Data elements

Data elements

In this blog I will be explaining the different data elements. The ones I will be explaining are cyclic redundancy check, encapsulation, datagrams, addresses and sequencing.

Cyclic redundancy check

Cyclic redundancy checking (CRC) is a method for checking errors in packets of data that has been sent via communications. This happens by using a technique called a polynomial. This attaches a code to check if the data is correct. The device that is receiving has the same code as the data being sent so it can check if it is correct or not. If it is not correct, the data will be requested again and it will be sent. This will happen until the data gets there correctly.

Encapsulation

Encapsulation uses frames and packets for sending information. A frame is the data sent from device to device. Larger items such as a video will be split up into smaller frames to be sent. Packets are a collection of frames and they are normally sent by protocols such as an IP (Internet Protocol). An example of a frame would be an Ethernet frame.

Datagrams

A datagram is very similar to a packet. Datagrams are used for sending information and they are used in protocols such as the Internet Protocol. The difference between datagrams and packets is that datagrams use UDP (User Datagram Protocol). This makes it less reliable because you do not get a response if it failed or not.

Addresses

Network addresses is a unique identifier for a computer on a network. There are many different types of network addresses. An example of one these would be an IP address or a MAC (Media Access Control).

Sequencing

Sequencing is when data packets are labelled. This allows them to be sent down separate paths in the network and still get to the device. When all of the packets are at the end they can be re sequenced. As all of the packets had been labelled they could be easily put back together and there would be no problems.

References

Anderson, K. Atkinson-Beaumont, D.Kaye, A. Lawson, J. McGill, R. Phillips, J and Richardson, D., 2011. Information Technology Level 3 Book 2 BTEC National. Harlow: Pearson Education Limited.

TechTarget (2015) Cyclic redundancy checking [Online] Available at: http://searchnetworking.techtarget.com/definition/cyclic-redundancy-checking [Accessed on: 26/01/15]

TechTarget (2015) Datagram [Online] Available at: http://searchnetworking.techtarget.com/definition/datagram [Accessed on: 26/01/15]

Communication models and protocols

Communications models and protocols

In this blog post I will be explaining the different communications models and the protocols. For the models I will be explaining the OSI (Open System Interconnect) model and the TCP/IP model. The protocols I will be covering are Wi-Fi, Bluetooth, 3G and 4G and the Wireless Security Protocols (WEP, WPA).

OSI model

The OSI model stands for (Open System Interconnect). The OSI model is made up with seven different layers that I will be explaining. The model is for how applications can communicate over a network. Down below is a simple description of all of the seven layers.  

Layer one: Physical

The first layer is where the hardware for the system is. This allows the devices to send and receive data on cables. This layer transfers the bit stream via the cables that I mentioned.

Layer two: Data link

The second layer is where the packets of data are encoded and decoded into bits of data. The data is split into sub layers. These are the MAC (Media Access Control) and Logical Link Control (LLC). The MAC sub layer controls how a computer gets access to the data and gets permission to send it.

Layer three: Network

The third layer is where routing and switching happens. This allows data to be sent from node to node.

Layer four: Transport

The fourth layer provides the transfer of data between the different systems. It also ensures that the data transfer was complete without any errors.

Layer five: Session

The fifth layer is where connections are created, managed and terminated between applications.

Layer six: Presentation

The sixth layer is for organising data into a format that can be used. Some examples of formats that can be used would be JPG (Joint Photographic Engineers Group), MP3 (Multimedia Players Engineers Group) or doc (word documents).

Layer seven: Application

The final layer is used by applications. An example of some of these applications would be email or web browsers. This layer has many protocols linked to all of the different applications.

TCP/IP model

The TCP / IP model stands for Transmission Control Protocol / Internet Protocol. It is like the OSI model as they both use layers for tasks. The development of the Internet was based on this model so it is quite well known. The TCP/IP model is made up of four layers that I will explain below.

Layer four: Application layer

This layer is like the application layer for the OSI model. It includes the processes that involve user interaction. This layer also determines the presentation of the data.  

Layer three: Transport layer

There are two different transport layers for this layer. They are TCP (Transmission Control Protocol) and UDP (User Datagram Protocol). TCP guarantees that information is received after it had been sent. UDP does not do any checks if the information has been sent.

Layer two: Internet layer

The internet layer is the TCP/IP network layer. All of the upper and lower layers go through the IP as they are passed through the model.

