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Table Of Contents  CertiGuide to A+ (A+ 4 Real)
 9  Chapter 13: Basic Networking Terminology
      9  Wide Area Networking (WAN)

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Main Interfaces

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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