Fundamentals of Mobile Computing CE00375-2 Network Technology [email protected] Ext 3292, Room C203, Beacon Building

Fundamentals of Mobile Fundamentals of Mobile ComputingComputing

CE00375-2CE00375-2

Network TechnologyNetwork Technology

[email protected]@staffs.ac.uk

Ext 3292, Room C203, Beacon BuildingExt 3292, Room C203, Beacon Building

Mobile ComputingMobile Computing

ContentContent• What is a network?What is a network?• Common Network TypesCommon Network Types• Network TechnologiesNetwork Technologies

Mobile ComputingMobile Computing NetworkNetwork

• Can be anything which needs to communicateCan be anything which needs to communicate Does not need to be electricalDoes not need to be electrical

• A group of friends who talk is a networkA group of friends who talk is a network Each person in the group is receiving and transferring Each person in the group is receiving and transferring

information (Voice)information (Voice) In a group they become a networkIn a group they become a network

• Telephone companies are a good example of a Telephone companies are a good example of a wide scale networkwide scale network

The phone being the device and the phone number being The phone being the device and the phone number being the unique addressthe unique address

Computer NetworkComputer Network• This is the same with a number of devices trying This is the same with a number of devices trying

to communicateto communicate The word devices is used, due to more than just The word devices is used, due to more than just

computers need to communicate i.e. printers, routers etccomputers need to communicate i.e. printers, routers etc

Mobile ComputingMobile Computing UsageUsage

• The increasing use of computers with network The increasing use of computers with network communications has allowed sharing of all communications has allowed sharing of all electronic resourceselectronic resources

Increasingly all devices are usage digital signalsIncreasingly all devices are usage digital signals With these developments it was then straight forward to With these developments it was then straight forward to

move these digital signals on to wires as 1’s and 0’smove these digital signals on to wires as 1’s and 0’s This allows sharing of an increasing number of devicesThis allows sharing of an increasing number of devices

• Beyond the “normal” office communications of files and Beyond the “normal” office communications of files and printersprinters

• Digital Cameras are a recent example where a picture can be Digital Cameras are a recent example where a picture can be placed on the networkplaced on the network

• Telecommunications with the introduction of Voice Over Telecommunications with the introduction of Voice Over Internet Protocol (VOIP)Internet Protocol (VOIP)

• CCTV cameras streaming the pictures to a console for viewingCCTV cameras streaming the pictures to a console for viewing Based on a digital stream that viewing console could be Based on a digital stream that viewing console could be

anywhere on the planetanywhere on the planet

Mobile ComputingMobile Computing To allow communication the devices need to To allow communication the devices need to

be connected via wires or wireless be connected via wires or wireless technologytechnology• This presentation will concentrate on wired as it is This presentation will concentrate on wired as it is

initially easier to followinitially easier to follow In the diagram below the two machines are In the diagram below the two machines are

connected and can send electronic message connected and can send electronic message between thembetween them• There are many ways of connecting devices to There are many ways of connecting devices to

allow them all to communicateallow them all to communicate

Types of NetworkTypes of Network Types of Wired NetworksTypes of Wired Networks

• Three main types for wired network but there are moreThree main types for wired network but there are more Local Area Network (LAN)Local Area Network (LAN)

• High speed networksHigh speed networks• Cheap to install and runCheap to install and run• Short distances between nodesShort distances between nodes• Usual environment, Offices, HomesUsual environment, Offices, Homes

Metropolitan Area Network (MAN)Metropolitan Area Network (MAN)• Medium speed but is increasingMedium speed but is increasing• Covers a large area of a townCovers a large area of a town• This universities network is an example of a MANThis universities network is an example of a MAN

Wide Area Network (WAN)Wide Area Network (WAN)• Slow throughputSlow throughput

Can be increased but at substantial costCan be increased but at substantial cost• Expensive to install and runExpensive to install and run• Networks can cover large areas, like countries or the global!Networks can cover large areas, like countries or the global!• Usual users large scale corporations, governments or the InternetUsual users large scale corporations, governments or the Internet

Types of NetworkTypes of Network Types of NetworksTypes of Networks

• For wireless communications we also haveFor wireless communications we also have Personal Area Network (PAN)Personal Area Network (PAN)

• These are device which transmit in a very small area around These are device which transmit in a very small area around the devicethe device

• Usually distance of 10 metres or lessUsually distance of 10 metres or less Due to the range of these devices Due to the range of these devices

• Common example is Bluetooth used to communicate with a Common example is Bluetooth used to communicate with a mobile phonemobile phone

• Transmissions are between 100 Kbps to 1 MbpsTransmissions are between 100 Kbps to 1 Mbps Usually slow to maximise the battery lifeUsually slow to maximise the battery life

Body Area Networks (BAN)Body Area Networks (BAN)• These operate is close proximity to the userThese operate is close proximity to the user

Very low Kbps but a long battery lifeVery low Kbps but a long battery life Healthcare is given as an example of using this techHealthcare is given as an example of using this tech There is a standards group There is a standards group IEEE 802.15.6, working on a IEEE 802.15.6, working on a

standardstandard http://ieee802.org/15/pub/TG6.htmlhttp://ieee802.org/15/pub/TG6.html

