Internet Engineering Task Force (IETF) A. Malis, Ed.
Internet-Draft Huawei Technologies
Intended status: Informational R. Skoog
Expires: April 13, 2015 H. Kobrinski
Applied Communication Sciences
G. Clapp
AT&T Labs Research
V. Shukla
Verizon Communications
October 10, 2014
Requirements for Very Fast Setup of GMPLS LSPs
draft-malis-ccamp-fast-lsps-03
Abstract
Establishment and control of Label Switch Paths (LSPs) have become
mainstream tools of commercial and government network providers. One
of the elements of further evolving such networks is scaling their
performance in terms of LSP bandwidth and traffic loads, LSP
intensity (e.g., rate of LSP creation, deletion, and modification),
LSP set up delay, quality of service differentiation, and different
levels of resilience.
The goal of this document is to present target scaling objectives and
the related protocol requirements for Generalized Multi-Protocol
Label Switching (GMPLS). The document also summarizes key factors
affecting current GMPLS signaling procedures in meeting these
application scaling requirements.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 13, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Background . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Motivation . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Driving Applications and Their Requirements . . . . . . . . . 5
4.1. Key Application Requirements . . . . . . . . . . . . . . 5
5. Potential GMPLS Limitations . . . . . . . . . . . . . . . . . 6
6. Requirements for Very Fast Setup of GMPLS LSPs . . . . . . . 8
6.1. Protocol and Procedure Requirements . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 9
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
10.1. Normative References . . . . . . . . . . . . . . . . . . 9
10.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
Generalized Multi-Protocol Label Switching (GMPLS) [RFC3945] includes
an architecture and a set of control plane protocols that can be used
to operate data networks ranging from packet-switch-capable networks,
through those networks that use Time Division Multiplexing, to WDM
networks. The Path Computation Element (PCE) architecture [RFC4655]
defines functional components that can be used to compute and suggest
appropriate paths in connection-oriented traffic-engineered networks.
Additional wavelength switched optical networks (WSON) considerations
were defined in [RFC6163].
This document refers to the same general framework and technologies,
but adds requirements related to expediting LSP setup, under heavy
connection churn scenarios, while achieving low blocking, under an
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overall distributed control plane. This document focuses on a
specific problem space - high capacity and highly dynamic connection
request scenarios - that may require clarification and or extensions
to current GMPLS protocols and procedures. In particular, the
purpose of this document is to address the potential need for
protocols and procedures that enable expediting the set up of LSPs in
high churn scenarios. Both single-domain and multi-domain network
scenarios are considered.
This document focuses on the following two topics: 1) the driving
applications and main characteristics and requirements of this
problem space, and 2) the key requirements which may be novel with
respect to current GMPLS protocols.
This document intends to present the objectives and related
requirements for GMPLS to provide the control for networks operating
with such performance requirements. While specific deployment
scenarios are considered as part of the presentation of objectives,
the stated requirements are aimed at ensuring the control protocols
are not the limiting factor in achieving a particular network's
performance. Implementation dependencies are out of scope of this
document.
It is envisioned that other documents may be needed to define how
GMPLS protocols meet the requirements laid out in this document.
Such future documents may define extensions, or simply clarify how
existing mechanisms may be used to address the key requirements of
highly dynamic networks.
2. Background
The Defense Advanced Research Projects Agency (DARPA) Core Optical
Networks (CORONET) program [Chiu], is an example target environment
that includes IP and optical commercial and government networks, with
a focus on highly dynamic and resilient multi-terabit core networks.
It anticipates the need for rapid (sub-second) setup and SONET/SDH-
like restoration times for high-churn (up to tens of requests per
second network-wide and holding times as short as one second) on-
demand wavelength, sub-wavelength and packet services for a variety
of applications (e.g., grid computing, cloud computing, data
visualization, fast data transfer, etc.). This must be done while
meeting stringent call blocking requirements, and while minimizing
the use of resources such as time slots, switch ports, wavelength
conversion, etc.
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3. Motivation
The motivation for this document, and envisioned related future
documents, is two-fold:
1. The anticipated need for rapid setup, while maintaining low
blocking, of large bandwidth and highly churned on-demand
connections (in the form of sub-wavelengths, e.g., OTN ODUx, and
wavelengths, e.g., OTN OCh) for a variety of applications
including grid computing, cloud computing, data visualization,
and intra- and inter-datacenter communications.
