Network Working Group Iftekhar Hussain
Abinder Dhillon
Zhong Pan
Marco Sosa
Internet Draft Infinera
Intended status: Standard Track October 26, 2011
Expires: April 2012
Generalized Label for Super-Channel Assignment on Flexible Grid
draft-hussain-ccamp-super-channel-label-01.txt
Abstract
To enable scaling of existing transport systems to ultra high data
rates of 1 Tbps and beyond, next generation systems providing super-
channel switching capability are currently being developed. To allow
efficient allocation of optical spectral bandwidth for such high bit
rate systems, International Telecommunication Union
Telecommunication Standardization Sector (ITU-T) is extending the
G.694.1 grid standard (termed "Fixed-Grid") to include flexible grid
(termed "Flex-Grid") support. This necessitates definition of new
label format for the Flex-Grid. This document defines a super-
channel label as a Super-Channel Identifier and an associated list
of contiguous or non-contiguous set of 12.5 GHz slices representing
optical spectrum of the super-channel. The label information can be
encoded using a fixed length or variable length format. This label
format can be used in GMPLS signaling and routing protocol to
establish super-channel based optical label switched paths (LSPs).
Status of this Memo
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Table of Contents
1. Introduction...................................................3
2. Terminology....................................................5
3. Motivation for Super-Channel Label.............................5
3.1. Flex-Grid Slice Numbering.................................5
3.2. Super-Channel Label.......................................6
3.2.1. Super-Channel Label Encoding Format..................8
3.2.2. LSP Encoding and Switching Type in Generalized Label
Request....................................................12
4. Security Considerations.......................................12
5. IANA Considerations...........................................12
6. References....................................................12
6.1. Normative References.....................................12
6.2. Informative References...................................13
7. Acknowledgments...............................................13
Appendix A. Super-Channel Label Format Example...................14
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1. Introduction
Future transport systems are expected to support service upgrades to
data rates of 1 Tbps and beyond. To scale networks beyond 100Gbps,
multi-carrier super-channels coupled with advanced multi-level
modulation formats and flexible channel spectrum bandwidth
allocation schemes have become pivotal for future spectral efficient
transport network architectures [1,2].
A super-channel represents an ultra high aggregate capacity channel
containing multiple carriers which are co-routed through the network
as a single entity from the source transceiver to the sink
transceiver [3]. By multiplexing multiple carriers, modulating each
carrier with multi-level advanced modulation formats (such as PM-
QPSK, PM-8QAM, PM-16QAM), allocating an appropriate-sized flexible
channel spectral bandwidth slot, and using a coherent receiver for
detecting closely packed sub-carriers, a super-channel can support
ultra high data rates in a spectrally efficient manner while
maintaining required system reach. Figure 1 contrasts channel
spectrum bandwidth allocation schemes for various bit rate optical
paths on fixed-grid (G.694.1) and flex-grid. ITU-T fixed-grid
permits allocation of channel spectrum bandwidth in "single" fixed-
sized slots (e.g., 50GHz, 100GHz etc) independent of the channel bit
rate. In contrast, a flex-grid can allocate "arbitrary" size channel
spectral bandwidth as an integer multiple of 12.5 GHz fine
granularity contiguous (or non-contiguous) slices depending on
channel bit rate. This means, a flex-grid can support multiple data
rates channels (optical paths) in a spectrally efficient manner as
it allocates appropriate-sized spectrum bandwidth slots, as opposed
to fixed-sized slots.
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ITU-T G.694.1
Center frequency (f) = 193.1 THz
n=-3 n=-2 n=-1 n=0 n=+1 n=+2
^ ^ ^ ^ ^ ^
... | | | | | | ...
| | | | | | | | | | |
+--------+-------+-------+-------+-------+---
<-- --> <-- -->
50 GHz 50 GHz
^ ^
| n=-2 | n= +1
| |
+------+ +------+
|50 GHz| |50 GHz|
+------+ +------+
(10 Gbps channel) (40Gbps channel)
(a fixed 50GHz chunk) (a fixed 50GHz chunk)
(a)
^ ^ ^ ^ ^ ^
| | | | | + +|
... |-|-|-|-|-|-|-|-| |+|+|+|+|+|+|+|+|+|1|1| ...
|8|7|6|5|4|3|2|1|0|1|2|3|4|5|6|7|8|9|0|1|
---+-------+-------+-------+-------+-------+---
^ ^ ^
|<-- 200 GHz -->|<- ->|
| | 50GHz |
+-------------------------------+-------+
| 1 Tbps super-channel |100Gbps|
| 16 slices of 12.5 GHz |Channel|
| |4slices|
+-------------------------------+-------+
(b)
Figure 1 ITU-T (a) 50 GHz fixed-grid (G.694.1) (b) 12.5 GHz granular
flex-grid
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2. 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 RFC 2119
[RFC2119].
