User guide

92 RealCT Direct API Developer Guide
Chapter 4: E1 Networking
Understanding E1 Trunks
E1 trunks provide digital communications in South America,
Europe, and Asia. An E1 trunk carries 30 64 Kb/s lines. Two
additional 64 Kb/s lines provide signaling information. The
combination of the 30 lines and the signaling channels yields a
2.048 Mb/s signal:
32 x 64 Kb/s = 2048 Kb/s or 2.048 Mb/s
The E1 board provides two 30-line E1 trunks for a total of 60 E1
lines. The E1 board only provides E1 line resources; RDSP or
Vantage series boards provide voice processing resources
through the MVIP bus.
Transmitting Digital Data
Digital data is composed of zeros and ones that the CO and CPE
transmit as an electrical signal. The waveform used to indicate
zeros and ones is called line coding. The CO and CPE must use
the same line coding method in order to communicate properly.
As with T1, the E1 boards support Alternate Mark Inversion
(AMI) line coding. In AMI, zeros are transmitted as 0V, and
ones alternate negative and positive pulses, as Figure 17 shows.
Two subsequent ones with the same polarity are called a bipolar
violation. Figure 17 shows a proper AMI signal, with
alternating negative and positive ones pulse and two bipolar
violations. Bipolar violations could lead to crackling on the line.