draft-ietf-ccamp-rwa-wson-framework-10.txt   draft-ietf-ccamp-rwa-wson-framework-11.txt 
Network Working Group Y. Lee (ed.) Network Working Group Y. Lee (ed.)
Internet Draft Huawei Internet Draft Huawei
Intended status: Informational G. Bernstein (ed.) Intended status: Informational G. Bernstein (ed.)
Expires: July 2011 Grotto Networking Expires: August 2011 Grotto Networking
Wataru Imajuku Wataru Imajuku
NTT NTT
January 10, 2011 February 7, 2011
Framework for GMPLS and PCE Control of Wavelength Switched Optical Framework for GMPLS and PCE Control of Wavelength Switched Optical
Networks (WSON) Networks (WSON)
draft-ietf-ccamp-rwa-wson-framework-10.txt draft-ietf-ccamp-rwa-wson-framework-11.txt
Abstract Abstract
This document provides a framework for applying Generalized Multi- This document provides a framework for applying Generalized Multi-
Protocol Label Switching (GMPLS) and the Path Computation Element Protocol Label Switching (GMPLS) and the Path Computation Element
(PCE) architecture to the control of wavelength switched optical (PCE) architecture to the control of wavelength switched optical
networks (WSON). In particular, it examines Routing and Wavelength networks (WSON). In particular, it examines Routing and Wavelength
Assignment (RWA) of optical paths. Assignment (RWA) of optical paths.
This document focuses on topological elements and path selection This document focuses on topological elements and path selection
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Copyright Notice Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the Copyright (c) 2011 IETF Trust and the persons identified as the
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Table of Contents Table of Contents
1. Introduction...................................................4 1. Introduction...................................................4
2. Terminology....................................................4 2. Terminology....................................................5
3. Wavelength Switched Optical Networks...........................6 3. Wavelength Switched Optical Networks...........................6
3.1. WDM and CWDM Links........................................6 3.1. WDM and CWDM Links........................................6
3.2. Optical Transmitters and Receivers........................8 3.2. Optical Transmitters and Receivers........................8
3.3. Optical Signals in WSONs..................................9 3.3. Optical Signals in WSONs..................................9
3.3.1. Optical Tributary Signals...........................10 3.3.1. Optical Tributary Signals...........................10
3.3.2. WSON Signal Characteristics.........................10 3.3.2. WSON Signal Characteristics.........................10
3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............11 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs............11
3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......11 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs.......11
3.4.2. Splitters...........................................14 3.4.2. Splitters...........................................14
3.4.3. Combiners...........................................15 3.4.3. Combiners...........................................15
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1. Introduction 1. Introduction
Wavelength Switched Optical Networks (WSONs) are constructed from Wavelength Switched Optical Networks (WSONs) are constructed from
subsystems that include Wavelength Division Multiplexed (WDM) links, subsystems that include Wavelength Division Multiplexed (WDM) links,
tunable transmitters and receivers, Reconfigurable Optical Add/Drop tunable transmitters and receivers, Reconfigurable Optical Add/Drop
Multiplexers (ROADM), wavelength converters, and electro-optical Multiplexers (ROADM), wavelength converters, and electro-optical
network elements. A WSON is a WDM-based optical network in which network elements. A WSON is a WDM-based optical network in which
switching is performed selectively based on the center wavelength of switching is performed selectively based on the center wavelength of
an optical signal. an optical signal.
In order to provision an optical connection (an optical path) through WSONs can differ from other types of GMPLS networks in that many
a WSON certain path continuity and resource availability constraints types of WSON nodes are highly asymmetric with respect to their
must be met to determine viable and optimal paths through the switching capabilities, compatibility of signal types and network
network. The determination of paths is known as Routing and elements may need to be considered, and label assignment can be non-
Wavelength Assignment (RWA). local. In order to provision an optical connection (an optical path)
through a WSON certain wavelength continuity and resource
availability constraints must be met to determine viable and optimal
paths through the WSON. The determination of paths is known as
Routing and Wavelength Assignment (RWA).
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes
a set of control plane protocols that can be used to operate data an architecture and a set of control plane protocols that can be used
networks ranging from packet switch capable networks, through those to operate data networks ranging from packet switch capable networks,
networks that use time division multiplexing, to WDM networks. The through those networks that use time division multiplexing, to WDM
Path Computation Element (PCE) architecture [RFC4655] defines networks. The Path Computation Element (PCE) architecture [RFC4655]
functional components that can be used to compute and suggest defines functional components that can be used to compute and suggest
appropriate paths in connection-oriented traffic-engineered networks. appropriate paths in connection-oriented traffic-engineered networks.
