HDLC is commonly used in leased-line connections in which the WAN link's endpoints are terminated with CSU/DSUs (Channel Service Unit/Data Service Units) connected to Cisco routers running Internetwork Operating System (IOS). Routers and access servers from other vendors often use PPP instead of HDLC.

Is HDLC used today?

The networking industry has used HDLC to derive several other standards used today, such as frame relay protocols like the ISDN protocol stack known as Link Access Procedure Balanced (LAPB).

Why HDLC is needed?

High-level Data Link Control (HDLC) is a group of communication protocols of the data link layer for transmitting data between network points or nodes. Since it is a data link protocol, data is organized into frames. A frame is transmitted via the network to the destination that verifies its successful arrival.