PCE Working Group Jun Kyun Choi (ICU) Internet Draft Dipnarayan Guha (ICU) Expiration Date: December 2004 Tai Won Um (ICU) Young Hwa Kim (ETRI) Byung Ho Yae (ETRI) July 2004 Fast End-to-End Restoration Mechanism with SRLG using Centralized Control draft-choi-pce-e2e-centralized-restoration-srlg-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC 2026 [RFC2026]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. J.K. Choi et al. - Internet Draft Expires December 2004 1 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 Abstract This draft describes the concept of the Shared Link Risk Group (SRLG) based logical ring configuration and recovery method using ring SRLG for the purpose of restoration in mesh networks. In this restoration architecture, backup paths can be easily established through the end-to-end path which follows from the logical ring configuration. It guarantees the establishment of backup path disjoint from the working path at all levels. To take advantage of bandwidth considerations and fast restoration mechanisms, a centralized Controller is used to provide dedicated protection to Optical Transport Networks using the SRLG concept. The Controller determines the logical rings over mesh optical networks and distributes information about primary and backup paths to the nodes in the optical transport layer. Conventions 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]. J.K. Choi et al. - Internet Draft Expires December 2004 2 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 Table of Contents 1. Introduction............................................................3 2. Network Architecture for centralized Control using SRLG.................5 2.1 Introduction to the centralized Controller.............................6 2.2 Network Structure......................................................6 2.3 Control Structure......................................................7 2.4 Control plane Hierarchy Architecture for SRLG protection and recovery..7 3. Logical Ring Configuration based on SRLG................................8 3.1 Logical ring with SRLG.................................................8 3.2 Segment wise logical ring using the centralized Controller.............9 3.3 Resource allocation with SRLG by the Controller.......................10 4. Integrated Layer Survivability and Recovery Mechanisms.................10 4.1 Protection and Recovery Mechanisms....................................10 4.2 Protocol based Ring Recovery Mechanisms using the Controller..........11 5. Signaling and Integrated Service Provisioning..........................12 6. Conclusion.............................................................12 7. References.............................................................13 8. Acknowledgement........................................................13 9. Authors' Addresses.....................................................14 10. Full Copyright Statement..............................................14 1. Introduction With the rapid growth of the Internet, the advance of wavelength division multiplexing (WDM) technology, and the integration of various communication technologies, the communication network is evolving to include huge bandwidth-intensive network applications. Survivability refers to the ability of the network to transfer the interrupted service onto spare network capacity to circumvent a point of failure in the network and it is a critical requirement for IP over WDM networks. In a WDM network, a link failure, fiber cut, node down may be due to human error or natural disasters leading to the loss of large amount of data and multiple failures of all the optical paths that traverse the fiber. So, we have to develop appropriate recovery architecture and strategies that minimize the data loss when a failure on a path occurs in WDM based GMPLS (Generalized Multi-Protocol Label Switching) networks that will offer fast recovery, with speeds comparable to SONET, and versatile survivable functions. Recovery techniques are broadly classified by computation timing as pre-computed and dynamic and by their type of rerouting as link-based, partial path-based and path-based. In dynamic techniques, a search for backup path is J.K. Choi et al. - Internet Draft Expires December 2004 3 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 initiated upon occurrence of a failure. A backup path is computed based on availability of resource at that time of failure. While dynamic techniques provide better resource utilization, they suffer from long delays to search and reroute the traffic on to the backup path and there is no guarantee that the connection can be restored upon failure. Dynamic techniques provide a best-effort type of service. In protection techniques the primary and backup routes are computed and resources are reserved for backup paths before the connection is established. Upon occurrence of a failure the backup path is established and traffic is immediately routed on to the backup path. A pre-computed method avoids long delays in setting up backup paths upon failure. The pre-computed techniques also provide guarantee that a connection can be restored in the event of failure. According to range of rerouting, the recovery techniques are classified into link-based, segment-wised based and path-based