Network Working Group Kohei Shiomoto (NTT)
Internet Draft Dimitri Papadimitriou (Alcatel)
Expires: August 2005 Jean-Louis Le Roux (France Telecom)
Martin Vigoureux (Alcatel)
Deborah Brungard (AT&T)
February 2005
Requirements for GMPLS-based multi-region networks (MRN)
draft-shiomoto-ccamp-gmpls-mrn-reqs-01.txt
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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
network where different types of switching capabilities coexist,
which we call multi-region networks (MRN). This draft defines a
framework for GMPLS based multi-region networks and lists a set
of functional requirements.
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 concept is
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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 capabilities exist. These networks consist of several
switching technology domains, each of which uses the same
switching capability. The representation, in a GMPLS control
plane, of a switching technology domain is referred to as a
region [HIER].
A network comprising of multiple switching capabilities,
controlled by a single GMPLS control plane instance is called a
Multi-Region Network (MRN). MRNs can be categorized according to
the distribution of the switching capabilities 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 interface switching
capability. A typical example is a network composed of PSC and
TDM LSRs with only PSC TE-links and with only TDM TE-links,
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
interface switching capabilities. 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 enabling rapid service provisioning
and efficient resource usage across all switching capabilities.
In GMPLS-based multi-region networks, TE Links are consolidated
into a single Traffic Engineering Database (TED). Since this TED
contains the information relative to all the different regions
existing in the network, a path across multiple regions can be
computed using this TED. Thus optimization of network resources
can be sought and take place in across multiple regions.
Consider, for example, a network 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 data links may be
created between the IP/MPLS routers across the TDM-region and
the LSP can be routed over those links. Further, even if the LSP
can be successfully established across the PSC-region, TDM FA-
LSPs across the TDM region between the IP/MPLS routers may be
established and used if doing so enables meeting an operatorÆs
objectives on network resources available (e.g., link bandwidth,
and adaptation port between regions) across the multiple
regions.
A service provider's network may be divided into different
network layers. The customer's network is considered the highest
layer network, and interfaces to the highest layer of the
service provider's network. 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 network. Such customer networks may
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take various kind of network layer. Services provided on top of
GMPLS-based multi-region network is refereed to as "Multi-region
network services". For example legacy IP and MPLS/IP networks
can be supported on top of the multi-region networks. Details
concerning requirements for such services and functionality
required from multi-region networks 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 networks.
This document describes the requirements for the multi-region
network. The rest of this document is organized as follows. In
Section 3, the region and layer terminology considerations are
provided. In Section 4, the key concepts for the Generalized
MPLS-based multi-region and multi-layer service networks are
described. In Section 5, the functional requirements are listed.
There is no intention to specify solution specific elements in
this document. The applicability of existing GMPLS protocol to
MRN, and any protocol extensions, 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
3.1. LSP Region and layer
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. Examples of regions are: PSC, L2SC,
TDM, LSC, and FSC regions. Hence, an LSP region is a technology
domain (identified by the Switching Capability) for which data
plane resources (i.e. data links) are represented into the
control plane as an aggregate of TE information associated to a
set of links (i.e. TE links). Example: VC-11 to VC4-64c capable
TE links are part of the same TDM Region.
On the other hand, a data plane layer is a network resource of a
certain topological type (using the same type of termination
functions, e.g. a VC-11 and a VC-4-64c represent two different
layers), that could be used for establishing LSPs or
connectionless traffic delivery.
Note also that 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 related to LSP
region, e.g., Forwarding Adjacency (FA) and Virtual FA Topology,
described as part of this document can also be described from a
data plane multi-layer perspective.
A service provider's network may be divided into different
service network layers. The customer's network is considered the
highest layer network, and interfaces to the highest layer of
the service provider's network. Connectivity across the highest
layer of the service provider's network may be provided with
support from networks of successively lower layers. Network
layers are commonly arranged according to the switching
capabilities of the devices in the networks so that, for example,
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there may be layer one networks (TDM, LSC and FSC) supporting
layer two networks (L2SC) supporting layer three networks (IP
and MPLS). The supported data plane relationship is, however, a
data-plane client-server relationship where the lower layer
provides a service for the higher layer using the data links of
the lower layer, and so the layering relationship is actually
administrative rather than dependent on the switching
capabilities of the networks. Note that a multi-region network
does not impact the arbitrary data plane layering of networks.
