Direct Data Link (DDL)

A direct data link connects two communication partners. The link is permanently established via a network or a dedicated line and does not need to be connected or disconnected as in the case of a dial-up line. A DDL can be used to transfer digital data for various applications such as phone calls, videos, or computer communication. In addition to physical direct data links in the form of copper pairs or fibre-optic cables, for example, many of these point-to-point connections are based on superordinate network infrastructures such as ATM or SDH. One key characteristic of a DDL is the bit-transparent transfer.

When setting up a direct data link, the network provider establishes a direct communication relationship between the two parties. Deutsche Telekom uses the term “direct data link” (Datendirektverbindung - DDV) as a product name for specific types of dedicated lines with high availability and a low error rate. 

Communication media and transfer rates of direct data links

A variety of media can be used for establishing direct data links. Dedicated lines were originally based on actual wired connections. DDLs make almost exclusive use of digital multiplex systems which can be set up and managed flexibly by means of a superordinate management system. The customer connection can be made via copper pairs, coaxial cable or fibre-optic cable. The available bandwidths range from a few kilobits to broadband connections of several megabits.

DDL availability and error rate

One key characteristic of DDLs is the high reliability and low error rate. This is achieved using intelligent alternate routing options in the superordinate network infrastructure and active monitoring via proactive network management. In the event of a malfunction, the system switches to backup lines, either automatically or via operator. Availabilities of well over 99 per cent and error rates below 10exp-6 are therefore typical. 

Possible applications for DDLs

The possible applications for direct data links are diverse and range from connecting branch offices, to interlinking computer centres and providing network connections for telephone systems. Even cloud telephone services can be used via point-to-point internet connections.