recovery. Link-based techniques reroute disrupted traffic around the failed link. This approach requires the ability to identify a failed link at both ends. It also makes recovery more difficult in the event of a node failure. Furthermore, it limits the choice of backup path and thus may use more capacity, while path-base techniques replace the whole path between the two endpoints of a demand. The path-based techniques have better resource utilization while span-based techniques have better recovery time. Therefore, we focus on the path-based recovery, called end-to-end recovery. Most backbone networks have a mesh physical topology. However, the mesh-based schemes have some shortcomings. They are not as fast in failure recovery as ring-based schemes and complicated working path and backup path routing arrangements are used to achieve optimality, and the optimization procedures used for mesh-based schemes are very computationally intensive that are virtually impossible to solve for very large networks. SONET networks are, for the most part, protected in the form of rings. The rings are interconnected in order to provide overall network connectivity and protection. It is possible to design a fast and simple recovery strategy for ring network so ring protection switching is well established and robust in these days. Therefore, we need the ring concept in the mesh optical network. This draft describes the Ring configuration based on SRLG information and the approach of using a centralized Controller that enables fast restoration in J.K. Choi et al. - Internet Draft Expires December 2004 4 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 optical transport networks. Using the centralized Controller guarantees the establishment of a disjoint end-to-end restoration path from failed working paths, and helps in achieving near real-time end-to-end restoration in optical transport networks. 2. Network Architecture for centralized Control using SRLG __________________Control/Management Network__________________________ / \ / +--+ +--+ +--+ \ / | |-------------------| |--------------------------| | \ / +--+Centralized +--+Centralized +--+Centralized \ \ /|| Controller /|| Controller / || Controller / \ / | \ / | \ / | \ / \___|_|__\_________________|_|__\______________________|__ |__\__________/ | | | | | \ | | \ / | \ / | | / | | Control / | \ / | \ / | \ Channel / | \ / | \ / | \ _______/____|_____ \___ _____/____|______\_____ ______|______ |______\_____ \ +--+ | +--+ | \ +--+ | +--+ | \ +--+ | +--+ | \ | |OXC | | | | \ | | | OXC| | | \ | |OXC | | | | \ +--+ | +--+ / \ +--+ | +--+ / \ +--+ | +--+ / \ \ | / / \ \ | / / \ \ | / / \ \ | / / \ \ | Xfail/ \ Data-> \ | / / \ \ | / / \ \ \ / / \Channel \ | / / \ +--+ / \ +--+ / \ +--+ / \ | | / \ | | / \ | | / \ +--+ / \ +--+ / Optical \ +--+ / \ / \ / Transport \ / \____/ \_____/ Network \________/ Figure 1. Network Architecture for Centralized Control using SRLG Generalized Multi-protocol Label Switching (GMPLS) enables service providers to build networks with the flexibility of IP, the reliability of SONET/SDH and the scalability of optics at costs to offer services at extremely competitive prices. GMPLS supports a concept of common control of packet, TDM, wavelength and fiber services, and is a key enabler of the new network architecture model. J.K. Choi et al. - Internet Draft Expires December 2004 5 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 2.1 Introduction to the centralized Controller: This draft addresses the coordination of the IP and optical network survivability based on a consolidated network element, the controller and a truly integrated control plane. This centralized Controller enables an integrated network architecture where each network layer can freely exchange topology and resource information. This allows network performance to be globally optimized across all layers. In addition, a single control plane and the central controller that manages all network layers greatly simplify network management tasks. As far as control and management types are concerned, they can be classified into three categories: centralized, distributed and hybrid control/management. Each control and management type has its' own advantages and disadvantages, but typical telecommunication networks and automatic switched optical networks (ASON) defined in ITU-T follows a centralized control/management architecture in which the control plane is separate from the data plane. In this draft, for path establishment and protection, we consider the control plane to be separated logically from the data plane. Separate Controllers or control/management networks comprising of a series of Controllers could be connected to each other by through signaling channels and appropriate control message exchanges. If the domains of the control/management networks increase, a hierarchical control/management structure could be applied. This can be fully realized in the centralized Controller through logical functional blocks. We do not restrict the interconnection architecture of the optical transport networks such as overlay model, peer model and augmented model. There is a channel interface between the Controller and any node in the optical transport network, and this can be realized using a number of methods, like Simple Network Management Protocol (SNMP), General Switch Management Protocol (GSMP) etc. In this architecture, the Controller is responsible for path calculation and recovery. Some of the recovery functions are also assigned to nodes in the optical network for the purpose of control and load balancing. 