T325: Technologies for digital media Block III - Part 1: Mobile evolution Arab Open University – Spring 2012 1

T325: Technologies for digital media Block III - Part 1: Mobile evolution

Arab Open University – Spring 2012 1

MOBILE EVOLUTION


Outline

• Introduction • Mobile and nomadic• What price data?• Mobile generations


Introduction

• Mobile broadband high data rate connection to mobile, or wireless devices

• Consensus about mobile broadband• Always on• High data rate• Data rate > 300 kbps (although considered slow by many

fixed-line broadband users)

• Small latency: Latency is the time taken by data packets to reach their destination (or to make around trip)• Latency < 200 ms (reduced to a few tens of milliseconds by

improvements to the technology)


Introduction

• Devices and services based on wireless broadband to the end user will become ubiquitous.

• Ubiquitous being able to do everything outdoors on mobile, handheld devices that can be done at home or in the office with a static computer and fixed broadband connection. • Example: WWW, checking email, download files, watch

videos, play online games and so on.


Mobile and Nomadic

• There are two broad approaches to providing wireless broadband connections for people on the move. • Mobile approach which evolved from voice-based

telecommunications• Nomadic approach which evolved from wireless local-area

networks (WLANs) for computers

• “mobile data communication” is often used rather loosely to cover both approaches to wireless communication.

• Distinction between mobile and nomadic communication:• Technology• Legacy and business orientation


Mobile approach

• The mobile approach uses cellular wireless networks • Wide geographical coverage is achieved by dividing the

terrain into adjacent cells, each served by a base station. • A cell is typically several kilometers across, but in urban

areas might only be a few hundred meters across.

• The usual business relationship with customers in this model is subscription based with differentiation between the services offered (voice, text and data) variable charging!

• The cellular phone system has developed to allow users to continue phone calls uninterrupted as they pass from cell to cell, possibly at high speed (ex. on a train)


Nomadic approach

• Nomadic approach typically uses Wi-Fi technology, based on the IEEE 802.11 a, b, g and n standards• The geographical area served by a Wi-Fi point is typically

only tens of meters across, and coverage zones are not adjoining.

• Compared to mobile approach, the relationship with customers is looser• Subscriptions are usually available with operators, but these

tend not to be differentiated by services available.

• No Mobility management (by nature of the services provided in nomadic approach)


Mobile and Nomadic

• Looking to the future, these two approaches appear to be converging• Cellular mobile data communication is expected to evolve

through an initiative called Long-Term Evolution (LTE) to networks that will offer higher data rates and shorter latencies.

• The nomadic approach is forecast to develop via WiMAX to a system that offers Wi-Fi-like data rates, but over longer distances than can currently be served by Wi-Fi. • Making WiMAX available over large geographical areas will

require a system of base stations and cells similar to that used in the mobile approach, and a similarly wide slice of electromagnetic spectrum.


Mobile and NomadicArab Open University – Spring 2012 10

What price data?

• A characteristic feature of the way the mobile-telecommunications business model has developed is through a careful differentiation of services, and the development of elaborate pricing structures based on them.

• The difference is not at a pure technical level (bytes being transmitted)

• The services are differentiated in the customer’s mind, then there is scope for pricing them according to their value to the customer.


What price data? (UK) - Activity

• With a particular cellular operator, £10 buys any one of the following: • Up to1GB of mobile broadband data download (which must be used

within 30 days)• Up to 200 minutes of phone calls• Up to 200 short message service (SMS) text messages (maximum 160

characters per message).

• What is the cost per megabyte in each case?• For texting, take each character to be represented by 8 bits. • For the phone calls, take the data rate to be 12.2 kbit/s in each

direction. • For the mobile broadband case, the user can upload and download

data, but, as with asymmetric digital subscriber line(ADSL), the usual form of fixed-line broadband, the upload data rate is much lower than the download. For this calculation, ignore uploaded data.


What price data?

• Data: A gigabyte consists of 1024 MB, so the cost per megabyte is £10 / 1024, which works out as 0.98 p/MB.

• Phone calls: A phone call occupies a channel in each direction. Each channel has a notional rate of 12.2 kbit/s. Hence, in 200 minutes, the amount of data that could be transferred is• 2 x (200 x60) x 12.2 x10^3 bits = 2.928 x108 bits• or, in bytes, 36.6 x106 bytes • Converting to megabytes: 36.6 x10^6 bytes /(1024)2 = 34.9MB • Hence, the cost per megabyte is £10/34.9 = 29 p/MB.

• SMS: Each character is 1 byte, so 200 text messages correspond to 200 x160 bytes = 32 000 bytes, or 32000/1024^2 MB = 0.0305 MB. Hence, the cost is £10/0.0305 per MB = £330 per MB.


