Domain Knowledge Mobile Applications Part 1

Posted on Dec 6 2007 - 6:02am by Raj

Available Mobile Applications in today’s Industry:

Wireless access: phone.com
Alerting services: myalert.com
Location services: airflash.com
Intranet applications: imedeon.com
Banking services: macalla.com
Web access: wapforum.com
Mobile agents: tryllian.com

Wireless Networks :
Infrastructure-based networks
cellular systems (base station infrastructure)

Ad hoc networks
useful when infrastructure not available, impractical, or expensive
military applications, rescue, home networking 

Cellular system: GSM :

  • GSM
  1. formerly: Groupe Spéciale Mobile (founded 1982)
  2. now: Global System for Mobile Communication
  • Communication: voice and data services
  • Mobility: International access, access control
  • Service Domains:
  1. bearer services: transfer of data between points
  2. telematic services: telephony, SMS messages
  3. supplementary services: forwarding, conferencing

Architecture of the GSM system

  • GSM is a PLMN (Public Land Mobile Network)
  1. Components
  2. MS (mobile station)
  3. BS (base station)
  4. MSC (mobile switching center)
  5. LR (location register)
  • Subsystems
  1. RSS (radio subsystem): covers all radio aspects
  2. NSS (network and switching subsystem): call forwarding, handover, switching
  3. OSS (operation subsystem): n/w management

Cellular Wireless:

  • Space divided into cells
  • A base station is responsible to communicate with hosts in its cell
  • Mobile hosts can change cells while communicating
  • Hand-off occurs when a mobile host starts communicating via a new base station

Multi-Hop Wireless:

  • May need to traverse multiple links to reach destination
  • Mobility causes route changes

Hand-Off Procedure

  • Each base station periodically transmits beacon
  • Mobile host, on hearing stronger beacon from a new BS, sends it a greeting
  1. changes routing tables to make new BS its default gateway
  2. sends new BS identity of the old BS
  • New BS acknowledges the greeting and begins to route MH’s packets
  • New BS informs old BS
  • Old BS changes routing table, to forward any packets for the MH to the new BS
  • Old BS sends an ack to new BS
  • New BS sends handoff-completion message to MH

Hand-off Issues:

  • Hand-offs may result in temporary loss of route to MH
  1. with non-overlapping cells, it may be a while before the mobile host receives a beacon from the new BS
  • While routes are being reestablished during handoff, MH and old BS may attempt to send packets to each other, resulting in loss of packets

Wireless LANs:

  • Infrared (IrDA) or radio links (Wavelan)
  • Advantages
  1. very flexible within the reception area
  2. Ad-hoc networks possible
  3. (almost) no wiring difficulties
  • Disadvantages
  1. low bandwidth compared to wired networks (1-10 Mbit/s)
  2. many proprietary solutions
  3. Infrastructure v/s ad-hoc networks (802.11)

Bluetooth:

Consortium

  • Ericsson, Intel, IBM, Nokia, Toshiba – many members

Scenarios

  • connection of peripheral devices
  1. loudspeaker, joystick, headset
  • support of ad-hoc networking
  1. small devices, low-cost
  • bridging of networks
  1. e.g., GSM via mobile phone – Bluetooth – laptop

About the Author

Leave A Response