Hello

Welcome to my blog! If this is the first time, you are here then I request you to kindly read my Introduction post because I have certain things to say and they are all there:)

Also, if somewhere while going through any of the posts, you feel that something is wrong, plz feel free to comment then and there. I love to get corrected and so, plz do not think a bit before commenting on anything you think I have mentioned is wrong. The only request is plz maintain your dignity and mine as well in the words you use! Kindly do not let your words be a slur on others:) I would be grateful.

Also, I assure you that before writing anything here I will get the same checked with some experienced people, I will do a research again and then only, I will post the same on my blog so you can trust me.


Disclaimer: All the posts on this blog are based on my personal learning, opinion and views. It has no connection, no connotation with the organization I am or I was working for or with any person associated with me.

Happy learning...
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Telecom's Technical Abbreviations


After so many chapters, I just thought to pen down all the abbreviations in one post which were used in last few chapters:
  • FDMA: Frequency division multiple access
  • CDMA: Code division multiple access
  • TDMA: Time division multiple access
  • NNS: Network Management Subsystem
  • BSS: Base Station Subsystem
  • NSS: Network Switching Subsystem
  • BTS: Base transceiver stations
  • BS: Base Station
  • AUC: Authentication Centre
  • OSS: Operation and Support System
  • MXE: Message Center
  • MISN: Mobile Intelligent Service Node
  • MSC: Mobile Switching Centre
  • HLR: Home location register
  • AuC:  Authentication centre
  • VLR: Visitor location register
  • EIR: Equipment Identity Register
  • BC: Billing centre
  • SMSC: Short message service centre
  • MMSC: Multimedia messaging service centre
  • VMS: Voicemail system
  • BSC: Base Station Controller:
  • PCU: Packet control unit
  • MS : Mobile station (a mobile phone)
  • PSTN: Public Switched Telephone Network

Difference between FDMA, CDMA and TDMA

I guess, one of the most basic questions which goes in our mind regarding telecom is what is the difference between the technologies which people generally talks about? Right? They talk about CDMA, TDMA, FDMA! We know that these technologies are different but we genearlly are unable to understand the thing that makes them difference! We think its too technical and stop ourselves from getting into it! Right? Guys believe me, understanding the difference between these technologies is just not difficult!

I will try to put it in a very simple wayJ

Frequency division multiple access (FDMA):
It is a technology by which the total bandwidth available to the system is divided into frequencies. This division is done between non overlapping frequencies that are then assigned to each communicating pair (2 phones)
FDMA is used mainly for analog transmission. Its not that this technology is not capable of carrying digital information, but just that it is not considered to be an efficient method for digital transmission. Because just imagine if the frequencies to handle the customers gets over? What if more capacity is required? The only option would be to drill down the existing frequencies to a much narrower amount which will not be very competent. In FDMA all users share the satellite simultaneously but each user transmits at single frequency.
To understand this technology better, just imagine how FM radio works. All the radios have their own frequency bands and they send their signals at the carefully allocated unique frequencies within the available bands.

Code division multiple access (CDMA):
Unlike FDMA, CDMA separates calls by code. Every bit of a conversation is been tagged with a specific and unique code. The system gets a call, it allocates a unique code to that particular conversation, now the data is split into small parts and is tagged with the unique code given to the conversation of which they are part of. Now, this data in small pieces is sent over a number of the discrete frequencies available for use at any time in the specified range. The system then at the end reassembles the conversation from the coded bits and deliver itJ Does it make sense?
Just think about how you recollect your luggage at the end of the flight journey. When you check in, a tag with a code is given to you which is also given to your luggageJ And at the destination, you collects your luggage on the basis of thatJ I know you will say that you recognize your bag, but then I have a habit of always matching the codes of my bag and the one on the tag given to me and that is how I become sure of not picking up the wrong luggageJ

