CCAMP Working Group S. Belotti
Internet-Draft P. Grandi
Intended status: Informational Alcatel-Lucent
Expires: January 9, 2011 D. Ceccarelli
D. Caviglia
Ericsson
F. Zhang
D. Li
Huawei Technologies
July 08, 2010
Information model for G.709 Optical Transport Networks (OTN)
draft-bccg-ccamp-otn-g709-info-model-01
Abstract
The recent revision of ITU-T recommendation G.709 [G.709-v3] has
introduced new fixed and flexible ODU containers in Optical Transport
Networks (OTNs), enabling optimized support for an increasingly
abundant service mix.
This document provides a model of information needed by the routing
process in OTNs to support Generalized Multiprotocol Label Switching
(GMPLS) control of all currently defined ODU containers both at sub-
lambdas and lambda level granularity.
Status of this Memo
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Copyright Notice
Copyright (c) 2010 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. OSPF requirements overview . . . . . . . . . . . . . . . . . . 3
3. G.709 Digital Layer TE Information and Requirement Analysis . 5
3.1. Tributary Slot type . . . . . . . . . . . . . . . . . . . 7
3.2. Signal type . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Unreserved Resources . . . . . . . . . . . . . . . . . . . 8
3.4. Maximum LSP Bandwidth . . . . . . . . . . . . . . . . . . 9
3.5. Distinction between link multiplexing capacity and
link rate capacity . . . . . . . . . . . . . . . . . . . . 9
3.6. Priority Support . . . . . . . . . . . . . . . . . . . . . 10
3.7. Multi-stage multiplexing . . . . . . . . . . . . . . . . . 10
4. Security Considerations . . . . . . . . . . . . . . . . . . . 11
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
An Opaque OSPF (Open Shortest Path First) LSA (Link State
Advertisements) carrying application-specific information can be
generated and advertised to other nodes following the flooding
procedures defined in [RFC5250]. Three types of opaque LSA are
defined, i.e. type 9 - link-local flooding scope, type 10 - area-
local flooding scope, type 11 - AS flooding scope.
Traffic Engineering(TE) LSA using type 10 opaque LSA is defined in
[RFC3630] for TE purpose. This type of LSA is composed of a standard
LSA header and a payload including one top-level TLV and possible
several nested sub-TLVs. [RFC3630]defines two top-level TLVs: Router
Address TLV and Link TLV; and nine possible sub-TLVs for the Link
TLV, used to carry link related TE information. The Link type sub-
TLVs are enhanced by [RFC4203] in order to support GMPLS networks and
related specific link information. In GMPLS networks each node
generates TE LSAs to advertise its TE information and capabilities
(link-specific or node-specific)through the network. The TE
information carried in the LSAs are collected by the other nodes of
the network and stored into their local Traffic Engineering Databases
(TED).
In a GMPLS enabled G.709 Optical Transport Networks (OTN), routing is
fundamental in order to allow automatic calculation of routes for
ODUk LSPs signaled via RSVP-TE protocol. The recent revision of
ITU-T Recommendation G.709 [G709-V3] has introduced new fixed and
flexible ODU containers that augment those specified in foundation
OTN. As a result, it is necessary to provide OSPF routing protocol
extensions to allow Generalized MPLS (GMPLS) control of all currently
defined ODU containers, in support of sub-lambda and lambda level
routing granularity.
This document provides a model of information needed by the routing
process in OTNs to support Generalized Multiprotocol Label Switching
(GMPLS) control of all currently defined ODU containers both at sub-
lambdas and lambda level granularity.
OSPF requirements are defined in [OTN-FWK], while protocol extensions
are defined in [OTN-OSPF].
2. OSPF requirements overview
OTN serves as the convergence layer for transporting a wide range of
services, including those whose bit rates do not allow efficient
usage of the entire bandwidth associated with a single lambda. In
such a case OTN allows aggregation (and recovery) of traffic to
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support optimization of overall network bandwidth allocation; i.e.,
OTN allows the aggregated service rate to be decoupled from the OTN
line system capacity. The heterogeneous multiplexing hierarchy
additionally supports various network architectures, including those
optimized to minimize stranded capacity, minimize managed entities,
support carrier's carrier scenarios, and/or enable ODU0/ODUflex
traffic to transit a region of the network that does not support
these capabilities.
Thus, it is necessary to define a scalable control plane solution
that is able to fully exploit OTN flexibility (both in terms of
architecture, aggregation and survivability).
[Ed note] (could be part of Framework but for the moment can provide
introduction to the overview).
