CCAMP Working Group S. Belotti
Internet-Draft P. Grandi
Intended status: Informational Alcatel-Lucent
Expires: April 14, 2011 D. Ceccarelli
D. Caviglia
Ericsson
F. Zhang
D. Li
Huawei Technologies
October 11, 2010
Information model for G.709 Optical Transport Networks (OTN)
draft-bccg-ccamp-otn-g709-info-model-02
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
and signaling process in OTNs to support Generalized Multiprotocol
Label Switching (GMPLS) control of all currently defined ODU
containers.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on April 14, 2011.
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-TE requirements overview . . . . . . . . . . . . . . . . 4
3. RSVP-TE requirements overview . . . . . . . . . . . . . . . . 4
4. G.709 Digital Layer Info Model for Routing and Signaling . . . 5
4.1. Tributary Slot type . . . . . . . . . . . . . . . . . . . 7
4.1.1. Tributary Slot type and Forwarding Adjacencies . . . . 7
4.2. Tributary Port Number . . . . . . . . . . . . . . . . . . 8
4.3. Signal type . . . . . . . . . . . . . . . . . . . . . . . 8
4.4. Bit rate and tolerance . . . . . . . . . . . . . . . . . . 10
4.5. Unreserved Resources . . . . . . . . . . . . . . . . . . . 10
4.6. Maximum LSP Bandwidth . . . . . . . . . . . . . . . . . . 10
4.7. Distinction between terminating and switching
capability . . . . . . . . . . . . . . . . . . . . . . . . 11
4.8. Priority Support . . . . . . . . . . . . . . . . . . . . . 11
4.9. Multi-stage multiplexing . . . . . . . . . . . . . . . . . 11
4.10. Generalized Label . . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 12
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
8.1. Normative References . . . . . . . . . . . . . . . . . . . 12
8.2. Informative References . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
GMPLS[RFC3945] extends MPLS to include Layer-2 Switching (L2SC),
Time-Division Multiplexing (e.g., SONET/SDH, PDH, and OTN),
Wavelength (OCh, Lambdas) Switching and Spatial Switching (e.g.,
incoming port or fiber to outgoing port or fiber).
The establishment of LSPs that span only interfaces recognizing
packet/cell boundaries is defined in [RFC3036, RFC3212, RFC3209].
[RFC3471] presents a functional description of the extensions to
Multi-Protocol Label Switching (MPLS) signaling required to support
GMPLS. ReSource reserVation Protocol-Traffic Engineering (RSVP-TE)
-specific formats,mechanisms and technology specific details are
defined in [RFC3473].
From a routing perspective, Open Shortest Path First-Traffic
Engineering (OSPF-TE) generates Link State Advertisements (LSAs)
carrying application-specific information and floods them to other
nodes as 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.
Type 10 LSAs are 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
and signaling are fundamental in order to allow automatic calculation
and establishment of routes for ODUk LSPs. 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-TE and RSVP-TE
extensions to allow GMPLS control of all currently defined ODU
containers.
This document provides the information model needed by the routing
and signaling processses in OTNs to allow GMPLS control of all
currently defined ODU containers.
OSPF-TE and RSVP-tE requirements are defined in [OTN-FWK], while
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protocol extensions are defined in [OTN-OSPF] and [OTN-RSVP].
2. OSPF-TE requirements overview
[OTN-FWK] provides a set of functional routing requirements
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 switching and terminating
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
networking flexibility.
3. RSVP-TE requirements overview
[OTN-FWK] also provides a set of functional signaling requirements
summarized below :
- Support for LSP setup of new ODUk/ODUflex containers with
related mapping and multiplexing capabilities
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- Support for LSP setup using different Tributary Slot granularity
- Support for Tributary Port Number allocation and negoziation
- Support for constraint signaling
4. G.709 Digital Layer Info Model for Routing and Signaling
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 exploit
different 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 considers the TE information needed for ODU path
computation and parameters needed to be signaled for LSP setup.
The following sections list and analyze each type of data that needs
to be advertised and signaled in order to support path computation
and LSP setup.
4.1. 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 case the bandwidth accounting is provided in number of TSs, the
type of TS is needed to perform correct routing operations.
Currently such information is not provided by the routing protocol
and not taken into account during LSP signaling.
The tributary slot type information is one of the parameters needed
to correctly configure physical interfaces, therefore it has to be
signaled via RSVP-TE.
4.1.1. Tributary Slot type and Forwarding Adjacencies
TS granularity is a TE link type information and is defined as
depicted in Section 4.1. The TS granularity information has to be
advertised when setting up a Forwarding Adjacency (FA) by end points
of the FA. With reference to Figure3 the FA between node A and D has
to be advertised by both nodes A and D. The nodes A and D have to be
aware of the TS granularity associated to the interfaces A1 and D1 in
order to produce consistent advertisement.
