SM3121 Communications Technology

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SM3121Communications Technology

• Mark Green
• School of Creative Media

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Introduction

• Most mobile devices need to communicate
• One of the main reasons for having them
• Mobile phone isnt very useful if you cant call
  anyone!!
• There are numerous communications systems that we
  can use, depend upon range and cost

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Introduction

• Technologies
• Infrared very local, but very cheap
• Bluetooth short range (10m), becoming widely
  available, fairly high speed
• Wireless Ethernet medium range (100m or more),
  high speed, high cost
• Mobile phone network long range, low speed, on
  most phones, quite expensive
• Need to know what to use and when

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WiFi

• Wireless Ethernet is the fastest wireless
  technology
• Currently most are 11Mbps, but new ones are at
  54Mbps
• WiFi hardware standard on many new PCs
• Becoming widely available in public places,
  coffee shops, universities, etc

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WiFi

• Two main components
• Access point AP, the interface between wireless
  and wired network, in control of the network
• Client the hardware that runs on the mobile
  device
• A client must connect to an AP before it can use
  the network

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WiFi

• A WiFi network can have a single AP, typical in
  homes
• Could have multiple APs, need to coordinate APs
  as users move around the area
• Dont want user to know when they switch from one
  AP to another, shouldnt cause a network
  disconnection

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WiFi

• Most WiFi systems use 2.4GHz radio band, this is
  divided into approximately 10 channels
• AP and client must agree on channel to use
• Newer clients and software can search channels
  for available APs, older ones not as smart

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WiFi

• This is a broadcast medium
• You are sharing the bandwidth with everyone else
  on the AP
• In public areas will not see full 11Mbps
  bandwidth, could be much less than 1Mbps
• Other clients see what you are sending and
  receiving
• Some attempt at security, but this can easily be
  broken

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WiFi

• Supports most Internet standards
• Can do almost anything you can do with a standard
  PC
• This is not always the case with the other
  communications technologies
• In terms of equipment the most expensive
  technology, but bandwidth usage can be quite cheap

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Hacking

• WiFi can be very insecure, need to know what you
  are doing
• Can have open AP, no security and anyone can
  use it
• Sometimes the default for home systems, easier to
  set up
• Some people look for open systems so they can
  steal bandwidth

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Bluetooth

• Originally developed to replace the wires in
  consumer devices
• Short range, relatively high speed networking
  technology
• Devices can be up to 10m apart, maximum bandwidth
  of about 1Mbps
• Very complicated standard with a wide range of
  optional features

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Bluetooth

• Bluetooth uses the same frequency band as WiFi,
  so they can interfere
• The Bluetooth standard is much more secure than
  WiFi and its easier for a group to share the
  bandwidth
• Now becoming standard on many mobile devices,
  such as mobile phones and PDAs, relatively easy
  to add to PC

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Bluetooth

• Example mobile phone and headset can use
  Bluetooth instead of wires
• Bluetooth is not as complete as WiFi, it may not
  support any of the Internet standards
• Could just be used for file transfers or simple
  data transfers, depending upon the devices used

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Bluetooth

• One of its strengths is discovery
• a Bluetooth device can easily detect other
  devices nearby and automatically connect to them
• Devices can easily move from one network to
  another and the connection is automatic
• More flexible network organization

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Bluetooth

• Since Bluetooth is short range it can be used for
  location based services
• Know that the other device is within 10m, can
  send information that is location dependent
• Send business cards, advertisements, maps,
  tourist information, connect to vending machine
  for payment, etc

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Infrared

• Send information on infrared light signal
• Very cheap technology, medium speed
• Typically IR connections are around 100Kbps, but
  they can be faster
• Need to be relatively close, typically less than
  4m and cannot block light path
• Used in remote controls, laptop computers,
  printers, etc

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Infrared

• Basically viewed as a serial connection, used for
  sending data
• Could be used for Internet and other services,
  but would require considerable programming
• Slowly being replaced by Bluetooth in mobile
  devices, only real advantage is price

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Mobile Phone Network

• This is a real mess
• Too many standards, some poorly thought out and
  didnt work
• Bandwidth is quite low, except for 3G
• Bandwidth is very expensive
• Little thought given to how it would actually be
  used and why people would pay for it
• We will try to make some sense out of this
  situation

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Mobile Phone Network

• Base technology is divided into generations
• 1G the initial analogue mobile phone network,
  no longer used
• Did not support data transmission in the phone
  itself, could use external modem for data, but
  usually limited to 9.6Kbps
• Only voice services