In this scope, Section 5.3 of the [draft-fwk] provides a set of
functional routing requirements. These requirements are summarized
below :
- Support for link multiplexing capability advertisement: The
routing protocol has to be able to carry information regarding the
capability of an OTU link to support different type of ODUs
- Support for TS granularity advertisement: Each ODUj can be
multiplexed into an OTUk using different TS granularities. For
example, ODU1 can be multiplexed into ODU2 with either 2.5Gbps TS
granularity or 1.25G TS granularity. The routing protocol should
be capable of carrying the TS granularity supported by the ODU
interface.
- Support of any ODUk and ODUflex: The routing protocol must be
capable of carrying the required link bandwidth information for
performing accurate route computation for any of the fixed rate
ODUs as well as ODUflex.
- Support for differentiation between link multiplexing capacity
and link rate capacity
- Support different priorities for resource reservation. How many
priorities levels should be supported depends on operator
policies. Therefore, the routing protocol should be capable of
supporting either no priorities or up to 8 priority levels as
defined in [RFC4202].
- Support link bundling either at the same line rate or different
line rates (e.g. 40G and 10G). Bundling links at different rates
makes the control plane more scalable and permits better
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networking flexibility.
3. G.709 Digital Layer TE Information and Requirement Analysis
The digital OTN layered structure is comprised of digital path layer
networks (ODU) and digital section layer networks (OTU). An OTU
section layer supports one ODU path layer as client and provides
monitoring capability for the OCh. An ODU path layer may transport a
heterogeneous assembly of ODU clients Some types of ODUs (i.e., ODU1,
ODU2, ODU3, ODU4) may assume either a client or server role within
the context of a particular networking domain. ITU-T G.872 amendment
2 provides two tables defining mapping and multiplexing capabilities
of OTNs, which are reproduced below.
+--------------------+--------------------+
| ODU client | OTU server |
+--------------------+--------------------+
| ODU 0 | - |
+--------------------+--------------------+
| ODU 1 | OTU 1 |
+--------------------+--------------------+
| ODU 2 | OTU 2 |
+--------------------+--------------------+
| ODU 2e | - |
+--------------------+--------------------+
| ODU 3 | OTU 3 |
+--------------------+--------------------+
| ODU 4 | OTU 4 |
+--------------------+--------------------+
| ODU flex | - |
+--------------------+--------------------+
Figure 1: OTN mapping capability
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+=================================+=========================+
| ODU client | ODU server |
+---------------------------------+-------------------------+
| 1,25 Gbps client | |
+---------------------------------+ ODU 0 |
| - | |
+=================================+=========================+
| 2,5 Gbps client | |
+---------------------------------+ ODU 1 |
| ODU 0 | |
+=================================+=========================+
| 10 Gbps client | |
+---------------------------------+ ODU 2 |
| ODU0,ODU1,ODUflex | |
+=================================+=========================+
| 10,3125 Gbps client | |
+---------------------------------+ ODU 2e |
| - | |
+=================================+=========================+
| 40 Gbps client | |
+---------------------------------+ ODU 3 |
| ODU0,ODU1,ODU2,ODU2e,ODUflex | |
+=================================+=========================+
| 100 Gbps client | |
+---------------------------------+ ODU 4 |
|ODU0,ODU1,ODU2,ODU2e,ODU3,ODUflex| |
+=================================+=========================+
Figure 2: OTN multiplexing capability
How an ODUk connection service is transported within an operator
network is governed by operator policy. For example, the ODUk
connection service might be transported over an ODUk path over an
OTUk section, with the path and section being at the same rate as
that of the connection service (see Table 1). In this case, an
entire lambda of capacity is consumed in transporting the ODUk
connection service. On the other hand, the operator might leverage
sub-lambda multiplexing capabilities in the network to improve
infrastructure efficiencies within any given networking domain. In
this case, ODUk multiplexing may be performed prior to transport over
various rate ODU servers (as per Table 2) over associated OTU
sections.
From the perspective of multiplexing relationships, a given ODUk may
play different roles as it traverses various networking domains.
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As detailed in [OTN-FWK], client ODUk connection services can be
transported over:
o Case A) one or more wavelength sub-networks connected by optical
links or
o Case B) one or more ODU links (having sub-lambda and/or lambda
bandwidth granularity)
o Case C) a mix of ODU links and wavelength sub-networks.
This document only considers the TE information needed for ODU path
computation.
The following sections list and analyze each type of data that needs
to be advertised in order to support path computation.
3.1. Tributary Slot type
ITU-T recommendations define two types of TS but each link can only
support a single type at a given time. The rules to be followed when
selecting the TS to be used are:
- if both ends of a link can support both 2.5Gbps TS and 1.25Gbps
TS, then the link will work with 1.25Gbps TS.
- If one end can support the 1.25Gbps TS, and another end the
2.5Gbps TS, the link will work with 2.5Gbps TS
In addition, the bandwidth accounting depends on the type of TS.
