Off-Net Calls
Figure 3-3 shows an example of an off-net call. To gain access to the PSTN, the user dials
an access code, such as 9, from a telephone directly connected to a Cisco voice-enabled
router or PBX. The connection to the PSTN is typically a single analog connection via a
Foreign Exchange Office (FXO) port or a digital T1 or E1 connection.
Chapter 3: Routing Calls over Analog Voice Ports 127
Note The act of routing voice data across the WAN instead of the PSTN is known as
toll-bypass. Originally, companies saved significant amounts of money using this strategy,
which was one of the first major business benefits of a VoIP-enabled network.
V
Gateway
Dial Access
Code: “9”
Ring!!
PSTN
Figure 3-3 Off-Net Calls
An example of an off-net call is a staff member calling a client who is located in the same
city. The call is sent from the local voice-enabled router that is acting as a gateway to the
PSTN. The call is then sent to the PSTN for call termination.