Aspects of the present disclosure includes a method and program product for clock synchronization of a networked computer system. The method records a time (t1) when a first codeword marker in a datastream is sent from a master computer to a slave computer and records a second time (t2) when the slave computer receives the first codeword marker. The method includes recording a third time (t3) when a third codeword marker in a datastream is sent from the slave computer to the master computer. The method includes recording a fourth time t4 when the master receives the third codeword marker from the slave. The method calculates a time offset θ, according to; θ = ( t ⁢ ⁢ 2 - t ⁢ ⁢ 1 ) + ( t ⁢ ⁢ 4 - t ⁢ ⁢ 3 ) 2 , and a roundtrip delay δ, according to δ=(t4−t1)−(t3−t2). The clock in the slave computer is synchronized with a clock in the master computer using θ and δ.