Data communication
Terminology
Data terminal equipment (DTE) is an end instrument that
converts user information into signals or reconverts received signals. These
can also be called tail circuits. A DTE device communicates with the data
circuit-terminating equipment (DCE). The DTE/DCE classification was introduced
by IBM.
Basically, V.35 is a high-speed serial interface designed to
support both higher data rates and connectivity between DTEs (data-terminal
equipment) or DCEs (data-communication equipment) over digital lines.
Two different types of devices are assumed on each end of
the interconnecting cable for a case of simply adding DTE to the topology (e.g.
to a hub, DCE), which also brings a less trivial case of interconnection of
devices of the same type: DTE-DTE or DCE-DCE. Such cases need crossover cables,
such as for the Ethernet or null modem for RS-232.
A DTE is the functional unit of a data station that serves
as a data source or a data sink and provides for the data communication control
function to be performed in accordance with the link protocol.
The data terminal equipment may be a single piece of
equipment or an interconnected subsystem of multiple pieces of equipment that
perform all the required functions necessary to permit users to communicate. A
user interacts with the DTE (e.g. through a human-machine interface), or the
DTE may be the user.
Usually, the DTE device is the terminal (or a computer
emulating a terminal), and the DCE is a modem or another carrier-owned device.
A general rule is that DCE devices provide the clock signal
(internal clocking) and the DTE device synchronizes on the provided clock
(external clocking). D-sub connectors follow another rule for pin assignment.
• 25 pin DTE
devices transmit on pin 2 and receive on pin 3.
• 25 pin DCE
devices transmit on pin 3 and receive on pin 2.
• 9 pin DTE
devices transmit on pin 3 and receive on pin 2.
• 9 pin DCE
devices transmit on pin 2 and receive on pin 3.
This term is also generally used in the Telco and Cisco
equipment context to designate a network device, such as terminals, personal
computers but also routers and bridges, that's unable or configured not to
generate clock signals. Hence a PC to PC Ethernet connection can also be called
a DTE to DTE communication. This communication is done via an Ethernet
crossover cable as opposed to a PC to DCE (hub, switch, or bridge)
communication which is done via an Ethernet straight cable.
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