Internet Engineering Task Force R. Kunze, Ed.
Internet-Draft Deutsche Telekom
Intended status: Informational G. Grammel, Ed.
Expires: January 1, 2018 Juniper
D. Beller
Nokia
G. Galimberti, Ed.
Cisco
J. Meuric
France Telecom Orange
June 30, 2017
A framework for Management and Control of DWDM optical interface
parameters
draft-ietf-ccamp-dwdm-if-mng-ctrl-fwk-06
Abstract
To ensure an efficient data transport, meeting the requirements
requested by today's IP-services the control and management of DWDM
interfaces are a precondition for enhanced multilayer networking and
for a further automation of network provisioning and operation. This
document describes use cases, requirements and solutions for the
control and management of optical interfaces parameters according to
different types of single channel DWDM interfaces. The focus is on
automating the network provisioning process irrespective on how it is
triggered i.e. by EMS, NMS or GMPLS. This document covers management
as well as control plane considerations in different management cases
of single channel DWDM interfaces. The purpose is to identify the
necessary information elements and processes to be used by control or
management systems for further processing.
Status of This Memo
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This Internet-Draft will expire on January 1, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Terminology and Definitions . . . . . . . . . . . . . . . . . 3
3. Solution Space . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Comparison of approaches for transverse compatibility . . 5
3.1.1. Multivendor DWDM line system with transponders . . . 5
3.1.2. Integrated single channel DWDM deployments on the
client site . . . . . . . . . . . . . . . . . . . . . 6
4. Solutions for managing and controlling single channel optical
interface . . . . . . . . . . . . . . . . . . . . . . . . . . 8
4.1. Separate Operation and Management Approaches . . . . . . 9
4.1.1. Direct connection to the management system . . . . . 9
4.1.2. Indirect connection to the DWDM management system
(first optical node) . . . . . . . . . . . . . . . . 11
4.2. Control Plane Considerations . . . . . . . . . . . . . . 13
4.2.1. Considerations using GMPLS signaling . . . . . . . . 14
5. Use cases . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.1. Service Setup . . . . . . . . . . . . . . . . . . . . . . 15
5.2. Link monitoring Use Cases . . . . . . . . . . . . . . . . 16
5.2.1. Pure Access Link (AL) Monitoring Use Case . . . . . . 18
5.2.2. Power Control Loop Use Case . . . . . . . . . . . . . 21
6. Requirements . . . . . . . . . . . . . . . . . . . . . . . . 23
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
9. Security Considerations . . . . . . . . . . . . . . . . . . . 25
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
11.1. Normative References . . . . . . . . . . . . . . . . . . 26
11.2. Informative References . . . . . . . . . . . . . . . . . 27
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
1. Introduction
The usage of the single channel DWDM interfaces (e.g. in routers)
connected to a DWDM Network (which include ROADMs and optical
amplifiers) adds a further networking option for operators allowing
new scenarios but require harmonised control and management plane
interaction between different network domains.
Carriers deploy their networks today based on transport und packet
network infrastructures as domains to ensure high availability and a
high level of redundancy. Both network domains were operated and
managed separately. This is the status quo in many carrier networks
today. In the case of deployments, where the optical transport
interface moves into the client device (e.g. router) an interaction
between those domains becomes necessary.
This framework specifies different levels of control and management
plane interaction to support the usage of single channel optical
interfaces in carrier networks in an efficient manner.
The objective of this document is to provide a framework for the
control and management of transceiver interfaces based on the
corresponding use cases and requirements to ensure an efficient and
optimized data transport.
Optical routing and wavelength assignment based on WSON is out of
scope although can benefit of the way the optical parameters are
exchanged between the Client and the DWDM Network. Also, the
wavelength ordering process and the process how to determine the
demand for a new wavelength path through the network is out of scope.
Note that the Control and Management Planes are two separate entities
that are handling the same information in different ways.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Terminology and Definitions
The current generation of WDM netwoks are single vendor networks
where the optical line system and the transponders are tightly
integrated. The DWDM interfaces migration from the transponders to
the colored interfaces change this scenario, by introducing a
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standardized interface at the level of OCh between the DWDM interface
and the DWDM network.
Black Link: The Black Link [ITU.G698.2] allows supporting an optical
transmitter/receiver pair of a single vendor or from different
vendors to provide a single optical channel interface and transport
it over an optical network composed of amplifiers, filters, add-drop
multiplexers which may be from a different vendor. Therefore the
standard defines the ingress and egress parameters for the optical
interfaces at the reference points Ss and Rs.
Single Channel DWDM Interface: The single channel interfaces to DWDM
systems defined in G.698.2, which currently include the following
features: channel frequency spacing: 50 GHz and wider (defined in
[ITU-T G.694.1]); bit rate of single channel: Up to 10 Gbit/s.
Future revisions are expected to include application codes for bit
rates up to 40 Gb/s.
Forward error correction (FEC): FEC is a way of improving the
performance of high-capacity optical transmission systems. Employing
FEC in optical transmission systems yields system designs that can
accept relatively large BER (much more than 10-12) in the optical
transmission line (before decoding).
