Hi there, glad to hear that you have applied for this in Cardiff Control. I am a conductor for ATW and both ATW and Network Rail are in the same room. Literally its mirrored on either side so they can liaise with each other when something goes wrong.
While I am not sure exactly what the role will be I have had to visit there multiple times and by the sound of it you will be stationed in the main control room. Like the other person said all the CIS boards, etc are dealt with from this central location. You wont have direct contact with any customers in there though. It will be other staff, mostly conductors and drivers contacting you for one thing or another.
Apart from the Duty Control Manager, CCTV operative and Maintenance Control everyone picks up each others calls.
We also have our phones which receive multiple emails to tell us what is going on on the network at any given time. The people at control are nice and it seems like a positive place to work. It is extremely quiet (Until something drastic goes wrong on the Cardiff lines XD)
I'm not sure if you will be dealing with the alterations and strengthening of services when needed but we certainly have to let Delays know if we are running late for whatever reason.
I don't particularly know what the job is you have applied for but I thought I could tell you a bit about my experience of being in the place where you have applied to work. If you are going to be learning about the operations in the control room it can vary from finding replacement transport, to taking a phone call that a conductor cant do ticket duties, delays to making sure conductors are aware of any problems on the line or trains needing to be terminated.
Either way good luck and perhaps I will be ringing you when things are going horribly wrong!