Let's take the CFM56-7B engine powering the Boeing 737 NG as an example.
The accessory gearbox (AGB) is located on the side of the fan containment case. It is a set of drive pads hosting accessories, including:
During borescope inspection, a square drive socket attached to a breaker bar is inserted into the handcranking drive pad, or a pneumatic motor is used. Alternatively on other CFM56 engines the core can be turned directly from a pad on the TGB (see below).
AGB to core shaft
There is a gear train within the AGB with its input gear used to transmit movement between the AGB and the engine core.
The AGB is connected to the N2 shaft by two bevel gear gearboxes:
The transfer gearbox (TGB) fixed just aft of the AGB, on the fan frame case. A horizontal shaft links the AGB input gear and the TGB. A radial shaft is also connected to the TGB.
The inlet gearbox (IGB) fixed close to the No 3 bearing, in the fan frame hub. One bevel gear is coaxial to the HPC shaft, the other is coaxial to the radial drive shaft.
At this stage I guess some drawing is necessary :-)
CFM56-7B AGB, horizontal and radial shaft, TGB, IGB and engine shafts
The radial drive shaft runs within the 9 o'clock strut of the fan frame.
All the mechanism described is bidirectional, the AGB is normally driven by the HPC shaft, but when using the starter or the hand cranking mechanism, the pads rotate the AGB input gear using the gear train, and the input gear then drives the intermediate shafts and gearboxes.
Regarding the rpm ratio of the gears (data taken from the engine manual):
- N2 is 14,460 rpm
- Radial drive shaft spins at 1.343 N2 (19,418 rpm)
- Horizontal drive shaft at 1,301 N2 (18,811 rpm)
- Starter shaft at 1,002 N2 (14,494 rpm)
- Handcranking shaft at 0.986 N2 (14,260 rpm)
The accessories have allocated pads on the AGB, the ones mentioned have been highlighted in green:
Accessories and their allocated drive pads on the AGB
You can also look at this other answer for actual photos of the gearboxes.
Details of the IGB near No 3 bearing:
CFM56-7B IGB and No 3 bearing