Mobile ComputingMobile Computing The most common communications in the The most common communications in the

LAN networks is EthernetLAN networks is Ethernet• Ethernet allows all of the devices to Ethernet allows all of the devices to

communicate on a single path/wirecommunicate on a single path/wire• All send the signals on this wireAll send the signals on this wire

The intended device will listen and receive the The intended device will listen and receive the data, the other machines ignore itdata, the other machines ignore it

• This is easy for sending a packet A and F, but consider This is easy for sending a packet A and F, but consider what happens when the network gets biggerwhat happens when the network gets bigger

A

F


Open System Interconnection (OSI) LayersOpen System Interconnection (OSI) Layers• This is an agreed standard for protocolsThis is an agreed standard for protocols

All devices use this as a standard, but certain protocols All devices use this as a standard, but certain protocols may combine layers for efficiencymay combine layers for efficiency

• Each layer in OSI can only communicate with the Each layer in OSI can only communicate with the layer above it or below itlayer above it or below it

As the data moves down the stack the protocol from the As the data moves down the stack the protocol from the layer above goes into the data part of the layer below itlayer above goes into the data part of the layer below it

The opposite being true when receiving the packetThe opposite being true when receiving the packet

• Only the layer which added a piece of data can Only the layer which added a piece of data can remove and process on the receiving machineremove and process on the receiving machine


Presentation

Session

Transport

Network

Data Link

Physical

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application

Sender Recipent


Open System Interconnection (OSI) LayersOpen System Interconnection (OSI) LayersLink for discussion of exactly what each layer does:http://webopedia.internet.com/quick_ref/OSI_Layers.asp


OSI LayersOSI Layers• This method allows a common interface for the This method allows a common interface for the

softwaresoftware• The operating system, does not need to know The operating system, does not need to know

what network technology is usedwhat network technology is used It just has to request access to the application layerIt just has to request access to the application layer

• As different technology is used this is changed at As different technology is used this is changed at the correct layerthe correct layer

So from wired Ethernet to ieee 802.11b the technology So from wired Ethernet to ieee 802.11b the technology at layers 1 and 2 will need to be changedat layers 1 and 2 will need to be changed

All other layers will remain the same !All other layers will remain the same !


Each device in a network has to have a Each device in a network has to have a unique addressunique address• This is like the post service to deliver mail you This is like the post service to deliver mail you

need a unique addressneed a unique address In networks this is mostly the Internet In networks this is mostly the Internet

Protocol (IP) addressesProtocol (IP) addresses• Open a command window on your machine and Open a command window on your machine and

type ipconfigtype ipconfig This will show you your unique addressThis will show you your unique address

• Every device attached to the Internet has to have Every device attached to the Internet has to have a unique address for message deliverya unique address for message delivery

There are ways around this, but it is beyond this lecture There are ways around this, but it is beyond this lecture to cover theseto cover these

Mobile ComputingMobile Computing Remember thoughRemember though

• IP addresses are needed by the Internet as the IP addresses are needed by the Internet as the packets get routedpackets get routed

As in they are moved beyond there local connectionAs in they are moved beyond there local connection If this is not true – then they are not routingIf this is not true – then they are not routing

• On this basis a unique address is still needed if there are On this basis a unique address is still needed if there are multiple destinations but you may not need a IP addressmultiple destinations but you may not need a IP address

• A hardware address is used for these communications MACA hardware address is used for these communications MAC• Point to point communicationsPoint to point communications

There is only one device sending one receiving you are There is only one device sending one receiving you are not routing anything only two devices can talk therefore not routing anything only two devices can talk therefore no unique address is requiredno unique address is required

Printer Mobile Phone


IP addressesIP addresses• Example output of ipconfigExample output of ipconfig

So this machines IP address is 194.66.179.218So this machines IP address is 194.66.179.218

Mobile ComputingMobile Computing A common language must be used between A common language must be used between

the devicesthe devices These are protocolsThese are protocols

• Most commonly used is the reliable TCP/IPMost commonly used is the reliable TCP/IP This is used for routing and transfer of the packetsThis is used for routing and transfer of the packets

• Internet Protocol (IP) gives each machine a unique addressInternet Protocol (IP) gives each machine a unique address• Transport Control Protocol (TCP) allows each packet to be Transport Control Protocol (TCP) allows each packet to be

error checked and ensures that the packets arrive at the error checked and ensures that the packets arrive at the correct rate (prevents buffer overflows)correct rate (prevents buffer overflows)

Both TCP and IP have a lot more functionality than this, Both TCP and IP have a lot more functionality than this, but is beyond the required information for this coursebut is beyond the required information for this course

• For layers 1 and 2, different technologies are usedFor layers 1 and 2, different technologies are used Ethernet in the home and officesEthernet in the home and offices Bluetooth in a Portable deviceBluetooth in a Portable device Asynchronous Transfer Mode (ATM) in phone networks or Asynchronous Transfer Mode (ATM) in phone networks or

