Network Working Group Y. Li
Internet-Draft ZTE
Intended status: Standards Track January 21, 2012
Expires: July 24, 2012
Link Management Protocol Extensions for Grid Property Negotiation
draft-li-ccamp-grid-property-lmp-00
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem statement . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Flexi-fixed Grid Nodes Interworking . . . . . . . . . . . 3
3.2. Flexible Grid Capability Negotiation . . . . . . . . . . . 4
4. LMP extensions . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Grid Property Subobject . . . . . . . . . . . . . . . . . 5
5. Messages Exchange Procedure . . . . . . . . . . . . . . . . . 7
5.1. Flexi-fixed Grid Nodes Messages Exchange . . . . . . . . . 7
5.2. Flexible Nodes Messages Exchange . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8.1. Normative references . . . . . . . . . . . . . . . . . . . 9
8.2. Informative References . . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
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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. Flexible grid network is
composed of arbitrarily assigned spectral slots. That is the
adjacent channel spacing and spectral bandwidth per wavelength are
variable. Mixed bitrate transmission systems can allocate their
channels with different spectral bandwidths so that they can be
optimized for the bandwidth requirements of the particular bitrate
and modulation scheme of the individual channels. This technique is
regarded to be a promising way to improve the network utilization
efficiency and fundamentally reduce the cost of the core network.
While during the practical deployment procedure, the fixed grid
optical nodes will be replaced by the flexible nodes gradually. This
will lead to the problem of interworking between fixed grid DWDM and
flexible grid DWDM nodes. Besides, even two flexible grid optical
nodes may have different grid properties, leading to link property
conflict. Therefore, 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 .
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. Problem statement
3.1. Flexi-fixed Grid Nodes Interworking
+---+ +---+ +---+ +---+ +---+
| A |---------| B |=========| C |=========| D +--------+ E |
+---+ +---+ +---+ +---+ +---+
figure 1
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^ ^ ^ ^ ^
| | | | |
__|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_|_
n= -16 -14 -12 -10 -8 -6 -4 -2 0 2 4 6 8 10 12 14 16
Central frequency granularity=6.25 GHz (Node B,D)
^ ^ ^ ^ ^
| | | | |
|<----50GHz---->|<----50GHz---->|<----50GHz---->|<----50GHz---->|
__|_______________|_______________|_______________|_______________|_
Fixed channel spacing of 50 GHz (Node C)
figure 2
Figure 1 shows an example of interworking between flexible and fixed
grid nodes. Node A, B, D, E support flexible grid. All these nodes
can support frequency slots with central frequency granularity of
6.25 GHz and slotwidth granularity of 12.5 GHz. At the same time,
the channel spacing and slotwidth can be configured to integral
multiple of 6.25 GHz and 12.5 GHz respectively. As shown in figure
2, they are backward compatible to the fixed grid situation (flexible
frequency slot with channel spacing of 8*6.25 and slotwidth of 4*12.5
GHz is equivalent to fixed-grid DWDM channel 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.
3.2. Flexible Grid Capability Negotiation
+---+ +---+
| 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
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Although the updated version of ITU-T [G.694.1] has defined the
flexible grid with a nominal central frequency granularity of 6.25
GHz and a slotwidth granularity of 12.5 GHz. However, devices or
applications that make use of the flexible grid may not have to be
capable of supporting every possible slotwidth or position. In other
words, applications may be defined where different grid granularity
can be supported. For example, an application could be defined where
the nominal central frequency granularity is 12.5 GHz and that only
requires slotwidths as a multiple of 25 GHz. Therefore the link
between the two grid granularity nodes must be set to align with the
larger one. Besides, different nodes may have different slotwidth
tuning ranges. For example, in figure 3, node F can only support
slotwidth 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
slotwidth tuning range between F and G sholud be chosen as an
intersection from 25 GHz to 100 GHz.
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. LinkSummary message contains negotiable and non-
negotiable DATA_LINK objects to carry a series of variable-length
data items called subobjects to illustrate the detailed link
properties. The subobjects are defined in Section 12.12.1 in
[RFC4204].
To slove the problems stated in section 3, this draft extends the LMP
by introducing a new DATA_LINK subobject called "Grid property" to
support 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 |Grid | C.S. | 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
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CWDM [G.694.2]. Value defined in
[I-D.farrkingel-ccamp-flexigrid-lambda-label] identifies flexible
DWDM.