2. The ability to setup circuit-like LSPs for large bandwidth flows
with low setup delays provides an alternative to packet-based
solutions implemented over static circuits that may require tying
up more expensive and power-consuming resources (e.g., router
ports). Reducing the LSP setup delay will reduce the minimum
bandwidth threshold at which a GMPLS circuit approach is
preferred over a layer 3 (e.g., IP) approach. Dynamic circuit
and virtual circuit switching intrinsically provide guaranteed
bandwidth, guaranteed low-latency and jitter, and faster
restoration, all of which are very hard to provide in a packet-
only networks. Again, a key element in achieving these benefits
is enabling the fastest possible circuit setup times.
Future applications are expected to require setup times as fast as
100 ms in highly dynamic, national-scale network environments while
meeting stringent blocking requirements and minimizing the use of
resources such as switch ports, wavelength converters/regenerators,
wavelength-km, and other network design parameters. Of course, the
benefits of low setup delay diminish for connections with long
holding times. The need for rapid setup for specific applications
may override and thus get traded off, for these specific
applications, against some other features currently provided in
GMPLS, e.g., robustness against setup errors.
With the advent of data centers, cloud computing, video, gaming,
mobile and other broadband applications, it is anticipated that
connection request rates may increase, even for connections with
longer holding times, either during limited time periods (such as
during the restoration from a data center failure) or over the longer
term, to the point where the current GMPLS procedures of path
computation/selection and resource allocation may not be timely, thus
leading to increased blocking or increased resource cost. Thus,
extensions of GMPLS signaling and routing protocols (e.g. OSPF-TE)
may also be needed to address heavy churn of connection requests
(i.e., high connection request arrival rate) in networks with high
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traffic loads, even for connections with relatively longer holding
times.
4. Driving Applications and Their Requirements
There are several emerging applications that fall under the problem
space addressed here in several service areas such as provided by
telecommunication carriers, government networks, enterprise networks,
content providers, and cloud providers. Such applications include
research and education networks/grid computing, and cloud computing.
Detailing and standardizing protocols to address these applications
will expedite the transition to commercial deployment.
In the target environment there are multiple Bandwidth-on-Demand
service requests per second, such as might arise as cloud services
proliferate. It includes dynamic services with connection setup
requirements that range from seconds to milliseconds. The aggregate
traffic demand, which is composed of both packet (IP) and circuit
(wavelength and sub-wavelength) services, represents a five to
twenty-fold increase over today's traffic levels for the largest of
any individual carrier. Thus, the aggressive requirements must be
met with solutions that are scalable, cost effective, and power
efficient, while providing the desired quality of service (QoS).
4.1. Key Application Requirements
There are two key performance scaling requirements in the target
environment that are the main drivers behind this draft:
1. Connection request rate ranging from a few request per second for
high capacity (e.g., 40 Gb/s , 100 Gb/s) wavelength-based LSPs to
around 100 request per second for sub-wavelength LSPs (e.g., OTN
ODU0, ODU1, and ODU2).
2. Connection setup delay of around 100 ms across a national or
regional network. To meet this target, and assuming pipelined
cross-connection, and worst case propagation delay and hop count,
it is estimated that the maximum processing delay per hop is
around 700 microseconds [Lehmen]. Optimal path selection and
resource allocation may require somewhat longer processing (up to
5 milliseconds) in either the destination or source nodes and
possibly tighter processing delays (around 500 microseconds) in
intermediate nodes.
The model for a national network is that of the continental US with
up to 100 nodes and LSPs distances up to ~3000 km and up to 15 hops.
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A connection setup delay is defined here as the time between the
arrival of a connection request at an ingress edge switch - or more
generally a Label Switch Router (LSR) - and the time at which
information can start flowing from that ingress switch over that
connection. Note that this definition is more inclusive than the LSP
setup time defined in [RFC5814] and [RFC6777], which do not include
PCE path computation delays.
5. Potential GMPLS Limitations
GMPLS protocols and procedures have been developed to enable
automated control of Label Switched Paths (LSPs), including setup,
teardown, modification, and restoration, for switching technologies
extending from layer 2 and layer 3 packets, to time division
multiplexing, to wavelength, and to fiber. Thus GMPLS enables
substantial improvement in connection setup delays relative to manual
procedures.