Administrative domain [G.805]: For the purposes of this
Recommendation an administrative domain represents the extent of
resources which belong to a single player such as a network operator,
a service provider or an end-user. Administrative domains of
different players do not overlap amongst themselves.
Intra-domain interface (IaDI) [G.872]: A physical interface within an
administrative domain.
Inter-domain interface (IrDI) [G.872]: A physical interface that
represents the boundary between two administrative domains.
Management Plane [G.8081]: The management plane performs management
functions for the transport plane, the control plane and the system
as a whole. It also provides coordination between all the planes.
The following management functional areas are performed in the
management plane: performance management, fault management,
configuration management, accounting management and security
management.
Control Plane[G.8081]: The control plane performs neighbour
discovery, call control and connection control functions. Through
signalling, the control plane sets up and releases connections, and
may restore a connection in case of a failure. The control plane
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also performs other functions in support of call and connection
control, such as neighbour discovery and routing information
dissemination.
Transponder: A Transponder is a network element that performs O/E/O
(Optical /Electrical/Optical) conversion. In this document it is
referred only transponders with 3R (rather than 2R or 1R
regeneration) as defined in [ITU.G.872].
Client DWDM interface: A Transceiver element that performs E/O
(Electrical/Optical) conversion. In this document it is referred as
the DWDM side of a transponder as defined in [ITU.G.872].
3. Solution Space
The solution space of this document is focusing on aspects related to
the management and control of single-channel optical interface
parameters of physical point-to-point and ring DWDM applications on
single-mode optical fibres and allows the direct connection of a wide
variety of equipment using a DWDM link, for example
1. A digital cross-connect with multiple optical interfaces,
supplied by a different vendor from the line system
2. Devices as routing, switching or compute nodes, each from a
different vendor, providing optical line interfaces
3. A combination of the above
3.1. Comparison of approaches for transverse compatibility
This section describes two ways to achieve transverse compatibility.
Section 3.1.1 describes the classic model based on well defined
inter-domain interfaces. Section 3.1.2 defines a model ensuring
interoperability on the line side of the optical network.
3.1.1. Multivendor DWDM line system with transponders
As illustrated in Figure 1, for this approach interoperability is
achieved via the use of optical transponders providing OEO (allowing
conversion to appropriate parameters). The optical interfaces can
then be any short reach standardized optical interface that both
vendors support, such as those found in [ITU-T G.957] [ITU-T G.691],
[ITU-T G.693], [ITU-T G.959.1], etc.
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IrDI IaDI
| |
. .
| +----------------------------|----+
. | + WDM Domain + . |
| | |\ /| | |
+------+ . | | \ |\ / | . | +------+
| TX/ |-->--+---+--T/-|OM|----|/-------|OD|--+-\T-+---->--| RX/ |
| RX |--<--+---+--T/-| |----- /|-----| |--.-\T-+----<--| TX |
+------+ | | | / \| \ | | | +------+
. | |/ \| . |
| | + + | |
. +----------------------------.----+
| |
TX/RX = Single channel non-DWDM interfaces
T/ = Transponder
OM = Optical Mux
OD = Optical Demux
Figure 1: Inter and Intra-Domain Interface Identification
In the scenario of Figure 1 the administrative domain is defined by
the Interdomain Interface (IrDI). This interface terminates the DWDM
domain. The line side is characterized by the IaDI. This interface
specifies the internal parameter set of the optical administrative
domain. In the case of a client DWDM interface deployment this
interface moves into the client device and extends the optical and
administrative domain towards the client node. ITU-T G.698.2 for
example specifies the parameter set for a certain set of
applications.
This document elaborates only the IaDI Interface as shown in Figure 1
as transversely compatible and multi-vendor interface within one
administrative domain controlled by the network operator.
3.1.2. Integrated single channel DWDM deployments on the client site
In case of a deployment as shown in Figure 2, through the use of DWDM
interfaces, multi-vendor interconnection can also be achieved while
removing the need for one short reach transmitter and receiver pair
per channel (eliminating the transponders).
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Figure 2 shows a set of reference points, for single-channel
connection (Ss and Rs) between transmitters (Tx) and receivers (Rx).
Here the DWDM network elements include an optical multiplexer (OM)
and an optical demultiplexer (OD) (which are used as a pair with the
peer element), one or more optical amplifiers and may also include
one or more OADMs.
|==================== Black Link =======================|
+-------------------------------------------------+
Ss | | DWDM Network Elements | | Rs
+---+ | | | \ / | | | +---+
Tx L1---|->| \ +------+ +------+ / |--|-->Rx L1
+---+ | | | | | +------+ | | | | | +---+
+---+ | | | | | | | | | | | | +---+
Tx L2---|->| OM |-|>|------|->| ROADM|--|------|->| OD |--|-->Rx L2
+---+ | | | | | | | | | | | | +---+
+---+ | | | | | +------+ | | | | | +---+
Tx L3---|->| / | DWDM | | ^ | DWDM | \ |--|-->Rx L3
+---+ | | / | Link +----|--|----+ Link | \ | | +---+
+-----------+ | | +----------+
+--+ +--+
|==== Black Link ====| | |
v |
+---+ +---+
RxLx TxLx
+---+ +---+
Ss = Reference point at the DWDM network element tributary output
Rs = Reference point at the DWDM network element tributary input
Lx = Lambda x
OM = Optical Mux
OD = Optical Demux
ROADM = Reconfigurable Optical Add Drop Mux
Linear DWDM network as per ITU-T G.698.2
Figure 2: Linear Black Link
The single administrative domain may consist of several vendor
domains. Even in that case a common network management and control
is required to ensure a consistent operation and provisioning of the
entire connection.
