The Truphone Network:
A Technical Overview
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The Truphone Network: A Technical Overview
This whitepaper is for people interested in understanding the Truphone network and
the benefits it can bring to international businesses from a technical perspective.
The document features a moderate level of technical detail, however all technical terms
are explained in plain English.
© 2014 Truphone Limited. All Rights Reserved. Confidential. 3
1. Executive summary 4
2. Global mobile communication – Situation analysis 6 3. A mobile infrastructure designed for global businesses 7 4. Technical innovation – The Truphone SIM and IMSI broker pair 9
– The status quo 9
– The Truphone approach 9
5. Technical innovation – Smart CLI and Smart Dialling 12
6. Technical scalability 13
7. The Truphone technical community 13
8. Appendix - Glossary of terms 14
Fig 1. High-level schematic of the Truphone network 7
Fig 2. Truphone maximum data speeds vs. a traditional carrier 8
Fig 3. Comparative savings with Truphone 8
Fig 4. ‘International routing, Truphone vs. standard operator’ diagram 9 Fig 5. Routing pathways using a traditional mobile network (US network example) 10
Fig 6. Routing pathways using the Truphone network 10
Fig 7. Multiple international numbers, one SIM card 11
Table of contents
1. Executive summary
1 http://www.truphone.com/ROW/White-Papers/2013-White-papers/Truphone-CCMI-International-Communications/
i. Many modern businesses are hyper-mobile, with diverse networks of suppliers and customers which span international borders.
ii. Independent research from telecoms specialist CCMI1, shows firms across all sectors and of all sizes suffer because mobile network providers do not supply the performance, support or pricing to enable effective international competition.
iii. The reason for this failing is that mobile networks are built with an integrated Radio Access Network (RAN) and core network point of presence (POP) in one country.
iv. These traditional mobile networks provide each subscriber with a single International Mobile Subscriber Identity (IMSI), which is used by foreign networks to recognise the subscriber’s origin and route traffic back through this single POP. Forcing traffic to travel long distances over third party networks slows data speeds, impairs voice quality and escalates costs.
v. Further, these networks are only able to manage the experience of subscribers in their home country. They have only limited ability to locate, monitor, control or improve network performance for subscribers once they travel abroad.
vi. Truphone has built a unique global infrastructure to address these issues. It is a GSMA standards-based system which is distributed across international borders to deliver a high-quality mobile service to businesses across the world. This service leverages a number of innovative features to bring subscribers closer to their international contacts, help them stay productive and provide support through a high-quality international service experience. vii. The network comprises full MVNO arrangements with
leading RAN networks in an expanding group of countries called the Truphone Zone – which currently includes UK, US, Germany, Spain, Poland, Australia, Hong Kong and the Netherlands.
viii. As each MVNO is signed with a tier one carrier partner, Truphone is able to provide a best-in-class service with broad geographic coverage in each marketplace.
ix. These networks are directly connected to six core network points of presence (POPs) across four continents via dedicated IP-based (secure, high-speed data) connections. Each POP features a GPRS Gateway (GGSN) and Media Gateway (MGW). This enables faster data and better quality voice calling by routing traffic more efficiently around the world.
x. By routing traffic to and from 220 countries through the nearest POP, Truphone reduces the physical distance traffic has to travel, thereby reducing latency, improving data speeds and voice quality and reducing cost.
xi. These POPs have ‘user plane’ management – the portion of a core network that carries users’ traffic. They are controlled by the ‘control plane,’ hosted in both London and Amsterdam – by dedicated high-speed IP/VPLS connections. The control plane manages all routing and signalling information, and hosts Truphone’s innovative network functionality and user experience management technology.
xii. Truphone can therefore manage the user experience internationally – so users go from one network to the next without disruption to their network performance or business productivity.
xiii. To facilitate this, Truphone has created two patented innovations – the Truphone SIM, and the International Mobile Subscriber Identity Broker (IMSI Broker). xiv. Each Truphone SIM features multiple International
Mobile Subscriber Identities – one for each country in the Truphone Zone.
xv. When a user arrives in a new Truphone Zone country, the SIM dialogues with the local network and is automatically switched to a local identity by the IMSI Broker. From that point forwards the SIM operates just as a local SIM would – with local data speeds (up to 42Mbps according to network conditions), local call quality (no echoes or fading) and local costs – even out of bundle.
xvi. Within the Truphone Zone, subscribers don’t roam and don’t need to turn on data roaming – they are local. xvii. Subscribers can choose to purchase additional numbers for
any country within the Truphone Zone. These additional, local numbers are always on and connect to a single voicemail – and are all on a single SIM. Subscribers can give contacts in the Zone a local number, so they are always seen as local by those contacts, no matter where they are in the world.
