CCAMP Working Group D. Papadimitriou Internet Draft Alcatel Document: draft-pbh-packet-optical-escalation-00 Category: Internet Draft Riad Hartani Expires: August 2001 Caspian Networks Debashis Basak Accelight February 2001 Packet-Optical Escalation Strategies Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. The following verbatim statement must follow the optional opening sentence: 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. Conventions used in this document: 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 [2]. Abstract The focus of this memo is on hybrid packet and optical layer restoration architectures. We start with an initial description of general restoration related aspects, and analyze various restoration schemes and focuses on one key aspect: efficient inter-working between packet and optical layer restoration mechanisms. This analysis results in potential control protocols enhancements required to achieve the fast-restoration targets. Internet Draft û CCAMP Working Group û Expires August 2001 1 Draft-pbh-packet-optical-escalation-00.txt February 2001 1. Introduction - Scope In the context of packet-over-optical networks, also known Packet û over-Wavelength (POW) networks, restoration depends on the service being offered. It can happen either at the packet layer, the optical layer or both. In the latter case, coordination between the various restoration schemes is required to maximize efficiency. 2. Restoration Strategies Prior to restoration, fault detection and fault localization must be performed. This can happen at the packet and/or optical layer. Nevertheless, fault detection and location can be performed simultaneously (within the same layer). Various mechanisms can be used to achieve this (some of them may be extended for the hybrid packet/optical case). Following propagation of failure to the nodes responsible for restoration, restoration is performed. In all possible cases, we assume that both the packet and optical layers have their own control entities (in a general case, these are instantiations of various signaling, routing and management protocols). No assumption is made on the physical location of these control entities. They could be centralized, distributed, with dynamic or static behavior. For efficient packet/optical interaction, an interaction between the packet and optical control entities is required. The so-called integrated packet/optical control entity (similar to the concept of a Packet/Optical Network Controller, we will call it PONC in the latter) should be informed as soon as possible of the failures and their location. PONC may or may not be involved in the restoration based on the selected scheme, but can be responsible for overall network re-optimization once the restoration is performed. Optical network re-optimization implies to define what a Lambda-LSP restoration requires. Consequently, we need to first define what re- optimization means. This in turn requires to define which are the constraints to keep the same topology that the one prior to the failure or take into account the updated "availability" values into account in order to have a new topology (in fact this could be mapped to a dampening mechanism). Our analysis covers different scenarios. All of these scenarios consider cases where failures occur at Layer1. In the case of Layer2/Layer3 failure, the packet layer is the entity responsibly for recovering the failure. Also, these scenarios consider failures within the optical network and not packet to optical access failures (physical connectivity between packet and optical device). In the latter case, alternative strategies may be used at both the packet and optical layer (most of these will have a M:N, 1:N, 1:1 or access path protection while relying on Sonet/SDH overhead for failure Internet Draft û CCAMP Working Group û Expires August 2001 2 Draft-pbh-packet-optical-escalation-00.txt February 2001 detection. If no physical protection then Layer3 should handle the restoration). The approach should be Sonet/SDH or even G.709 independent (the target of IPO and OIF are packet over lambda switching). It should also define the appropriate mechanisms to allow the packet and optical layers to efficiently cooperate while providing the required restoration. This implies that the control plane mechanisms currently defined in [GMPLS-SIG] need to be extended. 3. Escalation Strategies 3.1 Scenarios The various scenarios analyzed here are described as follows: 1. The optical layer handles the restoration: in this case, the restoration will be transparent to the packet layer. This is generally achieved by having pre-provisioned (or not) optical paths in a 1+1, 1:1 or 1:N scheme within the optical network or establishing them when required. See [IPO-REST] where optical-layer restoration mechanisms are fully detailed. 2. The packet layer handles the restoration. In this case, under the assumption that the packet layer is made aware of the Layer 1 failure within the optical network (through GMPLS Notification or through PONC for example), the packet layer handles the restoration by putting traffic over alternate paths that have not been affected by the failure. The restoration path can be either pre-established or established on request by the packet layer. PONC can in turn perform a longer term overall network optimization. 3. The packet and optical layer coordinate the overall restoration: This can happen in various scenarios. For example, the optical is responsible for restoration but is not able to find sufficient optical bandwidth within the optical network or in a similar way, the packet layer is responsible for restoration but can not fit the restored traffic onto alternate unaffected Layer-3 paths. In both of these cases, the optical and packet layers should cooperate to achieve the right recovery. In this case, it is important to make sure that restoration at both levels does interact positively. For example, hold-down timers may be used to inform one of the layers to wait until the results of the action performed by the other layer is known. However, by combining inter-layer synchronization a better restoration time should be achieved. 