1. Leased Line
Two most popular Data Link Protocol: HDLC and PPP
Functions in common:
- Both deliver data across a single point-to-point serial link
- Both deliver data on synchronous serial links; PPP also supports asynchronous serial links
WAN data -ink protocols are frame-oriented, just like LAN data-link protocols.
PPP
PPP was defined much later than HDLC, as a result, creator of PPP included many additional features that had not been seen in WAN data-link protocols up to that time. PPP has become the most popular and feature-rich WAN data-link layer protocol.
PPP LCP Features:
CHAP is the preferred method today because the identifying codes flowing over the link are created using a Message Digest 5 (MD5) one-way hash, which is more secure than the clear-text passwords sent by PAP.
2. Circuit switching/dial
3. Packet switching
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