Time division multiple access (TDMA):
Unlike FDMA and CDMA, In TDMA the division of calls happens on time basis.  The system first digitizes the calls, and then combines those conversations into a unified digital stream on a single radio channel. Now it divides each cellular channel into three time slots that means three calls get put on a single frequency and then, a time slot is assigned to each call during the conversation, a regular space in a digital stream. The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity.
This technology enables three different users to use one frequency at the same time.
Here there is no need for three separate frequencies like in FDMA. As in FDMA, instead of monopolizing a single radio channel for a single call, TDMA efficiently carries three calls at the same timeJ
BTW, this technology is the one used in our GSM system

Have tried to explain the above technologies via a diagram which is below:



In the above diagram, you will observe:

FDMA: Single frequency is used for single call
CDMA: Single frequency is used for multiple calls
TDMA: Multiple frequencies are used for multiple calls

I hope the difference is clear now:)

GSM Core Network: Network Management Subsystem


So after BSS and NMS, its turn of Network Management Subsystem (NMS).

The purpose of the NMS is to monitor various functions and elements of the network. The functions of the NMS can be divided into three categories: Fault management, configuration management and performance management

These functions cover the whole of the GSM network elements from the level of individual BTSs, up to MSCs and HLRs.

Network Management Subsystem (NMS) includes various entities and the purpose of the NMS is to monitor various functions and elements of the network. These functions can be divided into 3 categories:
Fault Management
Configuration Management
Performance management

All the above mentioned functions cover the whole of the GSM network elements from BTSs to MSCs. Lets have a look at all the functions one by one:

Fault Management: The purpose of fault management is to ensure the smooth operation of the network and quick correction of any sort of problem. It also provides the information on the current status of alarm events and maintains a history database of alarms.
Configuration Management:
The function of configuration management is to maintain the information about the operation and configuration status of all the network elements.
Performance management: In performance management, the NMS collects data from individual network elements and stores it in a database. This data helps the operator to evaluate the actual performance of the network and to spot the good and bad performance areas as well.

Below are the different entities of this subsystem:
Operation and Support System (OSS)
OSS monitors every aspect of a cellular system. It monitors several carrier's systems and do a variety of operation and maintenance works such as software upgrade, collecting network performance statistics, reconfiguring network elements frequency planning etc
Every OMC is staffed twenty four hours a day.
Mobile Intelligent Service Node
All the advanced intelligent network services are managed by mobile intelligent services node (MISN)
Message Center (MXE)
The MXE handles short message service, cell broadcast or cell info messages, voice mails, e-mails, fax and other kind of notifications

