What is a network ?
A network is a number of computer systems joined together
What are 3 advantages of networks?
- share hardware
- share software
- share files
- Easier for internal communication
- Can access data from any computer
- Easier to monitor data activity
- central security
- central backup
What are 2 disdvantages of networks?
- 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 then network are affected
- Initial cost of servers, communication devices, etc. can be expensive
What are the two main types of networks? Full names?
- Local Access Network
- Wide Area Network
What is LAN?
A lan network is a network in which the computer systems are all located relatively close to each other
What is a WAN network?
A network in which computer systems are located relatively distant from each other
How do computer systems communicate?
They use agreed upon protocols to communicate. If they do not agree on the protocols to use, the computer systems can’t communicate.
What are protocols?
They are common methods of sending data and consistent data formats?
What is a network tropology?
It is the theoretical layout of computer systems on a network
Describe how a bus network is laid out
Computer systems called nodes are each connected to a single cable called a bus. The bus has two terminators, one on each end.
How does data travel in a bus network?
The bus carries packets along the cable. As packets arrive to each computer it checks the destination address to check if it is its own then it decides to ignore it or process it. The terminators terminate the packet when it reaches the end.
Why do bus networks need terminators?
To stop the electrical signals being reflected back interfering
What are 3 advantages of a bus network?
- It is easy to implement and add more computers
- It is quick to set up
- It is cost effective as there is less cabling
What are 3 disadvantages of a bus network?
- A problem with the main cable or connection sends the whole network down
- There is low security as all computers can see data traveling along the bus
- Data collisions are more likely
- You can’t troubleshoot/add to it without taking the whole network down
Describe the layout of a ring network?
Computers are connected in a ring or loop
How does data travel along a ring network?
Packets are sent along the ring, being passed from one computer system to the next until they arrive at
What are some advantages of ring network topologies?
- Data is quickly transferred with no bottleneck
- It prevents network collisions
- Adding more nodes does not impact bandwidth much
What are 3 disadvantages of ring topology networks?
- if any computer system fails the ring is broken
- It is difficult to troubleshoot the ring
- A problem with the connection sends the entire system down
- To add another node the network needs to be shut down
Describe the layout of a star network?
In a star network, each computer system is connected to a central node, also known as a
hub (or switch)
What are 2 disadvantages of a star topology network?
- It is expensive to install as more cabling is needed
- Extra hardware is required (hub/switch)
What are some advantages of a star topology network?
P • 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
What is required to connect a computer to a network?
A Network Interface Card is required to connect a computer to a network
What tow ways can a computer be connected to a network with?
Using a physical hardware port cable or connecting your computer system using a wireless connection
What are the data transfer speeds for a physical connection to a network? (Copper, fiber optic)
A copper cable transfers between 100 mbps and 1gbps
A fiber-optic connection has typical data transfer speeds between 1-10 Gbps
What is the typical data transfer rate of a wifi connection?
54 – 108 Mbps.
What can the transfer rates of a wifi connection be affected by?
- Severely affected by the distance between device providing wifi and computer systems
- Severely affected by atmospheric conditions
What is circuit switching?
Circuit switching is a 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.
What are some advantages of circuit switching?
- It is reliable
- It is fast (once connection established) and error free
What are some disadvantages of circuit switching technology?
- During the connection no other data can be transmitted along
the same route
- It takes time to establish the connection
- A fail on the route breaks the connection
Describe what happens in circuit switching technology in terms of landline phones?
When you phone someone on a landline phone, a physical circuit connection is made between you and the receiver using switches which data can travel along
What does packet switching do that is different to circuit switching?
than relying on a dedicated connection packet switching breaks the data down into small
packets that can be sent by more than one route.
What is a packet?
A packet is a collection of data that is transmitted over a packet-switched network
What two parts does a packet contain?
A header and the data
What is within the header of a packet?
The source address, the destination address, information enabling the data to be re-assembled to its original form, other tracking information, a checksum
What is 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.
Explain how packet switching transfers data?
1) Data is split up into multiple packets of data and provided ti a network for delivery to a certain destination
2) Each packet of data is redirected by a computer system along the network, however packets can take different paths
3) This carries on until it arrives at the destination
4) when al, the packets have re-arrived the data is re-assembled using the packet info for re-assembling
What does the checksum do?
It checks that the data has not been corrupted
If data does not arrive or is corrupted what is done?
The computer sends a request for the packet to be re-sent
What is routing?
