1. LO3 – Understand Business IT Systems
3.4 – Connectivity Methods

2. Connectivity Methods LAN (Local Area Network)
A Local Area Network is one that has two or more machines connected within a fairly close geographical area. For example the LAN may be located within a single building such as a home or business office or it may cover a few nearby buildings as well, such as an University campus, hospital, library or school.
Home networks can be fairly sophisticated because there are now many devices other than computers that are able to connect to a local area network. The generic LAN is intended to 'share data' but at home that data can mostly be for entertainment rather than business use.
Computers and devices can be connected by physical cables, which are usually owned by the organisation. Alternatively, they can be connected wirelessly, using Wi-Fi.
An Ethernet1 cable is used to connect the nodes in the network (sometimes called a network cable)
Typical home network
1 Ethernet is a computer networking protocol.
In this protocol, all networked computers are connected together by a wire or channel. (The channel is often a type of radio link called "Wi-Fi").
The clever thing about Ethernet is that is can handle the problem of two computers trying to talk at exactly the same time. The fancy name for this is "Collision Handling".
The way it works is that the protocol can 'sense' a collision and so it tells one of the computers to stop talking for a bit. Once a little time has passed, this computer has another go, and the chances are it will be able to get through.
As you can imagine, if the network is very busy, then more and more 'collisions' happen and so the network seems to slow down as far as your computer is concerned.
Another important fact about Ethernet is that it makes use of 'packets' of data. This means that the Ethernet protocol will "slice and dice" a message into a number packets and send each one off into the network.
A token ring network is a local area network (LAN) in which all computers are connected in a ring or star topology and pass one or more logical tokens from host to host. Only a host that holds a token can send data, and tokens are released when receipt of the data is confirmed. Token ring networks prevent data packets from colliding on a network segment because data can only be sent by a token holder and the number of tokens available is controlled.
More Here

3. (WAN) Wide Area Networks
A wide area network (WAN) allows widely dispersed computers to be connected as a single network.
The WAN may cover a number of offices within a business. For example an estate agent with branches in a number of towns may have its computers connected as if they were one large wide area network.
The WAN may even be designed to span the world in order to support the offices of an international company. The WAN may connect a single computer, for example a home computer connecting to the internet, or it may connect LANs together as often happens in branches and offices.
The difference between a LAN and WAN is that some kind of external connection is needed to connect the computers together. This link is often a dedicated leased line from a telecom company but it could be other methods as well.
For instance it could make use of the mobile telephone network. It may be microwave towers linking factories in the same country. For world-wide coverage satellite links could be used to connect offices in different countries.
The point is that there must be a method for digital data to be transmitted from one location to another.
The largest wide area network on the planet is the Internet which connects millions of LANs together. The internet is actually a 'network of networks'. Most companies use the services of an Internet Service Provider (ISP) to connect to the internet. A router / modem in the office connects to the ISP router / modem. This allows data to be transferred in the form of , attachments and other messaging services.

4. ADSL stands for Asymmetric Digital Subscriber Line.
ADSL is the most common type of fast connection to the Internet (Broadband).
Asymmetric means that the upload speed is different to the download speed. For example, a typical 2Mb connection has a download speed of 1800Kb per second and an upload speed of 200Kb per second. More Here
ISDN stands for Integrated Services Digital Network.
This is a digital service provided by British Telecom to allow you to connect to the Internet and transmit digital data over ordinary telephone copper wire as well as other media.
It is now largely obsolete because it has been superceded by Broadband (ADSL). Although some areas of the country may be still using it because they do not have broadband.
ISDN was a service developed in the time when analogue modems were running at speeds from 32kbs to 56kbps. ISDN on the other hand offered speeds of 64kbps on a single channel or 128kbps on a double channel and there was no need to 'dial in' which could take ages on an analogue modem.
Leased Line
This is a dedicated connection between the business and an outside location. For instance the leased line could be intended for a high speed internet link or it may be part of the company extranet.
The major downside of a leased line is that it is very expensive. A quick search of prices today indicates that £1000 per month is not unusual for a high speed connection.
Speeds can range from 100 Mbps to even 10 Gbps and this has a direct bearing on the cost.
Characteristics of a leased line are
Symmetric - same upload and download speeds
High bandwidth Mbps to 10,000 Mbps
Expensive compared to domestic ADSL services
Guaranteed level of service - no contention
Note that the user may still experience a slow connection. This is because the bottleneck is somewhere upstream of the leased line. For instance a web site may be in heavy use and so the server itself is the bottleneck.

5. MAN -Metropolitan Area Network
This is a wide area network or WAN that is limited to a city and its immediate surroundings.
A MAN is similar to a local area network (LAN) but spans an entire city or campus. MANs are formed by connecting multiple LANs. Thus, MANs are larger than LANs but smaller than wide area networks (WAN).
MANs are extremely efficient and provide fast communication via high-speed carriers, such as fibre optic cables.
MAN is ideal for many kinds of network users because it is a medium-size network. MANs are used to build networks with high data connection speeds for cities and towns.
Voice

6. Voice
Data and voice communication can be sent over telephone wires or by cellular or satellite technology. The clearest and most reliable method is over fixed cables between the sender and receiver. If it is not possible to be linked to a handset or computer which is plugged into a Public Switched Telephone Network (PSTN) (e.g. while travelling or in remote parts of the world), cellular (mobile phone) and satellite communication is appropriate.
However, cellular technology requires the towers which carry transmitter/receivers to be in line of sight t o the user’s communication device. Disappearing into tunnels on a train, standing in a remote field or being shielded by large buildings can disrupt this point-to-point communication. Also, providers do not like to share their communication systems with other providers as they risk losing revenue from new customers.
Satellites
Satellites in geostatic orbit (those that appear to stay in a single location over Earth) are point-to-multipoint communication systems as they receive transmissions and rebroadcast them to receivers. If required, the satellite can be moved to another location relatively quickly. However, the distance between the satellite and the ground, normally about 75,000 km (46,603
miles), means there is a delay between the transmission of the signal and its receipt, which can be seen on television news reports from remote locations. Data transmission is also compromised by this issue, especially when trying to transfer large files.