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ABOUT C-DOT BRIEF HISTORY : - The Center for Development of Telematics (C-DOT) is the telecom technology development center of the government , It was established in August 1984 as an autonomous body. It was vested with full authority and total flexibility to develop state-of-the-art telecommunication technology to meet the needs of the Indian telecommunication network. The key objective was to build a center for excellence in the area of telecom technology . ORGANIZATION : - The management of C-DOT has a three-tier structure: - The governing Council: provides policy guidelines and approves the annual budget of the center. The Steering Committee: has the role of reviewing and monitoring the performance of the center. The Project Board: is responsible for the implementation of C-DOT’s project and the day-to-day function of the center. OBJECTIVES : - q Work on telecom technology products and services. q Provide solutions for current and future requirements of telecommunication and converged networks including those required for rural application. q Provide market orientation to R & D activities and sustain C-DOT as center of excellence. q Build partnerships and joint alliances with industry , solution provides, telcos and other development organizations to offer cost effective solution . q Support telcos and service provides in the introduction of new technologies , features and services by optimal utilization of installed network.
MANPOWER : - q Electronic Design automation (EDA) Tools for hardware and ASIC Design q Case Tools for Development and testing of software q Capative labs q Computing center q Pilot production plant q Existing manpower –907 q Planned Manpower - 963 The Center has state-of-the-art development environment comprising client/ server network of RISC workstation, latest software development tools and very mature and effective development ad support methodologies, Extensive use is made of case tools, object-oriented methodologies, software metric etc. The jobs have the latest test and measurement instrument, microprocessor development system and prototyping facilities. ACHIEVEMENTS : - q C-DOT Technology based system from 200 lines to 40,000 lines capacity in operation q More than 30,000 C-DOT Exchange totaling approximately 25 million telephone lines installed and operational in field q Deployed telecom equipment value of Rs.7500 crore q Significant technology transfer and royalty earnings q Technology development with low capital investment q Wide porfolio technologies, products and solution q Created large reservoir of technical manpower in telecom q Established a technology transfer process for production by multiple manufacturers The C-DOT DSS FAMILYGENERAL C-DOT DSS MAX is a universal digital switch can be configured for different application as local, transit or integrated local and transit switch. High traffic or capacity of 40000 lines as local exchange or 15000 trunks as Trunk automatic exchange. The design of C-DOT DSS MAX has seen by a family concept because of it’s advantages like standardized components, commonality in hardware, field hardware that used minimum number of cards, standard cards, racks, frames, cabinets and distribution frames are used which facilitated flexible system growth that make C-DOR DSS MAX easy to maintain and highly reliable. FLEXIBLE ARCHITECTUREC-DOT DSS is a modular and flexible digital switching system which provides economical means of serving metropolitan, urban and rural environments. It include all important feature and compulsory services, required by the user with option of up gradation to add new feature and services in future. The architecture for the C-DOT DSS is such that it is possible to upgrade a working C-DOT Single Base Module.(SBM) or Multi Base Module (MBM)exchange to provide Integrated Services Digital Network (ISDN) service by adding minimum addition hardware modules while continue to having existing hardware units. Another factor of architecture Remote Switching Unit(RSU). Is support ISDN. This RSU provides switching facility locally even in case of failure of the communication path to the parent exchange. The resources, which depend upon the number of terminal, 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 function. ARCHITECTURE OF C-DOT DSS MAX C-DOT DSS MAX exchanges can be configured using four basic modules.