GSM Core Network: Network Switching Subsystem

So after finishing Base station subsytem, today we are going to cover one of the most integral parts of GSM core network: Network Switching Subsystem
So what are we waiting for? Lets start:)
NSS is responsible for call connection, authorization and supervision of all the calls. This system is also liable for handling short messages and packet data, maintaining database of its own users as well as visitors, providing authentications and encryptions. It is a gateway to PSTN, other mobile networks and data networks including the Internet. In other words, this system allows mobile devices to communicate with each other and with landlines (PSTN). In layman’s terms, BSC transfers the call to MSC which is a part of NSS where call switching and mobility management functions are being taken care of. This system allows mobile devices to communicate with each other and with landlines (PSTN)
Lets discuss all the components of this system in details. Grab a coffee as it can get little boring L What to do, that’s the topic we are discussing, cant put much entertainment masala.
Anyways, back to studies:
Mobile Switching Centre
This is the main component of NSS as the BSCs coordinate with it. This component controls the entire network. It interacts with other databases and PSTN. The MSC sets up and releases the end-to-end connection, handles mobility and hand-over requirements during the call and takes care of charging and real time pre-paid account monitoring. The responsibilities of this entity included checking if a customer has a valid account or not, what profile he is in, what kind of services he had been activated for etc. In short, it provides the needed user registration and authentication information.
Each MSC manages dozens of cell sites and their base stations. Large systems may have two or more MSCs.
Home location register (HLR)
A MSC queries several databases before permitting a call. One of them is HLR which has been explained below:
The home location register (HLR) is a central database that contains details of each mobile phone subscriber that is authorized to use the GSM network. The HLRs store details of every SIM card issued by an operator. Each SIM has a unique identity no called an IMSI which is the most important key or the primary key to each HLR record.
Another important data coupled with the SIM is the MSISDN, which is basically nothing but the phone no of the subscribers which s/he uses for making calls (yes, we have a technical term for every damn thing!). The MSISDN is also a primary key to the HLR record. The HLR data is stored for as long as a subscriber remains with the operator.
Other keys of this database apart from MSISDN and IMSI are: Current TMSI (Temporary IMSI), IMEI (International Mobile Equipment Identity), Name and address of the subscriber, Current service subscription profile, Current location (MSC/VRL address), Authentication and encryption keys, Mobile Country Code (MCC) and MNC (Mobile Network Code).
The main function of the HLR is to manage the mobility of subscribers by means of updating their position in administrative areas. It is also responsible for sending the subscriber data to a VLR or SGSN when a subscriber first roams there. A subscriber’s data is removed from the previous VLR when a subscriber has moved away from it. One of major roles of HLR is also that it plays the role of a broker between the MSC and the subscriber's VLR in order to allow incoming calls or text messages to be delivered.
Authentication centre (AuC)
As the name suggests, the authentication center (AUC) provides authentication and encryption parameters that validates a user's identity and ensures the discretion of each call.
When a mobile makes a call, AUC authenticate the SIM card that attempts to connect to the GSM core network.  Once this authentication is done and is successful, the HLR is allowed to manage the SIM. During the process, an encryption key is also generated which is later used to encrypt all wireless communications be it voice, SMS or any other mean, between a mobile and the GSM network.
If the authentication fails, then no communication is possible from that SIM. The AUC actually protect the operators from different types of fraud. Also, GSM has standard encryption and authentication algorithm which are used for a call
Now lets have a look at how this whole process of security takes place. There is a secret key which is actually shared between the AuC and the SIM and is known as Ki. This Ki is burned into the SIM during manufacture and is also replicated onto the AuC. This Ki is combined with the IMSI to produce an encryption key called Kc which the MSC sends to the base station controller (BSC) so that all communications can be encrypted and decrypted.
Visitor location register (VLR)
The visitor location register (VLR) is a database attached to an MSC to contain information about the subscribers who have roamed into the premises of the MSC (Mobile Switching Center) which it serves. Each base station in the network is served by only one VLR and so, its just not possible for a subscriber to be present in more than one VLR at a time.
The data stored in the VLR has either been received from the HLR or from the MS. Whenever a MSC detects a new MS in its network, it creates a new record in the VLR for the same. It also updates the HLR of the mobile subscriber with the new location of that MS.
Data which is stored in a VLR is  Information of currently attached mobile stations, their IMSI/TMSI numbers, their MSISDN, location Area Identity i.e. where the MS is currently located), authentication and encryption information, List of base stations that belong to this MSC/VLR (by their Base Station Identity Code), List of location areas that belong to this MSC/VLR (by their LAI or Location Area Identity code)
Other entities
There are many other entities which are connected to NSS. They are:
Equipment Identity Register
The equipment identity register (EIR) is a database that contains information about the identity of mobile equipment that prevents calls from stolen, unauthorized, or defective mobile stations. It function can be implemented with AUC or can be made separate. The EIR keeps a list of mobile phones (identified by their IMEI) which are to be banned from the network or monitored
Billing centre (BC)
The billing centre is basically for postpaid subscribers. It is responsible for processing the toll tickets generated by the VLRs and HLRs and generating a bill for each subscriber. It is also responsible for generating billing data of roaming subscriber.
Short message service centre (SMSC)
SMSC supports the sending and receiving of text messages.
Gateway MSC
The Gateway MSC (GMSC) is an MSC that connects the PLMN (Public Land Mobile Network) to a PSTN/ISDN.
Multimedia messaging service centre (MMSC)
A MMSC supports the sending and receiving of multimedia messages
Voicemail system (VMS)
A VMC system records and stores voicemails.