Therefore, the type of the TS should be known during LO ODUk path
computation. Currently such information is not provided by the
routing protocol.
3.2. Signal type
[RFC 4328] allows advertising foundation G.709 (single TS type)
without the capability of providing precise information about
bandwidth specific allocation. For example, in case of link
bundling, dividing the unreserved bandwidth by the MAX LSP bandwidth
it is not possible to know the exact number of LSPs at MAX LSP
bandwidth size that can be set up. (see example fig. 3)
The lack of spatial allocation heavily impacts the restoration
process, because the lack of information of free resources highly
increases the number of crank-backs affecting network convergence
time.
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Moreover actual tools provided by OSPF-TE only allow advertising
signal types with fixed bandwidth and implicit hierarchy (e.g. SDH/
SONET networks) or variable bandwidth with no hierarchy (e.g. packet
switching networks) but do not provide the means for advertising
networks with mixed approach (e.g. ODUflex CBR and ODUflex packet).
For example, advertising ODU0 as MIN LSP bandwidth and ODU4 as MAX
LSP bandwidth it is not possible to state whether the advertised link
supports ODU4 and ODUflex or ODU4, ODU3, ODU2, ODU1, ODU0 and
ODUflex. Such ambiguity is not present in SDH networks where the
hierarchy is implicit and flexible containers like ODUFlex do not
exist. The issue could be resolved by declaring 1 ISCD for each
signal type actually supported by the link.
Supposing for example to have an equivalent ODU2 unreserved bandwidth
in a TE-link (with bundling capability) distributed on 4 ODU1, it
would be advertised via the ISCD in this way:
MAX LSP Bw: ODU1
MIN LSP Bw: ODU1
- Maximum Reservable Bandwidth (of the bundle) set to ODU2
- Unreserved Bandwidth (of the bundle) set to ODU2
Moreover with the current IETF solutions, ([RFC4202], [RFC4203]) as
soon as no bandwidth is available for a certain signal type it is not
advertised into the related ISCD, losing also the related capability
until bandwidth is freed.
In conclusion, the OSPF-TE extensions defined in [RFC4203] require a
different ISCD per signal type in order to advertise each supported
container. This motivates attempting to look for a more optimized
solution, without proliferations of the number of ISCD advertised.
With respect to link bundling, the utilization of the ISCD as it is,
would not allow precise advertising of spatial bandwidth allocation
information unless using only one component link per TE link.
3.3. Unreserved Resources
Unreserved resources need to be advertised per priority and per
signal type in order to allow the correct functioning of the
restoration process. [RFC4203] only allows advertising unreserved
resources per priority, this leads not to know how many LSPs of a
specific signal type can be restored. As example it is possible to
consider the scenario depicted in the following figure.
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+------+ component link 1 +------+
| +------------------+ |
| | component link 2 | |
| N1 +------------------+ N2 |
| | component link 3 | |
| +------------------+ |
+------+ +---+--+
Figure 3: Concurrent path computation
Suppose to have a TE link comprising 3 ODU3 component links with
32TSs available on the first one, 24TSs on the second, 24TSs on the
third and supporting ODU2 and ODU3 signal types. The node would
advertise a TE link unreserved bandwidth equal to 80 TSs and a MAX
LSP bandwidth equal to 32 TSs. In case of restoration the network
could try to restore 2 ODU3 (64TSs) in such TE-link while only a
single ODU3 can be set up and a crank-back would be originated. In
more complex network scenarios the number of crank-backs can be much
higher.
3.4. Maximum LSP Bandwidth
Maximum LSP bandwidth is currently advertised in the common part of
the ISCD and advertised per priority, while in OTN networks it is
only required for ODUflex advertising. This leads to a significant
waste of bits inside each LSA.
3.5. Distinction between link multiplexing capacity and link rate
capacity
As mentioned earlier, to enable optimization of overall network
bandwidth allocation, it is necessary to decouple the connection
service rate from the OTN link rate capacity, so as to support sub-
lambda switching agility. Thus, it is needed to provide the
possibility to separately advertise the bandwidth available at lambda
granularity from the bandwidth available at sub-lambda granularity.
For example consider a bundle link consisting of 5 OTU4 and 4 OTU3,
no support for ODUflex. The bandwidth advertised at full lambda
granularity should be :
-5 Full-lambda ODU4
-4 Full-lambda ODU3
The bandwidth advertised at sub-lambda granularity should be:
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-10 sub-lambda ODU3 (they are all from OTU4 link)
-66 sub-lambda ODU2 (5x10 ODU2 from 5xODU4 + 4x4 ODU2 from 4xODU3)
-264 sub-lambda ODU1 (5x40 ODU1 from 5xODU4 + 4x16 ODU1 from
4xODU3)
- 528 sub-lambda ODU0 (5x80 ODU0 from 5xODU4 + 4x32 ODU0 from
4xODU3)
The ability to distinguish between link rate capacity and link
multiplexing capacity is already a requirement as per [OTN-FWK]. As
discussed in Section 3.2, [RFC4203] could achieve this distinction by
advertising different bandwidths for full lambda and sub-lambda
signal granularities. However, this approach implies the usage of
multiple ISCDs and therefore it is not efficient. For example a link
with link rate capacity OTU3 and multiplexing capacity ODU1, ODU2 and
ODU3, [RFC4203] could require the utilization of up to three
different ISCDs, one for each capability.
