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Versions: 00 01 02
CCAMP working Group W. Imajuku
Internet-Draft Y. Sone
Updates: RFC 4202 NTT
Proposed Status: Standards Track I. Nishioka
Expires January 2008 NEC
S. Seno
Mitsubishi Electric Corporation
July 2007
Routing Extensions to Support Network Elements with Switching Constraint
draft-imajuku-ccamp-rtg-switching-constraint-02.txt
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Abstract
This document shares problem statements of the routing of optical
Label Switched Paths(LSPs) over network elements with blocking switch
architecture in fiber port selectivity. Also, this document provides a
direction of solution to take into account the switching constraint
within the scope of GMPLS Traffic Engineering (TE) over network elements
with blocking switch architecture in fiber port selectivity in addition
to wavelength selectivity.
Table of Contents
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
3. Problem Statements . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Problem Statements . . . . . . . . . . . . . . . . . . . . 3
3.2. Problem Example . . . . . . . . . . . . . . . . . . . . . 3
3.3. Comments on Necessity of Extension . . . . . . . . . . . . 4
4. Proposal for GMPLS Routing Enhancement . . . . . . . . . . . . 5
4.1. Possible Routing Enhancement . . . . . . . . . . . . . . . 5
4.2. Comments on Other Possible Solutions . . . . . . . . . . . 5
5. Compatibility and Inter-domain Issues . . . . . . . . . . . . 5
6. Security Considerations. . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative references . . . . . . . . . . . . . . . . . . 6
8.2. Informative references . . . . . . . . . . . . . . . . . . 6
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7
10. Authors' Addresses . . . . . . . . . . . . . . . . . . . . . 7
Intellectual Property and Copyright Statements . . . . . . . . . . 7
Copyright Statement. . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
The routing protocol extensions so far have been developed for
Generalized Multi-Protocol Switching (GMPLS)[OSPF-TE],[GMPLS-ROUTING],
[GMPLS-OSPF]. This document explains the necessity of routing
extensions required to support GMPLS Traffic Engineering (TE) over
network elements with blocking switch architecture in fiber port
selectivity in addition to wavelength selectivity.
A reconfigurable optical add/drop multiplexer (ROADM) is a network
element that employs the blocking switch architecture widely used in
commercialized networks. The ROADM has switching constraints with
respect to selecting the fiber port when adding/dropping a lambda path
from/to a tributary port. The lambda path added from each tributary
port is restricted to either east or west fiber port of the ROADM ring.
Similarly, the dropping of a lambda path connected to the tributary
port also has a constraint with respect to the selection of the
tributary port.
The objective of this document is to share problem statement within
this community and to provide a direction of solution to support the
routing of Optical Label Switched Paths with blocking switch
architecture having the constraint of selecting fiber ports.
2. 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].
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3. Problem Statements
3.1. Problem Statements
Many lambda switch capable (LSC) nodes such as ROADM and Optical
Cross-Connects (OXC) employ the blocking switch architecture to reduce
the cost of the switch fabric or wavelength converters. In particular,
the ROADM, which was already commercially deployed, employs a unique
switch architecture that has a constraint with respect to the TE link
selectivity, while the OXC without wavelength converters has a
constraint with respect to wavelength label selectivity.
For the wavelength label selectivity constraint, GMPLS has a
specification to control the label allocation mechanism for Label
Switch Paths (LSPs) based on the signaling mechanism [RFC3471],
[RFC3473]. On the contrary, for the TE link selectivity constraint,
there is currently no specification.
To address this issue regarding the TE link selectivity constraint,
it is clear that an extension to the GMPLS routing mechanism is
essential for all network elements in a domain in order to understand
which TE link can be selected to forward LSPs at the network elements
that have the constraint.
3.2. Problem Example
Figure shows a typical example using ROADM systems and ROADM ring
network architecture to illustrate the TE link selectivity constraint.
