Monday, August 6, 2018

Basic overview of satellite communication

Satellite Communication

Source: Wikipedia
The unique feature of satellite communication is their ability to simultaneously link all users on the earth’s surface. Satellite Provide insensitive point-to-multipoint communications. The capability applies to fixed terminals on earth.
And to mobile terminals on land, in the air, and at sea. Satellites offer a number of features not readily available with other means of communications.

As large areas of the earth are visible from satellite, the satellite can form the start point of the communications network and can simultaneously link geographically separated users.
Satellite communications system is economical only where the system is in continuous use. Thus costs can be reasonably spread over a large number
of users. Satellites form an essential part of telecommunications
  • Carrying large amounts of data and telephone traffic
  • Television signals
  • Remote sensing as detection of water pollution
  • Monitoring and reporting weather conditions.
  • Search and rescue operations.

Frequency allocations for satellite services

Allocating frequencies to satellite services is carried out under the auspices of the International Telecommunication Union (ITU). To facilitate the frequency planning, the world is divided into three regions:
  1. Region 1: Europe, Africa, formerly the Soviet Union and Mongolia
  2. Region 2: North and South America and Greenland
  3. Region 3: Asia(excluding region 1 areas), Australia and the south-west Pacific.
Within these regions, frequency bands are allocated to various satellite services. Although a given service may be allocated different freq band in different regions.

Satellite services

  • Fixed satellite services (FSS): links telephone N/Ws and transmitting TV signals to cables
  • Broadcasting satellite service(BSS): Direct broadcast to home(DBS), in Europe known as DTH
  • Mobile satellite services: land mobile, maritime mobile, aeronautical mobile
  • Navigational satellite services: GPS
  • Meteorological satellite services: search and rescue service.

Satellite frequency bands 

Communications systems employ the EM frequency spectrum. The frequencies used for satellite communications are allocated in super-high-frequency (SHF) and extremely high frequency (EHF) which are broken down into sub-bands.
Figure 1
Figure 2
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Friday, August 3, 2018

What is means by GSM BURST and its types


As we know that GSM uses time slot to transmit information and Burst is a type of information that contains in particular time slot of GSM. Bursts are designed to fit in these time slots to transmit information. GSM consist of five burst which are
  1. Normal Burst 
  2. Synchronization Burst 
  3. Frequency Correction Burst 
  4. Access Burst
  5. Dummy Burst

1. Normal Burst

Normal Burst
Typical burst contains 114 bit of valuable information and divided into two groups 57 bits each. These bits contain signaling and user data.
Stealing flag helps to indicate special events like Handovers etc. It also helps to verify that whether the block contains data or is stolen.
Tail bits found at the start and end of data. It is used as a guard time. Tail bit are three (3) in number and set to zero and placed at the beginning and at the end of a burst.
The Guard Period (GP) helps in to avoid overlapping with other bursts that may carry some other information. The length of the Guard Period is 8.25 bits.
Training sequence has a length of 26 bits and is used to synchronizes the receivers, hence this effects multipath propagation. The Training sequence helps in adapting the receiver parameters to the current path propagation.


2. Synchronization Burst:

Synchronization Burst
As its name suggests, this burst is used to synchronize Mobile Station
and BTS using a synchronization channel (SCH). The function of both Tail and Guard bit same as mention above in Normal Burst.
Coded Data tells about TDMA frame number.
Training sequence tells about base station number.
Mobile Station at first demodulates synchronization burst that's why the length is 64 bits. it helps to avoid Larger multipath delay spreads.

3. Frequency Correction Burst

Frequency Correction Burst
The most simple format of all the bursts is used for the frequency correction burst, which is transmitted only in the frequency correction channel (FCCH).
All 148 bits are coded with zeros and frequency which is a pure sine wave (GMSK modulator Produce sine wave) is transmitted that enable mobile to synchronize its frequency with the master frequency.
Frequency correction burst appears on frequency correction channel.

4. Random Access Burst:

Random Access Burst
Random Access Burst have a unique format as compare to other because of its special task. When first switched on, A mobile station (MS) uses the access burst for initial access to a BTS. The first job is to synchronize itself with BTS in frequency and time using synchronization burst.
Burst has a length of 88 bits plus 68.25 guard bits. Access burst length is set large because to make it possible that access burst appears at the BTS. It can be increased more by adding a guard band of 68.25.

