17
CHAPTER 2: Introduction
2.2.3 T
AIL
-E
ND
C
LOCKING
Transmit clock from the external DCE source is provided for applications
requiring the use of a modem in order to reach a remote DTE, as shown in
Figure 2-8 on the next page (see Figures A-2, A-7, and A-10 in the
Appendix
for pinouts). Use the LBT-DCE-timing mode with the G.703 Codirectional
Converter (see Figure 2-5 on page 15).
2.2.4 G.703 C
ODIRECTIONAL
R
ULES
G.703 codirectional signals, in each direction of transmission, are coded as
follows: The composite timing/ data signal conveys the 64-KHz bit-timing
information, the 8-KHz octet information (by introducing violations into the
signal), and the 64-kbps data pattern.
• A binary one (64-kbps bit period) is coded as a block of the four bits
“1100.”
• A binary zero (64-kbps bit period) is coded as a block of the four bits
“1010.”
The binary signal is converted into a three-level signal by alternating the
polarity of the blocks. The alternation of the polarity of the blocks is violated
every eight blocks (see Figure 2-9 on the next page).
