Network Working Group CCAMP
Internet Draft Y.Li
Intended status: Informational ZTE
Expires: August 2014 G. Zhang
CATR
X.Fu
ZTE
R. Casellas
CTTC
Y Wang
CATR
February 14, 2014
Link Management Protocol Extensions for Grid Property Negotiation
draft-li-ccamp-grid-property-lmp-03.txt
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Abstract
The recent updated version of ITU-T [G.694.1] has introduced the
flexible-grid DWDM technique, which provides a new tool that operators
can implement to provide a higher degree of network optimization than
is possible with fixed-grid systems. This document describes the
extensions to the Link Management Protocol (LMP) to negotiate link grid
property between the adjacent DWDM nodes before the link is brought up.
Table of Contents
1. Introduction ................................................ 3
1.1. Conventions Used in This Document ....................... 3
2. Terminology ................................................. 3
3. Requirements for Grid Property Negotiation ................... 4
3.1. Flexi-fixed Grid Nodes Interworking ..................... 4
3.2. Flexible-Grid Capability Negotiation .................... 5
3.3. Summary ................................................ 5
4. LMP extensions .............................................. 6
4.1. Grid Property Subobject................................. 6
5. Messages Exchange Procedure.................................. 8
5.1. Flexi-fixed Grid Nodes Messages Exchange ................ 8
5.2. Flexible Nodes Messages Exchange ........................ 9
6. Security Considerations..................................... 10
7. IANA Considerations ........................................ 10
8. References ................................................. 10
8.1. Normative references................................... 10
8.2. Informative References................................. 11
9. Authors' Address ........................................... 11
10. Contributors' Address...................................... 12
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1. Introduction
The recent updated version of ITU-T [G.694.1] has introduced the
flexible-grid DWDM technique, which provides a new tool that
operators can implement to provide a higher degree of network
optimization than is possible with fixed-grid systems. A flexible-
grid network supports allocating a variable-sized spectral slot to a
channel. Flexible-grid DWDM transmission systems can allocate their
channels with different spectral bandwidths/slot widths so that they
can be optimized for the bandwidth requirements of the particular
bit rate and modulation scheme of the individual channels. This
technique is regarded to be a promising way to improve the spectrum
utilization efficiency and can be used in the beyond 100Gb/s
transport systems.
Fixed-grid DWDM system is regarded as a special case of Flexi-grid
DWDM. It is expected that fixed-grid optical nodes will be gradually
replaced by flexible nodes and interworking between fixed-grid DWDM
and flexible-grid DWDM nodes will be needed as the network evolves.
Additionally, even two flexible-grid optical nodes may have
different grid properties based on the filtering component
characteristics, thus need to negotiate on the specific parameters
to be used during neighbor discovery process [draft-ietf-ccamp-
flexi-grid-fwk-00]. This document describes the extensions to the
Link Management Protocol (LMP) to negotiate a link grid property
between two adjacent Flexi-grid nodes before the link is brought up.
1.1. 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].
2. Terminology
For the flexible-grid DWDM, the spectral resource is called
frequency slot which is represented by the central frequency and the
slot width. The defined nominal central frequency and the slot width
can be referred to [FLEX-FWK].
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In this contribution, some other definitions are listed below:
Central frequency granularity: It is the granularity of the allowed
central frequencies and is set to the multiple of 6.25 GHz.
Slot width granularity: It is the granularity of the allowed slot
width, and is set to the multiple of 12.5 GHz.
Tuning range: It describes the supported spectrum slot range of the
switching nodes or interfaces. It is represented by the supported
minimal slot width and the maximum slot width.
Channel spacing: It is used in traditional fixed-grid network to
identify spectrum spacing between two adjacent channels.
3. Requirements for Grid Property Negotiation
3.1. Flexi-fixed Grid Nodes Interworking
Figure 1 shows an example of interworking between flexible and
fixed-grid nodes. Node A, B, D and E support flexible-grid. All
these nodes can support frequency slots with a central frequency
granularity of 6.25 GHz and slot width granularity of 12.5 GHz.