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The following documents[DWDM-interface-MIB], [YANG], [LMP] define
such a protocol- FIX-THE-REFERENCE specific information using SNMP/
SMI, Yang models and LMP TLV to support the direct exchange of
information between the client and the network management and control
plane.
4. Solutions for managing and controlling single channel optical
interface
Operation and management of WDM systems is traditionally seen as a
homogenous group of tasks that could be carried out best when a
single management system or an umbrella management system is used.
Currently each WDM vendor provides an Element Management System (EMS)
that also provisions the wavelengths. In a multi-vendor line system,
such single-vendor EMS requirement is no more effective. New methods
of managing and controlling line systems need to be looked at.
Therefore from the operational point of view the following approaches
will be considered to manage and operate optical interfaces.
1. Separate operation and management of client device and the
transport network whereas the interface of the client belongs to
the administrative domain of the transport network and will be
managed by the transport group. This results in two different
approaches to send information to the management system
a. Direct connection from the client to the management system,
ensuring a management of the DWDM interface of the optical
network (e.g. EMS, NMS)
b. Indirect connection to the management system of the optical
network using a protocol (LMP) between the client device and the
directly connected WDM system node to exchange management
information with the optical domain
2. Common operation and management of client device including the
single channel DWDM part and the Transport network
The first option keeps the status quo in large carrier networks as
mentioned above. In that case it must be ensured that the full FCAPS
Management (Fault, Configuration, Accounting, Performance and
Security) capabilities are supported. This means from the management
staff point of view nothing changes. The transceiver/receiver
optical interface will be part of the optical management domain and
will be managed from the transport management staff.
The second solution addresses the case where underlying WDM transport
network is mainly used to interconnect a homogeneous set of client
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nodes (e.g. IP routers or digital crossconnects). Since the service
creation and restoration could be done by the higher layers (e.g.
IP), this may lead to an efficient network operation and a higher
level of integration.
4.1. Separate Operation and Management Approaches
4.1.1. Direct connection to the management system
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As depicted in Figure 3 (case 1a) one possibility to manage the
optical interface within the client domain is a direct connection to
the management system of the optical domain. This ensures
manageability as usual.
+-----+
| NMS |
|_____|
/_____/
|
|
|
+---+---+
+----->+ EMS |
/ | |
/ +-------+
/ | MI SNMP or Yang
SNMP / or Yang | DCN Network
--------------------+-------------------------------
/ +------+-----------------------+
/ | +| WDM Domain + |
/ | |\ /| |
+---+--+ | | \ |\ / | | +------+
| CL |-/C------+-----|OM|----|/-------|OD|----+-------/C-| CL |
| |-/C------+-----| |----- /|-----| |----+-------/C-| |
+------+ | | / \| \ | | +------+
| |/ \| |
| + + |
+------------------------------+
CL = Client Device
/C = Single Channel Optical Interface
OM = Optical Mux
OD = Optical Demux
EMS = Element Management System
MI = Management Interface
DCN = Data Control Network
Figure 3: Connecting Single Channel optical interfaces to the
Transport Management system
The exchange of management information between client device and the
management system assumes that some form of a direct management
communication link exists between the client device and the DWDM
management system (e.g. EMS). This may be an Ethernet Link or a DCN
connection (management communication channel MCC).
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It must be ensured that the optical network interface can be managed
in a standardized way to enable interoperable solutions between
different optical interface vendors and vendors of the optical
network management application. RFC 3591 [RFC3591] defines managed
objects for the optical interface type but needs further extension to
cover the optical parameters required by this framework document.
Therefore an extension to this MIB for the optical interface has been
drafted in [DWDM-interface-MIB]. SNMP is used to read parameters and
get notifications and alarms, netconf and yang models are needed to
easily provision the interface with the right parameter set as
described in [YANG]
Note that a software update of the optical interface components of
the client nodes must not lead obligatory to an update of the
software of the EMS and vice versa.
4.1.2. Indirect connection to the DWDM management system (first optical
node)
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An alternative as shown in Figure 4 can be used in cases where a more
integrated relationship between transport node (e.g. OM or OD or
ROADM) and client device is aspired. In that case a combination of
control plane features and manual management will be used.
