6 The RA1” Function

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

The RA1” function shall be used for converting between synchronous user rates of 48 and 56 kbit/s and the ‘intermediate’ rate of 64 kbit/s in A/Gb mode.

Note, RA1” is a 3GPP-specific term which is used for the one-step adaptation of 48 and 56 kbit/s rates into 64 kbit/s as specified in ITU-T V.110. For the purposes of 3GPP specifications the term ‘intermediate rate’ is used for the resulting 64 kbit/s rate although this is not done in ITU-T V.110.

6.1 Rate adaptation of 48 kbit/s user rates with DTE/DCE status to 64 kbit/s

An ITU-T V.110 32 bits frame is constructed using the user data bits received.

The ITU-T V.110 32 bit frame shown in Figure 12 is used. The D bits are used for conveying the user data and the S and X bits are used for conveying channel control information according 3GPP TS 27.001.The order of transmission of the 32 bit frame is from left to right and top to bottom.

6.2 Rate adaptation of 56 kbit/s user rate to 64 kbit/s

An ITU-T V.110 64 bits frame is constructed using the user data bits received.

The ITU-T V.110 64 bit frame shown in figure 13 is used. The D bits are used for conveying the user data.

The order of transmission of the 64 bit frame is from left to right and top to bottom.