One document matched: draft-ietf-ccamp-gmpls-ason-reqts-07.txt
Differences from draft-ietf-ccamp-gmpls-ason-reqts-06.txt
Network Working Group D. Papadimitriou (Alcatel)
Internet Draft J. Drake (Calient)
Category: Informational J. Ash (ATT)
Expiration Date: April 2005 A. Farrel (Old Dog Consulting)
L. Ong (Ciena)
October 2004
Requirements for Generalized MPLS (GMPLS) Signaling Usage
and Extensions for Automatically Switched Optical Network (ASON)
draft-ietf-ccamp-gmpls-ason-reqts-07.txt
Status of this Memo
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Copyright Notice
Copyright (C) The Internet Society (2004). All Rights Reserved.
Abstract
The Generalized Multi-Protocol Label Switching (GMPLS) suite of
protocols has been defined to control different switching
technologies as well as different applications. These include support
for requesting Time Division Multiplexing (TDM) connections including
Synchronous Optical Network (SONET)/Synchronous Digital Hierarchy
(SDH) and Optical Transport Networks (OTNs).
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This document concentrates on the signaling aspects of the GMPLS
suite of protocols. It identifies the features to be covered by the
GMPLS signaling 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.
1. 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 [RFC2119].
While [RFC2119] describes interpretations of these key words in terms
of protocol specifications and implementations, they are used in this
document to describe design requirements for protocol extensions.
2. Introduction
The Generalized Multi-Protocol Label Switching (GMPLS) suite of
protocol specifications provides support for controlling different
switching technologies as well as different applications. These
include support for requesting Time Division Multiplexing (TDM)
connections including Synchronous Optical Network (SONET)/Synchronous
Digital Hierarchy (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 requirements related to the signaling
aspects of the GMPLS suite of protocols. It discusses functional
requirements required to support Automatically Switched Optical
Networks that may lead to additional extensions to GMPLS signaling
(see [RFC3471] and [RFC3473]) to support these capabilities. In
addition to ASON signaling requirements, this document includes GMPLS
signaling requirements regarding backward compatibility (Section 5).
A terminology section is provided in the Appendix.
3. Problem Statement
The Automatically 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 architecture
describes a reference architecture, i.e. it describes functional
components, abstract interfaces, and interactions.
The ASON model distinguishes reference points (representing points of
information exchange) defined (1) between a user (service requester)
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and a service provider control domain a.k.a. user-network interface
(UNI), (2) between control domains a.k.a. external network-network
interface (E-NNI) and, (3) within a control domain a.k.a. internal
network-network interface (I-NNI). The I-NNI and E-NNI interfaces are
between protocol controllers, and may or may not use transport plane
(physical) links. It must not be assumed that there is a one-to-one
relationship of control plane interfaces and transport plane
(physical) links, or that there is a one-to-one relationship of
control plane entities and transport plane entities, or that there is
a one-to-one relationship of control plane identifiers for transport
plane resources.
This document describes requirements related to the use of GMPLS
signaling (in particular, [RFC3471] and [RFC3473]) to provide call
and connection management (see [ITU-T G.7713]). The functionality to
be supported includes:
(a) soft permanent connection capability
(b) call and connection separation
(c) call segments
(d) extended restart capabilities during control plane failures
(e) extended label association
(f) crankback capability
(g) additional error cases.
4. Requirements for Extending Applicability of GMPLS to ASON
The next sections detail the signaling protocol requirements for
GMPLS to support the ASON functions listed in Section 3. ASON defines
a reference model and functions (information elements) to enable end-
to-end call and connection support by a protocol across the
respective interfaces, regardless of the particular choice of
protocol(s) used in a network. ASON does not restrict the use of
other protocols or the protocol-specific messages used to support the
ASON functions. Therefore, the support of these ASON functions by a
protocol shall not be restricted by (i.e. must be strictly
independent of and agnostic to) any particular choice of UNI, I-NNI,
or E-NNI used elsewhere in the network. In order to allow for
interworking between different protocol implementations, [ITU-T
G.7713] recognizes an interworking function may be needed.