+-----+
| NMS |
|_____|
/_____/
|
|
+---+---+
| EMS |
| |
+-------+
| MI SNMP or Yang
|
LMP +------+-----------------------+
+------------+---+ +| + |
| | | |\ /| |
+---+--+ | +-+ \ |\ / | | +------+
| CL |-/C------+--- -|OM|----|/-------|OD|--- +-------/C-| CL |
| |-/C------+--- -| |----- /|-----| |----+-------/C-| |
+------+ | | / \| \ | | +------+
| |/ \| |
| + + |
+------------------------------+
CL = Client Device
/C = Single Channel optical Interface
OM = Optical Mux
OD = Optical Demux
EMS= Element Management System
MI= Management Interface
Figure 4: Direct connection between peer node and first optical
network node
For information exchange between the client node and the direct
connected node of the optical transport network LMP as specified in
RFC 4209 [RFC4209] should be used. This extension of LMP may be used
between a peer node and an adjacent optical network node as depicted
in Figure 4.
The LMP based on RFC 4209 does not yet support the transmission of
configuration data (information). This functionality must be added
to the existing extensions of the protocol. The use of LMP-WDM
assumes that some form of a control channel exists between the client
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node and the WDM equipment. This may be a dedicated lambda or an
Ethernet Link.
4.2. Control Plane Considerations
The concept of integrated single channel DWDM interfaces equally
applies to management and control plane mechanisms. GMPLS control
plane protocols have been extended for WSON, e.g. [RFC7689] for
fixed grid signal and for flexi-grid [RFC7792]. One important aspect
of the [G.698.2] is the fact that it includes the wavelength that is
supported by the given link. Therefore, the link can logically be
considered as a fiber that is transparent only for a single
wavelength. In other words, the wavelength becomes a characteristic
of the link itself.
Nevertheless the procedure to light up the fiber may vary depending
on the implementation. Since the implementation is unknown a priori,
different sequences to light up a wavelength need to be considered:
1. Interface first, interface tuning: The transmitter is switched on
and the link is immediately transparent to its wavelength. This
requires the transmitter to carefully tune power and frequency
not overload the line system or to create transients.
2. Interface first, OLS tuning: The transmitter is switched on first
and can immediately go to the max power allowed since the OLS
performs the power tuning. This leads to an intermediate state
where the receiver does not receive a valid signal while the
transmitter is sending out one. Alarm suppression mechanisms
shall be employed to overcome that condition.
3. OLS first, interface tuning: At first the OLS is tuned to be
transparent for a given wavelength, then transponders need to be
tuned up. Since the OLS in general requires the presence of a
wavelength to fine-tune its internal facilities there may be a
period where a valid signal is transmitted but the receiver is
unable to detect it. This equally need to be covered by alarm
suppression mechanisms.
4. OLS first, OLS tuning: The OLS is programmed to be transparent
for a given wavelength, then the interfaces need to be switched
on and further power tuning takes place. The sequencing of
enabling the link needs to be covered as well.
The preferred way to address these in a Control Plane enabled network
is neighbour discovery including exchange of link characteristics and
link property correlation. The general mechanisms are covered in
RFC4209 [LMP-WDM] and RFC 4204[LMP] which provides the necessary
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protocol framework to exchange those characteristics between client
and black link. LMP-WDM is not intended for exchanging routing or
signaling information nor to provision the lambda in the transceiver
but covers:
1. Control channel management
2. Link property correlation
3. Link verification
4. Fault management
Extensions to LMP/LMP-WDM covering the parameter sets (application
codes) are needed. Additionally, when client and server side are
managed by different operational entities, link state exchange is
required to align the management systems.
4.2.1. Considerations using GMPLS signaling
The deployment of single channel optical interfaces is leading to
some functional changes related to the control plane models and has
therefore some impact on the existing interfaces especially in the
case of a model where the edge node requests resources from the core
node and the edges node do not participate in the routing protocol
instance that runs among the core nodes. RFC 4208 [RFC4208] defines
the GMPLS UNI that can be used between edge and core node. In case
of integrated interfaces deployment additional functionalities are
needed to setup a connection.
It is necessary to differentiate between topology/signalling
information and configuration parameters that are needed to setup a
wavelength path. RSVP-TE could be used for the signalling and the
reservation of the wavelength path. But there are additional
information needed before RSVP-TE can start the signalling process.
There are three possibilities to proceed:
a. Using RSVP-TE only for the signalling and LMP as described above
to exchange information to configure the optical interface within
the edge node or
b. RSVP-TE (typically with loose ERO) to transport additional
information
c. Leaking IGP information instead of exchanging this information
needed from the optical network to the edge node (UNI will be
transformed to a border-peer model, see RFC 5146)
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Furthermore following issues should be addressed:
a) The Communication between peering edge nodes using an out of band
control channel. The two nodes should exchange their optical
capabilities. An extended version of LMP is needed to exchange FEC
Modulation scheme, etc. that must be the same. It would be helpful
to define some common profiles that will be supported. Only if the
profiles match with both interface capabilities it is possible start
signaling.
b) Due to the bidirectional wavelength path that must be setup, the
upstream edge node must include a wavelength value into the RSVP-TE
Path message. But in the case of a UNI model the client device may
not have full information about which wavelength must/should be
selected, whereas this information must be exchanged between the edge
and the core node. The special value defined in
[Network-Assigned-Upstream-Label] allows the optical network to
assign the actual wavelength to be used by the upstream transponder,
which is a simple and efficient solution to this issue.
