Sunday, August 10, 2014

SDM (Subscriber Data Management)/ HLR (Home Location Register)

SDM is a database. It consists of following main features.
  • HLR (Home Location Register): HLR is a static database. 
  • AUC (Authentication  Centre):  Authenticate a subscriber into the network.

  • EIR  (Equipment  Identity  register):  An  EIR reduces  the  threats  of  theft  of  handsets  by enabling  individual  operators  to  prevent  the  use  of  stolen  handsets  in  their  own networks. This improves users' security by switching off stolen phones, making them useless for mobile phone thieves and thus less likely to be stolen in the first place
  • MNP  (Mobile  Number  Portability):  MNP  enables  mobile  telephone  users  to  retain their mobile telephone numbers when changing from one mobile network operator to another.

Services that can be configured using a HLR

  • PRBT (Phone Ring Back Tone)
  • CAMEL (Customized Applications for Mobile Enhanced Logic): Can set triggers when a call is originated (CCSI) or when a location changes (MCSI)
  • ODB (Operator Determined Barring) : i.e. suspend a post-paid customer 

A typical HLR profile will include below fields:

Power Installation Infrastructure of a SWITCHING Center- Example

Power system of a SWICH location is a very critical fact. We cannot tolerate any power  failures  in  Core  Network elements. Following  are some highlights of power system.

  • Battery  capacity  of  around  10,000 Ah
  • Typical  Consumption  of equipment  is  (observed)  around 1300-1400 Ah

Observed  power  consumption  will  vary as the network utilization changes. If we consider  a  day, network  utilization changes and it will be a maximum in the busy hour of the network. By using battery power only we can keep system  run  for  nearly  8  hours. Additionally  we  have  fuel  powered Generators in an Emergency situation.

To  make  sure  that  all  the  batteries function well we conduct a test in every six  m0nths  (discharging  all the  batteries is  a  part  of  that  test).  Batteries  are connected  through  Low  Voltage Detectors (LVDs) to disconnect batteries when the reach a certain minimum level. In practical environment we may bypass LVDs to supply power until batteries drain to their minimum limits. This may risk the battery health. But by doing this we can supply power for a longer period to critical loads (equipment).

Single Battery Unit Specification: There were two types of battery units used in Grandpass.
Majority of them are 2.2V, 1500 Ah and the others were 2.2V, 2500 Ah. Twenty four such units connected in series to build up a single bank of batteries. There were  six battery banks
inside this room.

High-level block diagram of a Power System (SWITCH Centre) shown below.

Fire Alarm System, Air Conditioning & Pest control

As the equipment works they get heated up. Air Conditioning system will limit the equipment temperature to an acceptable level. Inside temperature of the SWICHING Centre is monitored frequently. Fire  indicating sensors  were placed  inside;  if  they  are triggered  oxygen  is  removed  at once  and  inert  gas  (which  lies inside  the  cylinders)  will  be released instantly to stop the fire. If atleast  two  sensors  were 
triggered  due  to  fire  smoke detection; gasses released at a  high  pressure  (pressure  inside 
the  cylinder=  150  bar).  Because of  this agent release Hard  Disks  and  some other equipment may fail. 
Another  important  thing  is  pest control.  Due  to  pest  activity equipment and cables may get damaged. So pest controlling mechanisms should be adopted as well.

Magic Voice

Normally to set up a new VAS service, we need to connect them to SWITCH (NGN). Earlier
we  have  to  add  additional  dedicated  E1s  between  new  server  and  SWITCH.  But  now
situation is different. New services are implemented using IP technology. Magic voice is an
example for that.

What is Magic Voice?

You can call to another Same Network Customer using different predefined voice (Cartoon voices,
Kings  Voices,  etc.).  This  service  is  provided  through  an  Application  which  is  provided
by a 3 rd party company. That application will do the conversion of the voice.

We  can  use  Session  Initiation  Protocol  (SIP)  &  Real  Time  Protocol  (RTP)  protocols  to implement this service. We only have to configure IPs on both sides as shown in the Figure.
SIP will handle signaling phase and RTP will handle the data phase.
Call setup will be done in the usual manner and after successfully setting up the call VoIP
tunnels will be created between the called party and calling party.

Drive Test Results

Drive test tool records following data for both idle mode and dedicated mode MS:

  • Serving cell data

Signal strength, Cell ID, BSIC,  BCCH-  AFRCN, Hopping frequencies, Mobile Allocation
Index Offset (MAIO), Hopping Sequence Number (HSN), Received signal level (RSL) etc.

  • Neighbor cell data

Frequency data, RSL and parameters such as C1, C2 are recorded. C1 and C2 are important
to identify handover errors

  • Call Quality at dedicated mode: a measure of Bit Error Rate (BER) using a 0-7 scale
  • Handover details (neighboring  cell details): RSL, quality level of the  neighboring cells
TEMS tool snapshot is as follows: