Network Working Group JL. Le Roux, Ed.

Network Working Group JL. Le Roux, Ed.
Request for Comments: 5339 France Telecom
Category: Informational D. Papadimitriou, Ed.
Alcatel-Lucent
September 2008

Evaluation of Existing GMPLS Protocols
against Multi-Layer and Multi-Region Networks (MLN/MRN)

Status of This Memo

This memo provides information for the Internet community. It does
not specify an Internet standard of any kind. Distribution of this
memo is unlimited.

Abstract

This document provides an evaluation of Generalized Multiprotocol
Label Switching (GMPLS) protocols and mechanisms against the
requirements for Multi-Layer Networks (MLNs) and Multi-Region
Networks (MRNs). In addition, this document identifies areas where
additional protocol extensions or procedures are needed to satisfy
these requirements, and provides guidelines for potential extensions.

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Table of Contents

1. Introduction ....................................................3
1.1. Conventions Used in This Document ..........................4
2. MLN/MRN Requirements Overview ...................................4
3. Analysis ........................................................5
3.1. Aspects of Multi-Layer Networks ............................5
3.1.1. Support for Virtual Network Topology
Reconfiguration .....................................5
3.1.1.1. Control of FA-LSPs Setup/Release ...........5
3.1.1.2. Virtual TE Links ...........................6
3.1.1.3. Traffic Disruption Minimization
during FA Release ..........................8
3.1.1.4. Stability ..................................8
3.1.2. Support for FA-LSP Attribute Inheritance ............9
3.1.3. FA-LSP Connectivity Verification ....................9
3.1.4. Scalability .........................................9
3.1.5. Operations and Management of the MLN/MRN ...........10
3.1.5.1. MIB Modules ...............................10
3.1.5.2. OAM .......................................11
3.2. Specific Aspects of Multi-Region Networks .................12
3.2.1. Support for Multi-Region Signaling .................12
3.2.2. Advertisement of Adjustment Capacities .............13
4. Evaluation Conclusion ..........................................16
4.1. Traceability of Requirements ..............................16
5. Security Considerations ........................................20
6. Acknowledgments ................................................20
7. References .....................................................21
7.1. Normative References ......................................21
7.2. Informative References ....................................21
8. Contributors' Addresses ........................................23

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1. Introduction

Generalized MPLS (GMPLS) extends MPLS to handle multiple switching
technologies: packet switching, layer-2 switching, TDM (Time Division
Multiplexing) 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 capable, LSC (Lambda Switch Capable), and FSC (Fiber Switch
Capable). The representation, in a GMPLS control plane, of a
switching technology domain is referred to as a region [RFC4206]. A
switching type describes the ability of a node to forward data of a
particular data plane technology, and uniquely identifies a network
region.

A data plane switching layer describes a data plane switching
granularity level. For example, LSC, TDM VC-11 and TDM VC-4-64c are
three different layers. [RFC5212] defines a Multi-Layer Network
(MLN) to be a Traffic Engineering (TE) domain comprising multiple
data plane switching layers either of the same ISC (e.g., TDM) or
different ISC (e.g., TDM and PSC) and controlled by a single GMPLS
control plane instance. [RFC5212] further defines a particular case
of MLNs. A Multi-Region Network (MRN) is defined as a TE domain
supporting at least two different switching types (e.g., PSC and
TDM), either hosted on the same device or on different ones, and
under the control of a single GMPLS control plane instance.

The objectives of this document are to evaluate existing GMPLS
mechanisms and protocols ([RFC3945], [RFC4202], [RFC3471], [RFC3473])
against the requirements for MLNs and MRNs, defined in [RFC5212].
From this evaluation, we identify several areas where additional
protocol extensions and modifications are required in order to meet
these requirements, and we provide guidelines for potential
extensions.

A summary of MLN/MRN requirements is provided in Section 2. Then
Section 3 evaluates whether current GMPLS protocols and mechanisms
meet each of these requirements. When the requirements are not met
by existing protocols, the document identifies whether the required
mechanisms could rely on GMPLS protocols and procedure extensions, or
whether it is entirely out of the scope of GMPLS protocols.

Note that this document specifically addresses GMPLS control plane
functionality for MLN/MRN in the context of a single administrative
control plane partition. Partitions of the control plane where
separate layers are under distinct administrative control are for
future study.

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This document uses terminologies defined in [RFC3945], [RFC4206], and
[RFC5212].

1.1. 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 [RFC2119].

2. MLN/MRN Requirements Overview

Section 5 of [RFC5212] lists a set of functional requirements for
Multi-Layer/Region Networks (MLN/MRN). These requirements are
summarized below, and a mapping with sub-sections of [RFC5212] is
provided.