5. Use cases
A Comparison with the traditional operation scenarios provides an
insight of similarities and distinctions in operation and management
of DWDM interfaces. The following use cases provide an overview
about operation and maintenance processes.
5.1. Service Setup
It is necessary to differentiate between different operational issues
for setting up a light path (a DWDM connection is specific in having
defined maximum impairments) within an operational network.
The first step is to determine if transceivers located at different
end-points are interoperable, i.e. support a common set of
operational parameters. In this step it is required to determine
transceiver capabilities in a way to be able to correlate them for
interoperability purposes. Such parameters include modulation
scheme, modulation parameters, FEC to name a few. If both
transceivers are controlled by the same NMS or CP, such data is
readily available. However in cases like Fig.4 a protocol need to be
used to inform the controlling instance (NMS or CP) about transceiver
parameters. It is suggested to extend LMP for that purpose.
The second step is to determine the feasibility of a lightpath
between two transceivers without applying an optical signal.
Understanding the limitations of the transceiver pair, a route
through tho optical network has to be found, whereby each route has
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an individual set of impairments deteriorating a wavelength traveling
along that route. Since a single transceiver can support multiple
parameter sets, the selection of a route may limit the permissible
parameter sets determined in step1.
The third step is then to setup the connection itself and to
determine the Wavelength. This is done using the NMS of the optical
transport network or by means of a control plane interaction such as
signaling and includes the route information as well as the parameter
set information necessary to enable communication.
In a fourth step, Optical monitoring is activated in the WDM network
in order to monitor the status of the connection. The monitor
functions of the optical interfaces at the terminals are also
activated in order to monitor the end to end connection.
Furthermore it should be possible to automate this step. After
connecting the client device towards the first control plane managed
transport node a control connection may e.g. be automatically
established using LMP.
5.2. Link monitoring Use Cases
The use cases described below are assuming that power monitoring
functions are available in the ingress and egress network element of
the DWDM network, respectively. By performing link property
correlation it would be beneficial to include the current transmit
power value at reference point Ss and the current received power
value at reference point Rs. For example if the Client transmitter
power has a value of 0dBm and the ROADM interface measured power is
-6dBm the fiber patch cord connecting the two nodes may be pinched or
the connectors are dirty. As discussed before, the actual route or
selection of a specific wavelength within the allowed set is outside
the scope of LMP. The computing entities (e.g. the first optical
node originating the circuit) can rely on GMPLS IGP (OSPF) to
retrieve all the information related to the network, calculate the
path to reach the endpoint and signal the path implementation through
the network via RSVP-TE.
G.698.2 defines a single channel optical interface for DWDM systems
that allows interconnecting network-external optical transponders
across a DWDM network. The optical transponders are external to the
DWDM network. This so-called 'black link' approach illustrated in
Figure 5-1 of G.698.2 and a copy of this figure is provided below.
The single channel fiber link between the Ss/Rs reference points and
the ingress/egress port of the network element on the domain boundary
of the DWDM network (DWDM border NE) is called access link in this
contribution. Based on the definition in G.698.2 it is part of the
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DWDM network. The access link is typically realized as a passive
fiber link that has a specific optical attenuation (insertion loss).
As the access link is an integral part of the DWDM network, it is
desirable to monitor its attenuation. Therefore, it is useful to
detect an increase of the access link attenuation, for example, when
the access link fiber has been disconnected and reconnected
(maintenance) and a bad patch panel connection (connector) resulted
in a significantly higher access link attenuation (loss of signal in
the extreme case of an open connector or a fiber cut). In the
following section, two use cases are presented and discussed:
1) pure access link monitoring
2) access link monitoring with a power control loop
These use cases require a power monitor as described in G.697 (see
section 6.1.2), that is capable to measure the optical power of the
incoming or outgoing single channel signal. The use case where a
power control loop is in place could even be used to compensate an
increased attenuation if the optical transmitter can still be
operated within its output power range defined by its application
code.