© 2014 Truphone Limited. All Rights Reserved. Confidential. 5 xix. The decision of which phone number to present to
international contacts is managed by a patented innovation called Smart Caller Line Identification (Smart CLI), which automatically selects the correct number to display in every scenario – it requires no user interaction; users simply dial as normal.
xx. By physically abstracting the core network from the RAN network, Truphone can manage, route and rate all traffic in its core as Internet Protocol (IP) traffic. This enables new commercial and technical innovations, as well as seamless integration with other communication networks.
xxi. One such integration already being used is Truphone Mobile Recording, which integrates cloud recording into the Truphone network. This enables businesses to record and store their mobile communications in a secure system. The product is designed to help financial services comply with emerging regulations in the UK, USA, Europe and Asia.
xxii. Several new integrations are already planned, including integration with various enterprise Voice over Internet Protocol (VoIP) calling networks.
xxiii. The network is geography and technology agnostic and has been future-proofed by building it on the principles of extensibility, modularity and reuse. Additional Truphone Zone countries, subscriber volumes and innovations can be integrated without increasing the overall complexity of the system.
i. Modern businesses use a significant volume of mobile data – about 1.5 exabytes by the end of 2013 and growing2. Many companies have decided to host their information in the cloud, thereby enabling their workforce to access mission critical data at the point where it is most valuable; alongside a client or a supplier, for example.
ii. The global marketplace also requires businesses to work with customers, suppliers, partners and colleagues in multiple locations. Statistics from the UN World Trade Organisation3 show that, in 2012, over one billion people travelled internationally; a growing portion of this number can be attributed to international business.
iii. There’s a growing problem with this picture, however. Traditional GSM network systems fail to support global business communications requirements in four key ways – performance, cost, availability and service.
iv. Performance: Using a mobile device abroad is slow and
quality is reduced. Business users abroad typically receive
only a fraction of the data speeds they expect at home. This is because traditional mobile networks were constructed to serve one country at a time. The data businesses rely on to be productive, must travel back and forth between their current location and their home network. Traversing what can be many thousands of miles adds cost and lessens quality.
v. Cost: Calling internationally and roaming is expensive.
Independent research from telecoms analyst CCMI shows 70% of businesses across all sizes and sectors claim they suffer from the high cost of international communications. 45% of these businesses write this off as a cost of
doing business and don’t implement usage policies for international users.
vi. Availability: Users are less available to their
international contacts. When an international prospect
chooses to call a local provider, or an overseas supplier delays providing an important update, businesses suffer. The value of these lost conversations is much greater than the cost of the call – but also harder to track.
vii. As shown in CCMI’s report, businesses which implement international usage policies create a number of other problems. Over 40% of businesses claim to have lost productivity as a result of employees being forced to adopt unproductive or insecure ways of working – and one in five believe they have actually lost business.
viii. The most common policies and their downsides, are shown below:
Cost saving approach Business impact
Requiring staff disable roaming
Inhibits productivity Isolates staff from enterprise tools
Requiring staff use Wi-Fi to
communicate
Inhibits productivity Creates a security risk Issuing multiple
phones or mobile devices
High device costs Impractical for multi-country trips Inconvenient, requires multiple chargers
ix. Service: The single country based network structure of
other operators makes it impossible for them to have visibility into the network performance businesses experience when abroad. If there is a problem, they are unable to identify or fix it quickly.
x. Summary
In a hyper-mobile and globalised economy, businesses which seek competitive advantage need a mobile network designed for their international business patterns. One which enables employees to be as productive abroad as they are at home; which can scale to meet their evolving communications needs and one they can rely on for high-quality service and operational excellence. This document outlines how Truphone meets these requirements from a technical perspective.
2 http://www.cisco.com/c/en/us/solutions/collateral/service-provider/visual-networking-index-vni/white_paper_c11-520862.html 3 http://mkt.unwto.org/en/publication/unwto-tourism-highlights-2013-edition - page 2.