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Mobile Phone Network

• 2G switch to digital, matches land lines which
  are also largely digital
• Several standards, GSM is used in HK, available
  in most of the world
• Supports data transmission, rates up to 9.6Kbps
  in standard systems
• Start of data services, but not a major
  application or selling point

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Mobile Phone Network

• 2.5G basically 2G plus better data services,
  most HK networks are at this level
• Adds GPRS (General Packet Radio Services),
  theoretically capable of 170Kbps
• In HK GPRS seems to be limited to around 40 43
  Kbps, but can get 56Kbps services at considerable
  extra cost

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Mobile Phone Network

• 3G for HK service introduced in 2004, initially
  one carrier, now up to three
• Promises data speeds up to 2Mbps, dont know
  whether this will be available locally
• This high bandwidth may drop the cost of data
  services, currently 0.05 0.10 HK per Kbyte,
  very few unlimited usage plans, but they are very
  expensive

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Mobile Services

• There is a wide range of services built on top of
  the mobile phone network
• Some of these services have been poorly designed,
  others have died very quickly
• One solid standard would greatly help this part
  of the industry
• Convince consumers to buy
• Provide a standard for developers

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WAP

• Wireless Application Protocol, there are two
  versions of this standard WAP 1 and WAP 2
• These standards are quite different, both
  technically and philosophically
• Consumers usually not aware of the difference,
  but its significant for developers
• Market is moving to WAP 2

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WAP 1

• Want to bring web and related services to mobile
  phones
• Set of standards that are parallel to web
  standards, but not the same
• Assumption mobile phones are different, so need
  a different set of standards
• Very big mistake, cannot take content developed
  for web and move to phones

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WAP 1

• WML Wireless Markup Language, similar to HTML,
  but not the same
• Uses some of the same tags, but has different
  structure and new tags
• Can use standard web servers with minor
  modifications, but content must go through a WAP
  gateway to convert to mobile phone format

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WAP 1

• Different browsers interpret WML differently, so
  content can look different on different phones
• Similar to HTML situation in mid 1990s
• Has simple form processing, tables, user
  interaction
• Can use server side scripts to dynamically
  generate content

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WAP 1

• WMLScript scripting language for WML
• Sort of like JavaScript, but not quite the same
• Many phone browsers dont support it, but some do
• Somewhat limited scripting language, not clear
  how useful it is

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WAP 2

• Totally different approach, try to stay as close
  to the web standards as possible
• Use subset of HTML and CSS to maintain
  compatibility with standard web pages
• Can be developed and tested using standard web
  tools
• Should have more consistent appearance and
  behavior across a range of phones

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WAP 2

• Browser based on xHTML, the latest version of
  HTML
• Special mobile profile developed for xHTML, along
  with CSS mobile standard
• A number of new services being developed
• Based on the standard Internet protocols, can add
  email and other services

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Messaging

• One of the most popular mobile phone features
• Started with SMS Short Message Service, widely
  available, on most phones
• Basically a fixed size chunk of data that can be
  exchanged between phones, or with a central
  service
• Can have several formats

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Messaging

• Simplest format is English text, messages
  restricted to 160 characters, some services allow
  longer 190 characters
• Message goes from phone to SMSC short message
  service centre
• Routes message to destination phone when it
  becomes available
• Destination phone displays message on screen

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Messaging

• Most phones support text SMS
• Many phones support the underlying data protocol,
  can have other services
• Can assume at most 140 bytes of data, also a
  header, determines how the data is interpreted by
  phone
• Could use different character sets, for example
  Chinese 70 characters

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Messaging

• Service can send data to phone
• Bookmarks and service information
• Images
• Musical tones (ring tones)
• Business cards
• Anything that can be encoded as binary data can
  be sent to the phone, phone needs to understand
  the data

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Messaging

• SMSC is maintained by phone company, can connect
  to it from a PC or web server
• Messages can be sent to server to perform some
  action (a move in a game, buy some item)
• Server can then send back a response
• Programs downloaded to phone can also do this

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Messaging

• MMS Multimedia Messaging Service uses higher
  bandwidth of 2.5G and 3G networks to send larger
  messages
• Based on SMIL, can be used to send media and
  synchronize its playback
• Media includes images, sound, video and text
  (with formatting information)
• Played when it reaches phone, or stored for later
  viewing

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Messaging

• MMSC serves similar purpose to SMSC, stores
  messages and communicates with phones
• Can send MMS content from a PC or a web server
• Can build your own service on top of MMS for
  games, movie previews or other multimedia services