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Figure 5 Access Link Power Monitoring
+--------------------------+
| P(in) = P(Tx) - a(Tx) |
| ___ |
+----------+ | \ / Power Monitor |
| | P(Tx) | V P(in) |
| +----+ | Ss //\\ | | |\ |
| | TX |----|-----\\//------------------->| \ |
| +----+ | Access Link (AL-T) | . | | |
| | attenuation a(Tx) | . | |==============>
| | | . | | |
| External | | --->| / |
| Optical | | |/ |
|Transpond.| | P(out) |
| | | ___ |
| | | \ / Power Monitor |
| | P(Rx) | V P(out) |
| +----+ | Rs //\\ | | |\ |
| | RX |<---|-----\\//--------------------| \ |
| +----+ | Access Link (AL-R) | . | | |
| | Attenuation a(Rx) | . | |<==============
+----------+ | . | | |
| <---| / |
P(Rx) = P(out) - a(Rx) | |/ |
| |
| ROADM |
+--------------------------+
- For AL-T monitoring: P(Tx) and a(Tx) must be known
- For AL-R monitoring: P(RX) and a(Rx) must be known
An alarm shall be raised if P(in) or P(Rx) drops below a
configured threshold (t [dB]):
- P(in) < P(Tx) - a(Tx) - t (Tx direction)
- P(Rx) < P(out) - a(Rx) - t (Rx direction)
- a(Tx) =| a(Rx)
Figure 5: Extended LMP Model
5.2.1. Pure Access Link (AL) Monitoring Use Case
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Figure 6 illustrates the access link monitoring use case and the
different physical properties involved that are defined below:
- Ss, Rs: Single Channel reference points
- P(Tx): current optical output power of transmitter Tx
- a(Tx): access link attenuation in Tx direction (external
transponder point of view)
- P(in): measured current optical input power at the input port
of border DWDM NE
- t: user defined threshold (tolerance)
- P(out): measured current optical output power at the output port
of border DWDM NE
- a(Rx): access link attenuation in Rx direction (external
transponder point of view)
- P(Rx): current optical input power of receiver Rx
Description:
- The access link attenuation in both directions (a(Tx), a(Rx))
is known or can be determined as part of the commissioning
process. Typically, both values are very similar.
- A threshold value t has been configured by the operator. This
should also be done during commissioning.
- A control plane protocol is in place that allows
to periodically send the optical power values P(Tx) and P(Rx)
to the control plane protocol instance on the DWDM border NE.
This is illustrated in Figure 3.
- The DWDM border NE is capable to periodically measure the optical
power Pin and Pout as defined in G.697 by power monitoring points
depicted as yellow triangles in the figures below.
Access Link monitoring process:
- Tx direction: the measured optical input power Pin is compared
with the expected optical input power P(Tx) - a(Tx). If the
measured optical input power P(in) drops below the value
(P(Tx) - a(Tx) - t) a low power alarm shall be raised indicating
that the access link attenuation has exceeded a(Tx) + t.
- Rx direction: the measured optical input power P(Rx) is
compared with the expected optical input power P(out) - a(Rx).
If the measured optical input power P(Rx) drops below the value
(P(out) - a(Rx) - t) a
low power alarm shall be raised indicating that the access link
attenuation has exceeded a(Rx) + t.
- to avoid toggling errors, the low power alarm threshold shall be
lower than the alarm clear threshold.
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Figure 6 Use case 1: Access Link monitoring
+----------+ +--------------------------+
| +------+ | P(Tx), P(Rx) | +-------+ |
| | | | =================> | | | |
| | LMP | | P(in), P(out) | | LMP | |
| | | | <================= | | | |
| +------+ | | +-------+ |
| | | |
| | | P(in) - P(Tx) - a(Tx) |
| | | ___ |
| | | \ / Power Monitor |
| | P(Tx) | V |
| +----+ | Ss //\\ | | |\ |
| | TX |----|-----\\//------------------->| \ |
| +----+ | Access Link (AL-T) | . | | |
| | attenuation a(Tx) | . | |==============>
| | | . | | |
| External | | --->| / |
| Optical | | |/ |
|Transpond.| | P(out) |
| | | ___ |
| | | \ / Power Monitor |
| | P(Rx) | V |
| +----+ | Rs //\\ | | |\ |
| | RX |<---|-----\\//--------------------| \ |
| +----+ | Access Link (AL-R) | . | | |
| | Attenuation a(Rx) | . | |<==============
+----------+ | . | | |
| <---| / |
P(Rx) = P(out) - a(Rx) | |/ |
| |
| ROADM |
+--------------------------+
- For AL-T monitoring: P(Tx) and a(Tx) must be known
- For AL-R monitoring: P(RX) and a(Rx) must be known
An alarm shall be raised if P(in) or P(Rx) drops below a
configured threshold (t [dB]):
- P(in) < P(Tx) - a(Tx) - t (Tx direction)
- P(Rx) < P(out) - a(Rx) - t (Rx direction)
- a(Tx) = a(Rx)
Figure 6: Extended LMP Model
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5.2.2. Power Control Loop Use Case
This use case is based on the access link monitoring use case as
described above. In addition, the border NE is running a power
control application that is capable to control the optical output
power of the single channel tributary signal at the output port
of the border DWDM NE (towards the external receiver Rx) and the
optical output power of the single channel tributary signal at
the external transmitter Tx within their known operating range.
The time scale of this control loop is typically relatively slow
(e.g. some 10s or minutes) because the access link attenuation
is not expected to vary much over time (the attenuation only
changes when re-cabling occurs).
From a data plane perspective, this use case does not require
additional data plane extensions. It does only require a protocol
extension in the control plane (e.g. this LMP draft) that allows
the power control application residing in the DWDM border NE to
modify the optical output power of the DWDM domain-external
transmitter Tx within the range of the currently used application
code. Figure 5 below illustrates this use case utilizing the LMP
protocol with extensions defined in this draft.
