Paradise P300 specifications Closed Network Plus ESC

8.7CLOSED NETWORK PLUS ESC

8.7.1Overhead Rates

The following table shows example overhead rates for different async ESC Baud rates at a variety of main channel data rates. The table was generated (using a modem) with the async character format set for 8 bits no parity, the overhead percentages will vary slightly for async character formats different from this.

Figures: Overhead rate with backward alarm [/ Overhead rate without backward alarm, if different]

Main data channel rates

ESC rates

2400 Baud

4800 Baud

9600 Baud

19200 Baud

38400 Baud

9.6kbps

33.3%

100%

n/a

n/a

n/a

16kbps

20%

50%

100%

n/a

n/a

64kbps

5% / 4.8%

10%

20%

50%

100%

256kbps	512kbps		1024kbps		2048kbps
1.25% / 1.19%	0.62%	/ 0.59%	0.39% *		0.39% *
2.5% / 2.38%	1.25%	/ 1.19%	0.62%	/ 0.59%	0.39% *
5% / 4/76%	2.5% / 2.38%		1.25%	/ 1.19%	0.62%	/ 0.59%
10%	5% / 4.76%		2.5% / 2.38%		1.25%	/ 1.19%
20%	10%		5% / 4.76%		2.5% / 2.38%

* see notes on absolute minimum overhead in para 8.7.3 on page 148

The formula for deriving the overhead rate is moderately complex, and relies on many different parameters. For other mixes of data rate and async settings the simplest way to determine the overhead is to enter the parameters into a modem and then select Info, View Config, Tx. A screen such as the one shown below is displayed (as the second or third screen accessed by Down Arrow). This screen shows the exact overhead percentage as well as the Framed data rate ("Frm"), the data rate including any Reed-Solomon encoding ("RS"), and the final symbol rate including the effects of the `inner ` FEC and modulation ("Sym").

Rates: BB:2048000 Frm:2056031

(O/h=0.39%) RS:2056031 Sym:1370687

Info, View Config, Tx, (Down, Down)

There is of course a similar screen for the Rx path.

In addition a later screen summarises the ESC settings as show below

Tx ESC:All Intfc:RS485 (Async set:4800,8,N Avail:6413)

Info, View Config, Tx, (Down, Down, Down, Down,9Down etc)

Note that the displayed available ESC rate ("Avail") may well exceed the set ESC rate. This is because the hardware can only provide overhead in 1/Nth increments (eg 1/1=100%, ½=50%, 1/3=33%, 1/4=25% etc up to 1/256=0.39%) and so the modem must pick the appropriate value of N which provides at least the required async ESC Baud rate.

P300H P300 Series Modem Installation and Operating Handbook Page 147