GSM Core Network: Base Station Subsystem: BSC (3)

So after getting done with BTS and Frequencies, its time BSC i.e. Base Station Controller
So lets beginJ
A Base station contains the equipment for transmitting and receiving radio signals i.e. transceivers, antennas, and the equipments for encrypting and decrypting communications with the BSC
Base Station Controller:
All the BTS needs something to manage them. And that’s where the role of BSCs comes; they manage the intelligence behind the BTSs. And that’s the role of BSC. Its basically a combination of server and software, it’s a high-capacity switch which controls all the radio communication such as handover, management of network resources and handling of cell configuration data. Controlling the radio frequency power levels in the mobile phones is also the job of a BSC. In short, the device enables the base station to register mobile phones in the cell to perform handover, call setup and call termination. Base station controllers also set transceiver configurations and frequencies for each cell. It also provides all the required data to the operation support subsystem (OSS) as well as to the performance measuring centers.

Confused?? Even, I was in the same condition while penning all this down:( Don't worry, read once more and everything will be clear:)
Get it now?? So, lets carry on...

One more thing, the no of BSCs depends on the complexity and capacity of a carrier's system. Typically a BSC has tens or even hundreds of BTSs under its control.
Other entities:
 Transcoder
As the name suggests, the transcoder is responsible for transcoding the voice channel coding between the coding used in the mobile network, and the coding used by PSTN (would be covering that soon again). In a very layman’s term, PSTN can also be called as the landline or wireline phones that we use.
Packet control unit
As the name says, It performs all the processing tasks for the for packet data. The PCU takes full control over data channel once the same is handed over to it by a BSC
Guess its enough gyaan for today:)
Keep smiling and keep learning

GSM Core Network: Base Station Subsystem: Frequencies (2)

Ok, so now when we are done with the entities of a Base Station Subsystem and are on verge of getting into details of Network Switching Subsystem, I thought why not to finish a very important part of the network here itself and thats of frequencies which are assigned to each of the cells. I have to be really very careful here because it’s a technical topic and I need to explain the same in simple and kind of non technical wayJ I will try.
Definition (we all have read it in physics):

Frequency is defined as a number of cycles per unit time i.e. it is the number of occurrences of a repeating event per unit time. It is often denoted by f and the unit of frequency is the hertz (Hz) and 1 Hz means that an event repeats once per second.
In layman’s term, frequency is the reciprocal of period
J
So, lets come back to the telecom gyan.

How the frequencies work in cell sites:

As I mentioned above, each of the cells is assigned with multiple frequencies which are carefully chosen to reduce interference with neighboring cells. The group of frequencies can be reused in other cells, provided that the same frequencies are not reused in adjacent neighboring cells as that would cause co-channel interference. So, lets see how it happens with the help of below diagram:

f1: can be used for Cell1, Cell 3, Cell 8, Cell 10
f2: can be used for Cell2, Cell 4, Cell 9, Cell 11
f3: can be used for Cell5, Cell 7
f4: can be used for Cell6
Similar frequency cells are marked with same color. If you observe, you will see that there is no clash between the similar frequencies. The cells using the same frequencies are not sharing the borders

Allocated frequencies:

Below are the frequencies allocated for Telecom as per India’s National Frequency Allocation plan:
-       806-960 Used by GSM and CDMA mobile services
-       1710- 1930 Used for GSM mobile services
In India GSM technology works in the frequency bands of 900 and 1800 MHz and CDMA technology works in the 800 MHz band.
Point to be noted: Also lower frequencies cover large areas and higher frequencies cover small areas.

Multi band and Multi mode phones:
Before, mobiles could not tune themselves automatically to the frequencies they find, they needed the right hardware, not just software, to use different frequencies.
But today, most telephones support multiple bands as used in different countries to facilitate roaming. These are typically referred to as multi-band phones. Do not get confused with multi-modes phones as they are the ones which can operate on GSM as well as on other mobile phone systems using other technical standards or proprietary technologies for eg a phone that can support CDMA as well as GSM technology.
Multi band phones are the phones that can tune themselves to different frequencies. They can Dual-band phones , tri-band phones and quad-band phones
-       Dual band: that covers GSM networks in pairs such as 900 and 1800 MHz frequencies or 850 and 1900
-       Tri-band phones: that covers the 900, 1800 and 1900 or 850, 1800 and 1900
-       Quad-band phones:  that supports all four major GSM bands, allowing for global use.

