SNMP - Recognizing ports from switch or other stacks

[BenGordon]

Hi,

Regarding CiscoSG550 stackable switch.

The switch has 48 ports, and can be connected to 7 other switches (8 stacks).

I would like to fetch only the ports that are in use - If one switch, just the 48 ports.
If 2 switches are connected so these 96 ports.

I usually would get the "real" ports through ifType oid:

1.3.6.1.2.1.2.2.1.3.1.[PORT_NUMBER] = Int32: 6

but all the 400 ports show as 6, does anyone know another SNMP way? 

Thanks in advance