However, while the GMPLS protocols are geared for a wide scope of
applications and robust performance, they have not specifically
addressed the more aggressive characteristics envisioned here, e.g.,
applications requiring very fast connection setup while maintaining a
high success ratio (i.e., low blocking) in a high-churn environment.
Preliminary simulations and analyses of national and global scale
networks, both WSON and sub-wavelength OTN [Skoog], have shown that
using current GMPLS protocols and procedures does not meet the stated
performance targets with respect to blocking, setup delays, and
resource utilization. These simulations have also indicated limited
scalability of current protocols to increasing loads and churn beyond
the baseline design.
Some possible issues with existing components of GMPLS include:
1. Path selection and resource allocation in GMPLS networks is based
on TE information collected via OSPF-TE LSA updates. Thus,
scenarios with highly dynamic connection request activity, where
the connection request arrival rate is higher than the TE update
rate allowed by OSPF-TE, could lead to unacceptable blocking
ratios or low resource utilization. Recall that the minimum LSA
update interval is 5 seconds within which time several
connections are requested in the scenarios addressed here. Stale
TE information leads also, indirectly, to longer setup delays if
connection attempts are re-tried. One approach to address this
issue is to increase the frequency of LSA updates. Another
approach is where TE information collection is incorporated into
the signaling protocol which would provide a much more timely
view and thus reduced blocking. Furthermore, simultaneously
probing multiple paths can be another element to reduce blocking
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in scenarios with highly dynamic connection requests. It should
be noted that GMPLS supports distributed wavelengths allocation
during the signaling phase (i.e., not just based on LSA updates)
using the Label Set object and associated procedures of RSVP-TE
[RFC3471]. However, in highly dynamic scenarios even the choice
of route may be better made in real time rather than based on
perhaps stale information. Another recent approach that can
reduce the dependence of LSA updates is the use of a stateful PCE
that updates an LSP data base as LSPs are set up.
2. In current GMPLS procedures, path computation, and PCC-PCE and
PCC-PCC communications occur following the connection request,
thus increasing overall setup delays. Although pre-computed
paths are not specifically ruled out and thus can be implemented
by GMPLS and stored in the PCEs or source nodes, detailed
procedures need to be specified. A potential enhancement of
periodical off-line downloading of multiple pre-computed paths to
individual LSR nodes could, for example, significantly cut down
the setup delay.
3. Current GMPLS cross-connection procedures require, as a default,
a serial cross-connection processing - the cross-connection in
each node must be completed before the signaling message is
transmitted to the next node. This serial procedure results in
cross-connection delays being accumulated in each node along the
path. A procedure allowing simultaneous or pipelined cross-
connections could cut this delay contribution by a factor
proportional to the path hop count. Pipelined processing can be
used with the RSVP-TE Path objects Suggested Label (for the
forward direction) and Upstream Label (for the reverse
direction). However, their successful use requires accurate
resource availability information and wavelength conversion
capabilities at all the nodes along the path. In heavy churned
connection scenarios, the use of SL and UL objects will either
mostly amount to the default serial process or require a lot of
wavelength conversions. Note that this delay contribution is
significant in WSON - given current optical switching delays of ~
10-20 ms or more; it is less significant with TDM or L2
electronic switching.
Note that GMPLS allows for signaling crankbacks when a connection
setup fails. Such crankbacks increase the maximum and average setup
delays. Thus, reduction of blocking rates, for example, via multiple
path probing as in point 1 above, will also improve the worst case
and average setup delays.
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Note again that these potential GMPLS extensions should be optional
as they may entail increased cost or reduced functionality and thus
should only be used when needed.
6. Requirements for Very Fast Setup of GMPLS LSPs
This section lists the protocol requirements for very fast setup of
GMPLS LSPs in order to adequately support the service characteristics
described in the previous sections. These requirements may be the
basis for future documents, some of which may be simply
informational, while others may describe specific GMPLS protocol
extensions. While some of these requirements may be have
implications on implementations, the intent is for the requirements
to apply to GMPLS protocols and their standardized mechanisms.
