Internet DRAFT - draft-liao-mpls-obs

draft-liao-mpls-obs



Internet Engineering Task Force                             Jia Jia Liao                      
Internet Draft                                                Ping Zhang
Expires: October 2006                                       Zheng Bin Li  
                                                               An Shi Xu
          National Laboratory on Local Fiber-Optic Communication Network
                                 & Advanced Optical Communication System
                                                Peking University, China
                                                              April 2006


            Recovery in Optical Burst Switching Network
                  draft-liao-mpls-obs-00.txt 


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Copyright Notice

   Copyright (C) The Internet Society (2006). All Rights Reserved.

Abstract

   Protection and restoration at optical layer is critical to network
   integrity since data is transmitted and switched at a considerably 
   high speed in optical domain. A few second halt may cause tens to 
   thousands gigabit loss. Optical burst switching is a promising 
   technology, bridging optical circuit switching and optical package 
   switching. Unlike optical circuit switching and time division 
   multiplexing, OBS is featured with unidirectional reservation and 
   statistical multiplexing of wavelength resources. The general idea 
   behind protection and restoration techniques is to utilize redundant
   bandwidth resources as backup. The flexibility brought by OBS 
   provides alternatives for existed protection and restoration schemes 
   at optical layer. 

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Conventions

   The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 
   document are to be interpreted as described in RFC2119 [RFC 2119].

















































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Table of Contents

   1. Introduction.....................................................4 
      1.1. OBS Network Architecture....................................4
      1.2. Multi-layer Interoperation..................................5
   2. Fault Management.................................................5
      2.1. Failure Profiles............................................6
          2.1.1. Link Failure..........................................6
          2.1.2. Node Failure..........................................6
      2.2. Fault Detection.............................................7
          2.2.1. Link Fault Detection..................................7
          2.2.2. Node Fault Detection..................................7
      2.3. Fault Notification..........................................7
          2.3.1. Link Fault Notification...............................7
          2.3.2. Node Fault Notification...............................8
   3. Restoration at OBS Layer.........................................9
      3.1. Motivation to Restore at OBS Layer..........................9
      3.2. Single Layer Restoration Schemes...........................10
          3.2.1. Link Failure Restoration Schemes.....................10
          3.2.2. Node Failure Restoration Schemes.....................10
      3.3. Multi-layer Restoration Schemes............................11
          3.3.1. IP Dynamic Routing...................................11
          3.3.2. MPLS Protection Switching............................11
          3.3.3. Optical Layer Resilient Schemes......................12
          3.3.4. Recovery Scheme Comparison...........................12
          3.3.5. Operational Coordination.............................12
   4. Acknowledgements................................................13
   5. References......................................................13
   6. AUTHORS' ADDRESSES..............................................13
   7. IPR NOTICE......................................................13
   8. FULL COPYRIGHT STATEMENT........................................14
   





 
















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1. Introduction

   The basic difference among Optical Circuit Switching (OCS), Optical
   Burst Switching (OBS) and Optical Packet Switching (OPS) is that the 
   three work at different granularity. OCS, which has already been 
   widely deployed, aims to switch at wavelength, waveband or even fiber 
   level. However, in most cases, individual users can hardly afford a 
   whole wavelength, and thus TDM is applied to provide each channel 
   with fixed percentage of the total bandwidth by splitting wavelength 
   into recurring time-slots. This approach has been proved to be less 
   bandwidth efficient than OPS, which is able to switch packets like IP
   network in optical domain. However, some critical technologies 
   essential to OPS, such as optical random access memory, are far away 
   from maturity. OBS, supposed to bridge above two mechanisms, is able 
   to switch bufferlessly at sub-wavelength level. OBS, featured with 
   unidirectional reservation and statistical multiplexing of wavelength 
   resources, has brought great flexibility to optical bandwidth 
   distribution. 
   
1.1. OBS Network Architecture

   OBS network is composed of two sub-planes, namely data plane and 
   control plan, as shown in Figure 1. In data plane, traffic from OBS 
   client layer (e.g. IP or ATM layer) is aggregated into Data Bursts 
   (DBs) at ingress edge nodes which perform as an interface to the 
   upperlayer and local at the edge of OBS layer [IPOWDM]. DBs will be 
   sent through core nodes to their egress edge nodes without o-e-o 
   conversion, in which a few optical fiber delay lines may be applied 
   to reduce overall blocking probability. DBs usually contains tens to 
   thousands of thousand bits including payload and frame overhead. 
  
