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Versions: (draft-gray-mpls-tp-nm-req) 00 01
02 03 04 05 06 RFC 5951
Network Working Group Hing-Kam Lam
Internet Draft Alcatel-Lucent
Expires: August, 2009 Scott Mansfield
Intended Status: Informational Eric Gray
Ericsson
February 23, 2009
MPLS TP Network Management Requirements
draft-ietf-mpls-tp-nm-req-00.txt
Status of this Memo
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Abstract
This document specifies the requirements necessary to manage the
elements and networks that support an MPLS Transport Profile
(MPLS-TP). This document is a product of a joint International
Telecommunications Union - Telecommunications Standardization
Sector (ITU-T) and Internet Engineering Task Force (IETF) effort
to include a MPLS Transport Profile within the IETF MPLS
architecture. The requirements are driven by the management
functionality needs defined by ITU-T for packet transport
networks.
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Table of Contents
1. Introduction................................................3
1.1. Terminology............................................3
2. Management Interface Requirements...........................4
3. Management Communication Channel (MCC) Requirements.........4
4. Management Communication Network (MCN) Requirements.........5
5. Fault Management Requirements...............................5
5.1. Supervision Function...................................5
5.2. Validation Function....................................7
5.3. Alarm Handling Function................................7
5.3.1. Alarm Severity Assignment.........................7
5.3.2. Alarm Suppression.................................8
5.3.3. Alarm Reporting Control...........................8
5.3.4. Alarm Reporting...................................8
6. Configuration Management Requirements.......................9
6.1. System Configuration...................................9
6.2. Control Plane Configuration............................9
6.3. Path Configuration.....................................9
6.4. Protection Configuration..............................10
6.5. OAM Configuration.....................................10
7. Performance Management Requirements........................11
7.1. Path Characterization Performance Metrics.............11
7.2. Performance Measurement Instrumentation..............12
7.2.1. Measurement Frequency............................12
7.2.2. Measurement Scope................................12
8. Security Management Requirements...........................13
8.1. Management Communication Channel Security.............13
8.1.1. Security of Management Communications............13
8.2. Signaling Communication Channel Security..............14
8.3. Data Channel Security.................................14
8.4. Distributed Denial of Service.........................14
9. Security Considerations....................................14
10. IANA Considerations.......................................15
11. Acknowledgments...........................................15
12. References................................................15
12.1. Normative References.................................15
12.2. Informative References...............................16
13. Author's Addresses........................................16
Copyright Statement...........................................17
Acknowledgment................................................17
APPENDIX A: Communication Channel (CC) Examples...............18
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1. Introduction
This document describes the requirements necessary to manage the
elements and networks that support an MPLS Transport Profile
(MPLS-TP). It leverages the management requirements specified
in ITU-T G.7710/Y.1701 [1] and RFC 4377 [2]. ITU-T G.7710/Y.1701
[1] specifies generic management requirements for transport
(including packet-based and circuit-based) networks. RFC 4377
specifies the OAM requirements, including OAM-related network
management requirements, for MPLS networks. This document
expands on the requirements in [1] and [2] to cover fault,
configuration, performance, and security management for MPLS-TP
networks, and the requirements for object and information models
needed to manage MPLS-TP Networks and Network Elements.
1.1. Terminology
Although this document is not a protocol specification, 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 [6]
and are to be interpreted as instructions to protocol designers
producing solutions that satisfy the requirements set out in
this document.
MPLS-TP NE: a network element (NE) that supports MPLS-TP
functions
MPLS-TP network: a network in which MPLS-TP NEs are deployed
Data Communication Network (DCN): a network that supports Layer
1 (physical layer), Layer 2 (data-link layer), and Layer 3
(network layer) functionality for distributed management
communications related to the management plane, for distributed
signaling communications related to the control plane, and other
operations communications (e.g., order-wire/voice
communications, software downloads, etc.).
Management Communication Network (MCN): A DCN supporting
management plane communication is referred to as a Management
Communication Network (MCN).
