Determining Which WAN Technology to Use
297
Figure 9-2
Frame Relay
Figure 9-3
X-25
Cloud
Router A
Router C
Router D
Router B
1 physical connection,
3 virtual connections
1 physical connection,
1 virtual connection
to Router A
Application layer
Presentation layer
Session layer
Transport layer
Network layer
X.25
Data link layer
LADP
Physical layer
X.25 works at the network layer and uses LAPD for
error checking at Layer 2
87200333.book Page 297 Wednesday, August 22, 2001 2:53 PM