  
                                 [ core ]
                                /[ node ]\
                               /     |    \
                              /  |------|  \
                             /   | -\/- |   \
             |      [ core ]/   /| -/\- |\   \[ core ]      |
      from   |------[ node ]\  / |------| \  /[ node ]------|   to 
   upperlayer|          |    \/            \/    |          |upperlayer
     ------->|      |------| /\            /\ |------|      |-------->
     ------->|------| -\/- |/  \          /  \| -\/- |------|-------->
     ------->|      | -/\- |\   \[ core ]    /| -/\- |      |-------->
     traffic |      |------| \   [ node ]   / |------|      | traffic
             |                \      |     /                |
     Ingress edge node         \ |------| /          Egress edge node
                                \| -\/- |/
                                 | -/\- |
                                 |------|    

	      
   Figure 1:  OBS Network Architecture


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   Control plane mainly conduct routing and resource reservation by 
   configuring optical switching fabric according to signalling. An 
   offset time ahead of DB transmission, Control Packets (CPs) will be
   sent through core nodes to establish an available light path from 
   ingress edge node to the egress one. At each stop at core nodes, CPs 
   will experience o-e-o conversion and be processed electrically to 
   trigger switching fabric. As long as every configuration is 
   successful, DB is able to transmit across the network. However, once 
   one of the core nodes along light path fails to act, the DB will have 
   to be discarded and bandwidth that has already been reserved will be 
   released.
	      
1.2. Multi-layer Interoperation	      
	  
   OBS layer, viewed as an data-link layer, aims to provide reliable 
   end-to-end path for data transmission. As shown in Figure 2, its 
   server layer is optical layer with huge physical bandwidth and 
   its client layer can be network layer (e.g. IP) or others like ATM. 
   With the increase in volume and importance of IP traffic, 
   applications based on IP has become dominant. Thus in this draft, we 
   only consider IP as the client layer, for which OBS acts to provide 
   available bitpipe.
	 
	 
             |+++++++++++++++++++|          |+++++++++++++++++++|
             | Application Layer |<-------->| Application Layer |
             |+++++++++++++++++++|          |+++++++++++++++++++|
             |     IP Layer      |<-------->|   Network Layer   |
             |+++++++++++++++++++|          |+++++++++++++++++++|
             |     OBS Layer     |<-------->|  Data-link Layer  |
             |+++++++++++++++++++|          |+++++++++++++++++++|
             |   Optical Layer   |<-------->|   Physical Layer  |
             |+++++++++++++++++++|          |+++++++++++++++++++|
    
          	 
   Figure 2: Layered Network       	 

   Optical layer, lying under OBS layer, focuses on optical signal 
   transmission, amplifying, multiplexing and demultiplexing. From the 
   view of OBS, optical layer offers Optical Channel-Path (OCh-P), 
   connecting distributed OBS nodes. OCh-P represents the end-to-end 
   transport of a lightpath across multiple regenerators in the path
   [Optical]. 
	 	
   OBS nodes are classifies as edge nodes and core nodes. Edge nodes 
   consist of aggregating queues, CPs' generator and CPs' and DBs' 
   transmitter or receiver. Core nodes comprise CPs' processor, switch 
   driver, and switching fabric.

2. Fault Management
   



Liao,Zhang,Li,Xu                                             [Page 5]
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   Fault management involves detecting problems in the network and 
   alerting the management systems appropriately through alarms. If a 
   certain parameter is being monitored and its value falls outside its
   present range, the network equipment generates an alarm [Optical]. In
   other cases, alarms could also be triggered by outright failures, 
   such as the failure of switch driver or other components in the 
   system. Fault management also includes restoring service in the event 
   of failure, but we organize the latter as a separate section.

2.1. Failure Profiles
  
   Various failures may occur in a multi-layer network. Some are caused
   by OBS network elements; Some are not but may be restored by OBS 
   layer mechanisms. Providing an exhaustive list of all the possible 
   failure types is aimless, but it is worth listing the main categories
   of failures, namely link failures and node failures, from OBS 
   perspective. 

2.1.1. Link Failures

   Several types of failures may result in OBS link failure.
   
   Fiber cut may cause all the OCh-Ps in a physical link to fail. If 
   optical layer refuses to provide protection, it can be passed on to 
   OBS layer.
   
   Optical equipment failures such as amplifier failure also belong to 
   optical layer, but it may affect several OCh-Ps and decrease the 
   transmission capacity to some degree. Such failure can be protected 
   at optical layer too.
   
