AMR SID length?

Hi.

There seems to be a disagreement between Osmocom libraries as to which is the length of AMR SID RTP payload. According to libosmocodec it's 7 bytes (see amr_len_by_ft in gsm690.c), according to libosmo-netif it's 6 bytes (see amr_ft_to_bytes in amr.c). However, than I look at 3GPP TS 26.101 Table 6 it seems like it should be 8 bytes.

Reading http://www.rfc-base.org/txt/rfc-4867.txt did not shed a light except that it can't be lower than 5 bytes.

Please help me out - what's the right number of bytes?