Network Working Group Eiji Oki
Internet Draft NTT
Expiration Date: August 2002 Nobuaki Matsuura
NTT
Wataru Imajuku
NTT
Kohei Shiomoto
NTT
Naoaki Yamanaka
NTT
February 2002
Requirements of optical link-state information for traffic engineering
draft-oki-ipo-optlink-req-00.txt
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Abstract
In a limited/non-wavelength-convertible (LNWC) optical network, a
wavelength is restricted to be converted into another wavelength on
an optical path due to the limitation of wavelength converters at an
optical cross-connect. This document describes requirements of
optical link-state information for traffic engineering to solve the
routing and wavelength assignment (RWA) problem in LNWC network.
Additional link-information extensions for LNWC network are
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presented. By using the information, extensions of OSPF and RSVP-TE
are proposed.
1. Introduction
Traffic engineering (TE) in optical networks is useful to efficiently
utilize network resources, which are fibers, wavelengths, and node
capacities, etc. In GMPLS networks, a source node finds an
appropriate route and wavelength based on collected optical link-
state information with a routing protocol as such as Open Shortest
Path Finding (OSPF) [GMPLS-OSPF], and set up an optical path by using
a signaling protocol such as RSVP-TE [GMPLS-SIG][GMPLS-RSVP].
A wavelength-division multiplexing (WDM) optical network are mainly
categorized into two types in terms of wavelength conversion
capability. One is a limited/non-wavelength-convertible (LNWC)
optical network. The other is a wavelength-convertible (WC) optical
network.
In LNWC network, a wavelength is limitedly or not converted into
another wavelength on an optical path. Because of the limitation of
wavelength converters at optical cross-connects (OXCs), an optical
path must use the same or limited wavelength(s) through an optical
path. When an optical path is set up, the routing and wavelength
assignment (RWA) problem has to be solved. On the other hand, in WC
network, any wavelength can be converted into any wavelength at OXC
on an optical path.
This draft describe requirements of optical link-state information
for traffic engineering to solve the RWA problem. Additional link-
information extensions for LNWC network are presented. By using the
information, extensions of OSPF and RSVP-TE are proposed.
In this draft, an optical link is used as a TE-link between neighbor
OXCs or between neighbor OXC and a label switch router (LSR). We
refer OXC or LSR to a node. Component links (or ports), each of which
may corresponding to a wavelength, in one or multiple fiber(s) are
bundled into a TE-link [LINK-BUNDLE], where every wavelength
information is aggregated. Figure 1 shows an example of an optical
network model. OXC is used to refer to all categories of optical
cross-connects, irrespective of the internal switching fabric. The
left side of OXC 1 has a 3R. The right side of OXC 1, both sides of
OXC2, and LSR 2 have WDM functions. o-link 1 and o-link 2 are defined
as a single TE-link that budles multiple componet links.
LSR 1 ----- OXC 1 ====== OXC 2 ====== LSR 2
o-link 1 o-link 2
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Figure 1: Example of optical network model
2. Requirements of optical link-state information in LNWC network
Since wavelength is limitedly or not converted into another
wavelength in LNWC network, information which wavelength is reserved
in a TE-link is necessary for traffic engineering. Note that
wavelengths in more than one fiber are not considered to be bundled
into a TE-link in LNWC network, because the same wavelengths in more
than one fiber should be differently handled for a purpose of traffic
engineering. Wavelength status to indicate which wavelength is
reserved/unreserved in a TE-link. The wavelength status is used to
solve the RWA problem.
However, opaque LSA sub-TLVs, which is defined in [OSPF-TE][GMPLS-
OSPF], for a bundled TE-link between neighbor nodes do not express
the wavelength status and not advertise it. Therefore, link-
information extensions need to be added to achieve traffic
engineering in LNWC network.
3. Label Definition for Corresponding Wavelength Value
Wavelength value (e.g., 1550 nm) should be globally considered in
LNWC network. For a purpose of the advertisement of wavelength status
in a TE-link and signalling to set up an optical path, each
wavelength value should be globally defined as a label in the LNWC
network.
There are several possible ways to assign a label to the
corresponding wavelength value. One way to assign a label is to
express the wavelength value itself (unit: nm) with 4 octets field in
the IEEE floating point format. Another way is to use three types of
integer parameters, which are wavebands (C, L, S), ITU grid spacing
(e.g., 25, 50, and 100 GHz), and deviation from the reference center
frequency of the corresponding waveband.
4. OSPF extensions
To indicate the wavelength status in a TE-link between neighbor nodes,
there are two possible ways as follows.
4. 1 Explicit label scheme
Labels corresponding wavelengths with indication bits to express the
wavelength status in a TE-link between neighbor nodes are explicitly
advertised. If the status of a wavelength is changed, the
corresponding label with the indication bit are updated and
advertised. In the explicit label scheme, the information amount to
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advertise the wavelength status may be increased when the number of
used labels are large.
4. 2 Bitmap scheme
A set of labels that are used in LNWC network is advertised.
