User manual

10 SCOOP E-Z - User Manual 55 000 026 – Ed. B
This document is the property of AETA and can not be duplicated without authorisation November 2001
5.1.2. Notes about G722
With G722 coding, two synchronisation modes are available:
? “Statistical recovery” byte synchronisation method (alias SRT) ;
? H242 synchronisation; in this case, 1.6 kbit/s from the compressed data are
used for this.
H242 synchronisation is highly recommended when possible, as it features higher
reliability and faster recovery time, while degradation (because of the bit rate used for
framing) is minimal. This is recommended practice according to J52.
5.1.3. Notes about J52 and MPEG coding
The ITU-T J52 recommendation was defined in order to allow the interoperability of
various equipment over the ISDN
1
, using common coding standards. It includes the
following features:
? Interoperation procedures as per ITU-T H242 recommendation ;
? In the case of MPEG encoding, optional protection against transmission errors
(Reed-Solomon error correction codes).
It must be noted that, thanks to the interoperation protocol, J52 codecs, when setting up
a link, can negotiate automatically and agree on a configuration that is compatible with
the capability of both units (regarding bit rate, channel mode, etc.). In this way, when
the units differ in their capability (or make), the resulting configuration may be different
from expected beforehand, but in most cases the link will work and audio will be
transmitted.
As another useful consequence, this also gives users more tolerance to mistakes when
configuring the units on the two sides of the transmission links, as the codecs will adapt
automatically even with differences in the initial settings of the two units.
1
J52 is not needed nor applicable to leased line connections