New individual draft on "Requirements for MPLS over GMPLS"
Xu Shao <[email protected]> Thu, 16 Oct 2003 02:44:32 -0700 (PDT)
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Hi, all,
I think it is time for us to look ahead to focus on more specific and unique requirements on the interconnection of MPLS based Internet with GMPLS based optical networks, which is an important milestone in the evolvement of NGN.
After the completion of IP-centric control plane, it is time to concentrate "IP over WDM" study on how to connect other client networks with GMPLS-based optical networks.
Therefore, I write an individual draft named "Requirements for MPLS over GMPLS". It can be found at http://www.ietf.org/internet-drafts/draft-xushao-ipo-mplsovergmpls-00.txt or you can find it as attached.
Any comments are welcome.
Best regards,
Shao Xu
---------------------------------
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<DIV>
<DIV>Hi, all,</DIV>
<DIV> </DIV>
<DIV>I think it is time for us to look ahead to focus on more specific and unique requirements on the interconnection of MPLS based Internet with GMPLS based optical networks, which is an important milestone in the evolvement of NGN. </DIV>
<DIV> </DIV>
<DIV>After the completion of IP-centric control plane, it is time to concentrate "IP over WDM" study on how to connect other client networks with GMPLS-based optical networks. </DIV>
<DIV> </DIV>
<DIV>Therefore, I write an individual draft named "Requirements for MPLS over GMPLS". It can be found at <A href="http://www.ietf.org/internet-drafts/draft-xushao-ipo-mplsovergmpls-00.txt">http://www.ietf.org/internet-drafts/draft-xushao-ipo-mplsovergmpls-00.txt</A> or you can find it as attached.</DIV>
<DIV> </DIV>
<DIV>Any comments are welcome.</DIV>
<DIV> </DIV>
<DIV>Best regards,</DIV>
<DIV>Shao Xu</DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV>
<DIV> </DIV></DIV><p><hr SIZE=1>
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Content-Type: text/plain; name="draft-xushao-ipo-mplsovergmpls-00.txt"
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IP over Optical Working Group
Internet Draft
Expiration Date: April 2004 Xu Shao
Institute for Infocomm Research
Tee Hiang Cheng
Institute for Infocomm Research
Nanyang Technological University
Kumaran Veerayah
Institute for Infocomm Research
October 2003
Requirements for MPLS over GMPLS-based Optical Networks
(MPLS over GMPLS)
draft-xushao-ipo-mplsovergmpls-00.txt
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts. Internet-Drafts are draft documents valid for a maximum of
six months and may be updated, replaced, or obsoleted by other
documents at any time. It is inappropriate to use Internet- Drafts
as reference material or to cite them other than as "work in
progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
Abstract
MPLS over GMPLS-based optical networks (MPLS over GMPLS) is a subset
of IP over optical networks. To be more specific, in this draft it
refers to the technology of interconnection between MPLS networks and
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GMPLS-based optical networks with an overlay model or an interdomain
model. It is an important milestone in the evolutionary roadmap from
IP over static WDM to a peer model of network interconnections. The
most significant feature of the requirements for MPLS over GMPLS is a
much more dynamic interface between the two layers. The draft
discusses the evolutionary roadmap of IP over optical networks and
then highlights the significance of the concept of MPLS over GMPLS.
Some new requirements will be identified, including multi-lightpath
connections, MPLS network topology dynamic changes and dynamic
traffic grooming and so on. It is these requirements that bring some
challenges to the present routing, signaling and UNI protocols.
Table of Contents
1. Summary for Sub-IP Area........................................2
1.1 Summary....................................................3
1.2 Where does it fit in the Picture of the Sub-IP Work........3
1.3 Why is it Targeted at this WG..............................3
1.4 Justification of Work......................................3
2. Specification of Requirements..................................3
3. Introduction...................................................3
3.1 Terminology................................................4
4. Overview of MPLS over GMPLS Service Model and Requirements.....5
4.1 Evolutionary Roadmap of IP over Optical Networks...........5
4.2 Overview of MPLS over GMPLS................................6
4.3 Why MPLS over GMPLS?.......................................7
4.4 Requirements for MPLS over GMPLS...........................8
5. Dynamic Use of Multi-lightpath Connections between Two LSRs....9
6. Dynamic Topology Changes of MPLS Networks.....................11
7. Dynamic Traffic Grooming......................................12
8. Virtual Wavelength Assignment (VWA) Problem...................14
9. MPLS Survivability versus GMPLS Survivability.................14
9.1 MPLS survivability Only...................................15
9.2 GMPLS survivability Only..................................15
9.3 Integrated Survivability..................................15
9.4 QoS Mapping...............................................15
10. Topology Driven Label Assignment in MPLS over GMPLS Networks.15
11. Multicast in MPLS over GMPLS Networks........................16
12. Interdomain Interconnections.................................16
13. Security Considerations......................................16
14. Acknowledgements.............................................16
15. References...................................................16
16. Author's Addresses...........................................17
17. Full Copywrite Statement.....................................18
1. Summary for Sub-IP Area
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1.1 Summary
Please see the abstract above.
