Internet speed drops down

Hello,
i hve a broadband connection wit very high speed its ADSL router n its connected to network wit other pc..initaly wen i was useing my internet the speed was pretty gud but few days past the speed is fluctuating...sumtimes it tk so long to open the browser but sumtimes it opens quickly..so jus want 2 knw y is this happening...n wen i give ping command normally the rply should be (reply from 192.168.0.1: bytes=32 times=1ms TTL=64) but it shows me (reply from 192.168.0.1: bytes=32 times=2ms TTL=64),(reply from 192.168.0.1: bytes=32 times=4ms TTL=64) n goes on but not always...so plezz any1 can help me it this