2.2 Network Structure: In this draft, we develop the network architecture with a hierarchical structure following the existing network management architecture. We focus on the backbone part of networks where link capacity is at least OC-48 (2.5 Gb/s). Each network node is assumed to have OXC and IP router capabilities in the same hardware setup, which results in the support of multiple traffic types at the same location. The traffic manager in each optical network node also manages multiple traffic types. Each node can communicate directly with the centralized Controller to report its status. As mentioned in Section 2.1, this could be achieved via a network management standard, such as SNMP or GSMP. The Controller takes care of network nodes within the same administrative domain. It also has the responsibility of centralizing domain network management service and integrating the management of the transport network in its respective domain. This structure permits scalability, as well as internetworking of different administrative domains. J.K. Choi et al. - Internet Draft Expires December 2004 6 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 2.3 Control Structure: Network elements within each domain communicate with one another via a common control plane. We assume a dedicated out-of-band control channel between two adjacent nodes, and between each node and the centralized Controller. The common control plane can be implemented based on the GMPLS standard. The Resource Reservation Protocol (RSVP) and Constraint-Based Routing Label Distribution Protocol (CR-LDP) extensions to GMPLS can provide traffic engineering in this unified network architecture. Moreover, neighbor discovery and link state update can employ routing protocol Link State Advertisements (LSA), such as the Intermediate System to Intermediate System (IS-IS) and Open Shortest Path First (OSPF) extensions to GMPLS. 2.4 Control Plane Hierarchy Architecture for SRLG Protection and Recovery: In the integrated control plane proposed here, three levels of functional control hierarchy are mapped into one centralized Controller node and implemented as a single unit. The functional blocks involved in the controller node are: the network processor (the network management system with extended functionalities), the domain processor (the network element management system with extended functionalities), and the node processor. In the first level, the network processor acts as an interface between users and all sub-network domains. Its main functionality is to oversee the provisioning of new connections across multiple sub-networks and to maintain the network-wide topological view. The domain processor supervises tasks within a sub-network domain, such as service provisioning and network status monitoring. It handles requests for connection setup and teardown, and computes explicit paths that meet the SLA of each request. The network monitor observes the overall network health and detects failure and repair events. The databases maintained by the domain processor include the domain topology, the domain link state database gathered via the LSA protocol within its domain, and the domain connection database which keeps track of all established connections in the domain. The node processor manages specific functionalities that can be done in a distributed manner at each node, such as overload handling, failure recovery, and status monitoring. It also detects sudden link overloads, conducts a countermeasure and provides rapid protection and restoration capability in times of failure. The databases maintained by the node processor are the local link state and the local connection databases. The local link state is obtained automatically via the neighbor discovery protocol, while the list of local connections is obtained from all connections that traverse the node. The structure of the topology database may contain the combined IP and optical layer topology in a unified form. The link state database contains information not only about link connectivity, but also about the shared-risk link group (SRLG) J.K. Choi et al. - Internet Draft Expires December 2004 7 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 it belongs to, the resources available on that link, the link protection type, and the link status. This extra information is defined in the LSA extensions to the GMPLS. 3. Logical ring configuration based on SRLG In this part, we describe some of the logical ring configuration methods for optical networks and the functions of the centralized Controller in providing real-time protection and recovery. Ring-based schemes are essentially some extensions of self-healing ring in the mesh topology, and the study of logical ring in mesh network has been developed. 