User guide

Internetworking Primer A-17
LANs and WANs
Point-to-Point WANs
Point-to-point WANs only allow two endnodes on the WAN connection (as shown in
Figure A-6). The two common point-to-point WAN encapsulations are HDLC and PPP.
Because there are only two devices, there is no need for addressing at the data link layer.
Point-to-point encapsulations are generally used on leased WAN lines.
Figure A-6 Point-To-Point WAN
High-Level Data Link Control
If both ends of a leased-line connection are routers or access servers running Cisco IOS
software, HDLC encapsulation is typically used. As HDLC encapsulation methods may
vary, use PPP with devices that are not running Cisco IOS software.
HDLC is a bit-oriented, data link layer protocol derived from the Synchronous Data Link
Control (SDLC) encapsulation protocol. HDLC provides an encapsulation method for
synchronous serial links with a 32-bit checksum.
The serial interface on the access server does not require special configuration because
HDLC encapsulation is configured as the default.
CSUCSU
H3572
Router A Router B
WAN