1.2 Where does it fit in the Picture of the Sub-IP Work
This work fits in the IP over Optical (Ipo) working group.
1.3 Why is it Targeted at this WG
This draft is targeted at the IPO WG because it specifies the
requirements for MPLS over GMPLS-based optical networks, a subset of
IP over WDM. MPLS over GMPLS has many new features in requirements
that have not been discussed in related drafts so far [IPO-FRAMWORK].
1.4 Justification of Work
The IPO WG should consider this document since it provides many new
and practical features in requirements that have not been encompassed
by the current requirements of IP over optical networks.
2. Specification of Requirements
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. Introduction
MPLS over GMPLS-based optical networks (MPLS over GMPLS) is a subset
of IP over optical networks. In this draft it refers to the
technology of interconnection between MPLS networks and GMPLS-based
optical networks with an overlay model or an interdomain model. It is
an important stage in the evolution from IP over static WDM to a peer
model of network interconnections. Even if someday the peer model of
network interconnections is mature, the MPLS over GMPLS model is
still very useful and popular for technical and managerial reasons.
MPLS over GMPLS has some unique requirements, which are different
from the general requirements for IP over optical networks studied in
the IP over Optical (Ipo) working group of IETF. MPLS over GMPLS
allows a much more dynamic interface between the two layers. In view
of the important role played by MPLS over GMPLS now and in the
future, it is necessary for us to focus the study on the requirements
for MPLS over GMPLS.
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The draft discusses the evolutionary roadmap of IP over WDM and then
highlights the significance of the concept of MPLS over GMPLS. Some
new requirements will be identified and highlighted in the draft,
including multi-lightpath connections, MPLS network topology dynamic
changes and dynamic traffic grooming and so on.
3.1 Terminology
IP over static WDM (IP over WDM):
---------------------------------
In this kind of interconnection model, IP routers are directly
connected with lightpaths provided by optical networks. The route
computation and wavelength assignment of the lightpaths and the
establishment of the lightpaths are performed manually or by a
centralized network management system (NMS). The IP networks
connected by the optical networks do not support MPLS.
MPLS over static WDM (MPLS over WDM):
---------------------------------
In this kind of interconnection model, the clients of the optical
network are MPLS networks, which have explicit routing and Internet
Traffic Engineering (TE) capability. The optical network is still a
static network without GMPLS signaling support.
IP over GMPLS-based optical network (IP over GMPLS):
---------------------------------
In this kind of interconnection model, the clients of the optical
network are the traditional IP networks, but the optical network has
a proprietary or standard GMPLS-based control plane, which can
support dynamic lightpath provisioning and restoration.
MPLS over GMPLS-based optical network (MPLS over GMPLS):
---------------------------------
In this kind of interconnection model, the clients of the optical
network are the MPLS networks. It may be GMPLS-aware or GMPLS-
unaware. If an MPLS network can recognize the GMPLS signalings and
topology description of optical networks, it is called GMPLS-aware.
Otherwise, it is GMPLS-unaware. The optical networks have a
proprietary or standard GMPLS-based control plane. There is an UNI
between the two networks.
Virtual Wavelength Assignment (VWA):
---------------------------------
Across the interface between MPLS networks and GMPLS-based optical
networks, it may have several wavelength connections. The MPLS
network may use part or all the connections at any time according to
its instantaneous bandwidth requirements. In order to ensure all the
process to be dynamic and avoid any manual operation, the connections
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across the interface must be established in advance, although we need
not establish any real lightpaths. In the wavelength convertible
GMPLS-based WDM network, we can choose wavelength in random, but in
wavelength continuous network, the initial selection of wavelength
will affect the optical network performance in the future. We refer
this as Virtual Wavelength Assignment (VWA) problem in the context.