In support of the G.8080 end-to-end call model across different
control domains, end-to-end signaling should be facilitated
regardless of the administrative boundaries, protocols within the
network or method of realization of connections within any part of
the network. This implies that there needs to be a clear mapping of
ASON signaling requests between GMPLS control domains and non-GMPLS
control domains. This document provides signaling requirements for
G.8080 distributed call and connection management based on GMPLS,
within a GMPLS based control domain (I-NNI) and between GMPLS based
control domains (E-NNI). It does not restrict use of other (non
GMPLS) protocols to be used within a control domain or as an E-NNI or
UNI. Interworking aspects related to the use of non-GMPLS protocols
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as UNI, E-NNI, or I-NNI, including mapping of non-GMPLS protocol
signaling requests to corresponding ASON signaling functionality and
support of non-GMPLS address formats, is not within the scope of the
GMPLS signaling protocol. Interworking aspects are implementation-
specific and strictly under the responsibility of the interworking
function, and thus outside the scope of this document.
Any User-Network Interface (UNI) that is compliant with [RFC3473],
e.g. [GMPLS-OVERLAY] and [GMPLS-VPN] is considered, by definition, to
be included within the GMPLS suite of protocols and MUST be supported
by the ASON GMPLS signaling functionality.
Compatibility aspects of non-GMPLS systems (nodes) within a GMPLS
control domain i.e. the support of GMPLS systems and other systems
which utilize other signaling protocols or some which may not support
any signaling protocols is described. For instance, Section 4.5
'Support for Extended Label Association' covers the requirements when
a non-GMPLS capable sub-network is introduced or when nodes do not
support any signaling protocols.
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 node that initiates the switched connection
(also known as 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 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. This 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. Nodes B and Y are referred
to as the ingress and egress (respectively) of the network switched
connection.
--- --- --- ---
| 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 distributed
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control plane. Thus the SPC is composed of the stitching of link #1,
#2 and #3.
Thus, to support the capability to request an 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
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 signaling
controller addresses.
Note that the association at the ingress node between the permanent
connection and the switched connection is an implementation matter
that may be under the control of the EMS/NMS and is not within the
scope of the signaling protocol. It is, therefore, outside the scope
of this document.
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. Multiple connections may be
associated to each call. The call concept provides an abstract
relationship between two users, where this relationship describes (or
verifies) to what 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 call MAY be associated with zero, one or multiple connections. For
the same call, connections MAY be of different types and each
connection MAY exist independently of other connections, i.e., each
connection is setup and released with separate signaling messages.
The concept of the call allows for a better flexibility in how end-
points set up connections and how networks offer services to users.
For example, a call allows:
- An upgrade strategy for control plane operations, where a call
control component (service provisioning) may be separate from the
actual nodes hosting the connections (where the connection control
component 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
- 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.
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To support the introduction of the call concept, GMPLS signaling
SHOULD include a call identification mechanism and SHOULD 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 node 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 Call Segments
As described in [ITU-T G.8080], call segmentation MAY be applied when
a call crosses several control domains. As such, an end-to-end call
MAY consist of multiple call segments, when the call traverses
multiple control domains. For a given end-to-end call, each call
segment MAY have one or more associated connections and the number of
connections associated with each call segment MAY be different.
The initiating caller interacts with the called party by means of one
or more intermediate network call controllers located at control
domain boundaries (i.e., at inter-domain reference points, UNI or E-
NNI). Call segment capabilities are defined by the policies
associated at these reference points.
This capability allows for independent (policy based) choices of
signaling, concatenation, data plane protection and control plane
driven recovery paradigms in different control domains.
4.4 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 (i.e. single or multiple control channel
and/or controller failure and any combination) MUST NOT result in
releasing established calls and connections (including the
corresponding transport plane connections).
