Communication Flashcards
(40 cards)
What is a network?
A network consists of a number of computer systems connected together. There are many advantages and disadvantages of using a computer network over a stand-alone computer.
Advantages of networks
Share hardware
Share software
Share data/files
Easier for internal communication/can
send email
Central backup
Easier to monitor network activity
Centrally controlled security
Can access data from any computer
What are the disadvantages of network?
A network manager may need to be employed – expensive
Security problems – files sent between computers could spread a virus
Hackers can gain access to data more easily
If the server is down, all workstations on the network are affected
Initial cost of servers, communication devices etc. can be expensive
What is a lan
A 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, such as a school.
What is a wan
A WAN is a network in which the computer systems are all located relatively far from each other, for example in different buildings all over the country or in different countries. The internet is an example of a WAN. Note that many LANs could be linked using a WAN.
Network topologies
A network topology is the theoretical layout of computer systems on a network. There are a number of different network topologies. Common network topologies include:
bus network
ring network
star network
mesh network.
Bus network
The computer systems, also called the nodes of the network, are all connected to a single cable on which data can be sent, called the bus. A bus network has terminators on each end,
which are needed to ensure the network functions correctly.
The bus carries data packets along the cable. As the packets arrive at each computer system, it authenticates the destination address contained in the packet to see if it matches its own address. If the address doesn’t match, the computer system ignores the packet. If the address of the computer system matches the address contained in the packet, it processes the data.
Advantages of bus networks
Easy to implement and add more computer systems to the network
Quick to set up – well suited for temporary networks
Cost-effective – less cabling
Disadvantages of bus networks
It is difficult to troubleshoot the bus
Limited cable length and limited number of
stations – performance degrades as
additional computers are added
If there is a problem with the main cable or
connection, the entire network goes down
Low security – all computers on the bus
can see all data transmissions
Proper termination is required
Data collisions are more likely, which
causes the network to slow down. A collision is when two computers try to send a data packet at the same time
Ring network
In a ring network, computer systems are connected in a ring or a loop. Data packets are sent around the ring, being passed from one computer system to the next until they arrive at their destination.
Advantages of ring networks
Data is quickly transferred without a bottleneck – consistent data transfer speeds
The transmission of data is relatively simple as data packets travel in one direction only
Adding additional nodes has very little impact on bandwidth
It prevents network collisions
Disadvantages of ring networks
If any of the computer systems fail, the ring is broken and data cannot be transmitted efficiently
If there is a problem with the main cable or connection, the entire network goes down
It is difficult to troubleshoot the ring
Because all nodes are wired together, to
add a another you must temporarily shut down the network
Star networks
In a star network, each computer system is connected to a central node, also known as a hub.
Advantages of star networks
Good performance/fast network speed
Easy to set up
Possible to add more computer systems
without taking the network down
Any non-centralised failure will have very
little effect on the network
Minimal network collisions
Better security
Disadvantages of star networks
Expensive to install – more cabling required
Extra hardware required, such as a hub
Mesh networks
In a mesh network, each computer system is directly connected to as many other computer systems as possible. The image above shows a full mesh network, where all computer systems are connected to each other. It is also possible to have a partial mesh network, where only some of the computer systems are connected in similar fashion to a mesh topology, while the rest are only connected to one or two devices. This is called a partial mesh network. The mesh topology is the most common network topology used on wireless networks.
Advantages of mesh networks
Data can be transmitted from different nodes simultaneously
Mesh topologies can withstand high traffic
Each connection can carry its own data load
If one node fails, there is always an alternative present, so data transfer isn’t affected
A fault can be diagnosed easily
Expansion and modification in topology
can be done without disrupting other
nodes
Provides high levels of security and
privacy
Disadvantages of mesh networks
Installation and configuration can be difficult as the network grows
Cabling costs are high
There is a high chance that many of the
network connections will be redundant
Set-up and maintenance of mesh
topologies is very difficult
Administration of the network is difficult
Connectivity
To connect a computer system to a network, a Network Interface Card (NIC) is required. A physical hardware port allowing a cable to connect your computer system to the network provides one method of connection. The second method is to connect a computer system using a wireless connection, called Wi-Fi.
Typical network speeds
A physical connection may be made using:
a copper cable, with typical data transfer speeds of between 100 Megabits per
second (Mb) and 1 Gigabit per second (Gb)
a fibre-optic connection which has typical data transfer speeds of between 1 and 10
Gb
Wi-Fi connections have typical data transfer speeds of 54–108 Mb but can go much higher. However, this can be severely affected by the distance between the device providing the Wi-Fi connection and the computer system. The data transfer speed can also be severely affected by atmospheric conditions, such as the weather, and building infrastructure.
Circuit switching
Circuit switching is a type of networking technology that provides a temporary but dedicated link between two stations or nodes, regardless of the number of switching devices through which the data has to travel. During the connection, no other data can be transmitted along the same route. The landline telephone system is an example of a circuit switched network. When you phone someone and they answer, a circuit connection is made and you can pass data along the connection until you put down the telephone to end the connection.
The main advantage of circuit switching is that it is reliable. Once the connection is established, it is fast and generally error free. However, it takes time to establish the connection. Should anywhere on the route fail, the connection will be broken.
To overcome the problems with circuit switching, packet switching was developed. Rather than relying on a dedicated connection, packet switching breaks the data down into small packets that can be sent by more than one route.
Packet switching
Packet switching is the process of delivering packets from one computer system to another using a designated device, such as a switch or a router. Packets are provided to a network for delivery to a specified destination. Each data packet is redirected by a computer system along the network, until it arrives at its destination. Data may be split up into a number of packets. These packets are transmitted over a network and may take different routes to its destination. When all the packets have arrived, the data is reassembled. The internet is an example of a packet-switching network.
Packet
A packet is a collection of data that is transmitted over a packet-switching network.
Routing
Routing is the name given to the method of selecting paths along which packets are sent on
a computer network. Specialist computer systems such as routers, switches, bridges, firewalls and ports construct a routing table in their memory. This stores a number of routes which are the best to use to send packets to reach a specific destination. Maintaining accurate routing tables is essential for ensuring that packets are delivered as quickly as possible.