In this example, we assume that each ROADM switches optical signals
(LSPs) transparently and a ROADM system comprises four tributary
interfaces, i.e., w1, w2, e1, and e2. Lambda LSPs from TE-Wx can only
be dropped to w1 or w2, and lambda LSPs can only be added from e1 and e2,
if these LSPs are forwarded to TE-Ex. Similarly, lambda LSPs from TE-Ex
can only be dropped from e1 or e2, and lambda LSPs can only be added
from w1 and w2 if these LSPs are forwarded to TE-Wx. Thus, the ports
for each ROADM are grouped into "west" and "east" ports from the
viewpoint of TE link selectivity.
________________________________________________
| ROADM __ __ __ __ |
| |Rx| |Rx| |Tx| |Tx| |
| w1 |__| |__|w2 e1 |__| |__|e2 |
| /|\ /|\ \|/ \|/ |
| __|____|___ ___|____|__ |
| /|->-| |-->--| |->-|\ |
| | |->-| Drop |-->--| Add |->-| | |
--->----| |->-| |-->--| |->-| |---->----
| | |->-| switches |-->--| switches |->-| | |
| \|->-|___________|-->--|___________|->-|/ |
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TE-Wx | ___________ ___________ | TE-Ex
| /|-<-| |--<--| |-<-|\ |
| | |-<-| Add |--<--| Drop |-<-| | |
----<----| |-<-| |--<--| |-<-| |----<---
| | |-<-| switches |--<--| switches |-<-| | |
| \|-<-|___________|--<--|___________|-<-|/ |
| /|\ /|\ \|/ \|/ |
| |_ |_ |_ |_ |
| |Tx| |Tx| |Rx| |Rx| |
| |__| |__| |__| |__| |
| w1 w2 e1 e2 |
|________________________________________________|
In a ring network using ROADM systems, a lambda LSP added from a west
tributary port cannot be dropped to a "west" tributary port at another
node, and this is also true for the "east" bound case.
For example, a lambda LSP added from tributary port w1 of ROADM #1
cannot be dropped to tributary port w1 or w2 of ROADM #2, #3, or #4.
Similarly, a lambda LSP added from tributary port e1 of ROADM #1
Cannot be dropped to tributary port e1 or e2 of ROADM #2, #3, or #4.
_________ _________
| | TE #1-E | | TE #2-E
==========|ROADM #1|==============|ROADM #2|==========
|| TE #1-W |_________| TE #2-W |_________| ||
|| | | | | | | | | ||
||Tributary w1 w2 e1 e2 Tributary w1 w2 e1 e2 ||
|| ||
|| ||
|| _________ _________ ||
|| | | TE #4-W | | TE #3-W ||
==========|ROADM #4|==============|ROADM #3|==========
TE #4-E |_________| TE #3-E |_________|
| | | | | | | |
Tributary e1 e2 w1 w2 Tributary e1 e2 w1 w2
3.3. Comments on Necessity of Extension
The problem described in the previous section is not so critical if
the network comprises a single ROADM ring network. In such a case,
the routing of LSPs can be performed based on static routing without
using any routing protocols. Assignment of a destination node ID
with a loose option in the Explicit Route Object (ERO) of the
signaling message and execution of loose hop expansion [RFC3209]
in each ROADM may result in successfully establishing an LSP.
Employing an inter-domain routing architecture can also be a
solution [per-domain-calc]. By separating ROADM rings from a GMPLS
routing domain, the nodes outside the ROADM domain assign a ROADM
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node ID or boundary node adjacent to the ROADM domain with a loose
ERO to forward the Lambda LSP. Then, each ROADM node performs loose
hop expansion to forward the lambda LSP toward the destination.
The case that essentially requires an extension of the GMPLS routing
mechanism is the case in which the ROADM and other Lambda or Fiber
Switch capable nodes co-exist in the same routing domain. Packet and
TDM switch capable nodes attached to such a domain must also consider
the TE link selectivity constraint at the ROADM nodes when creating a
Lambda LSP.
