Block Diagram of Digital Telephone Exchange

Block Diagram of Digital Telephone Exchange Points : block diagram of digital telephone exchange The block diagram of a digital telephone exchange is shown.
The digital exchange includes the following hardware subsystems and components:

DIGITAL LINE UNIT (DLU) The DLU is connected to the LTG and is responsible for terminating subscriber lines and concentrating subscriber line traffic. The DLU can be installed locally or remotely. It has the following four primary functions:

1. Concentration of subscriber lines
2. Conversion of analog lines into digital format
3. Flexibility to accommodate variable traffic loads
4. Facilitation of ISDN (Integrated Services Digital Network) introduction LINE/TRUNK GROUP (LTG) The LTGs provide the interface between the digital switching network and the network environment of the exchange, which may be digital or analog. It performs the following functions:

1. Receive and evaluate information of trunks and subscriber lines
2. Send signals and tones
3. Send and receive message to and from the CP
4. Adapt the transmission format to the 8Mb/s highway of the switching network SN)
5. Report traffic measurements to the CP
6. Establish test connections
7. Display operating states of individual modules on LED indicators
8. Call charge registration
9. Detect LTG faults
10. Detect faults on the internal exchange interfaces during call processing
11. Report faults and routine messages to the CP
12. Evaluate faults and initiate processes SWITCHING NETWORK (SN) All types and sizes of exchanges can be implemented with a uniform, modularly expandable switching network. The switching network establishes a connection between two subscribers, belonging to different LTGs. The switching process consists of time stages and space stages to ensure a minimum of internal blocking. The switching network also provides connections for message channels, common channel signalling, and specific services. The connections are always duplicated to allow switch over to standby connections in case of failure. COORDINATION PROCESSOR (CP) The CP handles data base as vell as configuration and coordination functions. These functions are:
1. Storage and administration of all programs, exchange and subscriber data
2. Processing of received information for routing, path selection, zoning, and charges
3. Communication with operation and maintenance centres
4. Supervision of all subsystems, receipt of error messages, analysis of supervisory result messages and error messages, alarm treatment, error detections, error location and error neutralization and configuration functions.
9. Handling of the man-machine interface


In order to reduce the workload of the CP and to achieve faster processing times, some processing functions are distributed over several microprocessors within the digital exchange. A common processor for the coordination of tasks is extremely useful. These functions are handled by the CP complex which consists of the:

1. Coordination Processor (CP)
2. External Memory (EM)
3. Operation and Maintenance Terminal (OMT)
4. System Panel (SYP)
5. Message Buffer (MB)
6. Central Clock Generator (CCG) COMMON CHANNEL SIGNALING NETWORK CONTROL (CCNC) The CCNC is responsible for the transfer of messages through a common signalling channel between different exchanges using the CCS7.