Here is the list of requirements that apply to MLN (and thus to MRN):

- Support for robust Virtual Network Topology (VNT) reconfiguration.
This implies the following requirements:

- Optimal control of Forwarding Adjacency Label Switched Path
(FA-LSP) setup and release (Section 5.8.1 of [RFC5212]);

- Support for virtual TE links (Section 5.8.2 of [RFC5212]);

- Minimization of traffic disruption during FA-LSP release
(Section 5.5 of [RFC5212]);

- Stability (Section 5.4 of [RFC5212]);

- Support for FA-LSP attribute inheritance (Section 5.6 of
[RFC5212]);

- Support for FA-LSP data plane connectivity verification (Section
5.9 of [RFC5212]);

- MLN Scalability (Section 5.3 of [RFC5212]);

- MLN Operations and Management (OAM) (Section 5.10 of [RFC5212]);

Here is the list of requirements that apply to MRN only:

- Support for Multi-Region signaling (Section 5.7 of [RFC5212]);

- Advertisement of the adjustment capacity (Section 5.2 of
[RFC5212]);

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3. Analysis

3.1. Aspects of Multi-Layer Networks

3.1.1. Support for Virtual Network Topology Reconfiguration

A set of lower-layer FA-LSPs provides a Virtual Network Topology
(VNT) to the upper-layer [RFC5212]. By reconfiguring the VNT (FA-LSP
setup/release) according to traffic demands between source and
destination node pairs within a layer, network performance factors
(such as maximum link utilization and residual capacity of the
network) can be optimized. Such optimal VNT reconfiguration implies
several mechanisms that are analyzed in the following sections.

Note that the VNT approach is just one possible approach to
performing inter-layer Traffic Engineering.

3.1.1.1. Control of FA-LSPs Setup/Release

In a Multi-Layer Network, FA-LSPs are created, modified, and released
periodically according to the change of incoming traffic demands from
the upper layer.

This implies a TE mechanism that takes into account the demands
matrix, the TE topology, and potentially the current VNT, in order to
compute and setup a new VNT.

Several functional building blocks are required to support such a TE
mechanism:

- Discovery of TE topology and available resources.

- Collection of upper-layer traffic demands.

- Policing and scheduling of VNT resources with regard to traffic
demands and usage (that is, decision to setup/release FA-LSPs).
The functional component in charge of this function is called a VNT
Manager (VNTM) [PCE-INTER].

- VNT Path Computation according to TE topology, potentially taking
into account the old (existing) VNT in order to minimize changes.
The functional component in charge of VNT computation may be
distributed on network elements or may be performed on an external
element (such as a Path Computation Element (PCE), [RFC4655]).

- FA-LSP setup/release.

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GMPLS routing protocols provide TE topology discovery. GMPLS
signaling protocols allow setting up/releasing FA-LSPs.

VNTM functions (resources policing/scheduling, decision to
setup/release FA-LSPs, FA-LSP configuration) are out of the scope of
GMPLS protocols. Such functionalities can be achieved directly on
layer-border Label Switching Routers (LSRs), or through one or more
external tools. When an external tool is used, an interface is
required between the VNTM and the network elements so as to
setup/release FA-LSPs. This could use standard management interfaces
such as [RFC4802].

The set of traffic demands of the upper layer is required for the VNT
Manager to take decisions to setup/release FA-LSPs. Such traffic
demands include satisfied demands, for which one or more upper-layer
LSP have been successfully setup, as well as unsatisfied demands and
future demands, for which no upper layer LSP has been setup yet. The
collection of such information is beyond the scope of GMPLS
protocols. Note that it may be partially inferred from parameters
carried in GMPLS signaling or advertised in GMPLS routing.

Finally, the computation of FA-LSPs that form the VNT can be
performed directly on layer-border LSRs or on an external element
(such as a Path Computation Element (PCE), [RFC4655]), and this is
independent of the location of the VNTM.

Hence, to summarize, no GMPLS protocol extensions are required to
control FA-LSP setup/release.

3.1.1.2. Virtual TE Links

A virtual TE link is a TE link between two upper layer nodes that is
not actually associated with a fully provisioned FA-LSP in a lower
layer. A virtual TE link represents the potentiality to setup an
FA-LSP in the lower layer to support the TE link that has been
advertised. A virtual TE link is advertised as any TE link,
following the rules in [RFC4206] defined for fully provisioned TE
links. In particular, the flooding scope of a virtual TE link is
within an IGP area, as is the case for any TE link.

If an upper-layer LSP attempts (through a signaling message) to make
use of a virtual TE link, the underlying FA-LSP is immediately
signaled and provisioned (provided there are available resources in
the lower layer) in the process known as triggered signaling.

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The use of virtual TE links has two main advantages:

- Flexibility: allows the computation of an LSP path using TE links
without needing to take into account the actual provisioning status
of the corresponding FA-LSP in the lower layer;

- Stability: allows stability of TE links in the upper layer, while
avoiding wastage of bandwidth in the lower layer, as data plane
connections are not established until they are actually needed.

Virtual TE links are setup/deleted/modified dynamically, according to
the change of the (forecast) traffic demand, operator's policies for
capacity utilization, and the available resources in the lower layer.