Given the flexibility in flexible-grid nodes, it is possible to
configure the nodes in such a way that the central frequencies and
slot width parameters are backwards compatible with the fixed DWDM
grids (adjacent flexible frequency slots with channel spacing of
8*6.25 and slot width of 4*12.5 GHz is equivalent to fixed DWDM
grids with channel spacing of 50 GHz).
As node C can only support the fixed-grid DWDM property with channel
spacing of 50 GHz, to establish a LSP through node B, C, D, the
links between B to C and C to D must set to align with the fixed-
grid values. This link grid property must be negotiated before
establishing the LSP.
+---+ +---+ +---+ +---+ +---+
| A |---------| B |=========| C |=========| D +--------+ E |
+---+ +---+ +---+ +---+ +---+
Figure 1 An example of interworking between
flexible and fixed-grid nodes
^ ^ ^ ^
------->|<----50GHz---->|<----50GHz---->|<----50GHz---->|<------
..... | | | | .....
+-------+-------+-------+-------+-------+--------+------+-------+-
n=-2 -1 0 1 2
Fixed channel spacing of 50 GHz (Node C)
^ ^ ^ ^
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| | | |
--------+---------------+---------------+---------------+---------
..... | n=-8, m=4 | n=0, m=4 | n=8, m=4 | .....
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-
n=-16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16
|_|
Flexi-grid (Nodes B,D) 6.25 GHz
Central frequency granularity=6.25 GHz
Slot width granularity=12.5 GHz
Figure 2 Representation of fixed channel spacing
and flexi-grid spectrum slot
3.2. Flexible-Grid Capability Negotiation
The updated version of ITU-T [G.694.1] has defined the flexible-grid
with a central frequency granularity of 6.25 GHz and a slot width
granularity of 12.5 GHz. However, devices or applications that make
use of the flexible-grid may not be able to support every possible
slot width. In other words, applications may be defined where
different grid granularity can be supported. Taking node G as an
example, an application could be defined where the central frequency
granularity is 12.5 GHz requiring slot widths being multiple of 25
GHz. Therefore the link between two optical nodes with different
grid granularity must be configured to align with the larger of both
granularities. Besides, different nodes may have different slot
width tuning ranges. For example, in figure 3, node F can only
support slot width with tuning change from 12.5 to 100 GHz, while
node G supports tuning range from 25 GHz to 200 GHz. The link
property of slot width tuning range for the link between F and G
should be chosen as the range intersection, resulting in a range
from 25 GHz to 100 GHz.
+---+ +---+
| F +------------| G |
+---+ +---+
+------------------+-------------+-----------+
| Unit (GHz) | Node F | Node G |
+------------------+-------------+-----------+
| Grid granularity | 6.25 (12.5) | 12.5 (25) |
+------------------+-------------+-----------+
| Tuning range | [12.5, 100] | [25, 200] |
+------------------+-------------+-----------+
Figure 3 An example of flexible-grid capability negotiation
3.3. Summary
In summary, in a DWDM Link between two nodes, the following
properties can be negotiated:
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o Grid capability: flexible grid or fixed grid DWDM.
o Central frequency granularity: a multiplier of 6.25 GHz.
o Slot width granularity: a multiplier of 12.5 GHz.
o Slot width tuning range: two multipliers of 12.5GHz, each
indicate the minimal and maximal slot width supported by a port
respectively.
4. LMP extensions
4.1. Grid Property Subobject
According to [RFC4204], the LinkSummary message is used to verify
the consistency of the link property on both sides of the link
before it is brought up. The LinkSummary message contains negotiable
and non-negotiable DATA_LINK objects, carrying a series of variable-
length data items called subobjects, which illustrate the detailed
link properties. The subobjects are defined in Section 12.12.1 in
[RFC4204].
To solve the problems stated in section 3, this draft extends the
LMP protocol by introducing a new DATA_LINK subobject called "Grid
property", allowing the grid property correlation between adjacent
nodes. The encoding format of this new subobject is 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Grid | C.F.G | S.W.G | Min | Max |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Type=TBD, Grid property type.
Grid:
The value is used to represent which grid the node/interface
supports. Values defined in [RFC6205] identify DWDM [G.694.1] and
CWDM [G.694.2]. The value defined in [I-D.farrkingel-ccamp-
flexigrid-lambda-label] identifies flexible DWDM.