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In line with what described in [HIER-BIS] RSVP-TE is in charge of
providing all the information needed to allow automatic FA setup. As
a consequence the TS granularity information will have to be signaled
via RSVP-TE.
forwarding adjacency
________________________________________
| |
+--------+ +--------+ +--------+ +--------+
| | | | | | | |
| Node |A1 B1| Node |B2 C1| Node |C2 D1| Node |
| A +------+ B +------+ C +------+ D |
| | otu3 | | otu3 | | otu3 | |
+--------+ 1.25 +--------+ 1.25 +--------+ 2.5 +--------+
Figure 3: FA in mixed TS granularity
4.2. Tributary Port Number
[RFC4328] supports only the deprecated auto-MSI mode which assumes
that the Tributary Port Number is automatically assigned in the
transmit direction and not checked in the receive direction.
As described in [G709-V3] and [G798-V3], the OPUk overhead in an OTUk
frame contains n (n = the total number of TSs of the ODUk) MSI
(Multiplex Structure Identifier) bytes (in the form of multi-frame),
each of which is used to indicate the association between tributary
port number and tributary slot of the ODUk.
The association between TPN and TS has to be configured by the
control plane and checked by the data plane on each side of the link.
(Please refer to [OTN-FWK] for further details). As a consequence,
the RSVP-TE signaling needs to be extended to support the TPN
assignment function.
4.3. Signal type
From a routing perspetive, [RFC 4203] 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
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process, because the lack of information of free resources highly
increases the number of crank-backs affecting network convergence
time.
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.
On the other hand, from a singaling point of view, [RFC4328]
describes GMPLS signaling extensions to support the control for G.709
OTNs [G709-V1]. However,[RFC4328] needs to be updated because it
does not provide the means to signal all the new signal types and
related mapping and multiplexing functionalities.
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4.4. Bit rate and tolerance
In the current traffic parameters signaling, bit rate and tolerance
are implicitly defined by the signal type. ODUflex CBR and Packet
can have variable bit rates and tolerances (please refer to [OTN-FWK]
table 2); it is thus needed to upgrade the signaling traffic
patameters so to specify requested bit rates and tolerance values
during LSP setup.
4.5. 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.
+------+ component link 1 +------+
| +------------------+ |
| | component link 2 | |
| N1 +------------------+ N2 |
| | component link 3 | |
| +------------------+ |
+------+ +---+--+
Figure 4: 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.
4.6. 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.
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4.7. Distinction between terminating and switching capability
The capability advertised by an interface needs further distinction
in order to separate termination and switching capabilities. Due to
internal constraints and/or limitations, the type of signal being
advertised by an interface could be just switched (i.e. forwarded to
switching matrix without multiplexing/demultiplexing actions), just
terminated (demuxed) or both of them.
This piece of information needs to be advertised together with the
related unreserved bandwidth and signal type. As a consequence
signaling must have the possibility to setup an LSP allowing the
local selection of resources consistent with the limitations
considered during the path computation.
4.8. 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.
4.9. 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].
Modifications to ISCD/IACD , if needed, are FFS.
4.10. Generalized Label
The ODUk label format defined in [RFC4328] could be updated to
support new signal types defined in [G709-V3] but would hardly be
further enhanced to support possible new signal types.
Furthermore such label format may have scalability issues due to the
high number of labels needed when signaling large LSPs. For example,
when an ODU3 is mapped into an ODU4 with 1.25G tributary slots, it
would require the utilization of thirty-one labels (31*4*8=992 bits)
to be allocated while an ODUflex into an ODU4 may need up to eighty
labels (80*4*8=2560 bits).
A new flexible and scalable ODUk label format needs to be defined.
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5. Security Considerations
TBD
6. IANA Considerations
TBD
7. Acknowledgements
The authors would like to thank Eve Varma and Sergio Lanzone for
their precious collaboration and review.
8. References
8.1. Normative References
[HIER-BIS]
K.Shiomoto, A.Farrel, "Procedure for Dynamically Signaled
Hierarchical Label Switched Paths", work in
progress draft-ietf-lsp-hierarchy-bis-08, February 2010.
[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", work in
progress draft-ceccarelli-ccamp-gmpls-ospf-g709-03, August
2010.
[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.
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[RFC4328] Papadimitriou, D., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Extensions for G.709 Optical
Transport Networks Control", RFC 4328, January 2006.
[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.
8.2. 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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