3. Motivation for Super-Channel Label
[RFC3471] defines new forms of MPLS "label" for the optical domain
that are collectively referred to as a "generalized label".
[RFC6205] defines a standard wavelength label based on ITU-T fixed-
grids ([G.694.1] and [G.694.2]) for use by Lambda-Switch-Capable
(LSC) LSRs.
A new label format for super-channels assignment on flex-grid is
needed because the existing label formats (such as the waveband
switching label defined in RFC3471 and the wavelength label defined
in RFC6205) either lack necessary fields to carry required flex-grid
related information (e.g., channel spacing) or do not allow
signaling of arbitrary flexible-size optical spectral bandwidth in
an efficient manner (e.g., in terms of integer multiple of fine
granularity 12.5GHz slices). For example,
o Waveband switching label format (defined in section 3.3.1 of
RFC3471) lacks fields to carry necessary information to support
flex-grid.
o Wavelength label allows signaling of single fixed-size optical
spectrum bandwidth slot only.
o Wavelength label does not allow signaling of arbitrary flexible-
size optical spectrum bandwidth needed for super-channels
assignment on flex-grid.
3.1. Flex-Grid Slice Numbering
Figure 2 (a) shows a 50 GHz ITU-T G.694.1 grid based on nominal
central frequency (193.1 THz). In G.694.1, given a channel spacing
(C.S) value and a value "n", the desired wavelength frequency can
calculated as follows:
Frequency (THz) = 193.1 THz + n * channel spacing (THz).
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Where "n" is a two's-complement integer (i.e., positive, negative,
or 0) and "channel spacing" can be 0.0125, 0.025, 0.05, or 0.1 THz.
Figure 2 (b) shows a 12.5 GHz flex-grid with its nominal central
frequency (193.1 THz) aligned with ITU-T G.694.1 nominal central
frequency and with each 12.5 GHz slice represented by the "left-
edge". Given the left edge frequency of a slice, one can calculate
the value of n i.e., slice number as follows:
Frequency (THz) = 193.1 THz + n * channel spacing (THz).
Where "n" is a two's-complement integer (i.e., positive, negative,
or 0) and "channel spacing" can be 0.0125 THz in this case. For
example, slice number 0 is denoted by its left-edge frequency i.e.,
f= 193.1 THz, slice number 1 is represented by its left edge
frequency of 193.1125 THz (193.1 THz + 0.0125 THz) and so on (Note:
in the future, if necessary the slice numbering scheme will be
updated in accordance with the ITU-T G.694.1 Flex-Grid).
3.2. Super-Channel Label
In order to setup an optical path manual or dynamically, we need a
way to identify and reserve resources (i.e., signal optical spectral
bandwidth for the super-channel) along the optical path. For this
purpose, this document defines a super-channel label as consisting
of a Super-Channel Identifier and an associated list of contiguous
or non-contiguous set of 12.5 GHz slices representing arbitrary size
optical spectrum of the super-channel (Note: in the future, slice
granularity could be 6.25 GHz).
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ITU-T G.694.1
Center frequency (f) = 193.1 THz
n=-1 n=-1 n=0 n=+1 n=+2
^ ^ ^ ^ ^
... | | | | | ...
| | | | |
---+-------+-------+-------+-------+---
<-- --> |
50 GHz |
|
(a) |
|
|
^ ^ ^ ^ ^
| | | | |
... |-|-|-|-|-|-|-|-| |+|+|+|+|+|+|+| ...
|8|7|6|5|4|3|2|1|0|1|2|3|4|5|6|7|
---+-------+-------+-------+-------+---
^ ^
| |
| |
+-----------------------+
| A super-channel with |
| Spectral BW = 150 GHz |
|(12 slices of 12.5 GHz)|
| |
| n_start= -7 |
| n_end = +4 |
| |
| (see label encoding |
| format for details) |
+-----------------------+
(b)
Figure 2 ITU-T (a) 50 GHz fixed-grid (G.694.1) (b) 12.5 GHs flex-
grid with its nominal central frequency aligned with the ITU-T
G.694.1 nominal central frequency
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3.2.1. Super-Channel Label Encoding Format
This section describes two options (option A and B) for encoding
super-channel label by making extensions to waveband switching
label[RFC3471] and wavelength label [RFC6205] formats.
