Network Sales and Services Handbook (Cisco Press Networking Technology)
The foundation of any optical system is the fiber optic cabling. Basic fiber optic cables consist of the following components:
Silica core
Cladding
Coating, strength members, and a plastic jacket
Transceivers
Fiber optic transmission operates by sending light at a specific angle down a fiber optic cable. This fiber optic cable is made up primarily of a silica core and glass cladding. It is this glass cladding that acts as a mirror, reflecting the light signal down the cable to its (destination) termination point.
The reflective path taken by light in a fiber is considered the mode. There are two modes used in fiber optic networks:
MMF Multimode fiber is used for specific applications where the distance limitation of two kilometers is not an issue.
SMF Single-mode fiber can reach as far as 100 200 kilometers before a fiber optic repeater, or amplifier, is required.
SONET enables the interoperation of multiple technologies and vendor products by defining standard physical network interfaces. SONET was designed for the public telephone network where fiber optic cabling prevailed for long-distance voice traffic transmissions.
DWDM is an optical technology used to increase bandwidth over existing fiber optic backbones. DWDM combines and transmits multiple signals simultaneously at different wavelengths on the same fiber, in effect creating several virtual fiber connections over a single physical connection. DWDM-based networks are protocol and bandwidth independent, capable of sending data in IP, ATM, SONET/SDH, and Ethernet frame formats. DWDM-based networks can carry different types of traffic at different speeds over an optical channel, such as bandwidth rates of between 100 Mbps and 2.5 Gbps.
SONET and DWDM are both viable options for network service providers to implement in the network backbone, with each providing its own advantages. SONET has the advantage over DWDM in regard to automatic ring protection; DWDM has the advantage over SONET when it comes to available bandwidth capacity.