4. Overview of MPLS over GMPLS Service Model and Requirements
4.1 Evolutionary Roadmap of IP over Optical Networks
The evolvement of IP over optical networks relies on the progress of
IP technology, optical network technology and the common control
plane technology - GMPLS. The final objective of IP over optical
networks is to achieve a dynamic, flexible and resilient network
interaction architecture by using a standard common control plane.
Thus IP over optical networks has two aspects. One aspect is on the
IP-centric common control and measurement plane called GMPLS, and the
other aspect is on how to efficiently connect the IP networks with
the optical networks. The former aspect is mainly done by CCAMP
working group in IETF now. In the draft, we pay more attention to the
latter.
GMPLS is a universal control plane not only for IP networks but also
for WDM optical networks. It can support overlay model, interdomain
model and peer model of IP over optical networks. GMPLS may not be
achieved in one step. Therefore, it is important to find the roadmap
of evolution. The roadmap can be summarized as follows:
-- Initially, IP over static WDM (IP over WDM). In this stage, the
lightpaths required by IP routers are configured manually or by a
centralized network management system. There is no signaling involved
in the total process in terms IP network, optical network and their
interfaces. This is a static overlay interconnection model for IP
over optical networks.
-- Next, MPLS over static WDM (MPLS over WDM), or IP over GMPLS-based
optical networks (IP over GMPLS). With the independent evolution of
IP network technology and optical network technology, the
architecture of data communication networks and optical communication
networks are changing significantly. The next stage for IP networks
is the enhancement of MPLS capability, while he next stage for WDM
optical network is a GMPLS-based optical network, which can
dynamically provide lightpaths and restoration. During the course of
evolvement, IP over WDM becomes either MPLS over WDM or IP over
GMPLS. Generally speaking, in this stage, there may be a simple UNI
signaling, but sometimes manual operation and configuration is
unavoidable.
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-- Then, MPLS over GMPLS based optical networks (MPLS over GMPLS). In
this stage, the optical network can support GMPLS and the IP network
is upgraded into the MPLS network. Sometimes, the interconnection
model between the two layers is an overlay model or a loose inter-
domain model. This is a very important milestone, which enables us to
set up LSPs (MPLS LSPs or optical LSPs) across the interfaces totally
automatically on the basis of optimization of data and optical
network resources by taking advantage of the traffic engineering
capabilities from MPLS as well as GMPLS.
-- Eventually, integrated GMPLS networks. The premise is that both IP
networks and optical networks can support standard GMPLS. At this
stage, the two networks can be connected freely, with an overlay
model, a interdomain model or a peer model. If the overlay model or
interdomain model is used, in terms of requirements, actually there
are no essential differences from the MPLS over GMPLS in the last
stage. That is why to study the requirements for MPLS over GMPLS is
so meaningful.
The following figure shows the evolutionary roadmap of IP over
optical network technologies.
IP ----------------------->MPLS ---------------------->GMPLS
network network Aware
| \ / | |
| \ / | |
IP over IP over GMPLS MPLS over GMPLS Integrated
WDM or MPLS over WDM | Interconnection
| / \ | |
| / \ | |
Static ------------>Partially standard GMPLS------------>GMPLS
WDM network
|<- Stage I ->|<--Stage II-->|<--Stage III-->|<---Stage IV---->|
4.2 Overview of MPLS over GMPLS
As discussed above, Generally MPLS over GMPLS refers to an overlay
model or inter-domain model of interaction between GMPLS-based
optical network and MPLS-based Internet. For the overlay model, from
the perspective of the MPLS networks, MPLS LSRs are connected by the
Optical Virtual Private Networks (OVPNs). All the LSRs connected by
the optical networks can belong to the same routing area or the same
autonomous system (AS). For the interdomain model, the optical
network is regarded as an autonomous system, different autonomous
systems exchange topology information by some border routing
protocols, for instance, BGP4.
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It is necessary for us not only use the traffic engineering and
dynamic features in the MPLS network and GMPLS networks internally,
but also extend these features across their interfaces. Above of all,
once the interfaces are connected, MPLS and GMPLS provide the
possibility that these interfaces can be adaptively used according to
the bandwidth requirements. Therefore, the connection model between
MPLS layer and GMPLS-based optical layer should be a dynamic and
adaptive model. The following is an illustration of interconnection
of MPLS over GMPLS. There may be multi-lightpath connections between
LSR and OXC. Even if there are connections between an LSR and an OXC,
it does mean there should be equal lightpaths established in the
optical networks, since the LSR may select to use part of all the
connections according to its bandwidth requirements. Moreover, an LSR
connected with an OXC may try to request a lightpath with any LSRs
connected by the optical networks if it has its identifiers,
depending the interconnections models.