o Option A: Encode super-channel label as a first slice number of
the grid (denoted as "n_start of Grid") plus the entire list of
slices in the grid as a Bitmap
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Super-Channel Id (16-bit) |Grid | C.S. | Reserved (9-bit)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| n_start of Grid (16-bit) |Num of Slices in Grid (16-bit) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Bitmap Word #1(first set of 32 slices from the left most edge) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Bitmap Word #2 (next set of 32 contiguous slice numbers) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
...
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Bitmap Word #N(last set of 32 contiguous slice numbers) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Super-Channel Id: 16 bits
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This field represents a logical identifier for a super-channel.
To disambiguate waveband switching and super-channel label
applications, we propose to rename the Waveband Identifier (32-
bit) as a super-channel Identifier (16-bit).
Grid: 3 bits
This field indicates the Grid type. The value for Grid should be
set to xx (to be assigned by IANA) for the ITU-T flex-grid based
on ongoing [G.694.1] standard flex-grid extensions.
+----------------+---------+
| Grid | Value |
+----------------+---------+
| Reserved | 0 |
+----------------+---------+
|ITU-T DWDM | 1 |
+----------------+---------+
|ITU-T CWDM | 2 |
+----------------+---------+
|ITU-T Flex-Grid | xx (TBD)|
+----------------+---------+
|Future use | 3 - 7 |
+----------------+---------+
C.S. (channel spacing): 4 bits
This field should be set to a value of 4 to indicate 12.5 GHz in
both labels. ITU-T G694.1 has currently defined following DWDM
channel spacing.
+----------+---------+
|C.S. (GHz)| Value |
+----------+---------+
| Reserved | 0 |
+----------+---------+
| 100 | 1 |
+----------+---------+
| 50 | 2 |
+----------+---------+
| 25 | 3 |
+----------+---------+
| 12.5 | 4 |
+----------+---------+
|Future use| 5 - 15 |
+----------+---------+
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n_start of Grid: 16-bit
This field indicates the first slice number in Grid for the
band being referenced (i.e., the start of the or the left most
edge of the Grid).
Num of Slices in Grid: 16-bit
This field represents the total number of slices in the band.
The value in this field determines the number of 32-bitmap words
required for the grid.
Bit map (Word): 32-bit
Each bit in the 32-bitmap word represents a particular slice
with a value of 1 or 0 to indicate whether for that slice
reservation is required (1) or not (0). Bit position zero in
the first word represents the first slice in the band (Grid)
and corresponds to the value indicated in the "n_start of
Grid" field.
o Option B: Encode super-channel label as a list of start and end
slice numbers corresponding to N groups of contiguous slices with
each group denoted by its starting and ending slice number
(e.g., "n_start_1" and "n_end_1" represent contiguous slices in
group#1, "n_start 2" and "n_end 2" in group#2, ..., "n_start N"
and "n_end N" in group#N).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Super-Channel Id (16-bit) |Grid | C.S. | Reserved (9-bit)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved (16-bit) | Number of Entries(16-bit) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|n_start_1(contiguous group #1) | n_end_1(contiguous group #1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|n_start_2(contiguous group #2) | n_end_2(contiguous group #2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|n_start_N (contiguous group #N) | n_end_N (contiguous group#N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Super-Channel Id, Grid, and C.S fields are same as described
earlier in option A.
Number of Entries: 16-bit
This field represents the number of 32-bit entries in the
super-channel label (i.e., number of groups with contiguous
slices). For example, in the case of a super-channel with
contiguous optical spectrum, this field should have a value of 1
(indicating one group of contiguous slices).
n_start_i (i=1,2,...N): 16 bits
n_end_i (i=1,2,...N): 16 bits
A super-channel with contiguous or non-contiguous optical
spectrum can be represented by N groups of slices where two
adjacent groups can be contiguous or non-contiguous however each
group contains contiguous slices. Each group is denoted by
n_start_i (which indicates the lowest or starting 12.5 GHz slice
number of the group) and n_end_i (which indicates the highest or
ending 12.5 GHz slice number of the group). "n_start_i" and
"n_end_i" are two's-complement integer that can take either a
positive, negative, or zero value.
