CCAMP Working Group D. Papadimitriou (Alcatel)
Internet Draft Z. Lin (New York City Transit)
Category: Informational J. Drake (Calient)
J. Ash (ATT)
Expiration Date: December 2003 A. Farrel (Movaz)
L. Ong (Ciena)
June 2003
Requirements for Generalized MPLS (GMPLS) Usage and Extensions
for Automatically Switched Optical Network (ASON)
draft-ietf-ccamp-gmpls-ason-reqts-00.txt
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1. Abstract
The Generalized MPLS (GMPLS) suite of protocol has been defined to
control different switching technologies as well as different
applications. These include support for requesting TDM connections
including SONET/SDH and Optical Transport Networks (OTNs).
This document concentrates on the signaling aspects of the GMPLS
suite of protocols. It identifies the features to be covered by the
signalling protocol to support the capabilities of an Automatically
Switched Optical Network (ASON). This document provides a problem
statement and additional requirements on the GMPLS signaling
protocol to support the ASON functionality.
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2. Conventions used in this document
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.
3. Introduction
The GMPLS suite of protocol specifications provides support for
controlling different switching technologies as well as different
applications. These include support for requesting TDM connections
including SONET/SDH (see ANSI T1.105 and ITU-T G.707, respectively)
as well as Optical Transport Networks (see ITU-T G.709). In
addition, there are certain capabilities that are needed to support
Automatically Switched Optical Networks control planes (their
architecture is defined in [ITU-T G.8080]). These include generic
capabilities such as call and connection separation and more
specific capabilities such as support of soft permanent connections.
This document concentrates on the signaling aspects of the GMPLS
suite of protocols (see [RFC 3471]). It discusses functional
requirements that lead to additional extensions to GMPLS to support
the capabilities as specified in the above referenced document. A
terminology section is provided in Appendix.
Problem Statement:
The Automatic Switched Optical Network (ASON) architecture describes
the application of an automated control plane for supporting both
call and connection management services (for a detailed description
see [ITU-T G.8080]).
The ASON control plane specification is meant to be applicable to
different transport technologies (e.g., SDH/SONET, OTN) in various
networking environments (e.g., inter-carrier, intra-carrier). Also,
ASON model distinguishes reference points (representing points of
protocol information exchange) defined (1) between an administrative
domain and a user (2) between administrative domains and (3) between
areas of the same administrative domain and when needed between
control components (or simply controllers) within areas. A full
description of the ASON terms and relationship between ASON model
and GMPLS protocol suite may be found in [IPO-ASON].
This document describes the use of GMPLS signalling (and in
particular, [RFC 3471]) to provide call and connection management
(see [ITU-T G.7713]). The following functionality are expected from
the GMPLS protocol suite: (a) support for soft permanent connection
capability (b) support for call and connection separation (c)
support for extended restart capabilities during control plane
failures (d) support for extended label usage (e) support for
crankback capability (f) support for additional error cases.
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4. Requirements for Extending Applicability of GMPLS to ASON
The applicability statements regarding how the GMPLS suite of
protocols may be applied to the ASON architecture can be found in
[IPO-ASON] and [IPO-REQS]. The former includes a summary of the ASON
functions as well as a detailed discussion of the applicability of
the GMPLS protocol suite.
The next sections detail the requirements concerning the functions
including:
- Support for soft permanent connection capability
- Support for call and connection separation
- Support for extended restart capabilities during control plane
failures
- Support for extended label usage
- Support for crankback capability
- Support for additional error cases
Note: support of the above functions is independent of any user-to-
network interface and therefore not constrained or restricted by its
implementation specifics (see [ITU-T G.8080] and [ITU-T G.7713]).
4.1 Support for Soft Permanent Connection (SPC) Capability
An SPC is a combination of a permanent connection at the source
user-to-network side, a permanent connection at the destination
user-to-network side, and a switched connection within the network.
An Element Management System (EMS) or a Network Management System
(NMS) typically initiates the establishment of the switched
connection by communicating with the ingress node. The latter then
sets the connection using the distributed GMPLS signaling protocol.
