BHARAT SANCHAR NIGAM LIMITED (A Government of India Enterprise) BASIC SWITCHING SYSTEMS C-DOT MAX-XL 1
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BHARAT SANCHAR NIGAM LIMITED(A Government of India Enterprise)
BASIC SWITCHING SYSTEMS
C-DOT MAX-XL
1
C-DOT MAX-XL
INDEX
SECTION TOPIC PAGE
1 1.1 C-DOT DSS Family 2
1.2 Basic Growth/ Building Modules 3
1.3 System Features 6
2 2.1 C-DOT System Capacity 12
2.2 Subscriber Features 18
3 3.1 General 28
3.2 Base Module (BM) 28
3.3 Central Module (CM) 34
3.4 Administrative Module 34
2
C-DOT MAX-XL
Chapter1
1.1The C-DOT DSS Family1.1.1 GENERAL
C-DOT DSS MAX is a universal digital switch which can be configured
for different applications as local, transit, or integrated local and
transit switch. High traffic/load handling capacity up to 8,00,000
BHCA with termination capacity of 40,000 Lines as Local Exchange
or 15,000 trunks as Trunk Automatic Exchange, the C-DOT DSS
family is ideally placed to meet the different requirements of any
integrated digital network.
The design of C-DOT DSS MAX has envisaged a family concept. The
advantages of family concept are standardized components,
commonality in hardware, documentation, training, installation and
field support for all products and minimization of inventory of spares.
In fact this modular design has been consciously achieved by
employing appropriate hardware, software, and equipment
practices.
The equipment practices provide modular packaging. Common cards
and advanced components have been used in the system hardware
in order to reduce the number and type of cards. Standard cards,
racks, frames, cabinets and distribution frames are used which
facilitate flexible system growth. Interconnection technology has
been standardized at all levels of equipment packaging. All these
features, together with ruggedised design, make C-DOT DSS MAX
easy to maintain and highly reliable.
Another important feature of the design is the provision of both local and centralized
operation and maintenance. Beginning with local operation and maintenance, with the
installation of similar digital switches in the network, centralized operation and maintenance
will provide maintenance and administration services very economically. All these services
are provided through a simple, interactive man-machine interface.
3
1.2. BASIC GROWTH/BUILDING MODULES
C-DOT DSS MAX exchanges can be configured using four basic
modules
(Fig. 1.1)
Base Module
Central Module
Administrative Module
Input Output Module
i) BASE MODULE
The Base Module (BM) is the basic growth unit of the system. It
interfaces the external world to the switch. The interfaces may be
subscriber lines, analog and digital trunks, CCM and PBX lines. Each
Base Module can interface upto 2024 terminations. The number of
Base Modules directly corresponds to the exchange size. It carries
out majority of call processing functions and, in a small-exchange
application, it also carries out operation and maintenance functions
with the help of the Input Output Module.
In Single Base Module (SBM) exchange configuration, the Base
Module acts as an independent switching system and provides
connections to 1500 lines and 128 trunks. In such a configuration,
the Base Module directly interfaces with the Input Output Module for
bulk data storage, operations and maintenance functions. Clock and
synchronization is provided by a source within the Base Module. It is
a very useful application for small urban and rural environments.
With minimum modifications in hardware through only one type of
card, a Base Module can be remotely located as a Remote Switch
Unit (RSU), parented to the main exchange using PCM links.
ii) CENTRAL MODULE
4
Central Module (CM) consists of a message switch and a space
switch to provide inter-module communication and perform voice
and data switching between Base Modules. It provides control
message communication between any two Base Modules, and
between Base Modules and Administrative Module for operation and
maintenance functions. It also provides clock and synchronization on
a centralized basis.
iii) ADMINISTRATIVE MODULE
Administrative Module (AM) performs system-level resource
allocation and processing function on a centralized basis. It performs
all the memory and time intensive call processing support functions
and also administration and maintenance functions. It communicates
with the Base Module via the Central Module. It supports the Input
Output Module for providing man- machine interface. It also supports
the Alarm Display Panel for the audio-visual indication of faults in the
system.
iv) INPUT OUTPUT MODULE (I0M)Input, Output Module (IOM) consists of duplicated Input Output
Processor (IOP). The Input Output Processor (IOP) is a general-
purpose computer with UNIX Operating System. It is used as the
front-end processor in C-DOT DSS. It handles all the input and output
functions in C-DOT DSS. The IOP is connected to AP/BP via HDLC
links.
During normal operation, two IOP’s interconnected by a HDLC link,
operate in a duplex configuration. Working as front-end processor, it
provides initial code down load to the subsystems, man machine
interface and data storage for billing and other administrative
information.
IOP interfaces various secondary storage devices like' disk drives,
cartridge tape drive and floppy drive. It supports printers and upto 8
serial ports for video display units which are used for man- machine
5
communication interface. All the bulk data processing and storage is
done in this module
Thus, a C-DOT DSS exchange, depending upon its size and
application, consists of Base Modules (maximum 32), Central
Module, Administrative Module, Input/Output Module and Alarm
Display Panel. The Base Modules can be remotely located or co-
located depending on the requirement.
1.2.1. REMOTE SWITCH UNIT
Remote Switch Unit (RSU) is an integral part of C-DOT DSS
architecture. In order to realise a RSU, the normal BM can be
modified for remoting with the host exchange via 2 Mbps digital
links. The number of 2 Mbps links between the Main Exchange and
RSU is primarily determined by the traffic. A maximum 16 PCMs can
be provided between a RSU & Main exchange. Analog and Digital
trunk interfaces are also implemented in RSU to support direct
parenting of small exchanges from RSU itself instead of parenting it
to the main exchange which will ultimately save the media required
from main exchange. As far as call processing is concerned, RSU is
an autonomous exchange capable of local-call completion. Operation
and maintenance functions are handled by the host exchange. In the
event of failure of PCM links, RSU goes into standalone mode of
operation. In case it is not possible to process a call request due to
unavailability of links to the host, the subscriber is connected to
appropriate tone or announcement.