- Upon recovery from a control plane failure, the recovered control
entity MUST have the ability to recover the status of the calls
and connections established before failure occurrence.
- Upon recovery from a control plane failure, the recovered control
entity MUST have the ability to recover the connectivity
information of its neighbors.
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- Upon recovery from a control plane failure, the recovered control
entity MUST have the ability to recover the association between
the call and its associated connections.
- Upon recovery from a control plane failure, calls and connections
in the process of being established (i.e. pending call/connection
setup requests) SHOULD be released or continued (with setup).
- Upon recovery from a control plane failure, calls and connections
in the process of being released MUST be released.
4.5 Support for Extended Label Association
It is an ASON requirement to enable support for G.805 serial compound
links. The text below provides an illustrative example of such a
scenario, and the associated requirements.
Labels are defined in GMPLS (see [RFC3471]) 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. 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
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
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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
SHOULD 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 can 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 such
instances, the label association function provides a one-to-one
mapping of the received to local label values.
4.6 Support for Crankback
Crankback has been identified as an important requirement for ASON
networks. It allows a connection setup request to be retried on an
alternate path that detours around a blocked link or node upon a
setup failure, for instance, because a link or a node along the
selected path has insufficient resources.
Crankback mechanisms MAY also be applied during connection recovery
by indicating the location of the failed link or node. This would
significantly improve the successful recovery ratio for failed
connections, especially in situations where a large number of setup
requests are simultaneously triggered.
The following mechanisms are assumed during crankback signaling:
- the blocking resource (link or node) MUST be identified and
returned in the error response message towards the repair node
(that may or may not be the ingress node); it is also assumed that
this process will occur within a limited period of time
- the computation (from the repair node) of an alternate path around
the blocking link or node that satisfies the initial connection
constraints
- the re-initiation of the connection setup request from the repair
node (i.e. the node that has intercepted and processed the error
response message)
The following properties are expected for crankback signaling:
- Error information persistence: the entity that computes the
alternate (re-routing) path SHOULD store the identifiers of the
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blocking resources as indicated in the error message until the
connection is successfully established or until the node abandons
rerouting attempts. Since crankback may happen more than once
while establishing a specific connection, the history of all
experienced blockages for this connection SHOULD be maintained (at
least until the routing protocol updates the state of this
information) to perform an accurate path computation avoiding all
blockages.
- Rerouting attempts limitation: to prevent an endless repetition of
connection setup attempts (using crankback information), the
number of retries SHOULD be strictly limited. The maximum number of
crankback rerouting attempts allowed MAY be limited per connection
or per node:
- When the number of retries at a particular node is exceeded, the
node currently handling the failure reports the error message
upstream to the next repair node where further rerouting attempts
MAY be performed. It is important that the crankback information
provided indicates that re-routing through this node will not
succeed.
- When the maximum number of retries for a specific connection
has been exceeded, the repair node handling the current
failure SHOULD send an error message upstream indicating
"Maximum number of re-routings exceeded". This error message
will be sent back to the ingress node with no further
rerouting attempts. Then, the ingress node MAY choose to
retry the connection setup according to local policy but also
re-use its original path or compute a path that avoids the
blocking resources.
Note: after several retries, a given repair point MAY be unable to
compute a path to the destination node that avoids all of the
blockages. In this case, it MUST pass the error message upstream to
the next repair point.
4.7 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. Backward Compatibility
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As noted above, in support of GMPLS protocol requirements, any
extensions to the GMPLS signaling protocol in support of the
requirements described in this document MUST be backward compatible.
Backward compatibility means that in a network of nodes, some of
which support GMPLS signaling extensions to facilitate the functions
described in this document, and some of which do not, it MUST be
possible to set up conventional connections (as described by [RFC
3473]) between any arbitrary pair of nodes and traversing any
arbitrary set of nodes. Further, the use of any GMPLS signaling
extensions to set up calls or connections that support the functions
described in this document MUST not perturb existing conventional
connections.
