1.10 Communication Technologies

Communication technologies are used for carrying network layer services, whether for the Internet or PSTN.

In this sense, communication technologies provide transport services for both the Internet and PSTN. Unfortunately, the term transport is used in several ways in networking; these are two such examples.

To provide transport services, transport networks are deployed that may be based on one or more communication technologies.

At the real physical (duct) level though, fibers or coaxial cables are used for wired transport services. Such cables are either buried underground or carried over ground on poles; submarine cabling is used for connecting different continents. Nowadays, submarine cables are almost exclusively based on fiber cables.