User manual

55 000 033 – Ed. D SCOOP STUDIO - User manual 9

This document is the property of AETA AUDIO SYSTEMS and can not be duplicated without authorisation March 2006

5.1.2. Notes about G722

With G722 coding, two synchronisation modes are available:

• “Statistical recovery” byte synchronisation method (alias SRT) ;

• H221 synchronisation; in this case, 1.6 kbit/s from the compressed data are used

for this.

• H221 synchronisation and H242 protocol

H221 synchronisation is highly recommend when possible, as it features higher

reliability and faster recovery time, while degradation ( because of the bit rate used for

framing) is minimal.

H242 synchronisation is recommended by ITU-T, and is included in J52. However, the

mode with H221 synchronisation but without H242 protocol can be useful for

compatibility with old generation codecs which did not use this protocol.

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

, 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.

J52 is not needed nor applicable to leased line connections