فرق تو Impedance با مقاومت خط هست که با BNC مقدارش 75 اهم هست و با RJ-48c این مقدار 120 اهم.
همون rj-48 صحیح است .
Interface Characteristics E1
E1 is a differential communications interface using either two pairs (TX and RX) connected through a single RJ-48C connector (also frequently written as RJ48, RJ-48 or RJ48c and also often incorrectly called RJ-45 or RJ45 - it is an RJ connector with 8 contacts assigned according to specification RJ-48C) or using two coaxial connections (TX and RX) via two BNC connectors. To enable reliable transmission and reception over 1000s of metres of cable between customer premises and telephone exchanges, the data is encoded using HDB3 to produce a bipolar signal with the required characteristics. Note that timing information (i.e. the bit clock) is encoded within the signal to enable the receiver to recover a clock and correctly decode the received data
.