Internet DRAFT - draft-cbcs-ccamp-sson-guard-bands-reqs
draft-cbcs-ccamp-sson-guard-bands-reqs
CCAMP Working Group D. Ceccarelli
Internet-Draft G. Bottari
Intended status: Informational Ericsson
Expires: September 6, 2012 N. Sambo
Scuola Superiore S.Anna
F. Cugini
C.N.I.T.
F. Zhang
Huawei Technologies
R. Casellas
CTTC
March 5, 2012
Guard Bands requirements for GMPLS controlled optical networks
draft-cbcs-ccamp-sson-guard-bands-reqs-00
Abstract
The continuous increase of flexibility and bit rate in optical
networks has higher and higher impacts on inter-channel effects (e.g.
Cross-phase modulations). This effect leads to the introduction of
Guard Bands between adjacent light paths in order to reduce the
inter-channel detrimental effects.
This document provides requirements for the devolpment of protocol
extensions to support Generalized Multi-Protocol Label Switching
(GMPLS) and Path Computation Element (PCE) management of Guard Bands.
Status of this Memo
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Scenarios . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Guard Band definition . . . . . . . . . . . . . . . . . . . . . 4
5. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. PCE Requirements . . . . . . . . . . . . . . . . . . . . . 5
5.2. PCEP Requirements . . . . . . . . . . . . . . . . . . . . . 7
5.3. GMPLS Requirements . . . . . . . . . . . . . . . . . . . . 7
5.3.1. OSPF-TERequirements . . . . . . . . . . . . . . . . . . 7
5.3.2. RSVP-TE Requirements . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . . 8
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 8
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Introduction
Given the advancement of optical transmission technology, optical
channels may use thinner granularity of the spectrum, which are
configurable depending on the modulation format and bit-rate
[G.FLEXIGRID]. Thus, thanks to this flexibility, the capacity of
optical networks is strongly increasing. However, the spacing
between channels may be limited by the inter-channel effects (e.g,
cross-phase modulation - XPM) which can lead to a bit error rate
increase. Typically, as the case of XPM or cross-talk, the larger
the spectral distance among interfering signals, the less detrimental
the effect. Thus, a guard band (i.e., a spectral distance such that
detrimental effects are mitigated) may be considered to counteract
inter-channel detrimental effects [sambo-jlt].
Guard Bands (GB) may be required in either fixed- [RFC6163] or
flexible-grid networks [G.694.1v1] [G.FLEXIGRID]. As an example, in
fixed-grid networks, high-speed signals (100Gbit/s and beyond) may be
deployed together with low-speed signals (10Gb/s). In such a
scenario, high-speed signals utilizing phase-modulated formats (e.g.,
dual polarization quadrature phase shift keying - DP-QPSK - 100Gb/s)
suffer from XPM induced by low-speed signals, exploiting intensity
modulation (e.g. on off keying - OOK - 10Gb/s). Thus, GB may be used
to avoid problems of XPM between low- and high-speed signals.
Similarly, in flex-grid networks, high-speed signals may exploit
quadrature amplitude modulation (QAM), which experience both
intensity and phase modulation. Also in such a scenario, XPM may be
very detrimental.
The value of a guard band may depend on physical properties of the
traversed links and on the bit rate and modulation format of the
interfering signals. Given two interfering signals, inter-channel
effects among the two signals are counteracted if they are separated
by GB. This document describes the requirements of PCE and GMPLS
control to account for guard bands.
1.1. Terminology
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].
2. Definitions
Demeaning LSP: an LSP which induces a detrimental effect on
another LPS
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Degraded LSP: an LSP which may be degraded by inter-channel
effects induced by a demeaning GB: guard band
Working LSP: an active LSP
RSA: routing and spectrum assignment
IV: impairment validated (e.g., a route is impairment validated if
its bit error rate is acceptable for any channel)
3. Scenarios
Fixed-grid network is here assumed as a particular case of flex-grid
network, thus hereafter only the case of flex-grid networks will be
treated. Similarly, RWA is assumed as a particular case of RSA and
only RSA will be treated. The following PCE scenarios are considered
[draft-flexible]:
- IV and RSA PCE : From a GB point of view there is no difference
between IV+RSA and IV&RSA, so a general IV+RSA case will be
considered. In this case the PCE provides the ingress node with
an impairment-validated route and a set of frequency slots.
