standards - 1 Mbit = ? bytes -

i confused this. there "standard" conversion of megabits bytes?

is it:

 1 megabit == 1,000,000 bits == 125,000 bytes 

or:

 1 megabit == 2^20 bits == 1,048,576 bits == 131,072 bytes 

megabits unit of measure comes telecom, not cs. is:

 1 megabit == 1,000,000 bits == 125,000 bytes 

when it's cs based unit of measure, 1024 rules apply:

 1 megabyte = 1,024 kilobytes = 1,024 x 1,024 bytes