Additionally, when transit nodes, that do not need to participate in
the new functions described in this document, lie on the path of a
call or connection, the GMPLS signaling extensions MUST be such that
those transit nodes are able to participate in the establishment of
the call or connection by passing the setup information onwards,
unmodified.
Lastly, when a transit or egress node is called upon to support a
function described in this document, but does not, the GMPLS
signaling extensions MUST be such that they can be rejected by pre-
existing GMPLS signaling mechanisms in a way that is not detrimental
to the network as a whole.
6. Security Considerations
Per [ITU-T G.8080], it is not possible to establish a connection in
advance of call setup completion. 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
signaling (see [RFC3471]).
7. Acknowledgements
The authors would like to thank Nic Larkin, Osama Aboul-Magd and
Dimitrios Pendarakis for their contribution to the previous version
of this document, Zhi-Wei Lin for his contribution to this document,
Deborah Brungard for her input and guidance in our understanding of
the ASON model, and Gert Grammel for his decryption effort during the
reduction of some parts of this document.
8. References
8.1 Normative References
[RFC2026] S.Bradner, "The Internet Standards Process --
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Revision 3", BCP 9, RFC 2026, October 1996.
[RFC2119] S.Bradner, "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3209] D.Awduche et al., "RSVP-TE: Extensions to RSVP for
LSP Tunnels," RFC 3209, December 2001.
[RFC3471] L.Berger (Editor) et al., "Generalized Multi-
Protocol Label Switching (GMPLS) - Signaling
Functional Description," RFC 3471, January 2003.
[RFC3473] L.Berger (Editor) et al., "Generalized Multi-Protocol
Label Switching (GMPLS) Signaling - Resource
ReserVation Protocol-Traffic Engineering (RSVP-TE)
Extensions," RFC 3473, January 2003.
[RFC3667] S.Bradner, "IETF Rights in Contributions", BCP 78,
RFC 3667, February 2004.
[RFC3668] S.Bradner, Ed., "Intellectual Property Rights in IETF
Technology", BCP 79, RFC 3668, February 2004.
8.2 Informative References
[GMPLS-OTN] D.Papadimitriou (Editor), "GMPLS Signaling Extensions
for G.709 Optical Transport Networks Control," Work
in progress, draft-ietf-ccamp-gmpls-g709-08.txt,
September 2004.
[GMPLS-OVERLAY]G.Swallow et al., "GMPLS RSVP Support for Overlay
Model," Work in Progress, draft-ietf-ccamp-gmpls-
overlay-05.txt, October 2004.
[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-VPN] H.Ould-Brahim and Y.Rekhter (Editors), "GVPN Services:
Generalized VPN Services using BGP and GMPLS
Toolkit," Work in Progress, draft-ouldbrahim-ppvpn-
gvpn-bgpgmpls-05.txt, May 2004.
For information on the availability of the following documents,
please see http://www.itu.int.
[ITU-T G.7713] ITU-T "Distributed Call and Connection Management,"
Recommentation G.7713/Y.1304, November 2001.
[ITU-T G.8080] ITU-T "Architecture for the Automatically Switched
Optical Network (ASON)," Recommendation G.8080/
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Y.1304, November 2001 (and Revision, January 2003).
9. Author's Addresses
Dimitri Papadimitriou (Alcatel)
Francis Wellesplein 1,
B-2018 Antwerpen, Belgium
Phone: +32 3 2408491
EMail: dimitri.papadimitriou@alcatel.be
John Drake (Calient)
5853 Rue Ferrari,
San Jose, CA 95138, USA
EMail: jdrake@calient.net
Adrian Farrel
Old Dog Consulting
Phone: +44 (0) 1978 860944
EMail: adrian@olddog.co.uk
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 document makes use of 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 (E-NNI): interfaces are located between protocol
controllers between control domains.
Internal NNI (I-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.
User Network Interface (UNI): interfaces are located between protocol
controllers between a user and a control domain.
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Intellectual Property Statement
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D.Papadimitriou et al. - Expires April 2005 14
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