PRESENTED BY:-
RAJESH KUMAR
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EWSD - System Description
1.0 Introduction :
The Department of Telecom¬munications had announced ambitious plans for the addition of 7.5 million lines to the existing 5.8 million by the end of the 8th plan (1992-97) as compared to only 3.2 million in 1982-92.
Consequent upon delicensing of the Telecom. equipment and throwing it open to foreign investments, six new technologies were planned to be valida¬ted. These foreign suppliers set up their valida¬tion exchanges, each of 10,000 lines capacity (including two RSUs of 2K each), at different places, e.g. EWSD of Siemens (Germany) at Cal¬cutta, AXE-10 of Ericsson (Sweden) at Madras, Fetex-150 of Fujitsu (Japan) at Bombay, OCB-283 of Alcatel (France) at Delhi etc.
EWSD is one of the technologies selected for TAX and is also the technology for Intelligent Network and Mobile Communication. This article gives a general introduction to the EWSD system, its features, architecture and facilities.
2.0 System Features :
EWSD Digital switching system has been designed and manufactured by M/s Siemens, Germany. The name is the abbreviated form of German equivalent of Electronic Switching System Digital (Electronische Wheler Systeme Digitale). EWSD switch can support maximum 2,50,000 subscribers or 60,000 incom¬ing, outgoing or both way trunks, when working as a pure tandem exchange. It can carry 25,200 Erlang traffic. It is claimed that the system can withstand a BHCA of four million with CP-113C in case of EWSD Powernode (two million in case of EWSD Classic). However, the effective dynamic call set up performance depends on the available features and the actual call-mix. It can work as local cum transit exchange and supports CCS No.7, ISDN and IN and V5.X features.
3.0 System Architecture :
The main hardware units of an EWSD switch are as under:-
(1) Digital line unit (DLU) - functional unit on which subscriber lines are terminated.
(2) Line/Trunk Group (LTG) - Digital Trunks and DLUs are connected to LTGs
The access function determined by the network environment are handled by DLUs and LTGs .
(3) Switching Network (SN) - All the LTGs are connected to the SN which inter connects the line and trunks connected to the exchange in accordance with the call requirement of the subscrib¬ers. CCNC and CP are also connected to SN.
(4) Coordination Processor (CP) - It is used for system-wide coordination functions, such as, routing, zoning, etc. However each subsystem in EWSD carryout practically all the tasks arising in their area independently.
(5) Common Channel Signaling Network Control (CCNC) Unit or Signaling System Network Control (SSNC)- This unit functions as the Message Transfer Part (MTP) of CCS#7. The User Part (UP) is incorporated in the respective LTGs.
Block diagram of EWSD is given on previous page. It also shows that the most important controls are distributed throughout the system. This distributed control reduces the coordination overheads and the necessity of communication between the processors. It results in high dynamic performance standard.
For inter-processor communications , 64 kbps semipermanent connec¬tions are set through SN. This avoids the necessity for a sepa¬rate interprocessor network.
3.1 Digital Line Unit (DLU)
Analog or Digital (ISDN) subscribers, PBX lines or V5.1 interface are terminated on DLU . DLUs can be used locally within the exchange or remotely as remote switch unit , in the vicinity of the groups of subscribers.
DLUs are connected to EWSD sub-systems via a uniform interface standardized by CCITT, i.e., Primary Digital Carrier (PDC) to facilitate Local or Remote installation. A subset of CCS# 7 is used for CCS on the PDCs.
One DLU is connected to two different LTGs for the reasons of security. A local DLU is connected to two LTGs via two 4 Mbps (64 TSs) links, each towards a different LTG. In case of remote DLUs, maximum 4 PDCs of 2 Mbps (32 TSs) are used per DLU, two towards each LTG. Hence total 124 channels are available between a DLU and the two LTGs, out of which 120 channels are used for user information (speech or data) and signaling informa¬tion is carried in TS16 of PDC0 and PDC2. In case of a local DLU interface, TS32 carries the signaling informa¬tion.
Within the DLU, the analog subscribers are terminated on SLMA (Sub¬scriber Line Module Analog) cards (module). Similarly Digital (ISDN) subscribers are terminated on the SLMD modules. Each module can support 16 subscribers, hence has 16 SLCA/SLCDs (Subscribers Line Cir¬cuit Analog/Digital) and one processor SLMCP.