Unit 2 - Global Information LO1 1.4 The Internet Starter What is the difference between the difference between the Internet and the World Wide Web? Objectives Know and Understand what the internet is
Understand the characteristics of Internet connections The Internet Remember that the Internet and World Wide Web are separate things but are related. The Internet A massive network of networks. Connects millions of computers together globally, forming a network in which any computer can communicate with another, as longs as both are connected to the Internet. Information that travels over the Internet does so via a variety of languages known as protocols.
World Wide Web A way of accessing information over the medium of the internet. Is an information-sharing model that is built on top of the Internet. Uses HTTP protocol to transmit data. Web services that use HTTP to allow applications to communicate in order to exchange business logic, use the Web to share information. It also utilises browsers (IE, Chrome etc.) to access Web documents/web pages. The Web is a Portion of the Internet
The web is just one of the way that information can be distributed over the internet. The internet also used for email (which relies on SMTP), Usenet news groups, instant messaging and FTP. The web is just a portion of the Internet, albeit a large portion. The Internet is also explained in this video. DSL (Telephone Line)
DSL is an initialisation of Digital Subscriber Line. Phone companies developed a way to send a second signal down the phone lines/ they did this by sending it at a higher frequency. In real life, this is done by a signal filter. It filters out the high frequency so you can hear the voice better, otherwise there would be a high-pitched hiss on the phone line. What you can expect:
DSL ISPs promise speeds form 1.5 Mbps to 10 Mbps, however new technology could push it to 100 Mbps. A more realistic number about 80-90% of what you ISP advertises. DSL service cost range widely, as the speeds do. In the last 25 years internet has moved from being only available to military and universities in the early days to billions of ordinary people now having access all around the world. It has changed from being largely text based to full multimedia content (video, TV,
music, telephone streams, personal and commercial web sites. In the early days, you had to use a modem / computer setup to access the internet. This is no longer the case, as all kinds of devices can connect (smart phones, tablets, laptops and modern TVs) ADSL Subscriber Line Most connected homes now have an ordinary telephone line wired between the residence and the nearest telephone exchange or street cabinet. Wries are copper and were originally designed to carry voice traffic, which requires only a small amount of bandwidth (around 3.4 kHz). Luckily they
can handle much more than this and that is why broadband is possible over normal telephone lines. ADSL Asymmetric Digital Subscriber Line Subscriber Line What the telephone companies call the copper wire that links your home to the exchange. Digital Normal telephone traffic is analogue, but alongside this it is possible to send digital signals using a higher frequency. Asymmetric Means something that is uneven or not symmetric. In this case it means the download speed is different to the upload speed. It was quickly realised that the vast majority of the time, people at home download content far more than they upload. So ADSL shares out the
bandwidth available by allocating more bandwidth to downloading than uploading. ADSL ADSL is ideal for domestic use as it reflects the way we use the internet at home and makes use of the existing telephone line. However, for business use it is less useful. Often a business needs to send as much data as it receives, so the 'asymmetric' nature of the line may be an issue i.e. upload is as important as download speed.
Bandwidth is also an issue, if there are many people within the organisation and each want to use the internet connection, this would rapidly lead to a bottleneck. The business may also want a guaranteed quality of service where the speed is always what they have paid for. In domestic ADSL the contention ratio will change the speed according to the time of day. Therefore a business may look for a low contention ratio or even having sole use of the line (such as leased line). Video:
Cable v DSL Types of Internet connection 1 key thing that determines bandwidth is physical nature of the cables used. A signal becomes weaker the longer it travels along the cable, eventually becoming so weak that it is no longer detectable above natural noise. Therefore cable length determines bandwidth of the link. For instance the bandwidth of broadband to the home is determined by the length of copper cable between the house and
the nearest telephone exchange. This is the so called 'last-mile' bottleneck. Copper Cable/Coaxial Consists of a solid copper core surrounded by insulation. This is then surrounded by copper shielding and covered with a plastic sheath. These cables are widely used for television wiring due to the high bandwidth able to handle television signals. Early computer networks also used coaxial cable with a bandwidth of 10Mbps, however for higher speeds (100Mbps+) the coaxial cable is no longer sufficient.
Twisted pair was then introduced and has become the norm. This consists of 8 colour-coded wire with each related pair twisted around one another. This twisting reduces signal loss over any given length of cable. Twisted pair cable is widely used in 100Mbps and 1 Gbps networks. Fibre Optic Cable Copper cable is adequate for networks up to 100 metres but above that signal becomes too weak. Alternative technology was needed, therefore fire-optic was introduced. It has an astounding bandwidth.