MDF SBM CONFIGURATION Structure of C –DOT DSS MAX HARDWARE ARCHITECTURE C-DOT MAX exchange can be configured using four basic modules:- 1.BASE MODULE(BM) 2.CENTRAL MODULE(CM) C 3.ADMINISTRATION STRATIVE MODULE(AM) 4.INPUT OUTPUT MODULE(IOM&IOP)
(a) BASE MODULE (BM) : - The Base Module is the basic growth unit of the system . It interfaces the external world to the switch. The interfaces may be subscriber lines, Along and digital trunks. Each Base Module can interface up to 2024 terminations. The number of Base Modules directly corresponds to the exchange size. It carries out majority of call processing function and in a small exchange application, it also carries out operation and maintenance function with the help of Input-Output Module. The Basic functions of a base modules are:-
There are two types of Base Modules :-
2. Multi Base Module(MBM)
In SBM exchange configuration, the Base Module acts as an independent switching BM directly interface with the Input Output Module for bulk data storage, operations and maintenance function. Clock and synchronization is provided by a source within the BM. It is a very useful application for small urban and rural environments. The Base cabinet houses total 6 frames:- · Terminal Unit (TU, Top 4 Frames) system and provides connection to 1500 lines and 128 trunks. In such a configuration ,the · Base Processor Unit ( BPU,5th frame) · Time switch unit (TSU) There are following four terminals units:- 1. ANALOG TERMINAL UNIT (ATU):- The Analog Terminals Unit (ATU) is used for interfacing 128 analog termination which may be lines or trunks and providing special circuits as conference announcements and terminal tester. It consists of terminal cards, which may be a combination of Analog Subscriber Line Cards, Analog Trunk card & some Special Service Cards. (a) Analog Subscriber Ling Cards : - Two variants of subscriber line cards as LCC(Line Circuit Card) or CCM(Coin Collection Monitering) with interfaces upto 8 subscribers. Analog to digital conversion is done by per channel CODEC according to A-Law of Pulse Code Modulation so we can say that it for the subscriber connected for subscriber to exchange. A unit has 16 line cards so 16*8=128 subscribers. There are 4 unit so 4*128= 512 subscribers. 4 cards make 1 Terminal Group(TG) so TG = 4. (b) Analog Trunks Cards :- Analog trunk cards interface analog inter exchange trunks which may be of three types as TWT,EMT & EMF. These interfaces are similar to subscriber Line Cards, with only difference that the interfaces are designed to scan/drive events on the trunks as predefined signaling requirement. (c) Signaling Processor Cards : - SP Processes the signaling information received from the terminals cards. SP processes the signaling information consists of scan/drive function like original detection, answer detection, digit reception, reversal detection etc. The validated events are reported to Terminal interface controller for further processing. (d) Terminal interface controller (TIC) Cards : - TIC controls the four terminals group ( TG) of 32 channels and multiplex them to form a duplicated 128 channels, 8 mbps link towards the Time Switch. For Signaling information of 128 channels it communicates with signaling processor to receive/send the signaling event on analog terminations. It also uses to communicate with BPU. (e) Special Service Cards : - A Terminal unit has some special service cards such as Conference (CNF) cards to provide six party conference. Speech Samles from five parties are Terminal Test Controller (TTC) card is used to test analog terminal interfaces via the test access relays on the terminal cards. Announcement controller card provides 15 announcement on board cast basis. (2) DIGITAL TERMINAL UNIT( DTU ) : - Digital terminal unit is used to interface digital trunks, i.e. used between the exchanges. one set of Digital Trunks Synchronization (DTS) Card along with the Digital Trunk Controller(DTC) card is used to provide one E-1 interface of 2mbps. Each interface occupies one TG of 32 channels and four such interfaces share 4 TGs in a DTU. Here Terminal Unit Controller (TUC) is used of TIC and DSP cards. Out of 32 channels, 30 for voice communication and remaining two for Signaling and Synchronization. In DTU 4 TGs are there so total number of unit are 4*30 = 120 units in DTU. (3) # 7 or Signaling Unit Module(SUM) : - It is used to support SS7 protocol handlers and some call processing function for CCS7 calls. SS7 capability in C_DOT DSS MAX exchanges is implemented in the form of a SS& Signaling Unit Module (SUM). The sum hardware is packaged into a standard equipment frame, similar to that of terminal unit. It is a module by itself and contains global resources. It interfaces with the Time Switch via Terminal Unit Controller (TUC) on a 128 channel PCM link operating at 8mbps.