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Figure 7 Use case 2: Power Control Loop
+----------+ +--------------------------+
| +------+ | P(Tx),P(Rx),Set(Pout) | +-------+ +--------+ |
| | | | ====================> | | | | Power | |
| | LMP | | P(in),P(out),Set(PTx) | | LMP | |Control | |
| | | | <==================== | | | | Loop | |
| +------+ | | +-------+ +--------+ |
| | | | |
| +------+ | | P(in) = P(Tx) - a(Tx) |
| |C.Loop| | | ___ |
| +------+ | | \ / Power Monitor |
| | | P(Tx) | V |
| +------+ | Ss //\\ | | |\ |
| | TX |>----|-----\\//---------------------->| \ |
| +------+ | Access Link (AL-T) | . | | |
| VOA(Tx) | attenuation a(Tx) | . | |==============>
| | | . | | |
| External | | --->| / |
| Optical | | |/ |
|Transpond.| | P(out) |
| | | ___ |
| | | \ / Power Monitor |
| | P(Rx) | V |
| +----+ | Rs //\\ | | VOA(out) |\ |
| | RX |<---|-----\\//---------------------<|-------| \ |
| +----+ | Access Link (AL-R) | . | | |
| | attenuation a(Rx) | . | |<=======
+----------+ | VOA(out) | | |
| <--<|-------| / |
P(Rx) = P(out) - a(Rx) | |/ |
| |
| ROADM |
+--------------------------+
Figure 7: Power control loop
- The Power Control Loops in Transponder and ROADM controls
the Variable Optical Attenuators (VOA) to adjust the proper
power in base of the ROADM and Receiver caracteristics and
the Access Link attenuation
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6. Requirements
Even if network architectures becomes more complex the management and
operation as well as the provisioning process should have a higher
degree of automation or should be fully automated. Simplifying and
automating the entire management and provisioning process of the
network in combination with a higher link utilization and faster
restoration times will be the major requirements that has been
addressed in this section.
Data Plane interoperability as defined for example in [ITU.G698.2] is
a precondition to ensure plain solutions and allow the usage of
standardized interfaces between network and control/management plane.
The following requirements are focusing on the usage of DWDM
interfaces.
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1 To ensure a lean management and provisioning process of single
channel interfaces management and control plane of the client
and DWDM network must be aware of the parameters of the
interfaces and the optical network to properly setup the optical
connection.
2 A standard-based northbound API (to network management system)
based on Netconf should be supported, alternatively SNMP could
be supported too.
3 A standard-based data model for single channel interfaces must be
supported to exchange optical parameters with control/management
plane.
4 Netconf should be used also for configuration of the single
channel interfaces including the power setting
5 LMP should be extended and used in cases where optical
parameters need to be exchanged between peer nodes to correlate
link characteristics and adopt the working mode of the single
channel interface.
6 LMP may be used to adjust the output power of the single
channel DWDM interface to ensure that the interface works in
the right range.
7 RSVP-TE may be used to exchange some relevant parameters between
the client and the optical node (e.g. the label value), without
preventing the network to remain in charge of the optical path
computation
8 Power monitoring functions at both ends of the DWDM connection
should be used to further automate the setup and shoutdown
process of the optical interfaces.
9 A standardized procedure to setup an optical connection should
be defined and implemented in DWDM and client devices
(containing the single channel optical interface).
10 Pre-tested and configured backup paths should be stored in so
called backup profiles. In fault cases this wavelength routes
should be used to recover the service.
11 LMP may be used to monitor and observe the access link.
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7. Acknowledgements
The authors would like to thank all who supported the work with
fruitful discussions and contributions.
8. IANA Considerations
This memo includes no request to IANA.
9. Security Considerations
The architecture and solution space in scope of this framework
imposes no additional requirements to the security models already
defined in RFC5920 for packet/optical networks using GMPLS, covering
also Control Plane and Management interfaces. Respective security
mechanisms of the components and protocols, e.g. LMP security
models, can be applied unchanged.
As this framework is focusing on the single operator use case, the
security concerns can be relaxed to a subset compared to a setup
where information is exchanged between external parties and over
external interfaces.
Concerning the access control to Management interfaces, security
issues can be generally addressed by authentication techniques
providing origin verification, integrity and confidentiality.
Additionally, access to Management interfaces can be physically or
logically isolated, by configuring them to be only accessible out-of-
band, through a system that is physically or logically separated from
the rest of the network infrastructure. In case where management
interfaces are accessible in-band at the client device or within the
optical transport netork domain, filtering or firewalling techniques
can be used to restrict unauthorized in-band traffic. Authentication
techniques may be additionally used in all cases.
10. Contributors
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Arnold Mattheus
Deutsche Telekom
Darmstadt
Germany
email arnold.Mattheus@telekom.de
Manuel Paul
Deutsche Telekom
Berlin
Germany
email Manuel.Paul@telekom.de
Josef Roese
Deutsche Telekom
Darmstadt
Germany
email j.roese@telekom.de
Frank Luennemann
Deutsche Telekom
Muenster
Germany
email Frank.Luennemann@telekom.de
11. References
11.1. Normative References
[ITU.G.872]
International Telecommunications Union, "Architecture of
optical transport networks", ITU-T Recommendation G.872,
November 2001.