3.2 Packet/Optical Layer Interaction and Escalation Strategy This section focuses on the inter-working aspects of packet and optical restoration aspects. Internet Draft û CCAMP Working Group û Expires August 2001 3 Draft-pbh-packet-optical-escalation-00.txt February 2001 The escalation strategy is defined by the set of detection functions describing the originating failure, the protection functions applied within recovery process to recover the failure and the interaction between the upper and/or lower layers protection functions applied during the recovery process. The escalation strategies are governed either by arbitrarily setting failure detection and recovery completion time or by explicit message exchange between the layers. Two main escalation strategies (also referred to as inter-working strategy) are currently defined and briefly summarized here: - Bottom-up strategy starts at closest layer to the failure (generally the bottom layer) and escalates toward the upper layer upon expiration of the recovery timer (hold-off timer). This timer is defined in such a way that is allocates ôenough timeö the lower layer(s) to detect the failure, execute the recovery process and recovery completion time before triggering recovery process defined at the higher layer(s). - Top-down strategy starts at the upper(most) layer and escalates downward to the lower layer(s); depending on the working level, the top-down strategy is suitable when each of the layers define Class- of-Services (CoS) so that the escalation strategy might take this CoS into account when executing the recovery process. Combination of these strategies known as Hybrid Strategy refers to strategies where both upper (in this case the packet/MPLS) layer and the lower layer collaborate in order to achieve the fastest restoration. 3.3 Bottom-Up Strategy We assume here a classical Bottom-up strategy since it has the shortest recovery time (with respect to the Top-Down escalation strategy), and define the threshold at which the upper-layer protection needs to be ôexecutedö. In packet LSP over optical rings, the following escalation strategy can be defined, where the physical layer (optical transmission) triggers the OCh layer protection mechanism and Subsequently, if this mechanism does not restore the connection within a given maximum restoration time the upper layer (LSP restoration mechanism is performed). Packet Layer <==> PSC interface <==> GMPLS Signaling ^ ^ | | | | | | OCh Layer <==> LSC interface <==> GMPLS Signaling ^ | | Internet Draft û CCAMP Working Group û Expires August 2001 4 Draft-pbh-packet-optical-escalation-00.txt February 2001 | Fiber Layer <==> Physical Interface <==> Layer-1 Mechanisms In optical SDH/Sonet rings, the following escalation strategy can be defined, where the OTN layer generally refer to OMS/Line layer and be compared to classical TDM SDH/Sonet or G.709 based Rings: Packet Layer <==> PSC interface <==> GMPLS Signaling ^ ^ | | | | | | Path (OCh) Layer <==> TDM (G.709) interface <==> GMPLS Signaling ^ ^ | | | | | | MS (OMS) Layer <==> TDM (G.709) interface <==> GMPLS Signaling ^ | | | TS (OTS) Layer <==> Physical Interface <==> Layer-1 Mechanisms This approach is based on common coordination achieved by resorting escalation strategies. At each level, the resiliency scheme is activated sequentially starting from the lower to the upper layer. This imply that at each level the detection of a failure condition (and restoration time) triggers either a restoration/protection mechanism and if the restoration completion time is reached then triggers an upper-layer restoration/protection mechanism. 3.4 Top-Down Strategy Top-down strategy starts at the upper-(most) layer and escalates downward to the lower layer(s); depending on the working level, the top-down strategy is suitable when each of the layers define Class- of-Services (CoS) so that the escalation strategy might take this CoS into account when executing the recovery process. Packet Layer <==> PSC interface <==> GMPLS Signaling | | | | | | v v OCh Layer <==> LSC interface <==> GMPLS Signaling | | | v Fiber Layer <==> Physical Interface <==> Layer-1 Mechanisms Internet Draft û CCAMP Working Group û Expires August 2001 5 Draft-pbh-packet-optical-escalation-00.txt February 2001 3.5 Hybrid Strategy The hybrid strategy can be represented as follows: Packet Layer <==> PSC interface <==> GMPLS Signaling | ^ | | v | | | v OCh Layer <==> LSC interface <==> GMPLS Signaling ^ | | OTS Layer <==> Physical Interface <==> Layer-1 Mechanisms 4. Restoration Timing In the hybrid model, the timing plays a very important role. The idea is to define a restoration hold-off timer per layer but also a restoration quantum time (i.e. a restoration interval) during which synchronization of the restoration between layers can occur. 5. Protocol Extensions TBD. 6. Security Considerations Security considerations are of primary concern when speaking about multi-layer processes. However those are left for further study. 7. References [GMPLS-SIG] P.Ashwood et al., æGeneralized MPLS û Signaling Functional DescriptionÆ, Internet Draft, draft-ietf-mpls- generalized-signaling-01.txt, November 2000. 8. Acknowledgments 9. Author's Addresses Papadimitriou Dimitri (Editor) Alcatel IPO-NSG Francis Wellesplein, 1 Internet Draft û CCAMP Working Group û Expires August 2001 6 Draft-pbh-packet-optical-escalation-00.txt February 2001 B-2018 Antwerpen, Belgium Phone: +32 3 240-8491 Email: dimitri.papadimitriou@alcatel.be Debashis Basak Accelight Networks 70 Abele Road, Bldg.1200 Bridgeville, PA 15017, USA Phone: +1 412 220-2102(ext115) Email: dbasak@accelight.com Riad Hartani Caspian Networks 170 Baytech Drive, San Jose, CA 95134, USA Phone: +1 408 382-5216 Email: riad@caspiannetworks.com Internet Draft û CCAMP Working Group û Expires August 2001 7 Draft-pbh-packet-optical-escalation-00.txt February 2001 Full Copyright Statement "Copyright (C) The Internet Society (date). 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