Layer one: Data flow / Network access layer

This layer is the data link layer and the physical layer. In TCP/IP these are normally grouped together. TCP/IP uses existing data links and physical layers because it allows it to be adaptable and so it can work across many systems.

Protocols

Wi-Fi

Wi-Fi is a popular wireless technology that allows you to connect devices to the internet at high speeds. Wi-Fi uses radio waves to allow devices to connect to the internet. It also uses IEEE 802.11 (Institute of Electrical and Electronics). IEEE 802.11 has four different types. They are 802.11n, 802.11a, 802.11b and 802.11g and they all operate at a different frequency and speed.

Bluetooth

Bluetooth is a short range radio technology and it is aimed at making communications between internet devices simpler. It is available in many devices and it uses a range of frequencies and techniques.

3G & 4G

 3G stands for third generation. It is used in mobile technologies and it uses high frequency radio waves. It allows you to connect to the internet wirelessly without wireless. 4G is the same as 3G however it is a lot faster than 3G. 4G is not around a lot at the moment as it is quite a new technology.

Wireless Security Protocols (WEP)

WEP stands for Wired Equivalent Privacy. One of the issues with wireless networks is that security can be pretty poor. WEP keeps the wireless secure by encrypting every packet of data that has been sent.

References

Anderson, K. Atkinson-Beaumont, D.Kaye, A. Lawson, J. McGill, R. Phillips, J and Richardson, D., 2011. Information Technology Level 3 Book 2 BTEC National. Harlow: Pearson Education Limited.

Webopedia (2015) OSI Layers [Online] Available at: http://www.webopedia.com/quick_ref/OSI_Layers.asp [Accessed on: 26/01/15]

Webopedia (2015) Bluetooth definition [Online] Available at: http://www.webopedia.com/TERM/B/bluetooth.html [Accessed on: 26/01/15]

Access methods

Access methods

In this blog I will be explaining the different access methods. The ones I will be explaining is CSMA/CD, CSMA/CA and token passing. I will use diagrams to make it easier to understand what I am saying.

CSMA/CD

CSMA/CD stands for Carrier Sense Multiple Access / Collision Detection. This is a set of rules that control how network devices respond when two devices try to use the same line at the same. This creates a collision with the data. An example that uses CSMA/CD would be an Ethernet network. This checks the line if it is clear and then it will send the data. Figure one is a simple diagram on how it detects activity before it sends off. As you can see it also checks if there was a collision as well as if there is activity

An example of how CSMA/CD works

CSMA/CA

CSMA/CA stands for Carrier Sense Multiple Access / Collision Avoidance. This is like CSMA/CD but it works differently. CSMA/CA normally works before CSMA/CD to avoid the most data collisions.

Token passing

Token passing is a way of granting permission to a device to send data over a network. Token passing uses a token to allow access to the network. Only one device at a time can send data. Once the device is finished with the network, it passes onto the next device. This goes around till all of the devices have used it.

References

Webopedia (2015) CSMA/CD definition [Online] Accessed at: http://www.webopedia.com/TERM/C/CSMA_CD.html [Accessed on: 25/01/15]

Webopedia (2015) CSMA/CA definition [Online] Accessed at: http://www.webopedia.com/TERM/C/CSMA_CA.html [Accessed on: 25/01/15]

Webopedia (2015) CSMA/CD definition [Online] Accessed at: http://www.webopedia.com/TERM/T/token_passing.html[Accessed on: 25/01/15]

Images

Figure one: BlogSpot (2015) CSMA/CD diagram [Online] Accessed at:  https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhCg-npPmuAI9Rvna0RZraABQvxo7h0cm9T0iTuePHPoDUc7VFoqH6IYkTl4rJsb6q36FfZk5U0y1yWiFRu47BEJQK054eTwnhllqmIEb4aXwE9fuPW67j1-TODTGj865iJusBTvZkohBc/s1600/CSMA-CD+Process.docx.png [Accessed on: 25/01/15]

Network software

Network software

In this blog I will be covering what a network OS is (NOS) and the connection software there is. I will give examples of both network OS and connection software.

Network OS

The network OS (Operating System) is the main part to running a network. They include special features for connecting devices to LAN’s (Local Area Networks). An example of the features would be print servers, controlling access privileges and file management.  A normal operating system would not have these functions so you would need a network OS. An example of a network OS would be Microsoft Windows Server 2012. Other examples of network OS are Airisoft’s LANtastic, Banyan VINES and Novell's NetWare.