It is limited more by the electronics either side of the cable than the bandwidth of the cable itself. For instance in recent experiment, a 160 km length of high performance fibre-optic cable carried up to 14 Tera bits per second! Fibre optic cable uses light to transmit information rather than electrical signals. Therefore unlike copper cables, it is not prone to electrical interference. Fibre optic cable launches a light signal at one end of the glass thread core. It is then reflected internally down the fibre until it reaches the other end. Light sensitive electronics then pick up the signal. Downside of fibre is cost it is more expensive than ordinary UTP network. It is only cost effective if there is very high bandwidth required or if the networks has
long cable runs. The norm in the UK is that there is fibre-to-cabinet, where it is fibre from exchange to nearest junction box. Normal copper cable is then used to the home. Fibre-to-the-cabinet is rapidly becoming the norm - so there is a fast link from the cabinet to the exchange and a normal copper wire from the home to the cabinet. This shorter length allows for faster speeds -a good fibre-tothe-cabinet offers 20 to 80 Mbps. Some factors limiting bandwidth `Contention ratio. This is the number of people who are using the exchange line at the same time. This is often why the internet seems slower in the evenings - there are more people sharing your line at that
time of day. Length of wire between your home and the exchange. ADSL is only practical if you are within about three miles of the exchange. The signal simply gets weaker the longer it has to travel. Another factor often overlooked is the wiring inside your own house, your connection may be slower if your router is not connected directly to the master socket. Interference. Anything that causes electrical noise within the ADSL frequency band can cause it to slow down. For instance a strong AM radio transmitter nearby, or a poorly filtered telephone you have also connected to the line.
Satellite This is gaining internet access via a satellite dish. Signals get beamed to a satellite which turns around and beams the signal to you and vice versa. Like Wireless Broadband, it is a line-of-sight technology. Your dish needs to have a clear shot at where the satellite is. Each transmission takes around a 45,000 mile trip between you, the satellite and the ISP. As mentioned previously long distances affect strength of signal, therefore satellite internet service isnt normally the first choice. Another reasons is that all people in the areas using satellite internet has to
share the same bandwidth. If the area is the size of Utah or Ghana, that could be a lot of people. If youre hogging the bandwidth the ISP will slow your connection down to a crawl to give everyone else a chance. Satellites in geosynchronous orbit can cover large parts of the world and it appears at a fixed . point in the sky. This can be used as an internet broadband
link. Satellite broadband is an option for remote overseas areas, ships at sea and rural areas where there are slow ADSL lines and no cable. Latency is a major issue with satellite broadband The satellite is 37,000 Km away and so it takes about 0.7 seconds for a signal to pass between two locations on the ground. This is usually not a problem for downloading data but it is no good for real-time applications such as online gaming where you need very fast response time. Conversations in an internet conference call can also be awkward as you tend to talk over one another.
One Way and Two Way Broadband Microwave Long distance wireless connections can be established with microwave links. This is a line of sight technology. This means that each telecom tower containing a microwave dish needs to be in sight of another one a few miles away. A typical network speed of 3Gbps can be sustained. Large companies make use of this technology to create private
WANs. Characteristics Different types of internet connections have different characteristics. Examples: Speed of data transfer can differ for different internet connections (copper cables have lower bandwidth than fibre optic means slower connection) Range is the distance of which the signal is sent on each type of connection. Satellites are able to send signals from boundaries of space, while microwave only send to the devices that are in direct line of sight. Data differences because of the high frequency used, microwaves can carry a large amount of data (approx. 30x the capacity of other forms of radio
transmission) Task For the following scenarios, specify which is the best type of internet connection appropriate for the situation and state the reasons why, with advantages and disadvantages: 1. Charity worker in a disaster zone, following an earthquake when breaks in cables and optical fibre can disrupt information access 2. Home user just moved into a new house that currently does not have a live internet connection
3. Doctor within an ER looking for information to use within an operation 4. Students on a foreign field trip 5. Business who have gone live with a website that involves streaming videos 6. Postal worker using a handheld device to get customers to sign when a parcel is delivered 7. School providing limited Internet access within a 6th form centre 8. Restaurant setting up an Internet connection for customers 9. Caf setting up a live video feed for the football for customers Types of Broadband
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