protocol that you have to know in technology WAN

Almost sixth months i follow course specially in cisco. In last meeting my tutor said and tell about WAN. there are three protocol in WAN that you have to know if you want to implement that architecture in your office or just to study in network. 

Actually this is the first time i learn about WAN, i just know about meaning and for what this network we used before. what is three protocol in wan? there are HDLC, PAP & CHAP and the last is Frame-Relay.  Now lets knowing about that :

• HDLC is stands for High-Level Data Link Control. Like two other WAN protocols mentioned in this post, HDLC is a Layer 2 protocol in OSI. HDLC is a simple protocol used to connect point-to-point (PPP) serial device. For example, you have a point to point leased line connecting two locations, in two different cities. HDLC protocol will be the least configuration needed to connect the two locations. HDLC will be running over the WAN, between the two locations. Each router will de-encapsulating HDLC and in the drop-off in LAN. My tutor said is default encapsulation in interface serial cisco. but if you want to connecting another product, you can't use this setting. But, you can use another way likes PAP&CHAP and Frame-Relay.

• PAP & CHAP is the most of used for any dial up connection to the Internet. HDLC and PPP are based on very similar. The different are : PPP is not exclusive if we used in CISCO's Router, PPP have several sub-protocol but PPP have a many fitur dial-up network. to move from HDLC into PPP you just use 'encapsulation PPP' like this
  

• Frame-Relay

There is virtual circuit in Frame-Relay (PVC). PVC is a connection from one site to another site with carrier network. Frame-Relay almost same with PPP, but PPP only connected 2 routers, with Frame-Relay you can use more than two.

So, now we already now about protocol in WAN which different both of them. every network administrator must know about both of them. HDLC will becoming a basic protocol or default configuration encapsulation to connect with internet.