Network Working Group Fatai Zhang
Internet-Draft Huawei
Intended status: Standards Track Oscar Gonzalez de Dios
Telefonica
D. Ceccarelli
Ericsson
Expires: September 12, 2012 March 12, 2012
RSVP-TE Signaling Extensions in support of Flexible Grid
draft-zhang-ccamp-flexible-grid-rsvp-te-ext-01.txt
Status of this Memo
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This Internet-Draft will expire on September 12, 2012.
Abstract
This memo describes the signaling extensions of GMPLS control of
flexible grid network.
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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 RFC-2119 [RFC2119].
Table of Contents
1. Introduction ................................................. 2
2. Terminology .................................................. 3
3. Requirements for Flexible Grid Signaling ..................... 3
3.1. Slot Width .............................................. 4
3.2. Frequency Slot .......................................... 4
4. Extensions ................................................... 5
4.1. SSON Traffic Parameters ................................. 5
4.2. Generalized Label ....................................... 6
4.3. Signaling Procedures .................................... 8
4.3.1. Distributed SA ..................................... 8
4.3.2. Centralized SA ..................................... 9
5. Example ...................................................... 9
6. IANA Considerations ......................................... 10
6.1. RSVP Objects Class Types ............................... 10
6.2. DWDM Channel Spacing ................................... 10
6.3. PCEP Object ............................................ 11
7. Security Considerations ..................................... 11
8. References .................................................. 11
8.1. Normative References ................................... 11
8.2. Informative References ................................. 12
9. Contributors' Address ....................................... 12
10. Authors' Addresses ......................................... 13
1. Introduction
[G.694.1v1] defines the DWDM frequency grids for WDM applications. A
frequency grid is a reference set of frequencies used to denote
allowed nominal central frequencies that may be used for defining
applications. The channel spacing, i.e. the frequency spacing
between two allowed nominal central frequencies can be 12.5 GHz, 25
GHz, 50 GHz, 100 GHz and integer multiples of 100 GHz as defined in
[G.694.1v1]. All of the wavelengths on a fiber SHALL use different
central frequencies and occupy a fixed bandwidth of frequency.
[G.FLEXIGRID], an updated version of [G.694.1v1] has be consented in
December 2011 in support of flexible grids. The terms "frequency
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slot (i.e. the frequency range allocated to a specific channel and
unavailable to other channels within a flexible grid)" and "slot
width" (i.e. the full width of a frequency slot in a flexible grid)
are introduced to define a flexible grid. A channel is represented
as an LSC (Lambda Switching Capable) LSP in the control plane and
occupies a frequency slot on each fiber it traverses. In the case of
flexible grid, the different flexi-LSPs may have different slot
widths on a given fiber, referring to [SSON-FWK].
[WSON-SIG] describes the requirements and extensions for WSON
signaling. It focuses on the control of optical networks using a
fixed DWDM grid. This document describes the additional requirements
and extensions for signaling of LSPs using the felxi-grid
capabilities.
2. Terminology
Flexi-grid: See [SSON-FWK].
Slot Width: See [SSON-FWK].
Frequency Range: See [SSON-FWK].
SSON: Spectrum-Switched Optical Networks; See [SSON-FWK].
flexi-LSP: See [SSON-FWK].
RSA: See [SSON-FWK].
3. Requirements for Flexible Grid Signaling
A flexi-LSP SHOULD occupy a frequency slot, i.e. a range of
frequencies. The process of computing a route and the allocation of
a frequency slot is referred to as RSA (Routing and Spectrum
Assignment).
[SSON-FWK] describes three types of architecture approaches to RSA,
which are: combined RSA, separated RSA and distributed SA. The first
two approaches among them could be called "centralized SA", since
both routing and spectrum (frequency slot) assignment are performed
by centralized entity before the signaling procedure.
In the case of centralized SA, the assigned frequency slot SHOULD be
specified in the Path message. In the case of distributed SA, the
slot width of the flexi-LSP SHOULD be specified in the Path message,
allowing the involved network elements (e.g., the egress node) to
perform such distributed assignment.
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Similar to a fixed grid network, if the capability of shifting or
converting the whole optical spectrum allocated to a flexi-LSP is
not available, the flexi-LSP is subject to the Optical "Spectrum
Continuity Constraint", as described in [SSON-FWK].
3.1. Slot Width
The slot width is an end-to-end parameter representing how much
frequency resource is requested for a flexi-LSP. Since different
LSPs may request different amounts of frequency resource in flexible
grid networks, the slot width SHOULD be carried in the signaling
message, so that all the nodes along the LSP can know how much
frequency resource (including both central frequency and slot width)
will be allocated for the LSP.