The support of virtual TE links requires two main building blocks:

- A TE mechanism for dynamic modification of virtual TE link
topology;

- A signaling mechanism for the dynamic setup and deletion of virtual
TE links. Setting up a virtual TE link requires a signaling
mechanism that allows an end-to-end association between virtual TE
link end points with the purpose of exchanging link identifiers as
well as some TE parameters.

The TE mechanism responsible for triggering/policing dynamic
modification of virtual TE links is out of the scope of GMPLS
protocols.

Current GMPLS signaling does not allow setting up and releasing
virtual TE links. Hence, GMPLS signaling must be extended to support
virtual TE links.

We can distinguish two options for setting up virtual TE links:

- The Soft FA approach consists of setting up the FA-LSP in the
control plane without actually activating cross connections in the
data plane. On the one hand, this requires state maintenance on
all transit LSRs (N square issue), but on the other hand, this may
allow for some admission control. Indeed, when a Soft FA is
activated, the resources may no longer be available for use by
other Soft FAs that have common links. These Soft FA will be
dynamically released, and corresponding virtual TE links will be
deleted. The Soft FA LSPs may be setup using procedures similar to
those described in [RFC4872] for setting up secondary LSPs.

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- The remote association approach simply consists of exchanging
virtual TE link IDs and parameters directly between TE link end
points. This does not require state maintenance on transit LSRs,
but reduces admission control capabilities. Such an association
between virtual TE link end points may rely on extensions to the
Resource Reservation Protocol - Traffic Engineering (RSVP-TE)
Automatically Switched Optical Network (ASON) call procedure
[RFC4974].

Note that the support of virtual TE links does not require any GMPLS
routing extension.

3.1.1.3. Traffic Disruption Minimization during FA Release

Before deleting a given FA-LSP, all nested LSPs have to be rerouted
and removed from the FA-LSP to avoid traffic disruption. The
mechanisms required here are similar to those required for graceful
deletion of a TE link. A Graceful TE link deletion mechanism allows
for the deletion of a TE link without disrupting traffic of TE-LSPs
that were using the TE link.

Hence, GMPLS routing and/or signaling extensions are required to
support graceful deletion of TE links. This may utilize the
procedures described in [GR-SHUT]: a transit LSR notifies a head-end
LSR that a TE link along the path of an LSP is going to be torn down,
and also withdraws the bandwidth on the TE link so that it is not
used for new LSPs.

3.1.1.4. Stability

The stability of upper-layer LSP may be impaired if the VNT undergoes
frequent changes. In this context, robustness of the VNT is defined
as the capability to smooth the impact of these changes and avoid
their subsequent propagation.

Guaranteeing VNT stability is out of the scope of GMPLS protocols and
relies entirely on the capability of the TE and VNT management
algorithms to minimize routing perturbations. This requires that the
algorithms take into account the old VNT when computing a new VNT,
and try to minimize the perturbation.

Note that a full mesh of lower-layer LSPs may be created between
every pair of border nodes between the upper and lower layers. The
merit of a full mesh of lower-layer LSPs is that it provides
stability to the upper-layer routing. That is, the forwarding table
used in the upper layer is not impacted if the VNT undergoes changes.
Further, there is always full reachability and immediate access to
bandwidth to support LSPs in the upper layer. But it also has

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significant drawbacks, since it requires the maintenance of n^2
RSVP-TE sessions (where n is the number of border nodes), which may
be quite CPU- and memory-consuming (scalability impact). Also, this
may lead to significant bandwidth wastage. Note that the use of
virtual TE links solves the bandwidth wastage issue, and may reduce
the control plane overload.

3.1.2. Support for FA-LSP Attribute Inheritance

When an FA TE Link is advertised, its parameters are inherited from
the parameters of the FA-LSP, and specific inheritance rules are
applied.

This relies on local procedures and policies and is out of the scope
of GMPLS protocols. Note that this requires that both head-end and
tail-end of the FA-LSP are driven by same policies.

3.1.3. FA-LSP Connectivity Verification

Once fully provisioned, FA-LSP liveliness may be achieved by
verifying its data plane connectivity.

FA-LSP connectivity verification relies on technology-specific
mechanisms (e.g., for SDH using G.707 and G.783; for MPLS using
Bidrectional Forwarding Detection (BFD); etc.) as for any other LSP.
Hence, this requirement is out of the scope of GMPLS protocols.

The GMPLS protocols should provide mechanisms for the coordination of
data link verification in the upper-layer network where data links
are lower-layer LSPs.

o GMPLS signaling allows an LSP to be put into 'test' mode
[RFC3473].
o The Link Management Protocol [RFC4204] is a targeted protocol
and can be run end-to-end across lower-layer LSPs.
o Coordination of testing procedures in different layers is an
operational matter.

3.1.4. Scalability

As discussed in [RFC5212]), 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 Interface Switching Capability Descriptors (ISCDs) per
TE link.