Routing is the name given to the method of selecting paths along which packets are sent on
a computer network.
What does a routing table store and how is it made?
Specialist computer systems (e.g. switches, firewalls) construct a routing table which stores a number of paths along which it is best to send data to specific destinations. E.g. A->B->E->system
Why is maintaining accurate routing information important?
For ensuring packets are delivered as quickly as possible
Most routers use only one network path at a time, but what is the advantage of multipath routing techniques?
In multipath routing, the same packets are sent using multiple paths at the same time, so if a router further on fails to transmit the packet another same one is still taking an alternative route and so the packet will still arrive at its destination
What is a MAC address and what does it stand for?
A media access control address is a unique hexidecimal number given to any communication device (e.g. NIC)
Where is a mac adress usually stored?
In a communication devices’ ROM
Why do routing tables store the MAC address of communication devices on its network not ip adresses?
As MAC addresses do not change, is permanent
What is an IP address used for?
Ip adresses are used to uniquely identify computer systems on a network, thus allowing communication between them
What is a Domain Name System
A distributed database that matches IP addresses to computer system resources
How would a dns server match an IP adresses to a human-friendly domain name?
If you wanted to visit google, you would type in www.google.com. Your computer system will send a request to its DNS server for the IP address mapped to that domain name which will return the IP address allowing your computer system to communicate with the computer system where google is stored
If your local DNS server does not store the address of the resource you are requesting what will happen?
It will pass the request along to another higher level DNS server responsible for an entire zone e.g. .co.uk zone. It continues til, the address sis found or query fails
Give an example of a top and second level domain?
Second level - google
Top level - .com
What is a protocol?
A protocol is a set of rules that define how computer systems communicate
Give one example of a protocol rule?
- 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
What does TCP/IP protocol stand for?
Transmission control protocol/internet protocol
Describe the TCP/IP protocol?
These two protocols combine to allow communication between computer systems on a network. IP sets the format of packets and an addressing system, TCP allows packets to be sent and received between computer systems
Describe HTTP protocol?
The Hypertext Transfer
Protocol can be used to transfer multimedia web pages over the internet
Describe FTP (File Transfer Protocol)?
FTP is a protocol that can be used when copying a file
from one location to another via a network or the
What is FTP typically used for and why?
It is typically used for the transfer of large files,
as it allows broken communications to resume
transferring a file rather than having to restart.
What is a protocol stack?
A protocol stack is a set of protocols that work together to provide networking capabilities
What are the 5 layers of the TCP/IP transfer protocol?
1) Physical layer
2) Data link layer
3) Network layer
4) Transport layer
5) Application layer
Write the protocol layers implemented by a host, a switch, a router, a hub? (TCP/IP)
Host - All layers
Switch - data link, physical
Router - Physical, data link, network
Hub - physical
What does the physical layer of the TCP/IP transfer protocol do?
The physical layer defines the rules of transmitting raw bits over a physical data link (e.g. fiber optic cables) that connects network nodes (e.g. workstations, switches). Deals with the aspects of setting up and maintaining a link between communicating computers
Gove some examples of the tasks of the physical layer?
- What is the voltage to represent 1 bit and 0?
- How many nanoseconds a bit lasts?
- Can we transmit in both directions simultaneously or in one direction at a time?
- How many pins network connector has and what to use each pin for?
What does the data link layer in the TCP/IP protocol do?
The data link layer sends data from the network layer to the physical layer, and ensures that incoming data has been received correctly, and the the speed of the receiver matches that of the sender.
How does the data link layer send data?
It divides the data to be sent into data frames. A data frame consists of a link layer header (added) followed by the packet. The header contais the source and destination MAC addresses and a checksum.
How does the data link layer ensure that the incoming data has been received correctly?
It does this by analysing bit patterns in the frames. (It does it by analysing bit patterns in the checksum contained within the header of the received data frame)
Physical layer defines the rules of ___ ___ ___ over a ___ ___ ___ that connects network nodes (e.g. workstations, routers, switches). A few examples of the physical medium are ___ optic cabling and ___ cables.
Transmitting raw bits, physical data link, fiber, copper
How do switches operate at the data link layer of a TCP/IP protocol stack? Re worded: Describe the stages if the switching process?
- The switch receives a message frame
- It checks the destination MAC address of the frame
- The switch looks up in its switching table which port this frame should be sent to
- The switch sends the frame through the port that connects the computer indicated by the destination MAC address
What is the advantage of switches?