3.1 Logical Ring with SRLG: Shared Risk Link Groups (SRLGs) allow the definition of resources or groups of resources that share the same risk of failure. [6] The knowledge of SRLGs may be used to compute diverse paths that can be used for protection in optical networks. The concept of SRLG has been used to compute a path that is disjoint from a set of links sharing the same risk. When two or more links share the same risk, it may be the case that when a link fails, the others fail at the same time. Proper planning needs to be done for the network to recover from failures due to these risks. The risks are generally represented by SRLGs. The SRLG concept generates another dimension to the existing constraint-based path computation methods traditionally used in hierarchical networks Existing logical ring architectures for recovery do not consider the SRLG information for survivability of working paths and backup paths and is generally configured based on topology information and network characteristics. If the link from the first ingress node is broken, the network cannot provide LSP SRLG disjointness. This is a rather strong bottleneck to support survivability of connections with different bandwidth requirements and QoS constraints. The existing logical ring configuration does not take account into the probability of resource failure and risk of the link. Therefore, the disjoint path may, in some cases, have some problems in being computed and hence the probability of backup path failure increases though the backup path may exist. We need to consider the possibility of failure of the logical ring configuration at the connection setup stage. We propose the network architecture as the concept of the logical ring with the SRLG for reliable transmission in pre-configuration stage using the centralized Controller concept. The proposed network with ring-SRLG is the set of SRLGs with contribution weights per link to avoid backup path failure and guarantee the survivability of traffic. The controller manages the entire domain network, as discussed in Section 2.4. The description follows a logical ring configuration with SRLG for the purpose of restoration in mesh networks. In this architecture, backup paths can be easily established end-to-end using the logical ring configuration. It guarantees the establishment of a backup path that is disjoint from a primary path that is set up. The logical ring with ring-SRLG has both a primary path and a backup path in same ring with one ring-SRLG. Ring-SRLG must support two-way-connectivity, which supports the logical ring architecture in OXC based mesh network and helps in protection and recovery using the centralized Controller concept. Based on a given SRLG table, which is configured at each node by the centralized Controller, one can make rings between a source node and a destination node and many intermediate nodes between the two. J.K. Choi et al. - Internet Draft Expires December 2004 8 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 To extend network scalability, a distributed domain management system must be used, which is determined by the centralized Controller. In order to configure the SRLG-based logical ring, a control unit handling algorithm may be set up in the centralized Controller which then configures the SRLG-based logical ring as well as GMPLS signaling for LSP setups. Our restoration signaling on the SRLG-based logical ring can allow dynamic network configuration instead of static configuration by operators or management systems. The use of signaling with SRLG via the centralized Controller vastly reduces the complexity of network configuration. 3.2 Segment wise logical ring using the centralized Controller: As a network becomes large, the possibility of the size of the ring pattern also became large. So, applying ring does not promote efficiency in terms of end-to-end delay and recovery time. In this section we propose the method, called segment-wised ring [7] that can be effectively applied to real networks without those problems. Additionally, it can support fast recovery and can care for partially multiple simultaneous failures. The main concept of segment-wised ring is to partition a large network into several small networks to configure ring to each small network. This is one of the major functionalities of the centralized Controller, which effectively partitions the addressed domain using the three functional blocks, the Network Processor, Domain Processor and Node Processor. Sub-networks are chosen according to network provisioning such as physical layer conditioning, call demands or QoS demands, which may arise from the user. The following shows segment wise logical ring architecture, with the centralized Controller managing the different sub-networks: Subnetwork 1 Subnetwork 2 Subnetwork 3 +-----------------+--------------+------------------+ | +--+ | +--+ | +--+ | | | | | | | | | | | | //+--+\\ | /+--+\ | //+--+\\ | | // \\ | / \ | // \\ | | // \\ | / \ | // \\ | | +--+ +---+ +---+ +--+ | | | | | | | | | | | | +--+ +---+ +---+ +--+ | | \ / | \\ // | \ / | | \ / | \\ // | \ / | | \ / | \\ // | \ / | | +--+ | +--+ | +--+ | | | | | | | | | | | | +--+ | +--+ | +--+ | +-----------------+--------------+------------------+ // : Working path/ : backup path Figure 2. Segment-wise ring architecture J.K. Choi et al. - Internet Draft Expires December 2004 9 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 3.3 Resource allocation with SRLG by the Controller: The source node can pre-compute the ring configuration based on SRLG information during the primary path setup that it