Patton electronic IM 1/F Timing of Application 2 Network Replacement, Timing Mode Selections

The first G.703 interface is in Network Timed mode. The second is in Modem Timed mode. See Figure 1 above.

Timing of Application 2: Network Replacement

The first modem uses an internal timing source and supplies the timing for the entire system. The first G.703 recovers the timing and clocks the data into the FIFO. The Tx of the first modem takes its internal clock and sends it (TXCLK1) to the G.703 FIFO for data (TXD1). The Rx of the second modem recovers the clock and pres- ents a “jittery” clock and data to the second G.703’s transmitter. It has to smooth the clock before it uses the clock to transmit.

The Rx of the second G.703 recovers the timing and clocks the data into a FIFO. The Tx of the second modem sends the second modem’s recovered clock (TXCLK1) to the G.703 FIFO for data (TXD1). The Rx of the first modem uses its internal clock (RXCLK1) to send data (RXD1) into the FIFO. The Tx of the first G.703 smooths the first modem’s recovered timing and sends it to the FIFO for data.

Both G.703 interfaces are in Modem Timed mode. See Figure 2 above.

2.4 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 recovered timing to the modem as XCLK1, with the Rx data as TXD1, and also to the G.703 Tx side.

Modem Timed - 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 transmit- ting on the G.703 Tx side.

RX

TX

CSU

DTE

G.703 INTF-	G.703 TX	HOST
MODEM	SMOOTHS	MODEM -
	RX MODEM	RECOVERED
TIMED MODE
	CLOCK	TIMING

	TX	FIFO	RX
G.703	RX	FIFO	TX

SECOND MODEM

G.703 TX SMOOTHS

RX MODEM CLOCK

In both cases, the transmitter uses the smoothed clock.

2.5 OPERATING MODE SELECTIONS

There are two data modes in which the interface passes data and timing:

Octet Mode - Data is passed at a 128K rate. This mode pre- serves the byte integrity associated with Octet timing. The Octet tim- ing frame is embedded in the data.

Clear Channel Mode - Data is passed at a 64K rate. This does not preserve the byte integrity associated with Octet timing. Instead, an Octet timing alarm (on or off) is passed over the modem similar to

RX

TX

G.703

TX FIFO

RX FIFO

SMOOTHED

RX

TX

2 or 4 Wire

the way signaling leads are passed.

CSU DTE

G.703 INTF- FIRST MODEM	HOST
	MODEM -
MODEM	INTERNAL
TIMED MODE	TIMING

Figure 2. Network Replacement Configuration

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