During standalone mode of operation, the local and incoming
terminating calls in RSU are switched and the metering information
of all the RSU subscribers is stored in the RSU. It is sent to the host
whenever the PCM links are available again.
Only the even numbered BMs can be configured as RSU i.e. a
maximum 16 RSUs are possible in C-DOT DSS MAX-XL and 8 RSUs in
MAX-L.
6
1.3. SYSTEM FEATURES1.3.1 GENERAL FEATURES
This section includes system features related to the CTOD DSS MAX.
They are:
TYPES OF SERVICES
The CDOT DSS of different capacities can be put to use at various
switching nodes in the telecommunication network.
MAX
Main Automatic Exchange MAX is expandable to large capacities of
order of 2000 lines or beyond. The MAX may have Remote Modules
(RM) and Remote Line Concentrators (RLC) connected to it.
RAX
Rural Automatic Exchange (RAX) is a small exchange and is
expandable upto 2000 lines capacity. Single Base Module
configuration (i.e. CDOT SBM RAX with or without concentration)
comes under the RAX category.
TYPES OF APPLICATION
The system can be put to the following applications:
Replacements
The exchange can serve as replacement of an existing switching
system due to be phased out from the network.
7
New Exchanges
Wherever new exchanges are opened, the CDOT DSS MAX can
provide the switching network within the existing telecom network.
Extensions
The capacity of an existing CDOT switching system can be increased.
For example if the capacity of an existing CDOT exchange is 512
points, it can be increased, to say, 4000 lines.
TYPE OF SYSTEM
The system is Stored Programme Controlled (SPC) which makes it
possible to work in attended/non-attended type of working
environment.
TYPE OF NETWORK
The switching network within the system is 4-wire digital.
TYPE OF COMPONENTS
The different type of components used include integrated circuits,
miniature relays, PCB, etc. The connecting scheme between various
modules emphasis connectorised hardware.
1.3.2 NUMBERING PLAN FEATURES
This section includes features related the directory numbering plan.
LEVEL 0 FOR TAX STD
Digit 0 is used for getting access to the trunk automatic exchange to
route STD (Subscriber Trunk Dialing) traffic to subscribers connected
to the national TAX network.
LEVEL 1 SPECIAL SERVICES
CDOT DSS provides for three digit or more than three digit access
codes for level 1 special services.
8
LEVEL 9 POINT TO POINT STD
Digit 9 is used for getting access to the Strowger STD tandem for
point-to-point subscriber dialled calls. In CDOT DSS, ‘9’ is used for
checking STD barring etc.
MAXIMUM 16 DIGIT RECEPTION FROM TRUNKS
The system has a provision to receive a maximum of 16 digits from a
trunk.
MAXIMUM 40 DIGIT RECEPTION FROM SUBSCRIBERS LINES
The system has a provision to receive a maximum of 40 digits from
the subscriber’s line. A typical case when so many digits could be
expected in CDOT DSS is in case of credit card calling or when the
facilities of “Dialling by Equipment Number” is used etc.
PREFIX 00 FOR ISD THROUGH TAX
Code 00 is used as access code for ISD calls through TAX. In early
phases of ISD working in India, a second dial tone after dialling 00
was fed and was to be followed by further digits. The scheme has
changed now. CDOT DSS provides for both the schemes of working,
with second dial tone and without second dial tone.
The digits 00 are used when checking for ISD barring; similarly, for
near ISD barring checks, digits 09 are used.
PREFIX 900 FOR ISD CALLS
Code 900 was used as access code for ISD calls in Indian network
when ISD was initially introduced.
C-DOT DSS provides for this type of working also if needed. The
digits 900 are used in CDOT DSS for checking ISD and near ISD
restrictions (combined).
VARIABLE LENGTH DIRECTORY NUMBER OF SUBSCRIBERS
9
The national number of a subscriber in India can have a maximum of
9 significant digits (i.e., excluding the access code 0). It includes the
trunk code for the area to which the local exchange of the subscriber
belongs and his directory number within the local exchange/local
area. The director number can vary from 3 to 7 digits (including
exchange code). CDOT DSS supports this numbering scheme fully.
VARIABLE LENGTH ROUTE CODE
The access codes for various routes may be of variable length (1
digit to 12 digits). The trunk (ISD) codes allotted for the area are
handled in the same way as other “routes” in CDOT DSS therefore,
trunk codes of 2 to 7 digits length, required in India, can be
supported in CDOT DSS.
ANALOG LINE INTERFACE
The system is capable of being connected to the subscribers through
ordinary, CCB or PBX lines.
NORMAL LINE
Line resistance including subscriber’s instrument may go upto 1200
ohms for which minimum 30 mA loop current is guaranteed.
Insulation resistance between ‘a’ wire (or ‘b’ wire) and ground or
between ‘a’ and ‘b’ wires may be as low as 20K ohms.
1.3.3 LINE SERVICE FEATURES
This section relates to various types of lines that the exchange can
cater to, and briefly, services offered to such lines.
ORDINARY LINE
A subscriber may have an ordinary telephone instrument connected
to his/her line.
COIN TELEPHONE (CCB LINE)
10
The system provides a service by means of a special telephone
permitting outgoing calls after insertion of adequate coin(s) or
token(s) and incoming calls without payment. The two classes of
service are:
Local-calls within Unit Fee Zone (UFZ) can be made from coin
collection box telephone. STD – from STD coin box telephones, the
STD calls and calls to some special services are permitted (Not
available presently).
1.3.4 TRUNK INTERFACE FEATURES
ANALOG TRUNKS
The various types of analog trunk circuits possible to be terminated
on the system comprise physical circuits (analog circuits working
over physical wires).
