Internet DRAFT - draft-kdkgall-ccamp-dwdm-if-mng-ctrl-fwk
draft-kdkgall-ccamp-dwdm-if-mng-ctrl-fwk
Internet Engineering Task Force R. Kunze, Ed.
Internet-Draft Deutsche Telekom
Intended status: Informational G. Grammel, Ed.
Expires: April 21, 2016 Juniper
D. Beller, Ed.
ALU
G. Galimberti, Ed.
Cisco
October 19, 2015
A framework for Management and Control of DWDM optical interface
parameters
draft-kdkgall-ccamp-dwdm-if-mng-ctrl-fwk-01
Abstract
To ensure an efficient data transport, meeting the requirements
requested by today's IP-services the control and management of DWDM
interfaces is a precondition for enhanced multilayer networking and
for an further automation of network provisioning and operation.
This document describes use cases and requirements for the control
and management of optical interfaces parameters according to
different types of single channel DMDM 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 a single channel DWDM interface 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 April 21, 2016.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Terminology and Definitions . . . . . . . . . . . . . . . . . 4
3. Solution Space Client DWDM interface . . . . . . . . . . . . 5
3.1. Comparison of approaches for transverse compatibility . . 6
3.1.1. Multivendor DWDM line system with transponders . . . 6
3.1.2. Black Link Deployments . . . . . . . . . . . . . . . 8
4. Solutions for managing and controlling the optical interface 10
4.1. Separate Operation and Management Approaches . . . . . . 11
4.1.1. Direct connection to the management system . . . . . 11
4.1.2. Direct connection to the DWDM management system . . . 13
4.2. Control Plane Considerations . . . . . . . . . . . . . . 15
4.2.1. Considerations using GMPLS UNI . . . . . . . . . . . 16
5. Operational aspects using IUT-T G.698.2 specified single
channel DWDM interfaces . . . . . . . . . . . . . . . . . . . 17
5.1. Bringing into service . . . . . . . . . . . . . . . . . . 17
5.2. LMP Use Cases . . . . . . . . . . . . . . . . . . . . . . 18
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 25
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 25
8. Security Considerations . . . . . . . . . . . . . . . . . . . 25
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 25
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 26
10.1. Normative References . . . . . . . . . . . . . . . . . . 26
10.2. Informative References . . . . . . . . . . . . . . . . . 27
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 28
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1. Introduction
The usage of the Colored interfaces in the Client Nodes connected to
a DWDM Network (which include ROADMs and optical amplifiers) adds
further networking option for operators opening to new scenarios and
requiring more control/management plane integration.
Carriers deploy their networks today as a combination of transport
and packet infrastructures to ensure high availability and flexible
data transport. Both network technologies are usually managed by
different operational units using different management concepts.
This is the status quo in many carrier networks today. In the case
of a black link deployment, where the optical transport interface
moves into the client device (e.g. , router), it is necessary to
coordinate the management of the optical interface at the client
domain with the optical transport domain. There are different levels
of coordination, which are specified in this framework.
The objective of this document is to provide a framework that
describes the solution space for the control and management of single
channel interfaces and give use cases on how to manage the solutions.
In particular, it examines topological elements and related network
management measures. From an architectural point of view, the
network can be consideres as a black link, that is a set of pre-
configured/qualified unidirectional, single-fiber, network
connections between the G.698.2 reference points S and R. The
optical transport network is managed and controlled in order to
provide Oprical Connections at the intended centre frequencies and
the optical interfaces are managed and controlled to generate signals
of the intended centre frequencies and further parameters as
specified in ITU-T Recommendations G.698.2 and G.798. The Management
or Control planes of the Client and DWDM network must know the
parameters of the Interfaces to properly set the optical link.
Furthermore, support for Fast Fault Detection can benefit from the
solution proposed.
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.
Additionally, the wavelength ordering process and the process how to
determine the demand for a new wavelength from A to Z is out of
scope.