5. Dummy Burst:

Dummy Burst
Dummy burst contains no user data information. Dummy is used to fill out idle time slots on the channel when a user is not sending any data. Dummy burst sent by the base station on the base channel. When a mobile station is turned on, it easily discovers base channel. The pseudorandom bit sequence is used to avoid accidental confusion with frequency correction burst.

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Friday, July 13, 2018

How to Create Procedure in Ns2

How to Create Procedure in Ns2

Procedure in Ns2:

A procedure is a small piece of code that is used to perform some specific task like running, closing and executing etc. This piece of code is called at end of the program. Below you can see the code for a procedure that normally used in simple ns Program.

Example of Procedure:

# Define a ‘finish’ procedure
proc finish {} {
          global ns tracefile1 namfile
          $ns flush-trace
          #Close the NAM trace file
          close $tracefile1
          #Close the NAM file
          close $namfile
          #Execute NAM on the trace file
          exec nam out.nam &
          exit 0

Program Explanation:

proc finish {} {

The word “proc” is used to declare procedure and “finish” is the name of the procedure. So we declare a procedure with name finish without any arguments. You can also declare procedure with arguments. You can see the example below at the end of the post.

global ns tracefile1 namfile

If you have run simple ns programs before then you must be familiar with
Nam-file and trace-file but if not then don’t worry you can check it here.
Simple wired and wireless ns2 Programs code
Here with the help of word global, we tell to the procedure that the variable we using here is declared outside the procedure.

$ns flush-trace
“flush-trace” will dump the traces on the respective files.

close $tracefile1 and close $namfile
The close command simply closes both nam-file and trace-file that we define at the start of the ns program code.

exec nam out.nam &
The word “exec” is used to execute the nam program for visualization that we created at the start of the program.

exit 0
The command exit will end the application and return the number 0 as status to the system. Zero is the default for a clean exit. Other values can be used to say that it is an exit because something fails.

$ns at 125.0 "finish"
At the end of the program, we will call the procedure “finish” that we created early and specify at what time the termination should occur. For example, will be used to call “finish" at time 125 sec.

Reference Site:
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Tuesday, June 26, 2018

7 Things to Consider While Choosing Internet Service Providers


Today, the World Wide Web has become an integral part of our daily life. A large number of tech-savvy people all over the world use the global Internet to browse websites, book railway/bus/airplane tickets, apply for jobs, watch movies, operate social media websites, transfer money from one bank account to another, pay utility bills, and perform a lot of work. We can say that our life is totally dependent on the Internet.

The quality of the Internet services provided by companies directly affects the comfort of your stay in the network and the effectiveness of your work. While choosing an Internet service provider, most people usually look at the speed of connection and the cost of tariffs. They ignore the problems caused by a poor-quality Internet connection. So, what criteria should be kept in mind while choosing Internet Service Providers? Let's mull over the below-mentioned points.

1. Determine the Type of Internet connection You Need

There are several ways to access the Internet. All these Internet connection technologies differ from each other in terms of connection technology, the stability of the connection, response time, data transfer, hardware capacities of the computer or mobile device, etc. Just determine your daily Internet data consumption needs and choose anyone from the following:

Types of Internet Connection

I. Satellite Internet

The coverage of this type of Internet connection is the widest. So, you can use the Internet anywhere in the world without any hassle. But, the satellite Internet has remained not very popular among people because of many reasons. It provides one-way access, which means the transfer of information is possible only from the Web to the user. There is no reverse transfer of data at all. This type of connection has a relatively low reliability and depends on meteorological condition. If the satellite faces any problem, the Internet connection deteriorates sharply or disappears completely. There are other disadvantages of it also-very expensive equipment for connection, high cost of use, and low response speed. So, people use this type of Internet connection only when they live in remote areas where other there is simply no other way to use the global Internet.

