Internet DRAFT - draft-xushao-ipo-mplsovergmpls

draft-xushao-ipo-mplsovergmpls



                       
                
                  IP over Optical Working Group                                       
                  Internet Draft                 
                   
                  Expiration Date: November 2004                               Xu Shao 
                                                       Institute for Infocomm Research 
                                                                                       
                                                                       Tee Hiang Cheng 
                                                       Institute for Infocomm Research 
                                                      Nanyang Technological University 
                                                                                       
                                                                      Kumaran Veerayah 
                                                       Institute for Infocomm Research 
                                                                                       
                                                                              May 2004 
                                                                                       
                   
                   
                       Requirements for MPLS over GMPLS-based Optical Networks 
                                         (MPLS over GMPLS) 
                   
                                draft-xushao-ipo-mplsovergmpls-02.txt 
                   
                   
                   
               Status of this Memo 
                   
                  This document is an Internet-Draft and is in full conformance with  
                  all provisions of Section 10 of RFC2026.   
                       
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                  Task Force (IETF), its areas, and its working groups. Note that  
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                  http://www.ietf.org/ietf/1id-abstracts.txt  
                        
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               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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                     [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., “IP 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:  shaoxu@i2r.a-star.edu.sg                
                         
                         
                          Tee Hiang Cheng 
                          Institute for Infocomm Research 
                
                
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                               draft-xushao-ipo-mplsovergmpls-02.txt    May 2004 
                
                          Blk 2, 18 Nanyang Drive 
                          Unit 230, Innovation Centre 
                          Singapore 637723 
                   
                          Nanyang Technological University 
                          Nanyang Ave, Singapore, 639798 
                          Email:   ETHCHENG@ntu.edu.sg      
                   
                   
                          Kumaran Veerayah           
                          Institute for Infocomm Research 
                          Blk 2, 18 Nanyang Drive 
                          Unit 230, Innovation Centre 
                          Singapore 637723 
                          Email:  Veerayah@i2r.a-star.edu.sg 
                            
                         
               17. Full Copywrite Statement 
                   
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