One document matched: draft-shiomoto-ccamp-gmpls-mrn-reqs-02.txt
Differences from draft-shiomoto-ccamp-gmpls-mrn-reqs-01.txt
Network Working Group Kohei Shiomoto (NTT)
Internet Draft Dimitri Papadimitriou (Alcatel)
Jean-Louis Le Roux (France Telecom)
Martin Vigoureux (Alcatel)
Deborah Brungard (AT&T)
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Requirements for GMPLS-based multi-region and
multi-layer networks (MRN/MLN)
draft-shiomoto-ccamp-gmpls-mrn-reqs-02.txt
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2005). All Rights Reserved.
Abstract
Most of the initial efforts on Generalized MPLS (GMPLS) have
been related to environments hosting devices with a single
switching capability, that is, one data plane switching layer.
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. 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,
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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. LSP Region and layer.........................................4
4. Key mechanisms in GMPLS-based multi-region/multi-layer
networks..........................................................6
4.1. Interface Switching Capability...............................8
4.2. Multiple Interface Switching Capabilities....................8
4.2.1. MRN/MLN with Simplex nodes.................................9
4.2.2. MRN/MLN with hybrid nodes..................................9
4.2.3. Vertical and Horizontal interaction and integration.......10
4.3. Integrated Traffic Engineering (TE) and Resource Control....12
4.4. Triggered signaling.........................................12
4.5. TE LSP......................................................12
4.6. Virtual network topology (VNT)..............................13
5. Requirements..................................................13
5.1. Scalability.................................................13
5.2. TE-LSP resource utilization.................................14
5.3. TE-LSP Attribute inheritance................................16
5.4. Verify the TE-LSP before it enters service..................16
5.5. Disruption minimization.....................................16
5.6. Path computation re-optimization stability..................16
5.7. Computing paths with and without nested signaling...........17
5.8. Handling single-switching and multi-switching type capable
nodes............................................................17
5.9. Advertisement of the available adaptation resource..........18
6. Security Considerations.......................................18
7. References....................................................18
7.1. Normative Reference.........................................18
7.2. Informative References......................................19
8. Author's Addresses............................................19
9. Intellectual Property Considerations..........................20
10. Full Copyright Statement.....................................20
1. Introduction
Generalized MPLS (GMPLS) extends MPLS to handle multiple
switching technologies: packet switching, layer-two switching,
TDM switching, wavelength switching, and fiber switching (see
[GMPLS-ARCH]). 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
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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 LSP
associated to TDM, Packet LSP associated to PSC). 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 VC-4-256c. The Interface Switching Capability
Descriptor (ISCD) [GMPLS-RTG] identifying the interface switching
type, the encoding type and the switching bandwidth granularity,
supports this additional granularity. The ISCD uniquely
identifies a set of one or more network layers e.g. TDM ISC
covers from VC-11 to VC-4-256c.
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. All TE links
terminating on such nodes have the same switching type value.
A typical example is a network composed of PSC and
TDM LSRs with only PSC TE-link ends and with only TDM TE-link
ends, respectively.
- Network elements are multi-switching capable LSRs i.e. nodes
hosting at least more than one switching capability. TE links
terminating on such nodes may have a set of one or more
switching type value. A typical example is a
network composed of LSRs that are capable of switching with
PSC+TDM TE-links. 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.
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
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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 operators 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.
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, VC4-4c are different
layers of the TDM region.
3.1. Data plane layers
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 VC-4-64c
represent two different layers.
A network resource is atomic within the layer in which it is
defined except PSC layers. For example, it is possible to
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allocate an integer number of VC12 resources to create a VC12
layer LSP, but fractions of VC12 resources cannot be allocated
within the VC12 layer.
3.2. LSP Regions
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.
Examples of 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 VC-4-64c capable TE links are part of the same
TDM Region.
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.
Multiple layers can exist in a single region network. Moreover,
the control plane mechanisms introduced and defined for LSP
regions, for example the Forwarding Adjacency (FA), and the
Virtual FA Topology described as part of this document can
equally be described from the perspective of a multi-layer data
plane.
3.3. 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.
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
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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. Details
concerning the requirements for such services and the required
functionality to deliver such services will be addressed in a
future release of this document. It has, however, to be
emphasized that delivery of such services is a strong motivator
for the deployment of multi-region/multi-layer networks.
3.4. 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. 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.
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. 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 mechanisms in GMPLS-based multi-region/multi-layer networks
An example of Multi-Region Networks (MRN) consisting of PSC and
LSC is illustrated in Figure 1. The concept of region is by
nature hierarchical. PSC and LSC are defined from the upper to
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the lower regions in Figure 1. Network elements with different
switching technologies in the MRN are controlled by a unified
GMPLS control plane.
