Optical-fiber Technology

FITL (Fiber In The Loop) - Fiber in the Loop system

the latest offer of world telecommunication concerns are fiber in the loop systems which enable common realization of various telecommunication and TV services. Such type of systems includes FITL system. FITL enables construction of a common network for rendering services to telephone and TV subscribers with limitation or complete elimination of hitherto used copper wires. FITL systems constantly try to live up to forever growing requirements towards public telephone network operators. Apart from provision of basic telecommunication services, such as telephone connectivity, more and more is said about the possibility to render services out of the basic range, such as multimedia services: video on demand, videoconferences, video telephone, quick access to the Internet, electronic shopping and so on. FITL system widely uses the fiber technique, recognized and tested in cable transmission lines. It assumes application of optical carriers, mainly in main or distributive part of a classic access network. Depending on location of the optical network unit, ONU, three types of network architecture can be distinguished: FTTB (Fiber To The Building), FTTC (Fiber To The Curb) or FTTH (Fiber To The Home). Name of a given architecture describes the place of location of ONU. All of these solutions can use the transport part of a telecommunication network to obtain access to the group of services, which is also based on the optical-fiber cable.

Reference models for FITL architecture

FITL system consists of the following elements:

a) OLT (Optical Line Termination) - termination of the optical line, sometimes called HDT (Host Digital Termination),
b) ONU (Optical Network Unit) - optical network unit,
c) ODN (Optical Distribution Network) - optical distribution network.

OLT, optical line termination, is a type of access net contact point with the access point to telecommunication services (depending on configuration of the network, it can either be an access group or directly the service group. ex. the telephone exchange). Physically the connection between OLT and one or more of the optical network units is realized via ODN on one or two optical fibers, depending on the applied transmission method (possible duplex, diplex or simplex). ONU, delivers application information of the given telecommunication service between ODN and the subscriber and the other way around. The contact point of the user with the access network is subscriber`s plug.

FTTC, FTTB, FTTH Architectures Specification

Depending on location on ONU module in the access net, three FILT network architectures are distinguished:

a) FTTC - Fiber To The Curb,
b) FTTB - Fiber To The Building,
c) FTTH - Fiber To The Home.

It must be noted, however, that the above specifications determine the level of penetration of an optical-fiber medium into the access network. Transmission from ONU to the subscriber is based on classical access net, i.e. traditional copper strand using one of the available xDSL transmission techniques. All of the above-mentioned solutions provide a sufficient band for present and future interactive, distribution, narrow- or broad-band applications.

See also: Optical-fiber Technology - Architecture Optical-fiber Technology - modes