Internet DRAFT - draft-wang-ccamp-flexigrid-wavelength-range-ospf
draft-wang-ccamp-flexigrid-wavelength-range-ospf
Network Working Group Qilei Wang
Internet-Draft Xihua Fu
Intended status: Standards Track ZTE Corporation
Expires: August 29, 2013 Feb 25, 2013
OSPF extensions for support spectrum sub-band allocation
draft-wang-ccamp-flexigrid-wavelength-range-ospf-02.txt
Abstract
This document addresses the requirements and routing protocol
extension of spectrum sub-band allocation in order to help reduce
non-linear effect and raise spectrum utilization rate in the scenario
of indiscriminately positioning of various channels with different
bit rates.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions used in this document . . . . . . . . . . . . . . 4
3. Overview of the Solution . . . . . . . . . . . . . . . . . . . 5
4. Extension of routing protocol . . . . . . . . . . . . . . . . 6
4.1. Relationship with WSON . . . . . . . . . . . . . . . . . . 6
4.2. Extensions of OSPF Protocol to Support Spectrum Group
Allocation . . . . . . . . . . . . . . . . . . . . . . . . 7
4.2.1. Spectrum sub-band Allocation by Bitrates . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA considerations . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7.1. Normative References . . . . . . . . . . . . . . . . . . . 9
7.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
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1. Introduction
In current DWDM systems, completely freedom and indiscriminate
positioning of various channels with different bit rates is likely to
lead to dramatically impaired system performance due to XPM (Cross-
phased Modulation) effect and low spectrum utilization rate.
Cross phase modulation (XPM) is known as the phenomenon that
variations of intensity of one optical signal can change the
refractive index of the fiber, and modulate the phase of the other
optical signals co-propagating in the same fiber.
When DWDM was first introduced, the typical wavelength date rate was
2.5Gb/s. 10Gb/s wavelength was enabled because of the development of
higher performance optical modulators. However, the same simple
modulation format was used at both 2.5Gb/s and 10Gb/s. The
modulation technique is Intensity Modulation with Direct Detection
(IM-DD). Barrier appeared if we want a wavelength to transport data
with 40 Gb/s bitrate or more.After years of development, coherent
technology is introduced to broken the limit for 40Gb/s and soon for
100Gb/s transmission.
Intensity modulation direct detection (IM-DD) systems are less
sensitive to the variation of phase of the signal and is going to
bring the variation of the intensity, then the changes of refractive
index of the fiber. Just the reverse, optical coherent systems is a
phase sensitive system. The modulated phase due to XPM has
significant influence on the system performance.This is due to the
fact that the phase modulation due to XPM can be transformed into
intensity modulation through the chromatic dispersion of the fiber
and will result in the distortion of signal.For example, if we mix
10Gbit/s NRZ modulated channels with 100Gbit/s xPSK modulated
channels indiscriminately, XPM would have a detrimental effect on the
100Gbit/s signal if this are caused by 10Gbit/s signal; Complex
modulation formats (e.g., 16QAM) would be used to modulate signal
beyond 100Gbit/s (e.g., 400Gbit/s, 1Tbit/s), while QAM modulation
format experiences both intensity and phase modulation, a QAM signal
may affect another QAM signal due to XPM effect.
In current DWDM system with different bit rates, general advice is to
group the channels with the same bit rates into the same spectrum
sub-band to avoid the detrimental XPM effect.
Except the advantage described above, grouping of channels with the
same bitrates will help reduce fragment in flexible grid network.
Two kinds of DWDM application is described in the newest version of
[G.694.1], one is fixed grid, and the other is flexible grid. Fixed
grid is the traditional DWDM application with fixed channel slot
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width (e.g., 50GHz) which has been deployed in large scale in the
network and flexible grid is a new kind of DWDM application with
different channel slot widths which can be used to transport large
bandwidth data. The flexible grid technology is also a DWDM
application which is different from fixed grid application. Flexible
grid is a kind of new DWDM application with different channel slot
width (e.g., 50GHz, 87.5GHz etc). Signals with different bit rates
may occupy different slot widths and use different modulation format.
Grouping of signals with the same bit rates into the same spectrum
may also be a better choice than completely freedom positioning.
Frequently setup and release of flexible grid optical channels which
occupy different slot widths would result in the spectrum fragments
that can't be used anymore, and this will cause the decline of
spectrum utilization rate. Global Concurrent Optimization (GCO),
which combines with the implementation of the stateful PCE, can be
used for defragmentation and raise spectrum utilization rate. But
it's complicated to apply the GCO in current network, because this
will involve a large scale of resources and computation. Another
method that can be used is to group the channels with the same bit
rates into the same spectrum sub-band and this is also a feasible
solution to help raise spectrum utilization rate.