+---------------+-------+
| Grid | Value |
+---------------+-------+
| Reserved | 0 |
+---------------+-------+
| ITU-T DWDM | 1 |
+---------------+-------+
| ITU-T CWDM | 2 |
+---------------+-------+
| Flexible DWDM | 3 |
+---------------+-------+
| Future use | 4-7 |
+---------------+-------+
C.S.:
With respect to the fixed grid node/interface, the C.S. value is used
to represent the channel spacing, as the spacing between adjacent
channels is constant. While, for flexible grid node/interface, this
field should be used to represent the central frequency granularity.
+------------+-------+
| C.S. (GHz) | Value |
+------------+-------+
| Reserved | 0 |
+------------+-------+
| 100 | 1 |
+------------+-------+
| 50 | 2 |
+------------+-------+
| 25 | 3 |
+------------+-------+
| 12.5 | 4 |
+------------+-------+
| 6.25 | 5 |
+------------+-------+
| Future use | 6-15 |
+------------+-------+
Min & Max:
The slotwidth tuning range. For example, with regarding to a node
with central frequency granularity of 6.25 (slotwidth granularity of
12.5 GHz) and slotwidth tuning range from 25 GHz to 100 GHz, the
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values of Min and Max should be 2 and 8 respectively. For fixed grid
nodes, these two fields is meaningless and should be set to zeros.
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. The LMP meessages start running from
node B to node C.
o After inspecting its own node/interface property, node B will send
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, C.S. value in the grid property
subobject are set to be 3 and 5 respectively. The slotwidth
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 has received the LinkSummary message from B, it will
analyze the Grid, C.S., Min and Max values in the grid property
subobject. But node C can only support fixed grid DWDM and
recognize that flexible grid property is not acceptable for the
link. However, the receiving N bit in the DATA_LINK object is
set, indicating that the Grid property of B is negotiable. Then,
node C will respond B a linkSummaryNack containing a new
Error_code object and state that the property need 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 slotwidth of node B can be configured
to be any integral multiples of 6.25 GHz and 12.5 GHz
respectively, node B can be compatible to support the fixed DWDM
values. Then, node B will resend the LinkSummary message carrying
the grid property subobject with values of Grid=2 and C.S.=2.
o Once receiving the LinkSummary message from node B, node C will
reply with a LinkSummaryACK message. After all these are done,
the link between node B and C is brought up with a fixed channel
spacing of 50 GHz.
The above mentioned grid property correlation scenario starts sending
message from flexible grid node to fixed grid node. While for
message from fixed grid node to flexible grid node, the procedure is
as follows:
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o After inspecting its own interface property, Node C will send 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 slotwidth of node B can be configured
to be any integral multiples of 6.25 GHz and 12.5 GHz
respectively, node B can be compatible to support the fixed DWDM
parameters. Then, node B will make appropriate configuration and
reply node C the LinkSummaryACK message.
o After all these are done, 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, the model
shown in figure 3 is reused. The procedure of grid property
correlation (negotiating the grid granularity and slotwidth 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
slotwidth 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 be compatible to support the lager
granularity. And the suggested slotwidth tuning range is
acceptable for node F. Then, node F will resend the LinkSummary
message carrying the grid subobject with values of Grid=3, C.S.=4,
Min=1 and Max=4.
o Once receiving the LinkSummary message from node F, node G will
reply with a LinkSummaryACK message. After all these are done,
the link between node F and G is brought up supporting central
frequency granularity of 6.25 GHz and slotwidth tuning range from
25 GHz to 100 GHz.
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From the prospective of control plane, once the links have been
brought up, wavelength constraint informations can be advertised and
the wavelength label can be assigned hop-by-hop when establishing a
LSP based on the link grid property.
6. IANA Considerations
TBD
7. Security 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.
8.2. Informative References
[I-D.farrkingel-ccamp-flexigrid-lambda-label]
King, D., Farrel, A., Li, Y., Fei, Z., and R. Casellas,
"Generalized Labels for the Flexi-Grid in Lambda-Switch-
Capable (LSC) Label Switching Routers",
draft-farrkingel-ccamp-flexigrid-lambda-label-01 (work in
progress), October 2011.
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Author's Address
Yao Li
ZTE
Email: li.yao3@zte.com.cn
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