GSM, Mobile Connectivity, Roaming and Using Phones Abroad

Lesson Objectives

  • To understand how a phone connects and operates off a mobile network.  To understand the consequences of using a mobile phone abroad.

Learning Outcomes

Must – Understand what GSM is and how a phone connects to a network.

Should – Identify the types of mobile connectivity and the various pros and cons of each.

Could – Give practical advice about phones abroad and Data Roaming issues.


In order for a mobile phone to carry out its key functions, such as calls, texts and other uses such as data, it needs to be connected to a large network.  Unlike telephones in the UK which run off wired systems, a mobile network relies on the use of satellites and transmitters to work.  This network is called GSM (Global Systems for Mobile Communications).  A GSM network is primarily global which allows people in different parts of the UK and parts of the world the ability to connect to one another.

This video below explains how the SIM card in a mobile phone works, and how it lets the user connect to a GSM network.  For the exam, you are not required to know the communication protocols as they are not covered in the syllabus.

GSM World Coverage Frequency Bands

Different parts of the world have different frequencies.  These are called bands.  Countries usually have 2 frequency bands for mobiles to connect to, for example, the UK has the following two bands, 900MHz and 1800MHz.  All mobiles at least purchased and sold in the UK are at Dual Band enabled (Dual meaning 2) so that they will connect to either the 900MHz band or the 1800MHz band.  The problem however with dual-band phones is that not all parts of the world operate on the same frequencies as the UK.  The United States of America, for example, operates on the 850MHz and 1900MHz GSM frequencies.  This means a dual-band phone purchased in the UK would not work in the USA, and vice versa a phone purchased in the USA would not work in the UK.

In order to make calls abroad, a user would need a Tri-Band phone (tri meaning triple or 3).  This allows them to connect to 3 out of the 4 world frequencies.  Specialist Quad-band phones exist which connect to all 4 world frequencies.

The only parts of the world which don’t operate on GSM frequency bands are Hong Kong, Japan and South Korea.  These advanced nations have a network set up whereby 3G connectivity is the absolute minimum even out in rural parts of Japan for example.

Use this link to see which frequency bands cover which countries.

Task 1 – In your exercise book answer the following questions.  Include detailed examples where applicable.

  • What is GSM?
  • Which countries use the 900 or 1800MHz GSM band?  Give at least 3.
  • Which countries use the 850 or 1900MHz GSM band?  Give at least 3.
  • Include a map of the GSM World Coverage Map.
  • What are Dual band phones
  • What are Tri-band phones
  • What are Quad-band phones
  • Explain the situation in Hong Kong, Japan and South Korea.  Whats different?
  • What type of phone you would recommend to someone who travels the world a lot.  Justify your answer with reasons.

Types of Mobile Connectivity

When a mobile is on a GSM network it needs some on network connectivity to allow the device to make and receive calls, send and receive SMS and browse the Internet.  In terms of connectivity, the 2G is the slowest connection with the strongest connection is 4G.  5G networks are currently under development.  South Korea is currently developing a 5G network which should be universally available to its citizens by 2020.

  1. 2G  (original GSM)
  2. GPRS (General Packet Radio Service)
  3. EDGE (Enhanced Data Rates for GSM Evolution)
  4. 3G
  5. H (High-Speed Packet Access)
  6. 4G
  7. 5G

An easy way to think about the mobile connectivity is to think of its data transfer speed and relate it to modes of air travel.  A 2G network could be compared to a paper aeroplane, a GPRS network could be compared to a hot air balloon and the fastest network of them all currently, a 4G network could be compared to a space rocket.

Task 2 – In your exercise book create a diagram for revision purposes that compares the types of mobile connectivity to modes of air travel.  Ensure you make references to key features what that type of network can do.


Roaming is a term used when a mobile phone attempts to connect to another network that it does not use normally.  Mobiles phones in the UK are “locked” or “tied in” to one network only, this means that this mobile operator is responsible for data, coverage and billing etc.  Mobiles are designed to look up this network straight away when a phone is switched on.

The problems occur when the mobile loses the coverage when a user gets too far away from the transmission signal, for example leaving the UK and heading into France.  The mobile attempts to look for the network it usually connects to, but because it can’t find the transmission signal, it connects to a network that it usually does not use.  This is called Roaming.

Phones that are connected to a Roaming network no longer use the data and call package that they may normally use.  This means the user is faced with additional charges such as texting, calls and most costly of all data by using the phones data services.  This is known as Data Roaming.

If you look at the Internet there are various horror stories of people who have been faced with large bills when using their mobile abroad because they did not realise their phone was in Data Roaming mode.  Before the 30th April, mobile phone operators could charge whatever they wished for data downloads, charged by the MB.  Since the 30th April, the EU has put a cap in place of 4p per MB download.  Whilst still expensive, this is a huge cut in previous data rates which in some cases were as high as 25p per MB.  The article is here

Watch the report below about avoid data roaming charges whilst abroad.  It was taken from the Good Morning Britain programme on ITV earlier this year.

Task 3 – Write a minimum 250-word article to appear in a future edition of the Belper News which warns travellers about the pitfalls of Data Roaming abroad.  Ensure you include practical information to take to avoid them being “caught out”.


To use your class notes and the revision guide to prepare for your upcoming examination.