2-Wire Physical Circuits
The physical circuits employ DC Loop Signalling, MF Signalling (MFC
R2 modified for Indian Network) and Carrier Circuits with E&M
Signalling.
These circuits can employ any of the following register signalling
schemes.
Decadic, MFC R2 modified for Indian Network and MF Semi-
compelled Line signalling is as follows:
Ring down (i.e. sending of ringing current) for exchange to manual
board.
DC loop signalling for manual board to exchange.
DIGITAL TRUNKS: The inter working of a CDOT system with other
exchanges on a digital trunk is possible using register signalling
schemes viz. Decadic and MFC R2 modified for Indian Network.
Digital Trunk interfaces provided is 4 wire, 2048 bit/s HDB3 coded
PCM.
11
12
SYSTEM
ARCHITECTURE
FIG 1.1
Chapter 2
2.1 CDOT SYSTEM CAPACITY
2.1.1 INTRODUCTION
The capacity of C-DOT DSS is defined in terms of the following
parameters:
• .The termination capacity expressed as the number of lines and
trunks
• The amount of traffic (in Erlangs) that can be switched
• The number of Busy Hour Call Attempts (BHCA) that can be
processed with a given call-mix while meeting the overall service
quality requirements
This section indicates the maximum capacity of different system
elements as well as that of complete exchange, equipped to its
ultimate termination capacity. It has been ensured that the specified
parameters are valid to meet overall reliability objectives for the C-
DOT DSS as specified in ITU-T recommendations.
2.1.2. TERMINATION CAPACITY
A Terminal Card is the basic system element. It interfaces/
terminates the lines and trunks. The next higher element is a
Terminal Unit. The types of terminal cards and terminal units used in
C-DOT DSS along with its functions are explained in H/W description.
Termination capacity of a BM is 488 analog terminals and that of LM
is 768 analog terminals. A BM can be concentrated with 2 LMs to
provide maximum termination capacity of 2024 analog lines. In case
of a BM, a maximum of 256 B- channels can be provided for ISDN
terminations at the cost of 128 analog lines. In its maximum
configuration of one BM and 2 LMs with termination capacity of 2024
analog lines, 256 B-channels are provided at the cost of 512 analog
lines. One to one replacement of B-channels is planned in immediate
13
future.
Base Module and Line Module are the highest level of system
elements Each Base Module has four Terminal Units whereas a Line
Module has six Terminal Units.
A maximum of 16 BMs can be connected in MAX-L and 32 BMs can
be connected in MAX-XL configurations.
Table2.1 summarises the termination capacities of the various
system elements of CDOT DSS MAX.
2.1.3 EXCHANGE CONFIGURATIONS
C-DOT DSS MAX can be configured to support any combination of
lines and trunks. For different applications in the network as Local
Exchange, Local cum Tandem Exchange. Trunk Automatic Exchange
(TAX) or Integrated Local cum Transit (ILT) Exchange.
In its maximum configuration, upto 40,000 lines and 5.500 trunks
are supported when configured as Local/Local cum Tandem. When
configured as TAX, 14,500 trunks are supported.
Table 2.1
Termination Capacity of System Elements
Sl System Element Termination Capacity1 Termination Cards (TC):
A Analog Line CardLCC – 8 Analog Subscribers
CCM – 8 CCB subscribers with last
two ports supporting 16-kHz B Analog Trunk Card TWT/ EMF – 8 Trunks
C A set of DTS/DTC Cards One 2-Mbps E-1 link as CAS/CCS
trunksD #7 PHC Card (SHM) 8 Protocol Handlers/ Signalling
LinksE ISDN-BRI Card 8 BRI (2B+D) Interface i.e. 16 B-
channels 14
F ISDN-PRI Card One PRI (30B+D) Interface i.e. 30
B-channels2 Terminal Unit (TU):
A Analog TU (ATU)16 Analog Terminal Cards (LCC/
CCM/ TWT/ EMF) to support any
combination of Lines & Trunks in B Digital TU (DTU) Four 2-Mbps E-1 links as CAS/
CCS7C #7 Signalling Unit
Module (SUM)
64 Nos., #7 Protocol
Handlers/signalling linksD ISDN Terminal Unit
(ISTU)
256 Bearer Channels to be
configured as BRI, PRI or any 3 Base Module (BM):
A Base Module (Line)480 Analog Subscribers. A
maximum of 256 B-Channels for
ISDN interface can be provided at
B Line Module (LM)768 Analog subscriber lines. A
maximum of two LMs connected
with BM supports 2024 lines.C BM (Analog Trunks) 488 Analog Trunks
D BM (Digital Trunks) Fifteen 2-Mbps E-1 links as CAS/
CCS7E BM (Analog + Digital) Three possible configurations as
360 AT+ 4 PCMs/ 232 AT+ 8
Table-2.2
Termination Capacity of Exchange Configurations
Sl Exchange
Configuration
Termination Capacity
1Single Base Module
(SBM)
1,500 Lines & 128 Trunks. The
trunks can be analog and/or digital.
The number of trunks can be Multi-Base Module (MBM) (DSS MAX)
15
2
i) MAX-XL
Ideal configuration to support
40,000 lines and 5,500 trunks with
20 Line BMs and 12 Trunk BMs. The
trunk capacity can be increased by
450 at the cost of 2,000 subscribers
or vice versa.
ii) MAX-L
Ideal configuration to support
20,000 lines and 2,700 trunks with
10 Line BMs and 6 Trunk BMs. The
trunk capacity can be increased by
450 at the cost of 2,000 subscribers
or vice versa.
3 Remote Switching Unit
(RSU)
2,000 subscriber lines. Trunk
interface at the cost of subscriber 4 Multi-Base Module TAX 14,500 Trunks
Note: out of the total equipped capacity, a maximum of 30,000 lines
may be remote subscribers through RSUs in MAX-XL whereas 14000
lines may be Remote Subscriber through RSUs in MAX-L.
