Voice is sent FR-AMR-HR-EFR these are codec in air or between BSS and MS – except HR you can generally consider voice is 16k ,each channel of TS in E1 is 64kbps so each Chanel of E1 can carry 4*16kbps TCH. It means 2 ch of E1 belong to one TRX (just TCH ,not signalling) since TRX creates 8TS in air.now for signalling you can assign 16k,32k or 64kbps in E1 for each TRX.
don’t forget these codec (GSM codec) are changed in Transcoder to PCM(64kbps) it means 16kbps of a tch changes to 64kbps -wow, in 3g very simply you can use TRFO then no needs to adapt the codec , it is a perfect feature, even in 2g if you migrate A interface from TDM to IP , it is possibleto run it. with what being said one E1 in ABIS interface can carry maximum 12 TRX information with 12*32kbps signalling(12*2=24 (for voice)+ 12/2(6 for signalling)=30 +1 omu+1 syn=32). 15 trx is also possible but needs some features
so in uplinke/downlink+ ABIS interface before Transcoder all bit rate are same as MS after Transcoder 64kbps