Digital Data Service (DDS)


Digital Data Service is a family of leased line data communication technologies that provides a dedicated synchronous transmission connection at speeds of 56 Kbps.

What is Digital Data Service (DDS)?

DDS stands for Digital Data Service, is a family of leased line data communication technologies that provides a dedicated synchronous transmission connection at speeds of 56 Kbps. Digital data service (DDS) is only one example of a type of digital line; others include Integrated Services Digital Network (ISDN) and T1. DDS can be used in either multipoint or point-to-point communications and requires dedicated digital lines. DDS lines can also be used to connect buildings on a campus, usually with a maximum distance of about 3 miles.

How DDS Works?

“DDS” was originally a trademark for an AT&T all-digital service running at 56 Kbps, but the term has evolved into a general descriptor for a variety of digital services offered by different carriers under various names. DDS is usually available in both a dial-up version called switched 56 and a dedicated leased line service for continuous connections. The dial-up version can serve as a backup for the dedicated version.

Typically, DDS uses four wires to support digital transmission speeds of 56 Kbps, but it is actually a 64-Kbps circuit that uses 8 Kbps for sending signaling information. Some vendors provide a variant of DDS with a data transmission rate of a full 64 Kbps.

To use DDS services for wide area network (WAN) connectivity, route packets from your local area network (LAN) through a bridge or a router, which is connected by means of a V.35 or RS-232 serial interface to a CSU/DSU (Channel Service Unit/Data Service Unit).

The CSU/DSU is connected to the four-wire termination of the DDS line by means of an M-block connector, a screw terminal block, or some other connection mechanism. The Channel Service Unit (CSU) converts the data signal into a bipolar signal suitable for transmission over the telecommunications link.

The DDS lines themselves use four wires and support speeds of 64 Kbps, but 8 Kbps of bandwidth is usually reserved for signaling, so the actual data throughput is usually only 56 Kbps.

Digital data service (DDS)
Digital data service (DDS)

DDS lines are dedicated lines with negligible connection establishment latency; they are always “on” and never “busy”.

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