+-----+
| PSC |
----------| |---------
| | LSC | |
| +-----+ |
| | |
+-----+ +-----+ +-----+
| PSC | | | | |
| |-------| LSC |------| PSC |
| LSC | | | | |
+-----+ +-----+ +-----+
| | |
| +-----+ |
| | PSC | |
----------| |---------
| LSC |
+-----+
Figure 1: Example of multi-region network
An example of Multi-Layer Networks (MLN) consisting of two
network layers L2 and L1 belonging to the same LSP region (e.g.
TDM) is illustrated in Figure 2. Note that the two layers may
belong to the same or different regions. In the latter case the
network is also a multi-region network. The concept of data
plane layer is by nature hierarchical. L2 and L1 are defined as
higher and lower layers respectively in Figure 1. Network
elements with different switching capabilities in the MLN are
controlled by a unified (that is, a single) GMPLS control plane.
+-----+
| L2 |
----------| |---------
| | L1 | |
| +-----+ |
| | |
+-----+ +-----+ +-----+
| L2 | | | | |
| |-------| L1 |------| L2 |
| L1 | | | | |
+-----+ +-----+ +-----+
| | |
| +-----+ |
| | L2 | |
----------| |---------
| L1 |
+-----+
Figure 2: Example of multi-layer network
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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. For example,
packet switch capable (PSC) is a property of an interface, which
can distinguish IP/MPLS packets (for example, a router's
interface) while lambda switch capable (LSC) is a property of an
interface which models the switching of individual wavelengths
multiplexed within a fiber link (for example, an OXC's
interface).
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.
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
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.
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Additionally TE link advertisements issued by a simplex or a
hybrid node may need to advertise the internal node's link
adaptation capabilities. That is, the node's capability to
perform layer border node functions. The necessity of such
advertisements will be described later in separate document.
Networks with single switching capable nodes
4.2.1. Networks with single-switching capable nodes
In this case, the network consists of a set of single-switching
capable nodes, with at least two distinct switching capabilities
in the network. For instance, nodes in Figure 3 are all single
switching capable. There are two switching capabilities in the
network: PCS and LSC.
+-----+
| PSC |
----------| |---------
| | | |
| +-----+ |
| | |
+-----+ +-----+ +-----+
| PSC | | | | |
| |-------| LSC |------| PSC |
| |-------| |------| |
+-----+ +-----+ +-----+
| | |
| +-----+ |
| | PSC | |
----------| |---------
| |
+-----+
Figure 3: Network wit single-switching capable nodes
4.2.2. Networks with multi-switching capable simplex nodes
In this case, the network consists of at least one simplex node
and includes a set of single switching type capable nodes (that
is, all TE links terminating on such nodes have the same ISC).
For example, the node TL2 in Figure 4 is a simplex node, which
has data links with TDM switching type interfaces and data links
with lambda switching type interfaces.
At the layer boundary, the ISCs of the opposite ends of the
links are different. When an LSP crosses the boundary (for
example, an LSP from P2 to P4) from the upper layer to the lower
layer, it is nested in a lower-layer hierarchical LSP (for
example, an LSP from TL2 to T4).
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.........................................................
: ........................................... :
: : ............................. : :
: : : ............... : : :
: PSC : TDM : LSC : FSC : : : :
: +--+ : +--+ : +--+ : +--+ +--+ : +--+ : +--+ : +--+ :
: |P1|---|T1|---|L1|---|F1|---|F3|---|L3|---|T3|---|P3| :
: +--+ : +--+ : +--+ : +--+ +--+ : +--+ : +--+ : +--+ :
: | : | : | : | | : | : | : | :
: | : | : | : | | : | : | : | :
: +--+ : +---------+ : +--+ +--+ : +--+ : +--+ : +--+ :
: |P2|---| TL2 |---|F2|---|F4|---|L4|---|T4|---|P4| :
: +--+ : +---------+ : +--+ +--+ : +--+ : +--+ : +--+ :
: : : .............. : : :
: : ............................. : :
: ........................................... :
.........................................................
Figure 4: Simplex node network.
4.2.3. Networks with multi-switching capable hybrid nodes
In this case, 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 TDM
links (Link1 and Link2), which are connected to the TDM
switching element by interfaces that model TDM switching.
The two switching elements are internally interconnected in such
a way that it is possible to terminate some of the resources of,
say, Link1 and provide through them adaptation for PSC traffic
received/sent over the PSC links. This situation is modeled in
GMPLS by connecting the local end of Link1 to the TDM switching
element via an additional interface realizing the
termination/adaptation function.
Network element
.............................