4. Key mechanisms in GMPLS-based multi-region networks
An example of Multi-Region Networks (MRN) which consists 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
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
4.1. Interface switching capability
The Interface Switching Capability (ISC) concept is introduced
in GMPLS to support various kinds of switching technology in a
unified way [GMPLS-ROUTING]. An ISC refers to the ability of a
node to forward data of a particular type. PSC, L2SC, TDM, LSC,
and FSC are defined. Each end of the link in a GMPLS network is
associated with at least one switching capability. For example,
PSC is associated with an interface which can delineate IP/MPLS
packets (e.g., a router's interface) while LSC is associated
with an interface which can switch individual wavelengths
multiplexed in a fiber link (e.g., an OXC's interface). Links in
the TE database are identified by their switching capabilities
(at both ends).
An interface may have multiple interface switching capabilities.
A router has only interfaces with a single switching capability
(PSC) while a hybrid node has a mixture of interfaces with
single and multiple switching capabilities.
4.2. Multiple Switching Capabilities
In MRN, network elements may be single-switching or multiple
switching capable nodes. Single switching capable nodes will
advertise a unique switching capability value as part of their
Interface Switching Capability Descriptor (ISCD) sub-TLV(s) to
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describe the termination of all their TE Link(s). This case is
described in [GMPLS-ROUTING].
Moreover, in MRN, some network elements may be multiple
switching capable nodes. Two types of multi-switching capable
nodes are defined: simplex and hybrid nodes.
- A simplex node, has a single switching capability per
interface, but can comprise of interfaces with distinct
switching capabilities (example: an LSR with PSC only
interfaces and TDM only interfaces).
- A hybrid node, on the other hand, has interfaces with multiple
switching capabilities, and interfaces of the same hybrid node
may have different multiple switching capabilities (ex. LSR
with PSC + TDM interfaces). It may also have interfaces of a
single switching capability, in addition to its interfaces
supporting multiple switching capabilities.
Simplex and Hybrid nodes can also be categorized according to
the way they advertise these multiple switching capabilities.
- A simplex node advertises several TE Links each with a single
SC value as part of its ISCD sub-TLVs.
- An hybrid node advertises at least one TE Link containing
multiple ISCDs with different SC values (at least one per
supported SC value per interface).
Note: These cases are only partially described in [GMPLS-
ROUTING].
4.3.1 MRN with Simplex nodes
In this case, the MRN network consists of at least one simplex
node and include a set of single switching capable nodes (i.e.
all TE links terminating on such nodes have the same switching
capability).
For example, the node TL2 in Figure 2 is a simplex node, which
has links associated with TDM and links associated with LSC. At
the region boundary, the interface switching capabilities of the
ends of the link are different. When an LSP crosses the boundary
from the upper to the lower regions, it is nested in a lower-
region FA.
.........................................................
: ........................................... :
: : ............................. : :
: : : ............... : : :
: PSC : TDM : LSC : FSC : : : :
: +--+ : +--+ : +--+ : +--+ +--+ : +--+ : +--+ : +--+ :
: |P1|---|T1|---|L1|---|F1|---|F3|---|L3|---|T3|---|P3| :
: +--+ : +--+ : +--+ : +--+ +--+ : +--+ : +--+ : +--+ :
: | : | : | : | | : | : | : | :
: | : | : | : | | : | : | : | :
: +--+ : +---------+ : +--+ +--+ : +--+ : +--+ : +--+ :
: |P2|---| TL2 |---|F2|---|F4|---|L4|---|T4|---|P4| :
: +--+ : +---------+ : +--+ +--+ : +--+ : +--+ : +--+ :
: : : .............. : : :
: : ............................. : :
: ........................................... :
.........................................................
Figure 2: Simplex node MRN model.
4.3.2 MRN with hybrid nodes
In this case, the MRN network consists of at least one hybrid
node and include a set of single switching capable nodes (i.e.
