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2W-FXS and 2W-FXO Interface Module with VComp Bundles Overview

The CTP Series supports the following modules for extending analog service from the PBX voice switch to remote locations for remote phone extensions or for accessing central office (CO) dial-tone or other services:

  • 2W-FXS—Foreign eXchange Subscriber interface.

  • 2W-FXO—Foreign eXchange Office interface.

FXS and FXO interfaces support two types of signaling:

  • Loop start—Plain old telephone service (POTS), such as for residential telephones, commonly uses loop-start signaling.

  • Ground start—Trunk circuits between a central office (CO) and a PBX generally use ground-start signaling. Ground-start signaling prevents glare, which occurs when a call is established by the FXS device and the FXO device tries to make a call before the ring is detected.

Connecting Two 2W-FXS Interfaces or Two 2W-FXO Interfaces

Normally a 2W-FXS interface connects to a 2W-FXO interface across the IP network. However, you can connect two interfaces of the same type by using private line automatic ringdown (PLAR) signaling. With PLAR, two handsets are directly connected so that when someone picks up a handset, the handset at the remote end starts to ring. There is no call routing (dialing) involved. You can enable PLAR on VComp bundles for modules that are configured for loop-start signaling. Both ends of the VComp bundle must have PLAR enabled.