Wireless Networks

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Wireless Networks

• Cellular telephone system is responsible for
  providing coverage throughout a particular
  territory, called a coverage region or market.
• The interconnection of many such systems defines
  a wireless network over a country or continent.

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(Public Switched Telephone Network) PSTN
Mobile Switching Center (MSC)
Voice and Data Links
Radio Link
BS1
BS2

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Telephone Networks
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PSTN

• Highly integrated communications network that
  connects 70 of worlds people
• Each country is responsible for the regulation of
  PSTN within its borders. Over time, government
  to private transition takes place.

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City
Local Exchange Carrier (LEC)


City
Inter Exchange Carriers (IXC)
City
Local Exchange Carrier (LEC)
Local Access and Transport Area (LATA)
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• Controlled by long distance companies like ATT,
  Sprint etc.
• 1984 Modified Final Judgement (MFJ) gt Break up
  of ATT into 7 major Bell operating systems
  (BOCs) each with its own service region.

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Block Diagram of Local telephone network
IXCA
PBX
Other CO.s
Tandem Switch
Central Office
Home
IXCC
IXCB
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Local telephone network

• In 1980s PSTN was transformed into 2 parallel
  networks one dedicated to user traffic and one
  for signaling traffic common channel signaling.

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Wireless Network structure

• Wireless Network is extremely complex, unlike
  static local, fixed telephone network.
• Wireless network requires an air interface
  between base stations and subscribers for any
  possible user locations, complex propagation
  media, hundreds of base stations, each connected
  to a MSC.

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Wireless Network structure

• MSC must eventually provide connection to PSTN
• LEC, IXCs and other MSCs

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Wireless Networks
SS7
BS
BS
MSC-1 (Home MSC)
MSC-2 (Visitor MSC)
PSTN
HLR VLR
AUC
HLR VLR
AUC
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Wireless network comparison

• Generation- First, second or third
• Modulation techniques (Analog, Digital, Spread
  Spectrum)
• Switching techniques (Circuit switching, packet
  switching)
• Signaling techniques (in-band, CCS)
• Practical systems (USDC, GSM, CDMA)
• Network capabilities

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First Generation Networks

• Analog Technology FM modulation AMPS
  (Advanced Mobile Phone Services) in U.S.
• Mobile Terminals
• Base Stations
• MSCs
• PSTN is separate network from the SS7 signalling
  network

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MSC

• Provides overall System control for each region
• Maintains mobile related information and handoff
  control
• Performs all call processing billing fraud
  detection within the market

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• Base station to Mobile user Analog speech, low
  rate data
• Data transmission between BS user
• RVC RCC
• FVC FCC

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• Base station - MSC 9600 B/S Data Link
• MSC -
• PSTN Landline Trunked lines and Tandem Switch
• Digitized using standard TDM format

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IS 41

• Network protocol standard to allow automatic
  registration of roamers inter operator roaming
• Allow MSCs of different service providers to pass
  information about subscribers to other MSCs on
  demand
• HLR Home Location Register real time user
  list
• VLR Visitor Location Register

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IS 41

• AUC Authentication Center
• Mobile periodically keys up and transmits its
  identity information which allows MSC to
  constantly update its customer list.
• The registration command is sent in over control
  channels at 5-10 minute intervals -MIN Mobile
  Identification Number (Telephone No.)
• ESN Electronic Serial Number

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SS7 Network Services

• Switch controlled services for users
• Call return, call formatting, repeat dialing,
  call block, call tracing, caller ID
• 800 Series - Toll free access to calling party
  paid by service subscriber
• Alternated Billing Service and line information
  database (ADB/LIDB)
• Enables calling party to bill a call to a
  personal number (third party number, calling card
  or collect call) from any number

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Functioning Of SS7

• MSC controls the switching and billing functions
  and interacts with PSTN to transfer between
  global grid and its cluster of base stations
• MSC uses the SS7 signaling network for location
  validation and call delivery to its users which
  are roaming and relies on several information
  databases.

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Functioning Of SS7

• The databases are the home location register
  (HLR), the visitor location register (VLR) and
  the authentication (AUC)

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Registration

• By comparing MIN of roaming subscriber with MINs
  contained in its HLR database, the visited MSC
  quickly identifies roamers.
• MSC sends registration request over the landline
  signaling network to subscribers home MSC.
• Home MSC validates roamers MIN and ESN are
  correct, and returns a customer profile to
  visited MSC. (call waiting, forwarding, 3-way
  calling and international dialing etc.).

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Registration

• Home MSC also updates the HLR by storing MSC ID
  of visited MSC for roamers information.
• The visited MSC, updates its VLR with info from
  home MSC.
• The roamer is then registered in the visited MSC.

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Call Delivery

• Once a roamer is registered in a visited network,
  and if a call is made to a roaming subscriber
  from any telephone in the world, the phone call
  is routed directly to the home MSC.
• The home MSC routes the call immediately to the
  visited network, since the current MSCID is
  stored in HLR

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Call Delivery

• The home MSC is responsible for notifying the
  visited MSC of incoming call and delivers call to
  roamer
• The home MSC first sends a route request to
  visited MSC using signaling network
• The visited MSC returns a temporary directory
  number (TDN) to home MSC dynamically assigned.