II. Mobile Internet

As reflected by its name, you can use this type of the Internet wherever you are in the coverage area of the provider (mobile operator). 
You can access the Internet in two different ways-
(A) Via a mobile phone &
(B) Through a special modem.
A special modem can be connected to a smartphone, tablet or laptop via USB ports (mini USB) as a separate small device. These days, almost all modern mobile phones have access to the Internet. A few obsolete models of mobile phones are connected to the Internet using slow and expensive GPRS technology. For more modern mobile devices, such as smartphones and tablets mobile operators offer high-speed connection technologies that can provide access to the Internet, like CDMA, WiMAX, LTE, UMTS. If a mobile gadget does not have a built-in modem capable of supporting these technologies, almost all mobile operators can offer their branded connectable modem. Always keep in mind that the data transfer speed of these technologies can vary greatly in different locations of the user.

III. Telephone Connection (dial-up)

 It is one of the most common ways of connecting to the Internet, used by most of the people. You gain access to the Internet by connecting a computer or laptop via a wired modem to a telephone line. The phone line remains busy and can't be used until the end of the session on the Web. This type of Internet connection is expensive and its speed is slow or sometimes pathetic.

IV. Wi-Fi (Wireless Fidelity) 

Wi-Fi is one of the modern forms of wireless communication, which is widely used on smartphones, tablets and laptops. It is because these devices have a special module that allows you to access the Internet when you are the range of Wi-Fi access points (around 100 meters). You can purchase a Wi-Fi module separately and connect it to the PC as a separate embedded board, or as an external device connected via USB. This type of connection is not in great demand among business users of the Internet because the access points are usually overloaded and the final speed of the Internet becomes pathetic. You can have free access to the Wi-Fi Internet at various public places, such as airports, railway stations, cafes, hotels, petrol stations, etc.


It is a special kind of connection to the Internet through a telephone line. During this period, the Internet connection does not interfere with the work of the phone. The quality of such a connection is excellent with a high data transfer rate and stability.

VI. Direct connection 

It is perhaps the best way to connect to the Internet. The user's computer is connected to the service provider with the help of an ordinary network cable. This type of Internet connection has several advantages, such as high speed, stability, reliability, low cost.

2. Speed

Almost all Internet service providers always talk about high speeds of Internet connection. But, in most of the cases, their Internet speed is slow. So, is the maximum speed for each consumer so important? Of course Yes, which largely depends on their needs.

Speeds of Internet connection

Speed up to 10 Mb / sec 

It is sufficient for performing simple actions on the Internet, such as reading news, correspondence in social networks, using the Internet banking, checking e-mail, etc. It is suitable for all those people who use the Internet for non-commercial purposes.

Speed up to 50 MB / s  

 It is suitable for everyday operations, such as to watch videos and movies on the Internet, communicate with friends and relatives via Skype, download files, etc.

Speed up to 300 Mb / s

It is a high-speed Internet connection that is suitable for people who download a lot of information, receive and send large files, videos and photos playing computer games online. All those people who work from home and perform different business activities of the company may need a high-speed Internet connection on their PC or laptops.

3. Technical Support

While choosing an Internet service provider, you also need to consider how soon and in what time frame you will receive technical assistance if you face technical glitches. It is best to specify the timing and cost of eliminating technical problems immediately after connection. Always keep in mind that reliable service provider always solves problems as soon as possible. Just write down the phone numbers of the technical support service and contact with a specialist who is able to resolve the problem in a short time.

4. Go Through Customer Reviews

Reviews and feedback are important for selecting an Internet service provider. You can find candid reviews about the Internet service providers on Q-A websites, tech blogs, and simply by contacting your friends and relatives. Ask questions about the stability of the connection. Visit the social media pages of companies, see users comment and take an appropriate decision accordingly.

5. Free Additional Services or Discounts

Sometimes, companies offer additional free services to customers to attract them. For instance, most providers offer users free IPTV when they purchase an Internet connection. Some others offer seasonal discounts on their packages.

6. Price

If you use the Internet commercially, the bills of the rapidly increasing Internet consumption can make a big hole in your budget. So, don't choose a service provider randomly. Just gather information about the presence of service providers in your locality and collect more information about their performance on key parameters, such as the quality of services provided, the positive and negative aspects of each provider, etc. Call each provider and find out the cost of services per month along with other benefits. Choose a company that is ready to offer the maximum services at an affordable price tag.