For the SPC, the communication method between the EMS/NMS and the
ingress node is beyond the scope of this document (so it is for any
other function described in this document).
The end-to-end connection is thus created by associating the
incoming interface of the switched connection initiating network
node (also referred to as ingress node) with the switched connection
within the network and the outgoing interface of the switched
connection terminating network node (also referred to as egress
node). An SPC connection is illustrated in the following Figure,
which shows user's node A connected to a provider's node B via link
#1, user's node Z connected to a provider's node Y via link #3, and
an abstract link #2 connecting provider's node B and node Y.
--- --- --- ---
| A |--1--| B |-----2-//------| Y |--3--| Z |
--- --- --- ---
In this instance, the connection on link #1 and link #3 are both
provisioned (permanent connections that may be simple links). In
contrast, the connection over link #2 is set up using the
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distributed control plane. Thus the SPC is composed of the splicing
of link #1, #2 and #3.
Thus, to support the capability to request a SPC connection:
- The GMPLS signaling protocol must be capable of supporting the
ability to indicate the outgoing link and label information used
when setting up the destination provisioned connection.
- In addition, due to the inter-domain applicability of ASON
networks, the GMPLS signaling protocol should also support the
indication of the service level requested for the SPC. In the case
where an SPC spans multiple domains, indication of both source and
destination endpoints controlling the SPC request may be needed.
These may be done via the source and destination signalling
controller addresses.
4.2 Support for Call and Connection Separation
A call may be simply described as "An association between endpoints
that supports an instance of a service" [ITU-T G.8080]. Thus, it can
be considered as a service provided between two end-points, where
several calls may exist between them. To each call multiple
connections may be associated. The call concept provides an abstract
relationship between two users, where this relationship describes
(or verifies) at which extent the users are willing to offer (or
accept) service to each other. Therefore, a call does not provide
the actual connectivity for transmitting user traffic, but only
builds a relationship by which subsequent connections may be made.
A property of a call is to contain zero, one or multiple
connections. Within the same call, connections may be of different
type and each connection may exist independently of other
connections, i.e., each connection is setup and released with
separate Path/Resv messages. For example, a call may contain a set
of basic connection and virtually concatenated connections (see
[GMPLS-SONET] for corresponding connection signaling extensions).
The concept of the call allows for a better flexibility in how end-
points set up connections and how network offers services to users.
In essence, a call allows:
- Support for virtual concatenation where each connection can travel
on different diverse paths
- Facilitate upgrading strategy of the control plane operations,
where a call control (service provisioning) may be separate from
actual nodes hosting the connections (where the connection control
may reside)
- Identification of the call initiator (with both network call
controller as well as destination user) prior to connection, which
may result in decreasing contention during resource reservation
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- General treatment of multiple connections which may be associated
for several purposes; for example a pair of working and recovery
connections may belong to the same call.
To support the introduction of the call concept, GMPLS signaling
should include a call identification mechanism and allow for end-to-
end call capability exchange.
For instance, a feasible structure for the call identifier (to
guarantee global uniqueness) may concatenate a globally unique fixed
ID (e.g., may be composed of country code, carrier code) with an
operator specific ID (where the operator specific ID may be composed
of a unique access point code - such as source LSR address - and a
local identifier). Other formats shall also be possible depending on
the call identification conventions between parties involved in the
call setup process.
4.3 Support for Extended Restart Capabilities
Various types of failures may occur affecting the ASON control
plane. Requirements placed on the control plane failure recovery by
[ITU-T G.8080] include:
- Any control plane failure must not result in releasing established
connections.
- Upon recovery from a control plane failure, the recovered node
must have the ability to recover the status of the connections
established before failure occurrence.
- Upon recovery from a control plane failure, the recovered node
must have the ability to recover the connectivity information of
its neighbors.
- Upon recovery from a control plane failure, connections in the
process of being established (i.e. pending connection setup
requests) should be released or continued (with setup).
- Upon recovery from a control plane failure, connections in the
process of being released must be released.