   OBS node interface failure may occur in signalling channel, as unlike 
   DBs, CPs have to experience o-e-o conversion and electrical 
   process at core nodes. However, such type of failure can not be 
   protected by optical layer. (TBC)
   
2.1.2. Node Failures
     
   There are multiple possible causes of node failures whose nature has
   very different implications.
   
   Power supply outage provokes both a control and switching plane 
   failure. But in most cases, backup power supplier will take over to 
   work.
   
   Switching fabric failure at core nodes would cause traffic loss or 
   mis-forwarding. So measures should be taken to monitor switching 
   fabric status and report to the control model or even to other nodes.
   
   Software failures make impact on some specific features or software
   crash of the node operating system, for example, packets' aggregation
   failure at edge nodes or CPs' process failure at core nodes. 


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   Hence, besides software bug eradication by testing, a modular 
   architecture may limit software component failures to a controllable 
   scope and the failed software component may be restarted 
   independently of the other modules. (TBC)
   
2.2. Fault Detection

   Fault detection is the first phase in recovery cycle and its time 
   is part of total recovery time. This time may depend, for instance,
   on the speed of fault detection in a lower network layer and 
   notification toward upper layers, on the time it takes for the node 
   to gather all abnormal information from various signals and derive 
   the exact fault state from diagnosis and so on.

2.2.1. Link Fault Detection

   According to link failure profiles, most link failures can be 
   detected at optical layer from the perspective of OBS, for example by 
   optical channel-path trace. This trace can be inserted at the end of 
   the CPs and monitored at various locations at control plane along the 
   lightpath. Moreover, Optical receivers at each node can perform as 
   detectors at data plane. Once the optical signal-to-noise ratio falls 
   below a threshold, alarms would be triggered. (TBC) 
 
2.2.2. Node Fault Detection 
   
   When comes to node failure, in case of switching fabric failure, core 
   node may provide the function of self supervising at optical layer. 
   But, unlike link failures, most other node failures can hardly be 
   detected at optical layer and thus lower layer failure notification 
   is not suitable here. However, the mechanism based on hello protocol 
   could be feasible by sending a periodic hello message between two 
   neighbors. When one of the node stops receiving hello messages for a 
   configurable period, it concludes that a failure of the link between 
   them or the objective node itself has failed. (TBC)

2.3. Fault Notification 

   Once failures have been detected and located, other network elements
   in the same domain or network should be informed by fault alarming 
   and the propagation time is also part of recovery time. OBS network
   can be distributedly or centrally controlled. In the former case, 
   routing function is performed by each edge node, while in the latter 
   one, a central controller is responsible for scheduling. Here, we 
   only consider distributed situation.
   
2.3.1. Link Fault Notification

   OCh-Ps are usually unidirectional. Thus any failure at OCh-P, such as 
   fiber cut or amplifier outage, will be detected by Recovery Tail-End 
   (RTE) instead of Recovery Head-End (RHE)[Recovery]. On detecting, RTE 
   immediately starts to notify other nodes by Link State Advertisement 
   (LSA). LSA, can be broadcasted or transmitted from end to end.

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   In OBS network, edge nodes keep route's table, perform routing and 
   set offset time between CPs and DBs. Thus LSA must be firstly 
   reported to each edge node and every node in the network should keep 
   the routes to each edge node. As LSA is critical to DBs' routing, 
   LSA transmission must be reliable. So each edge node having received 
   LSA must return an acknowledgement to RTE. Sometimes, existed link 
   failure may cut off LSA transmission and thus alternative route 
   should be pre-computed.   
   
   In case of core node acting deflection, these core nodes need to be 
   alarmed too, otherwise deflected DBs would probably blocked by link 
   failures. (TBC)

2.3.2. Node Fault Notification

   According to node failure profiles, switching fabric at core node and 
   outright crash will be discussed in this paragraph.
   
   Single switch failure may reduce core node switching throughput and 
   may be resolved by substituting the outage switch with a new one. 
   However, when most part of switching fabric fails to work, the total 
   switching node must alarm other nodes about node failure by 
   broadcasting or transmitting Node State Advertisement (NSA) from end 
   to end. Similar to link fault propagation, NSA must be firstly sent 
   to edge node and then to deflective core node, if necessary. 
   

