PDF of this tutorialTo understand photonic networks in greater depth, examine the structure of the typical photonic network in Figure 1. The network elements shown on this topology map are all representative. Actual networks may contain all or only some of these network elements, and certain other common network elements are not represented here for simplicity’s sake.
Two key structures comprise the network:
- The core network, made up of a high-speed Internet protocol (IP) backbone or telephony switching network handling voice traffic (typically at 2.5 to 10 Gbps)
- A local or metropolitan network splitting off from the core through a wavelength division multiplexing (WDM) element (typically at 155 to 622 Mbps)
Figure 1. A Simplified Photonic Network with a Ring Architecture
In this illustration, the high-speed core network is configured as interconnected rings that make up a complete telecommunications network. Signals in the core ring pass from one DWDM link to the next core ring. Within each DWDM link, specific synchronous optical network (SONET) or synchronous digital hierarchy (SDH) colors or channels can be routed to metro or access network tributaries or to other core rings.
In the past, DWDM elements were not used in the network—SDH/SONET electro-optical add/drop multiplexers (ADMs) were used to move tributaries off of or onto the core. Today, the tributary channels can be routed to a DWDM link or an ADM. The light wave–based channel is converted into an electrical signal, then back into component SONET, SDH, DS–n (e.g., T-1) or plesiochronous digital hierarchy (PDH) (e.g., E-1) signals. These signals are then routed to tributaries at different locations. Within the ADM, the signal is decomposed further into different channels at lower, standard American National Standards Institute (ANSI) or European Telecommunications Standards Institute (ETSI) data rates such as T-1, E-1, DS–3, E-3, etc.
