This diagram shows two local area networks, A and B, connected via a hub/router. Each LAN has a telephone gateway that connects to a PABX central office system. The PABX central office has multiple telephone and fax extensions connected across the two LANs.

1. Local Area Network A Local Area Network B
HUB / Router HUB / Router
8 Line Ext.
101, 102 … 108
Telephone Gateway
Telephone Gateway 8 port FXS
8 port FXO
PABX Central
Ext. 101 Ext. 102 Ext. 103 Ext. 104
Ext 105 Ext. 106 Ext. 107 Ext. 108
FAX – CO Line
Ext. 123 Ext. 124 Ext. 125