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all TE links terminating on such nodes have the same switching
capability).
Figure 3a shows an example of a hybrid node. The hybrid node has
two switching elements, which have, for instance, interface
switching capabilities PSC and TDM. It has two external
interfaces (Link1 and Link2), which are directly connected to
the switching element of TDM. The two switching elements are
interconnected via an internal interface, which is not disclosed
outside the network element. The internal interface is used to
facilitate the "adaptation" between different switching
capabilities: PSC and TDM. By cross-connecting port #a and port
#b in the TDM switching element, if no reconfiguration of the
ISCD sub-TLVs for Link 2 is performed, Link 2 is still
advertised as being capable of TDM and PSC switching. Therefore,
since there are no free resources for having a PSC FA Link
terminating on this node, Link 2 should be advertised with a
PSC ISCD sub-TLV with Max LSP bandwidth set to 0 for all
priorities to described that only TDM resources are still
available on this link.
Network element
.............................
: -------- :
: | PSC | :
: +--<->---| | :
: | -------- :
TDM : | ---------- :
+PSC : +--<->--|#a TDM | :
Link1 ------------<->--|#b | :
Link2 ------------<->--|#c | :
: ---------- :
:............................
Figure 3a. Hybrid node.
Figure 3b illustrates that existing GMPLS Routing is not
sufficient and need to be extended to consider (internal)
adaptation capabilities for hybrid nodes.
Network element
.............................
: -------- :
: | PSC | :
: | | :
: --|#b1 | :
: | | #d | :
: | -------- :
: | | :
: | ---------- :
: /| | | #c | :
: | |-- | | :
Link1 ========| | | TDM | :
: | |----|#b2 | :
: \| ---------- :
:............................
Figure 3b. Hybrid node.
Let's assume that all interfaces are STM64 (with VC4-16c capable
as Max LSP bandwidth). So, initially, TE Link 1 composed 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 =
STM64
- ISCD #2 sub-TLV: PSC with Max LSP bandwidth = 2.5 Gb (i.e.
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and Unreserved bandwidth = 10 Gb
After, setting up several PSC LSPs via port #d, there is only
155 Mb capacity still available between on port #d, however a
622 Mb capacity remains on port b1 and VC4-5c 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 port b2
- 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. 622 (port #b1) + 155 (port #d) Mb
When computing the path for a new PSC LSP of 622 Mbps, one
cannot know, based on existing GMPLS routing advertisements (i.e.
two ISCD sub-TLVs), that it cannot setup a PSC-LSP that would be
nested into a new VC4-4c TDM FA-LSP 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).
4.3.3 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 (for example, PSC + LSC capable nodes).
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 (i.e. multiple
LSP regions). 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 elements that support a single common switching
technology (i.e. switching capability). For instance, the
control plane interactions between two LSC network elements is
an example of horizontal interaction. GMPLS protocol operations
handle horizontal interactions within the same routing area. For
the case where the interaction takes place across a domain
boundary, such as between two routing areas that support the
same switching technology, is currently being evaluated as part
of the inter-domain work [Inter-domain] and referred to as
horizontal integration. The latter refers thus to the
collaborative mechanisms between network partitions and/or
administrative boundaries such as routing areas or autonomous
systems. This distinction gets blurred when administrative
domains match LSP region 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 IP/MPLS over a
TDM switching capable network could either be associated to
horizontal integration (if each network is associated to an
separate area) or to vertical integration (if both capabilities
are located within the same area and driven by the same control
plane instance).
Networks where multiple switching capability (as defined in
[RFC3945]) exist and are controllable through vertical
interaction are termed "multi-region" networks. This document
focuses on multi-region networks as a way to realize effective
vertical integration.
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4.3. Integrated Traffic Engineering (TE) and Resource Control
In GMPLS-based multi-region networks, TE Links are consolidated
into a single Traffic Engineering Database (TED). Since this TED
contains the information relative to all the different regions
existing in the network, a path across multiple regions can be
computed using this TED. Thus optimization of network resources
across the multiple regions can be achieved.