7. Equipment

It matters a lot if you are looking for a good Internet connection service. Choose a company that offers good modems and routers and let you enjoy a high-speed Internet connection. Poor-quality hardware often causes the disturbance in the Internet connection and daily business operations.


While choosing an Internet service provider, you should use the above considerations and choose a company that offers maximum data reliability, technical support, and other related benefits. This will help you to enjoy the benefits of a good Internet connection and perform your personal and professional duties smoothly.

Author Bio:

Lisa Cooper works as a writer for Fixtel, an Australian owned and operated telecommunications company to provide quality telecommunications services and solutions. He is a web addict and spends too much time in front of the computer. When he manages to get away for more than 10 minutes, he will read books, travel or shoot photos.

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Thursday, April 19, 2018

Interaction Styles communicating with any machine to perform task

Interaction Styles communicating with any machine to perform task

Interaction Styles

When you are communicating with any machine to perform task on that system is called interaction. Here our concern is with computer system so we will talk about computer.
The translation/understanding between user and computer is called interaction. Translation means converting natural language into computer understandable language (machine language) which is 0 & 1 and machine language to the natural language (human understandable language) which makes it possible to generate communication between user and computer and to perform specific tasks i.e. playing music, opening files, writing documents and many more..

There are different interaction styles which are using nowadays in different organization. The interaction style depends on the requirements of the organization that what interaction style they provide for their employees. Following are some interaction styles:

1.     GUI (Graphical user interface).
It is the common interface use most widely in all over the world. Because of its user friendly environment, un-educated people or people with low education can also interact with it and understand it.

·         It is user friendly
·         Easy to remember
·         No need of remembering commands as there is no command used, you can open  folders, files through mouse.
·         Easy to use
·         With the help of icons, it is possible to open a software program quickly as compared to opening it by going to their root directory.

2.     CLI (Command Line Interaction).
Command line interaction is quite different from GUI. CLI is based on commands, you have to type commands. i.e. DOS (Disk Operating System) which is based on command and if you want to open a file you have to type command for it.

·         It is difficult for normal people to understand and to operate
·         Based on command
·       You have to memorize command which is very difficult to remember hundreds           of   commands.
·         Not user friendly
·         It can’t be hacked easily, on that bases it is more secure than that of the GUI.
·         It is suitable for remote access.

3.     Menu-Style Interaction. 
In this style of interaction the computer provide a list of different options from which user can select his/her desired option. i.e. pop-down or pop-up menus in GUI, when you right click on the screen a list of option opens from which you can select different options.

·         It has options to select
·         Based on text or visuals
·         It is easy to recognize
·         Menu-style interaction is in hierarchical structure

4.     Natural Language Interaction.
It is also called speaking interaction. Natural language interaction is based on natural language. You have to speak to the computer to perform tasks. It is AI (Artificial intelligence) technique i.e. robots. Robots can respond to human by speaking.
Another example is windows 10 Cortona which respond to the user when user speaks. Natural language interaction uses NLP (Natural language processing) technique in which the natural language is translated to machine language using specific programs and techniques. The NLP have associated dictionary which it use for understanding natural language.
5.     Questions-Answering Dialog.
 This type of interaction is used by the organization which provide online tests and quizzes     for students or other employees. i.e. when you want to take Computer certificate online,   you have to answer the questions which the organization provide online. After passing you   will get your certificate.

6.     Query Dialog.
Query dialog interaction is based on natural language style phrase. It is just like Natural Language Interaction but the difference is that in query dialog you have to write/type query(natural language phrase) while in Natural Language Interaction you have to speak. Query dialog example is database, google search engine etc.

7.     Form Filling Interaction.
Form filling interaction is used in online registration for different organization. You have to fill the form and provide the information which is required for the organization. i.e. University registration, Nadra online form.

8.     WIMP interaction.
It is also called widgets. WIMP stands for “Windows Icons Menus Pointers”.It is the combination of four (4) types of interaction. The common example of WIMP is windows 7, 8, 10 which is the combination of all these four (4) types of interaction. These windows operating systems uses four integrated interaction styles e.g Windows, icons, menus and pointer which is Explained below:
·         It is the area of the screen which we see.
·         It can be hide/unhide
·         Can be resize
·         Consist of task bar, title bar, control buttons etc
·         It is use to shrink (reduce the size) window
·         It may be texts or pictures

·         List of options
·         Pop-up or pop-down
·         Choice of selection
·         It is similar to icons
·         It provide guidlines
·         i.e mouse pointer.