+-------------+ +----------------------------+ +-------------+
| +---+ | | +---+ +---+ +---+--+====+-+---+ |
| +---+LSR+-+----+--+OXC+----+OXC+-----+OXC+--+====+-+LSR+---+ |
| | +-+-+ | | +---+ /+---+ +---+--+====+-+-+-+ | |
| +---+ | | | | / GMPLS-based | | | | +-+-+ |
| |LSR| | | | | / WDM Networks | | | | |LSR| |
| +-+-+ +-+-+ | | +---+/ +---+ | | +-+-+ +-+-+ |
| +---+LSR+-+----+--+OXC+--------------+OXC+--+----+-+LSR+---+ |
| +-+-+ | | +-+-+ +---+ | | +---+ |
| MPLS | | +-----\----------------/-----+ | MPLS |
+---------+---+ \ / +-------------+
| +---------\--------/---------+
| | \+---/ |
| | +------+LSR|-----+ |
| | | +---+ | |
| | +---+ MPLS +---+ |
+--------+---+LSR+------------+LSR+ |
| +---+ +---+ |
+----------------------------+
4.3 Why MPLS over GMPLS?
There are enormous reasons that make MPLS over GMPLS so attractive.
-- Even if a peer interconnection is possible, it is not always very
competitive due to its complexity in management and insecurity. A
functional division is necessary. Sometimes, a well-designed MPLS
over GMPLS architecture and interfaces can achieve the same optimal
objectives as a peer interconnection model is able to provide.
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-- MPLS network may not recognize the GMPLS protocols, i.e., the MPLS
network is GMPLS-unaware. In this scenario, the network architecture
is unable to be built with peer model.
-- The two networks sometimes belong to two different network
operators. The optical network operator does not want the customers
to have its topology for security reason.
-- In IP over GMPLS, the interface between IP networks and GMPLS
networks can only be dynamically used by the router directly
connected with the optical networks. Other routers have no means to
control the interface, although they may be aware of the interfaces.
With the enhancement of traffic cotrol ability in MPLS, the interface
will be able to be dynamically used by either LSRs in the MPLS
networks. This enables the dynamic use of the MPLS/GMPLS interfaces
to optimize the network resource from the perspective of total
network, on a node or interface.
-- As a connectionless routing network, IP has not provided the
measures to use backup or restoration paths. It relies on the
survivability from layer 2 and layer 1. Therefore, in an IP over
GMPLS networks, survivability should mainly depend on optical layer.
Working between the layer between layer 2 and layer 3, MPLS itself
can support flexible backup or restoration. Thus, MPLS over GMPLS
networks have the flexibility to choose from either or both. It is
crucial to study how to combine them together to achieve cost
effectiveness and scalability.
4.4 Requirements for MPLS over GMPLS
MPLS is the enhancement of IP protocols in traffic engineering,
explicit routing and QoS etc. Compared with IP over WDM, IP over
GMPLS, the main significant enhancement in MPLS over GMPLS is that it
makes it necessary and possible to support the more dynamic
interactions between the two layers. The dynamic interactions are
able to be controled by either LSRs across the MPLS networks.
Sometimes, these new features should be achieved by enhancing
respective protocols.
In the following sections, we will study these new requirements for
MPLS over GMPLS, including
-- Dynamic use of multi-lightpath connections between two LSRs
-- Dynamic topology changes of MPLS networks
-- Dynamic traffic grooming
-- Virtual Wavelength Assignment (VWA) problem
-- MPLS survivability versus GMPLS survivability
-- Topology driven label assignment in MPLS over GMPLS networks
-- Multi-cast in MPLS over GMPLS networks
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-- Interdomain interconnections
5. Dynamic Use of Multi-lightpath Connections between Two LSRs
In MPLS over GMPLS networks, two LSRs can be connected by more than
one lightpaths, i.e., multi-lightpath connections. This allows the
LSRs to dynamically decide to use one or more lightpaths according to
their bandwidth requirements, a cost-effective way for both optical
network operator and its clients.
