6.2.4.3 Data traffic – Internet access

In the near future, the area of fixed network services will experience a major change, as classical voice telephony is stagnating, while data traffic, especially on account of the Internet boom with the ever larger number of attractive Internet services (www, e-mail, FTP, Newsgroups, VoIP, etc.) is growing vigorously. This trend is even further enhanced by the up-and-coming
"e-commerce". One of the consequences of increased (private) Internet usage in the evening, which in many cases occurs via dial-up modems, is that the so-called "rush hour", i.e. that hour in the course of a day when most traffic can be observed, on an hourly average, is shifting from the classical mid-morning hour (10 - 11 hrs.) to the evening hours (approximately in the area of 19 to 20 hrs.).

Telecommunications providers offer their customers new high-bit-rate data services, in addition to the classical dial-up modem, where up to 56 kbit/s can be transmitted downstream, depending on the quality of the line. To some extent, this is done on the basis of alternative infrastructures, such as the network of the cable television operators (with the cables being adapted for bi-directional traffic).

Another technical variant, based on the telephone lines, is to implement high bit-rate DSL services (Digital Subscriber Line), the best-known of which is available on the market by the name of "ADSL" (Asymmetric Digital Subscriber Line). The term "asymmetric" refers to the different transmission rates in the downlink (to the subscriber, high bit-rate) and in the uplink (to the switching exchange, low bit-rate). The usefulness of this asymmetry, when used by private users, becomes apparent when looking at a typical Internet session, where the user keys in a few data and retrieves large data volumes from the Internet (to build up a new image or because the downloading of a 10-MB file has just been triggered).

The ADSL service may easily be conducted via an existing POTS or ISDN basic access, together with the existing subscriber line, since voice telephony (POTS, ISDN-BA) and the ADSL data service use disjunctive frequency bands (ADSL works in the higher frequency band).

The associated signals are divided at the customer's location by means of frequency filters ("splitter") and at the local connection exchange where there are also the ADSL modems. On the side of the switching exchange, the ADSL modems are implemented technically as so-called DSLAM (Digital Subscriber Line Access Multiplexer), where the data packets of the individual subscriber lines are compiled for further transmission (or where the packages are distributed in the direction of the subscribers). For the transport of the data packages from the DSLAM at the central distribution frame of the local exchange to the service provider (typically an Internet Service Provider) a separate data network is used (e.g. on the basis of ATM). In other words, the "classical" line-switched voice telephony network is not burdened with these data connections. In Austria, ADSL is currently offered with a downstream data rate of 512 kbit/s, which corresponds to about ten times the rate of a modern V.90/V.92 dial-up modem.

The V.90/V.92 dial-up modems and the ADSL service (upstream data rate - 64 kbit/s) are primarily of interest for private users and small companies. A special variant for business customers are ADSL accesses with upstream bit rates of up to 256 kbit/s, which are used for special applications. For large-account customers data services and the Internet access are normally implemented via leased lines ("dedicated lines"). Here, the provider makes available to the customer a fixed, pre-set data rate, on a permanent basis, 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 lower end to 155 Mbit/s at the upper end of the service range.