Before you start
Objectives: Learn about different technologies that can be used to connecto to the Internet.
Prerequisites: no prerequisites.
Key terms: Internet, connection, technology, Dial-up, ISDN, DSL, Cable, Satellite, Wireless
Public Switched Telephone Network (PSTN)
The first method to connect to the Internet is using was PSTN. With PSTN we use a modem device, which takes a binary data from our PC and converts it to analog signal that can be transferred over telephone network. On the other end of the line, there is also a modem which takes the analog signal, and converts it back to the digital data. The modem takes the whole phone line, and uses it as a single 64 Kbps data channel. In reality, common data transfer rates were 28.8 Kbps, 33.3 Kbps, and 56 Kbps.
The modem can be installed in the expansion slot in our PC, or we can have an external modem that’s connected to the PC using serial cable. On the back of the modem there is an RJ11 jack (telephone jack), that plugs in to a wall outlet which is also RJ11 jack. We also had to configure the connection on our computer. This type of connection is called a dial-up connection. To connect to the Internet, our computers dials an access server at the ISP. To configure the connection we had to know the ISP server’s phone number, our username and password to log on.
In addition to the slow speeds, the modem takes the entire channel. There is no multiplexing. That means that if we are on the Internet, no one else can use the phone. Also, if someone is using the phone, we can’t connect to the Internet.
The modems were great because we could use them anywhere that regular telephone service was available. Because of the low speed, today this method is not used any more. Telephone companies now use newer standards that allow us to get a lot more speed over the existing telephone wires.
Integrated Services Digital Network (ISDN)
ISDN can be used with existing phone lines or with T1 lines. ISDN takes the phone line, and divides it into multiple channels. However, there are different implementations of ISDN.
The basic implementation is called the Basic Rate Interface (BRI). With BRI, the phone line is divided to three channels. We have two 64 Kbps channels which are used for data, and we have one 16 Kbps channels used for connection control. BRI was typically used with home scenarios. It uses 4 wires on the existing phone installation. With BRI, we can use one channel for voice and one channel for data, or both channels for different voice calls. Also, depending on the implementation, we can also bond both data channels to use them together for faster data speeds.
The second interface is called the Primary Rate Interface or PRI. With PRI the phone line is also divided into channels. However, PRI provides more data channels and in fact, more than a single phone line can handle. So, for PRI we have to have a special wiring installed which will provide all the channels, and this is where T1 is used (or E1 in Europe). With PRI we can have up to 23 64Kbps data channels, and one 64Kbps channel for connection control (or 30 data channels on E1 line).
Phone calls use digital ISDN phones, or analog phones connected to a converter. ISDN isn’t widely implemented any more, because of the DSL which provides more bandwidth.
Digital Subscriber Line (DSL)
DSL uses digital signals over our regular phone wires. Also, it allows use to use telephone and Internet at the same time. That’s because DSL uses a form of multiplexing. Multiplexing means that the channel is divided into smaller parts. One part is used by the phone, and the other is used for the DSL.
There are different kinds of DSL implementations which use different protocols and which then provide different speeds. Protocols used with DSL are specific electrical implementations. For example, we can have ADSL, SDSL, etc (collectively referred to as xDSL).
ADSL (Asymmetrical DSL) provides different download and upload speeds. Splitters are often required to keep the analog signals from interfering with the digital signal.
SDSL (Symmetrical DSL) provides equal download and upload speeds. In this case the entire line is used for data, so there is no simultaneous voice and data. Because of that, splitters are not required.
VDSL or VHDSL (Very High DSL) is similar to ADSL, but provides higher speeds. With VDSL2, we have even higher speeds.
To connect to the Internet using DSL, first the telephone company has to enable DSL for our telephone line. Sometimes this can be a problem because we have to be close to the local telephone loop in order to have DSL capabilities. If we are too far from the local loop, we can’t get DSL. Also, the speed also depends on the distance. Once the DSL is enabled for us, we have to implement a DSL router. The DSL router is plugged in to our telephone line using RJ11 connector. We can use the other telephone jack to connect our telephone. Often the DSL router will have a port which we can use to connect our phone to.
The DSL router will also have one or more Ethernet jacks (RJ45) which we can use to connect our computer to. This will give us Internet connectivity on our computer. If we have multiple Ethernet jacks on the DSL router, we can connect multiple computers at the same time and share the same bandwidth from the DSL connection. Usually, DSL router will have a built in DHCP server, so all of the TCP/IP connection parameters will be provided automatically.
Internet trough Cable TV Company
In this scenario, the coaxial cable which provides cable TV service is used to provide a data channel on it for Internet connectivity. The advantage of this is that the wiring is already there, so there is nothing special we have to do. Also, the cable TV wire is already multiplexed for multiple TV channels, so it’s not difficult to add more channels for data.
In order for all this to work, we have to use a cable modem. With cable modem, we are talking about analog signal. The modem can be installed in the PC or it can be external. The cable modem is connected to the table TV connector in the wall. Cable modem can also come as a standalone router/switch device, which then has Ethernet ports which can be used to connect our computer to the Internet. In some implementations it only has USB port which is used to connect it to a USB port on our PC.
Satellite Internet Connection
Satellite Internet connection uses a satellite dish, just like satellite TV, to connect to the Internet. This scenario is typically used if we are in a remote location and we don’t have any other options to connect to the Internet. The satellite dish has to be pointed right at the orbiting satellite to get the connectivity. Also, there can be atmospheric interference as well.
There are different types of satellite Internet implementations. Some implementations use the dish for downloading the data, and for upload it uses some other technology, like PSTN modem.
Wireless Internet Connection
When we say wireless, we typically mean the 802.11 standard. With 802.11, we are talking about a wireless network which is then connected to a wired network at some point. The wired network is then connected to the Internet.
Today we often connect to the Internet using our mobile phone. In this case, the wireless Internet access is delivered through mobile phone towers. New mobile phone technology is introduced periodically, and generally involves a change in a service which is non-backwards-compatible. These transitions are referred to as generations. The first mobile data services became available during the second generation (2G), and than came 3G, 4G, etc.
Today we often use mobile phones to connect to the Internet.