Data service unit
Encyclopedia
A data service unit, sometimes called a digital service unit, is a piece of telecommunication
Telecommunication
Telecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...

s circuit terminating equipment that transforms digital data between telephone company lines and local equipment. The device converts bipolar digital signals
Bipolar signal
In telecommunication, a bipolar signal is a signal that may assume either of two polarities, neither of which is zero.A bipolar signal may have a two-state non-return-to-zero or a three-state return-to-zero binary coding scheme....

 coming ultimately from a digital circuit and directly from a Channel service unit
Channel service unit
In telecommunications, a channel service unit 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,...

 (CSU), into a format (e.g. RS- 530) compatible with the piece of data terminal equipment
Data terminal equipment
Data Terminal Equipment is an end instrument that converts user information into signals or reconverts received signals. These can also be called tail circuits. A DTE device communicates with the data circuit-terminating equipment...

 (DTE) (e.g. a router) to which the data is sent. The DSU also performs a similar process in reverse for data heading from the DTE toward the circuit. The telecommunications service a DSU supports can be a point-to-point or multipoint operation in a digital data network.

A DSU is a two or more port device; one port is called the WAN (Wide Area Network
Wide area network
A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...

) port and the 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, via a CSU, interfaces with a digital carrier such as DS1
Digital Signal 1
Digital signal 1 is a T-carrier signaling scheme devised by Bell Labs. DS1 is a widely used standard in telecommunications in North America and Japan to transmit voice and data between devices. E1 is used in place of T1 outside North America, Japan, and South Korea...

 or DS3
Digital Signal 3
A Digital Signal 3 is a digital signal level 3 T-carrier. It may also be referred to as a T3 line.*The data rate for this type of signal is 44.736 Mbit/s.*This level of carrier can transport 28 DS1 level signals within its payload....

 or a low speed Digital Data Service. 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.

DSUs usually include some maintenance capabilities. At minimum, they can loop data back at either the WAN or DTE ports, or at both. When only one port is looped back, the data received at that port is simultaneously sent back toward the port and passed in normal fashion to the other port. Most DSUs also allow various data patterns to be generated and monitored to measure error rate of the communication link. A DSU may be a separate piece of equipment, or may be combined in a CSU/DSU
CSU/DSU
A CSU/DSU is a digital-interface device used to connect a Data Terminal Equipment device or DTE, such as a router, to a digital circuit, such as a T1 line. The CSU/DSU implements two different functions...

.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.
 
x
OK