14
G.703 CODIRECTIONAL CONVERTER
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 (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).
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).
If necessary, the bit stream from the DTE can be inverted prior to the
conversion to G.703. (The binary signal being sent to the DTE is inverted
at the same time.) You can turn this data inversion on or off, as appropriate
for your application, by setting one of the Converter’s jumpers.