4. Proposal for GMPLS Routing Enhancement
4.1. Possible Routing Enhancement
This section proposes advertising the TE link selectivity constraint
as a solution. The extended sub-TLVs indicate the list of selectable
and/or unselectable TE links from the TE link indicated in sub-TLV
Type 2 (Link ID).
The possible extensions to sub-TLV are described below.
Sub-TLV Type Length Name
TBD variable Selectable numbered TE link list
TBD variable Unselectable numberd TE link list
TBD variable Selectable unnumberd TE link list
TBD variable Unselectable unnumberd TE link list
4.2. Comments on Other Possible Solutions
Employing a virtual TE link model as discussed in L1-VPN WG is also
a possible solution [l1-vpn-frwk]. An optical network domain that
has a switching constraint can be modeled as an abstract mesh network.
Note that this routing architecture requires a hierarchical routing
mechanism in each border node of the optical network domain.
5. Inter-domain and Compatibility Issues
Note that it is essential to share switching constraint information
pertaining to each node in order for the border nodes to advertise
abstract information to other network domains.
Also, note that it is essential to share switching constraint information
pertaining to each node with the Path Computation Element (PCE), if the
PCE based inter-domain routing architecture is employed.
There should be no interoperability issues with routers that do not
implement these extensions, as the Opaque LSAs will be silently
ignored.
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6. Security considerations
TBD
7. IANA considerations
TBD
8. References
8.1 Normative References
[RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic
Engineering (TE) Extensions to OSPF Version 2", RFC
3630, September 2003.
[RFC4202] Kompella, K., Ed., and Y. Rekhter, Ed., "Routing
Extensions in Support of Generalized Multi-Protocol
Label Switching (GMPLS)", RFC 4202, October 2005.
[RFC4203] Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF
Extensions in Support of Generalized Multi-Protocol
Label Switching (GMPLS)", RFC 4203, October 2005.
[RFC3471] Berger, L., et al, "Generalized Multi-Protocol
Label Switching (GMPLS) Signaling Functional
Description", RFC 3471, January 2003.
[RFC3473] Berger, L., et al, "Generalized Multi-Protocol
Label Switching (GMPLS) Signaling Resource
ReserVation Protocol-Traffic Engineering (RSVP-TE)
Extensions", RFC 3473, January 2003.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T.,
Srinivasan, V. and G. Swallow, "RSVP-TE:
Extensions to RSVP for LSP Tunnels",
RFC 3209, December 2001.
8.2 Informative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119,
March 1997
[per-domain-calc] Vasseur, J. P., Ayyanger, A., Zhang, R., "A Per-
domain path computation method for establishing
Inter-domain Traffic Engineering (TE) Label
Switched Paths (LSPs)", RFC 3471, January 2003.
[l1-vpn-frwk] Takeda, T (editor), "Framework and Requirements
for Layer 1 Virtual Private Networks",
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work in progress.
9. Acknowledgements
The authors would like to thank Eiji Oki, Tomonori Takeda, Akira
Nagata, and Akira Chugo for helpful discussion.
10. Authors' Addresses
Wataru Imajuku
NTT Network Innovation Laboratories
1-1 Hikari-no-oka, Yokosuka, Kanagawa 239-0847
Japan
Phone: +81 46 859 4315
Email: imajuku.wataru@lab.ntt.co. jp
Yoshiaki Sone
NTT Network Innovation Laboratories
1-1 Hikari-no-oka, Yokosuka, Kanagawa 239-0847
Japan
Phone: +81 46 859 2456
Email: sone.yoshiaki@lab.ntt.co.jp
Itaru Nishioka
NEC Corp.
1753 Simonumabe, Nakahara-ku, Kawasaki, Kanagawa 211-8666
Japan
Phone: +81 44 396 3287
Email: i-nishioka@cb.jp.nec.com
Shoichiro Seno
Mitsubishi Electric Corporation
5-1-1 Ofuna, Kamakura, Kanagawa 247-8501
Japan
Phone: +81 467 41 2881
Email: Senoo.Shoichiro@dc.MitsubishiElectric.co.jp
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