Signaling Communication Network (SCN): A DCN supporting control
plane communication is referred to as a Signaling Communication
Network (SCN).
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Communication Channel (CC): a logical channel between network
elements (NEs) that can be used - e.g. - for management plane
application or control plane applications. The physical channel
supporting the CC is technology specific. See APPENDIX A:
Management Communication Channel (MCC): a CC dedicated for
management plane communications.
Signaling Communication Channel (SCC): a CC dedicated for
control plane communications. The SCC may be used for GMPLS/ASON
signaling and/or other control plane messages (e.g., routing
messages).
Operations System (OS): A system that performs the functions
that support processing of information related to operations,
administration, maintenance, and provisioning (OAM&P) for the
networks, including surveillance and testing functions to
support customer access maintenance.
2. Management Interface Requirements
This document does not specify which management interface
protocol should be the standard protocol for managing MPLS-TP
networks. Managing an end-to-end connection across multiple
operator domains where one domain is managed (for example) via
NETCONF/XML or SNMP/SMI, and another domain via CORBA/IDL, is
allowed.
For the management interface to the management system, an MPLS-
TP NE is not expected to actively support more than one
management protocol in any given deployment. The protocol to be
supported is at the discretion of the operator.
3. Management Communication Channel (MCC) Requirements
An MPLS-TP management network SHOULD support seamless management
connectivity with remote MPLS-TP domains and NEs as well as with
termination points located in NEs under control by a third party
network operator. See ITU-T G.8601 [8] for example scenarios in
multi-carrier multi-transport-technology environments.
For management purpose, every MPLS-TP NE MUST connect to an OS
either directly or indirectly via another MPLS-TP NE. When an
MPLS-TP NE is connected indirectly to an OS, an MCC MUST be
supported between the MPLS-TP NE and the other MPLS-TP NE.
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4. Management Communication Network (MCN) Requirements
Entities of the MPLS-TP management plane communicate via a DCN,
or more specifically via the MCN. The MCN connects MPLS-TP NEs
with management systems, NEs with NEs, and management systems
with management systems. Transport DCN architecture and
requirements are specified in ITU-T G.7712/Y.1703 [7], including
network layer protocols and their interworking.
As a practical requirement, MCN connections require addressing.
See the section on addressing in [13] for further information.
In order to have the MCN operate properly, a number of
management functions for the MCN are required:
. Retrieval of DCN network parameters to ensure compatible
functioning, e.g. packet size, timeouts, quality of
service, window size, etc.;
. Establishment of message routing between DCN nodes;
. Management of DCN network addresses;
. Retrieval of operational status of the DCN at a given node;
. Capability to enable/disable access to the DCN.
5. Fault Management Requirements
The Fault Management functions within an MPLS-TP NE enable the
supervision, detection, validation, isolation, correction, and
reporting of abnormal operation of the MPLS-TP network and its
environment.
5.1. Supervision Function
The supervision function analyses the actual occurrence of a
disturbance or fault for the purpose of providing an appropriate
indication of performance and/or detected fault condition to
maintenance personnel and operations systems.
The MPLS-TP NE MUST support the following transmission
supervision functions:
. Supervision of continuity check functions used to detect a
broken connection;
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. Supervision of connectivity check functions used to detect
misconnection;
. Supervision of looping check functions used to detect loops
in the data-plane forwarding path (which result in non-
delivery of traffic, wasting of forwarding resources and
unintended self-replication of traffic);
. Supervision of Alarms based on native OAM, e.g., AIS (Alarm
Indication Signal) and FDI (Forward Defect Indication)
. Supervision of traffic loss measurement in both directions
of the bidirectional connection;
. Supervision of Misinsertion check function used to detect
misinserted packet in the connection
. Supervision of Diagnostic test;
. Supervision of Route determination;
. Supervision of Remote defect indication;
. Supervision of the detection of failure in the sequence of
a protocol exchange (e.g. automatic protection switching
protocol);
. Supervision of client failure indication.