The multi-region concept allows for the operation of one network
switching type over another switching type (for example, the use
of a PSC Forwarding Adjacency over an LSC network), the multi-
region concept offers a greater degree of control and
interworking including (but not limited too):
- dynamic establishment of FA-LSPs
- provisioning of end-to-end LSPs with dynamic FA-LSP triggering
Note that MRN including multi-switching capable nodes, as the
explicit route for establishing the end-to-end LSP can includes
nodes belonging to multiple region (e.g. strict route), a
mechanism to control the dynamic creation of FA-LSPs between
each pair of node is required.
There is a full spectrum of control as to how FA-LSPs can be
established dynamically. It can be subject to the control of a
policy, which may be set by a management component, and may
require that the management plane is consulted at the time of FA
establishment. Or FA-LSPs can be established at the request of
the control plane without any management control.
4.4. Triggered signaling
When a LSP crosses the boundary from an upper to a lower region,
it may be nested in or stitched to a lower-region LSP. If such
an LSP does not exist, the LSP may be established dynamically.
Such a mechanism is referred to as "triggered signaling".
4.5. Forwarding adjacency (FA)
Once an LSP across a lower region is created, it can be
advertised as a TE-link called a Forwarding Adjacency (FA) TE
link, allowing other nodes to use the LSP as a TE links for
their path computation [HIER]. The FA is a useful and powerful
tool for improving the scalability of GMPLS Traffic Engineering
(TE) capable networks.
The aggregation of TE Label Switched Paths (TE-LSPs) enables the
creation of a vertical (nested) TE-LSP Hierarchy. A set of FAs
across or within a lower region can be used by a higher region
as part of the path computation process, and higher region LSPs
may be carried across the FAs (just as they are carried across
any TE link). This process requires either the nesting of LSPs
through a hierarchical process [HIER]. In the MRN, since more
than one higher region paths computation and modification can
occur, FAs in the various regions are treated in a simple and
efficient way. A MRN traffic engineering database (TED) is a set
of FA information from multiple different regions. An FA's
region is identified by the interface switching capability
attached to the link state advertisement associated with the FA
[GMPLS-ROUTING].
4.6. Virtual network topology (VNT)
A set of lower-region FAs provides a set of information for
efficient path handling in the upper-region of the MRN, or
provides a virtual network topology to the upper-region. For
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instance, a set of FAs, each of which is instantiated by an LSC
LSP, provides a virtual network topology to the 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
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. Requirements for multi-region TE
5.1.1 Scalability
The MRN relies on a unified traffic engineering and routing
model. The Traffic Engineering Database in each LSR will be
populated with TE-links from all regions. This may lead to a
huge amount of information that has to be flooded and stored
within the network. Furthermore, path computation delays, which
may be of huge importance during restoration, will depend on the
size of the TE Database.
Thus MRN 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-LSP)
- Number of LSPs
- Number of regions
5.1.2 FA link resource utilization
It MUST be possible to utilize network resources efficiently.
Particularly, resource usage in each region SHOULD be optimized
as a whole (i.e. across all regions), in a coordinated manner.
The number of lower-region FA-LSPs carrying upper-region LSPs
SHOULD be minimized. Redundant lower-region FA-LSPs SHOULD be
avoided (except for protection purpose).
5.1.2.1 FA release and setup
Statistical multiplexing can only be employed in PSC and L2SC
regions. PSC or L2SC (FA-)LSP may or may not consume the maximum
reservable bandwidth of the FA-LSP. On the other hand, a TDM, or
LSC (FA-)LSP always consumes a fixed amount of bandwidth of the
FA-LSP 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 usage the nested LSPs can also be re-routed (make before
break, before releasing the nesting FA-LSP. Alternatively, the
FA-LSPs may be retained for future usage. Release or retention
of underutilized FA-LSPs is a policy decision.
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As part of the re-optimization process, the MRN solution MUST
allow rerouting of FA-LSPs while keeping interface identifiers
of FA links unchanged.
Additional FAs 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 FAs, the network
performance such as maximum residual capacity may be improved.
As the number of FAs grows, the residual resource may decrease.
In this case, re-optimization of FAs MAY be invoked according
the policy.
