VI.1.3 Increasing importance of data traffic

 

   

In the near future fixed network services will be subject to substantial change, since conventional voice telephony is stagnating while data traffic is sharply on the rise, in particular because of the Internet boom with its increasing number of attractive web pages.

This trend is even intensified by beginning E-Commerce. The telecommunications providers have already responded to this trend, offering their customers new high bit rate data services. Since the common voice telephony infrastructure is not suitable without upgrading¹, other infrastructures, such as coaxial cables of cable TV, have to be used or the existing infrastructure has to be modified.

The latter is done by means of DSL ("Digital Subscriber Line") services whose best known variant, "ADSL" ("Asymmetric Digital Subscriber Line") is already available on the market. This technology was developed in the USA about 10 years ago in the course of considerations to transmit videos over the subscriber line. This project, however, turned out a failure so that ADSL was consigned to oblivion to be rediscovered, but not reinvented, by the telecommunications operators for the purpose of providing faster data links to the customers.

  

The ADSL service can be easily carried over an existing subscriber line together with an existing POTS or ISDN line since voice telephony (POTS, ISDN-BA) and the ADSL data service use disjunct frequency bands. The associated signals are separated by frequency separating filters (splitters) located at the customer's premises and in the local exchange. For the transport of the data packages from the local exchange to the service provider (typically an ISP) a separate data network is used, i.e. the "classic" circuit switched voice telephony network does not carry the additional load. In Austria, ADSL is currently offered at a downstream data rate of 512 Kbit/s, which is ten times the rate of a V.90 modem.

While V.90 technology and ADSL services are of interest primarily to private users of telecommunications services, major customers are offered data services via leased lines. Thereby the provider makes a fixed data rate permanently available to the customer between two geographically defined network termination points. The data rates of these leased lines range from a multiple of the ISDN B channel (64 Kbit/s) at the bottom end up to 155 Mbit/s at the upper end of this service offering.
 
1) Without upgrading, a maximum of 56 Kbit/s can be transmitted via a POTS line using a modem (ITU-T Standard V.90); ISDN basic access allows data transmission at 64 Kbit/s, the second channel remaining free for speech or fax, or at 128 Kbit/s if the capacities of both B channels are combined.