1. Introduction to Computers
Internet Services

2. Internet Services
There are various Internet technologies that can be used to connect a home or a small office network to the internet
We’ll be focused on internet connections that are used in the home or in a small office environment
Larger businesses and corporations use enterprise level Internet services that cost thousands of dollars per month. The Internet connection types we're going to be looking at use a similar technology but are implemented on a much smaller scale
Some of these connection types may be slower and older, but note that they are still in use in rural areas without well developed internet infrastructure

3. Dial Up
Dial-up uses the public switched telephone network (PSTN) to connect to the internet. This type of Internet connection requires the computer to have a modem installed
The modem converts digital signals into analog signals that can travel along the analog telephone network
The computer connects to a telephone line that is then used to dial into the Internet service provider. It is very slow and rarely used outside of rural and undeveloped areas
Multiple standards define how to send digital data over the analog phone lines at various speeds and compression ratios.
Data transfer rates include 28.8 Kbps, 33.3 Kbps, and 56 Kbps.
Dial-up connections cannot be used for both voice (phone calls) and data at the same time

4. Digital Subscriber Line (DSL)
DSL (Digital Subscriber Line) is another technology using the PSTN to connect to the network, but it does so in a very different way
With dial-up the Internet connection uses the entire bandwidth of the telephone line and that means that voice calls cannot occur while the computer is using the internet, and vice versa
However, with DSL multiplexing is used to allow for two simultaneous signals on the same line. This means that you can use the same line for voice and data with most types of DSL
DSL is not available in all areas; the service location must be within a fixed distance of telephone switching equipment
DSL Internet connections require a DSL modem to connect the local network to the service provider's network

5. DSL Multiplexing
Multiplexing divides the telephone line’s bandwidth into two signal ranges, effectively creating two channels
The first channel is used for your standard telephone voice communications and it uses frequency ranges less than 4 kHz. The second channel is used for DSL communications and it uses frequency ranges above 4 kHz
Be aware though, that traditional telephones are not DSL aware. This means they can’t distinguish between the two channels on the line. They would try to accept and process both signals which would cause a lot of voice distortion
You can fix this by implementing a DSL filter on the telephones. This filter blocks DSL communications and just allows voice frequencies through.

6. DSL Symmetry
DSL providers frequently offer two different types or levels of DSL service
Asymmetric DSL (ADSL)
The upload speeds and the download speeds are not the same, they're asymmetric. ADSL will typically provide very fast download speeds but incredibly slow upload speeds. This allows you to access web pages, stream movies or download large files at relatively fast speeds.
However, uploading files is not nearly so fast. For example, when attaching a large file to an or trying to save files to a cloud server you'll find that the connection is a lot slower.
Symmetric DSL (SDSL)
SDSL uses the same upload and download speeds. ADSL is much cheaper than SDSL, however, if faster upload speeds are required for a particular implementation then SDSL should be used over ADSL

7. Integrated Services Digital Network (ISDN)
Integrated Services Digital Network (ISDN) is similar to DSL, since it too uses multiplexing on a standard phone line
ISDN is much more popular in Europe than North America, and requires the customer to be located close to the service provider’s networking equipment
ISDN offers two different levels of service - Basic Rate Interface (BRI) and Primary Rate Interface (PRI)
PRI offers a better service than BRI (we’ll see why on the next slide), but comes at a premium, since it requires higher quality telephone lines

8. BRI vs PRI Basic Rate Interface (BRI) Primary Rate Interface (PRI)
ISDN BRI divides the regular copper telephone line into three channels:
2 64-Kbps bearer channels can transfer data up to 128 Kbps. Only one bearer channel is used during phone use reducing maximum speed to 64 Kbps
1 16-Kbps delta (D) channel for connection control
Primary Rate Interface (PRI)
ISDN PRI divides the cable into 24 channels:
23 bearer channels (each at 64 Kbps) for data transmission
1 delta channel (at 64 Kbps) for connection control

9. Cable
Cable Internet provides an Internet connection using your existing cable TV coaxial cable infrastructure
Cable Internet connections require a cable modem in order to connect your local network to the service provider's network. Just like with technologies that use the telephone network, the digital signal from the computer needs to be translated to an analog signal to travel on the network media
Cable Internet uses multiplexing to be able to carry networking signals and cable TV signals on the same line, or a separate line can be installed for Internet access

10. Cable VS DSL
This technology appears similar in many ways to DSL since both use multiplexing, but the transmission medium and the network used is very different
Cable Internet providers usually offer much faster download speeds than DSL providers
One drawback you need to be aware of is that that cable Internet bandwidth is usually shared, and as such, during peak times the transmission speeds for cable internet can be much slower than what was promised by the service provider
DSL On the other hand provides a dedicated bandwidth, so your experience should be more consistent

