CONTROL FUNCTIONS-CONCEPT OF STATION
For all control function ocb uses concept of a station. Following type of
stations are available:
1. SMT - Trunk Multiprocessor Station
2. SMA - Auxiliary Multiprocessor Station
3. SMX - Switch Multiprocessor Station
4. SMC - Command Or Control Multiprocessor Station
5. SMM - Maintenance Multiprocessor Station
6. STS - Synchronisation And Time Base Station
The control stations communicate among themselves on a token ring called
“MIS”—Inter Station Multiplex, while the other stations are connected on 1 to 4
“MAS”—Station Access Multiplexes.
The “MAS”are connected to control stations also, so that the “MAS”domain units
can communicate with control stations. Most of the time cross over from “MAS”
to”MIS” domain or vice-versa may require a gateway function and this is
provided in the SMC with marker function.
1. SMT-Trunk Multiprocessors Station
It is also known as PCM trunk control station. The smt is a interface for
PCM’s coming from the particular exchange and the remaining world.The current
version of SMT being supplied to India is SMT 2G.
In each SMT 2G, there are 8 modules and in each module there are 16 PCMs.
Thus there are 128 PCMs, in a single SMT 2G. SMT 2G is built around
microprocessor 68030.
Function of SMT-
-Provides terminations of a maximum of 128 pcm’s from trunks
-Carrying out URM
-Transforming the intelligence in PCM to LR for switching to destinations and
transforming the switched LR time slot into PCM.
2. SMA-Auxiliary Multiprocessor Station
Function of SMA-
-Tone generation(GT)
Tone generators generate various tones required to be connected during call
processing. These tones are Dial tone, Busy tone, Ring back tone, Processing tone
etc.
-Conference call(CCF)
The conference circuits are used to set up connection
between a maximum of 4 subscribers. These 4 subscribers can hold conference on
the telephone i.e. they can talk to each other.
-Frequency Generation and Reception for R2 MF signalling or for receiving
DTMF frequencies(RGF)
The frequency receivers/generators recognizes the digits dialed through DTMF
instrument and also the MF(R2) signaling and testing etc.
-Clock
-PUPE signalling management
-Access Network management(AN)
The SMA is connected to the switch by one GLR,on the other side it is connected
to MAS token ring over which it communicates with control units. The time base
is obtained by the SMA from STS via the switch over GLR cable. Types of
software used are
ETA –frequency decoder
PUPE-to handle signaling
3. SMX-Switching Multiprocessor Station
A SMX is one module of the entire switch matrix system with
independent control. The station is responsible for carrying out connection of an
incoming LR time slot to an outgoing LR time slot.
Switching may effect connection between subscribers, subscriber to junction,
junction to junction subs. To tone or rf, junction to tone or rf etc or there may be a
semipermanent connection for certain data link.
Besides the connection function,the SMX performs following other functions:-
-clock reception from STS & distribution
-fault and alarm processing
-defence of the station etc.
The SMX is connected on 4Mbps links to units like SMT, SMA referred to as
peripherals. Also connected to control units over MAS token rings which provide
particulars of connections to be effected.
The network synchronised clock from STS is supplied to SMX. Switching is
done on the strobe of clock and also this clock is supplied to the service
peripherals-SMT, SMA on LR links.
4. SMC—Main Control Station
All the control functions are supported in SMC and one or more of these
functions can be used during call processing. The main control functions are
MR,TR,TX,MQ etc. Relative position of SMC in OCB exchange as shown in fig.
Control functions in SMC communicate on MIS while other communicate with
SMC on MAS.There are 6 common control functions in OCB-283. The following
list illustrates their minimum and maximum numbers.
Number of SMC’s depends on the capacity of exchange. There can be minimum
2 SMCs required and maximum number of SMC can be 32. Hardware of all SMC’s
is same but their software is different as per requirement. Types of softwares used
are:
• MQ-marker
• MR-multiregister,call analyser
• TR –translator
• TX-charging unit
-the switch in ocb-283 is a pure time switch.
-ultimate capacity of switch matrix is 2048*2048lr.
-modularity 256*256lr in 8 smx module
S.NO. NAME OF UNIT MINIMUM MAXIMUM
1. MR 2 7
2. TR 2 2
3. TX 2 2
4. MQ 2 2
5. PC 2 2
6. GX 2 2
64*64 lr matrix by adding pcb’s.
• each module of smx is duplicated and switching takes place in either branch
parallaly.
• 2 mbps access links la issuing from smt or sma are converted into 4 mbps lr
links.
• switching is done at 16mbps rate but reception & issue of lr links is at 4
mbps rate
5. SMM-Maintenance Multiprocessor Station
The smm provides the facility for carrying out operation and maintenance
of OCB units and also manage the data base.It carries out following functions:-
-database management and storage
-central defence of the OCB system
-supervisor of token rings
-processing of various commands
-general initialisation of the exchange
It provides local link for data processing devices and administration terminals.
This can also be connected to a network management system. It is accessible to
exchange units on one side and to the peripherals on the other side. The SMM also
have access to mass storage devices.
It consists of two units –one act as pilot and other as a standby. Both system share
a common communication bus supporting various communication peripherals.
The two subsystems are referred as SMMA and SMMB.
6. STS-Synchronisation And Time base Station
This is clock system of OCB-283 system which happens to be the most vital
unit of any digital switching system as switching takes place at the strobe of
clock. The clock needs to be synchronised with the network. This ensures almost a common clock at every switching station. The clock system in OCB-283,
therefore consists of two parts-synchronisation part and time base generator part.
The synchronization interface carries out following functions:-
-Receives max 4 clock inputs from PCM’s coming from other exchange
-In the event of a error detected on the chosen PCM it shifts to other PCM and
gives alarm concerning the faulty PCM
-It maintains reasonably high quality of clock in terms of precision of frequency.
-Counteracts losses of all synchronisation links by very high stability oscillator.
-In the event of loss of PCM synch. Runs on free run mode.