So TE-link declaring would need:
1 ISCD for ODU1 with MAX LSP BW = MIN LSP BW = ODU1
1 ISCD for ODU2 with MAX LSP BW = MIN LSP BW = ODU2
1 ISCD for ODU3 with MAX LSP BW = MIN LSP BW = ODU3 (full lambda)
Maximum Reservable Bandwidth (of the TE-link) set to ODU3
Unreserved Bandwidth (of the TE-link)) set to ODU3
3.6. Priority Support
The IETF foresees that up to eight priorities must be supported and
that all of them have to be advertised independently on the number of
priorities supported by the implementation. Considering that the
advertisement of all the different supported signal types will
originate large LSAs, it is advised to advertise only the information
related to the really supported priorities.
3.7. Multi-stage multiplexing
With reference to the [OTN-FWK] , introduction of multi-stage
multiplexing implies the advertisement of cascaded adaptation
capabilities together with the matrix access constraints. The
structure defined by IETF for the advertisement of adaptation
capabilities is ISCD/IACD as in [RFC4202] and [RFC5339].
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Modifications to ISCD/IACD , if needed, are FFS.
4. Security Considerations
TBD
5. IANA Considerations
TBD
6. Acknowledgements
The authors would like to thank Eve Varma for her precious
collaboration and review.
7. References
7.1. Normative References
[OTN-OSPF]
D.Ceccarelli,D.Caviglia,F.Zhang,D.Li,Y.Xu,P.Grandi,S.Belot
ti, "Traffic Engineering Extensions to OSPF for
Generalized MPLS (GMPLS) Control of Evolutive G.709 OTN
Networks", consented by ITU-T on Oct 2009.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
(TE) Extensions to OSPF Version 2", RFC 3630,
September 2003.
[RFC4202] Kompella, K. and Y. Rekhter, "Routing Extensions in
Support of Generalized Multi-Protocol Label Switching
(GMPLS)", RFC 4202, October 2005.
[RFC4203] Kompella, K. and Y. Rekhter, "OSPF Extensions in Support
of Generalized Multi-Protocol Label Switching (GMPLS)",
RFC 4203, October 2005.
[RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Extensions for G.709 Optical
Transport Networks Control", RFC 4328, January 2006.
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[RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The
OSPF Opaque LSA Option", RFC 5250, July 2008.
[RFC5339] Le Roux, JL. and D. Papadimitriou, "Evaluation of Existing
GMPLS Protocols against Multi-Layer and Multi-Region
Networks (MLN/MRN)", RFC 5339, September 2008.
7.2. Informative References
[G.709-v1]
ITU-T, "Interface for the Optical Transport Network
(OTN)", G.709 Recommendation (and Amendment 1),
February 2001.
[G.709-v2]
ITU-T, "Interface for the Optical Transport Network
(OTN)", G.709 Recommendation (and Amendment 1),
March 2003.
[G.709-v3]
ITU-T, "Rec G.709, version 3", approved by ITU-T on
December 2009.
[G.872-am2]
ITU-T, "Amendment 2 of G.872 Architecture of optical
transport networks for consent", consented by ITU-T on
June 2010.
[OTN-FWK] F.Zhang, D.Li, H.Li, S.Belotti, "Framework for GMPLS and
PCE Control of G.709 Optical Transport Networks", work in
progress draft-ietf-ccamp-gmpls-g709-framework-00, April
2010.
Authors' Addresses
Sergio Belotti
Alcatel-Lucent
Via Trento, 30
Vimercate
Italy
Email: sergio.belotti@alcatel-lucent.com
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Pietro Vittorio Grandi
Alcatel-Lucent
Via Trento, 30
Vimercate
Italy
Email: pietro_vittorio.grandi@alcatel-lucent.com
Daniele Ceccarelli
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
Email: daniele.ceccarelli@ericsson.com
Diego Caviglia
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
Email: diego.caviglia@ericsson.com
Fatai Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Shenzhen 518129 P.R.China Bantian, Longgang District
Phone: +86-755-28972912
Email: zhangfatai@huawei.com
Dan Li
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Shenzhen 518129 P.R.China Bantian, Longgang District
Phone: +86-755-28973237
Email: danli@huawei.com
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