a e1 or t1 interface on the radio interface two basic formats are also defined as fullrate fr and halfrate hr today there is a one to one mapping between using fr on the radio interface and 16 kbit s on the abis interface and using hr on the radio interface and 8 kbit s on abis respectively when using amr on a fr channel on the radio interface the remote transcoder protocol will use a 16 kb s subchannel on the abis interface fig2 a and when using amr on hr the remote transcoder protocol will use a 8 kbit s subchannel as depicted in fig2 b as mentioned above amr consists of collection of eight different speech coders using codec rates between 4 75 kbit s and 12 2 kbit s this allows for different amount of error control and correction coding on the radio interface which totally may carry 22 8 kb s for full rate and 11 4 kb s on half rate communications for amr fr all codec rates can be used for highly interfered radio environments a low rate codec e g 4 75 will be used allowing for very good error correction for less interfered radio environments a high rate codec e g 12 2 or 10 2 will be used this leads to good quality and high capacity for amr hr only six of the amr codecs can be used and the amount of error control and correction coding is significantly reduced since half rate on the radio interface is only 11 4 kb s this results in lower quality and capacity in interfered radio environments compared with amr fr for an active call a set of up to 4.