© 2014 Truphone Limited. All Rights Reserved. Confidential. 7
3. A mobile infastructure designed for global business
i. Traditional operators connect customers via one point of presence (POP) in their home country. All usage for that customer then travels via a number of intermediaries, through that single point, regardless of where the customer is physically located. A Dutch customer in the US cannot have their usage sent through the US POP, for example – all usage has to travel first to the Netherlands POP, then back to the customer. This increases cost and reduces quality. ii. See Fig 1. Truphone is different because it has MVNO
arrangements with top-tier Radio Access Network (RAN) operators across the Truphone Zone. The Zone currently includes eight countries – UK, US, Germany, Spain, Poland, Australia, Hong Kong and the Netherlands – and is still expanding.
iii. These international RAN networks connect to at least two of Truphone’s six POPs, which are positioned across four continents. Together, these create a global access network.
iv. Each POP has the ‘user plane’ layer which is geographically decentralized and is the section of the core network concerned with carrying traffic and delivering a better user experience. Truphone operates a GPRS Gateway Support Node (GGSN) to access the internet locally and a Media Gateway (MGW) to route voice traffic intelligently in each POP. This offers significant improvements in call quality and data speeds compared to traditional network set-ups. v. Truphone routes traffic to the POP which is geographically
nearest, rather than a single pre-designated POP. This enables faster data, improved call quality and reduced cost in many circumstances – even outside the Truphone Zone.
Fig 1. High-level schematic of the Truphone network
CONTROL PLANE LAYER Global product catalogue. Centralised control of international network. IP/VPLS CORE NETWORK USER PLANE LAYER Six Points of presence keep traffic local, improve quality, reduce costs. RADIO ACCESS NETWORK LAYER Last mile of connectivity. UK UK USA Germany
Australia Hong Kong
Poland Spain Netherlands Netherlands SOLUTION INTEGRATION LAYER USA New York USA California UK London Netherlands Amsterdam Hong Kong Hong Kong Australia Sydney AM ERIC AS EURO PE ASIA PACIFIC
vi. Using POPs that are physically closer to the user eliminates latency to the point that Truphone can reach speeds of up to 42MB/s in Truphone Zone countries – an order of magnitude faster than other operators can deliver.
vii. Additionally, if one POP goes down due to a major incident then the customer can still be served via other POPs. This distributed infrastructure makes the network more resilient to faults than other networks.
viii. Each POP is connected to the ‘control plane’ of the core network via a redundant IP transport infrastructure. The core is dual-located in London and Amsterdam. ix. By connecting the control plane to radio access networks
around the world, Truphone can see and manage each subscriber in real time, wherever they go. This is a unique, cornerstone capability for Truphone, enabling advanced services and network-level customer service internationally. x. Truphone has also invented and introduced new components
to the core network which were not previously available in the marketplace. These include the ability to change, add and manage International Mobile Subscriber Identities (IMSI) on the fly; update steering and routing pathways – and even amend handset configurations over the air in multiple countries.
xi. When a new country joins the Truphone Zone, a new IMSI is created and all the resulting benefits of being local are automatically applied to each account.
xii. The Truphone SIM is also important, it instructs the local network to route traffic to the appropriate POP. These advances have led to the Truphone SIM being recognised in a report commissioned by UK regulator OFCOM4 as the only SIM-based solution in the world which can manage international identities over the air.
xiii. Keeping traffic within the Truphone Zone and wholly within the Truphone network means Truphone fully controls call quality and provides on-net calls between the Zone countries. All usage within the Zone is rated as local traffic too,
providing a significant cost advantage.
xiv. Truphone’s real-world analysis of data from the past two years of customer and prospect information shows the following typical savings – notwithstanding the increased amount of communication that occurs when users no longer feel obliged to curtail their usage:
xv. Specific technical benefits of Truphone’s approach over other networks include:
• Improved call quality, with no echoes or fading calls • Improved data speeds, with higher throughput and lower
latency
• Improved network quality control, with better service management
• Improved signal resilience, with each Zone country connected to at least two POPs
xvi. Truphone is compliant with all relevant local and international regulations and, as an impressive client roster proves, offers a highly secure and stable network environment.
xvii. Truphone’s unique approach also means the network is a platform for innovation – one which has already led to the integration of value added services, such as cloud recording (which enables Truphone Mobile Recording). Further innovations are already planned for the future.