Handoff or Handover:
As the phone user moves from one cell area to another cell during a call is in progress (imagine if the
user is travelling in a car), the mobile station will search for a new channel to attach to in order not to drop the call. Once a new channel is found, the network will command the mobile unit to switch to the new channel and at the same time switch the call onto the new channel. There is NO indication to the user exactly which frequency you are using. The cell sites use sophisticated switching equipment to transfer your phone call from one cell site to the next. This is called a handoff . As you get too far from one cell site and the call quality becomes unacceptable, the cellular system looks for the next cell site and frequency to hand your call off to. All of this happens in split seconds and is not obvious to the user. So, next time your call drops while on phone on move, understand that the handover between the sites is not effective in that area.

Transmit and Receive Frequencies:

Transmit and receive frequency are often called paired frequencies. That seems logical enough since it takes two frequencies to pass information. Unfortunately, the forward and reverse channels refer to just a single frequency, making a channel definition little confusing
L
Transmit or Reverse frequency is the one which is used by the mobile to interact with the BSC and Receive or forward frequency is the one used by base station to interact with the mobile. They're what make talking at the same time possible.

Cell Signal Encoding:
To distinguish signals from several different transmitters, frequency division multiple access (FDMA) and code division multiple access (CDMA) were developed.
With FDMA and CDMA, the transmitting and receiving frequencies used in each cell are different from the frequencies used in each neighboring cell as shown above.
But polarization division multiple access (PDMA) and time division multiple access (TDMA) cannot be used to separate signals from one cell to the next since the effects of both vary with position and this would make signal separation practically impossible. Time division multiple access, however, is used in combination with either FDMA or CDMA in a number of systems to give multiple channels within the coverage area of a single cell.
We would be covering CDMA, TDMA, PDMA and FDMA in coming chapters and then, the above will be quite clearJ I promiseJ
Plz let me know your thoughts on this article. Is there anything else that can be added? Was it useful to you?

GSM Core Network: Base Station Subsystem: BTS (1)

As discussed in one of the last posts, the GSM network can be broadly divided into 3 parts:

- BSS: Base Station Subsystem

- NSS: Network Switching Subsystem

- NMS: Network Management Subsystem

As mentioned in last post, Base Station Subsystem takes care of all the radio related functions between a mobile and the network. It consists of Base transceiver stations (basically the tower, BTS) and a base station controller (a BSC)

Today we would be covering Base transceiver stations only. Would not be able to pen down all the entities of this subsystem in one post and so will explain them one by one:) 

So, lets go ahead with BTS:)
All mobiles use a network of well structured and well engineered network of base stations and antennas to cover a large area. In simple terms, a base station is that part of the network which is accountable for handling traffic and managing the signals between a mobile phone and other components in the network switching subsystem. 
A Base station contains the equipment for transmitting and receiving radio signals i.e. transceivers, antennas, and the equipments for encrypting and decrypting communications with the BSC (will explain in next chapter).
The area which a base station covers is called a cell and the place where the base station and antennas are located is called a cell site.
A cell is an area which is covered by each base station. This area is divided into regular shaped cells, which can be hexagonal, square, circular or some other regular shapes. Though the most commonly used are the hexagonal cells. It looks like a cell in a honeycomb as shown in the diagram below. Cell sizes can range from 1Km to 50 km in radius. Though, the cells built in GSM structure are much smaller, they generally do not go beyond 10km.

