Data Elements

Data Elements

Introduction:

In this blog post, I will be explaining the different types of data elements and why it is important. In addition to the explanations, I will also give its uses and why it is used. The data elements are:

• Cyclic Redundancy Check
• Encapsulation – Frames, Packets
• Datagrams
• Address
• Sequencing

Moreover, I will provide and show diagrams where appropriate for my points to be easier explained. In general, data elements are essentially data being broken up into manageable chunks. Additionally, although data is broken up into smaller sizes, additional information are set along with it which decreases the speed slightly but improves accuracy.

Cyclic Redundancy Check:

CRC (Cyclic Redundancy Check) is a checksum algorithm that is used whilst data packets are being transmitted across a device; this is to identify error detection and hopefully error correction. To do this, CRC will use a technique known as polynomial where it will divide the data (usually with a fixed divisor) and obtain a result. Furthermore, as the calculation is very specific, there will be a remainder. This remainder will be sent along with the data and will be re-calculated by the recipient device from the data it receives. This leads to error detection as if the comparison is incorrect, the data must have been corrupted during transmission. As a result, error correction will take place. Despite the importance of it improving the accuracy more than parity checks (counts the number of binary 1’s with an odd or even protocol), this increases the size slightly and thus slows the speed by a small percentage.

Encapsulation – Frames, Packets:

When large files are sent across the network to another device for download e.g. a video, the file will not only be split into smaller individual parts for convenience but also to assist in reliability. This is where encapsulation takes place as the frames will contain (encapsulate) each packet with a segment which holds user data and IP address. A common example is the Ethernet frame. Encapsulation is compulsory and is an important requirement because it gives the packet its destination, (see figure 1). Without this additional information the data would not be able to find its destination or know who to request a resend from.

Figure 1: Encapsulation

Datagrams:

When a file is sent, it is split into smaller manageable chunks – this can be in packets or in datagrams (consider datagram as a cousin to packets). However, datagrams are not reliable because it does not send an received acknowledgement (confirmation) to the sender of the data file, apart from this its function is identical to as of a packet – however this difference makes datagrams less reliable.

The difference between packets and datagrams is that packets are sent via TCP (transmission control protocol) and IP, this makes it reliable as it is only sent if the if it is connection-orientated (if it sends acknowledgement) whereas datagrams are sent through a UDP (user datagram protocol) and IP. This works by sending the data through different routes throughout the network and not having reliability as a priority.

Address:

Each device’s storage and components has its own unique identifier to the network; this is known as its address. Addresses are needed and are used by the devices because it is where the data will be transmitted to/sent from, like a destination for the data to go to or leave. This is also useful and is used by people who would like to access a specific array of a computer.

The main types of addresses are physical addresses and logical address. Physical addresses are an address that is given when the device is manufactured or hard coded; therefore it has its own identity and destination to where data goes to. This is useful for networks with computers that will be there in the long term. An example would be a MAC address.

On the other hand, a logical address is an address that is given (assigned) to the device every time by a server on a network. This address is more likely to be changed for security purposes; an example of a logical address is an IP address - a unique number that identifies a computer on the internet.

Sequencing:

When a file is split into packets and they sent from the device to the recipient, each packet will need to be reassembled at the end in chronological order for it to function accordingly. This is because without sequencing, the packets are not organised at the end and the data will be out of order – this is heavily dependent on the speed of the connection as well as the route it takes when it is sent through the network, (see figure 2). To avoid putting the data in the wrong order when the recipient device receives the data, they will beforehand add an identifier/sequence data element to let it know which order it goes.

Harvard Referencing: (In order of reference)
- Anderson, K. Atkinson-Beaumont, D.Kaye, A. Lawson, J. McGill, R. Phillips, J and Richardson, D. 2011. Information Technology Level 3 Book 1 BTEC National. Harlow: Pearson Education Limited.
- Figure 1: core0.staticworld, 2009. Encapsulation Frames Packets Segments. [Online] Available at: <http://core0.staticworld.net/images/idge/imported/article/nww/2009/07/01fig05-100277629-orig.jpg> [Accessed 22 January 2015].

Bibliography: (In alphabetical order)
- webopedia, 2015. CRC. [Online] Available at: <http://www.webopedia.com/TERM/C/CRC.html> [Accessed January 21 2015].