ATL Telecom OM25 - Manual (Page 18)

ATL User Guide
OM25 O
Optical M Modem
18
5.2 G.703 INTERFACE
5.2.1 TIMING MODES
There are three timing modes - Through, Local and Loop.
5.2.1.1 THROUGH TIMING
Through mode is plesiochronous - the two directions have independent timing and can transfer at
differing rates. The connected terminals are the source of timing. Each modem receives timing
from its terminal and passes it to the far end.
Fig 9 - Through timing
5.2.1.2 LOCAL TIMING
In Local timing mode, the clock source inside the CO is the reference clock for the system.
Transmission on the fibre is locked to this clock. Both terminals lock to this clock and return the
clock to the OM25s.
Fig 10 - Local timing
G703
CO
Tx
Rx
Terminal
Timing source
Terminal
G703
CPE
Tx
Rx
Timing looped
Timing looped
G703
CO
Tx
Rx
Terminal
Timing source
Terminal
G703
CPE
Tx
Rx
Timing source