ISDN To support termination of BRI/PRI interfaces and implementation of lower layers of DSSI Signalling protocol. They are used as carriers to transport bulk volume of data. With the increasing use of internet access, the use of ISDN interface is likely to go up as it provides the reliable access to the user at the rate of 64/128kbps. It is of two types i.e. circuit switched voice and data and packet switched data. In circuit switch the traffic is routed through ISDN and is packet switched data the traffic is routed through PSPDN. REMOTE SWITCH UNIT : - In this time switch card BMs are replaced by Enhanced Switch Cards(ETS). It is used when the e exchange is at a far distance from the central module. It can modified BM via 2 mbps digital links. Analog and Digital trunk interfaces are also implemented in RSU to support direct perenting of small exchanges from RSU. Instead of perenting it to the main exchange. RSU is an autonomous exchange capable of local call completion. 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 Maintenance and operation function are handled by the host exchange. Remoter Switch Unit Normal BMs 1.Tpe of connectivity used is 1.Type of connectivity is through E-1 data cables cards of 2mbps and E-3 cards of 32Mbs. 2. Contains Time Switch Cards. 2.Contains Enhanced Switch Card. 3. Situated at a Distance. 3. Should be in side of CM. TIME SWITCH UNIT (TSU):- Time Switch Unit (TSU) implements three basic function as time switching with in the Base Module, routing of control message within the Base Module and across Base Module and support services like DTMF circuit, answering circuit, tones etc. These functions are performed by three different functional unit, integrated as Time Switch Unit in a single frame. i.e. SERVICE UNIT : - It is integrated around three different cards as Tone Generator with Answering Circuit (TGA), Service circuit interface Controller (SCIC) and DTMF Controller, (MFC) Card. These three forms TGs towards Service Circuit interface (SCI). SCI multiplexes these TGs together with another terminal group from the Base Message. Switch (BMS) to form a 128 channel, 8 Mbps link & send it to the Time Switch. BASE MESSAGE SWITCH (BMS) : - Base Message Switch (BMS) route the control message with in the Base Module, across different Base Module and also Administrative Module via the Central Module. It is implemented around two cards as Message Switch Controller (MSC) with the Message Switch Device (MSD) with 16 HDCL links. So total 22 HDLC channels are implemented for communication with the Base Processor, Time Switch Controller, Service Circuit interface Controller with in the BM. It transfer the message between the Base processor and these controllers. To supports 8,00,000 BHCA,MSC AND MSD cards are replaced by a high Performance Switch(HMS) with high speed upto 750 Kbps, 32 bit microprocessor. TIME SWITCH ( TS ) : -The Time Switch complex is implemented using three different functional cards as multiplexer/demultiplexer (TSM),Time Switch (TSS) and Time Switch Controller (TSC). The Time Switch complex performs time switching with in the Base Module : -
BASE PROCESSOR UNIT :- Base Processor Unit (BPU) is the master controller in the Base Module. It is impleted as a duplicated controller with memory units. These duplicated sub-units are realised in the form of the following cards :- 1. Base Processor Controller(BPC) Cards. 2. Base Memory Extendra (BME) Card. 1. Base Processor Controller(BPC) Cards : - BPC control 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 interface with the Alarm Display Panel and the input Output Module. To support 8,00,000 BHCA, the BC card is replaced by High performance processor card.(HPC) i.e. Protocol Handler Card (PHC) which contain 26 slot,8slot for the power supply, 2 for memory and remaining 10 for message switching.