       upperlayer            
        traffic  |  2. NSA    |------|  1. Hello     |------|
        <------->| <--------  | core |  -------->    | core |
        <------->|------------| node |---------------| node |
        <------->|            |------|  no response  |------|
             edge node
                           (a) node failure

      upperlayer            
        traffic  |  2. NSA    |------|1. Hello       |------|
        <------->| <--------  | core |-------->X     | core |
        <------->|------------| node |---------------| node |
        <------->|            |------|  no response  |------|
              edge node
                           (b) link failure

      upperlayer            
        traffic  |  3. NSA    |------|  1. Hello     |------|
        <------->| <--------  | core |  -------->    | core |
        <------->|------------| node |---------------| node |
        <------->|            |------|   X<--------  |------|
                                           2. Hello
             edge node                              
                           (c) link failure
 
   Figure 3: Hello Message Loss

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   Power supply outage or software OS crash may lead to traffic 
   black-holded and the control model of core node is unable to report 
   failure by it self. Thus, such kind of failure must be discovered and
   notified of by neighbor nodes sending NSA. Once a neighbor node does 
   not receive hello message from the objective node for a given time, 
   this node should report the failure to others. However, in such case 
   as shown in Figure 3, the neighbor node can hardly distinguish node 
   failure from OCh-P failure. Therefore, such a NSA need to cooperate 
   with a LSA to identify the real problem. (TBC)

3. Restoration at OBS Layer

   OBS layer performs as a data-link layer located between optical layer 
   and network layer (IP layer). The major duties of this layer is to 
   provide reliable and quick bitpipes for its client layer (network 
   layer) and to make effective utilization of huge bandwidth of its 
   server layer. 
   
3.1. Motivation to Restore at OBS Layer

   OBS is a promising technology to explore huge optical bandwidth for 
   upperlayer applications. Besides OCh-P failure, network elements 
   outage at OBS layer, such as edge node or signalling process model 
   failure at core node, can be hardly protected by optical layer, 
   though upperlayer traffic can be partly restored by IP layer itself. 
   Thus, to restore at OBS layer could at least provides survivability 
   for OBS network elements.
   
   Restoration at IP layer is so versatile to deal with failures at 
   lower layer, but the problem is that total recovery process is rather
   time-consuming and even can not meet the QoS of real-time traffic. 
   Recovery time of IP restoration mechanisms usually ranges from 
   tens of seconds to minutes. However, restoration at OBS layer is more 
   responsive and faster than its IP's counterpart, as OBS is able to 
   allocate optical bandwidth directly.
   
   Protection schemes at optical layer is not mature in mesh topology as 
   compared to ring topology or point-to-point connection. So 
   restoration at OBS layer may offer alternatives for optical 
   protection at a finer granularity. For example, some link failure may 
   be detected at optical layer, but protection mechanisms at the same 
   layer will not be triggered with failure passed up on to OBS layer. 
   Then OBS restoration starts immediately to work.
   
   DBs play as containers to carry upper layer packets across OBS 
   switching nodes. At ingress edge node, packets sharing the same 
   destination or QoS could be enclosed into DBs. CPs could help to
   route according to not only addresses but also service level. IP 
   layer can also provide differentiated service for each packet, but
   obviously OBS is able to carry out it far more efficient as data can 
   be routed by larger containers, DBs, instead of packets.
 
 
 
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3.2. Single Layer Restoration Schemes

   Protection or restoration schemes should meet the need of performance
   evaluation criteria, such as recovery time, bandwidth efficiency and 
   so on. Performance criteria is defined by service level of traffic. 
   Hence a wide range of recovery mechanisms may exist to supplement 
   with each other to serve for various traffic.

3.2.1. Link Failure Restoration Schemes
   
   When comes to link failure, traditional optical protection mechanisms 
   aim to seek abundant wavelength resources to establish a new 
   lightpath for data transmission. However, as OBS works at 
   sub-wavelength granularity and is characteristic of statistical 
   multiplexing, in case of failure, what OBS restoration schemes seek 
   is time slot at different wavelength, as the multiplexing density of 
   DBs is controllable, unlike OCS or TDM.
   
   One or two channel in a link failing to work means the decrease of 
   transmission capacity of that link. Once nodes are equipped with 
   wavelength conversion, traffic can be easily multiplexed to other 
   channels in the same link without help of additional wavelength. When 
   the transmission capacity of a certain link has decreased below a 
   threshold and become intolerable, traffic that is used to pass this 
   link will have to be deflected or rerouted. For example, cable cut 
   can be considered as total channel failure at that link.

   Deflection is a local method, in which a new route will be selected 
   by RTE. This new route may be pre-computed or computed on-the-fly. 
   Then RTE transmits LSAs with the new route to each edge nodes by 
   broadcasting or end-to-end transmission. In case of core node able to 
   deflect, these core nodes need to be alarmed too, otherwise deflected 
   DBs would probably blocked by link failures.

