Transcript Mobile networks

T325: Technologies for digital media
Block III - Part 1: Mobile evolution
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MOBILE EVOLUTION
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Introduction
Mobile and nomadic
What price data?
Mobile generations
Outline
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• 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 fixedline 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
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• 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.
Introduction
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• 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 and Nomadic
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• 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)
Mobile approach
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• 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)
Nomadic approach
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• 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 Nomadic
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Mobile and Nomadic
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• A characteristic feature of the way the mobiletelecommunications 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?
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• 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? (UK) - Activity
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• 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
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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?
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• 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!
What price data?
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• 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
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• 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 generations
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Mobile generations
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T325: Technologies for digital media
Block III - Part 2: Network architecture
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Introduction
Key Terms
Network elements
Evolution from 2G to 3G
Outline
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• 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
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• 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
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• 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.
Introduction
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• 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
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• 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 - Signaling and user traffic
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• There are two basic ways of transmitting
data in a digital network, whether fixed or
mobile:
• Circuit switching
• Packet switching
Key terms - Data transmission
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• 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.
Key terms - Data transmission
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• 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 - Data transmission
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• 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
Key terms - Mobile radio
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• 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.
Key terms - Mobile radio
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• 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.
Key terms - Mobile radio
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• 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 - User equipment
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• 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
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 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 network
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• Radio Access Networks
Network elements
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• The 2G/3G circuit-switched network
Evolution from 2G to 3G
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• 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).
Evolution from 2G to 3G
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• 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 .
Evolution from 2G to 3G
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• 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.
Evolution from 2G to 3G
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• 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 twolevel 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.
Evolution from 2G to 3G
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• 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
Evolution from 2G to 3G
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• 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’.
2.5G - Adding packet switching
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2.5G - Adding packet switching
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• 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.
Migration to 3G
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Migration to 3G
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