The MPLS-TP NE transmission-related supervision mechanisms MUST
support the flexibility to be configured to perform on-demand or
proactively.
The MPLS-TP NE MUST support supervision for software processing
e.g., processing fault, storage capacity problem, version
mismatch, Corrupted data, Out of memory, etc.
The MPLS-TP NE MUST support hardware-related supervision for
interchangeable and non-interchangeable units, cable, and power
problem.
The MPLS-TP NE SHOULD support environment-related supervision
for temperature, humidity, etc.
The MPLS-TP NE MUST support supervision of the OAM mechanisms
that are deployed for supporting the OAM requirements defined in
[3].
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5.2. Validation Function
Validation is concerned with the integration of Fault Causes
into Failures. A Fault Cause indicates a limited interruption of
the required transport function. A Fault Cause is not reported
to maintenance personnel because it could exist only for a very
short time. Note that some of these events however are summed up
in the Performance Monitoring process, and when this sum exceeds
a certain value, a Threshold Report can be generated.
When the Fault Cause lasts long enough, an inability to perform
the required transport function arises. This Failure condition
is subject to reporting to maintenance personnel and/or an OS
because corrective action might be required. Conversely, when
the Fault Cause ceases after a certain time, clearing of the
Failure condition is also subject to reporting.
The MPLS-TP NE MUST perform persistency checks on fault causes
before it declares a fault cause a failure.
A transmission failure SHALL be declared if the fault cause
persists continuously for a configurable time (Time-D). The
failure SHALL be cleared if the fault cause is absent
continuously for a configurable time (Time-C). Typically the
default time values would be as follows:
Time-D = 2.5 +/- 0.5 seconds
Time-C = 10 +/- 0.5 seconds
These time values are as defined in G.7710 [1].
The failure declaration and clearing MUST be time stamped. The
time-stamp SHALL indicate the time at which the fault cause is
activated at the input of the fault cause persistency (i.e.
defect-to-failure integration) function, and the time at which
the fault cause is deactivated at the input of the fault cause
persistency function.
5.3. Alarm Handling Function
5.3.1. Alarm Severity Assignment
Failures might be categorized to indicate the severity or
urgency of the fault.
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An MPLS-TP NE SHOULD support the flexibility of assignment of
severity (e.g., Critical, Major, Minor, Warning) by the
management system.
See G.7710 [1] for more description about alarm severity
assignment.
5.3.2. Alarm Suppression
Alarms may be generated from many sources, including OAM, device
status, etc.
An MPLS-TP NE MUST provide alarm suppression functionality that
prevents the generation of a superfluous alarms.
Examples of alarm suppression mechanisms include simply
discarding the alarms (or not generating them in the first
place), or aggregating the alarms together, thereby greatly
reducing the number of alarm notifications to be emitted.
Note: An MPLS-TP NE supporting the inter-working of one or more
networking technologies (e.g., Ethernet, SDH/SONET, MPLS) with
MPLS-TP needs to translate an MPLS-TP fault into an existing
transport technology failure condition for reporting to the
management system.
See RFC 4377 [2] for more description.
5.3.3. Alarm Reporting Control
Alarm Reporting Control (ARC) supports an automatic in-service
provisioning capability. Alarm reporting MAY be turned off on a
per-managed entity (e.g., LSP) basis to allow sufficient time
for customer service testing and other maintenance activities in
an "alarm free" state. Once a managed entity is ready, alarm
reporting is automatically turned on.
An MPLS-TP NE SHOULD support the Alarm Reporting Control
function for controlling the reporting of alarm conditions.
See G.7710 [1] and RFC 3878 [9] for more description of ARC.
5.3.4. Alarm Reporting
Alarm Reporting is concerned with the reporting of relevant
events and conditions, which occur in the network (including the
NE, incoming signal, and external environment).
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Local reporting is concerned with automatic alarming by means of
audible and visual indicators near the failed equipment.
An MPLS-TP NE MUST support local reporting of alarms.