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Switching in Networks - Circuit Switching

• MSC dedicates a voice channel connection between
  base station and PSTN for duration of cell phone
  call
• As calls are initiated and completed, different
  radio circuits and dedicated PSTN voice circuits
  are switched in and out to handle traffic

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Switching in Networks - Circuit Switching

• Wireless data networks are not well supported by
  circuit switching, due to their short, bursty
  transmissions gt often, time required to
  establish a circuit exceeds the duration of data
  transmission.
• Circuit switching is best suited for dedicated
  voice-only traffic, or for instances where data
  is continuously sent over long periods of time.

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Switching in Networks - Packet Switching

• Packet Switching (or virtual switching)
  implements connectionless services for large
  number of data users, who remain virtually
  connected to the same physical network.

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Switching in Networks - Packet Switching

• Packet switching breaks each message into smaller
  units for transmission and recovery. When a
  message is broken into packets, a certain amount
  of control information is added to each packet to
  provide source/ destination information and
  identification.

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Packet Structure
Header User Data Trailer

• Header contains source address, destination
  address, packet sequence number, and other
  routing and billing information
• Trailer - contains cyclic redundancy checksum
  which is used for error detection at receiver.

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• Packet switching is also called Packet Radio (PR)
  when used by a wireless link
• Provides excellent channel efficiency for data
  transmission, since the channel is utilized only
  when sending or receiving bursts of information
• X25 is widely used packet radio protocol
  developed by CCITT (ITU-T) International
  Telecommunication Union.

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Second Generation Wireless Networks

• Employ digital modulation and have advanced call
  processing capabilities.
• Examples Global system for Mobile (GSM)
• IS-54 U.S TDMA IS-95 U.S CDMA
• DECT (Digital European Cordless
  Telephone)
• Cordless Telephone (CT2) British
  system

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Second Generation Wireless Networks

• New network architectures that reduce burden of
  MSC - BSC (base station controller) inserted
  between several base stations and MSC
• All systems are digital voice coding and employ
  digital modulation
• Systems employ common channel signaling for
  simultaneous voice and control information

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Second Generation Wireless Networks

• While 1st generation systems were primarily
  designed for voice, second generation networks
  provide paging, facsimile and high data rate
  network access
• Handoff is mobile-controlled-MAHO(Mobile assisted
  Handoff)

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Second Generation Wireless Networks

• The mobile units in this generation perform
  functions like received power reporting, adjacent
  base station scanning, data encoding.

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Common ChannelSignaling (CCS) 1980s

• Digital Technique that provides simultaneous
  transmission of user data, signaling data and
  other related traffic through a network.
• Mobile ltgt BS ltgt MSC ltgtMSC
• Uses out of band signaling channels which
  separate the network data from the user (voice or
  data) on the same channel or using TDM.

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Common ChannelSignaling (CCS) 1980s

• Advantage high speed signaling (50kbps Mbps)
  is not limited by low speed voice data (20bps
  20kbps)
• Substantial increase in the number of users

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Common Channel Signaling (CCS) network
STPs
SMS
SS7
SS7
MSC
SEPs
STPs
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Common Channel Signaling (CCS) network

• CCS network architecture is composed of
  geographically distributed central switching
  offices.
• Service Management system (SMS)
• Switching end points (SEPs)
• Signaling transfer points(STPs)
• Database service management system(DBAS)

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Common Channel Signaling (CCS) network

• SMS - contains all subscriber records, and house
  toll free databases for subscriber use
• DBAS administrative data base that maintains
  service records and investigates fraud throughout
  the network

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Common Channel Signaling (CCS) network

• MSC provides subscriber access to PSTN via the
  SEP
• The SEP controls the switching of messages
  between the CCS network. 2 STPS/SEP --matched
  pair, provides connectivity if one STP fails

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Integrated Services Digital Network (ISDN)

• Complete network framework designed around the
  concept of common channel signaling
• Parallel worldwide network for signaling traffic
  that can be used to either route traffic on PSTN
  or provide new services between network nodes and
  end users.

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Integrated Services Digital Network (ISDN)

• ISDN has 2 types of channels
• Information bearing channels called Bearer
  channels (B channels) 64kbps
• Out of band signaling channels, called data
  channels (D channels)

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Broadband ISDN (B-ISDN)

• End user applications require greater bandwidth
  for computer systems and video imaging
• Based on asynchronous transfer mode (ATM)
  technology which allows packet switching 100Gbps

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Third Generation Wireless Networks

• Future --- will evolve from mature second
  generation systems
• Aim is to provide a single set of standards that
  can meet a wide range of wireless applications,
  and provide universal access around the globe gt
  voice, data and video

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Third Generation Wireless Networks

• Based on B-ISDN to provide access to information
  networks such as Internet and other public and
  private databases
• PCS - Personal Communication System
• PCN - Personal Communication Network
• International Mobile Telecommunication (IMT
  2000)
• Universal Mobile Telecommunication System
  (UMTS)- Europe