What price data?

• VoIP calls made over a mobile broadband link could be significantly cheaper than those made using usual mobile phone protocols and could, therefore, threaten a mobile operator’s major income stream!


Mobile generations

• Cellular mobile communications technology is regarded as having evolved through a number of ‘generations’. • First generation (1G) : analogue cellular telephony.• Second generation (2G): digital transmission.• This was initially primarily a voice-centered technology, but

refinements have been developed to improve data communication.

• Informal ‘intergenerational’ descriptors, such as 2.5G, have arisen for developments that are not considered radical enough to count as a new generation. • 2.5G = GSM + GPRS (General Packet Radio Service)• Low data rate: around 50 – 70 kbit/s

• 2.75G: further adaptations of 2G to give higher data rates.


Mobile generations

• Mobile broadband begins with 3G • Regarded as marking a break with 2G, and potentially

giving data rates that can reasonably be described as ‘broadband’ (for example: 384 kbps )

• Note: The terms 1G, 2G and 3G do not refer to any particular technology.• The technologies used for 2G, for example, can differ -

especially between the USA and the rest of the world. • Even the adoption of similar technologies does not

guarantee compatibility.

• The implementation of particular technologies is generally decided by standardization bodies, or is a proprietary (commercial decision).


Mobile generationsArab Open University – Spring 2012 17

T325: Technologies for digital media Block III - Part 2: Network architecture


Outline

• Introduction • Key Terms• Network elements • Evolution from 2G to 3G


Introduction

• Network architecture: the way in which the required functions of the network are allocated to distinct physical network elements, sometimes referred to as nodes.

• Nodes can be geographically separated (example BS and BSC)

• Architectural divisions of a mobile network• Access network• Core network• User equipment


Introduction

• Access network• Gives users access to the core network• Consists of:• base stations • their associated wireless technologies• base station control nodes (are the elements that

immediately control the base stations)


Introduction

• Core network• largely a fixed communication network. • Among other functions: it authenticates users, routes calls

and data, works out billing charges, etc. • The core network employs many communication

technologies, including wire, fibre and sometimes fixed microwave links.

• User equipment (UE)• consists of the mobile devices used by subscribers.


Key terms - Signaling and user traffic

• For any network, mobile or fixed, it is usual to consider the structure and operation of the network from two perspectives: Signaling and user traffic.

• Signaling refers to the protocols used to set up the services for the user and to manage the network. • Examples of this could be the message sequence required to

set up a voice call .

• The view of the network which describes the Signaling protocols is referred to as the control plane


Key terms - Signaling and user traffic

• The other aspect of the network is the user traffic• Examples: voice call data, video streaming data, discrete

downloaded data blocks, etc.

• The view of the network which describes the protocols for transmission of the user traffic is referred to as the user plane.


Key terms - Data transmission

• There are two basic ways of transmitting data in a digital network, whether fixed or mobile:• Circuit switching • Packet switching



• Circuit switching • derives its name from earlier telephone technology, in which

a conducting circuit was established between caller and person called for the duration of a call.

• The participants had exclusive use of this resource for the duration of the call

• Packet switching• Enables the underlying communication resource (such as a

cable, fiber or wireless link) to be shared statistically among several users in such a way that each user has a significant possibility of access to the resource, and no one has exclusive use of it.

• Users’ data is divided into packets, and the network is structured as a series of lines interconnected by routers.



• Nowadays, telecommunications networks carry different kinds of data, not just voice, and use packet switching as well as circuit switching.

• The concept of a ‘call’ has accordingly been generalized to a session, which is an organized exchange of data between two or more users which can be of many kinds (for example, a video link), but includes a straightforward telephone conversation.

• The session initiation protocol (SIP) is a way of setting up and managing sessions that is becoming widely used .


Key terms - Mobile radio

• Users can be regarded as mobile or nomadic. • Networks can be divided into two classes depending on

whether or not the architecture supports continuous sessions with the mobile device as it moves around.

• Nomadic networks• Mobile networks



• Nomadic networks• Allow the user to log on to the network whenever they are within radio

coverage of the network. • If the user subsequently moves to the coverage area of a different radio

transmitter, the session is terminated and the user has to log on again. • Example: network based on Wi-Fi or fixed WiMAX

• Mobile networks• maintain a continuous session as the user moves around, by handover

of the session between one cell and the next.• Mobile networks need to be able to track the location of the user’s

mobile, in order to be able to send data to the mobile and to set up incoming services.

• This function is known as mobility management. • The ability to validate a mobile device requesting a connection is

known as authentication.



• The downlink refers to transmissions from the base station to the mobile, and the uplink refers to transmissions from the mobile to the base station.

