EWSD technology for INET for mobile communication

EWSD

EWSD

EWSD is one of the 2 technologies selected for tax and is also the

technology for INET for mobile communication. EWSD switch can support max

up to 2,50,000 subscribers or 60,000 incoming outgoing or both way trunks,

when working as a pure tandem/ tax exchange. It can carry 25200E traffic

and can withstand 1.4million BHCA. It can work as a local cum transit

exchange and has CCS-7, ISDN, and Inet capabilities.

System Architecture

The main hardware units of an EWSD switch are as under:

1. Digital line unit (DLU) functional unit on which subscribers lines are

terminated.

2. Line/trunk group (LTG) digital trunks and DLUs are connected to LTGs.

3. Switching network: all the LTGs are connected to Switching network (SN)

which interconnects the line and trunks connected to the exchange in

accordance with the call requirement of the subscribers. CCNC and CP are

also connected to SN.

4. Coordinator processor (CP) it is used for system wide co-ordination

functions, such as, routing, zoning etc. however sub-systems in EWSD

carry out practically all the tasks arising in their areas independently.

5. Common Channel signaling network control (CCNC unit) this unit functions

as message transfer part (MTP) of CCS-7. The user part (UP) is

incorporated in the respective LTGs.

Block diagram of EWSD:

It shows that most important controls are distributed through out the

system. This distributed control reduces the coordination overheads and the

necessity of communication between the processors. It results in high dynamic

performance standards.

For inter-processor communications, 64KBPs semi-permanent connections

are set through SN. This avoids the necessity for separate inter-processor

network.

42

Access

EWSD

DL

DLU

Common channel signaling

Coordination

CP

EM

OM

LT

G

LT

G

CCN

C

CCN

SYC SYP

MB^MB

CCG

Switching

network

SGC

Distrbuted controls in EW SD

43

DLU:

The main components of a DLU as shown in the figure below are:

Local

Subscribe Application

EWSD

Subscri

ber lines

& PBX

lines

SLM

A

SLM

D

DLU

DIUD

DLUC

DLUC

r lines &

PBX

PDC0with CCS

PDC1without

PDC2with CCS

D

L

U

L

T

G

L

T

G

SN

TU

DLUC

PDC3without

CCITT G.703

CP

Remote application

Applications for & connection of Digital Line

Unit

Analog or digital (ISDN) subscribers or PBX line are terminated on DLU.

DLUs can be used locally within the exchange or remotely as remote switch

units (RSU), in the vicinity of the group of subscribers.

DLUs are connected to EWSD system via a uniform interface

standardized by CCITT to facilitate local or remote installation called Primary

Digital Carrier (PDC). A subset of CCS7 is used for CCS on the PDCs. 1 DLU is

connected to 2 different LTGs for the reason of security. In case of remote

DLUs 4 PDCs of 2MBps (32TSs) are used for DLU, 2 towards each LTG. Hence

total 124 channels are available between a DLU and the 2 LTGs, out of which

120 channels are used for user information (speech or data) and signaling

information is carried on TS16. Within the DLU the analog subscribers are

terminated on SLMA (Subscriber line module analog) cards. Similarly digital

ISDN subscribers are terminated on the SLMD modules. Each module can

support 8 subscribers, hence has 8 SLCAs and 1 SLMCP.

1 DLU can carry traffic of 100E. A standard rack of DLU can

accommodate 1 DLU of 944 subscribers or DLUs of 432 subscribers each.

Smaller racks are available for remote DLUs in which lesser No of subscribers

can be equipped.

RSU:

In case of failure of link between remote DLU & main exchange, the

subscribers connected the remote DLU can still dial each other. For emergency

services, DLUC (DLU controller) can contain an up to date subscribers data.

SASC card (Stand alone service controller) provided in each RDLU is used for

interconnection of a max of six DLU in a cluster called RCU (remote control

44

EWSD

unit). An EMSP module (Emergency Service Equipment for Push button

subscribers) is used internally to make calls when RDLU link is broken. Test

unit, ALEX (alarm external) modules are provided with all DLU for performing

tests & measurements on SLCAs & forwarding external alarms respectively. No

of SLMAs are accordingly reduced to accommodate these modules.

SLMA/SLMD

2 digital interface units (DIUD) digital for connection with the PDC

2 DLUCs

2 4MBps networks for transmission of user information between SLMs &

DIUDs

2 control networks for transmission of control information between SLMs &

DIUDs

TU, EMSP, ALEX modules

LTU

DIU 30

or

LTU

COUB

or

LTU

CR

or

LTU

ATE:T

SPHI

SPHO

SIHI

SIHO

Address

signals

SU

CR

TOG

CTC

SILC

GS/

SMPX

8

Mbps

LIU

SN0

To/From

SN

8Mbps

SN1

LTG

Functional units of LTG

The LTG form the interface between the digital environment of EWSD

exchange & the SN. The LTGs are connected in any of the following ways

Via 2 or 4 Mbps PDCs with remote or local DLUs to which analog or

ISDN subscribers are connected.

Via 2MBps digital access lines to other digital exchange in network

Via signal converter multiplexor (SCMUX) to analog trunks from

analog exchange in network. The SCMUX doesnt form a part of EWSD

exchange equipment.

Via primary rater access lines to ISDN PBXs

45

Functions:

The primary functions of LTG are as follows:

EWSD

1. Call processing functions, i.e. receiving & analyzing line & register

signal, injecting audible tones, switching user channel from & to the

switching network.