3.2. Frequency Slot
The frequency slot information represents which part of the
frequency resource is allocated on each link for a flexi-LSP. This
information SHOULD be carried hop-by-hop in signaling message so
that each node can indicate its neighbor the resource reservation on
the link between them.
The frequency slot can be represented by the two parameters: central
frequency and slot width, as follows:
Frequency slot = [(central frequency) - (slot width)/2] ~
[(central frequency) + (slot width)/2]
Since the slot width information is carried in the signaling message
(as described in Section 2.1), also the central frequency parameter
SHOULD be carried in the signaling message for frequency slot
determination.
As described in [G.FLEXIGRID], for the flexible DWDM grid, the
allowed frequency slots have a nominal central frequency (in THz)
defined by:
193.1 + n * 0.00625, where n is a positive or negative integer
including 0, and 0.00625 is the nominal central frequency
granularity in THz.
and a slot width defined by:
12.5 * m, where m is a positive integer and 12.5 is the slot width
granularity in GHz.
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Applications may be defined where only a subset of the possible slot
widths and positions are required to be supported. For example, an
application could be defined where the nominal central frequency
granularity is 12.5 GHz (by only requiring values of n that are even)
and that only requires slot widths as a multiple of 25 GHz (by only
requiring values of m that are even).
Figure 1 shows an example of two flexi-LSPs traversing a link and
illustrates how to determine the frequency slot based on the central
frequency and slot width information.
Frequency Slot 1 Frequency Slot 2
------------- -------------------
| | | |
-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
...+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
------------- -------------------
^ ^
Central F = 193.1THz Central F = 193.14375 THz
Slot width = 25 GHz Slot width = 37.5 GHz
Figure 1 - Two flexi-LSPs traverse a Link
The two wavelengths shown in figure 1 have the following meaning:
flexi-LSP 1: central frequency = 193.1 THz, slot width = 25 GHz. It
means the frequency slot [193.0875 THz, 193.1125 THz] is assigned to
this flexi-LSP.
flexi-LSP 2: central frequency = 193.14375 THz, slot width = 37.5
GHz. It means the frequency slot [193.125 THz, 193.1625 THz] is
assigned to this flexi-LSP.
Note that the frequency slots of two flexi-LSPs on a fiber MUST NOT
overlap with each other.
4. Extensions
This section defines the extensions of signaling for flexible grid.
4.1. SSON Traffic Parameters
As described in Section 2, the slot width represents how much
frequency resource is requested for a flexi-LSP, i.e., it describes
the end-to-end traffic profile of the LSP. Therefore, the slot width
SHOULD be regarded as a traffic parameter for a flexi-LSP.
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The SSON traffic parameters are organized as follows:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| m | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
m (8 bits): the slot width is specified by m*12.5 GHz.
Note that the slot width of a fixed grid defined in [G.694.1v1] can
also be specified by m because the defined channel spacings (12.5
GHz, 25 GHz, 50 GHz, 100 GHz and integer multiples of 100 GHz) are
also the multiple of 12.5 GHz. Therefore, the traffic parameters are
general for SSON including both fixed grid (i.e. WSON) and flexible
grid.
The SSON traffic parameters are carried in the SENDER_TSPEC object
within a Path message and in the FLOWSPEC object within a Resv
message:
SSON SENDER_TSPEC: Class = 12, C-Type = to be assigned by IANA,
preferred 8.
SSON FLOWSPEC: Class = 9, C-Type = to be assigned by IANA, preferred
8.
4.2. Generalized Label
In the case of a flexible grid link, the allocated central frequency
is calculated as follows:
Central Frequency = (193.1 + n * 0.00625) THz
Where n can be a positive or negative integer, or 0.
The Generalized Label object is used to indicate the resource
reserved on a link. In Flexible Grid networks, it is used to
indicate which frequency slot is allocated on a link for the given
flexi-LSP.
Since the frequency slot assigned to a flexi-LSP can be determined
by the combination of [central frequency, slot width], while the
slot width of a flexi-LSP is specified in the traffic parameters,
the Label object just needs to carry the assigned central frequency.
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Therefore, the wavelength label format defined in [RFC6205] can be
reused to specify the central frequency of a flexi-LSP, without any
change on the label format.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Grid | C.S. | Identifier | n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The meaning of Grid, Identifier and n fields are not changed. The
usage of the label format is also not changed.
According to [G.FLEXIGRID], flexible grid still belongs to DWDM, so
there is no need to introduce a new type of Grid, i.e., Grid=1 (ITU-
T DWDM) SHOULD be used for flexible grid.
