what does t and s mean at the end?

[mando209]

i'm looking around on ali and ebay for dahua ptz and trying to figure out what t and s mean at the end.



[h=1]2 Megapixel Full HD 20x Network IR PTZ Dome Camera Dahua SD59220T-HN[/h]

[FONT=&quot] [/FONT][h=1]2 Megapixel 20x[/h][FONT=&quot] Dahua IP PTZ SD59220S-HN 2MP[/FONT]

 

[nayr]

loos like S is 1st gen and T is 2nd generation