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CCNA® Cisco Certified Network Associate: Study Guide, Seventh Edition by Todd Lammle

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High-Level Data-Link Control (HDLC) Protocol

The High-Level Data-Link Control (HDLC) protocol is a popular ISO-standard, bit-oriented, Data Link layer protocol. It specifies an encapsulation method for data on synchronous serial data links using frame characters and checksums. HDLC is a point-to-point protocol used on leased lines and ISDN dial-up connections. No authentication is provided by HDLC.

In byte-oriented protocols, control information is encoded using entire bytes. On the other hand, bit-oriented protocols use single bits to represent the control information. Some common bit-oriented protocols are SDLC and HDLC, and TCP and IP are byte-oriented protocols.

HDLC is the default encapsulation used by Cisco routers over synchronous serial ...

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