According to the previous description, grouping of channels with the
same bit rates maybe a good choice to reduce the XPM effect and raise
spectrum utilization rate, especially in network with different slot
widths. So in order to take the grouping into consideration during
the path computation, a sub-band spectrum of the available spectrum
SHOULD be allocated in advance and this spectrum allocation
information SHOULD be known by path computation element when compute
the path. This document mainly addresses the routing protocol
extension to support the advertisement of the spectrum allocation
information. Policy may be used by operator when split spectrum
supported on a link into several sub-bands. One spectrum sub-band
can only be used for path (optical channel) setup with specific
attributes, for example, with specific bitrates and/or modulation
format.
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 [RFC2119].
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3. Overview of the Solution
In current DWDM system with different bit rates, general advice is to
group the channels with the same bit rates and modulation format into
the same spectrum sub-band to avoid the detrimental XPM effect. As
signals of the same bitrates usually use the same modulation format
on a specific link, this document mainly pays attention to grouping
of channels with the same bitrates. Figure 1 shows an example, in
which part of the spectrum frequency slots (i.e., the left sub-band)
are allocated to 10 Gbit/s channels while another part of the
frequency slots (i.e., the right sub-band) are allocated to 100
Gbit/s channels. Currently an NRZ modulation format is employed for
10 Gbit/s channels, while 40 Gbit/s and/or 100 Gbit/s channels are
mostly phase-modulated (e.g. xPSK) signals. As noted above it is
common practice to keep an appropriate guard band between channels
with different bit rates and/or modulation format to minimize
nonlinear effects induced signal degradations and to group channels
with the same bit rate and modulation format.
10G OCh 50GHz 10G OCh 50GHz
+---+---+---+---+---+ +---+---+---+---+---+
| | | | | | guard band | | | | | |
__|___|___|___|___|___|____________|___|___|___|___|___|____
193.025 197.025
193.075 196.975
Figure 1: Group of Channels
[Notes: According to the simulation results about grouped spectrum
allocation and ungrouped spectrum allocation for 100Gbit/s and
400Gbit/s transmissions are carried. A grouped spectrum allocation
only resulted in a small improvement (about 0.2 and 0.5 dB) compared
to ungrouped spectrum allocation for 100G and 400G data transmissions
respectively. The penalty induced by mixed QPSK and 16QAM signals
seems to be much smaller than in a QPSK and NRZ hybrid system. This
may be explained by the similar spectrum of the QPSK and 16QAM
formats for the same baud rate. These results seem to indicate that
systems operated with only phase modulated signals may show
significantly lower impairments compared to systems operated with a
mix of NRZ and phase modulated signals.]
[Note: we are not sure if grouping of channels with the same bit rate
is needed in future. According to the discussion in ITU-T, a part of
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the experts express that: we should use grouping of channels with the
same bit rate in the short term, however, in the long term, it may be
forced to use indiscriminate positioning of the spectrum.]
Some other advantages are also brought if operator split available
spectrum into several sub-bands and one spectrum sub-band can only be
used for optical channel setup with the same bit rate. A spectrum
sub-band which can only be used for optical channel setup with the
same bit rate will help reduce fragments. Channels in the same
spectrum group sub-band with the same bitrates looks almost like
fixed grid technology with the same slot width, and they won't
generate fragments in the process of path setup and release. It may
also be convenient for operator to manage the network if the operator
groups the optical channel with the same bit rate.
When control plane uses path computation element to setup an end-to-
end path through the DWDM network, spectrum available information and
restriction information (e.g., spectrum partition information) should
be taken into consideration in order to compute a suitable end-to-end
path. The spectrum sub-band information needs to be advertised by
routing protocol in order to help the path computation. Section 4
describes the extension of OSPF routing protocol to advertise these
spectrum sub-band information in order to help path computation.
4. Extension of routing protocol
4.1. Relationship with WSON
WSON related work can be re-used in this document to advertise the
spectrum group information. This Section addresses the routing
extension work of the features which is describe in the previous
section base on the current WSON work in IETF CCAMP Group. In the
document [draft-ietf-ccamp-general-constraint-encode], a new link
sub-TLV called Port Label Restrictions sub-TLV is defined.
Descriptions about Port Label Restrictions sub-TLV in the draft
[draft-ietf-ccamp-gmpls-general-constraints-ospf-te] are introduced
here: "Port label restrictions describe the label restrictions that
the network element (node) and link may impose on a port. These
restrictions represent what labels may or may not be used on a link
and are intended to be relatively static. More dynamic information
is contained in the information on available labels. Port label
restrictions are specified relative to the port in general or to a
specific connectivity matrix for increased modeling flexibility" and
"For example, Port Label Restrictions describes the wavelength
restrictions that the link and various optical devices such as OXCs,
ROADMs, and waveband multiplexers may impose on a port in WSON".