5.1.2.2 Virtual FAs
If FAs are used to enable connectivity over part or all of the
lower-region, it may be considered disadvantageous to fully
instantiate (i.e. pre-provision) the FA-LSPs since this may
reserve bandwidth within the lower-region network that could be
used for other LSPs in the absence of the upper-region traffic.
However, in order that the upper-region can route traffic across
the lower-region, the FA links MAY (this is not a MUST
requirement as you can route an upper region LSP into a lower
region based on lower region TE-links, even if there is no FA)
still be advertised into the lower-region as TE links. Such FA
links that represent the possibility of an FA-LSP are termed
"virtual FAs".
If an upper-region LSP that makes use of a virtual FA is set up,
the underlying FA-LSP MUST be immediately signaled if it has not
already been signaled.
If virtual FAs are used in place of FAs, the TE links across the
lower-region can remain stable using pre-computed paths while
wastage of bandwidth within the lower-region, and unnecessary
reservation of adaptation ports at the border nodes is avoided.
The set of the virtual FAs defines the virtual FA topology
across the lower region. The solution is expected to deliver the
following mechanism in terms of the build-up of virtual FA
topology operations taking into account the (forecast) traffic
demand and available resource in the lower-region. The virtual
FA topology MAY be modified dynamically (by adding or removing
virtual FAs) according to the change of the (forecast) traffic
demand and the available resource in the lower-region.
The virtual FA topology can be changed by setting up and/or
tearing down virtual FA-LSPs as well as by changes to real links
and to real FAs. The maximum number of FAs that can be soft
provisioned on a given resources SHOULD be well-engineered. How
to design the virtual FA topology and its changes is out of
scope of this document.
5.1.3 FA LSP Attribute inheritance
FA TE-Link parameters SHOULD be inherited from FA-LSP parameters.
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
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Capability)
Inheritance rules MUST be applied based on specific policies.
Particular attention should be given to the inheritance of TE
metric and protection attributes.
5.1.4 Verify the FA before it enters service
When the FA is created, it SHOULD be verified before it enters
the in-service state. Data-plane connectivity, performance
SHOULD be examined.
5.1.5 Disruption minimization
When reconfiguring the virtual network topology according to the
traffic demand change, the upper-region LSP may be disrupted.
Such disruption MUST be minimized.
When residual resource decreases to a certain level, some FAs
may be released according to policies. Ideally, only FAs that
are not carrying LSPs would be released, but in some cases it
may be necessary to release FAs that are carrying traffic.
5.1.6 Path computation re-optimization stability
When the virtual network topology is reconfigured, the path
computation over the virtual network topology may be affected
(re-optimized). The re-optimization of the path computation
should be carefully controlled when the virtual network topology
is reconfigured.
The path computation is dependent on the network topology and
associated link state. The path computation stability of upper
region may be impaired if the Virtual Network Topology
frequently changes and/or if the status and TE parameters (TE
metric for instance) of links in the Virtual Network Topology
changes frequently.
In this context, robustness of the Virtual Network Topology is
defined as the capability to smooth changes that may occur and
avoid their subsequent propagation. Changes of the Virtual
Network Topology may be caused by the creation and/or deletion
of several LSPs.
Creation and deletion of LSPs may be triggered by adjacent
regions or through operational actions to meet change of 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 FAs 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-region (e.g., TDM). 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).
5.1.7 Computing paths with and without nested signaling
Path computation may take into account LSP region 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.
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Interface switching capability is used as a constraint in
computing the path. A TDM-LSP is routed over the topology
composed of TE links, both of whose ends has TDM switching
capability.
In Figure 4, a TDM-LSP is routed from LSR-P1, through TDM_SW-T1
and TDM_SW-T2, to LSR-P2. The path for the TDM-LSP is composed
of links, both of whose ends has TDM switching capability. Once
the TDM LSP is set up, it is advertised as an FA-LSP, both ends
of which are PSC. In calculating the path for the PSC-LSP, the
TE database is filtered to include the link, both ends of which
include only PSC. In this way hierarchical routing of the PSC-
LSP and TDM-LSP is done by using a TE database filtered with
respect to switching capability.
