XIII. IPPBX

The DrayTek Vigor IPPBX 2820 has two ISDN 2e ports supporting to 2 channels per port for a total of 4 channels.

ISDN 2e in the UK is usually supplied by BT which is installed using a BT NTE8 box, which provides a single ISDN 2e lines. Using both ISDN 2e ports on the IPPBX system does require having two ISDN 2e lines which would require two NTE8 boxes.

There are two potential modes that the ISDN line can be set to at the exchange end, which controls how the PBX would communicate with it. The VigorIPPBX 2820 is compatible with both modes but as explained below the configuration on the VigorIPPBX needs to match the line mode. The modes are:

Point to Point mode - This allows connecting a single device to the ISDN line, which would usually be a PBX system.

Point to Multipoint mode - This allows connecting up to eight devices to the same ISDN 2e line.

Either of these line types can have multiple numbers configured on it, which must be assigned by the telephone provider before a PBX can use them:

MSN telephone numbers are used by Point to Multipoint mode ISDN lines, which allows up to eight numbers.

DDI numbers are used by Point to Point mode ISDN lines, DDI numbers do not have a limit per line.

The DrayTek Vigor IPPBX system treats MSN and DDI numbers in the same way and it supports 100 MSN or DDI numbers in total. With the exception of total MSN vs DDI numbers there is no advantage / disadvantage of either mode from the point of view of the VigorIPPBX and it's configuration.

These numbers will usually be handled by the ISDN provider as the last six digits of the full number i.e. 0107 000 4509 would be handled as 004509, in the sense that on the PBX system it would be configured as 004509.
A caller would dial the full 0107 000 4509 number, the ISDN provider would put the call through and specify the incoming MSN used as 004509 so that it could be routed correctly on the PBX system.
Some ISDN lines used with older PBX systems may use fewer digits to differentiate the numbers so it's worth checking with the ISDN provider which format is used for MSN / DDI numbers.

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ISDN Port Configuration

The two ISDN ports can be configured to work as either S0 mode or TE mode.

TE (Terminal Equipment) mode – The PBX will use the ISDN port as a Trunk port to make and receive calls. This would be used with an ISDN line.

S0 mode – ISDN phones / PBX systems can be connected to the ISDN port (using the supplied adapter) to make and receive calls through the IPPBX system.

The Vigor IPPBX 2820’s factory default configuration has the ISDN1 port set up in S0 mode and the ISDN2 port set up in TE mode. To change the configuration of the ISDN ports, go to IPPBX – PBX System – Phone Setting page and select the mode required for each port. Changing the mode for the ports will require the IPPBX system to restart.

The codec used by ISDN is G.711 and it is recommended to use that codec on the ISDN ports for the best audio quality. That can be set by clicking the Index #2 or #3 links from the Phone Setting page to go to the settings for the ISDN ports then setting the Preferred Codec to G.711A (64Kbps). The other settings on that page do not need to be changed.

The Vigor IPPBX 2820 can also change the D-Channel mode used by the ISDN ports – the factory default configuration is set to Point-to-Multipoint mode and BT’s ISDN network usually uses Point-to-Point mode, this will need to be changed to match the mode used by the ISDN line for the IPPBX to be able to make / receive calls.
This is set from the IPPBX – ISDN – General Setup page and requires a reboot to apply the change:

Once those settings have been changed, the IPPBX system should then be able to receive calls.

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Making Calls

The IPPBX can be configured to use either of the two ISDN Trunk ports from the IPPBX – Dial Plan – Digit Map page but if the IPPBX system has both ISDN ports set up as ISDN Trunk ports then setting the Trunk for the Digit Map entry to “ANY_ISDN” will allow the PBX to attempt to call through either of the two trunks depending on which one has channels available for use:

For an extension to be able to make calls over the ISDN trunk, that extension must have the relevant Trunk ticked under the “Allow to access these Trunks” section:

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MSN / DDI Number configuration

The DrayTek Vigor IPPBX 2820’s ISDN ports support up to 100 additional numbers – these usually use a partial number that would be a segment of the full number dialled. They are configured under the IPPBX – ISDN – General Setup section.

On that page, there is an Own Number setting, which makes it possible to specify which number is used to make outbound calls using the ISDN line. This requires that the use of that number has been arranged with the telephone provider in the form of an MSN or DDI number. If this is configured but the telephone provider is unaware of this number or other MSN / DDI numbers, the number specified will be ignored by the telephone provider.

The "Blocked MSN numbers for the router" fields are used to specify which MSN numbers cannot be used by the PBX system.

To set up an MSN / DDI number, click on an un-used Index number link and enter the details for that number:

Please note that once an MSN / DDI number has been configured on the PBX system, the main number for the line must also have an entry so that the PBX is still able to receive calls on that number.

Each of the numbers can have its own Answer Mode configured i.e. going to Auto Attendant, a Hunt Group or an individual Extension.

Any extensions that are associated with an MSN / DDI number either as an individual extension or as members of a hunt group will use that number for Caller ID. This is processed in order so if you have an extension with an MSN on Index #1 but that extension is also a member of a Hunt Group linked with an MSN on Index #2, the extension will use the MSN from Index #1 for outbound Caller ID.

Showing / Hiding Caller ID for an MSN / DDI number

For each MSN, there are options to enable CLIP or CLIR for outbound Caller ID:

Enable CLIR – This means Calling Line ID Restrict, which hides the Caller ID

Enable CLIP – This means Calling Line ID Presentation, which shows the Caller ID

Diverting Calls to an MSN / DDI number

ISDN has a facility to divert calls under specific call conditions; this is a service that the ISDN provider would charge for. BT for instance charges for the forwarded calls and there is a subscription for the use of this facility, please check with the ISDN provider what the charges are before using these facilities:

CFU – This means Call Forward Unconditionally which will forward the call until this is disabled

CFB – This means Call Forward Busy, which will forward the call if extension being called gives a Busy response i.e. is on a call or has Do Not Disturb mode active on their phone

CFNR – This means Call Forward No Response, which will forward the call if not answered within approximately 20 seconds (this will vary depending on the on the ISDN provider)

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