2.1.4. TRAFFIC CARRYING CAPACITY
The traffic carrying capacity of C-DOT DSS MAX is ideally 8000
Erlangs in case of MAX-XL and 4000 Erlangs in case of MAX-L
exchanges.
This figure is based on the ideal traffic of one Erlang per switched
circuit. But the actual traffic carrying capacity of one switched path
is always less than one in practical application. Accordingly
capacities are reduced to not less than 7,500Erlangs incase of MAX-
XL and to 3800 in case of MAX-L exchanges.
2.1.5. BHCA HANDLING CAPABILITY
16
The basic processing elements of the exchange are the Base
Processor (in the Base Module). Base processor has the capability of
handling 12,500 Busy Hour Call Attempts which can be increased to
30,000 using upgraded processor card. The C-DOT DSS MAX (MAX-
XL) exchange with 32 Base Modules can handle upto 3,00,000 BHCA.
By upgrading the processor card in BM/CM/AM/SUM and message
switch in all the BMs, it is increased to 8,00,000 BHCA.
In case of MAX-L exchanges with 16 BMs connectivity, the BHCA
handling capability is 1,50,000.
Various exchange configurations and their traffic capacities are
summarised in Table2.3.
Table 2.3 Traffic Capacity of Exchange Configurations
Sl.No
.
Exchange
Configuration
Traffic Capacity Description
I. SBM-RAX 250 Erlangs. The BHCA capacity
depends on
the type of processor used and it may
be 12,500 or 30,000.
2. Remote Switching
Unit (RSU)
250 Erlangs. The BHCA capacity
depends on
the type of processor used. It may be
12,600 or 30,000.
3. DSS-MAX/TAX
i) MAX-XL
Not less than 7,500 Erlangs. The BHCA
capacity is more than 3,00,000 and
upgradable to 8,00,000 by upgrading
only processor cards.
ii) MAX-L Not less than 3800 Erlangs. The BHCA
capacityis 1,50,000.
17
Note: For some of the sites already commissioned with one of the
first three configurations, overall BHCA handling capacity may be
lower due to use of old processor cards.
2.1.6 SYSTEM RELIABILITY
The C-DOT DSS MAX is designed to meet the reliability standards as
defined in the specifications. The system uses fully digital techniques
for switching including the subscriber stage. The system is built
using a minimal number of standard units/modules which allow
flexible growth of the exchange and easy upgradation in technology
and new features.
A very important feature of C-DOT DSS MAX architecture is the
extensive duplication of units. All controller units are duplicated or
have n+1 redundancy. Software design matches the high degree of
redundancy provided by hardware to minimize the system down
time.
To minimize failures caused by human and/or software errors the C-
DOT DSS MAX has extensive software maintenance functions. The
design of software is such that propagation of software faults is
contained and it provides sufficient checks to monitor the correct
functioning of the system. The facilities are in-built to ensure
automatic software recovery on detection of software faults.
Whenever a faulty condition occurs the software provides for the
isolation of the faulty subsystem and automatically initiates
diagnostic programs for diagnostic purposes. The diagnostic
programs have a design objective of localizing 95 of the faults to a
single PCB level and the rest to a two PCB level. Provision is also
made for safety of charge-records. The charging information is
dumped at regular intervals to non-volatile duplicated back-up
memories automatically. The software maintenance functions
include data audits as well; as system integrity monitors and
controls.
Alarm Display Panel is provided for a continuous indication of the
system status. Audio-visual alarms are provided. 18
19
2.2 SUBSCRIBER FEATURES
2.2.1 INTRODUCTION
The C-DOT Digital Switching Systems offer a wide range of telephony
features and supplementary services. Further capabilities can be
developed to meet specific customer needs. Due to mandatory
requirement of exchange of messages between the switching systems and
user's equipment, some of the services are exclusively offered to ISDN-
subscribers. In case of few of the services offered to PSTN and ISDN
subscribers, the implementation of services to PSTN subscribers may be
partial and invocation procedure may also differ.
2.2.2 PSTN (ANALOG) AND ISDN SUBSCRIBER SERVICES
The subscriber services provided by C-DOT DSS MAX exchanges for
PSTN (Analog) as well as ISDN subscribers are-explained as per their
logical grouping:
Number Identification Services
i) Calling Line Identification Presentation (CLIP)
When this service is subscribed by a user as terminating facility, all
the incoming calls are offered to the user along with the details of
calling party's identity.
In exceptional cases as the calling party has subscribed CLIR or
interworking constraints in the network, it will not be possible to
provide caller's identity.
ii) Calling Line Identification Restriction (CLIR)
This service is offered to the calling party to restrict presentation of
it's number to the called party. When CLIR is subscribed, the
originating exchange notifies the destination exchange that the
calling party's number is not allowed to be presented to the called
20
party. The terminating local exchange may indicate to the called
user that the calling user identity is unavailable due to restriction.
iii) Calling Line Identification Restriction Override (CLIRO)
Subscriber with CLIRO as terminating facility instead of CLIP,
receives the call with the calling line identification even if the calling
party has requested that his (the calling party's) identification
should not b« presented to the called user.
The CLIRO facility is offered at the discretion of the administration to
special category subscribers like the police, hospitals, operator
positions and other emergency centres.
iv) Malicious Call Identification (MCID)
This facility is used for ascertaining the origin of malicious calls.
During conversation the subscriber has to use suitable procedure to
notify the exchange about the malicious call. The detail of the call is
recorded in the exchange which can be retrieved later on. If the caller
is from an exchange which does not support identification of calling
line, "junction identity" is found and an "identification request" may
be sent to the originating exchange by tee exchange personnel.