2. Base Memory Extender (BME) Card : - It is for the storage purpose i.e. saving memory purpose. It can store up to 16 bits CENTRAL MODULE Central module is responsible for space switching of inter-Base Module calls, communication between Base Module and Administrative Modules, clock distribution and network synchronization. For these function central module has a Space Switch, Space Switch Controller, a Administrative Processor and a Central Message Switches CMS(A,B,C,D). In a 32 Base Module configuration , there are 64 bit parallel buses carrying the voice information from Base Module to the Central Module, and also the Switched information in the reverse direction. The complete control conceptually is shown in following figure : -
Concept Control Scheme for Space Switch The administrative processor communicates with the IOPs which act like a central storage. Administrative processor is also connected to Central Message Switches CMSA and CMSB through which AP communicates to SSC. The SSC is connected to all the CMSs (A,B,C,D) so as to communicate with all the BMs through these Central Message Switches (CMS_A,B,C,D). There are two types of Central Module : - 1.CM-XL (Extra Large) 2.CM-L(large)
Each BM interfaces with CM via two 512 channel parallel buses as BUS-0 and BUS-1,each operating at 4 Mbps. These buses carry voice information of 512 termination of the Base Module towards CM. In the reverse direction, after space switching has been done in the Space Switch under the control of Space Controller (SSC), the same buses carry the switched voice information for 512 termination towards BM. Thus, in a 32 Base Module configuration, there are 64 parallel buses carrying the voice information from Base Modules to the Central Module, and also the switched information in the reverse direction. CM FRAME ORGANIZATION CM
Space Switch Administrative Central Switch Processor Message 1.Space Switch Mux 1.Bus Interface 1.CMS A Demux Card(SSM) Controller(BIC) Card (For TS0,Bus 0) 2.Space Switch 2.Bus interface 2.CMS B Switch Card(SS) CPU(BIC) Card (for TS0,Bus1) 3.Space Switch 3.Memory(MEM) 3.CMS C Clock Card (SCK) (For TS1,Bus 0) (Space Controller Unit) 4.CMS D 1.CPU Card (for TS1,Bus 1) 2. Bus Interface 1.Message Switch 3.Bus Interface Controller Card Device(BID) Card 2.Message Switch 4.Memory Device Card(MSD) (MEM) Card 5.Terminal Cards CM HARDWARE DISTRIBUTION :- CM Hardware is distributed in following frames : -
BUS TERMINATION UNIT : - It contains Multiplexer and Demultiplexer. It is Basically an Interface Unit Between the BM and Space Switch. There are two buses-Bus 0 and Bus 1.Bus 0 contain all even time slots and Bus 1 carries all odd time slots. Bus is terminated from the Base Modulation. It controls the Space Switching between Base Modules. BTU insert the message CMS to BMS and vice versa. FUNCTION : - (a) Caters to maximum 16 BMD in release one. (b) Multiplexes the data for Space Switching. (c) De multiplexes the Switched Bus. (d) Distributed 8 MHz clock and 8 KHz sync. To BMs. (e) Acts as a Gateway for CMS by message extraction/insertion scheme Types of cards used : - 1. Space Switch Mux Card(SSM) : - It multiplexes two BMs data. 2. Space Switch Mux Termination Card (SMT) :- It is used in an unequipped. SSM slot in the BTU frame to avoid any noise generated due to termination of a bus from BM in BTU frame. It offer 2A load at 5V. 3. Power Supply Card : - It supplies power to the cards and unit it work as a load sharing mode in each bus. 4. Space switch unit : Space Switch provide connectivity between two subscriber of two different BMs on time slot basis. It is responsible for switching of cards between various base modules FUNCTION : - (a) Establishes Inter Base Module Switching. (b) Caters for 16*16 Base Module switching. (c) Implements two 16*16 switching; one for bus 0 and other for bus 1. (d) Provides redundancy as copy 0,copy1(switch duplicated) Types of cards used : - 1. Space Switch Switch Cards (SSS) : - The switch card forms the part of the space switch which is situated in the Central Module. Each SSS Card caters for four base modules (16*4 switch in CM). 2. Space Switch Termination Card ( SST) : - It provides proper termination to the MUX data bus received from 16 space Switch MUX Cards. The card is used if corresponding SSS slot is unequipped. 3. Space Switch CU Bus Termination Cards (SCT) : - It is used in Space Switch Unit and Space Switch Control Unit frames of CM. It terminates CPU, address, data and control signals. 