Page 323 - Optical Communications Essentials

Network Management

Network Management 313

as the SONET/SDH standard enabled the management of single-wavelength
optical networks using equipment from many different vendors, the G.709 stand-
ard enables the broad adoption of technology for managing multiwavelength
optical networks. The structure and layers of the OTN closely parallel the path,
line, and section sublayers of SONET.
The model is based on a client/server concept. The exchange of information
between processes running in two different devices connected through a net-
work may be characterized by a client/server interaction. The terms client and
server describe the functional roles of the elements in the network, as Fig. 18.5
illustrates. The process or element that requests or receives information is
called the client (here the browser), and the process or element that supplies the
information is called the server.
Figure 18.6 illustrates the three-layer model for a simple link. Client signals
such as IP, Ethernet, or OC-N/STM-M are mapped from an electrical digital for-
mat into an optical format in an optical channel (OCh) layer. The OCh deals
with single wavelength channels as end-to-end paths or as subnetwork connec-
tions between routing nodes. As shown in Fig. 18.7, the optical multiplex sec-
tion (OMS) layer represents a link carrying groups of wavelengths between

Figure 18.5. The terms client and server describe the functional
roles of communicating elements in the network. Here the browser
is the client.

Ethernet Fibre Channel
IP ATM OC-n/STM-N Electric signals

Optical Channel
Optical Channel
Optical Channel (OCh)
Optical Channel (OCh)
Payload Unit (OPU)
Payload Unit (OPU)
Optical Multiplex Optical Channel
Optical Channel
Optical Multiplex
Section (OMS) Data Unit (ODU)
Data Unit (ODU)
Section (OMS)
Optical Transport Optical Channel
Optical Channel
Optical Transport
Section (OTS) Transport Unit (OTU)
Section (OTS)
Transport Unit (OTU)
Figure 18.6. Three-layer model for a simple link in an OTN.
The OCh is divided further into three sublayers.
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