Communication

Question 1

What is a network?

Answer 1

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.

Question 2

Advantages of networks

Answer 2

 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

Question 3

What are the disadvantages of network?

Answer 3

 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

Question 4

What is a lan

Answer 4

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.

Question 5

What is a wan

Answer 5

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.

Question 6

Network topologies

Answer 6

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.

Question 7

Bus network

Answer 7

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.

Question 8

Advantages of bus networks

Answer 8

 Easy to implement and add more computer systems to the network
 Quick to set up – well suited for temporary networks
 Cost-effective – less cabling

Question 9

Disadvantages of bus networks

Answer 9

 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

Question 10

Ring network

Answer 10

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.

Question 11

Advantages of ring networks

Answer 11

 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

Question 12

Disadvantages of ring networks

Answer 12

 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

Question 13

Star networks

Answer 13

In a star network, each computer system is connected to a central node, also known as a hub.

Question 14

Advantages of star networks

Answer 14

 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

Question 15

Disadvantages of star networks

Answer 15

 Expensive to install – more cabling required
 Extra hardware required, such as a hub

Question 16

Mesh networks

Answer 16

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.

Question 17

Advantages of mesh networks

Answer 17

 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

Question 18

Disadvantages of mesh networks

Answer 18

 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

Question 19

Connectivity

Answer 19

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.

Question 20

Typical network speeds

Answer 20

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.

Question 21

Circuit switching

Answer 21

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.

Question 22

Packet switching

Answer 22

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.

Question 23

Packet

Answer 23

A packet is a collection of data that is transmitted over a packet-switching network.

Question 24

Routing

Answer 24

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.

Question 25

Ip addresses

Answer 25

An IP address is an address which is allocated to a computer system on a network, usually by a DHCP (Dynamic Host Configuration Protocol) server. Alternatively, you may assign your own IP address if you do not wish to rely on the services of a DHCP server. An example of an IP address is 195.10.213.120.
It is used to uniquely identify computer systems on a network, thus allowing communication between them. In routing tables, the corresponding IP address of a unique MAC address is stored and updated as necessary.

Question 26

Internet domain name system

Answer 26

A Domain Name System (DNS) is a distributed database that matches IP addresses to computer system resources.
One example of this is to match an IP address to a human friendly domain name. For example, if you wanted to visit the Google search engine, the computer system on which the website is stored has an IP address assigned to it; 172.217.31.164. Try typing this into the address bar of your web browser. You should be able to view the website that you would be more familiar with when accessing the domain name www.google.co.uk. Here, your computer system sent a request to its DNS server for the IP address that is mapped to the domain name www.google.co.uk. The DNS server returned the IP address 172.217.31.164, which allowed your computer system to communicate with the computer system where the Google search engine is stored.
Of course there are many different DNS servers located world-wide. If your local DNS server does not store the address of the resource you are requesting, it will pass the request along to another higher level DNS server, such as the DNS server of your Internet Server Provider (ISP). If again the address is not found, your ISP’s DNS server will pass the request on to a higher level DNS server which may be the DNS server responsible for an entire zone, such as the .co.uk zone. This continues until the address is found (and returned to the local server) or the DNS query fails.

Question 27

Protocols

Answer 27

A protocol is an agreed format, which allows two devices to communicate. Put simply, a
protocol is a set of rules. These rules can include the following:
 handshaking, where two devices establish their readiness to communicate
 how the sending device will indicate that it has finished sending a message
 how the receiving device will indicate that it has received a message
 the type of error checking to be used
 agreement on the data compression method to be used.

Question 28

Protocol stacks

Answer 28

A protocol stack is a set of protocols that work
together to provide networking capabilities. It is
called a stack because it is designed as a hierarchy of
layers, each supporting the one above it and using
those below it. The use of a layered approach
enables different protocols to be substituted for
each other, e.g. to allow for new protocols and
different network architectures. The number of
layers varies according to the particular protocol stack. However, the lowest layer will deal with physical interaction of the hardware, with each higher layer adding additional features, and user applications interacting with the top layer.

Question 29

5 layer stack model

Answer 29

TCP stands for Transmission Control Protocol and IP stands for Internet Protocol. There are five layers to this model:
 Physical layer
 Data link layer
 Network layer
 Transport layer
 Application layer.

Question 30

Physical layer

Answer 30

The physical layer transmits the raw data. It consists of hardware such as switches. This layer deals with all aspects of setting up and maintaining a link between the communicating computers.

Question 31

Data link layer

Answer 31

The data link layer sends data from the network layer to the physical layer. It divides the data to be sent into data frames. A data frame consists of a link layer header followed by a packet. This layer handles the acknowledgements sent from the receiver and ensures that incoming data has been received correctly by analysing bit patterns in the frames.

Question 32

Network layer

Answer 32

The network layer is responsible for the addressing and routing of data. Routers belong to the network layer as they use logical addresses to direct the data from the sender to the receiver. A router determines the path the data should take based on network conditions. Routers manage traffic problems on the network such as the routing of packets to minimise congestion of data.

Question 33

Transport layer

Answer 33

The transport layer ensures that data is transferred form one point to another reliably and without errors. The transport layer is responsible for making sure data is sent and received in the correct order. The transport layer is implemented in the sending and receiving computers, but not in the routers on the path between them. It acts as an interface between the communicating computers and the network.

Question 34

Application layer

Answer 34

The application layer provides interfaces to the software to allow it to use the network. Examples of software include email, file transfer protocol (FTP) and the World Wide Web (WWW).

Question 35

Ethernet protocol

Answer 35

At the data link layer, Ethernet Protocols describe how network devices can format data for transmission using frames and packets. Ethernet protocols are also used to define standards for types of network cabling used at the physical layer, and the corresponding transmission speeds.

Question 36

Wi-fi protocol

Answer 36

Wi-Fi is a term used for certain types of wireless networks that use 802.11 wireless protocols for transmitting data using electromagnetic waves in place of cables. 802.11 wireless networks use security protocols, such as Wi-Fi Protected Access (WPA), to provide a level of security and privacy similar to that found on a wired network. Bluetooth is another example of a Wi-Fi protocol and WAPs (Wireless Application Protocols) are protocols to standardise the way wireless devices can be used for internet access.

Question 37

Email protocols

Answer 37

To use email, you must have an email client on your computer that has access to a mail server. Your Internet Service Provider (ISP) will often provide this server. The mail client and the mail server exchange information with each other using email protocols to transmit information.

Question 38

Imap protocol

Answer 38

IMAP is an email protocol that stores email messages on a mail server. It stands for Internet Messaging Access Protocol. It allows the email user to read and handle email messages as though they were stored locally on their own computer. The user can manage their email with facilities such as the ability to create folders to organise their messages, store draft messages in the server and delete unwanted messages.

Question 39

Pop3 protocol

Answer 39

Post Office Protocol 3 (POP3) is the third version of a protocol for receiving email. POP3 receives email for a client and stores it in a single file on the mail server. When the email client logs onto the mail server, the email is transfered to the user’s computer. There are no copies of the email stored permanently on the server after it’s been downloaded.

Question 40

SMTP

Answer 40

The Simple Mail Transfer Protocol (SMTP) is used to deliver email from the sender to an email server, or when email is delivered from one email server to another. SMTP can only be used to send emails, but not receive them.