TCU-100 integrates GSM dual-band module, data rate up to 9.6Kbps TCU-200 integrates GPRS dual-band module, data rate up to 85.6Kbps for downstream and up to 21.4Kbps for upstream RJ-11 jack for telephone line TCB-100/200 is an optional accessory, which adds GSM/GPRS access to TTIC's payphone series DB9 connector for RS232 Interface(option) Authentication of payphone system for SAC Battery backup (5 hours stand-by, 2 hours talk time)