In telecommunications, a Channel Service Unit (CSU) is a line bridging device for use with T-carrier that:
is used to perform loopback testing,
may perform bit stuffing,
may also provide a framing and formatting pattern compatible with the network, and
is the last signal regeneration point, on the loop side, coming from the central office, before the regenerated signal reaches a multiplexer or data terminal equipment (DTE).
A CSU/DSU (Channel Service Unit/Data Service Unit) is a digital-interface device used to connect a router to a digital circuit such as a T1 or T3 line.
A CSU/DSU operates at the physical layer (layer 1) of the OSI model. CSU/DSUs are also made as separate physical products; CSUs and DSUs. Either or both may be part of a T1 WAN card inserted into a Data Terminal Equipment such as a router.
For digital lines, a (CSU) and a (DSU) are required. The two are often combined into a single piece of equipment, called the CSU/DSU and both can be inserted as a network interface card (NIC) in a router slot.
The CSU provides termination for the digital signal and ensures connection integrity through error correction and line monitoring. The DSU converts the T-Carrie line frames into frames the LAN can interpret and vice versa. It also connects T-carrier lines with terminating equipment.
INL Communications specialize in installing and servicing Adtran CSUs.
Compact T-1 Network Facility Interface
The T1 CSU ACE is a compact, full-featured T1 channel service unit used to connect T1 data terminal equipment (DTE) and T1 facilities. The unit is designed to provide alarms, loopbacks, signal regeneration, line build out, and surge protection, as well as maintain 1s density for the DTE and T1 network.
The unit is suitable for wallmounting or desktop use. Five LEDs on the front of the unit (POWER, NET LOS, EQ LOS, NET LB, and EQ LB) display the status of the unit. On the back of the unit an eight position dip switch provides settings for customer premises equipment and network line build out (LBO) distances as well as manual loopback operation. The two network LBO switches provide four combination settings from 0 to 22.5dB in 7.5dB increments. The three switches allotted for the equipment LBO offer five combination settings for PBX termination at distances up to 655 feet. Two additional switches provide for manual loopback (LB) in both the Equipment (EQ) and Network (NET) directions. The last switch is a spare.
The unit provides three bantam jack pairs for testing purposes. Two pairs provide interruptive transmit and receive access toward the T1 network or the Data Terminal Equipment (DTE) device. The third pair is a non-interruptive connection for monitoring data flowing in either direction. Two RJ-48C modular jacks provide the network and DTE connections. A 12V DC wall-mount power supply that plugs into a receptacle, is included with the unit. The T1 CSU ACE also supports a customer-supplied 48V DC power source.
Adtran T-1 CSU ACE
T1 line-conditioning and jitter tolerance per ANSI T1.403,
T1.102 and AT&T TR 62411
Supports framed (B8ZS or AMI) or unframed signal formats
Transmits unframed “all 1s”during signal loss from DTE or
Bantam test jacks
Front panel status LEDs
12 VDC Powered
Desktop or wall-mount
Standard 5-year warranty
ADTRAN T-1 CSUs are compact and full-featured and the units are designed to transparently pass PRI, voice, data or frame relay traffic. These highly recommended CSUs are required when connecting our single-span and dual-span T-1 systems to your service provider's digital network.
Data Service Units
A Data Service Unit (DSU) is a device used for interfacing data terminal equipment (DTE) to the public switched telephone network.
A DSU is a two or more port device; one port is called the WAN (Wide Area Network) port and each other is called a DTE port. The purpose of the DSU is to transfer serial data synchronously between the WAN port and the DTE ports. If more than one DTE port is used, the DSU assigns the DTE data according to time slots (channels) on the WAN side.
On the WAN side, the DSU interfaces with a digital carrier such as DS1 (Ex. T1, DSL, ete,) or DS3. To accomplish that it generates the proper bit rate, and generates and consumes the proper framing. The WAN port also generates and consumes line coding as necessary. On the DTE side, the DSU provides control lines, timing lines and appropriate physical and electrical interface. To maintain the synchronous relationship between the ports, the DSU manages timing by slaving ports to the bit rate of another or to its internal clock. Typically, the DTE port provides timing to the data terminal equipment while the WAN port dictates the rate.
A DSU may be a separate piece of equipment, or may be combined as CSU/DSU.