12a The RAE Function

3GPP48.020Rate adaption on the Base Station System - Mobile-services Switching Centre (BSS - MSC) interfaceRelease 17TS

On the BSS side of the Iu interface, the RAE function shall convert in GERAN Iu mode between the E-TRAU format (3GPP TS 48.060) and a synchronous stream, i.e. the data in the payload of the Iu UP SDUs. It is the subsequent execution of the rate adaptation functions RAA’ and RAA".

It is used in the case of TCH/F14.4 and user rates less than 56 kbit/s.

The RAE function maps the data from the payload of the Iu UP SDUs directly into E-TRAU frames. It is not necessary to create the A-TRAU format that is the exchange format between RAA’ and RAA".

It shall perform the FPS (Frame Pattern Substitution) as specified in subclause 11.2.

In transparent operations, The RAE function shall handle the M1 and M2 bits as specified for the RA1′ function in 3GPP TS 44.021.

In non-transparent operations, the payload of the Iu UP SDU has a size of 576 bit and contains one RLP frame. This shall be mapped to two E-TRAU frames each of them consisting of

– 288 data bits making up half of an RLP frame,

– the bits M1 and M2 that shall be used as specified in subclause 15.2 and

– the control bits that shall be used as specified in 3GPP TS 48.060.