In networking and communication, a standard or mechanism for transferring data from one device to another. An interface specifies the nature of the boundary between two devices and determines the procedures and protocols that make it possible for the devices to exchange data.
Graphic I-5. An example of an interface between DTE and DCE devices.
The two main types of networking and communication interfaces are as follows:
The following table shows some common examples of serial interfaces used in networking. Serial interfaces are commonly used for connecting data terminal equipment (DTE), such as computers or routers, to data communications equipment (DCE), such as modems or CSU/DSUs (Channel Service Unit/Data Service Units).
| Serial Interface | Description |
| RS-232 | A common interface for communication over unbalanced lines. Uses DB-9 or DB-25 connectors. |
| RS-422/485 | For communication over balanced lines. More suitable than RS-232 for environments with significant electromagnetic interference (EMI) or with DB-9 or DB-37 connectors. |
| V.35 | A high-speed serial interface for data transmission at 48 Kbps. Combines balanced lines with unbalanced lines and is used in Integrated Services Digital Network (ISDN) and frame relay connections. Uses a 24-pin block connector. |
| X.21 | A high-speed serial interface that uses the International Telecommunication Union (ITU) standard for connecting DCE and DTE for synchronous communication. Uses a DB-15 connector. |
The type of interface a device uses is related to the kind of connector or cable used to connect to the device, but not in a one-to-one fashion. For example, you could say that a device has an RS-232 serial interface, but it is incorrect to say that you use an RS-232 connector or an RS-232 cable to connect to that device. RS-232 specifies the interface, but several cabling options can support it, such as a cable terminated with a DB-9 or a DB-25 male connector.
The term “interface” is also used in routing terminology, in which it describes the connection between a router and an attached network.