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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
LT
G
LT
G
CCN
C
CCN
SYC SYP
MBMB
CCG
Switching
network
SGC
Distrbuted
controls in
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
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 (
and either DLU or PA. One LTG can comprise 4
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
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