Diagram 1: Shows the honeycomb structure of a cell
Diagram 2: Shows the cell site placement
Diagram 3: Is a simpler representation of Diagram 2
Diagram 4: Shows the wrong intepretation what we generally assume that a tower is located at the center of a cell
Conclusion: Cell site is not located at the centre of a cell. It is located at the edges or the corners

Each cell site's base station uses a computerized 800 or 1900 megahertz transceiver with an antenna to provide coverage. Each of the cells is assigned with multiple frequencies which are carefully chosen to reduce interference with neighboring cells. The group of frequencies can be reused in other cells, provided that the same frequencies are not reused in adjacent neighboring cells as that would cause co-channel interference. As I said above, would be explaining frequencies in different chapter so this is all about the same in this one.
Coming back, the area served by a cell site completely depends on geography, population, and the traffic in that particular area. In some GSM systems, a base station hierarchy exists, with pico cells covering the building interiors, microcells covering the selected outdoor areas, and macrocells providing more extensive coverage to wider areas. Narrowly directed sites cover tunnels, subways and specific roadways.
In short, the macro cell controls all the cells overlaid beneath it. A macro cell is often built to provide coverage and smaller cells are built to provide capacity. Hope this all makes senseJ
Been a lot of gyaan for todayJ Hope I was clear. Plz let me know your feedback...

GSM Core Network: Diagram

So in the last post we got to learn the systems and their entities that are involved and makes a GSM network. In this post, I have tried to put all the entites in a diagram to depict a clear picture of the connection between all the systems and all the entities.

Abbreviations:
BSC: Base Station Controller
MSC: Mobile Station Controller
SMSC:Short message Service Centre
EIR: Equipment Identity Register
HLR: Home Location Register
AUC: Authentication Centre
PSTN: Public Switched Telephone Network

From next post, we will start going through each of the systems and entities in details so be ready for a lot of technical gyaan:D

Keep Smiling....

GSM Core Network: Basics

Ok, I guess I can start with exploring my knowledge on the core GSM network:) So, lets begin. The GSM network can be broadly divided into 3 parts:

- BSS: Base Station Subsystem
- NSS: Network Switching Subsystem
- NMS: Network Management Subsystem

We would be going through each one of them in detail in the next few chapters so for now, we need to maintain the patience:)

Though below is a brief about each one them to kill your curiosity.

- Base Station Subsystem :  This system takes care of all the radio related functions between a mobile and the network.It consists of Base transceiver stations (basically the tower) and a base station controller (a BSC)

- Network Switching Subsystem:This system takes care of the connection, authentication, encryption and supervision of a call.It consists of many elements/ entities. The main one being a Mobile Station Controller which handles many BSCs. Other entities being a Home location Register (HLR), Visitor location register (VLR), Authentication centre (AUC), Equipment identity register (EIR), Short message service centre (SMSC), Multimedia messaging service center (MMSC) etc.

- Network Management Subsystem:This system's responsibilities includes operations and management of the whole system

In next post, I have given a diagram depicting the connection between all these elements of the GSM network.

Whats up with Blackberry?

Today I really want to write about one of my fav mobiles - Blackberry! I have been using BB from last 4 years. The phone I am using now is my 4th BB. I had just bought this one a few days back, I was in love with BB till I came across one of my friend's Samsung Galaxy SI one day. And I immediately feel in love with it! The amount of apps (both utility and entertaining) available on android market seems to be never ending! I really regreted of buying a BB without doing a proper research on the phones available in the market! I was so much tempted to own a smart phone that I got a Samsung SI from my next sal:) And is too happy with it. I have kept BB too just for my friends and groups on BBM:)

From last few years, the magic of BB seems to be fading. Once a touchstone seems like to be on the way of being an anachronism! 4-5 years back, BB was one of the most amazing and highly praised mobiles in the market. Infact, owning a BB used to be status symbol. But now, all this seems to be like a myth! Thanks to Iphones and Androids...

BB's market share seems to be decreasing every quarter. In US, Smartphone market share of BB in Q1 2009 was nearly 50% which has come down to around 13.5% in 1st quarter of this year.

