Download Mobile Communication

Cellular Networks
1
What is mobility?
Spectrum of mobility, from the network perspective:
no mobility
mobile wireless user,
using same access
point
high mobility
mobile user,
connecting/
disconnecting from
wired network .
mobile user, passing
through multiple access
point while maintaining
ongoing connections
(like cell phone)
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Cellular Network Basics
• There are many types of cellular services.
• Cellular network/telephony is a radio-based technology;
• Radio waves are electromagnetic waves that antennas
propagate
• Most signals are in the 850 MHz, 900 MHz, 1800 MHz, and 1900
MHz frequency bands
Cell phones operate in this frequency range
(logarithmic scale)
3
Components of cellular network architecture
MSC
cell
 connects cells to wide area net
 manages call setup
 handles mobility
 covers geographical
region
 base station (BS)
 mobile users attach to
network through BS
 air-interface: physical
and link layer protocol
between mobile and BS
Mobile
Switching
Center
Public telephone
network, and
Internet
Mobile
Switching
Center
wired network
In a cellular network, a geographical region is divided into service
areas called “cells.”
A cell is represented as a hexagon.
At the center of a cell, is a Base Transceiver Station (BTS or BS) that
serves users within the cell.
Each cell is allocated a certain number of channels operating at a
certain frequency.
Base Station: It is a BS consisting of a transceiver that
receives or transmits signals over the radio interface. It
serves one cell only.
BS controller (BSC): controls one or more BSs.
Mobile switching center (MSC) sets up and maintains
calls made in the network.
An MSC connects the cellular network to the fixed
telephone network infrastructure (i.e., the Public
Switched Telephone Network [PSTN]).
It performs all switching and signaling functions for MSs
located in its area.
Databases
When you subscribe to a mobile telephony
service, your information is stored in a database
called:
a Home Location Register (HLR).
The HLR plays an important role in providing you
with the services offered by your Service Provider.
Databases
Home Location Register (HLR), stores data of participants,
which are reported in an HLR-area
– Semi-permanent data:
• Call number
• identity (International Mobile Subscriber Identity) - IMSI: MCC =
Mobile Country Code (262 for .de) + MNC = Mobile Network Code
• Personal data (name, address, mode of payment)
• Service profile ( call transfer, Roaming-limits etc.)
– Temporary data:
•
•
•
•
MSRN (Mobile Subscriber Roaming Number) (country, net, MSC)
VLR-address, MSC-address
Authentication Sets of AuC
Charge data
The Visitor Location Register (VLR)
VLR is a database in a mobile communications network
associated to a Mobile Switching Centre (MSC).
The VLR contains the exact location of all mobile
subscribers currently present in the service area of the
MSC.
This information is necessary to route a call to the right
base station.
Deleted when the subscriber leaves the service area.
Databases
Visitor Location Register (VLR)
• local database of each MSC with following data:
– IMSI, MSISDN
– service profile
– Accounting information
– TMSI (Temporary Mobile Subscriber Identity) pseudonym for data security
– MSRN
– LAI (Location Area Identity)
– MSC-address, HLR-address
Mobile Communication Networks
Mobile Communication Networks
UMTS (Universal Mobile Telecommunications System):
European Standard for future digital Mobile Radio
Networks
GSM (Global System for Mobile Communications):
worldwide standard for digital, cellular Mobile Radio
Networks
802.11: International standard for Wireless Local
Networks
Bluetooth, Zigbee.
Mobile Communication
Tied to electro-magnetic radio transmission
radio transmission
orbital (satellite)
terrestrial
beam radio
broadcast
radio
cellular
equatorial
orbit
non-equatorial
orbit
non-cellular
Principles:
– Propagation and reception of electro-magnetic waves
– Multiplex
– Satellite orbits/Sight- and overlap areas
GSM: Properties
• Cellular radio network (2nd Generation)
• Digital transmission, data communication up to 9600 Bit/s
• Roaming (mobility between different net operators,
international)
• good transmission quality (error detection and -correction)
• Scalable (large number of participants possible)
• Security mechanisms (authentication, authorization,
encryption)
• Good resource use (frequency and time division multiplexing)
• Integration within ISDN and fixed network
Wireless Local Networks, WLAN
Why do we need Wireless LANs?
Advantages
• No cables
• Flexibility
• Ad-hoc-networks
Disadvantages
• High error vulnerability on the transmission link in comparison
to Standard-LANs
• National restrictions, no international standards at used
frequency bands (Industrial Scientific Medical (ISM)- Band)
• Security, costs
Basic WLAN- structure
Ad-hoc-network:
3 connected infrastructure networks:
STA4
AP
AP
AP - Access Point
AP
STA5
Mobile IP (Internet Protocol)
Internet Protocol (IP)
• IP is the principal communications protocol in the
Internet protocol suite for relaying datagrams across
network boundaries.
• Its routing function enables internetworking, and
essentially establishes the Internet.
• IP has the task of delivering packets from the source
host to the destination host solely based on the IP
addresses in the packet headers.
• The first major version of IP, Internet Protocol
Version 4 (IPv4), is the dominant protocol of the
Internet (IPv6).