  9.     Point & Click Interaction.
Touch screen interaction is point and click interaction. You can open files and folders by touching the screen. Another example is google map where you point the position which you want to open and click it to zoom and expand.

  10.     3D Interaction.
3D stands for 3-dimension. 3D interaction is the advance technology in which you can interact with 3D environment also called virtual reality which looks like real environment. i.e. 3D games etc.
This type of interaction is also useful in training soldiers, drivers, pilots by providing specific 3D environment.If you want to know about Virtual Reality please comment your ideas..

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Tuesday, April 17, 2018

What are the three major multiplexing techniques?

Multiplexing Techiques

Multiplexing is the process/technique of dividing single channel into multiple portion to send/transfer multiple data simultaneously at same time.

Multiplexing techniques is very efficient/effective technology which reduces the cost of the cables. You don’t have to buy unique cable for each type of data. For example, if you want to send audio, video and documents etc, you don’t have to specify a cable for every type of data, rather you can multiplexing technique to send all these three types of data using a single cable simultaneously.

The following diagram shows the multiplexing technique:

In multiplexing, two devices are used Mux and De Mux


Mux stands for Multiplexer. It is responsible to multiplex (combine) multiple links to transfer in a single channel as shown in the above diagram. Commonly the multiplexer is specify at the sender side because if the sender wants to send different types of data , it has to be multiplexed first to send into a single channel.

De Mux:

De mux stands for De Multiplexer. It is responsible to separate the multiplexed links from a single channel into different separate links.  Commonly the de-multiplexer is specify at the receiver side because when the receiver receive different types of data from a single channel , it needs to be separate or de-multiplex.

There are two types of multiplexing

Analog :

Analog multiplexing is sub categorized into two types of multiplexing      
  1. Wavelength Division Multiplexing (WDM).
  2. Frequency Division Multiplexing (FDM).

Digital :

Digital multiplexing includes Time Division Multiplexing (TDM).

1. Wavelength Division Multiplexing : ( WDM )

In simple words the multiplexing on the base of wavelength is the wavelength division Multiplexing. It is an analog technique. WDM multiplex different numbers of optical light wavelength to transfer in a single fiber.  Each wavelength make a virtual fiber to transfer in a fiber so that it depends on the speed (frequency) of the wavelength. The wavelength of high speed will reach first and wavelength with low speed will reach later.

WDM is same as FDM but the difference is that the Multiplexing and De Multiplexing of WDM includes light wavelengths while that of FDM includes frequencies.
The best example of WDM is the prism , which shows the various colors after De Multiplexing the light.
WDM (Prism)
You can see that a single channel of light is divided into different colors using prism. If you pass the different number of colors from the side of the single light, it will show single light channel on the opposite side.

Wavelength division multiplexing is sub divided into two types:

1. Uni-Directional WDM:

In uni-directional WDM , data is send only from one side and receive on the other side. Multiplexing of the wavelength occurs on the sender side and de-multiplexing of the wavelengths take place on the receiver side.

The diagram below shows uni-directional WDM in which sender multiplex the wavelength and receiver de-multiplex it.
Uni-directional WDM

2. Bi-Directional WDM:

As the name shows the bi-directional mean both sides, In bi-directional WDM the wavelength can be send from both side which means that both sides (sender  & receiver) can do multiplexing and de-multiplexing.

The diagram below shows Bi-directional WDM in which sender and receiver both can multiplex and de-multiplex the wavelength
 Bi-directional WDM

2. Frequency Division Multiplexing : ( FDM )

Multiplexing on the base of frequency is called Frequency division multiplexing ( FDM ).  It is an analog technique of Multiplexing different frequencies of different links to pass through a single cable.
The link having high frequency will reach first and that is the link having low frequency will reach later as It depends on the frequency.

The diagram below shows the frequencies that are multiplexed in a single channel and by reaching its destination, it is then De multiplex to forward to the right destination.

3. Time Division Multiplexing : ( TDM )

Time division multiplexing is a digital technique of combining different links to transfer through a single channel. A single channel is divided into different time slots in which different type of data is sending on the base of time. Every link have specific time for transferring.