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GMPLS routing provides the necessary advertisement functions and is
based on IETF-designed IGPs. These are known to scale relatively
well with the number of nodes and links. Where there are multiple
regions or layers, there are two possibilities.

1. If a single routing instance distributes information about
multiple network layers, the effect is no more than to increase
the number of nodes and links in the network.

2. If the MLN is fully integrated (i.e., constructed from hybrid
nodes), there is an increase in the number of nodes and links
(as just mentioned), and also a potential increase in the
amount of ISCD information advertised per link. This is a
relatively small amount of information (e.g., 36 bytes in OSPF
[RFC4203]) per switching type, and each interface is unlikely
to have more than two or three switching types.

The number of LSPs in a lower layer that are advertised as TE links
may impact the scaling of the routing protocol. A full mesh of FA-
LSPs in the lower layer would lead to n^2 TE links, where n is the
number of layer-border LSRs. This must be taken into consideration
in the VNT management process. This is an operational matter beyond
the scope of GMPLS protocols.

Since it requires the maintenance of n^2 RSVP-TE sessions (which may
be quite CPU- and memory-consuming), a full mesh of LSPs in the lower
layer may impact the scalability of GMPLS signaling. The use of
virtual TE links may reduce the control plane overload (see Section
3.1.1.2).

3.1.5. Operations and Management of the MLN/MRN

[RFC5212] identifies various requirements for effective management
and operation of the MLN. Some features already exist within the
GMPLS protocol set, some more are under development, and some
requirements are not currently addressed and will need new
development work in order to support them.

3.1.5.1. MIB Modules

MIB modules have been developed to model and control GMPLS switches
[RFC4803] and to control and report on the operation of the signaling
protocol [RFC4802]. These may be successfully used to manage the
operation of a single instance of the control plane protocols that
operate across multiple layers.

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[RFC4220] provides a MIB module for managing TE links, and this may
be particularly useful in the context of the MLN because LSPs in the
lower layers are made available as TE links in the higher layer.

The traffic engineering database provides a repository for all
information about the existence and current status of TE links within
a network. This information is typically flooded by the routing
protocol operating within the network, and is used when LSP routes
are computed. [TED-MIB] provides a way to inspect the TED to view
the TE links at the different layers of the MLN.

As observed in [RFC5212], although it would be possible to manage the
MLN using only the existing MIB modules, a further MIB module could
be produced to coordinate the management of separate network layers
in order to construct a single MLN entity. Such a MIB module would
effectively link together entries in the MIB modules already
referenced.

3.1.5.2. OAM

At the time of writing, the development of OAM tools for GMPLS
networks is at an early stage. GMPLS OAM requirements are addressed
in [GMPLS-OAM].

In general, the lower layer network technologies contain their own
technology-specific OAM processes (for example, SDH/SONET, Ethernet,
and MPLS). In these cases, it is not necessary to develop additional
OAM processes, but GMPLS procedures may be desirable to coordinate
the operation and configuration of these OAM processes.

[ETH-OAM] describes some early ideas for this function, but more work
is required to generalize the technique to be applicable to all
technologies and to MLN. In particular, an OAM function operating
within a server layer must be controllable from the client layer, and
client layer control plane mechanisms must map and enable OAM in the
server layer.

Where a GMPLS-controlled technology does not contain its own OAM
procedures, this is usually because the technology cannot support
in-band OAM (for example, Wavelength Division Multiplexing (WDM)
networks). In these cases, there is very little that a control plane
can add to the OAM function since the presence of a control plane
cannot make any difference to the physical characteristics of the
data plane. However, the existing GMPLS protocol suite does provide
a set of tools that can help to verify the data plane through the
control plane. These tools are equally applicable to network
technologies that do contain their own OAM.

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- Route recording is available through the GMPLS signaling protocol
[RFC3473], making it possible to check the route reported by the
control plane against the expected route. This mechanism also
includes the ability to record and report the interfaces and labels
used for the LSP at each hop of its path.

- The status of TE links is flooded by the GMPLS routing protocols
[RFC4203] and [RFC4205] making it possible to detect changes in the
available resources in the network as an LSP is set up.

- The GMPLS signaling protocol [RFC3473] provides a technique to
place an LSP into a "test" mode so that end-to-end characteristics
(such as power levels) may be sampled and modified.

- The Link Management Protocol [RFC4204] provides a mechanism for
fault isolation on an LSP.

- GMPLS signaling [RFC3473] provides a Notify message that can be
used to report faults and issues across the network. The message
includes scaling features to allow one message to report the
failure of multiple LSPs.

- Extensions to GMPLS signaling [RFC4783] enable alarm information to
be collected and distributed along the path of an LSP for more easy
coordination and correlation.

