Transcript 2512 - Protocols

Types of Broadband
Learning Objectives:
By the end of this topic you should be able to:
 compare different types of broadband connection and
give suitable situations where the use of each would be
appropriate
Types of Broadband connection
Need to be able to describe:
•
•
•
•
asymmetric digital subscriber line (ADSL),
cable,
wireless,
leased line,
• satellite
Hunter’s Hints:
• Where am I?
• What am I doing?
• How fast do I need to do it?
Dial up Internet
• legacy Internet connection method
– 1 in 6 households still using dial-up Internet access (in 2011)!
• uses telephone line
• modem required to connect to computer
– converts digital signals into analogue sounds (and vice versa)
Dial up Internet
Dial up Internet
• legacy Internet connection method
– 1 in 6 households still using dial-up Internet access (in 2011)!
• uses telephone line
• modem required to connect computer to telephone line
– converts digital signals into analogue sounds (and vice versa)
• 56kbps theoretical maximum bandwidth
– 1% of current UK average broadband speed (i.e. 100x slower)
ADSL Broadband
• most common domestic broadband connection
‒ 99% UK coverage
• uses existing copper telephone line
– telephone can be used at the same time as Internet connection
 requires ADSL filters to be installed in ‘phone sockets
• router required to connect ADSL to computer
– router is often also a wireless access point
• 24Mbps theoretical maximum bandwidth
• average UK broadband speed 6 Mbps (in 2011)
– bandwidth variation due to:
• distance from telephone exchange,
• age/quality of telephone line,
• contention ratio….
ADSL Broadband
Merits:
• uses existing telephone line
– no extra installation of cable is required = no extra cost
– popular for domestic installation
• coverage: 99% availability in UK
• ADSL provides an ‘always on' Internet access
– telephone can be used at the same time
ADSL Broadband
Drawbacks:
• needs to be connected to a telephone exchange within a
workable distance (~6km)
– not possible for remote locations
Bandwidth v Distance from exchange
ADSL Bandwidth v Distance
30
25
Bandwidth (Mbps)
20
15
10
5
0
0
1
2
3
4
Distance from Exchange (km)
5
6
ADSL Broadband
Drawbacks:
• needs to be connected to a telephone exchange within a
workable distance (~6km)
– not possible for remote locations
• Asymmetric: upstream bandwidth is less than downstream
– takes longer to upload an image than to download
– takes longer send an email with attachments than to receive
• high contention ratio
– available bandwidth shared between connected users
– can be up to 50:1 ratio (more users = less bandwidth per user)
• electrical interference on the telephone line
– other devices connected to the telephone line
• fax machines, cordless ‘phones
Leased Line
• connection exists between two locations only
– customer & ISP
• a dedicated bandwidth service
– delivered over a leased fibre connection
• preferred by large businesses and organisations
– providing access into their own networks using an extranet
Leased Line
Merits:
• there are no contention ratios
– direct connection between one router and another router
– this means the bandwidth is guaranteed
• leased lines are symmetric (DSL),
– same amount of upstream bandwidth available as downstream bandwidth
• unlike ADSL
– essential for streaming media content providers (TV, radio, music)
• secure & private network connection
– dedicated exclusively to the customer
Drawbacks:
• the line is installed especially for an organisation
– makes leased lines very expensive
Wireless Broadband
• aka: mobile broadband
• 3G data on mobile telephone networks
• can use laptop, mobile ‘phone, tablet computer
• access wireless broadband by connecting computer:
– through a mobile ‘phone using Bluetooth (‘tethering’),
 alternatively use a USB cable,
– using a USB modem stick (dongle).
Wireless Broadband
Merits:
• can be online while not at home or when travelling
• can get broadband in areas where there are no fixed
line connections
• theoretical bandwidth of 14Mbps
– most providers claiming up to 6Mbps
 UK average bandwidth 1.5Mbps (2011)
• relatively high bandwidth Internet connections
– potentially fast downloading of images, apps …..
– sufficient bandwidth to enable video calls
Wireless Broadband
Drawbacks:
• needs a good 3G signal to be available
– not all areas have 3G access
• bandwidth currently often very low
– slow access to data & downloads
– ‘jerky’ video calls & media streaming
• can be expensive compared to ADSL:
– ~£1 per GB of data for limited contract
– cost of additional usage can be high (especially abroad)
• download/usage limits can be restrictive
– not designed for heavy users
Cable Broadband
• main infrastructure uses fibre-optic links
– coaxial copper cable connects a local cabinet to the home
• some movement towards Fibre to the Home (FTTH)
Cable Broadband
Cable Broadband
Cable Broadband
Cable Broadband
• main infrastructure uses fibre-optic links
– to connect ISP to local distribution cabinet (‘green box’)
• copper cable connects a local cabinet to the home
– some movement towards Fibre to the Home (FTTH)
• Internet access often provided by cable TV companies
– e.g. Virgin Media (cables already installed)
• higher bandwidths than ADSL are possible
– up to 100 Mbps available for UK home users.
 theoretical bandwidth of Gbps (1Gbps = 1000Mbps)
 ‘future-proofing’ bandwidth provision?
Satellite Broadband
Satellite Broadband
Satellite Broadband
Satellite Broadband
• uses satellite dish to transmit & receive data
– to/from telecommunications satellites in orbit above the Earth
• satellites are in geostationary orbit
– move at the same speed as Earth rotation
– always over the same point of the Earth
• data transmitted & received using microwaves
Satellite Broadband
Merits:
• can be used in remote areas
– where physical or wireless connections are not available
Satellite Broadband
Drawbacks:
• cost of hardware & installation is expensive
– + subscription £50pm for 10Mbps+ data cap limits
• a delay between data being sent and received (0.7s)
– problem for real-time communication:
• video conferencing, remote surgery …
• high contention ratios
– decrease in available bandwidth at peak times
• asymmetric
– downstream has a higher bandwidth than upstream
 uploads much slower than downloads (like ADSL)
Bandwidth
Communications
Bandwidth
Broadband (ADSL)
up to 24Mbps
Cable
up to 100Mbps
Wireless (3G)
7Mbps
Satellite
10Mbps
Leased Line (DSL)
up to 1Gbps
June 2011 Q9
All members of a Mountain Rescue Team based in a
town in the Peak District team are volunteers, living
across a wide area including some remote locations.
Not all team members have broadband Internet access.
A member of the team, who lives in a remote location,
has been offered a broadband internet connection.
Compare ADSL to a satellite connection for accessing
the Internet.
[3]
Mark Scheme
availability
ADSL requires the user needs to be within a certain distance from a compatible local exchange
whereas a satellite connection can be used in remote areas where physical and wireless
connections are not available
connection type
ADSL is uses copper cable to connect whereas a satellite connection relies upon microwaves
bandwidth
ADSL offers sufficient bandwidth (Mb/s) to allow more data to be sent at the same time meaning
large volumes of data can be handled at once whereas a satellite connection has a much lower
bandwidth (Kb/s) meaning lower volumes of data can be sent at any one time
multimedia
ADSL can handle simultaneous data and audio streaming whereas a satellite connection would
mean multimedia files suffer delays and stoppages during their presentation on screen
symmetry
both ADSL and satellite are asymmetric meaning downstream has a much higher bandwidth than
upstream