- Upon recovery from a control plane failure, a call must have
the ability to re-synchronize with its associated connections.
4.4 Support for Extended Label Usage
Labels are defined in GMPLS (see [RFC 3471]) to provide information
on the resources used on link local basis for a particular
connection. The labels may range from specifying a particular
timeslot, a particular wavelength to a particular port/fiber.
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In the ASON context, the value of a label MAY not be consistently
the same across a link. For example, the figure below illustrates
the case where two GMPLS capable nodes (A and Z) are interconnected
across two non-GMPLS capable nodes (B and C), where these nodes are
all SONET/SDH nodes providing, e.g., a VC-4 service.
----- -----
| | --- --- | |
| A |---| B |---| C |---| Z |
| | --- --- | |
----- -----
Labels have an associated implicit imposed structure based on
[GMPLS-SONET] and [GMPLS-OTN]. Thus, once the local label is
exchanged with its neighboring control plane node, the structure of
the local label MAY not be significant to the neighbor node since
the association between the local and the remote label may not
necessarily be the same. This issue does not present a problem in a
simple point-to-point connections between two control plane-enabled
nodes where the timeslots are mapped 1:1 across the interface.
However, once a non-GMPLS capable sub-network is introduced between
these nodes (as in the above figure, where the sub-network provides
re-arrangement capability for the timeslots) label scoping MAY
become an issue.
In this context, there is an implicit assumption that the data plane
connections between the GMPLS capable edges already exist prior to
any connection request. For instance, node A's outgoing VC-4's
timeslot #1 (with SUKLM label=[1,0,0,0,0]) as defined in [GMPLS-
SONET]) may be mapped onto node B's outgoing VC-4's timeslot #6
(label=[6,0,0,0,0]) may be mapped onto node C's outgoing VC-4's
timeslot #4 (label=[4,0,0,0,0]). Thus by the time node Z receives
the request from node A with label=[1,0,0,0,0], the node Z's local
label and the timeslot no longer corresponds to the received label
and timeslot information.
As such to support this capability, a label association mechanism
has to be used by the control plane node to map the received
(remote) label into a locally significant label. The information
necessary to allow mapping from received label value to a locally
significant label value may be derived in several ways including:
- Manual provisioning of the label association
- Discovery of the label association
Either method may be used. In case of dynamic association, this
implies that the discovery mechanism operates at the timeslot/label
level before the connection request is processed at the ingress
node. Note that in the case where two nodes are directly connected,
no association is required. In particular, for directly connected
TDM interfaces no mapping function (at all) is required due to the
implicit label structure (see [GMPLS-SONET] and [GMPLS-OTN]). In
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such instances, the label association function provides a one-to-one
mapping of the received to local label values.
4.5 Support for Crankback
Crankback has been identified as a requirement for ASON networks. It
allows an LSP setup request to be retried on an alternate path that
detours around a blocked link or node upon a setup failure.
Crankback mechanisms can also be applied to LSP restoration by
indicating the location of the failure link or node. This would
significantly improve the successful recovery ratio for failed LSPs,
especially in situations where a large number of setup requests are
simultaneously triggered. [GMPLS-CRANK] specifies crankback GMPLS-
based signalling mechanisms.
4.6 Support for Additional Error Cases
To support the ASON network, the following additional category of
error cases are defined:
- Errors associated with basic call and soft permanent connection
support. For example, these may include incorrect assignment of
IDs for the call or an invalid interface ID for the soft permanent
connection.
- Errors associated with policy failure during processing of the new
call and soft permanent connection capabilities. These may include
unauthorized request for the particular capability.
- Errors associated with incorrect specification of the service
level.
5. Security Considerations
Per [ITU-T G.8080], a connection cannot be established until the
associated call has been set up. Also, policy and authentication
procedures are applied prior to the establishment of the call (and
can then also be restricted to connection establishment in the
context of this call).
This document introduces no new security requirements to GMPLS
signalling (see [RFC3471]).
6. Acknowledgements
The authors would like to thank Nic Larkin, Osama Aboul-Magd and
Dimitrios Pendarakis for their comments and contributions to the
previous version of this document.
