Installation of the digital carrier system is increased rapidly in the telecommunication network, and most of systems are operating over a twisted pair conductor. Many systems are accommodated in multipair cable for their economical installation, therefore we must consider tha crosstalk interference between digital systesm. This paper considers the calculation method which determine crosstali interference between signals in multipair. And the transmission margin at a certain error rate is analyzed considering crosstalk power. Finally, this paper estimates the crosstalk noise susceptibility of 2.048Mbps relative to 1.544Mbps PCM system and 1.544Mbps relative to 2.048Mbps PCM system, and then considers the methos which both systems can operate together in a same cable.