3.2. Specific Aspects of Multi-Region Networks

3.2.1. Support for Multi-Region Signaling

There are actually several cases where a transit node could choose
between multiple Switching Capabilities (SCs) to be used for a
lower-region FA-LSP:

- Explicit Route Object (ERO) expansion with loose hops: The transit
node has to expand the path, and may have to select among a set of
lower-region SCs.

- Multi-SC TE link: When the ERO of an FA LSP, included in the ERO of
an upper-region LSP, comprises a multi-SC TE link, the region
border node has to select among these SCs.

Existing GMPLS signaling procedures do not allow solving this
ambiguous choice of the SC that may be used along a given path.

Hence, an extension to GMPLS signaling has to be defined to indicate
the SC(s) that can be used and the SC(s) that cannot be used along
the path.

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3.2.2. Advertisement of Adjustment Capacities

In the MRN context, nodes supporting more than one switching
capability on at least one interface are called hybrid nodes
[RFC5212]. Conceptually, hybrid nodes can be viewed as containing at
least two distinct switching elements interconnected by internal
links that provide adjustment between the supported switching
capabilities. These internal links have finite capacities and must
be taken into account when computing the path of a multi-region TE-
LSP. The advertisement of the adjustment capacities is required, as
it provides critical information when performing multi-region path
computation.

The term "adjustment capacity" refers to the property of a hybrid
node to interconnect different switching capabilities it provides
through its external interfaces [RFC5212]. This information allows
path computation to select an end-to-end multi-region path that
includes links of different switching capabilities that are joined by
LSRs that can adapt the signal between the links.

Figure 1a below shows an example of a hybrid node. The hybrid node
has two switching elements (matrices), which support TDM and PSC
switching, respectively. The node has two PSC and TDM ports (Port1
and Port2, respectively). It also has an internal link connecting
the two switching elements.

The two switching elements are internally interconnected in such a
way that it is possible to terminate some of the resources of the TDM
Port2; also, they can provide adjustment of PSC traffic that is
received/sent over the internal PSC interface (#b). Two ways are
possible to set up PSC LSPs (Port1 or Port2). Available resources
advertisement (e.g., Unreserved and Min/Max LSP Bandwidth) should
cover both ways.

Network element
.............................
: -------- :
PSC : | PSC | :
Port1-------------<->---|#a | :
: +--<->---|#b | :
: | -------- :
: | ---------- :
TDM : +--<->--|#c TDM | :
Port2 ------------<->--|#d | :
: ---------- :
:............................

Figure 1a. Hybrid node.

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Port1 and Port2 can be grouped together thanks to internal Dense
Wavelength Division Multiplexing (DWDM), to result in a single
interface: Link1. This is illustrated in Figure 1b below.

Network element
.............................
: -------- :
: | PSC | :
: | | :
: --|#a | :
: | | #b | :
: | -------- :
: | | :
: | ---------- :
: /| | | #c | :
: | |-- | | :
Link1 ========| | | TDM | :
: | |----|#d | :
: \| ---------- :
:............................

Figure 1b. Hybrid node.

Let's assume that all interfaces are STM16 (with VC4-16c capable as
Max LSP bandwidth). After setting up several PSC LSPs via port #a
and setting up and terminating several TDM LSPs via port #d and port
#b, a capacity of only 155 Mb is still available on port #b.
However, a 622 Mb capacity remains on port #a, and VC4-5c capacity
remains on port #d.

When computing the path for a new VC4-4c TDM LSP, one must know that
this node cannot terminate this LSP, as there is only a 155 Mb
capacity still available for TDM-PSC adjustment. Hence, the TDM-PSC
adjustment capacity must be advertised.

With current GMPLS routing [RFC4202], this advertisement is possible
if link bundling is not used and if two TE links are advertised for
Link1.

We would have the following TE link advertisements:

TE link 1 (Port1):
- ISCD sub-TLV: PSC with Max LSP bandwidth = 622 Mb
- Unreserved bandwidth = 622 Mb.

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TE link 2 (Port2):
- ISCD #1 sub-TLV: TDM with Max LSP bandwidth = VC4-4c,
- ISCD #2 sub-TLV: PSC with Max LSP bandwidth = 155 Mb,
- Unreserved bandwidth (equivalent): 777 Mb.

The ISCD #2 in TE link 2 actually represents the TDM-PSC adjustment
capacity.

However, if for obvious scalability reasons, link bundling is done,
then the adjustment capacity information is lost with current GMPLS
routing, as we have the following TE link advertisement:

TE link 1 (Port1 + Port2):
- ISCD #1 sub-TLV: TDM with Max LSP bandwidth = VC4-4c,
- ISCD #2 sub-TLV: PSC with Max LSP bandwidth = 622 Mb,
- Unreserved bandwidth (equivalent): 1399 Mb.

With such a TE link advertisement, an element computing the path of a
VC4-4c LSP cannot know that this LSP cannot be terminated on the
node.

Thus, current GMPLS routing can support the advertisement of the
adjustment capacities, but this precludes performing link bundling
and thus faces significant scalability limitations.

