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A key interface in the customer site
occurs between the data terminal equipment (DTE, typically is the router)
and the data circuit-terminating equipment (DCE, typically is the modem,
channel service unit/data service unit (CSU/DSU) witch is usually is
given by provider).
Several physical-layer standards
define the rules governing the interface between the DTE and the DCE:
- EIA/TIA-232: A common physical-layer interface
standard (RS-232), developed by EIA and TIA, that supports unbalanced
circuits at signal speeds of up to 115200 bps. Originally, it was developed
for the data transmission between the computer and modem with speed
up to 9600bps and on distances up to 15m. The special popularity it
received after its realization in the PC (COM ports support it), where
it works in an asynchronous mode and allows to connect to the PC peripheral
devices - mouse, graph plotter etc. For connection the 25-contact socket
or in the simplified variant - a 9-contact socket is used. In addition,
this given interface allows us to connect 2 computers directly on small
distance with the help of null - modem cable.
- EIA/TIA-449: A popular physical-layer
interface developed by EIA and TIA. It is essentially a faster (up
to 2 Mbps) version of EIA/TIA-232, capable of longer cable runs. For
connection, a 37-contact socket is used.
- EIA/TIA-612/613: A standard describing
High Speed Serial Interface (HSSI), which provides access to services
at T3 (45 Mbps), E3 (34 Mbps), and Synchronous Optical Network (SONET)
STS-1 (51.84 Mbps) rates. The actual rate of the interface depends
on the external DSU and the type of service to which it is connected.
- V.24: An ITU-T standard for a physical-layer
interface between DTE and DCE.
- V.35: An ITU-T standard describing a synchronous,
physical-layer protocol used for communications between a network access
device and a packet network. V.35 is dominant in the United States
and in Europe, and is recommended for speeds up to 2 Mbps.
- X.21: An ITU-T standard for serial communications
over synchronous digital lines. The X.21 protocol is used primarily
in Europe and Japan.
- G.703: An ITU-T electrical and mechanical
specification for connections between telephone company equipment and
DTE using British Naval Connectors (BNCs) and operating at E1 data rates.
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