D
DAMA
Demand Assigned Multiple Access, a method for sharing
satellite bandwidth, co-ordinated by a control station that brokers requests
for channels arising, on demand, from the users at each site.
DBR
A stand-alone system to receive and decode a satellite
broadcast data signal. Also available as a card to fit inside a PC.
DCE
Data Communications Equipment; the equipment that provides a data connection
from one point to another
D Channel
The ISDN signalling channel. Emerging as a low
volume general purpose data communications technology to replace the local
tail connection between a packet switched network and the user.
Delay
The
time it takes a piece of information to traverse a link or network. This
arises from the time it takes to serialise the information and the latency
in the network. In the case of a satellite system the latency will be
approximately 250ms for each direction of travel over a geostationary
satellite.
Dial-up
A system using the telephone network to establish
and provide a connection.
Digital
A system of representing information as a series
of distinct values that are suitable for representation as integer numbers.
Digital Signature
A one-way encrypted precis of a message, similar
to a checksum, that demonstrates the origin and integrity of the message.
Disaster Recovery
(1) A backup facility to be used in the event that
some critical component in a system fails.
(2)The act of switching to the backup facility.
Downlink
Transmission path from the satellite to the Earth
DRO
Dielectric Resonant
Oscillator, a simple, low cost frequency reference system commonly used
in satellite TV reception and, with appropriate compensation, in some
data communications systems. cf: PLL.
Drop and Insert
A
method of adding and extracting data from timeslots in a multiplexed E1
or T1 link as it passed through a device.
DTE
Data Terminal Equipment; interfaces with DCE and
acts as the end point for communications.
DVB
Digital Video Broadcast: the new standards for distributing TV and data,
including MPEG.