Fundamentals of Mobile Computing CE003752

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Fundamentals of Mobile ComputingCE00375-2

• Network Technology
• j.c.champion_at_staffs.ac.uk
• Ext 3292, Room C203, Beacon Building

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Mobile Computing

• Content
• What is a network?
• Common Network Types
• Network Technologies

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Mobile Computing

• Network
• Can be anything which needs to communicate
• Does not need to be electrical
• A group of friends who talk is a network
• Each person in the group is receiving and
  transferring information (Voice)
• In a group they become a network
• Telephone companies are a good example of a wide
  scale network
• The phone being the device and the phone number
  being the unique address
• Computer Network
• This is the same with a number of devices trying
  to communicate
• The word devices is used, due to more than just
  computers need to communicate i.e. printers,
  routers etc

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Mobile Computing

• Usage
• The increasing use of computers with network
  communications has allowed sharing of all
  electronic resources
• Increasingly all devices are usage digital
  signals
• With these developments it was then straight
  forward to move these digital signals on to wires
  as 1s and 0s
• This allows sharing of an increasing number of
  devices
• Beyond the normal office communications of
  files and printers
• Digital Cameras are a recent example where a
  picture can be placed on the network
• Telecommunications with the introduction of Voice
  Over Internet Protocol (VOIP)
• CCTV cameras streaming the pictures to a console
  for viewing
• Based on a digital stream that viewing console
  could be anywhere on the planet

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Mobile Computing

• To allow communication the devices need to be
  connected via wires or wireless technology
• This presentation will concentrate on wired as it
  is initially easier to follow
• In the diagram below the two machines are
  connected and can send electronic message between
  them
• There are many ways of connecting devices to
  allow them all to communicate

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Types of Network

• Types of Wired Networks
• Three main types for wired network but there are
  more
• Local Area Network (LAN)
• High speed networks
• Cheap to install and run
• Short distances between nodes
• Usual environment, Offices, Homes
• Metropolitan Area Network (MAN)
• Medium speed but is increasing
• Covers a large area of a town
• This universities network is an example of a MAN
• Wide Area Network (WAN)
• Slow throughput
• Can be increased but at substantial cost
• Expensive to install and run
• Networks can cover large areas, like countries or
  the global!
• Usual users large scale corporations, governments
  or the Internet

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Types of Network

• Types of Networks
• For wireless communications we also have
• Personal Area Network (PAN)
• These are device which transmit in a very small
  area around the device
• Usually distance of 10 metres or less
• Due to the range of these devices
• Common example is Bluetooth used to communicate
  with a mobile phone
• Transmissions are between 100 Kbps to 1 Mbps
• Usually slow to maximise the battery life
• Body Area Networks (BAN)
• These operate is close proximity to the user
• Very low Kbps but a long battery life
• Healthcare is given as an example of using this
  tech
• There is a standards group IEEE 802.15.6, working
  on a standard
• http//ieee802.org/15/pub/TG6.html

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Mobile Computing

• The most common communications in the LAN
  networks is Ethernet
• Ethernet allows all of the devices to communicate
  on a single path/wire
• All send the signals on this wire
• The intended device will listen and receive the
  data, the other machines ignore it
• This is easy for sending a packet A and F, but
  consider what happens when the network gets bigger

F
A
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Mobile Computing

• Open System Interconnection (OSI) Layers
• This is an agreed standard for protocols
• All devices use this as a standard, but certain
  protocols may combine layers for efficiency
• Each layer in OSI can only communicate with the
  layer above it or below it
• As the data moves down the stack the protocol
  from the layer above goes into the data part of
  the layer below it
• The opposite being true when receiving the packet
• Only the layer which added a piece of data can
  remove and process on the receiving machine

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Mobile Computing
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Mobile Computing

• Open System Interconnection (OSI) Layers

Link for discussion of exactly what each layer
does http//webopedia.internet.com/quick_ref/OSI_
Layers.asp
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Mobile Computing

• OSI Layers
• This method allows a common interface for the
  software
• The operating system, does not need to know what
  network technology is used
• It just has to request access to the application
  layer
• As different technology is used this is changed
  at the correct layer
• So from wired Ethernet to ieee 802.11b the
  technology at layers 1 and 2 will need to be
  changed
• All other layers will remain the same !