Problem definition of classical IP
• Computer mobility in heterogenic networks
• Relocation between different IP-subnets
• Goal: transparent migration and localization,
compatibility to IP, no changes of existing routers
• Idea: introduction of temporary/ actual IP-addresses
• Mapping of permanent to temporary IP-addresses
using localization technique
Requirements to MobileIP
Transparency:
– mobile computer is permanently reachable via its previous
“home-address”
– can change its network access point freely
– can also communicate after coupling/uncoupling
Compatibility:
– mobile computer can also communicate with each “nonmobileIP”-computer
– no changes to existing computer/routers
Security:
– all registering messages must be authenticated
3G Network Architecture
Core Network
Wireless
Access Network
Mobile Access
Router
Programmable
Softswitch
IP
Base Stations
Gateway
Application
Server
IP Intranet
Access
Point
Telephone
Network
IP Intranet
(HLR)
User Profiles &
Authentication
802.11
802.11
3G Air
Interface
Sridhar Iyer
Internet
Wired Access
Access
Point
IIT Bombay
23
What is 802.11?
• A family of wireless LAN (WLAN) specifications
developed by a working group at the Institute of
Electrical and Electronic Engineers (IEEE)
• Defines standard for WLANs using the following four
technologies
–
–
–
–
Frequency Hopping Spread Spectrum (FHSS)
Direct Sequence Spread Spectrum (DSSS)
Infrared (IR)
Orthogonal Frequency Division Multiplexing (OFDM)
• Versions: 802.11a, 802.11b, 802.11g, 802.11e, 802.11f,
802.11i
Performance
• 802.11a maximum rate of 54Mbps in the 5
GHz band
• 802.11b maximum rate of 11Mbps at in the
2.4 GHz spectrum band
• 802.11g is a new standard for data ratesup to
54 Mbps at 2.4 GHz.
Mobile Ad Hoc Networks
Introduction
• Two types of wireless networks:
– Infrastructured network:
• Base stations are the bridges
• A mobile host will communicate with
the nearest base station
• Handoff is taken when a host roams
from one base to another
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– Ad hoc network:
• infrastructureless: no fixed base stations
• without the assistance of base stations for
communication
• Due to transmission range constraint,
–two units need multi-hop routing for
communication
• quickly and unpredictably changing topology
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• MANET = Mobile Ad Hoc Networks
– a set of mobile hosts, each with a transceiver
– no base stations; no fixed network infrastructure
– multi-hop communication
– needs a routing protocol which can handle
changing topology
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• Single-Hop Ad Hoc
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• Multi-hop Ad Hoc
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Typical Ad-Hoc applications
• Personal area networking
– cell phone, laptop, ear phone, wrist watch
• Military environments
– soldiers, tanks, planes
• Civilian environments
– car network
• meeting rooms
– sports stadiums
– boats, small aircraft
• Emergency operations
– search-and-rescue
– policing and fire fighting
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• The Dynamic Host Configuration Protocol (DHCP)
is a standardized network protocol used on
Internet Protocol (IP) networks for dynamically
distributing network configuration parameters,
such as IP addresses for interfaces and services.
• With DHCP, computers request IP addresses and
networking parameters automatically from a
DHCP server, reducing the need for a network
administrator or a user to configure these settings
manually.
How do you contact a mobile friend:
Consider a friend frequently changing
addresses, how do you find her?
I wonder where
Alice moved to?
• search all phone books?
• call her parents?
• expect her to let you know
where he/she is?
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Mobility: approaches
• Let routing handle it: routers advertise permanent address of
mobile-nodes-in-residence via usual routing table exchange.
– routing tables indicate where each mobile located
– no changes to end-systems
• Let end-systems handle it:
– indirect routing: communication from correspondent to
mobile goes through home agent, then forwarded to
remote
– direct routing: correspondent gets foreign address of
mobile, sends directly to mobile
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Mobility: approaches
• Let routing handle it: routers advertise permanent address of
mobile-nodes-in-residencenot
via usual routing table exchange.
scalable
– routing tables indicate
where each mobile located
to millions of
– no changes to end-systems
mobiles
• Let end-systems handle it:
– indirect routing: communication from correspondent
to mobile goes through home agent, then forwarded
to remote
– direct routing: correspondent gets foreign address of
mobile, sends directly to mobile
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GSM: handoff with common MSC
• Handoff goal: route call via
new base station (without
interruption)
• reasons for handoff:
VLR Mobile
Switching
Center
old
routing
old BSS
new
routing
new BSS
– stronger signal to/from new BS
(continuing connectivity, less
battery drain)
– load balance: free up channel
in current BS
GSM: handoff with common MSC
VLR Mobile
Switching
Center 2
4
1
8
old BSS
5
7
3
6
new BSS
1. Old BS informs MSC of impending
handoff, provides list of 1+ new BSs
2. MSC sets up path (allocates resources)
to new BS
3. new BS allocates radio channel for use
by mobile
4. new BS signals MSC, old BS: ready
5. old BS tells mobile: perform handoff to
new BS
6. mobile, new BS signal to activate new
channel
7. mobile signals via new BS to MSC:
handoff complete. MSC reroutes call
8 MSC-old-BS resources released
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GSM: handoff between MSCs
• anchor MSC: first MSC
visited during call
home network
correspondent
Home
MSC
anchor MSC
PSTN
MSC
MSC
MSC
– call remains routed through
anchor MSC
• new MSCs add on to end of
MSC chain as mobile moves
to new MSC
• IS-41 allows optional path
minimization step to
shorten multi-MSC chain
(a) before handoff
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GSM: handoff between MSCs
 anchor MSC: first MSC
visited during cal
home network
correspondent
Home
MSC

call remains routed through
anchor MSC
 new MSCs add on to end of
anchor MSC
PSTN
MSC
MSC
MSC
MSC chain as mobile moves
to new MSC
 IS-41 allows optional path
minimization step to
shorten multi-MSC chain
(b) after handoff
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