This document provides a framework for applying GMPLS protocols and This document provides a framework for applying the GMPLS
the PCE architecture to the control and operation of WSONs. To aid architecture and protocols [RFC3945], and the PCE architecture
in this process this document also provides an overview of the [RFC4655] to the control and operation of WSONs. To aid in this
subsystems and processes that comprise WSONs, and describes RWA so process this document also provides an overview of the subsystems and
that the information requirements, both static and dynamic, can be processes that comprise WSONs, and describes RWA so that the
identified to explain how the information can be modeled for use by information requirements, both static and dynamic, can be identified
GMPLS and PCE systems. This work will facilitate the development of to explain how the information can be modeled for use by GMPLS and
protocol solution models and protocol extensions within the GMPLS and PCE systems. This work will facilitate the development of protocol
PCE protocol families. solution models and protocol extensions within the GMPLS and PCE
protocol families.
Note that this document focuses on the generic properties of links,
switches and path selection constraints that occur in WSONs.
Different WSONs such as access, metro, and long haul may apply Different WSONs such as access, metro, and long haul may apply
different techniques for dealing with optical impairments hence this different techniques for dealing with optical impairments hence this
document does not address optical impairments in any depth. See document does not address optical impairments in any depth. Note that
[WSON-Imp] for more information on optical impairments and GMPLS. this document focuses on the generic properties of links, switches
and path selection constraints that occur in many types of WSONs.
See [WSON-Imp] for more information on optical impairments and GMPLS.
2. Terminology 2. Terminology
Add/Drop Multiplexers (ADM): An optical device used in WDM networks Add/Drop Multiplexers (ADM): An optical device used in WDM networks
composed of one or more line side ports and typically many tributary composed of one or more line side ports and typically many tributary
ports. ports.
CWDM: Coarse Wavelength Division Multiplexing. CWDM: Coarse Wavelength Division Multiplexing.
DWDM: Dense Wavelength Division Multiplexing. DWDM: Dense Wavelength Division Multiplexing.
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traverses the optical network with elements that include traverses the optical network with elements that include
regenerators, Optical-to-Electrical (OEO) switches, or wavelength regenerators, Optical-to-Electrical (OEO) switches, or wavelength
converters. converters.
Bit rate and G-PID would not change since they describe the encoded Bit rate and G-PID would not change since they describe the encoded
bit stream. A set of G-PID values is already defined for lambda bit stream. A set of G-PID values is already defined for lambda
switching in [RFC3471] and [RFC4328]. switching in [RFC3471] and [RFC4328].
Note that a number of non-standard or proprietary modulation formats Note that a number of non-standard or proprietary modulation formats
and FEC codes are commonly used in WSONs. For some digital bit and FEC codes are commonly used in WSONs. For some digital bit
streams the presence of Forwarding Equivalence Class (FEC) can be streams the presence of Forward Error Correction (FEC) can be
detected, e.g., in [G.707] this is indicated in the signal itself via detected, e.g., in [G.707] this is indicated in the signal itself via
the FEC Status Indication (FSI) byte, while in [G.709] this can be the FEC Status Indication (FSI) byte, while in [G.709] this can be
inferred from whether the FEC field of the Optical Channel Transport inferred from whether the FEC field of the Optical Channel Transport
Unit-k (OTUk) is all zeros or not. Unit-k (OTUk) is all zeros or not.
3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs 3.4. ROADMs, OXCs, Splitters, Combiners and FOADMs
Definitions of various optical devices such as ROADMs, Optical Cross- Definitions of various optical devices such as ROADMs, Optical Cross-
connects (OXCs), splitters, combiners and Fixed Optical Add-Drop connects (OXCs), splitters, combiners and Fixed Optical Add-Drop
Multiplexers (FOADMs) and their parameters can be found in [G.671]. Multiplexers (FOADMs) and their parameters can be found in [G.671].
Only a subset of these and their non-impairment related properties Only a subset of these relevant to the control plane and their non-
are considered in the following sections. impairment related properties are considered in the following
sections.
3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs 3.4.1. Reconfigurable Add/Drop Multiplexers and OXCs
ROADMs are available in different forms and technologies. This is a ROADMs are available in different forms and technologies. This is a
key technology that allows wavelength based optical switching. A key technology that allows wavelength based optical switching. A
classic degree-2 ROADM is shown in Figure 1. classic degree-2 ROADM is shown in Figure 1.
