SCPC works in which layer in OSI model

At the very top of the layer is Application layer where SCPC work , SCPC(Single Channel Per Carrier )

it refers to single signal at a given frequency and bandwidth. In  SCPC System, Satellite bandwidth is dedicated to single source .This make sense if it is used for something like satellite radio, which broadcast continuously .

    Most often, this is used on broadcast satellites to indicate that radio stations are not multiplexed as subcarriers onto a single video carrier, but instead independently share a transponder. It may also be used on other communications satellites, or occasionally on non-satellite transmissions.

Advantages 

• simple and reliable technology
• low-cost equipment
• any bandwidth (up to a full transponder)
• usually 64 kbit/s to 50 Mbit/s
• easy to add additional receive sites (earth stations)

Disadvantages 

• inefficient use of satellite bandwidth for burst transmissions, typically encountered with packet data transmission
• usually requires on-site control
• When used in remote locations, the transmitting dish must be protected.