Nowadays, the typical bandwidth of a wavelength is from 2.5 Gbps to
10 Gbps. A fiber in a commercialized system can typically support up
to 160 channels. Generally speaking, it is difficult for IP network
to use multi-link connections between two routers due to the
limitation of IP protocols. Therefore, in IP network, to cope with
the traffic growth between two routers, the usual way is to upgrade
the interface bandwidth between the two routers. Given a wavelength
in an optical WDM network is fixed to 2.5Gbps, in traditional IP
networks, generally two adjacent routers can only be directly
connected with one wavelength. Once the two routers need a 10Gbps
interface, we have to either directly upgrade the wavelength to
10Gbps or redesign the topology of the IP networks by routing some IP
packets via other routes. Fortunately, it is easy for MPLS to support
parallel links between two LSRs and even balance the traffic among
all the links. Similarly, if the two LSRs are connected by lightpaths
provided by GMPLS network, MPLS can support multi-lightpath
connections. Note that the multi-lightpath connections may have
different routes in optical domain. Thus, if the pair of LSR needs a
10Gbps lightpath, alternatively, we can establish 4 parallel
lightpaths, each of which is 2.5 Gbps. This is a very significant
feature of MPLS because it allows the dynamic usage of the
wavelengths according to its bandwidth requirements between the two
LSRs. If the two LSRs have more traffic, they can use more
lightpaths. Otherwise, they can release some lightpaths to save cost.
This is a cost-effective method not only for MPLS network but also
for optical networks. With MPLS protocols, either LSR can determine
to use any quantities of wavelength according to their requirements.
Lightpaths are dynamically set up by GMPLS protocols driven by the
arrival of MPLS LSPs, or dynamically torn down driven by the release
of MPLS LSPs. The MPLS Label Switching Paths are nested to the
lightpaths, constructing an LSP hierarchy. In the MPLS over GMPLS
networks, all the procedures are expected to be totally automatic in
terms of the establishment of MPLS LSP or optical lightpath.
The advantages of multi-lightpath connections can be summarized as:
1. Cost effective. For the optical network operator, throughput will
be improved and thus the operator can get more operating revenue from
lightpath provisioning service. For the subscribers, costs will
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decline significantly since they do not need to pay a lightpath
unless they use it.
2. Survivability. The multi-lightpath connections can be scheduled to
use different routes, such as shared risk link group (SRLG)-disjoint.
That means from the perspective of subscribers the survivability has
been enhanced. Once there is a breakdown of a lightpath, other
lightpaths are still available.
3. Easy to access. When a pair of multi-lightpath connection is
required, initially we need not really set up all the optical
lightpaths, but one or part. This makes the optical network easy to
solicit all kinds of customers with different maximum bandwidth
requirements.
4. Seamless integration between electrical and optical layer. In
traditional network architecture, MPLS and GMPLS are both automatic
and intelligent networks in terms of resource usage, but the
interface between the two layers is fixed and dumb. Now we extend
those automatic and intelligent features to the interface.
In summary, it is really convenient that MPLS network can request or
release any lightpaths dynamically. But we are facing the risk that
part or all the lightpaths may be unavailable when they are required
as the optical network is a blocking network. Fortunately, this
usually does not bring any significant loss in MPLS network due to
the traffic engineering capability provided by MPLS. For example,
MPLS network can select other alternative route if it finds that one
route is too crowded. Another method is to try to make use of other
available lightpaths by changing MPLS network topology, which will be
discussed in the next section. But if the LSPs in MPLS networks have
QoS requirements, the unavailability of in setting up lightpaths may
not ensure the QoS of every LSP due to the limited bandwidth
resources.
Therefore, some tradeoffs must be made to reserve some lightpaths for
future use. If the MPLS networks can predict requests for more
bandwidth in the near future, it should try to establish part or all
lightpaths in advance. This is especially necessary when the blocking
probability in the optical networks becomes higher. Another way maybe
use the topology change method discussed in the next section.
As a result, it is necessary to enhance the UNI signaling for better
support multi-lightpath connections in MPLS over GMPLS networks.
1. It is necessary for the MPLS network to know the states of the
optical network, such as blocking probability, by the exchange of UNI
signaling. After knowing these states, the MPLS network can
positively use corresponding policies to avoid the loss when its
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lightpath requests are blocked. One policy is to reserve some
lightpaths in advance prepared for future use.
2. The multi-lightpath connections may have different QoS
requirements. It is necessary to map different QoS requirements to
the route selection of lightpath. So in the UNI signaling, some
parameters should be added to enable the necessary QoS mapping
between two networks.
6. Dynamic Topology Changes of MPLS Networks
From a traditional IP network point of view, network topology has to
be kept unchanged as long as possible. Any topology change will
invoke a link state advertisement (LSA) flooding process. It will
take considerable time for all the routers in the area to update
respective routing tables. As a result, during the unstable state, it
may cause some congestion in some nodes or links. Due to the lack of
traffic engineering capability, the topology after change may not be
well designed to route all the traffic uniformly in the total
network. Hence, topology change is generally regarded as a transitory
process and unstable network state in traditional IP networks.