7. References
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7.1 Normative References
[RFC-2026] S.Bradner, "The Internet Standards Process --
Revision 3", BCP 9, RFC 2026, October 1996.
[RFC-2119] S.Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC-3209] D.Awduche et al., "RSVP-TE: Extensions to RSVP for
LSP Tunnels," RFC 3209, December 2001.
[RFC-3471] L.Berger (Editor) et al., "Generalized MPLS -
Signaling Functional Description," RFC 3471, January
03.
[ITUT G.8080] ITU-T Rec. G.8080/Y.1304, "Architecture for the
Automatically Switched Optical Network (ASON),"
November 2001 (and Revision, January 2003).
[GMPLS-CRANK] A.Farrel (Editor), "Crankback Routing Extensions for
MPLS Signaling," Work in Progress, draft-iwata-mpls-
crankback-06.txt, May 2003.
[GMPLS-SONET] E.Mannie and D.Papadimitriou (Editors), "GMPLS
Extensions for SONET and SDH Control, Work in
Progress," draft-ietf-ccamp-gmpls-sonet-sdh-08.txt,
February 2003.
[GMPLS-OTN] D.Papadimitriou (Editor), "GMPLS Signalling
Extensions for G.709 Optical Transport Networks
Control," Work in progress, draft-ietf-ccamp-gmpls-
g709-04.txt, May 2003.
7.2 Informative References
[IPO-ASON] Aboul-Magd (Editor) et al., "Automatic Switched
Optical Network (ASON) Architecture and Its Related
Protocols," Work in progress, draft-ietf-ipo-ason-
02.txt, March 2002.
[IPO-REQS] Y.Xue (Editor) et al., "Optical Network Service
Requirements," Work in progress, draft-ietf-ipo-
carrier-requirements-05.txt.
[ITUT G.7713] ITU-T Rec. G.7713/Y.1304, "Distributed Call and
Connection Management," November 2001.
8. Author's Addresses
Dimitri Papadimitriou (Alcatel)
Francis Wellesplein 1,
B-2018 Antwerpen, Belgium
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Email: dimitri.papadimitriou@alcatel.be
Zhi-Wei Lin (New York City Transit)
2 Broadway, Room C3.25
New York, NY 10004
Email: zhiwlin@nyct.com
John Drake (Calient)
5853 Rue Ferrari,
San Jose, CA 95138, USA
Email: jdrake@calient.net
Adrian Farrel (Movaz Networks)
7926 Jones Branch Drive,
McLean, VA 22102, USA
Email: afarrel@movaz.com
Gerald R. Ash (ATT)
AT&T Labs, Room MT D5-2A01
200 Laurel Avenue
Middletown, NJ 07748, USA
Email: gash@att.com
Lyndon Ong (Ciena)
5965 Silver Creek Valley Road
San Jose, CA 95138, USA
Email: lyong@ciena.com
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Appendix - Terminology
This draft defines the following terms:
Administrative domain: See Recommendation G.805.
Call: association between endpoints that supports an instance of a
service.
Connection: concatenation of link connections and sub-network
connections that allows the transport of user information between
the ingress and egress points of a sub-network.
Control plane: performs the call control and connection control
functions. Through signaling, the control plane sets up and releases
connections, and may restore a connection in case of a failure.
(Control) Domain: represents a collection of entities that are
grouped for a particular purpose. G.8080 applies this G.805
recommendation concept (that defines two particular forms, the
administrative domain and the management domain) to the control
plane in the form of a control domain. The entities that are grouped
in a control domain are components of the control plane.
External NNI: interfaces are located between protocol controllers
between control domains.
Internal NNI: interfaces are located between protocol controllers
within control domains.
Link: See Recommendation G.805.
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,
fault, configuration, accounting and security management
Management domain: See Recommendation G.805.
Transport plane: provides bi-directional or unidirectional transfer
of user information, from one location to another. It can also
provide transfer of some control and network management information.
The Transport Plane is layered; it is equivalent to the Transport
Network defined in G.805.
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