4 stakeholders.ofcom.org.uk Reprogrammable SIMs
Fig 2. Truphone maximum data speeds vs. a traditional carrier Fig 3. Comparative savings with Truphone
Truphone
US Operator
In US Local speeds; max
throughput 42Mbs
Local speeds; max throughput 42Mbs
In UK Local speeds; max
throughput 42Mbs
Not local speeds; max throughput 6Mbs
Profile
Business impact
Domestic only Equal
Mean international profile Save 40%
© 2014 Truphone Limited. All Rights Reserved. Confidential. 9
4. Technical innovation (1)
The Truphone SIM and IMSI broker pair
i. Subscriber Identity Module (SIM) cards ordinarily have onephone number and one International Mobile Subscriber Identity (IMSI). When visiting a foreign country, the IMSI is used to apply all the appropriate rules for the user’s profile. ii. These rules determine how traffic is routed; with visiting
IMSIs automatically directed over the interconnection pathways back to their home network. This sets up a link between the home network, and the distant user. Each leg of the journey the media (voice, text or SMS) takes is charged at a rate negotiated between the organisations that carry it. When the media travels long distances, it picks up interference, latency and ever more incremental charges. These settlement charges are the root of the high costs associated with roaming.
iii. Truphone has a SIM card which it pairs to an IMSI broker held in the core of the Truphone network. When the subscriber arrives in a new country, the SIM and handset work with the network to apply the correct IMSI for the location from a pre-configured list.
iv. From this point, the network recognises the subscriber as a local user and applies the same rules as it would use for any other local user. Now traffic can be transported locally – which is much more efficient and offers a better connection speed and voice quality.
v. If the user is visiting a country which has recently joined the Truphone Zone, the SIM card may not have the
appropriate IMSI programmed onto it. Here, the IMSI broker automatically adds the IMSI to the SIM card over the air – and the SIM connects to the network as described above. vi. Inside the Truphone Zone, there’s no roaming – you’re at
home in all the Truphone Zone countries. In fact, subscribers can switch off data roaming altogether.
The Truphone approach
Fig 4. ‘International routing, Truphone vs standard operator’ diagram
Visitor Location
Register (VLR) IP Interconnection Border Gateway IP Interconnection IP Transfer Point(ITP) GGSN
A UK USER VISITING THE USA, ACCESSING THE INTERNET
1
2
3
4
5
6
US Europe
TRUPHONE MEDIA SIGNALLING
TRADITIONAL MEDIA & SIGNALLING SINGLE IMSI
3500 Miles (USA – UK) High cost | Slow connection speeds | Low quality data Low cost | Fast connection speeds | High quality data
MULTIPLE IMSI
Fig 5. Routing pathways using a traditional mobile network (US network example)
Fig 6. Routing pathways using the Truphone network
vii. Furthermore, just as domestic-focused operators offer businesses pools of minutes, texts and data which can be shared by employees in their home country; Truphone does exactly the same for users in all the countries of the Truphone Zone. This enables business to not only better predict and manage costs, but also to reduce the unused capacity they would typically accrue through different suppliers around the world.
viii. Outside the Zone, Truphone improves the quality and reduces the cost of making calls, using data and sending SMS’ in two ways. Firstly, a team of specialists continually negotiate rates with carrier partners and roaming partners around the world. Secondly, traffic is routed via the nearest POP. For data, this is via POPs hosted within the Truphone countries; for voice, there are a great number of nodes around the world to further reduce cost and enhance quality.
ix. Fig 5. and Fig 6. show the impact of this network topology or international calls, even outside of the Truphone Zone.
US London to Berlin Amsterdam to Hong Kong Sydney to Melbourne London to Berlin Amsterdam to Hong Kong Sydney to Melbourne
© 2014 Truphone Limited. All Rights Reserved. Confidential. 11
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+44
+31
+49
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+61
i. As already seen, the Truphone SIM card holds multiple identities (IMSI numbers). The mobile network uses this information to treat subscribers as local in the Truphone Zone. In the same way, subscribers can have local phone numbers for Zone countries added to their existing SIM card, so their network of contacts in that country treat them as a local too. This enables them to always be reachable on a local number, so there’s no burden of cost or complexity passed on to international contacts.
ii. However, there are a number of potential problems that multiple numbers could present to a user. Consider the following scenarios:
I’m a UK resident with a UK and US phone number I’m in the UK and call the US
• How do I ensure my US contacts see my US number? I visit the US and call the UK
• How do I ensure my UK contacts see my UK number? A US colleague visits me in the UK
• Which number will they see when I call?
