User guide

224 RealCT Direct API Developer Guide
Appendix A: T1 Line Protocols
Overview of Protocols
The Immediate Start, Wink Start, and Double Wink Start
protocols are symmetrical. The central office (CO) and customer
premise equipment (CPE) transmit identical bit patterns for
each line state. Your application uses the same protocol file
whether it functions as a CPE or emulates a CO.
The Loop Start and Ground Start protocols are asymmetrical.
The CO and CPE transmit a different bit pattern to indicate the
same condition. For example, the bit pattern the CO transmits
to indicate idle is different from the bit pattern the CPE
transmits to indicate idle. If you use these protocols, you load a
different protocol file depending on whether your application
acts as a CPE or CO.
If your system is in a loopback configuration using the Loop
Start or Ground Start protocols, the trunk emulating the CO
uses the CO protocol file and the trunk emulating the CPE uses
the CPE protocol file.
In Tables 36 through 42, the values indicate the A and B bits
transmitted by each party. The arrows point to the end
receiving the bits. The driver has several parameters that
control timing. For more information about the timing
parameters, see the RealCT Direct API Reference Manual.