1.      DTE

is a terminal equipment that changes user information into
signals or reconverts received signals. It is typically either a dumb terminal
or the serial port on a computer/workstation. DTE does not interface with
another one, however it often communicates with a DCE. DTE includes any components
that works either as a source of or as a destination for binary digital data
such as printer, terminal or any device that generates or receives digital


2.      DCE

is a device that sits between the data terminal equipment (DTE) and
a data transmission circuit.
DCE carries out tasks such as signal translation, coding,
and line clocking in a data station. A DCE takes data generated by a DTE,
converts them to an appropriate signal, and then introduces the signal onto the
communication link. Same modulating method must be used by both sending and
receiving DCEs in order to send the data.

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3.      DTE-DCE

the United States, most usual interface used to interlink I/O ports is the
DTE-DCE interface. This interface is used in serial communications systems obeys
the RS-232C standard as published by the Electronics Industry Association (EIA)
(Wickman, 1986, para. 2). A DTE-DCE interface involves both DCE and DTE devices
on one end and the other. The DTE will generate the data and passes it along
with any control information to a DCE on the same end. When the signal arrives
at the receiving end, the process is reversed.

DTE-DCE Interface.
Digital Image. Serial WAN Link. 20
September 2009. http://kb.guru-corner.com/admin/attachments/Cisco/cc_wan1j.jpg



In order to define the connection between
DCE and DTE has been made into many standards especially by EIA and ITU-T, who have
been the most active organization involved in developing DTE-DCE interface
standards. Each standard provides a model for mechanical, electrical,
functional characteristics of the connection. EIA standards include EIA-232,
EIA-442, EIA-449 while ITU-T standards comprise of V series and X series.


4.      EXAMPLES



ISA 2 Port RS232. Digital Image. Retrieved from


In 1960, RS-232 is a standard introduced
for serial communication transmission of data. EIA’s RS-232 or Recommended
Standard 232 as of 1969 defines the electrical signal characteristics such as
voltage levels, signalling rate, timing, and slew-rate of
signals, voltage withstand level, short-circuit behaviour,
and maximum load capacitance with digital signal, NRZ-L (NRZ) encoding.
Pluggable connectors (male DB-25 connector on DTE end (cable has female) and female
DB-25 connector on DCE end (cable has male)) and pin identification are used as
interface mechanical characteristics for the mentioned standard (Sanderson,

The functional
standards in RS-232 is most of the 25 pins have defined functions, few of them
are normally used, mostly for control. Pin 2 is used for transmitted data
(transmitted from DTE), pin 3 for received data (transmitted from DCE) and it can
be used for half or full-duplex.







device. Digital image. Retrieved from https://en.wikipedia.org/wiki/X.21
(left).                                      X.21 pin
assignments. Digital image. Retrieved from https://arcelect.com/X21_interface.htm

Launched in the
mid-1970s by the ITU-T, X.21 (also referred to as X21) is an interface specification
for differential communications. X.21 was first introduced as a medium to
provide a digital signalling interface for telecommunications between sender
and receiver devices. This includes specifications for DTE-DCE physical interface factors, alignment of call control characters
and error checking, elements of the call control phase for circuit
switching services, and test loops (“X.21”, n. d.). This
standard is a state-driven protocol running full duplex at 9600 bps to 64 Kbps
with subscriber networks (“The X.21 Interface”, n.d.).

As for the
mechanical aspects of this standard, it has got DB-15 connector and it uses
RS-422A, a cable that length up to 1km. The standard maximum bps is inverse of the
length of cable used. For example, for 10m it has bit rate of 10Mbps and
100kbps will be the bit rate for 1km-long cable. However, for digital
transmissions, typically 64kbps is sent and received using this standard. X.21
has fewer control pins than EIA-232. Most pin assignments are in pairs to make
it balance for the balanced mode. The pin assignments reflect the mechanical
and electrical specifications (Sanderson, 2000).










Wickman, M. X. (1986) Data communication
interconnect device. Retrieved from https://www.google.com/patents/US4607170

Corner, G. (2009) DTE-DCE Interface.
Retrieved from http://kb.guru-corner.com/admin/attachments/Cisco/cc_wan1j.jpg

Sanderson, P. (2000) DTE-DCE Interface.
Retrieved from http://faculty.otterbein.edu/psanderson/csc465/notes/spring00/DTE-DCE.html

X.21. Retrieved from https://en.wikipedia.org/wiki/X.21

The X.21 Interface. Retrieved from https://arcelect.com/X21_interface.htm


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