Note that the Control and Management Planes are two separate entities
that are handling the same information in different ways. This
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document covers management as well as control plane considerations in
different management cases of single channel DWDM interfaces.
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
Current generation 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 Client
interfaces changes this scenario, by introducing a standardized
interface at the level of OCh between the Client 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.
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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
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 Client DWDM interface
The management of optical interfaces using the Black Link approach
deals with aspects related to the management of single-channel
optical interface parameters of physical point-to-point and ring DWDM
applications on single-mode optical fibres.
The solution allows the direct connection of a wide variety of
equipments 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. Multiple optical client devices, each from a different vendor,
supplying one channel each
3. A combination of the above
Table 1 provides a list of management regarding the configuration of
optical parameters.
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+---------------------------------------+---------+----+----+---+---+
| Task | Domain | a | b | c | d |
+---------------------------------------+---------+----+----+---+---+
| determination of centre frequency | optical | R | R | R | R |
| configuration of centre frequency at | client | NR | NR | R | R |
| optical IF | | | | | |
| path computation of wavelength | optical | NR | NR | R | R |
| routing of wavelength | optical | NR | NR | R | R |
| wavelength setup across optical | optical | ? | ? | R | R |
| network | | | | | |
| detection of wavelength fault | client | R | R | R | R |
| fault isolation, identification of | optical | NR | R | R | R |
| root failure | | | | | |
| repair actions within optical network | optical | R | R | R | R |
| protection switching of wavelength | optical | NR | NR | R | R |
| restoration of wavelength | optical | NR | NR | R | R |
+---------------------------------------+---------+----+----+---+---+
Note: R = relevant, NR = not relevant
Table 1: List of tasks related to Client - Network interconnection
management
Furthermore the following deployment cases will be considered:
a. Passive WDM
b. P2P WDM systems
c. WDM systems with OADMs
d. Transparent optical networks supporting specific IPoWDM
functions, nterfaces, protocols etc.
Case a) is added for illustration only, since passive WDM is
specified in ITU-T Recommendations G.695 and G.698.1.
Case b) and case c)are motivated by the usage of legacy equipment
using the traditional connection as described in Figure 1 combined
with the BL approach.
3.1. Comparison of approaches for transverse compatibility
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
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labelled "single channel non-DWDM interfaces from other vendor(s)"
and "Single channel non DWDM interfaces to/from other vendor(s)" 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.
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 Client DWDM interface deployment this
interface moves into the client devices and extends the optical and
administrative domain towards the client node. ITU-T G.698.2
specifies the parameter set for a certain set of applications.
This document elaborates only the IaDI Interface as specified in
ITU-T G.698.2 as transversely compatible and multi-vendor interface
within one administrative domain controlled by the network operator.
This administrative domain can contain several vendor domains (vendor
A for the DWDM sub-network, and vendors B1 and B2 at the transmitter
and receiver terminal side).
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3.1.2. Black Link Deployments
In case of a Black Link deployment as shown in Figure 2, through the
use of the single channel DWDM interfaces defined in [ITU.G698.2],
multi-vendor interconnection can also be achieved while removing the
need for one s hort reach transmitter and receiver pair per channel
(eliminating the transponders).
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Figure 2 shows a set of reference points, for the linear "black-link"
approach, 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 |-|>|------|->| OADM |--|------|->| OD |--|-->Rx L2
+---+ | | | | | | | | | | | | +---+
+---+ | | | | | +------+ | | | | | +---+
Tx L3---|->| / | DWDM | | ^ | DWDM | \ |--|-->Rx L3
+---+ | | / | Link +----|--|----+ 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
OADM = Optical Add Drop Mux
Linear DWDM network as per ITU-T G.698.2
Figure 2: Linear Black Link
In Figure 2, if the administrative domain consists of several domains
(e.g. A for a DWDM network, B1 for the DWDM Tx, and B2 for the DWDM
Rx), it is typical that there will be a separate Element Management
Systems (EMS) will be used for each vendor domain (e.g. EMS-a for
domain A, EMS-b1 for domain B1, and EMS-b2 for domain B2). Each EMS
may have a common standard north bound management interface to a
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Network Management System (NMS), allowing consistent end-to-end
management of the connection.
