Tax liability

applicable provisions and taxes

1) Service tax - you have to pay service tax on 50000, as importer of service

2) TDS- you have to deduct TDS u/s 195, 

if the service provider has PAN in india, then normal provisions of 194C or 194J would be applicable as the case may be , dependent on type of services received. 

3) DTAA is the part of service provider, who has to ensure that he would be in position to avail credit of taxes deducted within india or not. so it must be taken in consideration by the service provider.