Call Offering Supplementary Services
Call offering services permit the served user to request the network to
divert the incoming calls to a specific number. In call forwarding, the
network forwards the call to a pre-registered number which can be
specified by the user or exchange administrator.
i) Call forwarding unconditional (CFU)
This service permits the served user to request the exchange to
forward all incoming calls to other Number. The served user's
originating service remains unaffected. The other number could be a
fixed pre-determined number or a number specified by the
subscriber in the activation request.
21
ii) Call Forwarding Busy (CFB)
This service permits the served user to request the exchange to
forward all incoming calls to other number if the served users
number is not free. The served user's originating service remains
unaffected.
iii) Call forwarding no reply (CFNR)
This service permits the served user to request the exchange to
forward all incoming calls which are not replied with in ring timeout
period. The served user's originating service remains unaffected.
Call Completion Services
i) Call Waiting
A subscriber engaged in an existing call, is given an indication (Call
Waiting tone or ZIP tone) that another caller is attempting to connect
to his number. The caller will hear ring back tone. By flashing the
hook-switch the called subscriber can talk with either party while
keeping the other on hold (acceptance without clearing). If the called
subscriber replaces his handset in response to the tone (acceptance
by clearing), the exchange will automatically extend ring to the
subscriber and re-establish the connection on answer with the party
waiting.
ii) Call Hold
This facility is used by the user to put the existing conversation on
hold for the time being and initiate a new call or receive a call in
waiting. The call, which has been put on hold, is retrieved by the
user as and when it is required. The procedure of invocation to put
the conversation on hold and its subsequent retrieval is different for
ISDN and PSTN subscribers.
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Multi-Party Services
i) Three party conference
The three party call service enables the served user to establish,
participate in, and control a simultaneous communication involving
the served user and two other parties. The served user can request
to convert two party conversation into a three party conference.
During the three party conversation, the served user can
disconnect one party, disconnect the 3-way conversation or choose
to communicate privately with one of the parties, in which case the
call to the other party is held.
ii) Multi party conference (Add-on conference)
The CONF (Add-on conference) service enables the served user to
establish and control a conference i.e. a simultaneous
communication, involving of users (max. up to 6).
When the CONF service is invoked, the serving local exchange
allocates conference resources to the served user and add any
existing call indicated by the served user to the conference. On
successful invocation of conference the served user becomes the
'conference controller'. The conference Controller may then add,
drop, isolate, and reattach parties from the conference. The
conference controller can also hold and retrieve the conference
(e.g. to add parties) and finally end the conference.
Miscellaneous Services
i. Hot Line (Timed)
This service is also referred as a Fixed Destination Call with Time-
out. This allows a subscriber to establish calls to a pre-registered
number. After getting dial tone, if the subscriber does not dial any
digit for a specified minimum time, he is automatically connected to
the number already registered in the system. If subscriber dials
digits before the time-out, a normal connection is established in
accordance with the dialled digits. Incoming calls are not affected by
this service.
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ii. Hot Line (Without Time-out)
This service is also referred a Fixed Destination Call - Immediate.
This allows a subscriber to establish calls to a pre-registered number
by just lifting the handset. In this service such a connection is set up
immediately upon lifting the handset, hence the subscriber cannot
dial normal outgoing calls. Incoming calls are not affected by this
service.
iii. Reminder Call/ Alarm Services
When this service is activated, the subscriber is offered a call
initiated by the exchange at a specified time/s. When the alarm call
matures and is answered an announcement follows to notify the
alarm call.
This service is available in two forms:
(i) In semiautomatic form, the booking is manual through
exchange operator and the execution is automatic. In this
case, the operator needs to be 'local' operator, connected to
the system via a VDU
(ii) (ii) In automatic form, the booking is done automatically by
the subscriber through a control procedure and its execution
is also automatic.
iv. Subscriber Controlled Call Restriction Services
Denying all calls to a line, while allowing it to originate calls as per
current access level, Denying various level of originations from a line
(no ISD calls, no STD and ISD calls, only local calls and selected Level
I services, etc.) while allowing incoming calls to terminate normally
on it.
Subscriber controlled barring offers flexibility to a subscriber to
change outgoing restriction by selecting one access level, using
predefined procedure through secret password. To maintain the
24
secrecy of the password, the user can modify the password by using
predefined procedure.
25
v. Intrusion Barring Service
For reasons of call security in terms of fully undisturbed call,
subscriber can avail of intrusion barring facility. This can be useful,
for example, when data transmission is being effected on the line.
vi. Dialling by Terminal Equipment Number
Sometimes, a specific line/trunk, tone or announcement is to be
accessed by its Terminal Equipment Number (TEN) in the exchange.
This is specifically required for dialling to lines which do not have a
directory number w in case of "directed calls" via outgoing trunks.
This facility is used by the maintenance personnel as part of routine
maintenance activities.
vii. Trunk Offer
This service makes it possible for the operator to interrupt a call in
progress, in order to allow another incoming call to be offered. The
choice of accepting or rejecting the new call rests with the
subscriber.
viii. Queuing Service
This enables the subscriber to have one or more calls placed in a
queue when his line/group of lines are busy. When the subscriber
line becomes free, the first caller in the queue is connected and the
other callers in the queue move one place ahead.
ix. Priority Subscriber
During overload and network congestion, priority service assures an
improved service level for priority subscribers such as those
responsible for maintenance of law and order or essential services.
The priority subscribers are served even during overload due to
heavy traffic in the exchange via alternate group of trunks. A few
trunks may be identified for this purpose which are exclusively used
by priority subscribers while normal subscribers are denied access to
them. The eligibility of priority subscribers for an alternate group of
trunks is programmed by the exchange administrator.
26
x. Distinctive Ringing for Long Distance Calls
The PSTN subscribers are connected different ringing cadence to
inform them that this call is a long distance STD/ISD call.