Hence, GMPLS routing must be extended to meet this requirement. This
could rely on the advertisement of the adjustment capacities as a new
TE link attribute (that would complement the Interface Switching
Capability Descriptor TE link attribute).

Note: Multiple ISCDs MAY be associated with a single switching
capability. This can be performed to provide (e.g., for TDM
interfaces) the Min/Max LSP Bandwidth associated to each layer (or
set of layers) for that switching capability. For example, an
interface associated to TDM switching capability and supporting VC-12
and VC-4 switching can be associated to one ISCD sub-TLV or two ISCD
sub-TLVs. In the first case, the Min LSP Bandwidth is set to VC-12
and the Max LSP Bandwidth to VC-4. In the second case, the Min LSP
Bandwidth is set to VC-12 and the Max LSP Bandwidth to VC-12, in the
first ISCD sub-TLV; and the Min LSP Bandwidth is set to VC-4 and the
Max LSP Bandwidth to VC-4, in the second ISCD sub-TLV. Hence, in the
first case, as long as the Min LSP Bandwidth is set to VC-12 (and not
VC-4), and in the second case, as long as the first ISCD sub-TLV is
advertised, there is sufficient capacity across that interface to
setup a VC-12 LSP.

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4. Evaluation Conclusion

Most of the required MLN/MRN functions will rely on mechanisms and
procedures that are out of the scope of the GMPLS protocols, and thus
do not require any GMPLS protocol extensions. They will rely on
local procedures and policies, and on specific TE mechanisms and
algorithms.

As regards Virtual Network Topology (VNT) computation and
reconfiguration, specific TE mechanisms need to be defined, but these
mechanisms are out of the scope of GMPLS protocols.

Six areas for extensions of GMPLS protocols and procedures have been
identified:

- GMPLS signaling extension for the setup/deletion of the virtual TE
links;

- GMPLS signaling extension for graceful TE link deletion;

- GMPLS signaling extension for constrained multi-region signaling
(SC inclusion/exclusion);

- GMPLS routing extension for the advertisement of the adjustment
capacities of hybrid nodes.

- A MIB module for coordination of other MIB modules being operated
in separate layers.

- GMPLS signaling extensions for the control and configuration of
technology-specific OAM processes.

4.1. Traceability of Requirements

This section provides a brief cross-reference to the requirements set
out in [RFC5212] so that it is possible to verify that all of the
requirements listed in that document have been examined in this
document.

- Path computation mechanism should be able to compute paths and
handle topologies consisting of any combination of (simplex) nodes
([RFC5212], Section 5.1).
o Path computation mechanisms are beyond the scope of protocol
specifications, and out of scope for this document.

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- A hybrid node should maintain resources on its internal links
([RFC5212], Section 5.2).
o This is an implementation requirement and is beyond the scope of
protocol specifications, and it is out of scope for this document.

- Path computation mechanisms should be prepared to use the
availability of termination/adjustment resources as a constraint in
path computation ([RFC5212], Section 5.2).
o Path computation mechanisms are beyond the scope of protocol
specifications, and out of scope for this document.

- The advertisement of a node's ability to terminate lower-region
LSPs and to forward traffic in the upper-region (adjustment
capability) is required ([RFC5212], Section 5.2).
o See Section 3.2.2 of this document.

- The path computation mechanism should support the coexistence of
upper-layer links directly connected to upper-layer switching
elements, and upper-layer links connected through internal links
between upper-layer and lower-layer switching elements ([RFC5212],
Section 5.2).
o Path computation mechanisms are beyond the scope of protocol
specifications, and out of scope for this document.

- 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.
([RFC5212], Section 5.3).
o See Section 3.1.4 of this document.

- Design of the routing protocols must not prevent TE information
filtering based on ISCDs ([RFC5212], Section 5.3).
o All advertised information carries the ISCD, and so a receiving
node may filter as required.

- The path computation mechanism and the signaling protocol should be
able to operate on partial TE information, ([RFC5212], Section
5.3).
o Path computation mechanisms are beyond the scope of protocol
specifications, and out of scope for this document.

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- Protocol mechanisms must be provided to enable creation, deletion,
and modification of LSPs triggered through operational actions
([RFC5212], Section 5.4).
o Such mechanisms are standard in GMPLS signaling [RFC3473].

- Protocol mechanisms should be provided to enable similar functions
triggered by adjacent layers ([RFC5212], Section 5.4).
o Such mechanisms are standard in GMPLS signaling [RFC3473].

- Protocol mechanisms may be provided to enable adaptation to changes
such as traffic demand, topology, and network failures. Routing
robustness should be traded with adaptability of those changes
([RFC5212], Section 5.4).
o See Section 3.1.1 of this document.

