Comtech EF Data CDM-625A - Manual (Page 647)

J–1
Appendix J. ESC++
J.1 Overview
ESC is the acronym for Engineering Service Channel. The ESC++ mode of operation is a closed
network frame structure that combines Automatic Uplink Power Control (AUPC) with a high
speed asynchronous order-wire channel. AUPC works identically to what is offered with EDMAC
and D&I++ framing, but is not compatible with either because ESC++ framing uses a different
overhead percentage than the other closed network framing modes.
J.2 Overhead Details
Baud rates from 1200 to 38400 bits/sec are offered using EIA-232 or EIA-485 format. Three data
formats are available: 8-N-1 (eight data bits, no parity, and one stop bit), 7-E-2 (seven data bits,
even parity, and two stop bits), and 7-O-2 (seven data bits, odd parity, and two stop bits). The
9-pin ESC port is used for this data channel (see Sect. 3.2.2.5 ESC (DB-9F) in Chapter 3. REAR
PANEL CONNECTORS AND PINOUTS for more information).
Because 38400 baud is the maximum rate available, the actual overhead percentage for ESC++
framing changes as the data rate increases, thereby saving bandwidth at high data rates. The
added overhead is as follows:
Data rate Overhead ratio (percentage)
64 kbps to < 768 kbps 19/17 (11.76%)
768 kbps to 1.5 Mbps 12/11 (9.09%)
> 1.5 Mbps to 2.5 Mbps 29/27 (7.4%)
> 2.5 Mbps to 7 Mbps 19/18 (5.56%)
> 7 Mbps 64/63 (1.58%)
Note that 64 kbps is the minimum data rate allowable with ESC++. Depending upon code rate
and modulation used, the modem’s maximum data rate of 25 Mbps may be used with ESC++. In
all cases, if the Reed-Solomon outer codec is used, the 126/112 ratio is employed with ESC++.
The new frame structure may be used with any FEC codec type available with the CDM-625A.