+---------------+-------+
| Grid | Value |
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+---------------+-------+
| Reserved | 0 |
+---------------+-------+
| ITU-T DWDM | 1 |
+---------------+-------+
| ITU-T CWDM | 2 |
+---------------+-------+
| Flexible DWDM | 3 |
+---------------+-------+
| Future use | 4-16 |
+---------------+-------+
C.F.G (central frequency granularity):
For a fixed-grid node/interface, the C.F.G value is used to
represent the channel spacing, as the spacing between adjacent
channels is constant. For a flexible-grid node/interface, this field
should be used to represent the central frequency granularity which
is the multiple of 6.25 GHz.
+------------+-------+
| C.F.G (GHz) | Value |
+------------+-------+
| Reserved | 0 |
+------------+-------+
| 100 | 1 |
+------------+-------+
| 50 | 2 |
+------------+-------+
| 25 | 3 |
+------------+-------+
| 12.5 | 4 |
+------------+-------+
| 6.25 | 5 |
+------------+-------+
| Future use | 6-15 |
+------------+-------+
S.W.G (Slot Width Granularity):
It is a positive integer value which indicates the slot width
granularity which is the multiple of 12.5 GHz.
Min & Max:
Min & Max indicate the slot width tuning range the interface
supports (as defined in section 2). For example, for slot width
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tuning range from 25 GHz to 100 GHz (with regard to a node with slot
width granularity of 12.5 GHz), the values of Min and Max should be
2 and 8 respectively. For fixed-grid nodes, these two fields are
meaningless and should be set to zero.
5. Messages Exchange Procedure
5.1. Flexi-fixed Grid Nodes Messages Exchange
To demonstrate the procedure of grid property correlation, the model
shown in Figure 1 is reused. Node B starts sending messages.
o After inspecting its own node/interface property, node B sends
node C a LinkSummary message including the MESSAGE ID, TE_LINK ID
and DATA_LINK objects. The setting and negotiating of MESSAGE ID
and TE_link ID can be referenced to [RFC4204]. As node B
supports flexible-grid property, the Grid and C.S. values in the
grid property subobject are set to be 3 and 5 respectively. The
slot width tuning range is from 12.5 GHz to 200 GHz. Meanwhile,
the N bit of the DATA_LINK object is set to 1, indicating that
the property is negotiable.
o When node C receives the LinkSummary message from B, it checks
the Grid, C.S., Min and Max values in the grid property subobject.
Node C can only support fixed-grid DWDM and realizes that the
flexible-grid property is not acceptable for the link. Since the
receiving N bit in the DATA_LINK object is set, indicating that
the Grid property of B is negotiable, node C responds to B with a
LinkSummaryNack containing a new Error_code object and state that
the property needs further negotiation. Meanwhile, an accepted
grid property subobject (Grid=2, C.S.=2, fixed DWDM with channel
spacing of 50 GHz) is carried in LinkSummaryNack message. At
this moment, the N bit in the DATA_LINK object is set to 0,
indicating that the grid property subobject is non-negotiable.
o As the channel spacing and slot width of node B can be configured
to be any integral multiples of 6.25 GHz and 12.5 GHz
respectively, node B supports the fixed DWDM values announced by
node C. Consequently, node B will resend the LinkSummary message
carrying the grid property subobject with values of Grid=2 and
C.S.=2.
o Once received the LinkSummary message from node B, node C replies
with a LinkSummaryACK message. After the message exchange, the
link between node B and C is brought up with a fixed channel
spacing of 50 GHz.
In the above mentioned grid property correlation scenario, the node
supporting a flexible-grid is the one that starts sending LMP
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messages. The procedure where the initiator is the fixed-grid node
is as follows:
o After inspecting its own interface property, Node C sends B a
LinkSummary message containing a grid property subobject with
Grid=2, C.S.=2. The N bit in the DATA_LINK object is set to 0,
indicating that it is non-negotiable.
o As the channel spacing and slot width of node B can be configured
to be any integral multiples of 6.25 GHz and 12.5 GHz
respectively, node B is able to support the fixed DWDM parameters.