MPLS is challenging this concepts due to its new features compared
with connectionless paradigm in traditional IP networks. For the MPLS
network, if we do not consider topology driven, MPLS can support
topology change, because explicit routing is used and traffic
engineering capability can balance the traffic from the whole network
perspective. Therefore, MPLS is insensitive to the topology change.
We can positively use topology change to solve the problem discussed
in last section. Multi-lightpath connection discussed above is only
one way to try to use lightpaths adaptively and cost effectively.
Topology dynamic change is another way. If an interface in an LSR
needs more bandwidth, it can try to establish lightpath to any
counterparts connected on the optical network if possible. We can
change the MPLS not only by dynamically decreasing or increasing its
interface bandwidth but also by dynamically simplifying or expanding
its topology. The method has many advantages:
1. If an LSR has not any lightpath resources to the intended LSR, it
can try to connect other LSRs connected with the optical network.
This will lower the possibility of blocking.
2. Cost effective. For the optical network operator, throughput will
be improved due to lower blocking probability and thus the operator
can get more operating revenue from lightpath provisioning service.
For the subscribers, costs will decline significantly because they do
not need to pay a lightpath unless they use it.
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3. Survivability. Once there are some faults on one UNI, the LSR may
not keep connected with the optical networks any longer. In this
scenario, its counterparts can establish lightpaths with other LSRs
on the optical networks. The dynamical adjustment of MPLS network
topology will minimize the effect by node or link failures. The UNI
failures of a pair of LSR connected by an optical network only
affects one LSR, other than two.
The problem of topology change is that it takes some time to converge
by LSA flooding. So we do not expect very frequent topology change
unless very necessary. This method does not suitable for topology
driven which will be discussed in section 10.
7. Dynamic Traffic Grooming
SONET/SDH can content with different granularities of bandwidth
requirements. However, WDM optical network only provides lightpaths
with fixed bandwidth. Nowadays, few subscribers are willing to employ
such high bandwidth, so traffic grooming is an efficient and cost
effective way to maximize the revenue of one wavelength by combining
more low-speed requests into one lightpath.
Traffic grooming refers to techniques used to pack low-speed traffic
streams onto high-speed wavelengths in order to minimize the network
wide cost in terms of line terminating equipment and/or electronic
switching. In MPLS over GMPLS network, the most significant objective
for traffic grooming is no longer the minimization of the amount of
electronic devices, but the maximization of optical network operating
revenue and minimization of the cost for using the lightpaths from
the MPLS network perspective. MPLS over GMPLS does not involve any
hardware costs and all the process expects to be completed
automatically without any manual operation, which makes traffic
grooming MPLS over GMPLS very interesting.
Traffic grooming in ring SONET/WDM networks and mesh WDM networks has
been studied intensively in recent years. However, as a dynamic and
automatic network, there are many new features in traffic grooming in
MPLS over GMPLS networks as follows:
1. In GMPLS, the required lightpath is dynamically established by
signaling protocols. Grooming should be performed at the edge, so a
lightpath is unable to be terminated to added some requests even if
the load on the lightpath may be very light. Thus, grooming in GMPLS
is single-hop grooming. The GMPLS does not support multi-hop
grooming and it is difficult to extend GMPLS protocols to support
multi-hop grooming. This is the main difference from traffic grooming
in static WDM mesh networks. Therefore, numerous studies on multi-hop
grooming and virtual topology design in mesh WDM networks cannot be
used in GMPLS networks. This feature makes the capability for
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grooming in GMPLS very limited compared with multi-hop grooming in
mesh WDM networks.
2. The opportunity to groom low-speed requests in GMPLS network is
much lower than in ring networks. For a mesh network, the new
requests may destine at any nodes in the network. It may not have any
pre-configured lightpaths along the path at that time when a request
arrives, depending on the load of the network and the scale of the
network.
3. Traffic grooming in MPLS over GMPLS is dynamic grooming, which
means not only the connection requests arrive randomly, but also the
groomed traffic in a wavelength may terminate at any time. However,
as long as there are connections existing, the lightpath will have to
be held. As a result, dynamic grooming makes grooming complex and not
always a cost effective way to make full use of network resource.
GMPLS is a dynamic network always with certain blocking probability.