[ITU.G698.2]
International Telecommunications Union, "Amplified
multichannel dense wavelength division multiplexing
applications with single channel optical interfaces",
ITU-T Recommendation G.698.2, November 2009.
[ITU.G709]
International Telecommunications Union, "Interface for the
Optical Transport Network (OTN)", ITU-T Recommendation
G.709, March 2003.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2578] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Structure of Management Information
Version 2 (SMIv2)", STD 58, RFC 2578,
DOI 10.17487/RFC2578, April 1999,
<http://www.rfc-editor.org/info/rfc2578>.
[RFC2579] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Textual Conventions for SMIv2",
STD 58, RFC 2579, DOI 10.17487/RFC2579, April 1999,
<http://www.rfc-editor.org/info/rfc2579>.
[RFC2580] McCloghrie, K., Ed., Perkins, D., Ed., and J.
Schoenwaelder, Ed., "Conformance Statements for SMIv2",
STD 58, RFC 2580, DOI 10.17487/RFC2580, April 1999,
<http://www.rfc-editor.org/info/rfc2580>.
[RFC2863] McCloghrie, K. and F. Kastenholz, "The Interfaces Group
MIB", RFC 2863, DOI 10.17487/RFC2863, June 2000,
<http://www.rfc-editor.org/info/rfc2863>.
[RFC3591] Lam, H-K., Stewart, M., and A. Huynh, "Definitions of
Managed Objects for the Optical Interface Type", RFC 3591,
DOI 10.17487/RFC3591, September 2003,
<http://www.rfc-editor.org/info/rfc3591>.
[RFC4209] Fredette, A., Ed. and J. Lang, Ed., "Link Management
Protocol (LMP) for Dense Wavelength Division Multiplexing
(DWDM) Optical Line Systems", RFC 4209,
DOI 10.17487/RFC4209, October 2005,
<http://www.rfc-editor.org/info/rfc4209>.
[RFC6205] Otani, T., Ed. and D. Li, Ed., "Generalized Labels for
Lambda-Switch-Capable (LSC) Label Switching Routers",
RFC 6205, DOI 10.17487/RFC6205, March 2011,
<http://www.rfc-editor.org/info/rfc6205>.
11.2. Informative References
[DWDM-interface-MIB]
Internet Engineering Task Force, "A SNMP MIB to manage the
DWDM optical interface parameters of DWDM applications",
draft-galimkunze-ccamp-dwdm-if-snmp-mib draft-galimkunze-
ccamp-dwdm-if-snmp-mib, July 2011.
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[ITU-TG.691]
ITU-T, "Optical interfaces for single channel STM-64 and
other SDH systems with optical amplifiers",
ITU-T Recommendation ITU-T G.691, 2008.
[ITU-TG.692]
ITU-T, "Transmission media characteristics -
Characteristics of optical components and sub-systems",
ITU-T Recommendation ITU-T G.692, 1998.
[ITU-TG.693]
ITU-T, "Optical interfaces for intra-office systems",
ITU-T Recommendation ITU-T G.693, 2009.
[ITU-TG.8081]
ITU-T, "Terms and definitions for Automatically Switched
Optical Networks (ASON)", ITU-T Recommendation G.8081",
ITU-T Recommendation ITU-T G.8081, September 2010.
[ITU-TG.957]
ITU-T, "Optical interfaces for equipments and systems
relating to the synchronous digital hierarchy",
ITU-T Recommendation ITU-T G.957, 2006.
[ITU-TG.959.1]
ITU-T, "Optical transport network physical layer
interfaces", ITU-T Recommendation ITU-T G.959.1, 2009.
[Network-Assigned-Upstream-Label]
Internet Engineering Task Force, "Generalized Multi-
Protocol Label Switching (GMPLS) Resource reSerVation
Protocol with Traffic Engineering (RSVP- TE) mechanism
that enables the network to assign an upstream label for a
bidirectional LSP", draft-ietf-teas-network-assigned-
upstream-label draft-ietf-teas-network-assigned-upstream-
label, June 2017.
Authors' Addresses
Ruediger Kunze (editor)
Deutsche Telekom
Winterfeldtstr. 21-27
10781 Berlin
Germany
Phone: +491702275321
Email: RKunze@telekom.de
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Gert Grammel (editor)
Juniper
Oskar-Schlemmer Str. 15
80807 Muenchen
Germany
Phone: +49 1725186386
Email: ggrammel@juniper.net
Dieter Beller
Nokia
Lorenzstrasse, 10
70435 Stuttgart
Germany
Phone: +4971182143125
Email: Dieter.Beller@nokia.com
Gabriele Galimberti (editor)
Cisco
Via S. Maria Molgora, 48
20871 - Vimercate
Italy
Phone: +390392091462
Email: ggalimbe@cisco.com
Julien Meuric
France Telecom Orange
2, Avenue Pierre Marzin
22307 Lannion Cedex
France
Phone: +33 2 96 05 28 28
Email: julien.meuric@orange.com
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