Subject Name: Digital Switching Systems Subject Code:10EC82 Prepared By: Aparna.P, Farha Kowser Department: Electronics and Communication Date:3-3-2015 11/21/2018

EVOLUTION OF SWITCHING SYSTEM UNIT 2 EVOLUTION OF SWITCHING SYSTEM

Circuit Switching Message Switching Crossbar switch Basic central office linkages Basic call processing

Switching Circuit Switching Message Switching Packet Switching Fixed and mobile telephone network Frequency Division Multiplexing (FDM) Time Division Multiplexing (TDM) Optical rings (SDH) Message Switching Not in core technology Some application (e.g. SMTP) Packet Switching Internet Some core networking technologies (e.g. ATM)

Circuit switching

Circuit switching creates a direct physical connection between two devices such as phones or computers. We can use switches to reduce the number and length of links.

A circuit switch is a device with n inputs and m outputs that creates a temporary connection between an input link and an output link. The number of inputs does not have to match the number of outputs. (e.g., Phone Network) • Establish (Setup) Phase: source creates circuit to destination – Node along the path store connection info – Nodes may reserve resources for the connection • Transfer Phase: source sends data over the circuit No destination address, since nodes know path Teardown Phase: source tears down circuit when done

Circuit Switching With Human Operator

MESSAGE SWITCHING In the case of message switching, no channels are established on which the information is exchanged, but rather individual messages units, most often packets, which contain all or a part of the information to be transmitted, are switched. The Message switching is often called store and forward switching. Typical for this configuration is that the packets are lead step for step (from switching system to switching system) through the network.

Packet switching Packet switching switches information that is divided into a number of packets. A packet in this sense has the following fig

Functions of a switching system The basic functions that all switching systems must perform are as follows: Attending Information Receiving Information Processing Busy Testing Interconnection Alerting Supervision Information Sending

CROSSBAR EXCHANGE The crossbar switch basically consists line link frames trunk, link frames and common control equipments. With crossbar switches and common control equipments, the crossbar exchange achieves full access and non blocking capabilities. A particular group of common control circuits to route connections through the switching network for many calls at the same time on a shared basis. The unique features of the crossbar switches are (i) Common control allows the customer and the switch to share the common equipments used to process the call. (ii) Wire logic computer allows specific routine functions of call processing to be hand wired into the switch. (iii) Flexible concentration ratios allows the system designer to select the appropriate ratio for a specific switch based on customer mix in a specific location. moving parts than strowger switching system.

3X4 cross bar switch

Basic Central Office Linkages

Digital X-connect: Provides cross connection of trunks to dss The central office has links to MDF: It is a location where all lines and other related links are cross connected. TDF: It is a location where all trunks and other related links are cross connected. Power Plant: It is a combination of power converters which supply DC and AC to a CO switch Carrier Facilities: These provide carrier or multiplex transmission mode. Digital X-connect: Provides cross connection of trunks to dss Special services: These are the services which require special interface to connect CO to a customer.

Outside Plant versus Inside Plant Most of the telephone companies classify their telephone equipment as outside plant or inside plant. This classification becomes important during the analysis of a switching system, since indirectly it defines the extent of a CO and consequently The scope of analysis CO equipment, such as central processors, switching fabric, and tone generators, are considered inside plant. Switching System Hierarchy

Stored Program Control Switching Systems The early versions of electronic switching systems had temporary memory for storing transient-call information and semi permanent memories that carried programming information and could be updated. A stored program control (SPC) switching system, shown in Fig. depicts a simplified view of a telephony switch. The basic function of an SPC system is to control line originations and terminations and to provide trunk routing to other central or tandem offices.

Building Blocks of a Digital Switching System The development of a DSS is described in four stages Stage 1: At this stage , all inputs and outputs to a DSS are defined. There can be many types of lines and trunks as shown in figure.

Stage 2: At this stage , the concept of line modules and trunk modules is introduced here. The line modules and trunk modules are the basic building blocks of a DSS. Stage 3: At this stage , the concept of distributed processing in a DSS environment is developed here

Stage 4: At this stage , the concept of duplicated scheme is used.

Basic Call Processing The basics call processing describes some basic types of calls that are usually processed through a digital switching system: Intra-LM calls Inter-LM calls Incoming calls Outgoing calls

Intra-LM calls: When a customer dials from a telephone that is connected to a specific line module and calls another customer who is also connected to the same LM, this type of call is classified as Intra-LM calls

Inter-LM calls: When a customer dials from a telephone that is connected to a specific line module and calls another customer who is connected to the other LM, this type of call is classified as Intra-LM calls

Incoming / Outgoing calls: When a LM processes a call which has terminating equipment outside the CO, the Lm requests a path through the switching fabric to a trunk module via the interface controller. An outgoing call from an originating office is an incoming call to a terminating office.

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