Broadband Communication Chapter 3

This presentation will: Help you understand different types of broadband connections including: ADSL Cable Wireless Leased Line Satellite You should be able to make comparisons between the different types of connection.

Introduction There are many different ways to connect to the internet. Different methods have their own advantages and disadvantages. It is therefore important to be able to compare them so that you can choose which is the most appropriate for a given situation.

ADSL (Asymmetric Digital Subscriber Line) This type of connection sends data down existing copper wires at different frequencies. Most of the data transmitted is downloaded so more frequencies are provided for the downstream than the upstream. This graph shows the frequencies used to transmit data. PSTN: Public Switched Telephone Network (The frequency you use to talk to others!) Frequency Diagram: http://services.exeter.ac.uk/cmit/modules/the_internet/figures/500px-ADSL_frequency_plan.svg.png

ADSL (Asymmetric Digital Subscriber Line) As you can see from this speed test… The download speed is far greater than the upload speed. ADSL connections are asymmetric because they have different upload and download speeds. Companies who host websites usually request to have a higher upload speed so web pages can be downloaded faster.

ADSL (Asymmetric Digital Subscriber Line) ADSL connections provide the ‘always on’ service. When people used dial up modems to connect to the internet they had to make sure no one was using the telephone. If someone tried to ring they would get an engaged sound! If someone picked up the telephone whilst you were connected to the internet your connection could drop. ADSL connections do not suffer from the same problems. Here is a link to a ‘mock’ video which highlights some of the issues I was having when I was in year 6! http://www.youtube.com/watch?v=JMLH_QyPTYM

ADSL (Asymmetric Digital Subscriber Line) The bandwidth of ADSL connections can be affected by: The distance your house is from the telephone exchange. Local AM frequencies can cause some interference…thus reducing the number of usable frequencies thus reducing the bandwidth. Other devices connected to the same telephone cable (e.g. fax machines). Electrical interference on the copper wire. The number of sockets in your house can also have an affect on your bandwidth.

ADSL (Asymmetric Digital Subscriber Line) ADSL is mainly used in households. Large companies tend to need higher upload speeds. ADSL also has the disadvantage being that the bandwidth is shared. This means that during busy periods bandwidth actually reduces.

Cable Broadband connections can be provided by television companies. The data is transmitted via fibre-optic cables resulting in higher bandwidth being achieved. Because of the nature of the service, the upstream/downstream ratios tend to be equal. In reality, as the cables are often shared, the ratio may change due to increased traffic on the cable.

Cable Switch in the street ISP

Wireless The introduction of 3G technology has made wireless broadband far more popular. Wireless speeds, as of 2009, were between 7.2 Mbps and 14.4 Mbps. Although the bandwidth is good, it does require a good 3G signal. Connecting to a 3G network requires the user to connect their device to a mobile using Bluetooth, a USB cable or a USB modem stick.

Wireless Tower from: http://www.great-lakesautomation.com/images/wireless_tower.jpg

Leased Line A leased line connects two locations together. Contention ratios are non-existent as the line directly connections two routers. Because this is a fixed line it requires specialists to set up the connection. This method is obviously more expensive but for large companies this is the preferred method. As the line is direct between two routers it is harder for those wanting to intercept transmissions as they do not have access to that line.

Leased Line Many schools make use of leased lines which connect schools to the local authority. At present, many schools use fibre-optic cables which allow bandwidth speeds of up to 10 Mbps. This obviously causes some bottlenecks to occur, especially when lots of data is being downloaded at the same time. For this reason many local authorities are planning on upgrading to 100 Mbps connections. It is important to note that this does not prevent bottlenecks...it merely eases the problem.

Satellite This is mainly used were physical and wireless connections are not possible. These tend to be in remote locations such as the countryside or in the desert!! There are two types of broadband available: One-way Two-way

One-Way Satellite Broadband This method uses a satellite to download data but uses a modem and the telephone line to upload information. Satellite The Internet Satellite Dish (one-way) Satellite Modem Computer Telephone Line Satellite up/down link Telephone Socket

Two-Way Satellite Broadband This method uses a satellite to upload and download data. It is asymmetric meaning upload and download speeds are different. Satellite The Internet Satellite Dish (one-way) Satellite Modem Computer Satellite up/down link

Satellite The satellites used are geosynchronous meaning they are currently hovering about 37,000 km above the Earth. Because of the large distance they are not particularly great for downloading large quantities of data. This makes them inappropriate for video conferencing and gaming. Line of sight is required also meaning satellites need to be positioned as far away as possible.

Summary ADSL Cable Wireless Leased Line Satellite Bandwidth 24 Mbps Generally 20kbps (very slow) but up to 3.2Gbps (Military has access to this sort of speed!) Cost Cheap Medium Highest High Asymmetric or Symmetric Asymmetric Symmetric Connection Type Copper Cable Fibre-optic backbone Mobile phone radio waves Fibre-optic Microwaves Contention Yes No Yes (Very high ratio)

Activity Describe the following broadband communication methods: ADSL Cable Wireless Leased Line Satellite Remember: Identify, Amplify and Exemplify Complete the following table Method Advantage Disadvantage Where is it used? ADSL Cable Wireless Leased Line Satellite

Example exam questions What does ADSL stand for? What does asymmetric stand for? Describe two factors that could affect bandwidth on ADSL lines. Why are cable broadband suppliers able to offer higher bandwidths? How can a laptop access the internet without wireless connections near by or any other cable solution. Why is bandwidth guaranteed on a leased line? How might a bottleneck occur when using a leased line? Why might a user want to use a satellite connection? Describe the term latency.