Then, node B will make appropriate configuration and reply node C
the LinkSummaryACK message.
o After the message exchange, the link between node B and C is
brought up with a fixed channel spacing of 50 GHz.
5.2. Flexible Nodes Messages Exchange
To demonstrate the procedure of grid property correlation between to
flexi-grid capable nodes, the model shown in figure 3 is reused. The
procedure of grid property correlation (negotiating the grid
granularity and slot width tuning range) is similar to the scenarios
mentioned above.
o The Grid, C.S., Min and Max values in the grid property subobject
sent from node F to G are set to be 3,5,1,8 respectively.
Meanwhile, the N bit of the DATA_LINK object is set to 1,
indicating that the grid property is negotiable.
o When node G has received the LinkSummary message from F, it will
analyze the Grid, C.S., Min and Max values in the Grid property
subobject. But node G can only support grid granularity of 12.5
GHz and a slotwdith tuning range from 25 GHz to 200 GHz.
Considering the property of node F, node G then will respond F a
LinkSummaryNack containing a new Error_code object and state that
the property need further negotiation. Meanwhile, an accepted
grid property subobject (Grid=3, C.S.=4, Min=1, Max=4, the slot
width tuning range is set to the intersection of Node F and G) is
carried in LinkSummaryNack message. Meanwhile, the N bit in the
DATA_LINK object is set to 1, indicating that the grid property
subobject is non-negotiable.
o As the channel spacing and slot width of node F can be configured
to be any integral multiples of 6.25 GHz and 12.5 GHz
respectively, node F can support the lager granularity. The
suggested slot width tuning range is acceptable for node F. In
consequence, node F will resend the LinkSummary message carrying
the grid subobject with values of Grid=3, C.S.=4, Min=1 and Max=4.
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o Once received the LinkSummary message from node F, node G replies
with a LinkSummaryACK message. After the message exchange, the
link between node F and G is brought up supporting central
frequency granularity of 12.5 GHz and slot width tuning range
from 25 GHz to 100 GHz.
From the perspective of the control plane, once the links have been
brought up, wavelength constraint information can be advertised and
the wavelength label can be assigned hop-by-hop when establishing a
LSP based on the link grid property.
6. Security Considerations
TBD.
7. IANA Considerations
TBD.
8. References
8.1. Normative references
[G.694.1] International Telecommunications Union, "Spectral grids
for WDM applications: DWDM frequency grid", Recommendation
G.694.1, June 2002.
[G.694.2] International Telecommunications Union, "Spectral grids
for WDM applications: CWDM wavelength grid",
Recommendation G.694.2, December 2003.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4204] Lang, J., "Link Management Protocol (LMP)", RFC 4204,
October 2005.
[RFC6205] Otani, T. and D. Li, "Generalized Labels for Lambda-
Switch-Capable (LSC) Label Switching Routers", RFC 6205,
March 2011.
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8.2. Informative References
[I-D.farrkingel-ccamp-flexigrid-lambda-label]
Farrel, A., King, D., Li, Y., Zhang, F.,
"Generalized Labels for the Flexi-Grid in Lambda-Switch-
Capable (LSC) Label Switching Routers", draft-farrkingel-
ccamp-flexigrid-lambda-label-08 (work in progress),
February 2014.
[FLEX-FWK]
Dios, O., Casellas, R., Zhang, F., Fu, X., Ceccarelli, D.,
and I. Hussain, "Framework for GMPLS based control of
Flexi-grid DWDM networks", draft-ietf-ccamp-flexi-grid-
fwk-00 (work in progress), October 2013.
9. Authors' Address
Yao Li (editor)
ZTE
Email: li.yao3@zte.com.cn
Guoying Zhang (editor)
China Academy of Telecom Research, MIIT
Email: zhangguoying@catr.cn
Xihua Fu (editor)
ZTE
Email: fu.xihua@zte.com.cn
Ramon Casellas
CTTC
Email: ramon.casellas@cttc.es
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Yu Wang
China Academy of Telecom Research, MIIT
Email: wangyu@catr.cn
10. Contributors' Address
Wenjuan He (editor)
ZTE
Email: he.wenjuan1@zte.com.cn
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