Sometimes we will face the risk that when a big customer arrives,
there are not enough resources to set up a lightpath because the key
resources are occupied by some small customers. So we are facing this
embarrassing situation: On one hand, we wish to accommodate more
subscribers no mater how much bandwidth they require; on the other
hand, we need to give preferential treatment to big subscribers to
maximize revenue, especially in the condition of limited network
resource. In fact, this is a fundamental conflict between short-term
network operating revenue and long-term network operating revenue. To
ensure that the long-term network revenue is as high as possible,
some low bandwidth requests and low bandwidth requests for grooming
should be rejected to make room for future high bandwidth requests.
In MPLS over GMPLS network, traffic grooming will be accomplished at
the UNI and all the process is expected to be dynamic.
In an integrated interaction model, a lightpath will be announced as
a forwarding adjacency (FA). Traffic grooming is achieved by
establishing a hierarchy of LSPs. In an overlay model, the lightpath
is regarded as a point-to-point link. To support dynamic traffic
grooming in MPLS over GMPLS networks, there are some requirements on
the UNI.
-- All the LSPs in a lightpath may not have the same recovery
requirements, so it is necessary to have some measures in the UNI to
bundle the same kind of LSPs together, and then map these
requirements in MPLS layer onto optical layer.
-- All the LSRs in an MPLS domain should have the information on how
much bandwidth a lightpath remains so as to decide if it is possible
to groom a current LSP request.
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-- A fragment bandwidth management policy is very important.
Sometimes it is necessary to reserve some bandwidth for the
forthcoming high bandwidth LSPs.
-- To prevent long time occupation by small bandwidth LSPs, it is
necessary to have a policy to manage these small bandwidth and long
holding time LSPs.
-- There should be some tradeoffs and optimization between setting up
a new lightpath or grooming it into a present lightpath, when an LSP
request comes.
8. Virtual Wavelength Assignment (VWA) Problem
It is essential to design the interface between client layer and
optical layer to make the blocking probability as low as possible. In
the case of multi-lightpath connections, if the pair of LSR needs up
to 4 lightpaths, we must configure 4 wavelengths in advance to avoid
any manual operation in the future, even if they may not need the
real establishment of corresponding lightpaths. We do not expect to
change the traditional interface architecture between client layer
and optical layer, in which clients are directly connected with
wavelengths without complex switching fabrics. Hence, which
wavelengths to be selected must be determined in advance, and
thereafter, all the requested wavelengths will have to select
wavelengths from these pre-configured wavelengths. How to perform the
wavelength assign at this stage will affect the network performance
in their future. We refer this as Virtual Wavelength Assignment (VWA)
problem in the draft. In the wavelength convertible GMPLS-based WDM
network, we can choose wavelength in random. But in wavelength
continuous network, the future wavelength assign will have to be
confined within the initial configuration. This makes the lightpath
requests from multi-lightpath connections have higher blocking
probability than lightpath for the total optical networks. Therefore,
in this case, we must study efficient virtual wavelength assignment
methods.
To lower the blocking probability in VWA, the preliminary
consideration is to ensure the wavelength usage throughout the total
optical network distributes as evenly as possible.
9. MPLS Survivability versus GMPLS Survivability
As mentioned above, both MPLS and GMPLS can provide network
survivability, including protect and restoration. Therefore, there
are 3 preliminary approaches to provide network survivability, namely
MPLS survivability only, GMPLS survivability only, and integrated
survivability from MPLS/GMPLS.
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9.1 MPLS survivability Only
With this model, MPLS networks treat GMPLS networks as abstract
links. There is no requirements to map the survivability parameters
from MPLS layer to GMPLS layer. It may take considerable long time
for MPLS layer to detect the fault from from optical layer.
9.2 GMPLS survivability Only
With this model, MPLS takes advantage of protect or restoration from
GMPLS to overcome the failures from optical layer. MPLS layer
protection or restoration always assumes connect ability from optical
layer. MPLS totally relays on the GMPLS network to provide
survivability across the segment of optical networks. This is in fact
an overlay survivability architecture between two layers. This
requires the UNI has the ability to allow optical network clients to
initialize protect or restoration lightpath.
9.3 Integrated Survivability
The integrated model tries to combine the survivability from the two
layers together. The couple should be cost effective, flexible and
scalable. This requires much more interchange messages between the
two networks. For example, if a node from MPLS network knows the
topology of GMPLS network, it may use a abstract shortest SRLG
protected path. The abstract shortest protected path is an
comprehension of hops in both MPLS and GMPLS networks. Nevertheless,
it does not mean the physical hops, but an abstract hop taking the
costs into account.