Line side input +---------------------+ Line side output Line side input +---------------------+ Line side output
--->| |---> --->| |--->
| | | |
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#2 1 0 0 0 0 #2 1 0 0 0 0
A = #3 1 0 0 0 0 A = #3 1 0 0 0 0
#4 1 0 0 0 0 #4 1 0 0 0 0
#5 1 0 0 0 0 #5 1 0 0 0 0
Where input ports 2-5 are add ports, output ports 2-5 are drop ports Where input ports 2-5 are add ports, output ports 2-5 are drop ports
and input port #1 and output port #1 are the line side (WDM) ports. and input port #1 and output port #1 are the line side (WDM) ports.
For ROADMs, this matrix will be very sparse, and for OXCs the matrix For ROADMs, this matrix will be very sparse, and for OXCs the matrix
will be very dense, compact encodings and examples, including high will be very dense, compact encodings and examples, including high
degree ROADMs/OXCs, are given in [GEN-Encode]. A degree-4 ROADM is degree ROADMs/OXCs, are given in [Gen-Encode]. A degree-4 ROADM is
shown in Figure 2. shown in Figure 2.
+-----------------------+ +-----------------------+
Line side-1 --->| |---> Line side-2 Line side-1 --->| |---> Line side-2
Input (I1) | | Output (E2) Input (I1) | | Output (E2)
Line side-1 <---| |<--- Line side-2 Line side-1 <---| |<--- Line side-2
Output (E1) | | Input (I2) Output (E1) | | Input (I2)
| ROADM | | ROADM |
Line side-3 --->| |---> Line side-4 Line side-3 --->| |---> Line side-4
Input (I3) | | Output (E4) Input (I3) | | Output (E4)
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| | bytes | signal), BDI(backward| | | bytes | signal), BDI(backward|
| | | defect indication)BEI| | | | defect indication)BEI|
| | | (backward error | | | | (backward error |
| | | indication) | | | | indication) |
+------------------+----------------------+-----------------------| +------------------+----------------------+-----------------------|
|Forward Error | P1,Q1 bytes | OTUk FEC | |Forward Error | P1,Q1 bytes | OTUk FEC |
|Correction (FEC) | | | |Correction (FEC) | | |
+-----------------------------------------------------------------+ +-----------------------------------------------------------------+
In the previous table it is seen that frame alignment, signal In the previous table it is seen that frame alignment, signal
identification, and FEC are supported. What this table also shows by identification, and FEC are supported. What table 2 also shows by its
its omission is that no switching or multiplexing occurs at this omission is that no switching or multiplexing occurs at this layer.
layer. This is a significant simplification for the control plane This is a significant simplification for the control plane since
since control plane standards require a multi-layer approach when control plane standards require a multi-layer approach when there are
there are multiple switching layers, but not for "layering" to multiple switching layers, but not for "layering" to provide the
provide the management functions of Table 2. That is, many existing management functions of Table 2. That is, many existing technologies
technologies covered by GMPLS contain extra management related layers covered by GMPLS contain extra management related layers that are
that are essentially ignored by the control plane (though not by the essentially ignored by the control plane (though not by the
management plane!). Hence, the approach here is to include management plane!). Hence, the approach here is to include
regenerators and other devices at the WSON layer unless they provide regenerators and other devices at the WSON layer unless they provide
higher layer switching and then a multi-layer or multi-region higher layer switching and then a multi-layer or multi-region
approach [RFC5212] is called for. However, this can result in approach [RFC5212] is called for. However, this can result in
regenerators having a dependence on the client signal type. regenerators having a dependence on the client signal type.
Hence depending upon the regenerator technology the following Hence depending upon the regenerator technology the following
constraints may be imposed by a regenerator device: constraints may be imposed by a regenerator device:
Table 3. Regenerator Compatibility Constraints. Table 3. Regenerator Compatibility Constraints.
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| Client Signal Dependence | | | x | | Client Signal Dependence | | | x |
+--------------------------------------------------------+ +--------------------------------------------------------+
Note that the limited wavelength range constraint can be modeled for Note that the limited wavelength range constraint can be modeled for
GMPLS signaling with the label set defined in [RFC3471] and that the GMPLS signaling with the label set defined in [RFC3471] and that the
modulation type restriction constraint includes FEC. modulation type restriction constraint includes FEC.
