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P300H P300 Series Modem Installation and Operating Handbook Page 135
Framing based on: [?]
1=Low rate format (T1/E1) 2=High rate format (T2/E2)
Change, Tx/Rx, Service, Custom, IDR, Format Menu
IDR o/h: [?] 1=Normal:96k 2=1xAudio:64k
3=No Audio:32k 4=16k ADPCM modes
Change, Tx/Rx, Service, Custom, IDR, Overhead Menu
IDR o/h: [?] 1=96k:2x16k-Audio+32k-BER
2=64k:2x16k-Audio only
Change, Tx/Rx, Service, Custom, IDR, O/H 16k Menu
three error rate improvement due to using the IBS/SMS scrambler instead of
the V.35 scrambler, the ESC channel and the backward alarm facility).
The operator can set the ESC channel Baud rate to 9600 Baud even at low
data rates. For example at 64kbps the high rate ESC would normally provide
a 2400 Baud channel, but if 9600 Baud is set in Minimum overhead mode,
the overhead will scale to provide it. The practical ESC rate limit is 70% of the
data rate, ie you can have a 9600 Baud ESC channel down to a data rate of
11kbps !
The final satellite data rate including overhead can be displayed on the INFO,
VIEW CONFIG, TX/RX screens.
NOTE: This is obvious, but it is stated here as a reminder. As the exact overhead
format is calculated based on your ESC requirement, for two Modems to
calculate the same overhead usage and therefore interwork, the following
parameters must be the same at both ends of the link:
Main Data Rate.
ESC async character format (bits / parity) & Baud rate.
Proportion of overhead assigned to ESC.
Baseband mode (ie continuous or Drop/Insert)
7.1.3 Change, Tx/Rx, Service, Custom, IDR Menu
If IDR is select from the menu Tx/Rx, Service, Custom screen this leads to the following question:
The frame format definition for IDR operation varies with the data rate. For rates of 1544 or 2048 kbps
(T1/E1) one format is defined, and for rates of 6312 and 8448kbps (T2/E2) another is defined (there is even
a third definition for rates > 10Mbps). In CUSTOM, IDR mode, you have a free choice of format whatever
the data rate and note that IDR operation is not limited to T1/E1 rates, but can be used at any data rate,
(even down to 64kbps, although INTELSAT define that IBS framing should be used on IDR carriers below
1544kbps).
LOW The 12 bit overhead defined for T1/E1 operation in IESS 308 is used.
HIGH The 4 bit overhead on each of three subframes defined for T2/E2 operation is
used.
Whichever format is selected, the following prompt appears:
If 16k ADPCM MODES are selected the following further prompt appears