Many small branch deployments of IP telephony require analog interfaces for connectivity to the PSTN, fax machines, security systems, analog phones, and other analog devices. There are many options available that we will explore in this post.

If there is a voice capable Cisco router at the branch office with available voice interface card (VIC) slots, the most economical choice would be to purchase FXO or FXS analog voice interface cards for the router. Foreign exchange station (FXS) ports generate dial tone and the devices that connect to the RJ-11 port expect dial tone. Analog phones and fax machines are good examples of the type of devices that would connect to an FXS port. Foreign exchange office (FXO) ports are ports that expect dial tone from the other side.  FXO ports are normally used for PSTN connectivity. Second generation VIC2 hardware must be used on new integrated services routers (ISR) like the 2800 or 3800 routers. The FXO and FXS modules come in two-port and four-port flavors as follows:

• VIC2-2FXS
• VIC2-4FXS
• VIC2-2FXO
• VIC2-4FXO

If there are no voice interface card slots available on the router, an analog telephone adaptor (ATA) or voice gateway (VG) device can be used at the branch office, but these devices only provide. The ATA and VG devices are stand-alone devices that provide. Both the ATA-186 and ATA-188 models provide two FXS voice interfaces, but the ATA-188 is end of sale. The voice gateway devices are available in the following form factors providing 2, 4, 24, and 48 FXS port respectively:

• VG202
• VG204
• VG224
• VG248

References:
Cisco VG 224, VG 204 and VG 202 Analog Phone Gateways

EOS/EOL Announcement for the Cisco ATA 188 Analog Telephone Adaptor

Cisco ATA 186 Analog Telephone Adapter

Cisco VG248 Analog Phone Gateway

Gateways (SRND)

Author: Dennis Hartmann