- IV PCE: PCE provides ingress node with an impairment-validated
route. Then, slot assignment is distributed and performed by the
egress node which may rely on collecting link status through the
signaling protocol (RSVP-TE).
- IV Candidate path PCE: PCE provides ingress node with a set of
candidate routes (i.e., a set of impairment-validated routes).
Then, a route is selected by the ingress node. Slot assignment is
distributed and performed by the egress node through the signaling
protocol (RSVP-TE).
4. Guard Band definition
GB is defined as the minimum frequency range which separates two
contiguous signals, S1 at bit rate B1 and modulation format M1 and S2
at a bit rate B2 and modulation format M2, such that detrimental
effects are negligible.
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S1(B1;M1) S2(B2;M2)
------------- -------------------
| | | |
-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
...+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
------------- -------------------
<--->
GB
Figure 1: Guard Band
Assuming fixed-grid networks, a number of channels (e.g. of a grid
spacing of 50 GHz), instead of a number of slots would be considered
for GB.
The computation of GB may require the knowledge of:
a. bit rate B and modulation format M of the interfering signals
b. the power P values of the signals at each span. In order to
limit the stored and exchanged information, an unique value of P
(worst-case scenario) may be considered for the demeaning LSP:
i.e., the maximum value P experienced by an LSP of type (B2,M2).
Similarly, an unique value P (worst-case scenario) may be
considered for the degraded LSP: the minimum value P experienced
by an LSP of type (B1,M1).
c. Fiber parameters: e.g. fiber attenuation, dispersion
parameter, and fiber nonlinear Kerr coefficient
Bit rate and modulation format should be mandatory information for GB
computation (e.g., PCE may select the value of GB from a stored set
of GB values, each one associated to a bit rate and modulation format
pair), thus treated in the rest of the document.
5. Requirements
5.1. PCE Requirements
- IV+RSA PCE: given an LSP request, by exploiting a TED, PCE may
account for GB in the IV+RWA (or IV&RSA) process, if needed. In
the case of:
+ Stateful PCE: PCE has a TED (in simple terms as disseminated
by OSPF-TE) plus an LSP-DB which are the active LSPs state.
(e.g., the route and the slot used by a working LSP). In order
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to identify the required GB, the TED plus the LSP-DB exploited
by the PCE should be extended to store the following
information:
++ Bit rate B of any working LSP in the network
++ Modulation format M of any working LSP in the network
++ Allocated central frequency and slot width for any active
LSP in the network.
+ Stateless PCE: PCE exploits a TED which includes per-link
information regarding the usage of the optical spectrum
resource (e.g., Available Frequency Ranges). If the PCE
obtains the TED via e.g. OSPF-TE this may also add additional
requirements to OSPF-TE as detailed later on. In order to
identify the required GB, the TED exploited by the PCE should
be extended to store the set of required information. An
example of such pieces of information could be:
++ Used frequency slots
++ Bit rate B associated to any frequency slot in use
++ Modulation format M associated to any frequency slot in
use
- IV PCE: given an LSP request, PCE provides the ingress node with
an impairment validated route. Then, wavelength or the slot
assignment is distributed, e.g. performed through a signaling
protocol (RSVP-TE). In this case, PCE should inform the ingress
node about the requirements of GB to separate the given LSP from
other LSPs of specific bit rate B and modulation format M. Thus,
PCEP and RSVP-TE may require extensions to account for GB.
- IV Candidate path PCE: given an LSP request, PCE provides the
ingress node with a set of impairment validated routes. A route
is selected by the ingress node. Then, wavelength or the slot
assignment is distributed, e.g. performed through a signaling
protocol (RSVP-TE). In this case, PCE should inform, for each
candidate route, the ingress node about the requirements of GB to
separate the given LSP from other LSPs of specific bit rate B and
modulation format M. Thus, PCEP and RSVP-TE may require extensions
to account for GB.