The MPLS-TP NE MUST support reporting of alarms to an OS. These
reports are either autonomous reports (notifications) or reports
on request by maintenance personnel. The MPLS-TP ME SHOULD
report local (environmental) alarms to a network management
system.
6. Configuration Management Requirements
Configuration Management provides functions to identify, collect
data from, provide data to and control NEs. Specific
configuration tasks requiring network management support include
hardware and software configuration, configuration of NEs to
support transport paths (including required working and
protection paths), and configuration of required path
integrity/connectivity and performance monitoring (i.e. - OAM).
6.1. System Configuration
The MPLS-TP NE MUST support the configuration requirements
specified in G.7710 [1] for hardware, software, and date/time.
6.2. Control Plane Configuration
If a control plane is supported in an implementation of MPLS-TP,
the MPLS-TP NE MUST support the configuration of MPLS-TP control
plane functions by the management plane. Further detailed
requirements might be provided along with progress in defining
the MPLS-TP control plane in appropriate specifications.
6.3. Path Configuration
The MPLS-TP NE MUST support the capability of configuring
required path performance characteristic thresholds (e.g. - Loss
Measurement [LM], Delay Measurement [DM] thresholds).
The MPLS-TP NE MUST support the capability of configuring
required LSPs as follows:
. configure LSP indentifier and/or other information
necessary to retrieve LSP status information.
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6.4. Protection Configuration
The MPLS-TP NE MUST support the capability of configuring
required path protection as follows:
. Designate specifically identified LSPs as working or
protection LSPs;
. define associations of working and protection paths;
. operate/release manual protection switching;
. operate/release force protection switching;
. operate/release protection lockout;
. set/retrieve Automatic Protection Switching (APS)
parameters, including -
. Wait to Restore time,
. Protection Switching threshold information.
6.5. OAM Configuration
The MPLS-TP NE MUST provide the capability to configure the OAM
entities and functions specified in [3].
The MPLS-TP NE MUST support the capability to choose which OAM
functions to use and which maintenance entity to apply them.
The MPLS-TP NE MUST support the capability to configure the OAM
entities/functions as part of LSP setup, including bidirectional
point-to-point connections, associated uni-directional point-to-
point connections, and uni-directional point-to-multipoint
connections.
The MPLS-TP NE MUST support the configuration of maintenance
entity identifiers (e.g. MEP ID and MIP ID) for the purpose of
LSP connectivity checking.
The MPLS-TP NE MUST have the flexibility to configure OAM
parameters to meet their specific operational requirements, such
as whether (1) one-time on-demand immediately or (2) one-time
on-demand pre-scheduled or (3) on-demand periodically based on a
specified schedule or (4) proactive on-going.
The MPLS-TP NE MUST support the enabling/disabling of the
connectivity check processing. The connectivity check process of
the MPLS-TP NE MUST support provisioning of the identifiers to
be transmitted and the expected identifiers.
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7. Performance Management Requirements
Performance Management provides functions to evaluate and report
upon the behavior of the equipment, NE, and network for the
purpose of Maintenance, Bring-into-service, Quality of service,
and Performance monitoring for signal degradation. ITU-T
Recommendation G.7710 [1] provides transport performance
monitoring requirements for packet-switched and circuit-switched
transport networks with the objective of providing coherent and
consistent interpretation of the network behavior, in particular
for hybrid network which consists of multiple transport
technologies. The performance management requirements specified
in this document are driven by such an objective.
7.1. Path Characterization Performance Metrics
The MPLS-TP NE MUST support collection of loss measurement (LM)
so that they can be used to detect performance degradation.
The MPLS-TP NE MUST support collection of delay measurement (DM)
so that they can be used to detect performance degradation.
The MPLS-TP NE MUST support reporting of Performance degradation
via fault management for corrective actions (e.g. protection
switching).
The MPLS-TP NE MUST support collection of loss ratio measurement
so that they can be used to determine Severely Errored Second
(SES).
