Saturday, January 26, 2013

Site Sharing

Site Acquisition (SAQ)

Overall Procedure of Commissioning a Site


This department is dealing with acquiring proposed location, conducting civil works, installing telecommunication equipment and Preliminary Acceptance Test (PAT) in the process of establishing a site or in any other project.  There are Civil, Electronic and Telecommunication Engineers in the PROJECT team (May differ from operator to operator). 

The main role of PROJECTS division is commissioning of new sites. Other functions of that section includes site validation, contract of site,   and acquisition of licenses, site construction, and installation of equipment, site testing and final acceptance. They are working very closely with the contractors, this department ensures the project completed within the given time limits.

Virtualization - Future of VAS

Future of VAS Services

Operators are providing large number of VAS services to their customers. They are very useful to the customers and they will directly help to make a unique name among other operators. Not only in services wise have they needed to use new technologies in implementing those services. To cater that now days they are going to introduce Virtualization Concept. So most of them have already started implementing, buying necessary equipment and acquiring required licenses for that.

What is Virtualization?

Virtualization is the creation of a virtual (rather than actual) version of something, such as a hardware platform, operating system (OS), storage device, or network resources.
While a physical computer in the classical sense is clearly a complete and actual machine, both subjectively (from the user's point of view) and objectively (from the hardware system administrator's point of view), a virtual machine is subjectively a complete machine (or very close), but objectively merely a set of files and running programs on an actual, physical machine (which the user need not necessarily be aware of).
Virtualization can be viewed as part of an overall trend in enterprise IT that includes autonomic computing, a scenario in which the IT environment will be able to manage itself based on perceived activity, and utility computing, in which computer processing power is seen as a utility that clients can pay for only as needed. The usual goal of virtualization is to centralize administrative tasks while improving scalability and overall hardware-resource utilization. With virtualization, several operating systems can be run in parallel on a single central processing unit (CPU). This parallelism tends to reduce overhead costs and differs from multitasking, which involves running several programs on the same OS.

Friday, January 25, 2013

Value Added Services (VAS)

All services beyond standard voice calls and fax transmissions which were provided by Telecommunication companies can be considered as Value Added Services. Also they are referred as non-core services. As its name implies it will simply add value to the standard services they provide. The ultimate goal of any company is to generate revenue. VAS plays a major role in generating revenue because it will increase the ARPU (Average revenue per user). Currently five mobile operators are there in Sri Lanka. Due to the high competition each and every operator tries to provide wide variety of services to their customers. Those unique services will differentiate the service providers and customers would like to get more services at their fingertips. In today’s world most of the new technologies and services becoming a reality inside the mobile devices. VAS team is there to try and make the network unique among others. In this section there are few sub sections which were handled by Engineers who are responsible of providing better services.

Few of the main VAS services: Web Patashala, BOOKHUB, Mobile TV, Magic Voice, PRBT (Phone Ring Back Tone), News Alerts, e-wallet, etc.I have explained few of services in this blog.

SIM (Subscriber Identity Module)

A subscriber identity module or subscriber identification module (SIM) is an integrated circuit that securely stores the IMSI and other related parameters used to identify and authenticate subscribers on mobile telephony devices. A typical SIM card is shown below.
There are two types of SIM cards are there, Native Cards and Java Cards. To generate a byte code in a Native card we can use Wireless Markup Language (WML). Java cards will run Java Scripts and are high cost.
There are two unique parameters for a SIM. Known as IMSI (International Mobile Subscriber Identity) and ICCID (Integrated Circuit Card Identifier).

IMSI (15 digits)

A unique identification associated with all GSM, UMTS and LTE network mobile phone users. It is stored as a 64 bit field in the SIM. It is also used for acquiring other details of the mobile in the HLR or as locally copied in the VLR. The first 3 digits are the Mobile Country Code (MCC), and is followed by the Mobile Network Code (MNC). The remaining digits are the Mobile Subscription Identification Number (MSIN).
We use IMSI for location updates, for charging, etc.  And IMSI is a network internal parameter. So we need to hide it from external parties to avoid any fraud. To access that another key is required (known as ADM). 

ICCID (19 digits)

Each SIM is internationally identified by its ICCID. First two digits named as Major industry identifier (MII), 89 for telecommunication purposes. Other digit representation is given in the image below. Last 12 digits will be defined by the mobile operator in a way they wanted.  For example Etisalat included SIM manufactured vendor (1 digit), date of manufacture, serial number and a random number. We can provide a format to the vendor and they will produce SIM cards according to that format.

Other important parameters

•    MSISDN - Mobile Station International Subscriber Directory Number (the telephone number to the SIM card)
•    Ki – Authentication key
•    KC  - Ciphering key
•    PIN - Personal Identification Number
•    PUK - Personal Unblocking Code
•    ADM Code – To view encrypted details of the SIM

Why MSISDN not unique to a SIM card? If you lose your SIM card you can obtain another SIM card with same MSISDN. In such situation we can remove existing mapping of IMSI, ICCID with MSISDN and redefine a new ICCID for the MSISDN. This is not possible if MSISDN is unique for a SIM.
When a mobile communicates with the Base Station the data will be encrypted using KC as a security measure. That will make it difficult for others to listen to the calls, etc.