3.5.2. OEO Switches 3.5.2. OEO Switches
A common place where OEO processing may take place is within WSON A common place where OEO processing may take place is within WSON
switches that utilize (or contain) regenerators. Regenerators may be switches that utilize (or contain) regenerators. This may be to
added to a switching system for a number of reasons. One common convert the signal to an electronic form for switching then
reason is to restore signal quality either before or after optical reconverting to an optical signal prior to output from the switch.
processing (switching). Another reason may be to convert the signal Another common technique is to add regenerators to restore signal
to an electronic form for switching then reconverting to an optical quality either before or after optical processing (switching). In
signal prior to output from the switch. In this later case the the former case the regeneration is applied to adapt the signal to
regeneration is applied to adapt the signal to the switch fabric the switch fabric regardless of whether or not it is needed from a
regardless of whether or not it is needed from a signal quality signal quality perspective.
perspective.
In either case these optical switches have essentially the same In either case these optical switches have essentially the same
compatibility constraints as those which are described for compatibility constraints as those which are described for
regenerators in Table 3. regenerators in Table 3.
3.6. Wavelength Converters 3.6. Wavelength Converters
Wavelength converters take an input optical signal at one wavelength Wavelength converters take an input optical signal at one wavelength
and emit an equivalent content optical signal at another wavelength and emit an equivalent content optical signal at another wavelength
on output. There are multiple approaches to building wavelength on output. There are multiple approaches to building wavelength
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wavelength converters in the pool. wavelength converters in the pool.
A three stage model is used as shown schematically in Figure 3. A three stage model is used as shown schematically in Figure 3.
(Schematic diagram of wavelength converter pool model). This model (Schematic diagram of wavelength converter pool model). This model
represents N input ports (fibers), P wavelength converters, and M represents N input ports (fibers), P wavelength converters, and M
output ports (fibers). Since not all input ports can necessarily output ports (fibers). Since not all input ports can necessarily
reach the converter pool, the model starts with a wavelength pool reach the converter pool, the model starts with a wavelength pool
input matrix WI(i,p) = {0,1} where input port i can reach potentially input matrix WI(i,p) = {0,1} where input port i can reach potentially
reach wavelength converter p. reach wavelength converter p.
Since not all wavelength can necessarily reach all the converters or Since not all wavelengths can necessarily reach all the converters or
the converters may have limited input wavelength range there is a set the converters may have limited input wavelength range there is a set
of input port constraints for each wavelength converter. Currently it of input port constraints for each wavelength converter. Currently it
is assumed that a wavelength converter can only take a single is assumed that a wavelength converter can only take a single
wavelength on input. Each wavelength converter input port constraint wavelength on input. Each wavelength converter input port constraint
can be modeled via a wavelength set mechanism. can be modeled via a wavelength set mechanism.
Next a state vector WC(j) = {0,1} dependent upon whether wavelength Next a state vector WC(j) = {0,1} dependent upon whether wavelength
converter j in the pool is in use. This is the only state kept in the converter j in the pool is in use. This is the only state kept in the
converter pool model. This state is not necessary for modeling converter pool model. This state is not necessary for modeling
"fixed" transponder system, i.e., systems where there is no sharing. "fixed" transponder system, i.e., systems where there is no sharing.
In addition, this state information may be encoded in a much more In addition, this state information may be encoded in a much more
compact form depending on the overall connectivity structure [GEN- compact form depending on the overall connectivity structure [Gen-
Encode]. Encode].
After that, a set of wavelength converter output wavelength After that, a set of wavelength converter output wavelength
constraints is used. These constraints indicate what wavelengths a constraints is used. These constraints indicate what wavelengths a
particular wavelength converter can generate or are restricted to particular wavelength converter can generate or are restricted to
generating due to internal switch structure. generating due to internal switch structure.
Finally, a wavelength pool output matrix WE(p,k) = {0,1} indicating Finally, a wavelength pool output matrix WE(p,k) = {0,1} indicating
whether the output from wavelength converter p can reach output port whether the output from wavelength converter p can reach output port
k. Examples of this method being used to model wavelength converter k. Examples of this method being used to model wavelength converter
pools for several switch architectures are given in reference [GEN- pools for several switch architectures are given in reference [Gen-
Encode]. Encode].
I1 +-------------+ +-------------+ E1 I1 +-------------+ +-------------+ E1
----->| | +--------+ | |-----> ----->| | +--------+ | |----->
I2 | +------+ WC #1 +-------+ | E2 I2 | +------+ WC #1 +-------+ | E2
----->| | +--------+ | |-----> ----->| | +--------+ | |----->
| Wavelength | | Wavelength | | Wavelength | | Wavelength |
| Converter | +--------+ | Converter | | Converter | +--------+ | Converter |
| Pool +------+ WC #2 +-------+ Pool | | Pool +------+ WC #2 +-------+ Pool |
| | +--------+ | | | | +--------+ | |
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Possible mechanisms to improve scaling of dynamic information Possible mechanisms to improve scaling of dynamic information
include: include:
o Tailor message content to WSON. For example the use of wavelength o Tailor message content to WSON. For example the use of wavelength
ranges, or wavelength occupation bit maps. ranges, or wavelength occupation bit maps.
o Utilize incremental updates if feasible. o Utilize incremental updates if feasible.
