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C-DOT DSS MAX-VE
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Introduction
1.1. PURPOSE & SCOPE
This document gives an overview of C-DOT DSS MAX-VE family products. The
contents of the document include details of hardware, software, signalling,
interfaces, subscriber services etc.
1.2. ORGANISATION
The product details are distributed over the following chapters.
Chapter 2 provides a brief description of C-DOT DSS family products. The basic
building blocks of C-DOT DSS have been introduced which are
explained in detail in subsequent chapters.
Chapter 3 describes the hardware architecture of the MAX-VE switching system
in detail. The contents include the architecture of different switching
modules and user/network interfaces upto block level. The
implementation details of other features like Network
Synchronisation, Remote Switching Unit are also included in this
chapter alongwith details of Common Channel Signalling No. 7
(CCS7), Integrated Services Digital Network (ISDN) and V5.X
implementation.
Chapter 4 explains the software architecture of C-DOT MAX-VE. The contents
include the core architecture of different software modules.
Chapter 5 describes the telephony features, supplementary services and system
features. Brief description of each service with the constraints of its
functioning in a few exceptional cases are included.
Chapter 6 contains details regarding the termination and traffic handling
capacity of C-DOT MAX-VE.
Chapter 7 provides details of system packaging, exchange layout, climatic and
environmental conditions etc.
Annex - A lists down the technical specifications of C-DOT MAX-VE as a ready
reference for network planners.
8 C-DOT DSS MAX-VE
Chapter 2.
System Architecture
2.1. GENERAL
C-DOT Value Engineered MAX (MAX-VE) is a recent addition to the family of
C-DOT Digital Switching Systems. Products in this family cater to a wide range of
network requirements with respect to capacity and applications, as described below:
• 256 Port Rural Automatic Exchange (RAX) - for use as local/integrated local
cum transit switch in non-air-conditioned rural environment.
• Single Base Module RAX Based on XL Hardware (SBM-XL) - for application
as local, transit or local cum transit switch upto 1536 lines.
• Single Base Module RAX based on VE hardware (SBM-VE) - for application
as local, transit or local cum transit switch upto 4K lines with 480 trunks.
The line to trunk ratio can be configured as needed.
• Multi Base Module exchange based on XL hardware (MAX-XL) - for
application as local, transit or local cum transit switch with 56000 lines
(including Access Network subscribers working on V5.2 interface) and 8100
trunks. The line to trunk ratio can be configured as needed. This is possible
with 14 line BMs and 18 trunk BMs.
• Multi-base Module exchange based on VE hardware (MAX-VE) - for
application as local, transit or local cum transit switch with 1,00,000 lines
and 15000 trunks. The line to trunk ratio can be configured as needed. This is
possible with 17 line BMs and 15 trunk BMs.
The design of these products follows a family concept. The advantages of family
concept include standardised components, commonality in hardware,
documentation, training, installation and field support for all products and
minimization of inventory of spares. The modular design of these products has been
consciously achieved by employing appropriate hardware, software, and equipment
practices.
2.2. SALIENT FEATURES OF C-DOT MAX-VE
C-DOT MAX-VE is a versatile digital switch which can be configured for various
applications e.g. local, ILT or TAX. This is possible due to distributed software
architecture & modular hardware. This product provides capacity expansion over
MAX-XL and also takes care of the hardware obsolescence in MAX.
Some design features of MAX-VE are described in the following section:
SYSTEM ARCHITECTURE
2.2.1. Flexible Architecture
C-DOT MAX-VE is a modular and flexible digital switching system which
provides economical means of serving metropolitan, urban, and rural
environments. It incorporates all important features and mandatory services
required by the user with the option of upgradation to provide additional
capacity as well as new features and services in future. The architecture for
C-DOT DSS is such that it is possible to upgrade a working C-DOT SBM or
MBM Exchange to provide ISDN, CCS7 & V5.2 service by adding minimum
additional hardware modules while retaining existing hardware units.
Another feature of the architecture is to support PSTN, ISDN and V5
subscribers through Remote Switching Unit (RSU). This unit can provide
switching facility locally even in case of failure of the communication path to
the parent exchange. The system employs an open-ended architecture for
flexibility of configuration and growth. The processor architecture is
characterised by distributed control and message-based communication in
order to achieve a loosely-coupled network for a flexible system architecture.
Software is written in high level language 'C’ and distributed over various
processors. The application software is structured as a hierarchy of virtual
machines. The software is packaged such that, depending upon the actual
switch configuration, it can be distributed over appropriate controllers. The
software features are implemented by communicating processes.
For inter-processor communication, messages are exchanged over HDLC
links that are implemented either as direct links or switched network paths.
This approach hides the physical details of processes from each other and
provides a flexible communication network between the processors. New
modules can be added and existing modules can be modified without affecting
other modules in the system.
Resources are identified as 'global' or 'local' depending upon their distribution
in the system. The resources which depend upon the number of terminals are
provided within the basic growth unit, the Base Module. Base processors are
provided for handling call processing locally. In a small system application,
these processors independently support call processing, exchange operation
and maintenance functions.
