Frame Relay interface types

	NOTE: The router does not support NNI interfaces. You can learn about NNI interfaces for informational purposes.

As shown in Figure 49:

• A Frame Relay network provides data communications between user devices such as routers and hosts. The user devices are also called data terminal equipment (DTE).

• The devices that provide access to the Frame Relay network for DTEs are called data circuit-terminating equipment (DCE).

Frame Relay interfaces include the following types:

• User-to-network interface (UNI)—A DCE is connected to a DTE through UNI interfaces. UNI interfaces include the following types:

  • DTE interface—The UNI interface on the DTE side.

  • DCE interface—The UNI interface on the DCE side.

• Network-to-network interface (NNI)—A DCE is connected to a Frame Relay switch in the Frame Relay network through an NNI interface. The switches in the Frame Relay network are interconnected with NNI interfaces.

A DTE interface can connect only to a DCE interface, and an NNI interface can connect only to an NNI interface. On a Frame Relay switch, the Frame Relay interface type must be NNI or DCE.

As shown in Figure 49:

• Router B and Router C form a simple Frame Relay network.

• DTE devices Router A and Router D are attached to the network.

The interface type DTE or DCE is identified only for the UNI interfaces. A virtual circuit between two DTE devices can be assigned different DLCIs on different segments.