Also BB's addiction and obsession seems to be parable now. Acc to a research, only a third of BB's users plan to stick to BB on their next change. Infact BB has seen a degrowth of 75% in their stocks! They had to change their CEO a few weeks back in hope of bringing back the same command and authority in the market!

What could be the reason for it? The easiest explaination would be the entry and popularity of android and Iphones have been resulting in the diminishing market share of BB. But is that so simple? No, if BB would have acted on time, they would have definately been able to sustain their position in the market. But guess, the issue with BB is that they had been living with the perception of being the leader of the business world and probably they thought, nobody could shake them from that position. Infact, BB had launched their first touchscreen much later than Iphone and other touchscreen makers. Also, if you look at all their models, all of them have almost the same look and feel. There is very less difference in all of them! They definately do not have much range and models. And I have no idea why they never thought of launching something different, something new to the market. Their latest model BB bold touchscreen has so much resemblence to BB Bold's ancestor 9000. Could'nt they think of anything unique, anything inimitable?

Also, intially BB had completely restricted themselves to the business world and people working in ITs loved BB because it offered them what they needed the most: security and reliability. BB had their own closed systems and so, there was less chances of any kind of fraud. At that time, BB did not try to reach the ordinary people and when they decided to enter this segment of the market, they were just not aware of ordinary people's needs, their demands and thus, again failing here.

But in this whole havoc, BB was able to safeguard their position a bit. Thanks to their BB curve's new models which definately helped them in saving a bit of their position in this competitive market. Ordinary people who once dreamt of owning a BB now got a chance to have hands on the same. But most of them do not want to continue with BB as their next phone. Second thing which have been saving their position is BBM. But guess Whats app will be able to override the same somewhere soon in future.

Can you believe that BB, which made texting a mainstream practice, which once dominated the smart phone market now have been trying hard to just safeguard their position in market!!!  Once a staple in the business world run the risk of becoming a technological dodo now!

Well its a brave wide world now! Its just not the same for which BB had built itself for...

GSM Core Network: Base Station Subsystem

As discussed in one of the last posts, the GSM network can be broadly divided into 3 parts:

- BSS: Base Station Subsystem
- NSS: Network Switching Subsystem
- NMS: Network Management Subsystem
Today we would be covering Base Station Subsystem. So this system takes care of all the radio related functions between a mobile and the network.It consists of Base transceiver stations (basically the tower) and a base station controller (a BSC)
We have already covered Base Transceiver Station or BTS. You can read the same here
Just to give you a brief, a base station is that part of the network which is accountable for handling traffic and managing the signals between a mobile phone and other components in the network switching subsystem. 
A Base station contains the equipment for transmitting and receiving radio signals i.e. transceivers, antennas, and the equipments for encrypting and decrypting communications with the BSC
Base Station Controller:
All the BTS needs something to manage them. And that’s where the role of BSCs comes; they manage the intelligence behind the BTSs. And that’s the role of BSC. Its basically a combination of server and software, it’s a high-capacity switch which controls all the radio communication such as handover, management of network resources and handling of cell configuration data. Controlling the radio frequency power levels in the mobile phones is also the job of a BSC. In short, the device enables the base station to register mobile phones in the cell to perform handover, call setup and call termination. Base station controllers also set transceiver configurations and frequencies for each cell. It also provides all the required data to the operation support subsystem (OSS) as well as to the performance measuring centers.

Confused?? Even, I was in the same condition while penning all this down:( Don't worry, read once more and everything will be clear:)
Get it now?? So, lets carry on...

One more thing, the no of BSCs depends on the complexity and capacity of a carrier's system. Typically a BSC has tens or even hundreds of BTSs under its control.
Other entities:
 Transcoder
As the name suggests, the transcoder is responsible for transcoding the voice channel coding between the coding used in the mobile network, and the coding used by PSTN (would be covering that soon again). In a very layman’s term, PSTN can also be called as the landline or wireline phones that we use.
Packet control unit
As the name says, It performs all the processing tasks for the for packet data. The PCU takes full control over data channel once the same is handed over to it by a BSC
Guess its enough gyaan for today:)
Keep smiling and keep learning