3 X.25 over PSI
In accordance with CCITT X.25 Recommendations, three layers of protocol (Layer 1, Layer 2 and
Layer 3) are functional when X.25 is used over PSI cards. Figure 2 shows the three protocol layers
in X.25 over PSI.
Figure 2 Three layers of protocol in X.25 over PSI
6 X.25 over PSI