On the other hand, in order to avoid replication of large data and memory
intensive functions, some features and facilities are provided centrally.
Program backup, bulk data storage, man- machine interface and operations
and maintenance facilities are therefore provided centrally in order to
provide a means of separating the switch from the operations and
maintenance interface.
Chapter 2.
10 C-DOT DSS MAX-VE
2.2.2. Technology
The system employs a T-T-T switching configuration and is based on a 32-
channel PCM structure. It uses a basic rate of 64Kbps and 2Mbps primary
multiplexing rate. Control is distributed over the system by using 32-bit, 16-
bit microprocessors. All the critical control circuitry has built-in redundancy.
System hardware utilises advanced concepts in micro electronics for a
compact and optimum design. Basic memory unit has been implemented as a
32 to 128MB dynamic RAM board. Single-chip digital signal processors are
used for implementing DTMF and MF and tone receivers. This approach
reduces costs, power dissipation and saves space on the PCBs.
Customisation based on ASICS/FPGAs has been used to optimize space
utilisation and reduce the number of components on various cards.
2.2.3. Redundancy
To meet the stringent availability requirements, C-DOT DSS employs 'hot
standby' technique for all processor complexes so that in the event of the
failure of any one security-block the duplicate copy takes over.
Hardware cross-links between processors have been planned in such a way
that even the failure of two dissimilar processors will not affect system
performance. Also, wherever there is no duplication of hardware units,
multiple units are provided to work in a load-sharing mode. In the event of
failure of one of the units, other units will share its load preventing
disruption of service.
2.2.4. Common Hardware Units
Various hardware units such as controller complexes and message switches
have been standardised for multiple applications. This interchangeability is
an important feature of the system hardware that helps in reducing
inventories and increasing system availability. Some of these standardised
units are -
♦ Module Control Unit
Module Control Unit is a 32-bit microprocessor complex with
associated memory unit. The same unit can be used as the Base
Processor Unit in the Base Module or as the Administrative Processor
Unit in the Administrative Module or Central Switch Controller in
Central Module. It is also used in the CCS7 unit and the V5.X unit as
the CPU.
SYSTEM ARCHITECTURE
GENERAL DESCRIPTION 11
♦ Interface Controller
This is a 16-bit microprocessor based unit with a time-switching
network that can be used to control either terminal interface in the
Terminal Unit or service circuit interface in the Time Switch Unit. In
both the cases, its function is to assign time-slots on the 128- channel
link between the terminals (subscribers, trunks, etc.) and the time
switch.
♦ Message Switch
Message Switch is implemented as a 32-bit message switch controller
which provides upto 39 HDLC links for message communication
between controllers. It is used in base modules as well as the central
module of an MBM system.
2.2.5. Optimisation
In C-DOT DSS, distribution of functions has been optimised. There are local
functions which are entrusted to the growth units, i.e., the Base Modules, for
local switching and interfacing. The resources required by these, functions
are directly linked with the number of lines and trunks equipped.
These functions are -
♦ Terminal Interfacing - interfacing analog/ISDN lines, analog and
digital trunks, CCM & PBX lines.
♦ Circuit Switching - switching within the Base Module.
♦ Call Processing - majority of call processing functions.
♦ Concentration - for providing upto 4046 subscribers on 1024 time-slots.
On the other hand, the functions that are shared globally over the
switch are provided by a central facility which may either be the
Central Module or the Administrative Module. These functions are -
♦ Inter-module Communication
Inter-BM and BM-AM communication via the Central Module.
♦ Message Switching
Inter-BM and BM-AM control-message communication via the Central
Message Switch in the Central Module.
♦ Resource Allocation
Done by the Administrative Module.
Chapter 2.
12 C-DOT DSS MAX-VE
♦ Operations and Maintenance
Bulk data storage by the Input Output Module and man-machine
interface provided by the Administrative Module via the Input Output
Module.
♦ Services
Announcements and conference circuits.
2.2.6. Modular Packaging
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 standardised at all levels of equipment
packaging. All these features, together with ruggedised design, make C-DOT
DSS MAX easy to maintain and highly reliable.
2.2.7. Centralised O & M
Another important feature of the design is the provision of both local and
centralised operation and maintenance. Beginning with local operation and
maintenance, with the installation of similar digital switches in the network,
centralised operation and maintenance will provide maintenance and
administration services very economically. All these services are provided
through a simple, interactive man-machine interface.
2.3. BASIC GROWTH MODULES
C-DOT MAX-VE architecture is based on the following four basic modules (Fig. 2.1)
a. Value Engineered Base Module (VE-BM)
b. Value Engineered Central Module (VE-CM)
c. Administrative Module
d. Input Output Module
2.3.1. Value Engineered Base Module (VE-BM)
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 and access networks. Each
Base Module can interface upto 6000 subscribers. The number of Base
Modules directly corresponds to the exchange size.
There can be various configurations of MAX-VE