The Assad regime is out of soldiers. They had no choice but to get help from their patrons.
Assad said so himself that he was out of soldiers.
Russia wouldn’t do this....unless it was paid as a service...likely from the Saudis. In recent months, the Saudis have come to realize the bigger issue is ISIS and they need to be put down. The only military thug-Army left....is Russia. It would be curious to know the actual number involved.
This is so, let’s not forget the stories that Afghanis were being recruited to fight there as well as a dire situation of Hezbollah fighting ISIS.
Maybe the Russians can run some decent bombing campaigns instead of these barrel bombs which are very limited in effect but probably has kept the regime above water.