In case of Grid=1 (ITU-T DWDM), according to [G.697v2.1], a new
value of C.S. is defined for flexible 6.25 GHz grid. The
C.S.(Channel Spacing) field is defined as follows:
+--------------+---------+
|C.S. (GHz) | Value |
+--------------+---------+
| Reserved | 0 |
+--------------+---------+
| 100 | 1 |
+--------------+---------+
| 50 | 2 |
+--------------+---------+
| 25 | 3 |
+--------------+---------+
| 12.5 | 4 |
+--------------+---------+
|Flexible grid | 5 (TBA) |
+--------------+---------+
|Future use | 6 ~ 15 |
+--------------+---------+
The frequency is calculated as such in [G.FLEXIGRID]:
Frequency (THz) = 193.1 THz + n * channel spacing (THz)
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For the case where the channel spacing value is set to "Flexible
grid", a channel spacing of 6.25 GHz MUST be used in the above
formula.
4.3. Signaling Procedures
This section describes the signaling procedures for distributed SA
and centralized SA (See [SSON-FWK]).
4.3.1. Distributed SA
In this case, only the route is provided by a PCE or ingress node
before the signaling procedure. The available central frequencies
SHALL be collected hop by hop and the egress node SHOULD select a
proper central frequency for the LSP.
After the route is computed, the ingress node SHOULD find out the
available central frequencies for the LSP on the next link of the
route. If the frequency slot does not overlap with the existing
flexi-LSPs, the central frequency is considered to be available for
the requesting flexi-LSP.
Then a Path message is sent to the next node on the route. The Path
message MUST contain a SSON SENDER_TSPEC object to specify the slot
width of the flexi-LSP. A LABEL_SET object SHALL be added to the
Path message, which contains the candidate central frequencies for
the LSP on the next link.
When an intermediate node receives a Path message, it can get the
slot width from the SSON SENDER_TSPEC object. Then it SHOULD find
the available central frequencies for the LSP on the next link of
the route similar to the ingress node. The common part of the two
available central frequency sets, i.e. the set received from the
Path message and the set of the next link, SHALL be selected as the
new available central frequency set for the LSP. If the new set is
null, the Path message SHALL be rejected by a PathErr message.
Otherwise, the LABEL SET object in the Path message SHALL be updated
according to the new set and the Path message is forwarded to the
next node on the route.
When an egress node receives a Path message, it SHOULD select an
available central frequency from the LABEL SET object based on local
policy and determine the frequency slot based on the slot width and
the selected central frequency (See section 2.2). Then a Resv
message is responded so that the nodes along the LSP can establish
the optical cross-connect based on the frequency slot determined by
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the slot width in the traffic parameters and the central frequency
in the label.
4.3.2. Centralized SA
In this case, both of the route and the frequency slot are provided
by the PCE or ingress node. When signaling the LSP, the slot width
is carried in the traffic parameters, and the assigned central
frequency is carried in the Label ERO. When the nodes along the LSP
receive the Path message carrying this information, they can
determine the frequency slot by the slot width and the central
frequency, so that they can establish the optical cross-connect
based on the central frequency. The procedures of ERO and Label ERO
are the same as described in [RFC3209] and [RFC3473].
5. Example
An example is provided as below. In this example, assume that there
are two links and three nodes for the network topology and a flex-
LSP is assumed to be created from Node N1 to Node N3.
+------+ link1 +------+ link2 +------+
| N1 +----------+ N2 +----------+ N3 |
+------+ +------+ +------+
Frequency resources on link1 (central frequency granularity = 12.5
GHz):
-9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10 11
...+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
|--Available Frequency Range--|
Frequency resources on link2 (central frequency granularity = 12.5
GHz):
-8 -6 -4 -2 0 2 4 6 8 10
...+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--+--...
|--Available Frequency Range--|
The symbol '+' represents the allowed nominal central frequency. The
symbol "--" represents a 6.25 GHz frequency unit. The number on the
top of the line represents the 'n' in the frequency calculation
formula (193.1 + n * 0.00625). The nominal central frequency is
193.1 THz when n equals zero.
A flexi-LSP establishment request:
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o Source node: N1
o Sink node: N3
o Slot width: 25 GHz
The usable central frequencies set for the flexi-LSP is
[n=0,1,2,3,4,5,6] on link1. But on link2, because the central
frequency granularity is 12.5 GHz, The usable central frequencies
set for the flexi-LSP is [n=0,2,4].
In the case of Centralized SA, PCE or ingress node (N1) could
allocate an available frequency slot to the flexi-LSP, e.g. n=2 and
slot width=50 Ghz. During the LSP setup procedures, the slot width
(50 GHz, i.e. m=4) should be specified in the traffic parameters
objects and the central frequency (n=2) should be specified in the
label objects.
6. IANA Considerations
6.1. RSVP Objects Class Types
This document introduces two new Class Types for existing RSVP
objects. IANA is requested to make allocations from the "Resource
ReSerVation Protocol (RSVP) Parameters" registry using the "Class
Names, Class Numbers, and Class Types" sub-registry.