2.2.3. ISDN-SUPPLEMENTARY SERVICES
In addition to the services available for PSTN/Analog as well as ISDN
subscribers, a number of supplementary services are offered only to
ISDN-subscribers.
Charging Related Supplementary Services
The Advice Of Charge service provides charging information to the
user paying for a call. The option of providing the information at a
predefined stage of the call is based on the type of AOC facility
subscribed.
i) AOC-E, Charging information at the end of the call
The charging information is provided by the serving local exchange
at the end of a call. It is sent in the charge advice information
element of the call clearing message.
ii) AOC-D, Charging information during a call
In this case the charging information is provided by the serving local
exchange every time a quantum of charge has been added. The
charging information is sent in an appropriate message. When the
call is cleared, the remaining number of charge units (incremental
case) or the total charge units (cumulative case) is transferred to the
user in the call clearing message.
27
Group Line Supplementary Services
i) Direct Dialling In (DDI)
This service enables a user of ISPBX to be called without attendant
intervention. This service is based on the ISDN number. The DDI
user, while being a subscriber of an ISPBX, is allocated an ISDN
number from directory number set of the serving public exchange.
The administration allocates a range of ISDN numbers towards the
ISPBX, one for each DDI user.
ii) Multiple Subscriber Number (MSN)
This service provides the facility of assigning multiple ISDN numbers
to more than one user on a single interface. This service allows
direct dialling to one of the terminals connected to an access and
enables the network to determine ISDN number which is applicable
for originating calls for subscriber characteristics and charging
services. The addressing of terminals is achieved by applying a set
of ISDN numbers which need not be consecutive. When a call with
one of these ISDN numbers is delivered, the corresponding MSN
number is indicated to the MSN user.
iii) Sub - Addressing (SUB)
This service is offered to the called user that expands its addressing
capability beyond that provided by the ISDN number. The sub-
address is used by the served user to identify a particular terminal
on a multi- drop access, or a, virtual terminal or process within a
terminal. If the calling party provides a sub-address in 'SET-UP
message, the network delivers this sub-address unchanged and
without interpretation to the called user's installation. It is the called
user's responsibility to interpret the significance of the sub-address.
Number Identification Service
i) Connected Line Identification Presentation (COLP)
It is a supplementary service offered to the calling party to know the
complete ISDN number of the connected party, on answer. It should
28
be noted that if the called user belongs to an ISPBX, the connected
number shall only identify the ISPBX and not the called user's
extension. The extension itself can be identified only if the called
user has subscribed to the DDI service and has included his DDI
digits during call confirmation.
ii) Connected Line Identification Restriction (COLR)
This is a service offered to the connected party to restrict the
presentation its identity to the calling party. When COLR is
subscribed, the destination exchange informs originating exchange
with a notification that the connected party's identity is not allowed
to be presented to the calling party.
Iii) Connected Line Identification Restriction Override (COLRO)
Subscriber with the COLRO facility is given the connected line
identification even if the connected party has requested that his (the
connected party's) identification not to be presented to the calling
user (by the invocation of the COLR service).
Miscellaneous Services:
i) Terminal Portability (TP)
Terminal Portability (TP) is a supplementary service that allows the
user to move a terminal from one socket to another within the same
basic access during the active phase of the call. It also allows the
user to move a call from one terminal to another with the same basic
access in the active phase of the call. It allows a user with an
established call to suspend communication by an appropriate
signalling procedure and resume communication at a later time.
This service permits the user:
To move the terminal from one socket to another within the
same basic access.
To suspend the will and subsequently resume it at the same
terminal & socket.
29
To replace one terminal by another compatible terminal at the
same socket
To move the call from one terminal, to another compatible
terminal at the same basic access.
This service is used only in the active phase of a call and not in the
call establishment and clearing phases. In addition the service shall
independently apply to the calling and called user.
30
Chapter 3
Hardware Architecture
3.1 GENERAL
The hardware architecture of C-DOT DSS MAX is mapped closely on
the System Overview described in the previous chapter. In the
following sections, the hardware architecture of each constituent
module is described.
3.2 BASE MODULE (BM)Base Module (BM) is the basic building block of C-DOT DSS MAX. It
interfaces the subscribers, trunks and special circuits. The
subscribers may be individual or grouped PBX lines, analog or digital
lines. The trunks may be Two Wire Physical, E&M Four Wire, E&M
Two Wire, Digital CAS or CCS.
The basic functions of a Base Module:
Analog to digital conversion of all signals on analog lines
and trunks
Interface to digital trunks and digital subscribers
Switching the calls between terminals connected to the
same Base Module
Communication with the Administrative Module via the
Central Module for administrative and maintenance
functions and also for majority of inter-BM switching (i.e.
call processing) functions
Provision of special circuits for call processing support
e.g. digital tones,
announcements, MF/DTMF senders/receivers
31
Provision for local switching and metering in stand alone
mode of Remote Switch Unit as well as in case of Single
Base Module Exchange (SBM-RAX)
For these functions, the Base Module hardware is spread over
different types of Units.
(Ref. fig. 3.1)
Analog Terminal Unit - to interface analog lines/trunks,
and providing special circuits as conference,
announcements and terminal tester.
Digital Terminal Unit - for interfacing digital trunks i.e.
2Mbps E-1/PCM
Links
#7 Signalling Unit Module - to support SS7 protocol
handlers and some call processing functions for CCS7
calls.
ISDN Terminal Unit - to support termination of BRI/PRI
interfaces and
implementation of lower layers of DSS1 signalling
protocol.
Time Switch Unit - for voice and message switching and
provision of service circuits.
Base Processor Unit - for control message
communication and call processing functions.