Connection software

Network connection software is also referred to as clients. They allow you to connect to a server and access the services provided. There are many different clients that you can use. An example for a user to connect to web servers they would need a browser client like Internet Explorer. Skype is a client for a VOIP (Voice Over Internet Protocol).

References

 TechTarget (2015) Network Operating Software (NOS) [Online] Accessed at: http://searchnetworking.techtarget.com/definition/network-operating-system [Accessed on 22/01/15]

Network topologies

Network topologies

In this blog I will be explaining the five different network topologies. I will add in a diagram, explaining the uses and talking about the limitations. The five different topologies are Star, Mesh, Bus, Tree and Ring.

Star

A star network has its own cable for each device. These cables are normally connected to a switch or a hub. The hub sends all the packets of data to all of the different devices. If a switch was used, it would only send packets of data to the device that needs it. Figure one shows how the star topology works. The information is sent out to the devices. A benefit of the star network is that it is very reliable. If one of the cables or device fails then all of the other devices can still work. Also no data collisions can happen with the data being sent around. A limitation of the star network is that is expensive to install. There is many cables used for this and the cables do cost quite a bit of money. Another limitation would be if the hub went down, the whole system would go down and no one would have a connection to the network.

Figure one: An example of the star network.

Mesh

The mesh topology is a network where each device is connected to each other. This network is normally used for wireless networks as everything is connection. As you see in figure two, everything is connected to everything else. A benefit of mesh would be if one device in the network goes down it can still function properly. This is good if there are many networks in the service. If one of the devices went down, the other people would not get affected. A limitation of the mesh topology would be is that it is very expensive to set up and maintain. This would not be a good choice for a company because it would cost a lot to maintain.

Figure two: An example of the mesh network.

Bus

A bus network works by having all of the devices connects via one cable. Each end of the cable there is a terminator installed. This is to stop the signals reflecting back down the cable. Figure three shows how a bus network works. As you can see all of the devices are connected up to the one cable. A benefit to the bus topology is that is easy to install. If you do not have a lot of money or you want to set up a simple network you could easily set up the bus network. Another benefit for the bus topology is that it is cheap to install. If your business was on a budget you could install the bus network to save money. You need less cable to install so it is cheaper. One limitation to the bus network is that if the cable fails the whole network goes down. If the cable got damaged you would have to get it repaired and then the network would work again. Another limitation would if there were too many people on the network. The more people you have on there, there would be more data collisions. For example, if you have 100 people on the network, there would be many data collisions.

Figure three: An example of the bus network.

Tree

The tree topology is like the star topology and the tree topology. As you can see in figure four, there is a bus topology with two star topologies connected to it. If the main cable failed between the two star topologies, they would not be able to communicate with each other. A benefit of a tree topology is that expansion of the network is easy to do. If you were expanding your company you could easily make it bigger and add on another star topology. Another benefit of the tree topology is that error detection and correction is easy to do. This is good if you have errors in your network or with packets of data being sent around. A limitation of the tree topology is that it relies on the main bus cable. If that cable goes down the whole network could be broken.

Figure four: An example of the tree network.

Ring

In the ring network all of the different devices connected are connected to two other devices. This creates a ring for the data to travel around. All the data that gets sent around in one direction and each device receives each packet. Figure five shows how the ring network works. As you can see all of the devices that are connected in a ring and the data would get passed round. A benefit of the ring system is that the data can be transferred around quickly. This is good because if someone wanted some data in the network, it would not take too long to get there. A limitation would be if there was one problem with the ring the whole server would go down. This would be a problem if you wanted to send some important information to someone then the server goes down.

Figure five: An example of the ring network.

  

References

BBC (2015) Star network topology [Online] Available at: http://www.bbc.co.uk/schools/gcsebitesize/ict/datacomm/networktopsrev3.shtml [Accessed on 20/01/15]

BBC (2015) Ring network topology [Online] Available at: http://www.bbc.co.uk/schools/gcsebitesize/ict/datacomm/networktopsrev2.shtml [Accessed on 20/01/15]

BBC (2015) Bus network topology [Online] Available at: http://www.bbc.co.uk/schools/gcsebitesize/ict/datacomm/networktopsrev1.shtml [Accessed on 20/01/15]

Computer Hope (2015) Tree network topology [Online] Available at: http://www.computerhope.com/jargon/t/treetopo.htm [Accessed on 22/01/15]

