Difference between HDLC and PPP
High-Level Data Link Control (HDLC) was born from Synchronous Data Link Control (SDLC) which was the creation of IBM. They are both data link layer by nature.
HDLC which is a bit oriented protocol of synchronous nature was born because of the modification of the SDLC. There are three main types of transfer modes that HDLC is compatible with namely NRM, ARM and ABM. In the first type secondary nodes are prohibited to communicate to the primary until they are permitted to do so. According to the second type or ARM- secondary nodes can communicate without getting permission from the primary node and in case of the third type or the ABM there are a new breed of combined nodes which are generated and the communication happens through them only. HDLC allows full-duplex operations and Point to Point & Multipoint configurations. HDLC is not compatible with both synchronous and non synchronous connections.
PPP is data link layer protocol which resembles the HDLC in many aspects. It is a great resource for the ISPs who use this protocol to provide Internet. PPPoE[Point to Point Protocol over Ethernet] and PPPoA[Point to Point Transfer over ATM] are the various forms of PPP that are used by the ISPs to provide the customers with DSL service. Unlike the HDLC, PPP supports both synchronous and non synchronous connections.PPP is perfectly compatible with network protocols like IP[internet protocol], IPX, NBF, AppleTalk etc. PPP facilitates the direct communication between two nodes. PPP can provide easy authentication, compression and privacy of a transmission. PAP (Password Authentication Protocol) and CHAP (Challenge Handshake Protocol) are those protocols that authenticate a transmission. Networks comprising of physical mediums like fiber optics, serial cable, trunk line, cellular telephone and phone line use PPP. PPP is also used by broadband. Unlike HDLC, PPP is compatible with a Cisco router.