Page 316 - Optical Communications Essentials

Network Management

306 Chapter Eighteen

groups of people, since each organization may take a different approach to fit
its own needs.
As the first topic, Sec. 18.1 describes the constituents of a network management
architecture and outlines their purposes. Section 18.2 presents the basic concepts
of the five generic network management areas outlined by the ISO. The gathering
of status information from network devices is done via some type of network man-
agement protocol. The Simple Network Management Protocol (SNMP) is one
example of this, as Sec. 18.3 shows. This section also addresses a set of remote-
monitoring standards that extends and improves on the SNMP framework.
To deal with standardized management functions in the optical layer, the
ITU-T created document ITU-T Recommendation G.709, Network Node Interface
for the Optical Transport Network (OTN), which also is referred to as the Digital
Wrapper standard. As discussed in Sec. 8.4, whereas the SONET/SDH standard
enabled the management of single-wavelength optical networks, the G.709
standard enables the broad adoption of technology for managing multiwave-
length optical networks. Section 18.5 gives details on functions that are specific
to optical communication elements directly, such as optical line terminals
(OLTs), optical amplifiers, optical add/drop multiplexers (OADMs), and optical
cross-connects (OXCs). Finally, Sec. 18.6 describes the use of a separate optical
service channel (OSC) in links that contain optical amplifiers. The OSC operates
on a wavelength that is outside of the standard WDM transmission grid being
used. This allows the OSC to control and manage traffic without deploying a
separate Ethernet control connection to each active device in the network.

18.1. Management Architecture
Figure 18.1 shows the components of a typical network management system and
their relationships. The network management console is a specialized workstation
that serves as the interface for the human network manager. There can be sev-
eral of these workstations that perform different functions in a network. From
such a console a network manager can view the health and status of the network
to verify that all devices are functioning properly, that they are configured cor-
rectly, and that their application software is up to date. A network manager also
can see how the network is performing, for example, in terms of traffic loads and
fault conditions. In addition, the console allows control of the network resources.
The managed devices are network components, such as optical line terminals,
optical amplifiers, optical add/drop multiplexers, and optical cross-connects. Each
such device is monitored and controlled by its element management system (EMS).
Management software modules, called agents, residing in a microprocessor within
the elements continuously gather and compile information on the status and
performance of the managed devices. The agents store this information in a
management information base (MIB) and then provide this information to
management entities within a network management system (NMS) that resides
in the management workstation. A MIB (typically pronounced mib) is a logical
base of information that defines data elements and their appropriate syntax and

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