Initially each divisional station had a CAD terminal on a desk known as the relief desk. The Information Room at New Scotland Yard would receive the 999 calls for police across London (including City of London area) and add these to a CAD message - this would then be sent across to the local division relief desk for onward dispatch. This was seen in The Bill from the start of series 1.
Urgent calls would be transmitted via the Pan London 'mainset' directly by IR to area cars and operations vehicles.
The CAD Room
The CAD Room first appeared in series 3 of The Bill, being installed. CAD Rooms fulfilled the same function as the relief desk however enabled quicker transactions and information exchange across the Met. A control room sergeant and 2 dispatchers would sit in the room. Later series saw civilians brought into CAD (most notably Polly Page). Realistically the Met had introduced civilians into CAD in the early 1990s to free up officers on relief.
Radio traffic and some non-emergency telephony would be received into CAD, with the suite acting as a central switchboard for the division that Sun Hill sat on.
The CAD Room used a localised version of the CAD software written specifically for the programme by Sperry-Univac and used the same terminals as the MPS (Lynwood Alpha to begin with, changed to Lynwood J500s with green housing in later series). When MetRadio was introduced in 1996, each control room received a SmartNet monitor terminal for emergency button and radio tracking.
Later in life, around 2003, the CAD terminals were changed from their 90s design to an LCD screen and mockup of the emulated terminal access CAD the Met were using at the time. This was achieved through a PowerPoint approximation of a CAD message as it was easier to edit for screen use. The previous set up needed a person to create a CAD message and then retrieve it when filming.
Integrated Borough Operations (I.B.O.) Suite
IBO is the base of Control in Sun Hill, all non-emergency telephone calls, CCTV Camera's, SO Radio communication travel through it. Contrary to popular belief, it was not a C.A.D. replacement, it is in fact an aid for the new MetCall system (which replaced C.A.D.) operated by Central Communications Command.
I.B.O was installed at Sun Hill in Early 2007 after the C.A.D Room was removed. C.A.D. was replaced by MetCall (or Central Communications Command), which is based at 3 locations; Hendon, Bow and Lambeth. Due to it's location, Sun Hill's MetCall operator would be based at Bow CCC. 999 calls for police are now received at Scotland Yard or Hendon (when Scotland Yard reaches capacity) and routed via an internal network the the relevent IBO operator for the respective borough, it would then be routed to I.B.O. so any information could be relayed.
I.B.O. houses a small number of PCs and a Sergeant who's job would be to monitor CCTV and assist the MetCall operators should an urgent call require it.