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Mobile Computing

• Each device in a network has to have a unique
  address
• This is like the post service to deliver mail you
  need a unique address
• In networks this is mostly the Internet Protocol
  (IP) addresses
• Open a command window on your machine and type
  ipconfig
• This will show you your unique address
• Every device attached to the Internet has to have
  a unique address for message delivery
• There are ways around this, but it is beyond this
  lecture to cover these

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Mobile Computing

• Remember though
• IP addresses are needed by the Internet as the
  packets get routed
• As in they are moved beyond there local
  connection
• If this is not true then they are not routing
• On this basis a unique address is still needed if
  there are multiple destinations but you may not
  need a IP address
• A hardware address is used for these
  communications MAC
• Point to point communications
• There is only one device sending one receiving
  you are not routing anything only two devices can
  talk therefore no unique address is required

Mobile Phone
Printer
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Mobile Computing

• IP addresses
• Example output of ipconfig
• So this machines IP address is 194.66.179.218

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Mobile Computing

• A common language must be used between the
  devices
• These are protocols
• Most commonly used is the reliable TCP/IP
• This is used for routing and transfer of the
  packets
• Internet Protocol (IP) gives each machine a
  unique address
• Transport Control Protocol (TCP) allows each
  packet to be error checked and ensures that the
  packets arrive at the correct rate (prevents
  buffer overflows)
• Both TCP and IP have a lot more functionality
  than this, but is beyond the required information
  for this course
• For layers 1 and 2, different technologies are
  used
• Ethernet in the home and offices
• Bluetooth in a Portable device
• Asynchronous Transfer Mode (ATM) in phone
  networks or Multimedia intensive environments

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Mobile Computing

• Packet switched vs Circuit Switched networks
• Circuit switched is the same as the telephone
  network
• You specify who you wish to talk to and then a
  circuit is created between the two locations
  before communications are allowed
• Resources are reserved when the circuit is set up
• This is good for multimedia which may require
  defined latency and throughput during the
  transmission
• All communication packets travel through this
  circuit
• The packets should always arrive in the sequence
  sent

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Mobile Computing

• Circuit Switched

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Mobile Computing

• Packet switched vs Circuit Switched networks
• Packet Switched can be considered as sending a
  letter in the post
• An address is put on the envelope and you put the
  letter in the post box
• How the letter gets to its destination you do not
  care
• No route is worked out first as the best between
  the sites
• The packets can arrive out of sequence
• A sequence of packets can all take different
  routes to the same destination
• No guarantees can be offered in terms of latency
  or throughput
• This is changing with the newer but not widely
  used IPv6
• No delay in communications starting up
• No network resources are wasted reserving routes
  before
• Larger amount of devices can use the same
  connections
• When one device is silent, another can communicate

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Mobile Computing

• Packet Switched Diagram

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Networking

• Networking
• So to send a packet of information you need
• Hardware to physically send the packet
• Ethernet, GSM, ATM, GPRS
• Software to encapsulate the data from the
  application
• TCP/IP is the most common
• There are other protocols which replace TCP, like
  RTP
• Both the receiving and sending device need to
  have the correct protocols agreed and ability to
  receive them

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Networking

• Networking
• Using this technology will allow for information
  to be sent from one person to another
• The increasing use of wireless technology has
  introduced additional considerations like
• Potential high error rates on packets
• Number of unique IP addresses
• Problems with the use of TCP error checking in a
  wireless environment
• Here is a research paper on the subject of TCP
  across a wireless link looking at the issues
• (http//www.cs.kau.se/alfs/licmaterial/tcpreport.
  pdfsearch22tcp20wireless22, 2005)

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Networking

• Usefulness of Mobile Computing
• At some stage each device will need attaching
  into a wider scale wired network
• This allows the transfer of the information from
  and to the device
• Returning your emails you have written and
  placing them onto the work network
• Downloading updates to the software of your phone
  by using Bluetooth via your home PC
• So mobile/wireless DO NOT replace wired
  communications they enhance the functionality
• This is what this course is looking at
• How the technologies and which ones assist in
  differing environments
• As stated in lecture 1 no technology is perfect
  for all uses they are designed with an intention
  of use and they are usually good at that

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Conclusion

• What we have discussed today
• OSI layer
• TCP/IP
• Packet switched networks
• Circuit switched networks
• Types of LAN