WAN Encapsulation Facts

WAN Encapsulation Facts

WAN Physical layer protocols specify the hardware and bit signaling methods. Data Link layer protocols control some or all of the following functions:

• Error checking and correction
• Link establishment
• Frame-field composition
• Point-to-point flow control

Data Link layer protocols also describe the encapsulation method or the frame format. WAN encapsulation methods are typically called HDLC (high-level data link control). This term is both a generic name for Data Link protocols and the name of a specific protocol within a WAN protocol suite or service. Depending on the WAN service and connection method, you will select one of the following encapsulation methods.

• Cisco HDLC for synchronous, point-to-point connections with other Cisco routers. This is the default encapsulation method for synchronous serial links on Cisco routers. Note: Cisco HDLC does not communicate with other vendors' implementations of HDLC.
• LAPB for X.25 networks.
• LAPD in combination with another protocol for the B channels in ISDN networks. LAPD is a Layer 2 ISDN protocol that manages flow and signaling.
• PPP for dial-up LAN access, circuit-switched WAN networks, and ISDN networks. PPP is non-proprietary, so it works in implementations that use products from multiple vendors.
• Cisco/IETF for Frame Relay networks.

Note: Routers on each side of a WAN link must use the same encapsulation method to be able to communicate.