There may be a case, in which we can set up the LSP if we build
new lower-region LSPs along the computed path. Suppose that we
set up the TDM-LSP between P1 and P2 in Figure 5. The TDM-LSP is
routed over the path T1-L1-L2-T2. At this time, there is no
direct link between T1 and T2. Then, the LSC-LSP is set up
between T1 and T2. The LSC-LSP setup request (between T1 and T2)
is triggered by the TDM-LSP setup request (between P1 and P2).
If triggered signaling is allowed, the path computation
mechanism may produce a route containing multiple regions.
..................................................
: .................................. :
: : ................. : :
: : : : : :
: PSC : TDM : LSC : : :
: +--+ : +--+ : +--+ +--+ : +--+ : +--+ :
: |P1|-----|T1|-----|L1|---|L2|-----|T2|----|P2| :
: +--+ : +--+ : +--+ +--+ : +--+ : +--+ :
: : | ................. | : :
: : | | : :
: : ------------------------ : :
: .................................. :
..................................................
Figure 4 and 5. Path computation in MRN.
5.1.8 Handling single-switching and multi-switching TE links
The MRN can consist of single-switching capable and multi
switching capable TE links. The path computation mechanism in
the MRN SHOULD be able to compute the paths consisting of both
types of TE-links.
Recall the simplex node model shown in Figure 2. The switching
capability of both ends of a TE-link may or may not be the same.
For a TE-link between an LSR and a TDM switch, the switching
capability of the end-point on the LSR-side is PSC while the one
on the TDM switch-side is TDM. For a TE-link between two TDM
switches, the switching capability of the both end-points is TDM.
The links of the hybrid node shown in Figure 3 are advertised as
TE-links with multiple interface switching capabilities: PSC and
TDM. The hybrid node is used as a transit node for a TDM-region.
At the same time, the hybrid node is used as an ingress, egress,
or transit node for the PSC-region.
5.1.9 Advertisement of the available adaptation resource
A multi-switching capable node is required to hold and advertise
resource information on its internal links.
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For example, if the hybrid node shown in Figure 3a is used as an
ingress or egress node, once the cross-connection is made
between port #a and #b in the TDM switching element, a new FA
link is advertised as with a single switching capability: PSC.
After that, there is no available internal link to connect port
#b to the PSC. Therefore, a mechanism is required such that Link
2 ISCD sub-TLVs are advertised with Max LSP bandwidth values
reflecting that only TDM resources are still available on this
link.
However, as shown in Figure 3b, the above mechanism is not
realizable anymore when a given switching capability is accessed
directly from the incoming link and from another switching
capability hosted by the same node. Therefore, within multi-
region networks, the advertisement of the so-called adaptation
capability to terminate LSPs is required, as it provides
critical information when performing multi-region path
computation.
6. Security Considerations
The current version of .his 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
[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-03.txt (work in progress), July 2004.
[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-00.txt, work in prgoress, July 2004.
[HIER] K.Kompella and Y.Rekhter, "LSP hierarchy with
generalized MPLS TE," draft-ietf-mpls-lsp-
hierarchy-08.txt, work in progress, Sept. 2002.
[LMP] J. Lang, "Link management protocol (LMP)," draft-
ietf-ccamp-lmp-10.txt (work in progress), October
2003.
[RFC3945] E.Mannie (Ed.), "Generalized Multi-Protocol Label
` Switching (GMPLS) Architecture", RFC 3945, October
2004.
7.2. Informative References
[MAMLTE] K. Shiomoto et al., "Multi-area multi-layer traffic
engineering using hierarchical LSPs in GMPLS networks", draft-
shiomoto-multiarea-te-01.txt (work in progress).
8. Author's Addresses
Kohei Shiomoto
NTT Network Service Systems Laboratories
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Requirements for GMPLS-based multi-region network Feb. 2005
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
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
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respect to rights in RFC documents can be found in BCP 78 and
BCP 79.
By submitting this Internet-Draft, each author represents that
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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
Shiomoto et al Expires August 2005 14
Requirements for GMPLS-based multi-region network Feb. 2005
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
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The IETF has been notified by Tellabs Operations, Inc. of
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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
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This document and the information contained herein are provided
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Shiomoto et al Expires August 2005 15