1.1 Remote Access
1.1.7 X.25 and frame encapsulations
X.25 encapsulation is typically seen in a packet-switched environment. LAPB is the data link protocol used to encapsulate X.25 packets. X.25 evolved in the days of analog circuits when error rates were much higher than today, so reliability was built into the X.25 framework. X.25 can transport LAN packets end-to-end through a packet-switched network. A Virtual Circuit (VC) is established, and LAN datagrams use the connection-oriented reliable-transfer X.25 packet switching.

Like X.25, Frame Relay is an industry-standard data link layer protocol that is commonly used in packet-switched networks. Frame Relay is a well-understood, connection-oriented service that relies on digital switching to achieve very respectable throughput. Frame Relay supports technological advances such as fiber-optic cabling and digital transmission.

Frame Relay circuits run over more reliable types of data links, such as fiber optic links and higher quality circuits, and thus don't require the complex error correction that is needed with older, less reliable WAN media types. Since error correction and flow control are time consuming processes, Frame Relay links of a given speed can be more efficient than equal speed links of other types. Customers purchase a committed information rate from the carrier to ensure their minimum bandwidth requirements are met. Additional DS0 channels can be easily added to meet growth requirements. Because you are using a public network, you must consult with your service provider and obtain information specific to your link.