4. Power Supply Cards : - SSU employs 4 cards for supplying power and it is used in BPU,TSU,IOP. 3. Space Switching Controller Unit(SCU) : - It is a CPU complex and interfaces with space switch and clock for controlling the space switch. SSC communicates with the CMSs which in turn enable the SSC to communicate with the BMs. It contain Power Unit FUNCTION : - (a) Controller for the Switch · Time slot management and allocation · Switch monitoring for sanity · Switch diagnosis (b) Communication b/w the central message switch and Aps, BMs (c) System clock generation (d) Management of power alarms in BTU,SSU and SCU Space Switch(SS) and Space Switch Controller (SSC) : - 1. In order to take care of the large number of interface signals, the switch portion of CM is divided into three stages viz. MUX stage, Switch stage and DEMUX stage. The MUX and DEMUX stage are implemented on single card to provide the Base Module to Central Module interface in each direction. Interfacing and switching are controlled by SSC which provides control signals for the MUX/DEMUX cards and the space Switch cards. 2.MUX/DEMUX Cards extract the information from time slots 0 and 1 of Bus 0 and Bus 1 from the Base Modules. These time-slot carry control message from each base Module and these messages are sent to the Central Message Switch (CMS). The CMS sends these message to the Space Switching controller (SSC) on a 128 kbps link to control space switching based upon the information. 3. Four 512-channel buses from four BMs are multiplexed to form a 2048-channel,16Mbps multiplexed BUS which is sent to both copies of the Space Switch Switch Card. Space switching of these 2048 channels is done based upon the switching information received by Space Switch Controller (SSC) from CMS Central Message Switch (CMS) : - It consists of four different message switches and each one of them is implemented by using high speed 32 bit microprocessor. All Central Message Switches (CMS 1,2,3 & 4) are used for routing of messages across the Base Modules. Only CMS1 and CMS2 interface with the Administrative Module for routing control message between Base Processors and Administrative Processor. Type of Cards used : - 1. CPU Complex · Space Switch Controller Card (SSC) (CPU) : - This is to serve as central processing engine for the C-DOT DSS both in the BM & the CM mode. It coordinates system activities and perform call processing functions. It is used as Base Processor (BP) in the BM& as administrative processor (AP) and Space Switch Controller (SSC) in CM. · Bus interface-CPU(BIC) Card : - It is used to access memory and space switch in plane copy-0 & copy –1. · Bus interface Device (BID) Card : - It along with bus interface CPU (BIC) card provides the cross connection b/w duplicate CPU’s (controller) an duplicate device (memory) in such a way that any one failure either at CPU or at device does not bring down the whole processor complex. · Memory Card (2MB) : -It provides storage space and interfaces to a standard 6800 CPU bus. Both word & byte accessory are possible on the memory space. 2. Switch Interface · BIC Card · Bid Card · Space Switch Controller Termination (SCT) 3. System Clock and PSU errors · Space Switch Clock Card(SCK) : - It is the source of clock signal to the space switch switch cards & the space switch mux cards which constitute the space switch. It is used for the control of timing and for synchronizing of the space switches. Administrative Processor Unit (APU) : - · Status of all module of the exchange is maintained by the AP and whenever a problem is reported required action is initiated to clear the problem. All the global resource like trunks. Time slots etc are managed by the A.P. Directory to equipment number translation for the establishment of a call is performed by AP All global data is managed by the AP. In a multimodule exchange all the call processing. Administration and maintenance function are supervised by the AP. Function of APU : -
Types of Card used : - 1. CPU Complex (APU) · CPU Card · BIC Card · BID Card · Memory Card(2MB)
2. Central Message Switch-CMS (A,B,C,D)
CALL PROCESSING GENERAL CONCEPT There are five function steps of call processing including the location of the originating and terminating equipment. These steps are : - · Origination : - Origination begins when the subscriber line goes off hookor incoming trunks seized. It receives the incoming digits, selects the digit analysis tables, and determines the screening information for this call. · Digit Analysis: - It interprets the digits it receives from origination ,select a destination for each call, and passes the dialed digits to routing. · Routing/Screening:- Routing uses the destination information from digit analysis and screening information origination to select the terminating trunk group or line. · Charging : - It uses the charging information from routing to expand the charging data into a formate usable by call accounting process. · Termination : - The last step in call processing is termination. Termination Processor is different for calls destined for lines and call destined for trunks.
Trunk termination : - A trunk member of the trunks group is selected based on a predetermined pattern. After selection the digits are out pulsed to the distant office. Line termination : - The line identified in routing is checked to determine the line has any special features. Ringing is applied to the line if applicable or the special feature is activated.
