The configuration screen is accessed by pressing the Configuration main menu key. This menu is used to configure the Signal Setup and the Payload Setup. The Signal Setup allows the user to set up the Test Mode, Line Code, Tx Clock, Tx LBO, Rx Input, and Framing information. The Payload Setup allows the user to set up the Payload Type, Payload DS1 Channel, Payload DS0 Channel, Payload Frame, and Other Channels.
Pressing the DS3 submenu key sets the instrument in T3 testing mode. The
DS1 submenu key is for T1/DS1 signals only and is not appropriate for testing DS3 signals.
In the AMI format, a binary one is represented by a pulse, and a zero is indicated by the lack of a pulse. To eliminate any DC offset, the binary one pulses alternate in polarity. Because the pulses are alternating in polarity, the line code is called Alternate Mark Inversion (AMI). If two consecutive pulses have the same polarity, then a Bipolar Violation (BPV) has occurred.
When no traffic is present on a channel, AMI coding can result in long strings of zeros on the circuit. These zeros can cause the receiving equipment to have timing errors. The method used in T3 systems to maintain the density of ones (as opposed to zeros) in the data stream is known as binary 3‑zero substitution, or B3ZS.
B3ZS (Bipolar 3‑Zero Substitution) is a line code in which bipolar violations (BPV) are deliberately inserted if the stream of user data contains strings of 3 or more consecutive zeros. It is used to ensure that the system has a sufficient number of bipolar transitions to maintain system synchronization when the user data stream contains an insufficient number of ones to do so. Compare this with B8ZS,
“T1 Configuration Menu”.
The Internal clock uses an internal oscillator, 44.736 Mb/s ± 5 ppm. With
Recovered clock, the transmit clock uses the frequency that is recovered from the received signal.
Tx LBO sets the Tx signal level. Select
Low when testing the signal near the receiving equipment (less than 225 feet), and select
DSX when testing from more than 225 feet.
Select DSX3 for testing at the cross‑connect point of a T3 line. Select
Monitor when the connection to the circuit is made through a monitor jack. The jack is isolated from the circuit with resistors, and the signal is typically 20 dB down from the nominal signal level. When
Monitor is selected, 20 dB of flat gain is added at the receiver input.
Payload Type 45Mb is selected for testing a full T3 data stream.
1.544Mb is selected for testing 1 channel of the 28 DS1 channels.
Nx64kb is selected for testing combinations of 64 kb channels.
64kb is selected for testing a single 64 kb channel.
56kb is selected when the data stream is created as a result of bit robbing.
16kb is selected for testing 2 consecutive bits within a single 64 kb channel.
8kb is selected for testing a single bit within a selected 64 kb channel.
Uses the Edit Channel submenu key to set up the necessary channels and sub‑channels, selecting 1 of 28 DS1 channels.
Uses the Edit Channel submenu key to set up the necessary channels and sub‑channels when testing payloads Nx64kb to 8kb.
