WAN Encapsulation Protocols

There are many WAN encapsulation protocols that operate at layer 2 to provide consistent
transport at the Data Link layer. It is important to note that some of these protocols extend into
layer 3, especially X.25. These protocols include the Point-to-Point Protocol (PPP); the X.25
Link Access Procedure, Balanced (LAPB) protocol; and the Frame Relay protocol. Additional
WAN encapsulation protocols include the Serial Line Internet Protocol (SLIP), the High-Level
Data Link Control (HDLC) protocol, and Asynchronous Transfer Mode (ATM).
Again, the Remote Access exam omits many these protocols, both older and newer encapsulations.
SLIP has been largely replaced by PPP, and ATM is quite common, but both are outside
the scope of the exam. The omission of HDLC is significant if only because this protocol
is the foundation for many other transports. In addition, it remains the default encapsulation for
Cisco serial interfaces.
The encapsulations covered within the Remote Access exam include the following:
 Point-to-Point Protocol
 X.25
 Frame Relay
In later sections of this chapter and in other chapters, you will learn about each of these in
greater detail.

Note:The current Remote Access exam does not include ATM, HDLC, or SLIP. Here
you will find brief descriptions of these three protocols for reference only.