Communications Technology

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  • 1. SM3121 Communications Technology Mark Green School of Creative Media
  • 2. Introduction
    • Most mobile devices need to communicate
    • One of the main reasons for having them
    • Mobile phone isn’t very useful if you can’t call anyone!!
    • There are numerous communications systems that we can use, depend upon range and cost
  • 3. 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
  • 4. 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
  • 5. 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
  • 6. 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
    • Don’t want user to know when they switch from one AP to another, shouldn’t cause a network disconnection
  • 7. 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
  • 8. 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
  • 9. 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
  • 10. 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
  • 11. 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
  • 12. 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
  • 13. 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
  • 14. 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
  • 15. 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
  • 16. 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
  • 17. 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
  • 18. Mobile Phone Network
    • This is a real mess:
      • Too many standards, some poorly thought out and didn’t 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
  • 19. 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
  • 20. 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
  • 21. 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
  • 22. Mobile Phone Network
    • 3G – for HK service introduced in 2004, initially one carrier, now up to three
    • Promises data speeds up to 2Mbps, don’t 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
  • 23. 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
  • 24. 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
  • 25. 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
  • 26. 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
  • 27. 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
  • 28. WAP 1
    • WMLScript – scripting language for WML
    • Sort of like JavaScript, but not quite the same
    • Many phone browsers don’t support it, but some do
    • Somewhat limited scripting language, not clear how useful it is
  • 29. 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
  • 30. 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
  • 31. 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
  • 32. 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
  • 33. 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
  • 34. 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
  • 35. 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
  • 36. 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
  • 37. 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