Class Number Class Name Reference
------------ ----------------------- ---------
9 FLOWSPEC [RFC2205]
Class Type (C-Type):
(TBA) SSON FLOWSPEC [This.I-D]
Class Number Class Name Reference
------------ ----------------------- ---------
12 SENDER_TSPEC [RFC2205]
Class Type (C-Type):
(TBA) SSON SENDER_TSPEC [This.I-D]
6.2. DWDM Channel Spacing
The IANA has created a registry and manages the space of DWDM
Channel Spacing as described in section 5.2 of [RFC6205]. It is
requested that the IANA makes assignments from the DWDM Channel
Spacing.
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Value Channel Spacing (GHz) Reference
----- ------------------------- ----------
TBA Flexible grid [This.I-D]
6.3. PCEP Object
This document introduces a new Object-Type for existing PCEP objects.
It is requested that the IANA makes an assignment from the object-
type of GENERALIZED-BANDWIDTH.
Object-Class Name Reference
------------ ----------------------- ---------
TBA GENERALIZED-BANDWIDTH [GMPLS-PCE]
Object-Type:
(TBA) SSON [This.I-D]
7. Security Considerations
This document introduces no new security considerations to [RFC3473].
8. References
8.1. Normative References
[RFC2119] S. Bradner, "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[WSON-PCE] Y. Lee, G. Bernstein, Jonas Martensson, T. Takeda and T.
Tsuritani, "PCEP Requirements for WSON Routing and
Wavelength Assignment", draft-ietf-pce-wson-routing-
wavelength-05, July 2011.
[WSON-SIG] G. Bernstein, Sugang Xu, Y. Lee, G. Martinelli and
Hiroaki Harai, "Signaling Extensions for Wavelength
Switched Optical Networks", draft-ietf-ccamp-wson-
signaling-02, September 2011.
[RFC3209] D. Awduche et al, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC3209, December 2001.
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[RFC3473] L. Berger, Ed., "Generalized Multi-Protocol Label
Switching (GMPLS) Signaling Resource ReserVation Protocol-
Traffic Engineering (RSVP-TE) Extensions", RFC 3473,
January 2003.
[RFC6163] Y. Lee, G. Bernstein and W. Imajuku, "Framework for GMPLS
and Path Computation Element (PCE) Control of Wavelength
Switched Optical Networks (WSONs)", RFC 6163, April 2011.
[RFC6205] T. Otani and D. Li, "Generalized Labels for Lambda-Switch-
Capable (LSC) Label Switching Routers", RFC 6205, March
2011.
[SSON-FWK] F.Zhang et al, "Framework for GMPLS and PCE Control of
Spectrum Switched Optical Networks" , draft-zhang-ccamp-
sson-framework, in progress.
[G.FLEXIGRID] Revised G.694.1 version 1.6, Consented in December
2011, ITU-T Study Group 15.
[GMPLS-PCE] C. Margaria, O. Gonzalez de Dios, Desarrollo, and F.
Zhang, "PCEP extensions for GMPLS", draft-ietf-pce-gmpls-
pcep-extensions-04, October 2011.
8.2. Informative References
[G.694.1v1] ITU-T Recommendation G.694.1, Spectral grids for WDM
applications: DWDM frequency grid, June 2002.
[G.697v2.1] Draft revised G.697 version 2.1, Consented in December
2011, ITU-T Study Group 15.
9. Contributors' Address
Ramon Casellas
CTTC - Centre Tecnologic de Telecomunicacions de Catalunya
Av. Carl Friedrich Gauss n7
Castelldefels, Barcelona 08860
Spain
Phone:
Email: ramon.casellas@cttc.es
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10. Authors' Addresses
Fatai Zhang
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972912
Email: zhangfatai@huawei.com
Oscar Gonzalez de Dios
Telefonica Investigacion y Desarrollo
Emilio Vargas 6
Madrid, 28045
Spain
Phone: +34 913374013
Email: ogondio@tid.es
Felipe Jimenez Arribas
Telefonica Investigacion y Desarrollo
Emilio Vargas 6
Madrid, 28045
Spain
Email: felipej@tid.es
Daniele Ceccarelli
Ericsson
Via A. Negrone 1/A
Genova - Sestri Ponente
Italy
Email: daniele.ceccarelli@ericsson.com
Xiaobing Zi
Huawei Technologies
F3-5-B R&D Center, Huawei Base
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28973229
Email: zixiaobing@huawei.com
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Yi Lin
Huawei Technologies Co., Ltd.
F3-5-B R&D Center, Huawei Base,
Bantian, Longgang District
Shenzhen 518129 P.R.China
Phone: +86-755-28972914
Email: yi.lin@huawei.com
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