Network Working Group Fatai Zhang
Internet-Draft Huawei
Intended status: Standards Track Oscar Gonzalez de Dios
Telefonica
D. Ceccarelli
Ericsson
Expires: April 16, 2012 October 16, 2011
RSVP-TE Signaling Extensions in support of Flexible Grid
draft-zhang-ccamp-flexible-grid-rsvp-te-ext-00.txt
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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. Requirements for Flexible Grid Signaling ..................... 3
2.1. Slot Width .............................................. 3
2.2. Frequency Slot .......................................... 3
3. Extensions ................................................... 4
3.1. WSON Traffic Parameters ................................. 5
3.2. Generalized Label ....................................... 5
3.3. Signaling Procedures .................................... 7
3.3.1. Distributed SA ..................................... 7
3.3.2. Centralized SA ..................................... 8
4. IANA Considerations .......................................... 8
5. Security Considerations ...................................... 8
6. References ................................................... 8
7. Authors' Addresses ........................................... 9
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] will be consented
in December 2011 in support of flexible grids. The terms "frequency
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 flexible grid. A channel is represented as
an LSC (Lambda Switching Capable) LSP in the control plane and
SHOULD occupy a frequency slot on each fiber it traverses. In the
case of flexible grid, the different LSC LSPs may have different
slot width on a fiber, i.e. the slot width is flexible on a fiber.
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[WSON-SIG] describes the requirements and extensions for WSON
signaling. It focuses on the fixed grids control. This document
describes the additional requirements and extensions for signaling
control brought by flexible grids.
2. Requirements for Flexible Grid Signaling
An LSC LSP SHOULD occupy a frequency slot, i.e. a range of frequency.
The route computation and frequency slot assignment could be called
RSA (Routing and Spectrum Assignment).
[FLEXIGRID-REQ] describes three types of architecture approaches to
RSA, which are: combined RSA, separated RSA and distributed SA. In
the case of combined RSA and separated RSA, both the routing and the
spectrum (frequency slot) are provided by the RSA algorithm before
the signaling procedure. It could be called "centralized SA". In the
case of distributed SA, only the route is provided before the
signaling procedure and the spectrum assignment is done during the
signaling procedure.
In the case of centralized SA, the frequency slot SHOULD be
specified in the Path message. In the case of distributed SA, the
slot width of the LSC LSP SHOULD be specified in the Path message
for the purpose of frequency slot assignment.
Similar to fixed grid network, if there is no wavelength converter
in an optical network, there is "wavelength continuity constraint"
of a LSC LSP which is described as section 4 of [RFC 6163].
2.1. Slot Width
The slot width is an end-to-end parameter representing how much
spectrum resource is requested for a LSC LSP. Since different LSPs
may request different amounts of spectrum portion 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 spectrum
portion will be allocated for the LSP.
2.2. Frequency Slot
The frequency slot information represents which part of the spectrum
portion is allocated on each link for an LSC 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.
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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.
Figure 1 shows an example of two LSC 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 LSC LSPs traverse a Link
The two wavelengths shown in figure 1 have the following meaning:
LSC 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 LSC LSP.
LSC 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 LSC LSP.
Note that the frequency slots of two LSC LSPs on a fiber MUST NOT
overlap with each other.
3. Extensions
This section defines the extensions of signaling for flexible grid.
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3.1. WSON Traffic Parameters
As described in Section 2, the slot width represents how much
spectrum resource is requested for an LSC 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 an LSC LSP.
The WSON 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 fixed grid defined in [G.694.1v1] can be
also specified by m because the defined channel spacing (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 WSON including both fixed grid and flexible grid.
The WSON traffic parameters SHOULD be carried in SENDER_TSPEC or
FLOWSPEC objects:
WSON SENDER_TSPEC: Class = 12, C-Type = to be assigned by IANA,
preferred 8.
WSON FLOWSPEC: Class = 9, C-Type = to be assigned by IANA, preferred
8.
3.2. Generalized Label
In the case of flexible grid, the allowed central frequency is
calculated as follows:
Central Frequency = (193.1 + n * 0.00625) THz
Where n is a two's-complement integer (positive, negative, or 0).
The 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 LSC LSP.
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Since the frequency slot assigned to an LSC LSP can be determined by
the combination of [central frequency, slot width], while the slot
width of an LSC LSP is specified in the traffic parameters, the
Label object just needs to carry the assigned central frequency.
Therefore, the wavelength label format defined in [RFC6205] can be
reused to specify the central frequency of an LSC 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), 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 |
+-------------+---------+
| 6.25 | 5 (TBA) |
+-------------+---------+
|Future use | 6 ~ 15 |
+-------------+---------+
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The value for flexible 6.25 GHz is to be assigned by IANA, preferred
5.
3.3. Signaling Procedures
This section describes the signaling procedures for distributed SA
and centralized SA (See [FLEXIGRID-REQ]).
3.3.1. Distributed SA
In this case, only the route is provided by a PCE or ingress node
before the signaling procedure. The available central frequencies
will 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 which is determined by a central
frequency and slot width of the LSC LSP (See section 2.2) does not
overlap with the existing LSC LSPs, the central frequency is
considered to be available for the requesting LSC LSP.
Then a Path message is sent to the next node on the route. The Path
message MUST contain a Flexible Grid SENDER_TSPEC object to specify
the slot width of the LSC LSP. A LABEL_SET object SHALL be added to
the Path message, which contains the available 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 Flexible Grid 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.
3.3.2. Centralized SA
In this case, both of the routing and frequency slot are provided by
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 these information, they can
determine the frequency slot by the slot width and the central
frequency and then 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].
4. IANA Considerations
TBD.
5. Security Considerations
TBD.
6. References
[RFC2119] S. Bradner, "Key words for use in RFCs to indicate
requirements levels", RFC 2119, March 1997.
[G.694.1v1] ITU-T Recommendation G.694.1, Spectral grids for WDM
applications: DWDM frequency grid, June 2002.
[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.
[FLEXIGRID-REQ] F.Zhang et al, "Requirements for GMPLS Control of
Flexible Grids",draft-zhang-ccamp-flexible-grid-
requirements, in progress.
[G.FLEXIGRID] Draft revised G.694.1 version 1.3, Unpublished ITU-T
Study Group 15, Question 6.
7. 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
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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
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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