Switches will transmit the message frame only to a computer that needs to receive it so the network will be faster
What does a switch’s switching table contain?
It contains the mapping between MAC addresses and it’s ports
What does the network layer of a TCP/IP protocol stack do?
The network layer is responsible for the routing of IP packets between different networks
At what layer of the TCP/IP protocol stack do routers work?
At the network layer
What is a router?
A router is a networking device that connects different data paths of a computer network (At least two LANs or WANs or a LAN and it’s ISP)
How do routers direct data from sender to receiver between LANs / WANs?
A router maintains a routing table with the associations between IP addresses and a number of quickest paths by which this IP address can be reached. When a packet arrives at the router, it checks its destination IP address and based on the routing table will make the decision not which data path the packet should be forwarded.
Why is a router;s routing table constantly updated?
As some of the paths can become slower due to network traffic or be broken
What does a routing table store?
The corresponding IP address of a unique MAC address is stored
What does the transport layer of the TCP/IP protocol do?
The transport layer endures that data is transferred reliably from one part to another reliably and without error. It acts as an interface between communicating computers
Where is the transport layer of the TCP/IP protocol stack implemented?
It is implemented in the sending and receiving computers but not in the routers on the path between them
Depending on the application, what is one way in which the transport layer may make sure data is sent reliably?
Making sure that it is sent and received in the correct order
The ___ layer ensures that data is ___ from one point to another ___ and without ___. The transport layer is responsible for making sure that data is sent and received in the ___ ___. The transport layer is ___ in the ___ and receiving ___. Examples of the transport layer ___ are TCP and __.
Transport, transferred, reliably, error, correct order, implemented, sending, computers, protocols, UDP
What does the application layer of the TCP/IP protocol do?
The application layer provides interfaces to the software to allow it to use the network
What are some examples of the application layer of a TCP/IP protocol stack?
Email client software, file transfer protocol (FTP), the World Wide Web, DNS
Give some examples of the protocols in the application layer of the TCP/IP protocol stack?
HTTP, simple mail transfer protocol (SMTP), File Transfer Protocol (FTP)
Give an example of a protocol in the transport layer of the TCP/IP protocol stack?
TCP - Transmission Control Protocol
Give an example of a protocol in the network layer of the TCP/IP protocol stack?
Internet Protocol (IP)
Give an example of a protocol in the data link layer of a TCP/IP protocol stack?
What does Ethernet protocol do and at what layer of the TCP/IP protocol stack is it?
At the data link layer Ethernet Protocol describes how network devices can format data for transmission using frames and packets. They also define standards for types of network cabling used at the physical layer and corresponding transmission speeds
What is Wi-Fi?
Wi-Fi is a term for certain types of wireless networks using the 802.11 wireless protocols for transmitting data. Data is transmitted using electromagnetic waves instead of cables
What are some examples of wireless protocols?
Bluetooth, WAP (Wireless Application Protocol)
What is an example of a security protocol used by 802.11 wireless networks? Why do these networks use security protocols?
Wi-Fi Protected Access (WPA). They use them to provide a level of security comparable to that of a wired network
What is needed to use email?
To use email on your computer, your computer needs access to a mail server. This is often supplied by the ISP
How does a mail client and mail server exchange information?
Using email protocols to transmit information
What is the IMAP protocol?
The Internet Messaging Access Protocol is an email protocol that stores email messages on an email server
What does the IMAP protocol allow for?
The IMAP protocol allows the email user to read and handle emails as though they were stored locally on their computer. It allows the use to organise their messages with facilities such as creating folders, deleting unwanted messages
What kinds of facilities would be provided by the IMAP protocol for managing emails?
- Ability to make folders for organisation
- Deleting unwanted messages
- Store draft messages in the server
What is Post Office Protocol 3 (POP3)?
POP3 is the third version of a protocol used for receiving emails; It receives emails for a client and stores them in a single file on the mail server
Where are mails stored by the POP3 protocol before and after a user logs on to the mail server?
POP3 stores emails on a single file on a mail server at first.
When the email client logs one to the mail server, the email is transferred to their computer.
After they have been downloaded, no copies of the email are stored permanently on the mail server.
What is Simple Mail Transfer Protocol (SMTP)?
SMTP is used to deliver email from the sender to an email server or when email is delivered from one server to another. It is only used for sending emails
What (main) three protocols are used for email transfer?
Internet Messaging Access Protocol (IMAP)
Post Office Protocol 3 (POP3)
Simple Mail Transfer Protocol (SMTP)