLN
or in a separate network instance distinct from the MRN/MLN. There
could also be an administrative boundary between the customer
network and the MRN/MLN operated by the service provider. All
requirements described in this document SHOULD be applicable if
there is an administrative boundary between the customer network
and the MRN/MLN operated by service provider.
Impact on the customer network design, operation, and
administration SHOULD be minimized. For instance, the design for
address assignment and IGP area division should be kept independent
from the underlying MRN/MLN.
The MRN/MLN SHOULD provide mechanisms to allow an administrative
boundary between the customer network and the MRN/MLN.
6. Requirements
6.1. 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.
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6.2. 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, (ie taking
all layers into account). The number of lower-layer LSPs carrying
upper-layer LSPs SHOULD be minimized as much as possible (Note that
multiple LSPs may be used for load balance) . Unneccesary lower-
layer LSPs SHOULD be avoided.
6.2.1. 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 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, which do not carry
any LSP may be released so that resources are released. Note that
if a small fraction of the available bandwidth is still under use,
the nested LSPs can also be re-routed optionally using the make-
before-break technique. Alternatively, the FA LSPs may be retained
for future usage. Release or retention of underutilized FA LSPs is
a policy decision.
As part of the re-optimization process, the solution MUST allow
rerouting of FA LSPs while keeping interface identifiers of
corresponding TE links unchanged.
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
the policy.
Any solution MUST include measures to protect against network
destabilization caused by the rapid set up and tear down of LSPs as
traffic demand varies near a threshold.
6.2.2. Virtual TE-Link
It may be considered disadvantageous to fully instantiate (i.e.
pre-provision) the set of lower layer LSPs since this may reserve
bandwidth that could be used for other LSPs in the absence of the
upper-layer traffic.
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However, in order to provision upper-layer LSPs across the lower-
layer, the LSPs MAY still be advertised into the upper-layer as
though they had been fully established. Such TE links that
represent the possibility of an underlying LSP are termed "virtual
TE-link". Note that this is not a mandatory (MUST) requirement
since even if there are no LSPs advertised to the higher layer, it
is possible to route an upper layer LSP into a lower layer based on
the lower layer's TE-links and making assumptions that proper
hierarchical LSPs in the lower layer will be dynamically created 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
if it has not been established.
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 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 across 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) 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 configured
SHOULD be well-engineered.
How to design the VNT and how to manage it are out of scope of this
document and will be treated in a companion document on solution.
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6.3. 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)
Inheritance rules MUST be applied based on specific policies.
Particular attention should be given to the inheritance of TE
metric (which may be other than a strict sum of the metrics of the
component TE links at the lower layer) and protection attributes.
6.4. Verification of the LSP
When the LSP is created, it SHOULD be verified that it has been
established before it can be used by an upper layer LSP. Note, this
is not within the GMPLS capability scope for non-PSC interfaces.
6.5. Disruption minimization
When reconfiguring the VNT according to a change in traffic demand,
the upper-layer LSP might be disrupted. Such disruption MUST be
minimized.
When residual resource decreases to a certain level, some 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 LSPs 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).
6.6. Stability
The 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
status and TE parameters (TE metric for instance) of links in the
virtual network topology changes frequently.
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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 of the VNT may be caused by the creation
and/or deletion of several LSPs.
Creation and deletion of LSPs MAY be triggered by adjacent layers
or through operational actions to meet traffic demand change,
topology change, signaling request from the upper layer, and
network failure. Routing robustness SHOULD be traded with
adaptability with respect to the change of incoming traffic
requests.
A full mesh of LSPs MAY be created between every pair of border
nodes of the PSC region. The merit of a full mesh of PSC TE-LSPs is
that it provides stability to the PSC-level routing. That is, the
forwarding table of an PSC-LSR is not impacted by re-routing
changes within the lower-layer (e.g., TDM layer). Further, there is
always full PSC reachability and immediate access to bandwidth to
support PSC LSPs. But it also has significant drawbacks, since it
requires the maintenance of n^2 RSVP-TE sessions, which may be
quite CPU and memory consuming (scalability impact). Also this may
lead to significant bandwidth wasting if LSP with a certain amount
of reserved bandwidth is used.
Note that the use of virtual TE-links solves the bandwidth wasting
issue, and may reduce the control plane overload.