Before SIM goes to the customer

According to our previous orders we receive SIM batches from the vendors. They come with their details. To define SIM cards in the HLR we need to upload the corresponding file (Which contains IMSI, ICCID, KC, Ki, etc.).

How the authentication happens

When you switch on the phone a Network Attach Request comes with IMSI. HLR will generate a random number and pass it to the mobile. Then both HLR and mobile independently generate SRES according to the A8 Algorithm using that random number and Ki. It will be passed into VLR where both SRESs will be compared. If the match mobile can attach to that mobile network. If the mobile is using a SIM of a different network SRESs will be different and attachment fails.

Why a Random number instead of a fixed number?

If we use a unique number, generated SRES will be same at all the times. And an outsider may track it and identify Ki so they will be able to make copies of SIM cards. But with the use of random number it is difficult to do so.

What if your SIM locked?

If our SIM gets locked and we may try to unlock it using a PIN. We may fail up to three times and after that SIM will be locked permanently. By entering PUK code we can unlock SIM. That’s why some operators provide the PUK code along with the SIM card.

Inside the SIM

With the use of a SIM card reader we can view parameter of a SIM. To get the correct IMSI we have to interchange each pair of digits named as IMSI in the SIM. Ki and IMSI visible. PIN numbers are invisible. We need ADM code to view them. Our contact list is named as Aggregated Dialing number which can store 250 records each consist of 26Bytes. We can also set Fixed dialing numbers and if we do so we can only dial those numbers using the SIM. Service provider name can be changed too. We can also define VAS applications inside to a SIM. If we are to change internal parameter we have to give them in Hexadecimal format.

Mobile TV

How the Service deployed

We first have to download the Mobile TV application and then register to a particular TV channel. For example imagine that you are going to register for the channel TenCricket. Content providers main server is in India alongside with a customer database. Our customer attached to the SGSN and the normal procedure going to the internet will take place as usual. When he clicks “subscribe for a channel”, his request will reach the server located at India as a HTTP request. To do that authentication part should be handled by our Fire Wall and according to the request server will take necessary actions. Then the server will send an HTTP/XML request to our External Charging Gateway (ECG) to check the details of our customer. Refer the image below for further details.
ECG will direct it to OCS to check for the balance of the customer. We can directly charge prepaid customers in OCS if they have got enough balance. For postpaid customers OCS will generate a CDR (Call Detail Record) and send it to OFCS for billing him later. After that OCS will send a response back to ECG indicating the status. It will forward again to Main server.
If the charging process of the customer succeeded he will be given separate RTP (Real Time Protocol) addresses for video and audio (i.e. RTP://video, RTP://audio) for that channel. 
            E.g.: RTP://

You can’t see above addresses or you can’t identify them. Because when the addresses

assigned you will see a “Play” button in the Mobile TV interface. When you press the button above mentioned two addresses will be opened through mobile’s default player. 
Company prefer customers under 3G coverage but even with a 2G coverage (will depend on traffic, weather, etc.) you may able to get an uninterrupted service. This application requires at least 248kbps (3G) or 64kbps (2G). There are 3 profiles defined for the convenience of the customer.
     1.      MPEG4 (video),AAC (audio) – specially for older mobiles
          2.      H.264,AAC – high (i.e. android phones)
          3.      H.264,AAC – low (for customers in 2G coverage)

Giver URLs were all internal private IPs. Because we don’t need to use over internet bandwidth for streaming. That is handled using an Encoder as shown below. After successful subscription from the main server side Encoder will send a unicast RTP addresses (mentioned above) for the customer. Now customer can watch the TV channel. For streaming only bandwidths between mobile and Encoder will be used.
When we get the content from a content provider (i.e. Sky TV) we have to get it as shown in the image. Because the switching room is isolated from outside world to protect it from lightning and etc. It will only get power from outside. So we connect roof top cabin and switch using fiber. This much of security measurements taken in order to protect all the high cost equipment located inside the room.

How the charging happens

To charge a particular customer we need to get his mobile number through the main server in India. In order to pass that information; we send a HTTP enriched header request to the server which consist of following details.
  •          MSISDN
  •          Bearer (2G or 3G)
  •          SGSN ID (We don’t allow this service to roaming customers. If a customer is roaming his SGSN ID will be different from ours. So we can restrict him by looking at this ID)

Why the Main Server is not in Sri Lanka (Can’t we set up it in Sri Lanka)

Major distribution points of the content provider are not located in Sri Lanka. If we are going set up those facilities here in Sri Lanka, the cost will be high. It is not hard (very easy) to configure and get connected with existing facilities. We only have to get the authentication done because we have to connect through public internet. Authentication will be done using IPs, ports, usernames, passwords, etc. only when we subscribe we have to communicate with the Main Server. Especially as I mentioned above while we stream, it is controlled inside our network.