6.1. Protocol and Procedure Requirements
R1 Protocol extensions must be backward compatible with existing
GMPLS control plane protocols. The purpose of this obvious
requirement is to indicate that applications that do not need
the performance addressed here and thus do not need the required
protocol extensions should be able to use currently existing
GMPLS protocols.
R2 Use of optional GMPLS protocol extensions for this application
must be selectable by provisioning or configuration.
R3 LSP Establishment time should scale linearly based on number of
traversed nodes.
R4 LSP Establishment time should be bounded by a single (worst
case) per-node data path (cross-connect) establishment time and
not scale linearly based on number of traversed nodes, i.e.,
support parallel or pipelined cross-connection establishment.
R5 LSP Establishment time shall depend on number of nodes
supporting an LSP and link propagation delays and not any off
(control) path transactions, e.g., PCC-PCE and PCC-PCC
communications at the time of connection setup, even when PCE-
based approaches are used.
R6 Must support LSP holding times as short as one second to one
minute.
R7 The protocol aspects of LSP signaling must not preclude LSP
request rates of tens per second.
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R8 The above requirements should be met even when there are
failures in connection establishment, i.e., LSPs should be
established faster than when crank-back is used.
R9 These requirements are applicable even when an LSP crosses one
or more administrative domains / boundaries.
R10 The above are additional requirements and do not replace
existing requirements, e.g. alarm free setup and teardown,
Recovery, or inter-domain confidentiality.
7. IANA Considerations
This memo includes no requests to IANA.
8. Security Considerations
Being able to support very fast setup and a high churn rate of GMPLS
LSPs is not expected to adversely affect the underlying security
issues associated with existing GMPLS signaling.
9. Acknowledgements
The authors would like to thank Ann Von Lehmen, Joe Gannett, and
Brian Wilson of Applied Communication Sciences for their comments and
assistance on this document. Lou Berger provided editorial comments
on this document.
10. References
10.1. Normative References
[RFC3471] Berger, L., "Generalized Multi-Protocol Label Switching
(GMPLS) Signaling Functional Description", RFC 3471,
January 2003.
[RFC3945] Mannie, E., "Generalized Multi-Protocol Label Switching
(GMPLS) Architecture", RFC 3945, October 2004.
[RFC4655] Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
Element (PCE)-Based Architecture", RFC 4655, August 2006.
[RFC5814] Sun, W. and G. Zhang, "Label Switched Path (LSP) Dynamic
Provisioning Performance Metrics in Generalized MPLS
Networks", RFC 5814, March 2010.
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[RFC6163] Lee, Y., Bernstein, G., and W. Imajuku, "Framework for
GMPLS and Path Computation Element (PCE) Control of
Wavelength Switched Optical Networks (WSONs)", RFC 6163,
April 2011.
[RFC6777] Sun, W., Zhang, G., Gao, J., Xie, G., and R. Papneja,
"Label Switched Path (LSP) Data Path Delay Metrics in
Generalized MPLS and MPLS Traffic Engineering (MPLS-TE)
Networks", RFC 6777, November 2012.
10.2. Informative References
[Chiu] A. Chiu, et al, "Architectures and Protocols for Capacity
Efficient, Highly Dynamic and Highly Resilient Core
Networks", Journal of Optical Communications and
Networking vol. 4, No. 1, pp. 1-14, January 2012,
<http://dx.doi.org/10.1364/JOCN.4.000001>.
[Lehmen] A. Von Lehmen, et al, "CORONET: Testbeds, Demonstration
and Lessons Learned", Journal of Optical Communications
and Networking vol. 7, No. 1, January 2015 (expected).
[Skoog] R. Skoog, et al, "Analysis and Implementation of a 3-Way
Handshake Signaling Protocol for Highly Dynamic Transport
Networks", OFC 2014, <http://www.opticsinfobase.org/
abstract.cfm?URI=OFC-2014-W1K.1>.
Authors' Addresses
Andrew G. Malis (editor)
Huawei Technologies
Email: agmalis@gmail.com
Ronald A. Skoog
Applied Communication Sciences
Email: rskoog@appcomsci.com
Haim Kobrinski
Applied Communication Sciences
Email: hkobrinski@appcomsci.com
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George Clapp
AT&T Labs Research
Email: clapp@research.att.com
Vishnu Shukla
Verizon Communications
Email: vishnu.shukla@verizon.com
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