Cause and effect in data transmission

• • Different parts of network use different media;

  • Network congestion;

  • Packets may take different routes;

  • The receiver may be busy;

  • Physical size of the network;

  • Fiber is faster than coax;

  • Some packets may be delayed by congestion;

  • There may be longer transmission times over large distances;

Network Protocols

• • Definition: (Protocol) A set of rules or procedures that are used for transmitting data between electronic devices.

  • Definition: (Protocol) An agreed-upon format for transmitting data between two devices.

    • • Without a set of rules, computers would not be able to “talk” or communicate with each other across networks.

      • Network protocols were created to allow computers to communicate in an organized manner without room for misinterpretation.

  • They are usually a part of a set of Network Standards developed for Open Systems.

  • They allow computers to communicate with others without the users being aware of what is happening in the background, which is known as encapsulation.

  • Network protocols use a set of rules to exchange information between network nodes.

    • • The client sends a signal to the server.

      • The client provides key information about what kind of data is being requested.

      • This allowed the modernization of the Internet to occur.

  • A protocol defines the format and the order of messages exchanged between two or more communicating entities.

  • Some protocols support data compression, which is designed for high-performance network communication.

Why are protocols necessary?

• • Protocols are necessary in order to ensure that devices, regardless of the mechanics and formats that they are comprised of, are compatible and can interact with each other.

  • To ensure data integrity

  • To control data flow and allow data flow

  • Provide error checking mechanism

  • Minimize congestion

  • Prevent deadlock

  • Allows interoperability

Advantages of Packet Switching

• • • Network Efficiency

      • In circuit switching network, reserved circuit cannot be used by others till the sender and receiver leave it. This is inefficient, because other devices can’t use the network until the two have finished communicating, resulting in network bandwidth wasting. Packet switching reduces this.

    • Reliability / Fault Tolerance

      • All networks lose data in transit time to time, but using packet switching reduces this, because the receiving device comes to examine the packets and can easily detect missing packets and request them to be resent. In circuit switching, if data is lost, most of the time it is gone for good.

    • Resilience

      • Resilient to change. Packets find destination using routers, which use their knowledge to send traffic on the most effective route. If a node shuts down, the router can resend it to another route. Circuit switching networks, however, needs manual intervention to get things running.

    • Cost / Scalability

      • Can be used to carry voice and video traffic, meaning a separate computer and phone network is unneeded. Easy to expand network cost-effectively, due to the router's ability.

Disadvantages of Packet Switching

• • • Variable Connection Speeds / Possible Latency

      • Time taken to put back data packet changes each time can be a problem for time-critical information - emergency signal - also known as ‘latency’

      • This makes it difficult to guarantee a fixed amount of continuous bandwidth for a connection.

    • Hardware Requirements

      • Switching nodes requires more processing power as the packet switching protocols are more complex

      • Routers need to continuously process the optimal route for each packet.

    • These packets must also be reassembled. Switching nodes for packet switching require large amount of RAM to handle large quantities of packets. This all requires multiple nodes with processors and memory.

Error detection technique

Techniques to ensure data integrity during data transmission

Checksum 

a method of checking for errors in data transmission by counting the number of bits in a data packet. If the count matches, it is assumed that a complete transmission was received.

• • • Data stream has a unique value determined and this is checked at the receiving end; 

    • often used to verify data integrity but are not relied upon to verify data authenticity

How a checksum could ensure data integrity in the transmission of data.

• • Checksum is computed from data; 

  • Groups of bits are added before transmission and the sum appended to the group; 

  • When the data is received the actual sum is compared with the check sum; 

  • If the two are the same it is assumed that the data has not been corrupted; 

  • Otherwise a re-send would be requested; 

Parity check 

is a method of checking for errors in data transmission using an additional bit called a parity bit. When an odd parity is chosen, the number of ones in the nine bits must be odd. If an error has occurred in a single bit, then the parity will be different and an error in transmission has occurred.

• • • Odd or even parity digit is appended - A parity bit is appended to the original data bits to create an even or odd bit number; the number of bits with value one

    • Parity check is performed at the receiving end;

How a parity check is used to ensure data integrity in the transmission of data. 

• • Before sending data a parity bit is calculated from data; 

  • To make the number of 1s an even/odd number; 

  • This bit is added to the data and sent as an integral unit; 

  • After receiving data number of 1s is calculated; 

  • If it is not an even/odd number an error is indicated; 

NOTE: Parity checking is arguably the safest method, because within the checksum method a bit can be out of place and the receiving end of the data packet would not be able to identify which bit was misplaced.