The more countries the subscriber has numbers for, the more complicated these issues could become.
iii. Truphone resolves these issues using a patented technology called Smart CLI (Smart Caller Line Identification). The user has no interaction with Smart CLI; it’s an element of the Intelligent Network which automatically selects the correct number to display in every scenario.
iv. Similarly, being local in many countries could pose problems when dialling. Smart Dialling means a Truphone subscriber can visit the Truphone Zone or roam internationally without worrying about country dialling codes. Users don’t need to prefix numbers with local country codes or adjust home numbers to include international dialling codes – they can just dial as normal. v. For example, a UK subscriber dialling home from various
locations around the world would typically need to remember the prefix for dialling home for each location. So, In Australia they dial 001144, in the USA 01144, in Hong Kong 00144 – it’s confusing. Smart Dialling means they just ‘press call’ and the system takes care of the rest.
The network allows users around the Truphone Zone to reach you on a number that’s local to them.
Example: A Truphone user in London calls a friend in New York and their local US number is displayed to the recipient. Their friend can equally use that US number to reach the caller at local rates, even when the Truphone user isn’t in the US.
Fig 7. Multiple international numbers on a single SIM card
5. Technical innovation (2)
i. In 2011, the UK financial regulator introduced new rules that require some financial traders to record trading-related conversations, text messages, instant messages and emails. They must retain this data for at least 12 months. Until this point banks did not record mobile communication because mobile phones fell outside their technology stack; so communication was invisible and open to abuse. ii. Truphone integrated with a recording provider (which it
subsequently acquired) to enable the capture and storage of all communications within its phone network.
iii. In 2013, the US’s Dodd-Frank Act introduced similar requirements and further technical hurdles. The Dodd-Frank Act applies globally, hence, US bankers in the UK may need to have their communications routed via recording suites in the US.
iv. This causes three problems:
• Firstly, calls become very expensive because they must be treated as two international calls – one to the recording suite and one to the UK.
• Secondly, call quality is significantly reduced because of the extra distance the call data must travel.
• Thirdly, call latency increases so severely as to render many calls unusable.
v. In July 2013 Truphone was granted a worldwide patent for overcoming these issues through a new technique called Call Forking.6
vi. Call Forking allows Truphone’s global mobile network to route calls to a nearby POP before splitting the stream in two directions. Both users continue to experience a high-quality call and the recorded stream is routed back to the recording suite.
vii. Call Forking ensures the same high call quality, with no additional costs and no delays on the line. It helps offer a way for financial institutions to comply with regulations without sacrifices. No other mobile recording platform in the world can do this.
6http://patentscope.wipo.int/search/en/detail.jsf?docId=WO2013072683&recNum=268&docAn=GB2012052825&queryString=a&maxRec=2234741
6. Technical innovation (3)
© 2014 Truphone Limited. All Rights Reserved. Confidential. 13
The Truphone network is designed to meet the international needs of today and tomorrow and is built to scale in three dimensions:
i. Scalable by volume
Truphone enterprise architecture is built on the principle of modularity. In today’s configuration the network can scale to manage many millions of customers. When it becomes appropriate, additional capacity can be added seamlessly.
ii. Scalable by geography
There is no theoretical limit to the number of Truphone Zone countries. The technology stack is designed using internationally recognised standards and this provides two key advantages. Firstly, the network can connect to any GSM operator in the world. Secondly, the transition from one partner to another in a particular country is a straightforward process. This provides Truphone with significant advantages in terms of commercial negotiation.
iii. Scalable for innovation
Truphone has a heritage in bringing ground-breaking technology to market, having created the world’s first voice app for a commercial phone in 2006.
By having complete control of the media sent between different parties across the world, Truphone is able to continually create products that businesses need.