- Reconfiguration of the VNT must be as non-disruptive as possible
and must be under the control of policy configured by the operator
([RFC5212], Section 5.5).
o See Section 3.1.1.3 of this document

- Parameters of a TE link in an upper layer should be inherited from
the parameters of the lower-layer LSP that provides the TE link,
based on polices configured by the operator ([RFC5212], Section
5.6).
o See Section 3.1.2 of this document.

- The upper-layer signaling request may contain an ERO that includes
only hops in the upper layer ([RFC5212], Section 5.7).
o Standard for GMPLS signaling [RFC3473]. See also Section 3.2.1.

- The upper-layer signaling request may contain an ERO specifying the
lower layer FA-LSP route ([RFC5212], Section 5.7).
o Standard for GMPLS signaling [RFC3473]. See also Section 3.2.1.

- As part of the re-optimization of the MLN, it must be possible to
reroute a lower-layer FA-LSP while keeping interface identifiers of
the corresponding TE links unchanged and causing only minimal
disruption to higher-layer traffic ([RFC5212], Section 5.8.1).
o See Section 3.1.1.3.

- The solution must include measures to protect against network
destabilization caused by the rapid setup and tear-down of lower-
layer LSPs, as traffic demand varies near a threshold ([RFC5212],
Sections 5.8.1 and 5.8.2).
o See Section 3.1.1.4.

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- Signaling of lower-layer LSPs should include a mechanism to rapidly
advertise the LSP as a TE link in the upper layer, and to
coordinate into which routing instances the TE link should be
advertised ([RFC5212], Section 5.8.1).
o This is provided by [RFC4206] and enhanced by [HIER-BIS]. See
also Section 3.1.1.2.

- If an upper-layer LSP is set up making use of a virtual TE link,
the underlying LSP must immediately be signaled in the lower layer
([RFC5212], Section 5.8.2).
o See Section 3.1.1.2.

- The solution should provide operations to facilitate the build-up
of virtual TE links, taking into account the forecast upper-layer
traffic demand, and available resource in the lower layer
([RFC5212], Section 5.8.2).
o See Section 3.1.1.2 of this document.

- The GMPLS protocols should provide mechanisms for the coordination
of data link verification in the upper-layer network where data
links are lower layer LSPs ([RFC5212], Section 5.9).
o See Section 3.1.3 of this document.

- Multi-layer protocol solutions should be manageable through MIB
modules ([RFC5212], Section 5.10).
o See Section 3.1.5.1.

- Choices about how to coordinate errors and alarms, and how to
operate OAM across administrative and layer boundaries must be left
open for the operator ([RFC5212], Section 5.10).
o This is an implementation matter, subject to operational
policies.

- It must be possible to enable end-to-end OAM on an upper-layer LSP.
This function appears to the ingress LSP as normal LSP-based OAM
[GMPLS-OAM], but at layer boundaries, depending on the technique
used to span the lower layers, client-layer OAM operations may need
to be mapped to server-layer OAM operations ([RFC5212], Section
5.10).
o See Section 3.1.5.2.

- Client-layer control plane mechanisms must map and enable OAM in
the server layer ([RFC5212], Section 5.10).
o See Section 3.1.5.2.

- OAM operation enabled for an LSP in a client layer must operate for
that LSP along its entire length ([RFC5212], Section 5.10).
o See Section 3.1.5.2.

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- OAM function operating within a server layer must be controllable
from the client layer. Such control should be subject to policy at
the layer boundary ([RFC5212], Section 5.10).
o This is an implementation matter.

- The status of a server layer LSP must be available to the client
layer. This information should be configurable to be automatically
notified to the client layer at the layer boundary, and should be
subject to policy ([RFC5212], Section 5.10).
o This is an implementation matter.

- Implementations may use standardized techniques (such as MIB
modules) to convey status information between layers.
o This is an implementation matter.

5. Security Considerations

[RFC5212] sets out the security requirements for operating a MLN or
MRN. These requirements are, in general, no different from the
security requirements for operating any GMPLS network. As such, the
GMPLS protocols already provide adequate security features. An
evaluation of the security features for GMPLS networks may be found
in [MPLS-SEC], and where issues or further work is identified by that
document, new security features or procedures for the GMPLS protocols
will need to be developed.

[RFC5212] also identifies that where the separate layers of a MLN/MRN
are operated as different administrative domains, additional security
considerations may be given to the mechanisms for allowing inter-
layer LSP setup. However, this document is explicitly limited to the
case where all layers under GMPLS control are part of the same
administrative domain.

Lastly, as noted in [RFC5212], it is expected that solution documents
will include a full analysis of the security issues that any protocol
extensions introduce.

6. Acknowledgments

We would like to thank Julien Meuric, Igor Bryskin, and Adrian Farrel
for their useful comments.

Thanks also to Question 14 of Study Group 15 of the ITU-T for their
thoughtful review.

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7. References

7.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.

[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC
3471, January 2003.

[RFC3945] Mannie, E., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Architecture", RFC 3945, October 2004.

[RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing
Extensions in Support of Generalized Multi-Protocol Label
Switching (GMPLS)", RFC 4202, October 2005.

