Applications and Associated Timing
There are two typical applications that result in two different timing modes for the G.703 interface. These are described in the following sections.
Timing of Application 1: Network Loop Extension. In this application, the network supplies the timing for the entire system. The first G.703 recovers the timing. It has to smooth the clock before it supplies the clock (XCLK1) and the data (TXD1) to the first modem transmitter, so it can directly use the clock. The Rx of the second modem recovers the clock and presents a “jittery” clock (RXCLK1) and data (RXD1) to the second G.703’s transmitter. This transmitter 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 takes its recovered clock and sends it (TXCLK1) to the G.703 FIFO for data (TXD1). The Rx of the first modem recovers the timing and clocks (RXCLK1) the data (RXD1) into a FIFO. The Tx of the first G.703 uses the first G.703’s recovered clock and sends it to the FIFO for data.
8