Computer Hope (2015) Mesh network topology [Online] Available at: http://www.computerhope.com/jargon/m/mesh.htm [Accessed on 22/01/15]

Images

Figure one: BBC (2015) Star network topology diagram [Online] Available at: http://www.bbc.co.uk/staticarchive/babaaeda24aa3798f67ae3548e58bd94e306f661.gif [Accessed on 20/01/15]

Figure two: Tutorials point (2015) Mesh network topology diagram [Online] Available at: http://www.tutorialspoint.com/data_communication_computer_network/images/mesh_topology.jpg [Accessed on 22/01/15]

Figure three: BBC (2015) Bus network topology diagram [Online] Available at: http://www.bbc.co.uk/staticarchive/9933e41867b45fa9319fa74db5ac7f33b71d44c8.gif [Accessed on 20/01/15]

Figure four: Webopedia (2015) Tree topology diagram [Online] Available at: http://www.webopedia.com/imagesvr_ce/6353/tree_topology.gif [Accessed on 22/01/15]

Figure five: BBC (2015) Ring network topology diagram [Online] Available at: http://www.bbc.co.uk/staticarchive/a5ed94c8c3d50b8e5f859dc5601d4d6a489a64b5.gif [Accessed on 20/01/15]

Networks

Networks

In this blog post I will be explaining all the different networks and I will be giving examples of those networks. The three types of networks I will be explaining are WAN (Wide Area Networks), LAN (Local Area Networks) and Wireless.

A WAN (Wide Area Network) is a large network that normally covers a wide area. WAN’s are normally built up of two or more LAN’s. Figure one is an example of how a WAN works. As you can see there is three LAN’s and they are connected together to create a WAN. The biggest WAN would be the internet as all of the servers are connected together and they serve you information.

Figure one: An example of WAN

A LAN also known as a Local Area Network is like a WAN but it covers a smaller area. LAN’s can cover up to a city if the server is powerful enough. LAN’s are generally used in a workplace or in a college. A LAN could be only two computers that are connected together with a cable or it could be a college. Figure two shows how a LAN works. As you can see there is a server and seven computers connected to each other.

Figure two: An example of LAN

A wireless network is a way of connecting to the internet wirelessly with a device such as a wireless router. Wireless networks are cheaper to use compared to a wired network because you will need to buy different cables for connecting. Wireless is normally used to connect smart phones or laptops. Smart phones do not have Ethernet cables so they have to be connected wirelessly.

References

Anderson, K. Atkinson-Beaumont, D.Kaye, A. Lawson, J. McGill, R. Phillips, J and Richardson, D., 2011. Information Technology Level 3 Book 2 BTEC National. Harlow: Pearson Education Limited.

Images

Figure one: BBC (2015) WAN example [Online] Available at: http://www.bbc.co.uk/staticarchive/17d1c375cab9c86e64c0b5987e1d6fc5109739c3.gif [Accessed on: 20/01/15]

Figure two: BBC (2015) LAN example [Online] Available at: http://www.bbc.co.uk/staticarchive/30dd6ccf1df35e81482db0b2e1f3f62edd760733.gif  [Accessed on: 20/01/15] 

Communication devices

Communication Devices

DTE (Data Terminal Equipment) is the device that controls the data coming to or from a device such as a computer.  A DTE connects by a wired connection to a DCE (Data Communications Equipment). An example of a technology that can connect is a laptop. A laptop connects with a wired connect. A limitation would be if you do not have enough RAM (Random Access Memory) to hold the information of the internet connection. Another limitation would be the range of the connection. If you are too far away you would not have a very good connection to the internet.  

DCTE (Data Circuit-terminating Equipment) works together with the DTE. This allows you to connect to the internet or to the network service. The DCE controls the communication so it makes it easier to connect. An example would be a wireless router in your home. This would allow you to connect your laptop or other devices to the internet. A limitation could be if you do not have enough Ethernet ports to connect multiple devices. Another limitation of DCE would be if there was too much data. A DCE can only take a certain amount of data so if there was too much data it would get overloaded.

A laptop is a type of DTE that connects to a DCTE to connect to a network or the internet. Laptops can be either connected by a wired or a wireless connection. The connection is made by connecting the DCTE to the DTE then connecting the DCTE to the laptop. There are some limitations for a laptop. One of these limitations would be the range. If you could not reach to a connection you would not be able to get internet. This would be a problem if you were using an Ethernet cable.

