D.1 RFC 4867 Framing Parameters for GAN

3GPP44.318Generic Access Network (GAN)Mobile GAN interface layer 3 specificationRelease 17TS

When carrying AMR or AMR-WB voice in GAN, the following RTP framing parameters shall be used:

– Octet-aligned

– No frame CRCs

– No robust sorting

– No frame interleaving

– Single channel per session

– Mode-change-period = 2 i.e. mode can change every 2nd speech frame

– Mode-change-neighbor = 1 i.e. mode can only change to neighbouring mode in the active mode set

– Mode-set: signalled in Multirate Configuration IE

– Forward error correction: single or double retransmission of the previously transmitted frame (s) (i.e. window size of 2 or 3). To request a concurrent AMR and redundancy mode adaptation, the decoder (speech receiver) signals the encoder (speech sender) the new AMR mode it prefers in Codec Mode Request (CMR). The redundancy mode for each mode of the Active Codec Set is signaled in the Redundancy Configuration IE. This way the preferred redundancy mode is also implicitly requested with the CMR. (Triple redundancy is not used, as it would add too much network load. When the third redundant frame has to be used, there would also be too long delays.)

The frame loss rate for the received speech data is continuously monitored by the MS and the network. If the sender is currently using codec mode N where increasing N means a codec mode with higher bitrate, the following applies.

– When the frame loss rate goes above Threshold N-1, the receiver signals the sender to change to codec mode N-1 and thereby also to the redundancy mode associated with codec mode N-1.

– When the frame loss rate goes below Threshold N – Hysteresis N, the receiver signals the sender to change to codec mode N+1 and thereby also to the redundancy mode associated with codec mode N+1.

The frame loss rate threshold and hysteresis values used for triggering a switch in AMR mode shall be given by the network in a consistent order, i.e. such that:

– THR_1 ≥ THR_2 ≥ THR_3, and

– THR_1 – HYST_1 ≥ THR_2 – HYST_2 ≥ THR_3 – HYST_3.

The initial codec mode, and associated redundancy mode, to use, is signaled in Multirate Configuration IE, at channel activation or at channel mode modify.

Annex E (normative):
GAN Specific Requirements for Interworking with UTRAN