A SES is declared for a one second interval when the ratio of
lost packets to total transmitted packets in that one second
interval exceeds a predetermined threshold.
The packet lost threshold for declaring SES MUST be
configurable.
The number of SESs MUST be collected per configurable intervals
(e.g. 15-minute and 24-hour).
The MPLS-TP NE MUST support collection of SES measurement so
that they can be used to determine service unavailable time.
A period of unavailable time (UAT) begins at the onset of 10
consecutive SES events. These 10 seconds are considered to be
part of unavailable time. A new period of available time begins
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at the onset of 10 consecutive non-SES events. These 10 seconds
are considered to be part of available time.
The MPLS-TP NE MUST support collection of Unavailable Seconds
(UAS) so that they can be used to determine service
availability.
The number of UAS MUST be collected per configurable intervals
(e.g. 15-minute and 24-hour).
SES and UAS history (the number of readings to be retained and
available) is as defined in ITU and ANSI documents associated
with specific transport technologies (for instance, ITU-T
G.7710, and ANSI T1.231-2003 [T1.231.01-2003 for DSL,.02 for
DS1,.03 for DS3 and T1.231.04-2003 for SONET] - see [1] and [14]
respectively), however these are fairly consistently defined as
follows:
- Current and previous 1-day statistics
- Current and 16 recent 15-minute statistics (ITU-T)
- Current, previous and 31 recent 15-minute statistics (ANSI)
Note that - worst case (ANSI) requires 2 copies of 1-day
statistics (current and previous) and 33 copies of 15-minute
statistics (current, previous and 31 recent).
7.2. Performance Measurement Instrumentation
7.2.1. Measurement Frequency
The performance measurement mechanisms MUST support the
flexibility to be configured to operate on-demand or proactively
(i.e. continuously over a period of time).
7.2.2. Measurement Scope
On measurement of packet loss and loss ratio:
- For bidirectional P2P connections -
. on-demand measurement of single-ended packet loss,
and loss ratio, measurement are required;
. proactive measurement of packet loss, and loss
ratio, measurement for each direction are required.
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- For associated unidirectional P2P connections -
. on-demand measurement of single-ended packet loss,
and loss ratio, measurement are required;
. proactive measurement of packet loss, and loss
ratio, measurement for each direction are required.
Note: for associated unidirectional P2P connections, this data
can only be measured at end-points.
- For unidirectional (P2P and P2MP) connection, proactive
measurement of packet loss, and loss ratio, are required.
On Delay measurement:
- For unidirectional (P2P and P2MP) connection, on-demand
measurement of delay measurement is required.
- For bidirectional (P2P) connection, on-demand measurement
of one-way and two-way delay are required.
8. Security Management Requirements
The MPLS-TP NE MUST support secure management and control
planes.
8.1. Management Communication Channel Security
Secure channels MUST be provided for all network traffic and
protocols used to support management functions. This MUST
include, at least, protocols used for configuration, monitoring,
configuration backup, logging, time synchronization,
authentication, and routing. The MCC MUST support application
protocols that provide confidentiality and data integrity
protection.
8.1.1. Security of Management Communications
If management communication security is provided, the MPLS-TP NE
MUST support the following:
- Use of open cryptographic algorithms (See RFC 3871 [5])
- Authentication - allow management connectivity only from
authenticated entities.
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- Authorization - allow management activity originated by an
authorized entity, using (for example) an Access Control
List (ACL).
Port Access Control - allow management activity received on an
authorized (management) port.
8.2.Signaling Communication Channel Security
Security considerations for the SCC are similar to the
considerations driving the requirements described in section
8.1. Security Requirements for the control plane are out of
scope for this document and are expected to be defined in the
appropriate control plane specifications. Management of the
control plane security must also be defined at that time.
