Error correction also includes the additional ability to reconstruct the original message, with error-free data.
Two basic methods have been designed to handle the error correcting system. These are called the Automatic repeat-request (ARQ), and the Forward Error Correction (FEC). The ARQ sends that data with an error detection code, which the receiver user to check for errors. In the FEC method the transmitter includes an error-correcting code (ECC) and sends the coded message. The receiver never sends any data to the transmitter, it just decodes what it thinks is the most "likely" data.
The Network Layer deals with errors via a variety of means (Wikipedea, 2008). These are to ensure the QOS is maintained. These can be items such as the Parity check, which means that if any bits are corrupted in the message, they are replaced to the expected format. A checksum, which involves an algorithm to check the validity of the data, Hash functions, which perform a similar function and repetition schemes. The full list of methods is stated here:
The Transport Layer uses 2 two way error correction protocol, which involves a discussion between the sender and the receiver. This is where the receiver informs the transmitter to resend a message when an error occurs. ...
Cyclic redundancy checks
Hamming distance based checks
Cryptographic message digest
Horizontal and vertical redundancy check
The Transport Layer uses 2 two way error correction protocol, which involves a discussion between the sender and the receiver. This is where the receiver informs the transmitter to resend a message when an error occurs. The two basic types for each packet transferred are called a NACK (Not Acknowledged), when a failure occurs and an ACK (Acknowledged) when a packet has been successfully received. The way it does this is to check the header/footers of packets to see if it is in the format expected. This is usually achieved by CRC (Cyclic Redundancy Check) checksums which are calculated based on the data transmitted.
Basically, the Network Layer function is to check the validity of the data at a lower level than the Transport Layer, and communicates the problem up the hierarchy. The Transport Layer in turn, informs the transmitter to resend the erroneous data. The Transport layer has other functions, such as allowing a mechanism where the receiver informs the transmitter what to send next and what is expected.
Question 2 (5 marks)
What are the different types of collisions that can occur on an Ethernet network
Briefly explain each.
There are the types of collision where two packets are sent over the network at the same time, and this is handled by the CSMA/CD (Carrier Sense Multiple Access / Collision Detect) protocol and a 'Collision Domain'.
A Collision Domain happens when two devices on the network transmit at the same time (The TCP/IP Guide, 2005). An Ethernet network can be composed of a single or a multiple