Description of synchronous/asynchronous serial interfaces of AR routers

1

The serial interface is one of the most commonly used WAN interfaces. A serial interface can work in synchronous mode or asynchronous mode. Therefore it is also called the synchronous/asynchronous serial interface.
Devices support the following synchronous serial interfaces:
- Synchronous interfaces generated from synchronous/asynchronous serial interfaces that work in synchronous mode, which are named as Serial

Devices support the following asynchronous serial interface:
- Asynchronous interfaces generated from synchronous/asynchronous serial interfaces that work in asynchronous mode, which are named as Serial
- Dedicated asynchronous serial interfaces which are named as Async

1. Serial interfaces have the following features in synchronous mode:
- Serial interfaces can work in data terminal equipment (DTE) mode or data circuit-terminating equipment (DCE) mode. Devices on which DTE cables are connected to the serial interface are named as DTE devices. Devices on which DCE cables are connected to the serial interface are named as DCE devices. In general, devices are used as DTE devices and receive the clock provided by DCE devices.
- Serial interfaces support the following link-layer protocols: PPP, X.25, LAPB, FR, and HDLC.
- Serial interfaces support protocols in the IP network layer.

2. In asynchronous mode, serial interfaces can work in protocol mode or stream mode.
? Protocol mode
- In protocol mode, after the physical link of a serial interface is established, the serial interface uses the existing link-layer protocols to configure parameters and establish the link.
- In protocol mode, the type of link-layer protocol is PPP.
- In protocol mode, serial interfaces support protocols in the IP network layer.
? Stream mode
- In stream mode, when the devices connected to both ends of a serial interface begin to interact with each other, a device can send configuration information to the peer device to configure the physical-layer parameters of the peer device and establish the link.
- In stream mode, serial interfaces do not support protocols in the IP network layer or link layer.

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