Help > Functions and applications > a/b-Gateway > Overview of Functions
Overview of Functions
Existing systems with analogue telephones can be migrated to a COMtrexx system by using the existing PBXs as a/b gateways.
*Note: Alternative for COMtrexx Business: Upgrading the system by adding a 4FXS module provides four internal ports for analogue devices (telephones, fax machines, door terminals, announcement outputs).
PBXs supported as an a/b gateway
The following Auerswald/FONtevo PBXs can be used as an a/b gateway in a COMtrexx. The value shown in brackets is the maximum number of VoIP channels that can be used in the direction of the COMtrexx. This value depends on the extension level (modules or releases required).
COMpact 4000 (10)
COMpact 5000/R (14)
COMpact 5200/R (20)
COMpact 5500 (32)
COMmander 6000/R/RX (38)
Supported Functions
The following functions can be used in the normal way on the analogue telephones connected via the a/b gateway.
Incoming call with phone number and name display
In an external call, the name is only displayed if the phone number has been entered as a contact in the COMtrexx.
Outgoing call
Every call (including those to analogue devices) is sent via the COMtrexx.
Transfer with an announcement
The second VoIP channel on the a/b gateway is always used to transfer the call.
Splitting and targeted disconnection

Analogue telephones connected to the a/b gateway must be used in a different way to perform the following functions.
Use of function codes (e.g. for pick-up, logging into/out of groups, do not disturb)
This requires an exchange line access with ** account number
Example of Do not disturb on, with account number 9201: ** 9201 ## 8* 21 1

Telephones connected to the COMtrexx can be used in the normal way to perform the following functions, even when used together with the analogue telephones.
Incoming calls from analogue telephones with phone numbers and name display
Outgoing calls to analogue telephones
BLF status of the analogue telephones (free, call, busy)
Unsupported Functions
The following functions cannot be used:
Cross-system busy statuses
Transfer without announcement (blind transfer)
Three-way call
Address books of the PBX being used as an a/b gateway
Provisioning by the COMtrexx of the PBX being used as the a/b gateway (or vice versa)