Page 310 - Optical Communications Essentials

Optical Networks

300 Chapter Seventeen

17.5.1. Optical network services
Traditionally, optical networks such as SONET were designed for backbone net-
works for enabling a large number of voice and data channels to be multiplexed
and transported efficiently and reliably. The growth of the Internet changed
that scenario to one in which optical services are delivered directly to the customer.
These services include LAN-based packet-oriented services using Ethernet and
circuit-oriented applications such as data storage, video, and file transfers. In
setting up optical services, a key point to remember is that not all traffic is cre-
ated equally. Traffic from free Internet services needs only a low grade of service,
whereas business traffic such as banking transactions requires a high grade of
service. However, no matter who they are, customers demand that their services
be provisioned rapidly. Another important factor that needs to be taken into
account when establishing the criteria for optical network services is that the
dynamic nature of demands from metro area users requires a flexible network
that can handle service churns, service mixes, and variable service growths.

17.5.2. OTN standards
Many people are working on OTN concepts, and the ITU-T is establising rec-
ommendations. In November 2001 the ITU-T agreed on the following nine new
and revised OTN documents (see also G.984.1 and G.984.2).

■ G.872, The Architecture of Optical Transport Networks
■ G.709, Interface for the OTN
■ G.798, Characteristics of OTN Hierarchy Equipment
■ G.8251, The Control of Jitter and Wander within the OTN
■ G.7041, Generic Framing Procedure (GFP)
■ G.7710, Common Equipment Management Function Requirements
■ G.874, Management Aspects of the OTN Element
■ G.874.1, OTN Protocol-Neutral Management Information Model for the
Network Element View
■ G.7712, Architecture and Specification of Data Communications Network

17.5.3. Wavelength routing
Recently systems have been devised that use optical wavelength switches or
optical cross-connects to enable data to be routed entirely in the optical domain.
Wavelength-routed networks need a control mechanism to set up and take
down all-optical connections. The functions of the control mechanism are (1) to
assign a communications wavelength when a connection request arrives and to
configure the appropriate optical switches in the network and (2) to provide
information on usage and status of the wavelengths so the nodes can make rout-
ing decisions. The wavelength routing can be static or dynamic. In static routing

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