Indication bits to express the wavelength status as a label set are
advertised by using a bitmap format. In the bitmap format, the
indication bits appear in an increasing order with label values. If a
value of the indication bit is 1, the label is reserved. If a value
of the indication bit is 0, the label is reserved. Every time the
status for each wavelength is changed, label values themselves do not
need to be advertised. Instead of that, only the indication bits with
the bitmap format are advertised. When a set of the labels that are
used in the LNWC network is updated, the updated set of the labels is
advertised.
5. RSVP-TE extensions
5. 1 AND scheme
When a path message attempts to set up an optical path at each
source/transit OXC, it carries a set of unreserved labels that are
unreserved through all the TE-links from the source OXC to the
transit OXC. The label set is called an AND label set. If there is
at least a reserved label in a TE-link from the source OXC to the
transit OXC, the label is excluded in the transit node from the AND
set. If there is no label in the AND set, the transit OXC should
perform a wavelength conversion. Otherwise, the request of the
optical path set-up is rejected.
There are two possible ways to carry an AND label set of unreserved
labels, the explicit label scheme and the bitmap scheme as described
in Section 4. The explicit label scheme is considered in [GMPLS-
RSVP] as 'label set'.
5. 2 ALL scheme
When a path message attempts to set up an optical path at each
source/transit node, it carries a set of unreserved labels for all
TE-links on an optical path. The label set is called an ALL label
set. A destination node receives the ALL label set and decides which
labels should be used on the optical path. In the ALL scheme, the
destination node has several options on which node should use a
wavelength-conversion function if it is needed.
There are two possible ways to carry a set of unreserved label, the
explicit label scheme and the bitmap scheme in the same way as the
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AND scheme. Note that the ALL scheme carries each label set for all
the TE-links on the optical path, while the AND scheme carries a
label set for each optical path.
6. Requirements of optical link-state information in WC Network
Since any wavelength can be converted into any wavelength at OXC,
information which wavelength is reserved in a TE-link is not
necessary. The number of wavelengths (NW) and the number of
unreserved wavelengths (NUW) in a TE-link are used for traffic
engineering. For example, a least-loaded path finding algorithm is
employed to find an appropriate optical path.
The optical-link information in a TE-link between two neighbor nodes
is advertised. Therefore, multiple ports of OXC, each of which is
corresponding to each wavelength may be combined into a TE-link. In
OSPF extensions, opaque LSA sub-TLVs includes maximum reservable
bandwidth and unreserved bandwidth, which sub-TLV types are 7 and 8,
respectively. NW and NUW are expressed by using maximum reservable
bandwidth and unreserved bandwidth for a bundled TE-link between
neighbor nodes in the following. .nf NW = maximum reservable
bandwidth for a bundled TE-link
= sum of maximum reservable bandwidth of all component links
and
NUW = unreservable bandwidth for a bundled TE-link
= sum of unreservable bandwidth of all component links.
Note that NW is not the number of wavelength in a fiber, but is the
number of ports, in other words, wavelengths, of OXC in a TE-link.
However, the units of the maximum reservable bandwidth and
unreservable bandwidth are defined as byte per second [GMPLS-OSPF].
Since the values of NUW and NW are independent of byte per second,
the modification of the units or a sub-TLV definition is needed.
7. References
[OSPF-TE] Katz, D., Yeung, D., "Traffic Engineering Extensions to
OSPF", draft-katz-yeung-ospf-traffic-06.txt (work in progress)
[GMPLS-OSPF] Kompella, K., Rekhter, Y., Banerjee, A. et al, "OSPF
Extensions in Support of Generalized MPLS", draft-ietf-ccamp-ospf-
gmpls-extensions-00.txt (work in progress)
[GMPLS-SIG] "Generalized MPLS - Signaling Functional Description",
draft-ietf-mpls-generalized-signaling-04.txt (work in progress)
[GMPLS-RSVP] "Generalized MPLS Signaling - RSVP-TE Extensions",
draft-ietf-mpls-generalized-rsvp-te-07.txt (work in progress)
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[GMPLS-ROUTING] "Routing Extensions in Support of Generalized MPLS",
draft-ietf-ccamp-gmpls-routing-02.txt (work in progress)
[LINK-BUNDLE] Kompella, K., Rekhter, Y., Berger, L., "Link Bundling
in MPLS Traffic Engineering", draft-ietf-mpls-bundle-01.txt (work in
progress)
8. Authors' Addresses
Eiji Oki
NTT Corporation
3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan
Email: oki.eiji@lab.ntt.co.jp
Nobuaki Matsuura
NTT Corporation
3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan
Email: matsuura.nobuaki@lab.ntt.co.jp
Wataru Imajuku
NTT Corporation
1-1 Hikari-no-oka,
Yokosuka, Kanagawa, 239-0847 Japan
Email: imajyuku@exa.onlab.ntt.co.jp
Kohei Shiomoto
NTT Corporation
3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan
Email: shiomoto.kohei@lab.ntt.co.jp
Naoaki Yamanaka
NTT Corporation
3-9-11 Midori-cho,
Musashino-shi, Tokyo 180-8585, Japan
Email: yamanaka.naoaki@lab.ntt.co.jp
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