To facilitate consistent end-to-end network management, the north
bound management interface from the EMS to the NMS should be
consistent (frome a management information point of view) with the
standard protocol-neutral (or protocol-specific) information model
used in the EMS south bound management interface to its subtending
NEs (TX and/or RX). The [Interface-MIB] defines such a protocol-
specific information using SNMP/SMI, Yang models and LMP TLV to
support the direct exchange of information between the Client and the
Network control planes.
4. Solutions for managing and controlling the 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 administers the wavelengths.
Therefore from the operational point of view there are the following
approaches will be considered to manage and operate optical
interfaces.
<vspace>:
1. Separate operation and management of client device and the
transport network
a.Direct link between the client device and the management system
of the optical network (e.g. EMS, NMS)
b.Indirect link to the management system of the optical network
using a protocol 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 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.
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The second solution addresses the case where underlying WDM transport
network is mainly used to interconnect a homogeneous set of client
nodes (e.g. IP routers or digital crossconnects). Since the service
creation and restoration could be done by to higher layers (e.g.
IP), this may lead to more 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
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 standardised 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 [Black-Link-MIB]. In that case SNMP is used to exchange
data between the client device and the management system of the WDM
domain. Yang models are as well needed to enable and SDN controller
to easily read/provision the interfaces parameters.
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. Direct connection to the DWDM management system
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The alternative as shown in Figure 4 can be used in cases where a
more integrated relationship between transport node (e.g. OM or OD)
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] can (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.
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The LMP based on RFC 4209 does not yet support the transmission of
configuration data (information). This functionality has to 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
node and the WDM equipment. This may be a dedicated lambda, an
Ethernet Link, or other signaling communication channel (SCC or
IPCC).
4.2. Control Plane Considerations
The concept of black link equally applies to management and control
plane mechanisms. The general GMPLS control Plane for wavelength
switched optical networks is work under definition in the scope of
WSON.One important aspect of the BL is the fact that it includes the
wavelength that is supported by the given link. Thus a BL 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 BL implementation.
Since the implementation of the BL itself is unknown a priori,
different sequences to light up wavelength need to be considered:
1. Transponders first, transponder tuning: The transmitter is
switched on and the BL 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. Transponder 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, Transponder 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 it is internal facilities there may be a
period of time 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 transponders need to be switched
on and further power tuning takes place. The sequencing of
enabling the link needs to be covered as well.
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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
protocol framework to exchange those characteristics between client
and black link. LMP-WDM is not intended for exchanging routing or
signalling information but covers:
1. Control channel manangement
2. Link property correlation
3. Link verification
4. Fault Manangement
Extensions to LMP/LMP-WDM covering the code points of the BL
definition 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 UNI
The deployment of G.698.2 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 an overlay 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 will be used between edge and core node.
In case of a black link 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 will be used to transport additional information
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c. Leaking IGP information instead of exchanging this information
needed from the optical network to the edge node (overlay will be
transformed to a border-peer model)
Furthermore following issues should be addressed:
a) The Communication between peering edge nodes using an out of band
control channel. The two nodes have to 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
signalling.
b) Due to the bidirectional wavelength path that must be setup it is
obligatory that the upstream edge node inserts a wavelength value
into the path message for the wavelength path towards the upstream
node itself. But in the case of an overlay model the client device
may not have full information which wavelength must/should be
selectedand this information must be exchanged between the edge and
the core node.
5. Operational aspects using IUT-T G.698.2 specified single channel
DWDM interfaces
A Comparison of the Black Link with the traditional operation
scenarios provides an insight of similarities and distinctions in
operation and management. The following four use cases provide an
overview about operation and maintenance processes.
5.1. Bringing into service
It is necessary to differentiate between two 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 the preparation of the connection if no optical signal
is applied. Therefore it is necessary to define the path of the
connection.