: -------- :
: | PSC | :
: +--<->---| | :
: | -------- :
TDM : | ---------- :
+PSC : +--<->--|#a TDM | :
Link1 ------------<->--|#b | :
Link2 ------------<->--|#c | :
: ---------- :
:............................
Figure 5a. Hybrid node.
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Figure 5b illustrates how existing GMPLS Routing is not
sufficient and needs to be extended to advertise and consider
termination/adaptation capabilities for hybrid nodes.
Network element
.............................
: -------- :
: | PSC | :
: | | :
: --|#b1 | :
: | | #d | :
: | -------- :
: | | :
: | ---------- :
: /| | | #c | :
: | |-- | | :
Link1 ========| | | TDM | :
: | |----|#b2 | :
: \| ---------- :
:............................
Figure 5b. Hybrid node.
Let's assume that all interfaces are STM64 (with VC4-16c capable
as Max LSP bandwidth). So, initially, TE Link 1 is
advertised with two ISCD sub-TLVs:
- ISCD #1 sub-TLV: TDM with Max LSP bandwidth = STM16 (i.e. VC4-
16c capable as Max LSP bandwidth) and Unreserved bandwidth (of
the whole incoming link) = STM64
- ISCD #2 sub-TLV: PSC with Max LSP bandwidth = 2.5 Gb (i.e.
and Unreserved bandwidth (of the whole incoming link) = 10 Gb
After, setting up several PSC LSPs via port #b1 qnd terminating
several TDM LSPs via port #b2 (and #d), there is only 155 Mb
capacity still available on port #d. However a 622 Mb capacity
remains on port b1 and VC4-5x capacity in port b2. TE Link 1 is
now advertised with the following ISCD sub-TLVs:
- ISCD #1 sub-TLV: TDM with Max LSP bandwidth = VC4-4c, the
Unreserved bandwidth reflects the VC4-5c capacity still
available for the whole link
- ISCD #2 sub-TLV: PSC with Max LSP bandwidth = 622 Mb, the
Unreserved bandwidth reflects the capacity still available for
the whole link i.e. 777 Mb.
When computing the path for a new VC4-4c TDM LSP, one cannot
know, based on existing GMPLS routing advertisements (i.e. two
ISCD sub-TLVs), that this node cannot be used to setup this LSP
terminated on port #d, as there is only 155M still available for
TDM-PSC adaptation. Thus, in that case additional routing
information is required to advertise the available TDM-PSC
internal adaptation resources (i.e. 155 Mb here).
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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. If such an LSP does not already exist, the LSP may
be established dynamically. Such a mechanism is referred to as
"triggered signaling".
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 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. An FA has the
special quality of not requiring a routing adjacency (peering)
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between its ends yet still guaranteeing control plane
connectivity between the FA-LSP ends. 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]. Note that
ISCD contains the switching type (i.e. interface switching
capability), the data encoding type, and the bandwidth
granularity.
4.3.3. Virtual network topology (VNT)
A set 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. 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 easily
adapted to traffic demands.
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 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. 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
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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.
5.2. LSP resource utilization
It MUST be possible to utilize network resources efficiently.
Particularly, resource usage in each layer SHOULD be optimized
as a whole (i.e. across all layers), in a coordinated manner.
The number of lower-layer LSPs carrying upper-layer LSPs SHOULD
be minimized. Redundant lower-layer LSPs SHOULD be avoided
(except for protection purpose).
5.2.1. 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 be
improved.
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.
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5.2.2. 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.
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 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.
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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.
5.3. 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.
5.4. 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.
5.5. 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).
5.6. 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 changes in traffic
demand. 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.
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-1.
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.
5.8. 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.
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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
5.9. 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 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.
6. 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.
7. References
7.1. 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.
7.2. Informative References
[MPLSGMPLS] D.Brungard, J.L.Le Roux, E.Oki, D. Papadimitriou,
D.Shimazaki, K.Shiomoto, "Migrating from IP/MPLS to GMPLS
networks," draft-oki-ccamp-gmpls-ip-interworking, work in
progress.
[MAMLTE] K. Shiomoto et al., "Multi-area multi-layer traffic
engineering using hierarchical LSPs in GMPLS networks", draft-
shiomoto-multiarea-te, work in progress.
8. 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
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
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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
9. 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.
By submitting this Internet-Draft, each author represents that
any applicable patent or other IPR claims of which he or she is
aware have been or will be disclosed, and any of which he or she
becomes aware will be disclosed, in accordance with Section 6 of
RFC 3668.
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, see http://www.ietf.org/ietf/IPR/tellabs-ipr-draft-
shiomoto-ccamp-gmpls-mrn-reqs.txt
10. 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
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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 21]
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