In addition to the Truphone Mobile Recording example already stated, Truphone has planned and tested GSM-to-VoIP integration with its own Internet Calling Application, the Truphone App, and VoIP integration with customers’ enterprise VoIP networks.
i. The Technical Networks group comprises around 100 personnel. The group is based mainly in our Lisbon office, with clusters in London and New Jersey (attached to the New Jersey Institute of Technology). The group also includes a Business Support Services team in London.
ii. The team includes several senior industry leaders, some of whom hold cornerstone worldwide patents in GSM and IP communications technologies. While the group has built a standards-based network, they have also moved the standards forwards to deliver a unique experience.
iii. Managing this network sustainably for the long term requires a high degree of technical training and flexibility. This was one of the reasons Truphone sited its main network office in Lisbon, close to the Instituto Superior Técnico; one of Europe’s leading telecommunications universities.
iv. Recruits are highly educated telecoms engineers who undergo advanced Truphone networks training through the Truphone Networks Academy, run by the heads of the Network Teams - of which there are nine;
v. Truphone Operations Centre – which takes care of all Truphone environments on a 24/7 basis.
vi. Architecture Team – which ensures the network is scalable, the roadmap can be delivered upon, and that the technology evolves in the right way.
vii. Project Management – which keeps all cross-functional groups organised and working to a cohesive plan.
viii. Service Management – which continually tests and iterates upon processes to find incremental improvements.
ix. Development Team – which designs and builds network elements to meet the needs of the business, but which cannot be bought off-the-shelf.
x. Network Performance Group – which monitors and reports on the performance of each network element.
xi. Testing and Quality – which ensures all elements are tested prior to roll-out; this includes documentation and training of all changes and processes.
xii. IP Network Team – which designs, builds and manages the datacentre networks, IP transport between countries and interconnects to external partners.
xiii. Operations Support Services – which ensure we have the right tools to drive efficient operations.
© 2014 Truphone Limited. All Rights Reserved. Confidential. 15
Control Plane The part of the core GSM mobile network responsible for directing mobile telephony traffic, and creating value
added services for mobile network subscribers.
COTS Commercial off-the-shelf: Refers to a product or component that is purchased and used in a largely
un-customised fashion. This strategy ensures suppliers maintain performance of their product in a standardised and efficient way.
GGSN GPRS Gateway Support Node: A core network element in 3G data networks. It allows mobile networks to
send IP traffic to external networks, such as the internet.
GPRS General Packet Radio Service: A standards-based approach which allows mobile devices to send packets of
data between mobile devices and networks. It is the standard for data transmission in 3G networks.
GSMA GSM Association: GSM is the internationally accepted mobile digital telephony standard. The GSM Association
publishes standards and documentation to enable operators to interconnect and work together.
HLR Home Location Register: The main database of permanent information about subscribers in a mobile network.
It details the IMSI, account settings, authorisation codes and access rights for each user.
IMSI International Mobile Subscriber Identity: A 64-bit code which uniquely identifies subscribers. IMSI information
is held within the HLR of the subscriber’s network.
IMSI broker International Mobile Subscriber Identity broker: A Truphone innovation. It recognises when a subscriber has
arrived in a location for which they have a local IMSI and switches the SIM card to that IMSI.
IN Intelligent Network: A component within a core network which enables operators to add value-added services
for subscribers.
ITP IP Transfer Point: A switch that sits in between mobile networks, enabling IP traffic to move from one network
to another.
IP/VPLS Internet Protocol/Virtual Private Local Area Network Services: A dedicated high-speed internet connection
between multiple locations over a fixed, managed network.
MGW Media Gateway: A part of a communications network that can translate digital traffic between different types of
network, for instance from fixed line to mobile. Important for enabling multimedia communications.
MSS Mobile Switching Subsystem: Applies the permissions and access rights to a user’s communications, as dictated
by their account profile.
MVNO Mobile Virtual Network Operator: A mobile operator with dedicated mobile bandwidth which it rents from a
network operator.
OCS Online Charging System: The component of a mobile network that rates call records and associates them with
the products in a user’s profile.
On-Net On-Network: Communications sent between users on the same mobile network. Often provided at very low
cost, in bundle or free of charge to subscribers.
Petabyte About one million gigabytes.
POP Point of Presence: A location through which mobile traffic can be routed to access the core network.
RAN Radio Access Network: The mobile masts that deliver the ‘last mile’ of connectivity between the mobile
network and the device.
SIM card Subscriber Identity Module: An integrated circuit which stores IMSIs and related information about a mobile
subscriber. Used in most mobile devices around the world.
SMS-C Short Message Service – Centre: A network element in the mobile telephone network. Its purpose is to store,
forward, convert and deliver SMS messages.
User Plane The part of the core network responsible for carrying voice and data traffic.
VLR Visitor Location Register: Takes a local copy of the IMSI information from the HLR and instructs the MSS to
route traffic in accordance with the subscriber’s account information.