SIGNALING What is Signaling ? Signaling refers to the exchange of information between call components required to provide and maintain service. As users of the pubic Switched telephone network, we exchange signaling with network element all the time. Examples of signaling between a telephone user and the telephone network include. Dialing digits, providing dial tone, accessing a voice mailbox, sending a call waiting tone, dialing *66(to retry a busy number), etc. Signaling system 7 is means by which element of the telephone network exchange information. Information is conveyed in the form of messages. Signaling System 7 messages can convey information such as : SS7 is characterized by high-speed packet data, and out-of-band signaling. OUT OF BAND SIGNALING Out-of-band signaling is signaling that does not take place over the same path as the conversation. We are used to thinking of signaling as being in-band. We hear dial tone, dial digits, and hear ringing over the same channel on the same pair of wires. When the call completes, we talk over the same path that was used for the signaling. Tradition telephony used to work in this way as well. The signals to set up a call between one switch and another always took place over the same trunk that would eventually carry the call. Signaling took the form of a series of multi frequency (MF) tones, much like touch tone dialing between switches. Out-of-band signaling information. This channel is called a signaling links are used to carry all the necessary signaling messages between nodes. Thus, when a call is placed, the dialed digits, trunk selected, and other pertinent information are sent between switches using their signaling links, rather than the trunks which will ultimately carry the conversation. Today, signaling links carry information at a rate of 56 or 64 kilobyte per second (kbps). It is interesting to note that while SS7 is only used for signaling between network elements, the ISDN D channel extends the concept of out-of-band signaling to the interface between the subscriber and the switch. Win ISDN service, signaling that must be conveyed between the user station and the local switch is carried on a separate digit channel called the D channel. The voice or data which comprise the call is carried on one or more B channels. Why Out-of-Band Signaling ? Out of-band signaling has several advantages that make it more desirable than tradition in-band signaling: · It allow for the transport of more data at higher speeds (56 kbps can carry data much faster than MF outpulsing) · It allow for signaling at any time in the entire duration of the call, not only at the beginning. · It enables signaling to network element to which there is no direct trunk connection. BASIC OF SIGNALING SYSTEM # 7 Common channel Signaling System no.7 (i.e.,SS7 or C7) is a global standard for telecommunication defined by the international Telecommunication Union(ITU), Telecommunication Standardization Sector(ITU-T).The standard defines the procedures and protocol by which network element in the public switched telephone network (PSTN) exchange information over a digital signaling network to effect wireless(Cellular) and wireline call setup, routing control. The ITU definition of SS7 allow for national variants such as the American Nation Standards Institute (ANSI) and Bell Communication Research (bellcore) standards used in North America and the European Telecommunication Standards Institute(ETSI) standard used in Europe. The SS7 network and protocol are used for : · Basic call setup, management and tear down · Wireless service such s personal communications services (PCS),wireless roaming, and mobile subscriber authentication. · Local number portability (LNP) · Toll-free(800/888) and toll(900) wireline services · Enhanced call features such as call forwarding, calling party name/number display,and three-way calling · Efficient and secure worldwide telecommunication. Signaling Links SS7 messages are exchanged between element over 56 or 64 kilobit per second (KBPS) bi-directional channels called signaling links. Signaling occurs out-of-band on dedicated channels rather than in-band on voice channels. Compared to in band signaling out-of-band signaling provides. · Faster call setup times(compared to in-band signaling using multifrequency (MF) signaling tones) · More efficient use of voice circuits · Support for intelligent Network(IN) services which require signaling to network element without voice trunks (e.g., database system) · Improved control over fraudulent network usage Signaling Points Each signaling point in the SS7 network is uniquely identified by a numeric point code. Point codes are carried in signaling messages exchanged between signaling point to identify the source and destination of each message. Each signaling point uses a routing table to select the appropriate signaling path for each message. There are three kinds of signaling points in the SS7 network.
SS7 Signaling Points SSPs are switches that originate terminate, or tandem calls. An SSP sends signaling message to other SSPs to setup, manage, and release voice circuit required to complete a call. An SSP may also send a query message to a centralized database (an SCP) to determine how to route a call (e.g., a toll-free 1-800/888 call in North America). An SCP sends a response to the originating SSP containing the routing number(s) associated with the dialed number. An alternate routing number may be used by the SSP if the primary number is busy or the call is unanswered within a specified time. Actual call features vary from network and form service to service. Network traffic between signaling points may be routed via a packet switch called an STP. An STP routes each incoming message to an outgoing signaling link based on routing information contained in the SS& message. Because it act as a network hub, an STP provides improved utilization of the SS7 Network by eliminating the need for direct links between signaling points. An STP may perform global title translation, a procedure by which the destination signaling point is determined f |