9.4 QoS Mapping
QoS mapping is to map QoS requirements of MPLS LSPs onto respective
lightpaths for the computation of primary lightpath, protect or
restoration. This will be even more complicated if a lightpath
contains groomed MPLS LSPs that have different QoS requirements.
10. Topology Driven Label Assignment in MPLS over GMPLS Networks
In MPLS network, for scalability, some LSPs may be set up or torn
down by topology changes. These kinds of LSPs are sensitive to the
topology change. Normally, they have not clear bandwidth and QoS
requirements on an LSP, so for the requirements of topology driven in
MPLS over GMPlS network, they are basically the same as the generic
requirements discussed in the IP over optical networks [IPO-FRAMWORK]
and the new features discussed in section 7 & 8 are not applicable.
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Sometimes, in MPLS, topology driven label assignment and request
driven label assignment are mixed together. In this scenario, the
requirements discussed above still can be used in the LSPs from
request driven label assignment.
11. Multicast in MPLS over GMPLS Networks
Under consideration.
12. Interdomain Interconnections
Generally speaking, the new features discussed above are suitable for
not only overlay models, but also interdomain models.
13. Security Considerations
No additional security considerations are beyond the present drafts
of IP over optical networks [IPO-FRAMWORK] and OVPN.
14. Acknowledgements
We would like to thank Dr. Ye Yabin (I2R), Dr. Cheng Xiaofei
(I2R), Dr. Chin Soon Hwa (NTU), Dr. Chai Teck Yoong (I2R), Dr. Zhou
Luying (I2R) and Dr. Liu Qiang(I2R) for the discussions with them
within the optical network design lab in I2R, Singapore.
15. References
14.1 Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[MPLS-ARCHITECTURE] Rosen, E., Viswanathan, A., and R. Callon,
"Multiprotocol Label Switching Architecture", RFC
3031, January 2001.
[GMPLS-OVERLAY] G.Swallow et al., "GMPLS RSVP Support for the
Overlay Model," Work in Progress, draft-ietf-ccamp-
gmpls-overlay-01.txt.
[HIERARCHY] K.Kompella and Y.Rekhter, "LSP Hierarchy with
Generalized MPLS TE," Work in Progress, draft-ietf-
mpls-lsp-hierarchy-08.txt.
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draft-xushao-ipo-mplsovergmpls-00.txt October 2003
[IPO-REQS] Y.Xue (Editor) et al., "Optical Network Service
Requirements," Work in progress, draft-ietf-ipo-
carrier-requirements-05.txt.
[IPO-FRAMWORK] Bala Rajagopalan et al., 揑P over Optical
Networks: A Framework ?Work in Progress,
draft-ietf-ipo-framework-05.txt.
[GMPLS-OSPF] K. Kompella and Y. Rekhter, "OSPF Extensions
in Support of Generalized MPLS", Work in Progress,
draft-ietf-ccamp-ospf-gmpls-extensions-09.txt.
[RFC3386] W.Lai, D.McDysan, et al., "Network Hierarchy and
Multi-layer Survivability," IETF RFC 3386, November
2002.
[IPO-ASON] Aboul-Magd (Editor) et al., "Automatic Switched
Optical Network (ASON) Architecture and Its Related
Protocols," Work in progress, draft-ietf-ipo-ason-
02.txt, March 2002.
14.2 Informative References
[OIF-UNI] The Optical Internetworking Forum, "User Network
Interface (UNI) 1.0 Signaling Specification -
Implementation Agreement OIF-UNI-01.0," October 2001.
[ITUT-G709] ITU-T, "Interface for the Optical Transport Network
(OTN)," G.709 Recommendation (and Amendment 1),
February 2001.
16. Author's Addresses
Xu Shao
Institute for Infocomm Research
Blk 2, 18 Nanyang Drive
Unit 230, Innovation Centre
Singapore 637723
Tel: +65 6792 2824
Email: [email protected]
Tee Hiang Cheng
Institute for Infocomm Research
Xu Shao et al, Expires - April 2004 [Page 17]
draft-xushao-ipo-mplsovergmpls-00.txt October 2003
Blk 2, 18 Nanyang Drive
Unit 230, Innovation Centre
Singapore 637723
Nanyang Technological University
Nanyang Ave, Singapore, 639798
Email: [email protected]
Kumaran Veerayah
Institute for Infocomm Research
Blk 2, 18 Nanyang Drive
Unit 230, Innovation Centre
Singapore 637723
Email: [email protected]
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