Precios

-The time division-switching network is a 3-stage system (time space time). It provides a 4 W switching between the time slot allocated to the called party and the time slot allocated to the called party. For one call two sample connections are set up. The principal in the switching network is shown below:

-PRINCIPLE OF A CONNECTION IN THE SWITCHING NETWORK 1. Speech samples (a) from the time slot ‘L’ of the incoming network

line (LRE) associated with the calling subscriber are switched to the time slot ‘j’ of the outgoing network line (LRS) associated with the called subscriber,

2. Speech samples (b) from the time slot ‘j’ of the incoming network (LRE) associated with the called subscriber are switched to the time slot ‘I’ of the outgoing network line (LRS) associated with the calling subscriber.

Each time switch handles 16 PCM links (LRE +LRS) and four time switches catering 4 *16 = 64 PCMs are contained in one switching network rack.

A complete switching network comprises six identical racks for connecting 384 PCMs. A diagram showing the structure of a switching network is shown in figure 1.

3. Control Units : -

The control units are partly based on dedicated mini-computers and are used to carry out all the switching operations required to set up release connections

• Marker (MQ)

• Switching network control unit (UGCX)

• Multi register (MR)

• Translator (TR).

• Charging unit (TX)

To ensure uninterrupted telephone service, these units are duplicated and operate on load sharing basis.

Management units:

-• Standby charge recording unit (DSF).

• Monitoring unit (OC).

Switching network diagram

Marker (MQ)

The marker is responsible for routing switching messages between the connection units, the switching network and the multi register.

Switching network control unit (UGCX):

-The switching network control unit co-ordinates operations executed by the switching network (path finding, connection marking etc.). This involves:

-• Checking the speech paths.

• Receiving transfer link status indications from each switch module.

• Connecting and disconnecting speech channels, tones, recorded announcements and signals when ordered to do so by multi-registers or charging units.

Checking marking operations.

Multiregister (MR):

-The multi-register is in charge of the setting up and releasing of calls. It is at the heart of the system and is only control unit, which can take initiative and send orders to other units in real time. It has access to all data from subscribers and trunk circuits (E & M wires) and to all units in the exchange.

The main functions of the multiregister involve:

-• Servicing new call and on-hook conditions on subscriber lines and circuits, detected by connection units.

• Releasing subscriber lines and circuits.

• Receiving and sending signals from/to connection units.

• Ordering the transmission of various tones.

• Requesting the characteristics of a subscriber line or circuit.

• Requesting the translator to determine the connection address of the subscriber line or circuit at the exchange, on the basis of directory number.

• Sending and receiving messages to/from OMC.

The multi-register uses a programmed logic. A call processing register

includes 1024 bits (extendable up to 1536 bits) stored in cyclic RAMs with a processing time of 8ms.

Each multi-register comprises of 256 registers and can handle the setting up of releasing of 254 calls simultaneously. The two registers (0 & 255 are assigned

registers varies from 2 to 6, depending upon the traffic load. These multi-registers are working on a traffic-sharing basis.

Translator (TR):

-The translator provides the multi-registers on request, with data on subscribers and trunks required to setup and release of calls. Data (categories,

corresponding between directory number and subscriber or trunk equipment in the exchange) are held in TR files. This data may be written, deleted or

modified from the operating and maintenance center with operating requirements. The translator executes the following operations:

-• Seeking subscriber’s lines or circuit class of service data when a new call or on-hook condition is detected.

• Translating pre-fixes or the first digits dialed by the calling party.

• Translating translation operations for chaining and overflow or circuit number.

• Handling translation operations for chaining and overflow routing functions.

• Managing additional services.

• Handling all management maintenance and test operations in conjunctions with OMC.

The total capacity of the translator files is 768k words, each of sixteen bits, i.e., 12288 Mbits.

Charging unit (TX):

-The charging unit handles the subscriber line accounts, computes the number of basic metered units chargeable for a given telephone calls and outputs detailed billing data for subscribers entitled to this service. Multi-registers initiate the charging unit operations. At the start of each telephone call, on receiving instructions form MR, the charging unit seeks and assigns a charging register.

• It receives charge-metering pulses from trunk circuits.

• It orders signal transmission where required.

• It sends detailed billing messages and observation messages to standby charge recording unit (DSF) where the OMC is down or unavailable.

• It sends subscriber meter readings (periodically demand from OMC), detailed billing messages and traffic observation messages to OMC.

• It stores traffic observation data.

Each charging unit can be configured as follows:

-1000 charging registers of 512 bits, or 2000 charging registers of 256 bits or a combination of 256 & 512 bits charging registers. Each charging unit can therefore handle up to 2000 calls simultaneously.

Charging registers compute the charge for a given telephone call. At the end of the call, the subscriber meter is incremented simultaneously in both

changing units and these two values are read periodically by the OMC.

Standby charge recording unit (DSF):

-In normal conditions, detailed billing and traffic observation messages are send from the exchange to OMC. In the event of failure of OMC or

interruption of the link between the OMC and the monitoring unit, the standby charge-recording unit can receive these messages and record them onto

magnetic tape. This unit can also reload the translator memories, the charge rates, and the charge-based data in the charging units. The DSF does not participate in traffic handling functions of the exchange.

Monitoring unit (OC):

-The monitoring unit is an interface between the OMC and the other units of an E-10B exchange. It has access to all the units and handles the transfer of all the messages between the OMC and the exchange. The messages involve: -Message from the OMC to the exchange units:

• Operating messages (subscriber line creations, circuit creation etc.).

• Unit positioning messages.

• Maintaining messages.

• Control messages addressed to test modules.

Messages from exchange unit to OMC:

• Answer messages.

• Fault messages.

• Messages specify the number of calls in progress for each type of traffic.

• Constant or temporary messages.

• Routine test messages.

Time base (Base Time):

-The time base supplies basic timing signals to various exchange units synchronizing and coordinating operations, which are necessary in time division switching system. Each exchange has its own base, which is not duplicated and is therefore constructed from components offering high levels of operating security. It operates independently but can be derived by an external signal. The time base generates two sets of signals:

-• A set of four signals distributed to all exchange units except switching network and the switching network control unit.

• A set of two signals sent to switching network and the switching network control unit.

A basic signal sent by the time base must reach all other exchange units at the same moment since propagation time cannot be ignored, it is essential to use same cable length for signal distribution. For this reason the time base is located at the center of the exchange.