Multimedia intensive environmentsMultimedia intensive environments


Packet switched vs Packet switched vs Circuit SwitchedCircuit Switched networks networks• Circuit switched is the same as the telephone Circuit switched is the same as the telephone

networknetwork You specify who you wish to talk to and then a circuit is You specify who you wish to talk to and then a circuit is

created between the two locations before created between the two locations before communications are allowedcommunications are allowed

Resources are reserved when the circuit is set upResources are reserved when the circuit is set up• This is good for multimedia which may require defined This is good for multimedia which may require defined

latency and throughput during the transmissionlatency and throughput during the transmission All communication packets travel through this circuitAll communication packets travel through this circuit The packets should always arrive in the sequence sentThe packets should always arrive in the sequence sent


Circuit SwitchedCircuit Switched

192.168.0.2 192.168.0.3

Router

Router

Router

Router

Router

Router

Mobile ComputingMobile Computing Packet switchedPacket switched vs Circuit Switched networks vs Circuit Switched networks

• Packet Switched can be considered as sending a Packet Switched can be considered as sending a letter in the postletter in the post

• An address is put on the envelope and you put the An address is put on the envelope and you put the letter in the post boxletter in the post box

How the letter gets to its destination you do not careHow the letter gets to its destination you do not care No route is worked out first as the best between the sitesNo route is worked out first as the best between the sites The packets can arrive out of sequenceThe packets can arrive out of sequence

• A sequence of packets can all take different routes to the same A sequence of packets can all take different routes to the same destinationdestination

No guarantees can be offered in terms of latency or No guarantees can be offered in terms of latency or throughputthroughput

• This is changing with the newer but not widely used IPv6This is changing with the newer but not widely used IPv6 No delay in communications starting upNo delay in communications starting up No network resources are wasted reserving routes beforeNo network resources are wasted reserving routes before

• Larger amount of devices can use the same connectionsLarger amount of devices can use the same connections When one device is silent, another can communicateWhen one device is silent, another can communicate


Packet Switched DiagramPacket Switched Diagram

192.168.0.2 192.168.0.3

Router

Router

Router

Router

Router

Router

NetworkingNetworking NetworkingNetworking

• So to send a packet of information you needSo to send a packet of information you need Hardware to physically send the packetHardware to physically send the packet

• Ethernet, GSM, ATM, GPRSEthernet, GSM, ATM, GPRS Software to encapsulate the data from the Software to encapsulate the data from the

applicationapplication• TCP/IP is the most commonTCP/IP is the most common

There are other protocols which replace TCP, like RTPThere are other protocols which replace TCP, like RTP• Both the receiving and sending device need to have the Both the receiving and sending device need to have the

correct protocols agreed and ability to receive themcorrect protocols agreed and ability to receive them

NetworkingNetworking NetworkingNetworking

• Using this technology will allow for information to be Using this technology will allow for information to be sent from one person to anothersent from one person to another

• The increasing use of wireless technology has The increasing use of wireless technology has introduced additional considerations likeintroduced additional considerations like

Potential high error rates on packetsPotential high error rates on packets Number of unique IP addressesNumber of unique IP addresses

• Problems with the use of TCP error checking in a wireless Problems with the use of TCP error checking in a wireless environmentenvironment

• Here is a research paper on the subject of TCP across a wireless Here is a research paper on the subject of TCP across a wireless link looking at the issueslink looking at the issues

((http://www.cs.kau.se/~alfs/licmaterial/tcpreport.pdf#search=http://www.cs.kau.se/~alfs/licmaterial/tcpreport.pdf#search=%22tcp%20wireless%22%22tcp%20wireless%22, 2005), 2005)

NetworkingNetworking Usefulness of Mobile ComputingUsefulness of Mobile Computing

• At some stage each device will need attaching into a At some stage each device will need attaching into a wider scale wired networkwider scale wired network

• This allows the transfer of the information from and This allows the transfer of the information from and to the deviceto the device

Returning your emails you have written and placing them Returning your emails you have written and placing them onto the work networkonto the work network

Downloading updates to the software of your phone by using Downloading updates to the software of your phone by using Bluetooth via your home PCBluetooth via your home PC

• So mobile/wireless DO NOT replace wired So mobile/wireless DO NOT replace wired communications they enhance the functionalitycommunications they enhance the functionality

This is what this course is looking at This is what this course is looking at • How the technologies and which ones assist in differing How the technologies and which ones assist in differing

environmentsenvironments• As stated in lecture 1 – no technology is perfect for all uses As stated in lecture 1 – no technology is perfect for all uses

they are designed with an intention of use and they are usually they are designed with an intention of use and they are usually good at thatgood at that

ConclusionConclusion

What we have discussed todayWhat we have discussed today• OSI layerOSI layer• TCP/IPTCP/IP• Packet switched networksPacket switched networks• Circuit switched networksCircuit switched networks• Types of LANTypes of LAN

Documents

Fundamentals of Mobile Computing CE00375-2 Network Technology [email protected] Ext 3292, Room C203, Beacon Building