3.2.1. Analog Terminal Unit (ATU) (Figure 3.2A)
The Analog Terminal Unit (ATU) is used for interfacing 128 analog
terminations which may be lines or trunks. It consists of terminal
cards which may be a combination of Line Circuit Cards (LCC), CCB
32
with Metering (CCM) cards, Two Wire Trunk (TWT) cards, E&M Two
wire (EMT) Trunk cards and E&M Four wire (EMF) trunk cards,
depending upon the module configuration. Also, provision has been
made to equip Conference (CNF) card to support “six party”
conference, Announcement (ANN) to support 15 user-friendly
announcement messages, and Terminal Test Controller (TTC) for
testing of analog terminations. Power Supply Unit (PSU-I) provides
logical voltages and ringing current in the ATU.
Analog Subscriber Line Cards:
Two variants of subscriber line cards as LCC or CCM with interfaces
upto 8 subscribers, provide basic BORSCHT functions for each line.
Analog to digital conversion is done by per-channel CODEC according
to A-law of Pulse Code Modulation. Each CCM card has the provision
of battery reversal for all the 8 lines with the last two lines having
provision to generate 16 KHz metering pulses to be sent to
subscriber's metering equipment.
The 8-bit digital (voice) output of four LCCs is multiplexed to form a
32-channel, 2 Mbps PCM link - also called a terminal group (TG).
Since a Terminal Unit has a maximum of 16 terminal cards, there are
four such terminal groups. The signalling information is separated by
a scan/drive logic circuit and is sent to the signalling processor on
four different scan/drive signals. The LCC/CCM also provides test
access relay to isolate the exchange side and line side to test it
separately by using the Terminal Test Controller (TTC).
Analog Trunk Cards:
Analog trunk cards interface analog inter-exchange trunks which
may be of three types as TWT, EMT and EMF. These interfaces are
similar to Subscriber Line Card, with only difference that the
interfaces are designed to can/drive events on the trunks as per
predefined signalling requirement.
33
Signalling Processor (SP) Card
Signalling Processor (SP) processes the signalling information
received from he terminal cards. This signalling information consists
of scan/drive functions like origination detection, answer detection,
digit reception, reversal detection, etc. The validated events are
reported to Terminal Interface Controller for further processing to
relieve itself from real-time intensive functions. Based on the
information received from the Terminal Interface Controller, it also
drives the event on the selected terminal through scan/drive signals.
Terminal Interface Controller (TIC) Card
Terminal Interface Controller (TIC) controls the four terminal groups
(TG) of 32 channels, and multiplex them to form a duplicated 128-
channel, 8 Mbps link towards the Time Switch (TS). For signalling
information of 128- channels, it communicates with Signalling
Processor (SP) to receive/send the signalling event on analog
terminations. It also uses one of the 64 kbps channel out of 128
channels towards Time Switch, to communicate with Base Processor
Unit (BPU). In concentration mode, three other Terminal Units share
this 128-channel link towards the Time Switch to have 4:1
concentration.
Terminal Interface Controller is built around 8-bit microprocessor
with associated memory and interface and it is duplicated for
redundancy.
Special Service Cards:
A Terminal Unit has some special service cards such as Conference
(CNF) Card to provide six party conference. Speech samples from
five parties are added by inbuilt logic and sent to the sixth party to
achieve conferencing. Terminal Test Controller (TTC) Card is used to
test analog terminal interfaces via the test access relays on the
terminal cards.
34
Announcement Controller (ANN) Card provides 15 announcements
on broadcast basis. Only one service card of each type is equipped in
a Base Module with provision of fixed slot for TTC and variable slots
for CNF/ANNC.
Announcement and Conference Cards are equipped in Terminal Unit
through S/W MMC command. Two slots are occupied by each card
i.e. 16 channels for each card is used out of 128 channels available
on a Bus between a TU &TS.
3.2.2. Digital Terminal Unit (DTU) (Ref. Fig. 3.2B)
Digital Terminal Unit (DTU) is used exclusively to interface digital
trunks. One set of Digital Trunk Synchronization (DTS) card along
with the Digital Trunk Controller (DTC) card is used to provide one E-
1 interface.
Each interface occupies one TG of 32 channels and four such
interfaces share 4 TGs in a Digital Terminal Unit. The functions
performed by TIC and SP in Analog Terminal Unit, are collectively
performed by the Terminal Unit Controller (TUC) in the Digital
Terminal Unit. The scan functions are - HDB3 to NRZ code
conversion, frame alignment and reconstitution of the received
frame. The drive functions include insertion of frame alignment
pattern and alignment information. Each interface can be configured
as CAS or CCS interface.
3.2.3. SS7 Signalling Unit Module (SUM) (Ref. Fig.3.2D) Any one of the ATU or DTU in a BM can be replaced by SUM frame to
support CCS7 signalling. Only one such unit is equipped in the
exchange irrespective of its configuration or capacity. For details of
SUM architecture, refer to chapter no.4.
35
36
3.2.4. ISDN - Terminal Unit (ISTU) (Ref. Fig. 3.2C) One of the four ATUs/ DTUs in a BM can be replaced by ISTU to
provide BRI/PRI interfaces in C-DOT DSS. The only constraint is that
ISTU has to be principal TU i.e. directly connected to TSU on 8 Mbps
PCM link. The ATU/DTU cannot be used in concentration with ISTU.
By equipping one ISTU in the exchange, a max. of 256 B channels
are available to the administrator which can be configured as BRI,
PRI or any mix as per site requirement. Depending on the
requirement of number of ISDN-Interfaces, one or more ISTUs can be
integrated in C-DOT DSS, either in one BM or distributed across
different BMs. For details, refer chapter no. 4.
3.2.5. Time Switch Unit (TSU) (Ref. Fig. 3.2 F)Time Switch Unit (TSU) implements three basic functions as time
switching within the Base Module, routing of control-messages within
the Base Module and across Base Modules and support services like
MF/DTMF circuits, answering circuits, tones, etc. These functions are
performed by three different functional units, integrated as time
switch unit in a single frame (Refer Fig. 3.2).