11. Fiber Optic
Fiber Internet uses fiber optic cabling to connect subscribers to the internet
Fiber optic Internet connections have the potential to be the very fastest way to connect to the internet
With fiber internet, most home subscribers connect to the fiber optic network using standard twisted pair copper cabling and an RJ45 connector
Larger business and corporations can get a direct fiber connection provided at a higher price
Fiber Internet can provide speeds much faster than DSL or cable for both upload and download speeds but because it can't use an existing infrastructure the way cable and DSL do, fiber Internet usually isn't available in most areas
In addition, creating a fiber infrastructure is very costly and takes a lot of planning to implement

12. Cellular
Cellular networking uses the cellular phone infrastructure for Internet access
Mobile phones with digital data plans use cellular signals to connect to the Internet, but devices can connect to a cellular Internet connection in a variety of ways:
Tethering - Smartphones can use a technique known as tethering to provide cellular Internet to another device. Tethering may require the smartphone to be connected via a USB cable
Mobile Hotspot -A cellular device that provides Internet by creating a small Wi-Fi network to which multiple hosts can connect. Most smartphones have built-in mobile hotspot functionality
Cellular Antennas - Some mobile devices (e.g., notebook computers and tablets) have integrated cellular antennas. If not, USB cellular adapters can be connected to most mobile devices to provide cellular access
Internet access is limited to areas with cell phone coverage, and coverage will be dictated by the service provider's network

13. Cellular Details
Cellular networking is a truly mobile solution. You can often move around between one connection point and another and still have Internet access without manually having to reconnect
Cellular networks used for voice and data include the following types:
2G (second generation) networks were the first to offer digital data services. 2G data speeds are slow (14.4 Kbps) and were used mainly for text messaging and not Internet connectivity.
2.5G was an evolution that supported speeds up to 144 Kbps.
EDGE (also called 2.75G) networks are an intermediary between 2G and 3G networks. EDGE is the first cellular technology to be truly Internet compatible, with speeds between 400 and 1,000 Kbps
3G (third generation) offers simultaneous voice and data. The minimum speed for stationary users is quoted at 2 Mbps or higher.
4G (fourth generation) offers minimum speeds of around 38 Mbps, with up to 100 Mbps possible.

14. Satellite
Satellite networking uses radio signals sent and received from a satellite to connect to the Internet using orbiting satellites
This type of Internet connection is well suited to remote locations where other types of Internet connectivity is not available. Satellite Internet is the only internet service that isn't dependent upon your location, it's available anywhere in the world as long as there's a clear line of sight to the sky
Since Satellite Internet requires line-of-sight to the satellite, dish placement is crucial and it is affected by mild atmospheric and weather conditions (fog, rain, or snow can disrupt service)

15. Satellite Latency
Satellite Internet access can provide reasonably fast download speeds, however, upload speeds are usually painfully slow
This connection typically has excessive latency, meaning it takes a long time for data to travel through the network, since the signal has to travel very far
For example, let's say a computer sends a request to access a website. That request needs to be sent all the way up to a satellite, which is orbiting the Earth, usually at an altitude of about 22,000 miles. The satellite needs to send that signal back down another 22,000 miles to the provider's receiving system. The requested information then makes the same journey from the web server back to the source computer following the same path
This latency makes satellite Internet is a very poor choice for time-sensitive applications such as computer games, voice data, and video calls

16. Other Satellite Options
Line of site Internet access (also called fixed wireless broadband) is similar to satellite Internet; however, instead of antennas being directed to a satellite in orbit, they are pointed at a large antenna on land. The antennas use radio signals (typically microwaves) to transmit and receive data
Requires a direct line of sight to the antenna, so like satellite networking, it can be disrupted by weather conditions
Provides Internet access without needing to run cables or lines to each subscriber's premise, only needs a single large antenna
Another option that is being researched is low altitude satellites. SpaceX plans to launch satellites in 2019 that will orbit at around 800 miles above the Earth

17. Other Consideration
Regardless of the method, Internet connections are made from the subscriber location to an Internet Service Provider (ISP). The ISP might be the cable TV company, the phone company, or another company offering Internet access
Internet requests are sent to the ISP, who forwards the request to the Internet
Most wireless networks are local area networks that are connected to the Internet using a wired method (such as DSL or another broadband solution)
Some metropolitan areas provide free, city-wide wireless or wired Internet. This type of network is known as a metropolitan area network (MAN)
Because many Internet service providers also provide other services (such as cable TV or telephone), you can often combine services to get Internet access with other services
VoIP is provided by many ISPs to replace existing analog telephone lines (even using the same phone number)