   Rerouting is a global and more radical method by edge nodes selecting 
   a new path. Once a link failure occurs, RTE simply reports the 
   location of the failure to each edge node, which will figure out a 
   new path by pre-computing or computing on-the-fly. 

   Deflecting method is usually faster than rerouting, but rerouting can 
   be more bandwidth effective as it focuses on the global resources 
   [Restoration]. So in practice, two methods may work sequencially or 
   integratedly to collaborate with each other. (TBC)
   
3.2.2. Node Failure Restoration Schemes

   Node failure is much severer than link failure, which can obviously
   cause all the links connected to it to fail and even change the 
   topology of network. So a backup node and backup switching fabric is 
   indispensable. Once failures occur, all traffic could be switched to 
   the backup one. In case of planned node failure, resulted from 
   hardware and software of switching node updating, traffic may be 
   gracefully rerouted to the backup node. 

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   If no backup node is available, recovery schemes for node failure at 
   OBS layer can only restore traffics forwarded by the fault core node. 
   Traffics that begin or end with the fault node can not be restored.
   And as well edge nodes can not be restored either.   

   With respect to core nodes, there are two different kinds, namely 
   ingress/egress switching node and intermediate switching node 
   according to JIT protocol. Ingress switching node is the outlet of 
   traffic from edge node and egress switching node is the destination, 
   so any failure at above two nodes is similar to that at edge nodes.
   Only traffic forwarded by fault intermediate switching node can be 
   restored by deflecting or rerouting. (TBC)
   
3.3. Multi-layer Restoration Schemes

   OBS layer is an intermediate layer between optical layer and IP 
   layer. In realistic network, each of them has its own recovery 
   mechanisms. However, not every failure in a particular network layer
   can be resolved by recovery mechanism in that same layer. Upon 
   detection of a fault, more than one layers could initiate recovery
   actions. If these recovery mechanisms are merely triggered by 
   detection of a fault, an uncoordinated and inefficient action may 
   result.

3.3.1. IP Dynamic Routing
   
   Restoration at IP layer is mainly accomplished by exchanging, between
   adjacent routers, control messages that are used to update the 
   routers' tables, thus enabling IP packets to be dynamically rerouted 
   around link and node failures. However, it is usually slow, from
   several to hundreds seconds, and its behavior is unpredictable. 

   Some enhancements of the protocol have been proposed to overcome its 
   drawbacks. One approach is equal cost multi-path forwarding, in which 
   the router relies on more than one path for transmitting packets 
   sharing a common destination by maintaining multiple next-hop entries 
   for the same destination within each router's routing table. Another 
   approach partitions the network into multiple areas, as defined in 
   hierarchical link state routing protocols such as OSPF and IS-IS.
   
3.3.2. MPLS Protection Switching

   MPLS protection switching is an alternative approach to circumvent 
   the latency drawback of dynamic routing. MPLS protection entities can 
   be set up either dynamically or in a prenegotiated way. Protection
   entities, dynamically set up, restore traffic based on failure
   information, bandwidth allocation, and optimized reroute assignment.
   Prenegotiated protection consists of working LSPs that have
   preestablished protection paths. In general, dynamic protection
   increase resource utilization but requires longer restoration times
   than preestablished protection.



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3.3.3. Optical Layer Resilient Schemes

   Both the optical channel (OCh) section and optical multiplex section
   (OMS) feature dynamic restoration and preplanned protection. The main
   difference between OCh and OMS resilient schemes is represented by 
   the granularity at which layers operate. OCh resilient schemes 
   protect individual lightpaths, thus allowing selective recovery of 
   optical line terminal failures. OMS resilient schemes work at the 
   aggregated signal level, thus recovering all lightpaths present on 
   the failed line concurrently.
   
   Protection schemes, namely Dedicated Path Protection (DPP), Shared
   Path Protection (SPP), Optical Unidirectional Path Switched Ring 
   (OUPSR), Optical Bidirectional Path Switched Ring (OBPSR) and so on, 
   guarantee service restoration completion times of hundreds, tens and 
   even fractions of milliseconds. However, restoration schemes at 
   optical layer are slower and less mature than protection schemes.
 
