Objectives of Protection and Restoration in Software Printer Quick Response Code in Software Objectives of Protection and Restoration

Objectives of Protection and Restoration use software quick response code integration toencode qr code jis x 0510 in software Microsoft Office Excel Website It is obvious from t Software QR-Code he enumeration of different failures and their impact on the networks described earlier that a fast and reliable carrier link and network equipment protection or restoration method is required. In the current literature, protection and restoration have different meanings. Protection refers to a preplanned system where a protection path.

Survivability is precomputed for e Software QR Code ach potential failure (before the failure occurs) and the path uses preassigned resources for failure recovery (dedicated for speci c failure scenarios or shared among different failure scenarios). In restoration, the recovery route is computed in real time (after the failure occurs) and spare capacity available in the network is used to reroute traf c around the failure. (This is typically used in mesh networks using recon gurable optical cross-connects [Ramamurthy+99a].

) The objective of the protection or restoration methods is to reroute the affected traf c accurately and rapidly using the redundant capacity and equipment available in the network. Even though failures cannot be avoided, quick failure detection, identi cation, and recovery make the network more robust and reliable and ultimately increase the level of customer con dence. For this to be possible, the network s topology must have inherent survivability properties, which determine its ability to survive single or multiple link or equipment failures.

For a network to be survivable, its topology must allow rerouting around a fault condition. This issue falls under the category of network design and planning. For example, for survivability in the face of single link failures, the graph of the network must at least be two-edge connected.

Even if a network has a survivable topology, and robust operating conditions have been established, redundancy is always necessary to ensure that a signi cant amount of information is not lost in the case of ber, equipment, or complete node failure. Together with redundancy, rapid failure detection, identi cation, and recovery features must be present. Service recovery time is important because faster recovery means that less data are lost during the outage.

Recovery speed is important not only because of the economic impact of the outage time but also because of the vital services that are currently supported in the network. Whereas previously an outage meant that a telephone caller had to hang up and try again later, an outage nowadays may affect banks, stock exchanges, airlines, or public safety. Much of the early research in fault protection and restoration was concentrated on point-to-point systems, self-healing rings (SHRs), and centralized/distributed restoration in mesh networks using digital cross-connect systems (DCSs).

This chapter rst reviews some of the important protection/restoration techniques currently used for networks employing SONET and WDM technologies. It then presents some new methods developed in the past few years for protection in optical networks with mesh topologies. The chapter is organized as follows.

Section 8.2 describes current fault recovery techniques used in SONET and DCS networks. These are subdivided into point-topoint and ring (and ring interconnection) protection techniques, and mesh restoration techniques.

Although the techniques presented in Section 8.2 focus on failure recovery using SONET equipment and DCSs, similar approaches have been studied for networks employing SDH, ATM, and a number of other technologies [Ayanoglu+96, Grover04, Kajiyama+92, +94; Kawamura+94, +95; May+95, Nederlof+95, Sato+90, Veitch+96]. Section 8.

3 presents optical-layer protection techniques in networks employing WDM point-to-point and ring architectures. Optical-layer protection in mesh topologies is covered in Section 8.4, including shared optical-layer line-based protection, optical path-based protection, and optical segment protection.

. Multiwavelength Optical Networks Current Fault Protection and Restoration Techniques in the Logical Layer Because of its well- developed protection mechanisms and widespread deployment, we use the SONET network architecture as an example of current practice. The SONET terminology is adopted throughout this section, and the key terms are de ned and explained in Appendix F. SONET standards specify an end-to-end two-way availability objective of 99.

98% for interof ce applications (0.02% unavailability or 105 min/year maximum downtime) and 99.99% for loop transport between the Central Of ce and the customer s premises [Bell91].

To conform to these standards, failure recovery times have to be short. For both point-to-point and SHR systems, automatic protection switching (APS) is used, enabling the network to perform failure recovery in tens of milliseconds (of the order of 50 ms to detect the failure and to complete the switching process)..

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