A three level serial line code for transmitting binary digits. A format in T1 transmission systems in which binary digits are sent with equal time periods and in which zeros have zero amplitude, and ones (marks) have equal amplitudes that alternates in polarity (positive and negative).
A term that is commonly used for a circuit that is used to carry signals from one point in a network back to another point, For example, a signal may be carried from the Base Transceiver Station (BTS) site back to the Mobile Switching Center (MSC).
Channel Service Unit or CSU/DSU (where DSU is Data Service Unit) is a device that terminates a digital channel on a customer’s premises. A CSU is located between the incoming digital line and the customer’s equipment.
Extended Super Frame is a framing format that is employed in T1 systems. The ESF format consists of 24 consecutive T1 frames (each T1 frame containing 24 DS0 signals). This format provides FPS bits for framing, CRC bits for error checking, and FDL bits for maintenance‑signaling information that is out-of-band from payload data.
The digital bit stream is organized into fixed units, called frames. A frame typically consists of a block of data (payload) plus overhead bits that are used for frame synchronization and for out‑of‑band communication.
A type of diagnostic test in which the transmitted signal is returned to the sending device after passing through a network or devices. A transmission facility may be said to be in loopback when it is set up in a condition such that a received signal is returned towards the sender.
Network Interface Unit, may also be called a Network Interface Device (NID). The NIU is a device that is placed at the demarcation point between the network and the customer premises. It typically provides regeneration, isolation, and testing loopback capabilities. It may also provide performance monitoring information, which is available either locally or via the FDL on ESF circuits.
