TABLE OF CONTENTS Ghani Abbas,
Marconi Communications Ltd.
To the memory of my wife, Lynda
Network Survivability is a term that refers to the ability of the network to maintain an acceptable level of service during a network or equipment failure or traffic signal degradation. There are several survivability mechanisms covering a wide range of network architectures, technologies, and allocation of network resources.
In the last ten years, the ITU-T has developed a number of recommendations for generic and technology-specific protection schemes. This chapter will review these recommendations and their applications in the network using the ITU-T terminology.
Generally, there are two types of network survivability techniques:
Network Protection: This is the replacement of a failed or degraded working resource with a preassigned standby resource. Protection mechanisms tend to be deterministic in nature. When a failure occurs, what will happen is fairly easy to predict and cater for. Generally, the protection action is completed in tens of milliseconds. Protection mechanisms are autonomous and operated independently from the control or management planes. There are several protection schemes of various architectures and for various technologies. Most of these schemes are defined in the following ITU-T recommendations:
Rec. G.808.1 [1], Generic Protection Switching linear trail and subnetwork protection,
Rec. G.873.1 [2], Optical Transport Networks (OTN) Linear protection,
Rec. G.841 [3], Types and characteristics of SDH network protection architectures,
Rec. 1.630 [4], ATM protection switching, and
Rec. Y.1720 [5], Protection switching for MPLS networks.
Network Restoration: This is the replacement of...
