Network Working Group Iftekhar Hussain
Internet Draft Abinder Dhillon
Intended status: Standard Track Zhong Pan
Expires: April 2012 Marco Sosa
Infinera
Bert Basch
Steve Liu
Andrew G. Malis
Verizon Communications
October 31, 2011
Generalized Label for Super-Channel Assignment on Flexible Grid
draft-hussain-ccamp-super-channel-label-02.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 (draft revised ITU-T G.694.1, revision
1.4, Oct 2011). 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 12.5 GHz slices
representing the 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
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
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Copyright Notice
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Table of Contents
1. Introduction...................................................3
2. Terminology....................................................6
3. Motivation for Super-Channel Label.............................6
3.1. Flex-Grid Slice Numbering.................................6
3.2. Super-Channel Label.......................................7
3.2.1. Super-Channel Label Encoding Format..................8
3.2.2. LSP Encoding and Switching Type in Generalized Label
Request....................................................11
4. Security Considerations.......................................11
5. IANA Considerations...........................................11
6. References....................................................11
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6.1. Normative References.....................................11
6.2. Informative References...................................12
7. Acknowledgments...............................................12
Appendix A. Super-Channel Label Format Example...................13
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 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 slices. 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. As in the examples in the figure, the
optical spectrum slices assigned will be to a given super-channel in
a contiguous manner. However, for flexibility in finding available
optical spectrum on fragmented fibers and to reduce signaling
message overhead, the two schemes proposed in this document also
allow for identification of a split-spectrum super-channel with
optical spectral slices that are non-contiguous, spread across
multiple slots. Note that the channel capacity available on a given
number of optical spectral slices depends on (among other factors)
how many contiguous optical slots are used. The definition of the
channel capacity available for a split-spectrum super-channel split
across multiple slots of different widths is outside the scope of
this document.
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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
Given a slice spacing value (e.g., 0.0125 THz) and a slice number
"n", the slice left edge frequency can be calculated as follows:
Slice Left Edge Frequency (THz)= 193.1 THz + n*slice spacing (THz).
Where "n" is a two's-complement integer (i.e., positive, negative,
or 0) and "slice spacing" is 0.0125 THz conforming to ITU-T Flex-
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Grid. (Note: in the future, if necessary the slice numbering scheme
will be updated in accordance with the Flex-Grid.)
Figure 2 shows an example using the slice number scheme described
earlier.
3.2. Super-Channel Label
In order to setup an optical path manually or dynamically, we need a
way to identify and reserve resources (i.e., signal optical spectral
bandwidth for the super-channels) along the optical path. For this
purpose, this document defines a super-channel label to cover the
cases of split-spectrum super-channels as well, such that the label
consists 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-channels (Note: in the
future, slice granularity could be 6.25 GHz.)
(n=0 is 193.1 THz)
n=-2 n=-1 n=0 n=+1 n=+2
^ ^ ^ ^ ^
| | | | |
... |-|-|-|-|-|-|-|-| |+|+|+|+|+|+|+| ...
|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) |
+-----------------------+
Figure 2 flex-grid example of the proposed slice numbering scheme.
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3.2.1. Super-Channel Label Encoding Format
This section describes two options (option A and B) for encoding the
super-channel label by making extensions to the waveband switching
label[RFC3471] and wavelength label [RFC6205] formats.
o Option A: Encode super-channel label as a list of start and end
slice numbers corresponding to N groups, each consisting 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 | S.S. | Reserved (9-bit)|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved (16-bit) | Number of Entries(16-bit) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|n_start_1(contiguous group #1) | n_end_1(contiguous group #1) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|n_start_2(contiguous group #2) | n_end_2(contiguous group #2) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|n_start_N (contiguous group #N) | n_end_N (contiguous group#N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Super-Channel Id: 16 bits
This field represents a logical identifier for a super-channel or
split-spectrum 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.
+----------------+---------+
| Grid | Value |
+----------------+---------+
| Reserved | 0 |
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+----------------+---------+
|ITU-T DWDM | 1 |
+----------------+---------+
|ITU-T CWDM | 2 |
+----------------+---------+
|ITU-T Flex-Grid | xx (TBD)|
+----------------+---------+
|Future use | 3 - 7 |
+----------------+---------+
S.S. (slice spacing): 4 bits
This field should be set to a value of 4 to indicate 12.5 GHz in
both labels.
+----------+---------+
|S.S. (GHz)| Value |
+----------+---------+
| Reserved | 0 |
+----------+---------+
| 100 | 1 |
+----------+---------+
| 50 | 2 |
+----------+---------+
| 25 | 3 |
+----------+---------+
| 12.5 | 4 |
+----------+---------+
|Future use| 5 - 15 |
+----------+---------+
Number of Entries: 16-bit
This field represents the number of 32-bit entries in the
super-channel label (i.e., number of slots 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 slot 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 spectrum or a split-spectrum super-
channel with non-contiguous optical spectrum can be represented by N
slots of slices where two adjacent slots can be contiguous or non-
contiguous, however each slot contains contiguous slices. Each slot
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is denoted by n_start_i (which indicates the lowest or starting 12.5
GHz slice number of the slot) and n_end_i (which indicates the
highest or ending 12.5 GHz slice number of the slot). "n_start_i"
and "n_end_i" are two's-complement integers that can take either a
positive, negative, or zero value.
o Option B: 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 | S.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, Grid, and S.S fields are same as described
earlier in option A.
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 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
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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.
Both options allow efficient encoding of a super-channel label with
contiguous and non-contiguous slices. Option B yields a fixed length
format while option A a variable length format. Option B is
relatively simpler, more flexible, however, might be less compact
than option A for encoding a single super-channel with contiguous
optical spectrum. In contrast, option A provides a very compact
representation for super-channels with contiguous optical spectrum,
however, might be less flexible in encoding split-spectrum 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.
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[RFC6163] Lee, Y., Ed., "Framework for GMPLS and Path Computation
Element (PCE) Control of Wavelength Switched Optical
Networks (WSONs)", RFC 6163, April 2011
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 A 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 | S.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
S.S. = 4 : 12.5 GHz Slice Spacing
n_start_1 = -130 : left-most 12.5 GHz slice number for slot 1
n_end_1 = -115 : Right-most 12.5 GHz slice number for slot 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
Bert Basch
Verizon Communications
60 Sylvan Rd., Waltham, MA 02451
Email: bert.e.basch@verizon.com
Steve Liu
Verizon Communications
60 Sylvan Rd., Waltham, MA 02451
Email: steve.liu@verizon.com
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Andrew G. Malis
Verizon Communications
60 Sylvan Rd., Waltham, MA 02451
Email: andrew.g.malis@verizon.com
Contributor's Addresses
Rajan Rao
Infinera
140 Caspian Ct., Sunnyvale, CA 94089
Email: rrao@infinera.com
Biao Lu
Infinera
140 Caspian Ct., Sunnyvale, CA 94089
Email: blu@infinera.com
Subhendu Chattopadhyay
Infinera
140 Caspian Ct., Sunnyvale, CA 94089
Email: schattopadhyay@infinera.com
Harpreet Uppal
Infinera
140 Caspian Ct., Sunnyvale, CA 94089
Email: harpreet.uppal@infinera.com
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