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5.2. PCEP Requirements
- IV&RSA PCE: in this case, no extensions for GB are required by
PCEP because PCEP client (e.g., the ingress node) does not require
to know GB information
- IV PCE: in this case, an extension may be needed in the PCEP
Path Computation Reply message to inform the ingress node about
required GBs along the route. Then, GB information should be
considered in the routing and slot assignment.
- IV candidate path PCE: in this case, an extension may be needed
in the PCEP Path Computation Reply message to inform the ingress
node, for any candidate route, about required GBs along the
candidate routes. Then, GB information should be considered in
the routing and slot assignment.
5.3. GMPLS Requirements
5.3.1. OSPF-TERequirements
- Stateful PCE: the LSP-DB is not filled through OSPF-TE, thus no
OSPF-TE extension is required.
- Stateless PCE: the TED may be filled through OSPF-TE, thus
OSPF-TE extensions may be required to carry used frequency slot
information, such as the associated bit-rate B and modulation
format M.
5.3.2. RSVP-TE Requirements
If the PCE only provides the ingress node with a route (IV PCE and IV
candidate path PCE), the slot assignment is performed at the egress
node. To this aim, RSVP-TE Path message gathers frequency range slot
availability information along the route.
- IV&RSA PCE: no extensions for GB are required by RSVP-TE
- IV PCE: extensions to RSVP-TE may be required to enable
distributed RSA process which accounts for GB. In particular,
extensions to RSVP-TE may be required to identify the frequency
spectrum along the route that should be not selected because of
GB.
- IV candidate path PCE: extensions to RSVP-TE may be required to
enable distributed RSA process which accounts for GB. In
particular, extensions to RSVP-TE may be required to identify
frequency spectrum along the route that should be not selected
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because of GB.
6. Security Considerations
TBD
7. IANA Considerations
TBD
8. Contributors
Fabio Cavaliere, Ericsson
Email: fabio.cavalier@ericsson.com
Paola Iovanna, Ericsson
Email: paola.iovanna@ericsson.com
Piero Castoldi, Scuola Superiore S.Anna
EMail: castoldi@sssup.it
9. Acknowledgements
10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[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.
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10.2. Informative References
[G.694.1v1]
ITU-T, "Spectral grids for WDM applications: DWDM
frequency grid", G.694.1 Recommendation (v1),
December 2011.
[draft-flexible]
F.Zhang, Y.Lee, O. Gonzales de Dios, R.Casellas,
D.Ceccarelli, "Framework for GMPLS Control of Spectrum
Switched Optical Networks, work in progress
draft-zhang-ccamp-sson-framework-00", March 2011.
[sambo-jlt]
Sambo, N.; Secondini, M.; Cugini, F.; Bottari, G.;
Iovanna, P.; Cavaliere, F.; Castoldi, P, "Modeling and
Distributed Provisioning in 10-40-100-Gb/s Multirate
Wavelength Switched Optical Networks, Lightwave
Technology, Journal of , vol.29, no.9, pp.1248-1257",
May 2011.
Authors' Addresses
Daniele Ceccarelli
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
Email: daniele.ceccarelli@ericsson.com
Giulio Bottari
Ericsson
Via G.Moruzzi, 1
Pisa
Italy
Email: giulio.bottari@ericsson.com
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Nicola Sambo
Scuola Superiore S.Anna
Via G.Moruzzi, 1
Pisa
Italy
Email: nicola.sambo@sssup.it
Cugini
C.N.I.T.
Via G.Moruzzi, 1
Pisa
Italy
Email: filippo.cugini@cnit.it
Fatai Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Shenzhen 518129 P.R.China Bantian, Longgang District
Phone: +86-755-28972912
Email: zhangfatai@huawei.com
Ramos Casellas
CTTC
Av. Carl Friedrich Gauss, 7
Castelldefels
Spain
Email: ramon.casellas@cttc.es
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