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The first G.703 modem is in
Internal Clock
mode. The second modem is
in
Receive Recover
mode. See Figure 3.
Figure 3.
Network Replacement Configuration
2.5 TIMING MODE SELECTIONS
Based on the timing arrangements and clock sources mentioned above,
there are two timing modes in which the interface can work. These two
modes select the clock sources mentioned above and determine which
clock gets smoothed.
•
Network Timed
—This sets the interface to pass the smoothed recov-
ered timing to the modem as XCLK1, with the Rx data as TXD1, and
also to the G.703 Tx side.
•
Internal/Receive Recovered
—This sets the interface to use the
modem’s Tx timing (recovered or internal source) to send the Rx data
(as TXD1) to the modem and to smooth the modem’s recovered timing
for transmitting on the G.703 Tx side.
RX
TX
CSU
DTE
G.703
RX
RX
RX
RX
RX
2 Wire
TX
G.703 INTF-
MODEM
TIMED MODE
SECOND MODEM
FIFO
TX
SMOOTHED
TX
TX
TX
FIFO
FIFO
G.703
FIFO
HOST
MODEM -
RECOVERED
TIMING
FIRST MODEM
HOST
MODEM -
INTERNAL
TIMING
G.703 INTF-
MODEM
TIMED MODE
CSU
DTE
G.703 TX
SMOOTHS
RX MODEM
CLOCK
G.703 TX SMOOTHS
RX MODEM CLOCK