A smartphone is another example of a DCTE. A smartphone connects wirelessly to the DCTE as there is no Ethernet cable built into smartphones. A smartphone uses a chip to communicate with the DCTE so you can still get internet. A limitation with smartphone is that you cannot connect via an Ethernet cable so the internet would be slower.

A switch is used for connecting multiple computers together to create a network. This allows all of the connected computers to have access to the internet. The switches have Ethernet ports that are used to connect to the internet.

A router also allows different networks to connect to each other. Routers allow you to connect to the internet. They can also manage the amount of bandwidth that each computer gets. This allows the internet to run smoothly to all of the computers connected.

 A wireless Access Point such as a router allows wireless devices to connect to a network. An example of a WAP would be Wi-Fi as you can connect to hotspot. These are mainly used in a public area. WAP’s are easy to connect to if there is a hotspot near. With public networks you normally have to just join the network but in some cases you have to put in some details.

A modem is a device that encodes digital signals into analog signals and transfers data via telephone lines. This allows you to connect to the internet easily and with no fuss. Today the routers have the modem built in so it makes it easier to set up when connecting to the internet.

A server is a computer that sends information to other computers. It can be used either in a LAN connection (Local Area Network) or in a WAN connection (Wide Area Network) via the internet. LAN servers are normally used in offices or in a school as it is all in the same area. An example of a WAN server would be a website server. This serves you the information and allows you to view the website.

References

Tech Terms (2014) Server definition [Online] Accessed at:  http://techterms.com/definition/server [Accessed on: 20/01/15]

Webopedia (2015) DTE – Data Terminal Equipment [Online] Accessed at: http://www.webopedia.com/TERM/D/DTE.html [Accessed on: 20/01/15]

Tech Terms (2014) Switch definition [Online] Accessed at:  http://techterms.com/definition/switch [Accessed on: 20/01/15]

Anderson, K. Atkinson-Beaumont, D.Kaye, A. Lawson, J. McGill, R. Phillips, J and Richardson, D., 2011. Information Technology Level 3 Book 2 BTEC National. Harlow: Pearson Education Limited.

Network Services

Packet switching

Packet switching is a way of sending information with small packets over a network. Packet switching is mainly used in WAN’s (Wide Area Networks). The information is split into small packets and they are sent individually to the network. The small packets allow the data to be sent easily across the network.

Benefits

·         It is reliable. If there is any data lost the packets can be resent so no data is lost.

·         It can direct the traffic via a variety of routes

Limitations

·         It takes time to put together the data so it is not good if you are sending important information.

·         Packet switching is not very good for small data packets. For example, if the data packet is 600            bytes long, it would need to be split up into two 512 bytes.

ISDN

ISDN is short for integrated services digital network. It is a telephone line that shares voice and data communications. There are two types of ISDN, BRI which is basic rate interface which consists of two 64bps B channel lines and 1 D channel line. To further explain, a B (bearer) channel line is the main data transfer line in an ISDN, a D (delta) channel line is for transmitting control information. The Second type of ISDN is PRI or primary rate interface. This contains 23 B channels and 1 D channel unless you are in Europe there are 30 B channels and one D channel.

Benefits

Quick connection time (2 seconds) ISDN provides a high data rate

Limitations

• ISDN line can be very expensive
• ISDN requires special digital devices

Wireless Access Protocol

Wireless Access Protocol (WAP) is an older way to connect to the internet. It allows you to easily connect to the internet wirelessly. There is new ways to connect now such as 3/4G but WAP is still used on some phones. WAP allows you to connect to simple things such as your emails or Google. 

Benefits

·         It is a simple way to connect to the internet. 

·         Could be used on your phone.

·         Can access simple things such as your email.  

  

Limitations

·         It is out dated. 

·        Cannot connect to more complex sites that have a lot  of information.

·        It is slow to connect to.

Broadband is general heading for a variety of technologies which include Asymmetric digital subscriber line (ADSL) for transmitting data at higher speeds and allows you to connect to the Internet and provides a continuous connection. For some internet service providers (ISP) which is a company that provides internet. Broadband is provided by sharing a range or frequencies unused by other services.

Positives

·         A broadband connection is "always on" - no waiting for dial-up connectivity if you still use                  this route to the Internet.

·         Fixed price, you can budget effectively.

Negatives

·         Hackers who may either live in nearby neighborhood or pass around can hack into your                      wireless broadband network without your permission and can misuse it.

·         The network can be less stable.