8.3. Data Channel Security
8.4.Distributed Denial of Service
Denial of Service (DoS) attack is an attack which tries to
prevent a target from performing an assigned task, or providing
its intended service(s), through any means. A Distributed DoS
(DDoS) can multiply attack severity (possibly by an arbitrary
amount) by using multiple (potentially compromised) systems to
act as topologically (and potentially geographically)
distributed attack sources. It is possible to lessen the impact
and potential for DDOS by using secure protocols, turning off
unnecessary processes, logging and monitoring, and ingress
filtering. RFC 4732 [4] provides background on DOS in the
context of the Internet.
9. Security Considerations
Section 8 lists a set of security requirements that apply to
MPLS-TP network management.
Provisions to any of the network mechanisms designed to satisfy
the requirements described herein are required to prevent their
unauthorized use. Likewise, these network mechanisms MUST
provide a means by which an operator can prevent denial of
service attacks if those network mechanisms are used in such an
attack.
Solutions MUST provide mechanisms to prevent this private
information from being accessed by unauthorized eavesdropping,
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or being directly obtained by an unauthenticated network
element, system or user.
Performance of diagnostic functions and path characterization
involves extracting a significant amount of information about
network construction that the network operator MAY consider
private.
10. IANA Considerations
<insert IANA considerations, if any, here)
11. Acknowledgments
The authors/editors gratefully acknowledge the thoughtful
review, comments and explanations provided by Adrian Farrel,
Andrea Maria Mazzini, Ben Niven-Jenkins, Bernd Zeuner, Diego
Caviglia, Dieter Beller, He Jia, Leo Xiao and Maarten Vissers.
12. References
12.1. Normative References
[1] ITU-T Recommendation G.7710/Y.1701, "Common equipment
management function requirements", July, 2007.
[2] Nadeau, T., et al., "Operations and Management (OAM)
Requirements for Multi-Protocol Label Switched (MPLS)
Networks", RFC 4377, February 2006.
[3] Vigoureus, M., et al., "Requirements for OAM in MPLS
Transport Networks", work in progress.
[4] Handley, M., et al., "Internet Denial-of-Service
Considerations", RFC 4732, November 2006.
[5] Jones, G., "Operational Security Requirements for Large
Internet Service Provider (ISP) IP Network
Infrastructure", RFC 3871, September 2004.
[6] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", RFC 2119, March 1997.
[7] ITU-T Recommendation G.7712/Y.1703, "Architecture and
Specification of Data Communication Network", June 2008.
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[8] ITU-T Recommendation G.8601, "Architecture of service
management in multi bearer, multi carrier environment",
June 2006.
[9] Lam, H., et al., "Alarm Reporting Control Management
Information Base (MIB)", RFC 3878, September 2004.
12.2. Informative References
[10] Chisholm, S. and D. Romascanu, "Alarm Management
Information Base (MIB)", RFC 3877, September 2004.
[11] ITU-T Recommendation M.20, "Maintenance Philosophy for
Telecommunication Networks", October 1992.
[12] Telcordia, "Network Maintenance: Network Element and
Transport Surveillance Messages" (GR-833-CORE), Issue 5,
August 2004.
[13] Bocci, M. et al., "A Framework for MPLS in Transport
Networks", Work in Progress, November 27, 2008.
[14] ANSI T1.231-2003, "Layer 1 In-Service Transmission
Performance Monitoring", American National Standards
Institute, 2003.
13. Author's Addresses
Editors:
Scott Mansfield
Ericsson
5000 Ericsson Drive
Warrendale, PA, 15086
Phone: +1 724 742 6726
EMail: Scott.Mansfield@Ericsson.com
Hing-Kam (Kam) Lam
Alcatel-Lucent
600-700 Mountain Ave
Murray Hill, NJ, 07974
Phone: +1 908 582 0672
Email: hklam@Alcatel-Lucent.com
Eric Gray
Ericsson
900 Chelmsford Street
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Lowell, MA, 01851
Phone: +1 978 275 7470
Email: Eric.Gray@Ericsson.com
Author(s):
Contributor(s):
Copyright Statement
Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with
respect to this document.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
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APPENDIX A: Communication Channel (CC) Examples
A CC may be realized in a number of ways.
