3.4 - Connection Methods
Exam Board:
OCR
Specification:
2016 - Unit 1
Local Area Network (LAN)
A Local Area Network (LAN) is a network in which the computer systems are all located relatively close to each other, for example, in the same building or on the same site, like a school.
A type of LAN is a Wired Ethernet LAN (technically Ethernet is a protocol that controls how data is transmitted over a LAN). Wired Ethernet LANs have a high bandwidth so data can be transferred quickly and because it uses cables the data is harder to intercept than a wireless network.
Metropolitan Area Network (MAN)
A Metropolitan Area Network (MAN) covers the range of a town or city, for example a university campus network.
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MANs are usually very efficient at providing fast communication for cities, with high connection speeds through the use of fibre optic cables.
Wide Area Network (WAN)
A Wide Area Network (WAN) is a network spanning a large geographical area, such as multiple cities or countries.
The internet is the ultimate example of a WAN as it stretches across the entire world. There are different types of WAN rules and standards that are used:
ADSL
ADSL (Asymmetric Digital Subscriber Line) is a method of transferring data across copper wire telephone lines.
Because ADSL uses the telephone system it requires a modem at both the sending and receiving end of the connection. A microfilter is also required to allow internet and telephone access at the same time.
While bandwidth is high with this method, is not as secure as other methods such as leased lines so a firewall and/or VPN (Virtual Private Network) would be needed to improve security.
ADSL is contended which means that connection speeds are affected and slowed down with more systems that use the network at the same time.
ADSL is contended -
shared between sites.
Internet Service Provider
ADSL requires a modem
Leased Line
Leased Line is a method of providing an uncontended, fixed-bandwidth data connection.
The user maintains a dedicated connection that is more secure and, because it is uncontended, will have the same speed all of the time, regardless of how busy the network is.
Bandwidth is high, security is better, the connection speed is constant and the network is full-duplex (allowing for data transmission both ways simultaneously).
These advantages come at a high price tag - possibly hundreds of pounds per month.
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A CSU/DSU (Channel Service Unit/Data Service Unit) device is required to properly terminate the leased line.
Internet Service Provider
Leased Line is dedicated.
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A CSU/DSU is required for a leased line.
ISDN
ISDN (Integrated Services Digital Network) transmits video and voice data simultaneously over traditional copper telephone wires. This method uses a circuit-switched network where all data packets take the same route between computer systems.
Voice Networks
Voice networks primarily transfer audio data using phones and telephone lines.
PSTN
PSTN (Public Switched Telephone Network) is the global collection of wired public telephone networks that are used to transmit data over a long distance.
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PSTN is fixed into position using underground cables and therefore the connection quality is much more consistent than other voice networks.
Using a wired connection like a PSTN is more reliable and communication will be clearer than alternatives such as cellular or satellite methods.
Cellular
Cellular networks require a cell or transmitting tower to be in close proximity to the communication device.
Cellular networks have a greater range than PSTN but this point-to-point communication method (where line of sight is necessary) can be disrupted by buildings and poor weather.
Each cell tower is also connected to the PSTN.
Satellite
Satellite networks use point-to-multipoint communication by using satellites above the Earth's atmosphere that receive a transmission and rebroadcast them back to Earth.
Because of the distance between the communication device and the satellite (roughly 45,000 miles), there is a delay between data transmission and it being received.
Satellite networks are beneficial in remote locations, such as natural disaster zones, where the cell tower may not be present or may be damaged. Transmitting large files using satellites may take longer and it is not recommended for low latency needs such as video gaming.
Diagrammatical Representation
In an exam you may be asked to draw a diagram that represents how networks are connected to each other. This is different from drawing a network topology (e.g. ring or mesh) and refers to:
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Connection type (e.g. ADSL / Leased Line).
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Devices (e.g. router / modem),
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Security methods (e.g. firewall / VPN)
Two LANs connected using a Leased line
Two LANs connected using an ADSL line
Rules for drawing a network diagram:
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Label each device and label your LANs.
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Use appropriate symbols and be neat. There are no set symbols, just be consistent (e.g. both modems are the same shape).
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ADSL must have a modem and VPN router + Firewall.
(ADSL is not very secure so it needs to be protected with the VPN router and firewall. It also uses the telephone line across the internet so it requires a modem at both ends). -
Leased Line must have a router, a direct connection and CSU/DSU.
(Leased line is a secure and direct connection - so it doesn’t need a firewall or VPN router and should be direct (not across the internet)).
Questo's Questions
3.4 - Connection Methods:
1a. What is the definition of a LAN? [2]
1b. Describe two benefits of using a wired Ethernet LAN. [4]
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2. What is the definition of a MAN? [2]
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3a. What is the definition of a WAN? [2]
3b. What is the difference between a contended and an uncontended network? [2]
3c. Describe the differences between a leased line and ADSL. You should discuss security, connection speed and contention (contended or uncontended). [6]
3d. Describe the use of any two network devices required for either a leased line and/or for ADSL. [4]
3e. Describe the purpose of ISDN. [2]
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4a. Compare the use of PSTN and Cellular methods to make telephone calls. [4]
4b. Explain 1 way that a satellite network should be used and 1 way it shouldn't be used. [4]
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5. Draw a diagram to show how a leased line or ADSL network can be set up between two existing LANs. [6]