See the picture below to understand it clearly.
For example:  the slot 1 is for downloading, slot 2 is for youtube, slot 3 is for searching and slot 4 is for facebook. When downloading completes the slot 1 (downloading slot) will go empty. Similarly when slot 2 finishes the slot  2 will go empty.

Reference Book: Data Communication And Networking 2nd Edition
Reference Site:
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Monday, April 2, 2018

What is MAC Address?

MAC Address

MAC stands for “Media Access control”. It is also called Physical address, Burn-in  address, Hardware address or Unique address.
MAC address is 48 bit address which is labeled on your system NIC (Network Interface Card). MAC address depends on the number of NIC card , if your system have one NIC card then your system has one MAC address similarly if your system have three NIC cards then your system has three MAC addresses.
For example: one MAC address is of LAN card , one is of Bluetooth and one is of Wireless connection.

How to find MAC address ?

To find your system’s MAC address , follow the simple steps
  1.         Open CMD
  2.         Type ipconfig/all
  3.       Hit enter

      There you will see your MAC address. Following picture shows MAC address of my system

MAC address is in Hexadecimal digits like “28-80-23-00-EA-A3” where A=10 , B=11 ….. F=15. It is divided into two portion of 24 bits. See the following picture

The first three pairs are called OUI (Organizational Unique Identifier). Every organization have their own unique OUI for all of its products . For Example “The first three pairs of all HP products must be same” in the same way the first three digits of all DELL products also must be the same.
The second portion is called NIC (Network Interface Controller) which is specific. It cannot be duplicated for other products for example if one HP laptop has NIC portion “00-EA-A3” then this address can never be used for other HP laptop.

To find which company my MAC address related to :
  • 1      Open google
  • 2      Search “MAC Vendor lookup”
  • 3      Paste your MAC address their

You will get your company name which your MAC address related to.
If you want to get all the information related to your MAC address i.e. where my MAC address developed etc , you can check it by going to the following website

There you can paste your MAC address in the given box and it will show your MAC address information.


MAC address can be used for tracking. It can track your location as it is labeled on your NIC card and which can show your location.

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Wednesday, March 28, 2018

What is Network Mode and the best preferred network mode is?

What is Network Mode?

Network Mode enables to you switch between different network like UMTS, LTE, WCDMA, GSM, EDGE etc. The switching can be done automatically or you have to select preferred network. You can check in image below the network mode for Android (lollipop). Now here we have four Option that we are going to discuss.
Mobile Network Mode


GSM Only

GSM only means 2G only. That's mean your mobile will look for only 2G signals whether you are in 2G network area or not. GSM (2G) will provide slow internet connection and it is good for voice services.


WCDMA or UMTS both are 3G network and it allows you surf internet faster then 2G. Using this mode your mobile will look only for 3G signal. Use this option with care because still 3G is not available in some countries.

WCDMA/GSM (Auto Connect)

Using this mode user allows mobile user to switch between WCDMA and GSM. If WCDMA (3G) signal is not available then mobile will automatically look for 2G signals. Sometime device switch the mode from one to another because of low signals.

LTE/WCDMA/GSM (Auto Connect)

In simple terms LTE means 4G. If the above mode option is available in your smart phone it means your device is 4G supportive. LTE Provide fast Internet speed as compared to 3G and 4G. Using this user allows device to switch automatically between LTE, WCDMA, and GSM. Same case here the switching occurs on the basis of network availability and signal strength.

what is the best preferred network mode?

Best preferred Network Mode is LTE/WCDMA/GSM because you allow device to select best and strong Network for you but the disadvantage is it will consume battery 🔋. In case you are not using internet on your device you I will recommend you to select GSM Only because it will save your battery and GSM is almost available everywhere.

how to change my phone network?

Everyday new devices are coming to market. These devices have different method to change their mode so will go general but you can google "How to change Network Mode in [YOUR MODLE]" to get method for your deivce.

In general you can follow below steps that may help you

Step 1: Click on setting

Step 2: More Network

Step 3: Mobile Network

Step 4: Network Mode

That way you can change your network. Still have problem or failed to Google your answer, comment below I will look for it.

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