Migrating an ISDN PMP connection to All-IP (the german "Mehrgeräteanschluss")

The german PMP Point-to-multipoint) ISDN connection is rather special and particular. It features:

• 2 B-Channels
• dynamical layer 1 and 2 
• multiple MSNs 

It is designed to connect end devices like telephones and FAX-machines. But it is also often used to connect small PBX systems. To connect a ISDN PBX to the beroNet Gateway you will need to setup:

1. one Port needs to be set to "NT" and "PMP" under Hardware
2. This port needs to be grouped under PSTN→ISDN

The PBX system recognizes incoming calls and forwards the calls to internal extensions based on the called MSN. When such a PBX system is moved to a VoIP Trunk there are different topologies possible, depending on the VoIP Provider:

1. single SIP Account with multiple MSNs
2. multiple SIP Accounts for each single MSN

In the first case the user will only have one SIP Account with credentials. The MSN is normaly transmitted in the SIP To header. The beroNet gateway will simply forward all incoming SIP calls to the the configured internal ISDN Port. No MSN needs to be configured in the gateway. The Mapping is simple with 2 dialplan rules :

VoIP Account → beroNet Gateway (destination = (.*)  new_destination=\1 source=(.*) new_source=\1 ) →  ISDN PBX

ISDN PBX → beroNet Gateway (destination = (.*)  new_destination=\1 source=(.*) new_source=\1 ) →  VoIP Account

In the second case each SIP account stands for one MSN. All SIP Accounts need to be configured in the beroNet Gateway. Since the gateway will only have a single ISDN Port, all the SIP Accounts need to be mapped to this single port. On outbound calls the gateway needs to differentiate the calls based on the MSN to choose the right SIP account. 

VoIP Account MSN 1 → beroNet Gateway (destination = (.*)  new_destination=\1 source=(.*) new_source=\1 ) →  ISDN PBX

VoIP Account MSN 2 → beroNet Gateway (destination = (.*)  new_destination=\1 source=(.*) new_source=\1 ) →  ISDN PBX

...

ISDN PBX → beroNet Gateway (destination = (.*)  new_destination=\1 source=(MSN 1) new_source=\1 ) →  VoIP Account MSN 1

ISDN PBX → beroNet Gateway (destination = (.*)  new_destination=\1 source=(MSN 2) new_source=\1 ) →  VoIP Account MSN 2

....