5. Modeling Examples and Control Plane Use Cases 5. Modeling Examples and Control Plane Use Cases
This section provides examples of the fixed and switch optical node This section provides examples of the fixed and switched optical node
and wavelength constraint models of Section 3. and WSON control and wavelength constraint models of Section 3. and WSON control
plane use cases related to path computation, establishment, plane use cases related to path computation, establishment,
rerouting, and optimization. rerouting, and optimization.
5.1. Network Modeling for GMPLS/PCE Control 5.1. Network Modeling for GMPLS/PCE Control
Consider a network containing three routers (R1 through R3), eight Consider a network containing three routers (R1 through R3), eight
WSON nodes (N1 through N8) and 18 links (L1 through L18) and one OEO WSON nodes (N1 through N8) and 18 links (L1 through L18) and one OEO
converter (O1) in a topology shown below. converter (O1) in a topology shown below.
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+----+-----------------+---------------------+ +----+-----------------+---------------------+
Note that the possible output links for the links connecting to the Note that the possible output links for the links connecting to the
routers is inferred from the switched connectivity matrix and the routers is inferred from the switched connectivity matrix and the
fixed connectivity matrix of the Nodes N1 through N8 and is show here fixed connectivity matrix of the Nodes N1 through N8 and is show here
for convenience, i.e., this information does not need to be repeated. for convenience, i.e., this information does not need to be repeated.
5.2. RWA Path Computation and Establishment 5.2. RWA Path Computation and Establishment
The calculation of optical impairment feasible routes is outside the The calculation of optical impairment feasible routes is outside the
scope of this document. In general impairment feasible routes serve scope of this document. In general optical impairment feasible routes
as an input to RWA algorithm. serve as an input to RWA algorithm.
For the example use case shown here, assume the following feasible For the example use case shown here, assume the following feasible
routes: routes:
+Endpoint 1+Endpoint 2+Feasible Route + +Endpoint 1+Endpoint 2+Feasible Route +
| R1 | R2 | L1 L3 L5 L8 | | R1 | R2 | L1 L3 L5 L8 |
| R1 | R2 | L1 L3 L5 L9 | | R1 | R2 | L1 L3 L5 L9 |
| R1 | R2 | L2 L4 L6 L7 L8 | | R1 | R2 | L2 L4 L6 L7 L8 |
| R1 | R2 | L2 L4 L6 L7 L9 | | R1 | R2 | L2 L4 L6 L7 L9 |
| R1 | R2 | L2 L4 L6 L10 | | R1 | R2 | L2 L4 L6 L10 |
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In the routing extensions for GMPLS [RFC4202], requirements for In the routing extensions for GMPLS [RFC4202], requirements for
layer-specific TE attributes are discussed. RWA for optical networks layer-specific TE attributes are discussed. RWA for optical networks
without wavelength converters imposes an additional requirement for without wavelength converters imposes an additional requirement for
the lambda (or optical channel) layer: that of knowing which specific the lambda (or optical channel) layer: that of knowing which specific
wavelengths are in use. Note that current DWDM systems range from 16 wavelengths are in use. Note that current DWDM systems range from 16
channels to 128 channels with advanced laboratory systems with as channels to 128 channels with advanced laboratory systems with as
many as 300 channels. Given these channel limitations and if the many as 300 channels. Given these channel limitations and if the
approach of a global wavelength to label mapping or furnishing the approach of a global wavelength to label mapping or furnishing the
local mappings to the PCEs is taken then representing the use of local mappings to the PCEs is taken then representing the use of
wavelengths via a simple bit-map is feasible [GEN-Encode]. wavelengths via a simple bit-map is feasible [Gen-Encode].
6.2.3. WSON Routing Information Summary 6.2.3. WSON Routing Information Summary
The following table summarizes the WSON information that could be The following table summarizes the WSON information that could be
conveyed via GMPLS routing and attempts to classify that information conveyed via GMPLS routing and attempts to classify that information
as to its static or dynamic nature and whether that information would as to its static or dynamic nature and whether that information would
tend to be associated with either a link or a node. tend to be associated with either a link or a node.
Information Static/Dynamic Node/Link Information Static/Dynamic Node/Link
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