• Duplexing refers to the means of separating the transmissions in either direction to prevent them interfering with each other.

• Two principal duplexing techniques are used in mobile and nomadic networks.• Frequency-Division Duplexing (FDD): the uplink and

downlink signals are transmitted simultaneously, but on different frequencies.

• Time-Division Duplexing (TDD): the signals share the same frequency but are transmitted at different times.


Network elements - User equipment

• The user equipment (UE) is another name for mobile devices such as mobile phones, PDAs and data cards (built-in or external) for laptop computers

• User equipment comprises two principal components:• The phone, PDA or data card • Removable smart card known as the subscriber identity

module (SIM) card.

• In 3G, the SIM card is called the UMTS SIM (USIM) card.


Network elements

• The mobile device contains all the circuitry and software required to interface to a mobile network and to provide the interface to the user.

• The SIM card contains:• the key user information required to enable the mobile

device to authenticate itself to the network and• Other user information, such as contact lists and text

messages received from other users.• It also stores a four-digit personal identification number

which can be used to prevent unauthorized users from accessing the personal information stored on the SIM card

• Why to separate the functions of the SIM card from the mobile phone?


Network elements - Radio access network

The user equipment communicates with the radio base stations over the radio interface (air interface), using a frequency band exclusively allocated to a particular operator.

In the 2G standards the base stations are known as base transceiver stations (BTSs), whereas in the 3G standards the base stations are known as Node Bs.

In 3G, the radio access network is also referred to as the UMTS radio access network (UTRAN).

In both 2G and 3G networks, the base stations are controlled by another element In 2G: the base station controller (BSC) In 3G: the radio network controller (RNC)


Network elements

• Radio Access Networks



Evolution from 2G to 3G

• The 2G/3G circuit-switched network

36


• In the 2G standards• User Equipment: UE is known as the mobile station (MS).• Access network: base transceiver station (BTS) and the

base station controller (BSC). • Core network• Each mobile switching centre (MSC) either switches

calls between users within the area covered by its BSCs, or routes them to other MSCs for onward routing within or outside the network.

• One or more of the MSCs are used to interface to fixed networks, including interconnections with other mobile networks, and this role is called the gateway MSC (GMSC).

Arab Open University – Spring 2012


• Below the MSCs we can see three key support elements. The equipment identity register (EIR) is used to track the identity of physical mobile devices, and can be used to bar access by stolen devices.

• The home location register (HLR) holds the master record of each mobile user and is used by the other network elements to check whether access to a given service should be granted or not.

• The authentication centre (AuC) is used to store the keys required for authentication .


37

38


• The MSC includes another function called the visitor location register (VLR), which works together with the HLR to maintain a record of the current location of each mobile device.

• In order to set up incoming calls to mobiles, the network needs to know the location of the mobile down to the individual cell level.

• Issue: What is the frequency of cell location update? • Continuous cell location update high levels of signaling

traffic drain the mobile’s battery.


39


• Mobile location update • The network is divided up into larger areas known as

location areas (LAs)• When the mobile has no calls in progress, it reports only on

a change of location area, not on a change of cell.• To minimize Signaling traffic on the core network, a two-

level process is used to track the location of the mobile.• The HLR contains the user details plus the address of the VLR

in whose area the mobile is currently situated.• The VLR contains a record of the location area and the last

known cell location of the mobile.

• Paging: To contact the mobile, it is then necessary to send out a message to all the cells in the location area inviting the mobile to reply.



• Location area size: too small or too large? • too small a size leads to high signaling traffic• too large a size results in an unacceptable level of paging

traffic, given that paging messages have to be sent to all the cells in the location area whether the mobile is there or not.

• There is a trade-off to be made in location area size


41

2.5G - Adding packet switching

• Adds the ability to transport IP packets across the GSM radio network through the addition of two new elements to the core network• Serving GPRS Support Node (SGSN) • Gateway GPRS Support Node (GGSN).

• The result was the general packet radio service (GPRS), also often referred to as ‘2.5G’.


42

2.5G - Adding packet switchingArab Open University – Spring 2012

43

Migration to 3G

• Required new mobile devices, known in the 3G standards as the user equipment (UE), and the addition of the 3G radio access network.

• The Node B and the radio network controller provide the same functions in 3G as the BTS and the BSC respectively provide in 2G.

• Unlike the base station controllers, the radio network controllers have a peer-to-peer interface, which means they can communicate directly with each other.

• This interface can be used to coordinate handovers between Node Bs, reducing the workload on the MSC or SGSN.


44

Migration to 3G Arab Open University – Spring 2012

Documents

T325: Technologies for digital media Block III - Part 1: Mobile evolution Arab Open University – Spring 2012 1