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hdlc with ppp?

hdlc with ppp?

(OP)
I undertsand that there are 3 types of WAN encapsulation methods: PPP, Frame-Relay and HDLC. The confusion for me comes when reading that HDLC is actually one of the components of PPP.

How can this be possible? Is HDLC not an encapsulation method on its own?

Please help me understand this.

Thanks!

RE: hdlc with ppp?

HDLC isn't one of the components of PPP, it is a precursor. The ISO defined HDLC but vendors such as Cisco modified the frame to carry multiple routed protocols (TCP/IP, IPX/SPX, AT, CDP, etc.) Standardization of the changes occurs with PPP so that all vendors implement the same functionality.

Cisco uses their HDLC as the default framing for serial interfaces so Cisco devices connected to Cisco devices can communicate with that frame. However, other vendors have slight differences in their frames so going Cisco to non-Cisco wasn't possible with HDLC. PPP became the alternative. PPP has numerous advantages such at multilink, CHAP authentication, callback, magicnumber for link quality, and compression capability. It has scaled so well we can use it to secure Frame Relay (PPPoFR) or with PPPoE and PPPoA.

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