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According to the previous description, the restrictions information
carried in the port label restriction sub-TLV are used to represent
what wavelength/spectrum may or may not be used on a link and are
relatively static. The spectrum group allocation information
described in this document can be regarded as label restrictions
which are imposed by network element (node) on a port, and the
network element include various optical devices such as OXCs, ROADMs
and waveband multiplexers and so on. These spectrum sub-bands
restrictions represent the spectrum allocation information and a
spectrum sub-band can only be used for channels setup with specific
bitrates and/or modulation format. This restriction is relative
static and can be carried in Port Label Restrictions sub-TLV.
4.2. Extensions of OSPF Protocol to Support Spectrum Group Allocation
Spectrum sub-band allocation information should be known by path
computation element if operators want to compute an end-to-end
optical channel path. As described in the previous section, Port
Label Restrictions sub-TLV can be used to carry this spectrum sub-
band allocation restriction information. Figure 1 is the format of
Port Label Restrictions sub-TLV which is described in
[draft-ietf-ccamp-general-constraint-encode] and definition of the
parameters included in this sub-TLV can be found in this document.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MatrixID |RestrictionType| Reserved/Parameter |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
: Additional Restriction Parameters per RestrictionType :
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Port Label Restrictions sub-TLV
4.2.1. Spectrum sub-band Allocation by Bitrates
As described in section 3, channels on a single fiber with the same
bitrates usually use the same modulation format, especially when the
equipments come from one vendor. So here operator can split spectrum
into several spectrum sub-bands by bitrates. In this section, OSPF
protocol is extended to cover the spectrum sub-bands allocation
information by bitrates.
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The spectrum sub-bands allocation information by bitrates is needed
in the process of path computation if an end-to-end path needs to be
computed by path computation element and this information SHOULD be
advertised by routing protocols. Figure 3 gives a new kinds of Port
Label Restrictions sub-TLV which mainly extent the Additional
Restriction Parameters field to cover the spectrum sub-bands
allocation information. The parameters in the Additional Restriction
Parameters field include Bit Rate which indicates the bitrates of the
specific spectrum sub-bands and spectrum boundaries information of
the sub-band.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MatrixID |RestrictionType| Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bit Rate |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
: Spectrum Sub-band Range :
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3
Definition of MatrixID and RestrictionType field can be found in the
document [draft-ietf-ccamp-general-constraint-encode]. Value of
RestrictionType needs to be assigned by IANA.
[Note: As several routing documents exist in the CCAMP and the
label_set object encoding is not determined, this document use
"spectrum sub-band range" to represent spectrum allocation
information temporarily.]
"Bit Rate" field indicates the bitrates of the specific spectrum sub-
band.
In some situation, modulation format information may also be needed
to help allocation wavelength range, as signals with the same
bitrates on a single fiber can use different modulation format. In
this case, modulation formats information is needed to be carried in
Port Label Restrictions sub-TLV. Wavelength that is supported by
subsystems can be partitioned to service traditional fixed grid
technology.
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5. Security Considerations
TBD
6. IANA considerations
TBD.
7. References
7.1. 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.
7.2. Informative References
[Cross Phase Modulation]
International Journal of Electronics and Computer Science
Engineering, "Effect on WDM due to Cross Phase
Modulation".
[G.694.1 v1]
International Telecommunications Union, "Draft revised
G.694.1 version 1.3".
[WD6-12] International Telecommunications Union, "Discussion on
progressing Q.6/15's work on DWDM applications using
flexible grid".
[flexible-grid-ospf-ext]
Fatai Zhang, Xiaobing Zi, Ramon Casellas, O. Gonzalez de
Dios, and D. Ceccarelli, "GMPLS OSPF-TE Extensions in
support of Flexible-Grid in DWDM Networks",
draft-zhang-ccamp-flexible-grid-ospf-ext-00.txt .
[flexigrid-lambda-label]
D. King, A. Farrel, Y. Li, F. Zhang, and R. Casellas,
"Generalized Labels for the Flexi-Grid in Lambda-Switch-
Capable (LSC) Label Switching Routers",
draft-farrkingel-ccamp-flexigrid-lambda-label-01.txt .
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[super-channel-label]
Iftekhar Hussain, Abinder Dhillon, Zhong Pan, Marco Sosa
and Bert Basch, Steve Liu, Andrew G. Malis, "Generalized
Label for Super-Channel Assignment on Flexible Grid",
draft-hussain-ccamp-super-channel-label-02.txt .
Authors' Addresses
Qilei Wang
ZTE Corporation
Email: wang.qilei@zte.com.cn
Xihua Fu
ZTE Corporation
ZTE Plaza, No.10, Tangyan South Road, Gaoxin District
Xi'an 210012
P.R.China
Email: fu.xihua@zte.com.cn
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