Quantum and Evolution Series Installation and Operating Handbook
8-17
8.2.2
IDR Framing
IDR Service Features
The Intelsat definition of IDR framing is in IESS 308. Eutelsat have a similar system defined
in EESS 203 "Intermediate Rate Digital Carriers (IDC), Earth Station Standard" which
simply cross refers back to the Intelsat IESS 308 standard for the Channel Unit
Characteristics, and so the Modem equipment required for these services is identical. From
here on we will refer to IDR framing, but the text applies equally to Eutelsats IDC framing.
Standard Features (specified in IDR definitions)
The addition of standard IDR framing increases the data rate by exactly 96kbps. IDR
framing is added to provide the following extra features compared to `closed network` links:
∋
Two Audio ESC channels, encoded as 32kbps ADPCM. As IDR is intended to replace
all FDM links, these Audio ESCs replace the analog audio engineering service circuits
of the FDM service.
∋
An 8kbps digital ESC circuit.
∋
Four independent backward alarms, to signal to up to four sites receiving a
multidestinational carrier, that there is trouble with the link in the other direction.
Additional Features (Paradise products)
∋
Where many IDR carriers exist between sites, the Audio ESC on the second and
subsequent carriers are not required (as the mandatory station to station ESC is met
with the first carrier). The modem equipped with the IDR option allows 32 or 64kbps
access to the bandwidth occupied by these audio channels on the Aux port. Allowing
either one or both of the ESC channels to be replaced with either revenue bearing
data, or possibly a PRBS for on-line BER measurement (with either the internal or an
external BERT).
∋
A far more useful
asynchronous
interface to the synchronous 8kbps digital ESC circuit,
allowing for example M&C information to be conveyed providing the possibility to
provide distant end control via the satellite channel.
∋
The use of 16kbps ADPCM instead of 32kbps, allowing both audio ESC's to be
compressed into 32kbps not 64kbps. This allows either:
ι
All normal IDR facilities in a 64kbps overhead
ι
All normal IDR facilities
plus
a 32kbps Aux channel in the normal 96kbps
overhead (which allows an internal or external PRBS test to run in parallel with
the traffic to monitor the service quality)
∋
Reduced IDR facilities with 64kbps or 32kbps overhead.