receives from the centralized Controller. The network architecture with the concept of logical ring with SRLG for reliable transmission is established via pre-configuration. To discuss about the survivability of logical topology, we consider that the logical topology is redundant (two-connectivity); the logical topology remains connected when a physical link goes down. The ingress nodes should have the SRLG history and Ring-SRLG combined with logical ring. This can be received from the centralized Controller, as described in Section 2.2 and 2.4. The controller can pre-compute the ring architecture before a failure based on network topology information and SRLG contribution weight factors and also configure the ring architecture after failure by allocating resources via signaling for backup purposes. This information is also conveyed to the individual ingress nodes in the domain. 4. Integrated Layer Survivability and Recovery Mechanisms: In this section we discuss of the integrated layer protection mechanisms appropriate for the central Controller. 4.1 Protection and Recovery Mechanisms: A request of LSP establishment from a client network is handled by the Domain Processor of the centralized Controller, as described in Section 2.4. This is mapped by the Controller to the optical transport network and conveyed to the corresponding nodes. When the Controller receives the request, it will try to compute a logical ring encompassing the ingress and the egress node based on the requested traffic parameters and the SRLG properties. There can be two cases what the Controller can do, based on the number of connection setup requests and the number of already established connections in a domain. It can either distribute the LSP mapping information to the participating nodes in the optical transport domain and clear the domain link state database and domain connection database, or provide the mapping links to the participating nodes. i) Distribution of direct mapping information to nodes in the optical network: In this method, the role of Controller is to find a logical ring, to distribute the mapping table and SRLG information between a primary path and a backup path to the nodes in the optical network, and to trigger the establishment of a J.K. Choi et al. - Internet Draft Expires December 2004 10 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 backup path once a failure occurs. Each node is responsible for maintaining the mapping table and establishment of primary and backup path by using signaling messages. When a node detects a failure, it reports the failure to its corresponding domain Controller. If an end-to-end path protection is used, the Controller triggers the changeover from the primary path to the backup path to the ingress nodes. If the backup path is already established, the ingress node simply changes the direction of the traffic flow from the primary path to the backup path. However, if there is not an established backup path, the ingress node tries to set up a backup path in the network when it receives the trigger from the Controller. Since the ingress node has been maintaining the route object for the backup path received from the Controller, the path setup message from the ingress node will propagate via a route that is disjoint with the primary path. ii) Distribution of mapping information link to nodes in the optical network: In this method, the nodes in the optical transport network performs failure detection and switching operation based on the pointers provided by the forwarding table given by the corresponding domain processor. The Controller performs the roles of finding a logical ring as well as signaling to establish a primary and backup path. When a failure is reported from a node in the optical network to the corresponding Controller, the Controller should look up its' internal table in the domain link state and domain connection databases that maintains the backup path mapped to the failed primary path. By using the Backup Route Object [7], the Controller tries to establish the backup path. Once it is done, the setup message of the backup path will be sent from the Controller managing the ingress node domain to the Controller managing the egress node domain. When the backup path is established through the logical ring configuration, each Controller on the path should send the forwarding table to the corresponding node to configure its' forwarding databases. GSMP could be adapted for this purpose and suitable extensions proposed. 4.2 Protocol based Ring Recovery Mechanisms using the Controller: ITU-T G.otnpro.2 [9] provides protection switching by using logical ring concept. However, it does not take account into the probability of resource failure and risk of the link according to a lack of true diverse fiber routes. We may need to consider the possibility of failure of the logical ring configuration at the connection setup stage. J.K. Choi et al. - Internet Draft Expires December 2004 11 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 The APS protocol (ITU-T G.otnpro.2) can be used between the Controller and the optical network nodes in the ring topology. It is ideal to overcome the bottleneck of the usual 50 ms communications delay between Controller and nodes in the optical transport network. 