[RFC5212] Shiomoto, K., Papadimitriou, D., Le Roux, JL., Vigoureux,
M., and D. Brungard, "Requirements for GMPLS-Based
Multi-Region and Multi-Layer Networks (MRN/MLN)", RFC
5212, July 2008.

7.2. Informative References

[RFC3473] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation
Protocol-Traffic Engineering (RSVP-TE) Extensions", RFC
3473, January 2003.

[RFC4203] Kompella, K., Ed., and Y. Rekhter, Ed., "OSPF Extensions
in Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4203, October 2005.

[RFC4204] Lang, J., Ed., "Link Management Protocol (LMP)", RFC
4204, October 2005.

[RFC4205] Kompella, K., Ed., and Y. Rekhter, Ed., "Intermediate
System to Intermediate System (IS-IS) Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4205, October 2005.

[RFC4206] Kompella, K. and Y. Rekhter, "Label Switched Paths (LSP)
Hierarchy with Generalized Multi-Protocol Label Switching
(GMPLS) Traffic Engineering (TE)", RFC 4206, October
2005.

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[RFC4220] Dubuc, M., Nadeau, T., and J. Lang, "Traffic Engineering
Link Management Information Base", RFC 4220, November
2005.

[RFC4655] Farrel, A., Vasseur, J.-P., and J. Ash, "A Path
Computation Element (PCE)-Based Architecture", RFC 4655,
August 2006.

[RFC4783] Berger, L., Ed., "GMPLS - Communication of Alarm
Information", RFC 4783, December 2006.

[RFC4802] Nadeau, T., Ed., and A. Farrel, Ed., "Generalized
Multiprotocol Label Switching (GMPLS) Traffic Engineering
Management Information Base", RFC 4802, February 2007.

[RFC4803] Nadeau, T., Ed., and A. Farrel, Ed., "Generalized
Multiprotocol Label Switching (GMPLS) Label Switching
Router (LSR) Management Information Base", RFC 4803,
February 2007.

[RFC4872] Lang, J., Ed., Rekhter, Y., Ed., and D. Papadimitriou,
Ed., "RSVP-TE Extensions in Support of End-to-End
Generalized Multi-Protocol Label Switching (GMPLS)
Recovery", RFC 4872, May 2007.

[RFC4974] Papadimitriou, D. and A. Farrel, "Generalized MPLS
(GMPLS) RSVP-TE Signaling Extensions in Support of
Calls", RFC 4974, August 2007.

[ETH-OAM] Takacs, A., Gero, B., and D. Mohan, "GMPLS RSVP-TE
Extensions to Control Ethernet OAM", Work in Progress,
July 2008.

[GMPLS-OAM] Nadeau, T., Otani, T. Brungard, D., and A. Farrel, "OAM
Requirements for Generalized Multi-Protocol Label
Switching (GMPLS) Networks", Work in Progress, October
2007.

[GR-SHUT] Ali, Z., Zamfir, A., and J. Newton, "Graceful Shutdown in
MPLS and Generalized MPLS Traffic Engineering Networks",
Work in Progress, July 2008.

[HIER-BIS] Shiomoto, K., Rabbat, R., Ayyangar, A., Farrel, A., and
Z. Ali, "Procedures for Dynamically Signaled Hierarchical
Label Switched Paths", Work in Progress, February 2008.

[MPLS-SEC] Fang, L., Ed., "Security Framework for MPLS and GMPLS
Networks", Work in Progress, July 2008.

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[PCE-INTER] Oki, E., Le Roux , J-L., and A. Farrel, "Framework for
PCE-Based Inter-Layer MPLS and GMPLS Traffic
Engineering", Work in Progress, June 2008.

[TED-MIB] Miyazawa, M., Otani, T., Nadeau, T., and K. Kunaki,
"Traffic Engineering Database Management Information Base
in support of MPLS-TE/GMPLS", Work in Progress, July
2008.

8. Contributors' Addresses

Deborah Brungard
AT&T
Rm. D1-3C22 - 200 S. Laurel Ave.
Middletown, NJ, 07748 USA
EMail: [email protected]

Eiji Oki
NTT
3-9-11 Midori-Cho
Musashino, Tokyo 180-8585, Japan
EMail: [email protected]

Kohei Shiomoto
NTT
3-9-11 Midori-Cho
Musashino, Tokyo 180-8585, Japan
EMail: [email protected]

M. Vigoureux
Alcatel-Lucent France
Route de Villejust
91620 Nozay
FRANCE
EMail: [email protected]

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Editors' Addresses

Jean-Louis Le Roux
France Telecom
2, avenue Pierre-Marzin
22307 Lannion Cedex, France
EMail: [email protected]

Dimitri Papadimitriou
Alcatel-Lucent
Francis Wellensplein 1,
B-2018 Antwerpen, Belgium
EMail: [email protected]

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Full Copyright Statement

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