1. The CC may be provided by a link in a physically distinct
network. That is, a link that is not part of the transport
network that is being managed. For example, the nodes in the
transport network may be interconnected in two distinct physical
networks: the transport network and the DCN.
This is a "physically distinct out-of-band CC".
2. The CC may be provided by a link in the transport network
that is terminated at the ends of the DCC and which is capable
of encapsulating and terminating packets of the management
protocols. For example, in MPLS-TP an single-hop LSP might be
established between two adjacent nodes, and that LSP might be
capable of carrying IP traffic. Management traffic can then be
inserted into the link in an LSP parallel to the LSPs that carry
user traffic.
This is a "physically shared out-of-band CC."
3. The CC may be supported as its native protocol on the
interface alongside the transported traffic. For example, if an
interface is capable of sending and receiving both MPLS-TP and
IP, the IP-based management traffic can be sent as native IP
packets on the interface.
This is a "shared interface out-of-band CC".
4. The CC may use overhead bytes available on a transport
connection. For example, in TDM networks there are overhead
bytes associated with a data channel, and these can be used to
provide a CC. It is important to note that the use of overhead
bytes does not reduce the capacity of the associated data
channel.
This is an "overhead-based CC".
This alternative is not available in MPLS-TP because there is no
overhead available.
5. The CC may provided by a dedicated channel associated with
the data link. For example, the generic associated label (GAL)
[GAL-GACH] may be used to label DCC traffic being exchanged on a
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data link between adjacent transport nodes, potentially in the
absence of any data LSP between those nodes.
This is a "data link associated CC".
It is very similar to case 2, and by its nature can only span a
single hop in the transport network.
6. The CC may be provided by a dedicated channel associated with
a data channel. For example, in MPLS-TP the GAL [GAL-GACH] may
be imposed under the top label in the label stack for an MPLS-TP
LSP to create a channel associated with the LSP that may carry
management traffic. This CC requires the receiver to be capable
of demultiplexing management traffic from user traffic carried
on the same LSP by use of the GAL.
This is a "data channel associated CC".
7. The CC may be provided by mixing the management traffic with
the user traffic such that is indistinguishable on the link
without deep-packet inspection. In MPLS-TP this could arise if
there is a data-carrying LSP between two nodes, and management
traffic is inserted into that LSP. This approach requires that
the termination point of the LSP is able to demultiplex the
management and user traffic. Such might be possible in MPLS-TP
if the MPLS-TP LSP was carrying IP user traffic.
This is an "in-band CC".
These realizations may be categorized as:
A. Out-of-fiber, out-of-band (types 1 and 2)
B. In-fiber, out-of-band (types 2, 3, 4, and 5)
C. In-band (types 6 and 7)
The MCN and SCN are logically separate networks and may be
realized by the same DCN or as separate networks. In practice,
that means that, between any pair of nodes, the MCC and SCC may
be the same link or separate links.
It is also important to note that the MCN and SCN do not need to
be categorised as in-band, out-of-band, etc. This definition
only applies to the individual links, and it is possible for
some nodes to be connected in the MCN or SCN by one type of
link, and other nodes by other types of link. Furthermore, a
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pair of adjacent nodes may be connected by multiple links of
different types.
Lastly note that the division of DCN traffic between links
between a pair of adjacent nodes is purely an implementation
choice. Parallel links may be deployed for DCN resilience or
load sharing. Links may be designated for specific use. For
example, so that some links carry management traffic and some
carry control plane traffic, or so that some links carry
signaling protocol traffic while others carry routing protocol
traffic.
It should be noted that the DCN may be a routed network with
forwarding capabilities, but that this is not a requirement. The
ability to support forwarding of management or control traffic
within the DCN may substantially simplify the topology of the
DCN and improve its resilience, but does increase the complexity
of operating the DCN.
See also RFC 3877 [10], ITU-T M.20 [11], and Telcordia document
GR-833-CORE [12] for further information.
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