The problem of thinking too hard

This case is a problem from all levels. The customer has three floors of office. Initially, only the Main Office wanted a PABX to replace its ageing NEC system. So no problem there. Then the upper floor office wanted a PABX as well. And we were reccommended to them since out job was satisfactory. And when the second floor job was done, we were introduced to the third floor office was well! By this time, we realised they were all inter-related with the lowest office being the Headquarters. The two upper floor offices were not "shown" at the main office's board because they were relatively new. We did introduce a bigger Panasonic model which is capable of serving all three offices but were refused. So, we had to install three Panasonic KX-TDA200 instead.

Now, here is the big problem: All the three offices would like to communicate with each other.

They would like to talk to each other without having to use the Telekom lines which charges for every call. So I was tasked to solve this problem. Having been servicing Toshiba systems for years, the most obvious solution would be to use the DISA (Direct Inward System Access - a Toshiba Term). All I would have to do is to connect a SLT (single-line port) to an incoming CO port and vice versa between each system, and thus a pair of channels were born!. After having created three pairs of channels, I realised I took a bit off more than I could chew because in the Panasonic TDA PABX, a DISA system requires you to have some external cards. So, I was literally knocking my head on the wall for days or even weeks.

It was not until went to my Sundance Forum that MrGemini pointed out the obvious to me. I was so engrossed with using DISA that I overlooked the answer which was right in front of me! So, now all I have to do is to follow up on my SLT-CO channel creation with a series of codes where each extension on each floor (except for the Main Office which would prefer to have to SLT ports instead) would have to enter in order to access any one of the three channels available to them. The reason is because almost 98% of the extensions are SLT. And then, once they got through to the other Panasonic PABX, all they have to do is to dial the extension. I had to deny these systems from giving the caller the ability to grab an outgoing line as this might have detrimental effect for all offices concerned. The solution is then to place these SLT ports in COS (Class of Service) that denies them from dialing a 9 followed with any digit after it.

It sounded almost to easy but then, because the Panasonic is relatively new to me, I had to struggle with the TDA software for a while as the Trunk Groups, COS and External Call Block segments are my main obstruction.

So, the solution is as follows:

Original code to access CO Line 13 and then dial the extension 211, and they cannot dial any numbers starting with 90- to 99:
[*37013 + 211]

Modified code to access CO Line 13 and then dial the extension 211, and they cannot dial any numbers starting with 90- to 99:
[7013 + 211]

We installed the Panasonic system but using
Toshiba cabling methods using Krone connection
modules. pardon the mess as I was testing both
connections using SLT ports from both floors.