3.3.4. Recovery Scheme Comparison

   From the view of rerouting, restoration schemes at OBS layer is 
   similar to MPLS protection switching. But MPLS is processing and 
   routing in electronic domain, while DBs in OBS network is switched in
   optical domain and CPs need o-e-o conversion. In MPLS protection 
   schemes, labels are followed closely by payload and distributed by 
   LDP. However, OBS CPs are set out an offset time prior to BDs and the 
   route is computed at edge nodes according to Dijsktra algorithm.
   
   OBS enables optical network to become more flexible and intelligent 
   by enhancing signalling at control plan. DBs with proper size is 
   multiplexed statistically onto a wavelength, which can lead to more 
   efficient utilization of wavelength bandwidth than TDM. So 
   restoration schemes at OBS layer may provide alternatives for 
   traditional optical protection mechanisms, for example, deflection 
   according to DBs' quality of service.
     
3.3.5. Operational Coordination
 
   Coordination between resilient schemes, at distinct layers, is 
   required to avoid multiple schemes concurrently activated upon a 
   single network fault. Two kinds of coordinating strategies are 
   sequential approach and integrated approach [Recovery]. In the former 
   scheme, the server layer may start recovery immediately, whereas the 
   recovery mechanism in the client layer has a build-in hold-off time 
   before initiating the client recovery process. The latter one 
   combines several mechanisms into one integrated multi-layer recovery 
   schemes coordinated by management plane. 
   
   However, the sequential approach is easier to apply than the 
   integrated one as the latter may cause great complexity to control 
   and management planes. When comes to restoration at OBS layer, as the 
   sequential approach requested, the recovery time should be shorter 
   than that of IP layer and near to that of optical layer, for example 

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   total recovery time ranging from tens milliseconds to several seconds.   

4. Acknowledgements

   This research is funded by the National High Technology Research and
   Development Program of China (863 Program).

   The authors are grateful to other colleagues for their work and 
   useful suggestions.
   
5. References

   [Recovery]     J. Vasseur et al., "Network Recovery". Morgan Kaufmann 
                  Publishers, 2004.
   [Optical]      R. Ramaswami and K. N. Sivarajan, "Optical Networks". 
                  Morgan Kaufmann Publishers, 2004.
   [IPOWDM]       S. Dixit, "IP OVER WDM: Building the Next-Generation 
                  Optical Internet". WILEY-INTERSCIENCE, 2002.
   [Restoration]  Y. Xin et al., "Fault Management with Fast Restoration for
                  Optical Burst Switched Networks". BROADNETS'04.       
    
6. AUTHORS' ADDRESSES
   
   Jia Jia Liao
   National Laboratory on Local Fiber-Optic Communication Network 
   & Advanced Optical Communication System, Peking University, 100871
   P.R. China
   Email: jjliao@ele.pku.edu.cn

   Ping Zhang
   National Laboratory on Local Fiber-Optic Communication Network 
   & Advanced Optical Communication System, Peking University, 100871
   P.R. China
   Email: zhangping@pku.edu.cn
      
   Zheng Bin Li
   National Laboratory on Local Fiber-Optic Communication Network 
   & Advanced Optical Communication System, Peking University, 100871
   P.R. China
   Email: lizhengbin@pku.edu.cn
   
   An Shi Xu
   National Laboratory on Local Fiber-Optic Communication Network 
   & Advanced Optical Communication System, Peking University, 100871
   P.R. China
   Email: lyrxas@pku.edu.cn
   
7. IPR NOTICE

   The IETF takes no position regarding the validity or scope of any
   Intellectual Property Rights or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights

Liao,Zhang,Li,Xu                                            [Page 13]
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   might or might not be available; nor does it represent that it has
   made any independent effort to identify any such rights. Information
   on the procedures with respect to rights in RFC documents can be
   found in BCP 78 and BCP 79.

   Copies of IPR disclosures made to the IETF Secretariat and any
   assurances of licenses to be made available, or the result of an
   attempt made to obtain a general license or permission for the use of
   such proprietary rights by implementers or users of this
   specification can be obtained from the IETF on-line IPR repository at
   http://www.ietf.org/ipr.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights that may cover technology that may be required to implement
   this standard.  Please address the information to the IETF at ietf-
   ipr@ietf.org.

8. FULL COPYRIGHT STATEMENT

   Copyright (C) The Internet Society (2006). This document is subject
   to the rights, licenses and restrictions contained in BCP 78, and
   except as set forth therein, the authors retain all their rights.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
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   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for

   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
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   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns.

   This document and the information contained herein are provided on an
   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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Liao,Zhang,Li,Xu                                            [Page 14]
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Internet Draft         Recovery in OBS Network             April 2006