Pros:

Reliable protocol makes the data transfer safe, thus contains numerous pros with it$.$ The process works by the receiver acknowledging when data is received, the sender receives the delivery of content that is free of errors in a PDU. In case PDUs are lost or received with errors, they will get resent by the sender until they are received. Through this process, the delivery of messages $($PDUs$)$ is reliable and guaranteed. When the data is being sent from one end to another, reliable protocol guarantees the delivery of PDU in intact and unaltered form. To maintain the accuracy, error checking is performed at each point of the message to ensure delivery without any issues. The order of the data is also maintained to ensure the delivery in the same order that it has been received. Reliable protocols are connection oriented protocols, the sender establishes the connection with the receiver beforehand and when the message is received, the receiver sends a confirmation message of the receipt.

Cons:

Although reliable protocols have many pros for its reliability and accuracy, it can also come with a few cons. One of the common cons are the take it may take time to send the message and it requires and uses great amount of bandwidth

Unreliable Protocols:

Pros:

With unreliable protocols, the benefit is that it doesn't take long to deliver the message. Another pro is that the receiver discards any PDUs with errors and does not save any lost PDUs which results in saving time and delivering PDU instantly.

Cons: Unreliable protocols do send the message but are not able to keep track of the messages, which results in unguaranteed and unconfirmed delivery. Another issue with unreliable protocols is that there are no corrections for errors during the process, and no data integrity when it comes to confidential data.