3.2.6. Base Processor Unit (BPU) (Ref. Fig. 3.2 E)Base Processor Unit (BPU) is the master controller in the Base
Module. It is implemented as a duplicated controller with memory
units. These duplicated sub-units are realised in the form of the
following cards:
Base Processor Controller (BPC) Card
Base Memory Extender (BME) Card
BPC controls time switching within the Base Module via the Base
Message Switch and the Time Switch Controller. It communicates
with the Administrative Processor via Base Message Switch for
operations and maintenance functions. In a SBM configuration, BPC
directly interfaces with the Alarm Display Panel and the Input Output
Module.
37
To support 8,00,000 BHCA, the BPC card is replaced by High
performance Processor Card (HPC). It is pin to pin compatible for
hardware and also for software so that they are interchangeable at
any site to meet specific traffic requirement.
3.3. CENTRAL MODULE (CM)Central Module (CM) is responsible for space switching of inter-Base Module calls,
communication between Base Modules and the Administrative Module, clock distribution and
network synchronisation. For these functions, Central Module has a Space Switch, Space
Switch Controller and a Central Message Switch. Figure 3.3 summarises the various units and
sub-units of the CENTRAL MODULE.
3.4. ADMINISTRATIVE MODULE (AM)Administrative Module (AM) consists of a duplicated 16/32-bit controller called the
Administrative Processor (APC). It communicates with Base Processors via the Central
Message Switch for control messages and with the duplicated Input Output Processors in the
Input Output Module for interfacing peripheral devices Administrative processor is
responsible for global routing, translation, and resource allocation and all other functions that
are provided centrally in C-DOT DSS MAX.
The implementation of AM is similar to Base Processor Complex of BM, using the same
hardware configuration. As explained earlier, HPC instead of BPC is used to support 8,00,000
BHCA.
38
TERMINAL UNIT-1(TU-1)
1
TERMINAL UNIT-2(TU-2)
2
TERMINAL UNIT-3(TU-3)
3
TERMINAL UNIT-4(TU-4)
4
BASE PROCESSOR UNIT(BPU)
5
TIME SWITCH UNIT(TSU)
6
NOTE: TU CAN BE ATU, DTU, ISTU or #7SU WITH ONLY EXCEPTION
THAT TU-4 SHOULD BE ATU IN CASE OF LINE BM AND ANALOG
TRUNK BM
FIG: 3.1 BASE MODULE (BM) CONFIGURATION
1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
P
S
U
I
T
C
T
C
T
C
T
C
T
C
T
C
T
C
T
C
T
I
C
S
P
C
/
I
S
P
T
U
I
T
U
I
T
I
C
S
P
C
/
I
S
P
T
C
T
C
T
C
T
C
T
C
T
C
T
C
T
C
P
S
U
I
NOTE: 1) TC MAY BE LCC, CCM, TWT or EMF
2) IN CASE OF TU4 AS ATU IN BM, SLOT 24 WILL BE TTC
FIG: 3.2A ANALOG TERMINAL UNIT (ATU) CONFIGURATION
1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
P
S
U
I
D
T
S
0
D
T
C
0
D
T
S
1
D
T
C
1
T
U
C
T
U
I
T
U
I
T
U
C
D
T
S
2
D
T
C
2
D
T
S
3
D
T
C
3
P
S
U
I
FIG: 3.2B DIGITAL TERMINAL UNIT (DTU) CONFIGURATION
1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
39
P
S
U
1
P
S
U
2
L
C
1
L
C
2
L
C
3
L
C
4
L
C
5
L
C
6
L
C
7
L
C
8
I
T
C
0
I
C
C
0
I
I
C
0
I
I
C
1
I
C
C
1
I
T
C
1
L
C
9
L
C
1
0
L
C
1
1
L
C
1
2
L
C
1
3
L
C
1
4
L
C
1
5
L
C
1
6
NOTE: LC MAY BE BRL or PRL CARDS
FIG: 3.2C ISTU CONFIGURATION
40
1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
P
S
U
1
P
S
U
2
B
M
E
S
H
M
1
S
H
M
2
S
H
M
3
S
H
M
4
H
P
C
/
B
P
C
T
U
C
T
U
I
T
U
I
T
U
C
H
P
C
/
B
P
C
S
H
M
5
S
H
M
6
S
H
M
7
S
H
M
8
B
M
E
P
S
U
4
P
S
U
3
NOTE: 1) SHM IS #7 PROTOCOL HANDLER CARD
2) WITH BPC, ONLY SHM 1-4 CAN BE EQUIPPED
3) HPC IS USED TO SUPPORT SHM1-8 CARDS AND HIGHER
MESSAGE PROCESSING CAPABILITY
FIG: 3.2D #7SU CONFIGURATION
1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
P
S
U
II
B
M
E
H
P
C
/
B
P
C
H
P
C
/
B
P
C
B
M
E
P
S
U
II
NOTE: HPC USED TO SUPPORT 800K BHCA
FIG: 3.2E BASE PROCESSOR UNIT (BPU) CONFIGURATION
41
1 2 3 4 5 6 7 8 9 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2
P
S
U
II
T
G
A
M
F
C
M
F
C
S
C
I
C
A
F
B
M
S
D
M
S
C
T
S
I
T
S
M
T
S
C
T
S
S
T
S
S
T
S
C
T
S
M
T
S
I
M
S
C
M
S
D
A
F
B
S
C
I
C
M
F
C
M
F
C
T
G
A
P
S
U
II
NOTE: 1) REPLACE TSS CARDS BY ETS CARDS IN CASE OF
REMOTE BASE MODULES (RSU)
2) MSC AND MSD CARDS ARE REPLACED BY HMS FOR 800K
BHCA
FIG: 3.2F TIME SWITCH UNIT (TSU) CONFIGURATION
42
43
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