Overview of Serial Interfaces

Synchronous and Asynchronous Serial Interfaces Supported by the Device

• The device supports the following synchronous serial interfaces:

  • When a synchronous/asynchronous serial interface works in synchronous mode, the interface is called the serial interface.

• The device supports the following asynchronous serial interfaces:

  • When a synchronous/asynchronous serial interface works in asynchronous mode, the interface is called the serial interface.

  • A dedicated asynchronous serial interface is called the async interface.

Serial Interfaces Working in Synchronous Mode

Synchronous serial interfaces have the following features:

• Works in data terminal equipment (DTE) or data circuit-terminating equipment (DCE) mode. A DTE refers to the device on which serial interfaces are connected to DTE cables; a DCE refers to the device on which serial interfaces are connected to DCE cables. When functioning as a DTE, the device receives clock signals from a DCE.
• Supports link layer protocols including Point-to-Point Protocol (PPP), X.25, Link Access Procedure Balanced (LAPB), Frame Relay (FR), and High-Level Data Link Control (HDLC).
• Supports the network layer protocol IP.

• A user's device is called a DTE.

• A network device is called a DCE.

Serial Interfaces Working in Asynchronous Mode

Asynchronous serial interfaces can work in protocol or flow mode.

• Protocol mode

  • Serial interfaces on both ends establish a link based on the existing link layer protocol parameters after a physical connection is established between them.

  • The link layer protocol is PPP.

  • The network layer protocol is IP.

• Flow mode

  • Serial interfaces on both ends interact with each other, the local interface sends configuration information to the remote interface to set physical layer protocol parameters for the remote interface, and then the two interfaces establish a link based on the configured parameters.

  • The link layer protocol and network layer protocol (IP) are not supported.