Frame relay is a WAN protocol and used by telecom companies/service providers. Routers of geographically separated offices talk to each other using WAN network. Router (DTE) of one branch office connects to service provider's Frame Relay Switch (DCE) , from here multiple frame relay switches comes into path as part of WAN and finally reaches to destination branch office switch and then finally reaches to destination router.
DLCI plays a major role in frame relay switching. Each DTE and DCE has unique DLCI values on each interface. It means DLCI values can be re-used for different interfaces in same switches(DCE/DTE).