5. Signaling and Integrated Service Provisioning: A robust and efficient signaling protocol should be used to distribute the mapping table from the Controller to the nodes in the optical transport network and for informing a failure from a node to the corresponding Controller. Signaling for restoration is also needed along the primary path and the backup path at the time of connection setup. GMPLS mechanisms are similar to those used for setting up primary paths and backup paths. In order to support our mechanism, GSMP or APS may be extended or a totally new protocol could be proposed. 6. Conclusion Network survivability is a critical requirement in high-speed networks. So, recovery mechanisms that can provide fast recovery and efficient capacity are needed. Our proposed network architecture using the centralized Controller considered high survivability of backup path, called ring-SRLG that has grouped traffic driven logical rings and shared resources in GMPLS based networks. Ring-SRLG with the centralized Controller can guarantee the survivability of backup paths with constraints to the other logical ring configuration. Our proposed backup paths can be easily established through the end-to-end path, which follows the logical ring configuration. It guarantees the establishment of backup path disjoint from the working path. We have shown that our proposed integrated provisioning, which combines protection efforts from both IP and optical layers, is favorable over the traditional provisioning approach. The integrated protection effort achieves efficient resource allocation in terms of total bandwidth reservation, bandwidth utilization, and connection blocking probability. The level of improvement largely depends on the type of pre-configured underlying lightpath protection. While we expect that the choice of lightpath protection should depend on the nature of service requests, we leave it up to the service provider to make this choice. The scheme takes advantage of information sharing across network layers which is facilitated by GMPLS. The proposed scheme uses GMPLS capabilities to provide end-to-end survivability against network failures. This integrated provisioning scheme can deliver rapid service provisioning dynamically on demand. The consolidated effort simplifies the provisioning process and reduces network management complexity by eliminating the cumbersome coordination of provisioning in separate network layers. J.K. Choi et al. - Internet Draft Expires December 2004 12 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 7. References [1] Mannie, E. et al., "Generalized Multi-Protocol Label Switching Architecture", Internet Draft, draft-ietf-ccamp-gmpls-architecture-07.txt, November 2003. [2] Papadimitriou, D. and Mannie, E. (Editors), "Analysis of Generalized Multi-Protocol Label Switching (GMPLS) based Recovery Mechanisms (Including Protection and Restoration)", Internet Draft, draft-ietf-ccamp-gmpls-recovery-analysis-03.txt, October 2004. [3] Mannie, E. and Papadimitriou, D. (Editors), "Recovery (Protection and Restoration) Terminology for Generalized Multi-Protocol Label Switching (GMPLS)", Internet Draft, draft-ietf-ccamp-gmpls-recovery-terminology-04.txt, October 2004. [4] Lang, P. and Rajagopalan, B. (Editors), "Generalized Multi-Protocol Label Switching (GMPLS) Recovery Functional Specification", Internet Draft, draft-ietf-ccamp-gmpls-recovery-functional-02.txt, October 2004. [5] Papadimitriou, D. et al., "Shared Risk Link Groups Inference and Processing", Internet Draft, draft-papadimitriou-ccamp-srlg-processing-02.txt, December 2003 [6] Czezowski, P. et al., "Optical Network Failure Recovery Requirements", Internet Draft, draft-czezowski-optical-recovery-reqs-01.txt, December 2003. [7] Choi, J.K. et al., "Signaling Extension for the End-to-End Restoration with SRLG", Internet Draft, draft-choi-ccamp-e2e-restoration-srlg-01.txt, August 2004 [8] Lang, J.P., Rekhter, Y., Papadimitriou, D., "RSVP-TE Extensions in support of End-to-End GMPLS-based Recovery", Internet Draft, draft-lang-ccamp-gmpls-recovery-e2e-signaling-03.txt, August 2004. [9] ITU-T SG15 G.otnpro.2 Work In Progress 8. Acknowledgement This work was supported in part by the Korean Science and Engineering Foundation (KOSEF) through the OIRC project. J.K. Choi et al. - Internet Draft Expires December 2004 13 draft-choi-pce-e2e-centralized-restoration-srlg-00.txt July 2004 9. Author's Addresses Jun Kyun Choi Information and Communications University (ICU) 119 Munjiro, Yuseong-gu, Daejeon, 305-714, Korea Phone: +82-42-866-6122 Email: jkchoi@icu.ac.kr Dipnarayan Guha Information and Communications University (ICU) 119 Munjiro, Yuseong-gu, Daejeon, 305-714, Korea Phone: +82-42-866-6282 Email: dg236@cornell.edu Tai Won Um Information and Communications University (ICU) 119 Munjiro, Yuseong-gu, Daejeon, 305-714, Korea Phone: +82-42-866-6282 Email: twum@icu.ac.kr Young Hwa Kim Electronics and Telecommunications Research Institute (ETRI) 161 Gajeong-dong, Yuseong-gu, Daejeon, 305-350, Korea Phone: +82-42-860-5819 E-mail: yhwkim@etri.re.kr Byung Ho Yae Electronics and Telecommunications Research Institute (ETRI) 161 Gajeong-dong, Yuseong-gu, Daejeon, 305-350, Korea Phone: +82-42-860-5819 E-mail: bhyae@etri.re.kr 10. Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved. 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