2. Safe guarding functions, i.e. detecting errors in the LTG & on

transmission paths within the LTG, analyzing the extent of errors &

initiating counter measures such as disabling channels or lines.

3. O&M functions, i.e. acquiring traffic data carrying out QOS

measurements

The LTGs can work with all standard signaling systems (CCITT5, R2,

7). Echo suppressors can be incorporated for in connection of long haul circuits

(example via satellite)

Although the subscriber lines & trunks employ different signaling

systems, the LTGs present a signal independent interface. This facilitates the

following

Flexible introduction of additional or modified signaling procedures

A signaling independent software system in the CP for all applications

The bit rate on all highways linking the line/trunks groups and the

switching network is 8Mbps. Each 8Mbps highway contains 128 channels at 64

kbps each.

The functional units of line/trunk group are as shown

Line/trunk unit (LTU) is a logical unit comprising of 8 different functional

units viz.

o Digital interface unit (DIU 30) for connection of 2mbps digital trunks

and either DLU or PA. One LTG can comprise 4 DIU 30.

o Code receivers (CR) are multifrequency code receivers for trunks and

DTMF subscribers.

o Conference unit, module B (COUB) for conference calls.

o Automatic test equipments for trunks (ATE:T) checks trunks and

tone generators (TOG) during routine tests.

Signaling unit (SU) comprises TOG for audible tones, code receivers (CR)

for MFC signaling and push button dialing and receiver module for

continuity check.

Group switch (GS) or speech multiplexor (SPMX) are used for DLUs or

trunks respectively. These are non-blocking time stage switch controlled by

the GP.

line interface unit connects LTG or SM via 2 parallel 8 Mbps SDCS.

GP controls the functional units of LTG.

One LTG rack can accommodate 40 pcms in 5 LTGG frames.

Switching network

46

EWSD

Different peripheral units of EWSD are connected to the switching

network via 8 Mbps highways called SDCs, which has 128 channels each. The

SN consists of several duplicated time stage groups and stage groups housed

in separate racks, switched by the switch group controls (SGC). The SGCs are

independently generating the setting data and the message channels for

exchange of data between the controls. Each connection in the SN is

duplicated.

Coordination processor (CP)

The CP handles the database as well as configurations and coordination

functions.

1. storage and administration of all programs, exchange and subscriber data.

2. processing of received info for routing, path selection, etc.

3. communication with O&M centers.

4. supervision of all subsystems, error checking and analysis, etc.

5. handling of man machine interface.

CP113 has a maximum call handling capacity of 1000000 BHCA and two or

more identical processors operating in parallel with load sharing.

Time

LTG1

LTGn

CCNC

CP

SDC

SDC

SDC

MB

SDC

SDC

SDC

Stage

Group

SGC

SDC

SDC

SN

Space

Stage

Group

SGC

Switching network

47

PBX

ISDN

PBX

Range

PABX

NT

NT

NT

Remote

DLU

Local

DLU

PDC

PDC

LTGG

(B)

LTGG

(B)

LTGG

(B)

LTGG

(B)

SDC

SDC

SDC

SDC

EWSD

SN1

SN0

Trunks with MFC

Large PABX

International trunks with signaling system

48

LTGG

(C)

LTGD

CCNC

CP

MB

SDC

SDC

SDC

SDC

CAP

B:CMY0

B:CMY0

CAP

BAP

CMY1

15

B:IOC

BAP

IOP

IOP

IOC1

IOC0

15

B:IOC

IOP

IOP

IOC3

IOC2

EWSD

CMY0

Structure of CP113

The basic functional units of CP113 are as follows:

a. base processor (BAP) for O&M and call processing.

b. Common memory (CMY) 64 to 1024 MB in four memory banks

consisting of 4MB DRAM.

c. Input and output controller (IOC) 2 to 4 IOCs are used to connect

the CP113 to other subsystems and functional units of the

exchange.

The other functional units of CP113 are call processor (CAP), message buffer

(MB) for coordinating internal message traffic, central clock generator (CCG)

for synchronization of the exchange, system panel displays (SYPD) to display

system alarms, O&M terminals and external memory (EM) for programs and

data that do not reside in the CP.

The EM also has a magnetic tape device for input and output mounted in a

separate device rack.

Common channel signaling network control (CCSNC)

The CCS-7 signaling system is one of the systems used in EWSD for

interexchange signaling. To promote flexibility in the use of the system a

distinction is made between a message transfer part (MTP) and the user parts

(UP). The common MTP functions in an EWSD exchange are handled by the

CCNC. The UP is incorporated in the software of the relevant LTG.

A maximum of 254 common signaling channels can be connected to the

CCNC via either digital or analog links. The channels carry signaling data via

both switching network planes to and from the LTGs at a speed of 64 kbps via

modems.

For reason of reliability the CCNC has a duplicated processor connected

by means of a system bus.

Up to 32 signaling link terminal (SILT) groups have 8 signaling links

and one duplicated CCNP.

49

EWSD

The functions of CCNC depend on its position on a signaling link in the

originating or destination exchange, in associated signaling, it operates as a

signaling point and in transit exchange in quasi associated signaling, it

operates as signaling transfer point.

The CCNC equipped in one rack can handle up to 48 signaling links.

Equipments handling up to 96 signaling links can be equipped in additional

racks.

CCS

via

analog

Modem

0

7

Multiplexer

0

7

CCS

via

digital

SILT group 0

SILT group 31

0

CCNP 0

31

CP Bus system

0

CCNP 1

31

Common Channel Signaling Network