6.7. 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 computing
the path. 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 TE database 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 TE database 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.
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The upper-layer signaling request may contain a loose ERO, and the
boundary node is responsible for creation of the lower-layer FA-LSP.
When the boundary node receives the signaling setup request and
determines that it has to expand the loose ERO content by creating
the lower-layer FA-LSP, it will create the lower layer FA-LSP
accordingly. Once the lower-layer LSP is established, the ERO
contents for the upper-layer signaling setup request are expanded
to include the lower-layer FA-LSP and signaling setup for the
upper-layer LSP are carried in-band of the lower-layer LSP.
The upper-layer signaling request may contain a strict 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.
We should note that 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.
6.8. 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 capable and multi-switching (simplex or
hybrid) capable nodes could play the role of layer boundary.
MRN/MLN Path computation SHOULD handle TE topologies built of any
combination of single switching, simplex and hybrid nodes
6.9. Advertisement of the available adaptation resource
A hybrid node SHOULD maintain resources and advertise the resource
information on its internal links, the links required for vertical
(layer) integration. 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 because of the lack
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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).
7. Security Considerations
The current version of this document does not introduce any new
security considerations as it only lists a set of requirements. In
the future versions, new security requirements may be added.
8. References
8.1. Normative Reference
[RFC3979] Bradner, S., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3979, March 2005.
[GMPLS-ROUTING] K.Kompella and Y.Rekhter, "Routing Extensions in
Support of Generalized Multi-Protocol Label
Switching," draft-ietf-ccamp-gmpls-routing-09.txt,
October 2003 (work in progress).
[Inter-domain] A.Farrel, J-P. Vasseur, and A.Ayyangar, "A
framework for inter-domain MPLS traffic
engineering," draft-ietf-ccamp-inter-domain-
framework, work in progress.
[HIER] K.Kompella and Y.Rekhter, "LSP hierarchy with
generalized MPLS TE," draft-ietf-mpls-lsp-hierarchy-
08.txt, work in progress, Sept. 2002.
[STITCH] Ayyangar, A. and Vasseur, JP., "Label Switched Path
Stitching with Generalized MPLS Traffic Engineering",
draft-ietf-ccamp-lsp-stitching, work in progress.
[LMP] J. Lang, "Link management protocol (LMP)," draft- ietf-
ccamp-lmp-10.txt (work in progress), October 2003.
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[RFC3945] E.Mannie (Ed.), "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October
2004.
8.2. Informative References
[MAMLTE] K. Shiomoto et al., "Multi-area multi-layer traffic
engineering using hierarchical LSPs in GMPLS
networks", draft-shiomoto-multiarea-te, work in
progress.
[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-leroux-ccamp-gmpls-mrn-
eval, work in progress.
[IW-MIG-FW] Shiomoto, K., Papadimitriou, D., Le Roux, J.L.,
Brungard, D., Oki, E., Inoue, I., " Framework for
IP/MPLS-GMPLS interworking in support of IP/MPLS to
GMPLS migration ", draft-shiomoto-ccamp-mpls-gmpls-
interwork-fmwk-00.txt, work in progress.
9. Author's 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
Francis Wellensplein 1,
B-2018 Antwerpen, Belgium
Phone : +32 3 240 8491
Email: dimitri.papadimitriou@alcatel.be
Jean-Louis Le Roux
France Telecom R&D,
Av Pierre Marzin,
22300 Lannion, France
Email: jeanlouis.leroux@francetelecom.com
Martin Vigoureux
Alcatel
Route de Nozay, 91461 Marcoussis cedex, France
Phone: +33 (0)1 69 63 18 52
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Email: martin.vigoureux@alcatel.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
Contributors
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)
Route de Nozay, 91461 Marcoussis cedex, France
Phone : +33 1 6963 4723 Email: emmanuel.dotaro@alcatel.fr
10. 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
this standard. Please address the information to the IETF at ietf-
ipr@ietf.org.
The IETF has been notified by Tellabs Operations, Inc. of
intellectual property rights claimed in regard to some or all of
the specification contained in this document. For more information,
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see draft-shiomoto-ccamp-">http://www.ietf.org/ietf/IPR/tellabs-ipr-draft-shiomoto-ccamp-
gmpls-mrn-reqs.txt
11. 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.
Expires December 2005 [Page 20]