The second step is to setup the connection between the Cleint DWDM
interface and the ROADM port. This is done using the NMS of the
optical transport network. From the operation point of view the task
is similar in a Black Link scenario and in a traditional WDM
environment. The Black Link connection is measured by using BER
tester which use optical interfaces according to G.698.2. These
measurements are carried out in accordance with ITU-T Recommendation
M.xxxx. When needed further Black Link connections for resilience
are brought into service in the same way.
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In addition some other parameters like the Transmit Optical Power,
the Received Optical Power, the Frequency, etc. must be considered.
If the optical interface moves into a client device some of changes
from the operational point of view have to be considered. The centre
frequency of the Optical Channel was determined by the setup process.
The optical interfaces at both terminals are set to the centre
frequency before interconnected with the dedicated ports of the WDM
network. Optical monitoring is activated in the WDM network after
the terminals are interconnected with the dedicated ports 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 last 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 to exchange configuration information.
If tunable interfaces are used in the scenario it would be possible
to define a series of backup wavelength routes for restoration that
could be tested and stored in backup profile. In fault cases this
wavelength routes can be used to recover the service.
5.2. LMP 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 (OXC1) has a value of 0dBm and the ROADM interface measured
power (at OLS1) is -6dBm the fiber patch cord connecting the two
nodes may be pinched or the connectors are dirty. More, the
interface characteristics can be used by the OLS network Control
Plane in order to check the Optical Channels feasibility. Finally
the OXC1 transceivers parameters (Application Code) can be shared
with OXC2 using the LMP protocol to verify the Transceivers
compatibility. The actual route selection of a specific wavelength
within the allowed set is outside the scope of LMP. In GMPLS, the
parameter selection (e.g. central frequency) is performed by 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 considered to be
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
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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 considered to be part of the DWDM network. The access link
typically is 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 as long as 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
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Pure Access Link (AL) Monitoring Use Case
Figure 4 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 the same.
- A threshold value t has been configured by the operator. This
should also be done during commissioning.
- A control plane protocol (e.g. this draft) 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 llustrated 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.
AL 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 power 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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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: Extended LMP Model
- 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. Acknowledgements
The author would like to thank Ulrich Drafz for the very good
teamwork during the last years and the initial thoughts related to
the packet optical integration. Furthermore the author would like to
thank all people involved within Deutsche Telekom for the support and
fruitful discussions.
7. IANA Considerations
This memo includes no request to IANA.
8. 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 authentification 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.
9. 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
10. References
10.1. Normative References
[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>.
[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>.
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[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>.
[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>.
[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>.
[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>.
[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.
[ITU.G.872]
International Telecommunications Union, "Architecture of
optical transport networks", ITU-T Recommendation G.872,
November 2001.
10.2. Informative References
[Black-Link-MIB]
Internet Engineering Task Force, "A SNMP MIB to manage
black-link optical interface parameters of DWDM
applications", draft-galimbe-kunze-g-698-2-snmp-mib draft-
galimbe-kunze-g-698-2-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.693]
ITU-T, "Optical interfaces for intra-office systems",
ITU-T Recommendation ITU-T G.693, 2009.
[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.
[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.
Authors' Addresses
Ruediger Kunze (editor)
Deutsche Telekom
Dddd, xx
Berlin
Germany
Phone: +49xxxxxxxxxx
Email: RKunze@telekom.de
Gert Grammel (editor)
Juniper
Oskar-Schlemmer Str. 15
80807 Muenchen
Germany
Phone: +49 1725186386
Email: ggrammel@juniper.net
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Dieter Beller (editor)
ALU
Lorenzstrasse, 10
70435 Stuttgart
Germany
Phone: +4971182143125
Email: Dieter.Beller@alcatel-lucent.com
Gabriele Galimberti (editor)
Cisco
Via S. Maria Molgora, 48
20871 - Vimercate
Italy
Phone: +390392091462
Email: ggalimbe@cisco.com
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