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Both options allow efficient encoding of super-channel label with
contiguous and non-contiguous slices. Option A yields a fixed length
format while option B a variable length format. Option A is
relatively simpler, more flexible, however, might be less compact
than option B for encoding super-channel with contiguous optical
spectrum. In contrast, option B provides a very compact
representation for super-channels with contiguous optical spectrum,
however, might be less flexible in encoding super-channels with
arbitrary non-contiguous set of slices.
3.2.2. LSP Encoding and Switching Type in Generalized Label Request
For requesting a super-channel label in a Generalized Label Request
defined in section 3.1.1 of RFC3471, this document proposes to use
LSP Encoding Type = Lambda (as defined in RFC4328) and Switching
Type = Super-Channel-Switch-Capable(SCSC) (as defined in [6]).
4. Security Considerations
<Add any security considerations>
5. IANA Considerations
IANA needs to assign a new Grid field value to represent ITU-T Flex-
Grid.
6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3471] Berger, L., Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Functional Description", RFC
3471, January 2003.
[RFC6205] Otani, T., Ed., "Generalized Labels for Lambda-Switch-
Capable (LSC) Label Switching Routers", RFC 6205, March
2011.
[RFC6163] Lee, Y., Ed., "Framework for GMPLS and Path Computation
Element (PCE) Control of Wavelength Switched Optical
Networks (WSONs)", RFC 6163, April 2011
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6.2. Informative References
[1] Gringeri, S., Basch, B. Shukla,V. Egorov, R. and Tiejun J.
Xia, "Flexible Architectures for Optical Transport Nodes and
Networks", IEEE Communications Magazine, July 2010, pp. 40-50
[2] M. Jinno et. al., "Spectrum-Efficient and Scalable Elastic
Optical Path Network: Architecture, Benefits and Enabling
Technologies", IEEE Comm. Mag., Nov. 2009, pp. 66-73.
[3] S. Chandrasekhar and X. Liu, "Terabit Super-Channels for High
Spectral Efficiency Transmission",in Proc. ECOC 2010, paper
Tu.3.C.5, Torino (Italy), September 2010.
[4] ITU-T Recommendation G.694.1, "Spectral grids for WDM
applications: DWDM frequency grid", June 2002
[5] [4] "Finisar to Demonstrate Flexgrid(TM) WSS Technology at
ECOC 2010", press release.
[6] Abinder D., Iftekhar, Rajan, "OSPFTE extension to support
GMPLS for Flex Grid", draft-dhillon-ccamp-super-channel-
ospfte-ext-00.txt, October 2011.
7. Acknowledgments
<Add any acknowledgements>
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Appendix A. Super-Channel Label Format Example
Suppose node A and Node Z are super-channel switching capable and
node A receives a request for establishing a 1 Tbps optical LSP from
itself to node Z. Assume the super-channel requires a "contiguous"
spectral bandwidth of 200 GHz with left-edge frequency of 191.475
THz for the left-most 12.5 GHz slice and left-edge frequency of
191.6625 THz for the right-most slice. This means n_start = (191.475
- 193.1)/0.0125 = -130 and n_end = (191.6625 - 193.1)/0.0125 = -115
(i.e. we need 16 slices of 12.5 GHz starting from slice number -130
and ending at slice number -115).
Node A signals the LSP via a Path message including a super-channel
label format encoding option B defined in section 3.3:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Super-Channel Id (16-bit) |Grid | C.S. | Reserved (9-bit)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved (16-bit) | Number of Entries(16-bit) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|n_start_1 (contiguous group #1) | n_end_1(contiguous group #1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Super-Channel Id = 1 : super-channel number 1
Number of Entries: 1
Grid = xx : ITU-T Flex-Grid
C.S. = 4 : 12.5 GHz slices
n_start_1 = -130 : left-most 12.5 GHz slice number for group 1
n_end_1 = -115 : Right-most 12.5 GHz slice number for group 1
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Authors' Addresses
Iftekhar Hussain
Infinera
140 Caspian Ct., Sunnyvale, CA 94089
Email: ihussain@infinera.com
Abinder Dhillon
Infinera
140 Caspian Ct., Sunnyvale, CA 94089
Email: adhillon@infinera.com
Zhong Pan
Infinera
140 Caspian Ct., Sunnyvale, CA 94089
Email: zpan@infinera.com
Marco Sosa
Infinera
140 Caspian Ct., Sunnyvale, CA 94089
Email: msosa@infinera.com
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