CSIS174 Chapter 2 OSI Model Team Exercise – 10 points

A secret agent must write a three-page letter to another secret agent in a small town 25 miles outside of Paris, France. Each page of the letter will be mailed separately because of the highly sensitive nature of the material. In order for the recipient to understand the entire letter, the recipient must have all three pages. Each word will be encrypted by the sending agent and again decrypted by the receiving agent. The sending agent will send the letter through the regular mail service but will use the return receipt to guarantee delivery. The letter will be first sent to Paris and then forwarded to the small town.

1.Compare the secret letter’s journey through the postal system to the progress of a packet of data through the layers of the OSI model.

· Physical - The letters being transferred from one place to the other. And the postal workers transferring from one place to the other.

· Data Link- The data link layer would be the regular mail service instead of express(or protocol of how it would be sent).As well as would be putting the 3 letters into 3 to envelops. Broken down into the sub layers MAC equivalent would equal the postal worker knowing to pick up of the letter form the mailbox. The LLC equivalent would be to make sure that the letter was sent out at the correct time and there were no more letters than the postal worker could handle. The Data link layer would also be responsible for making sure the letters were not destroyed in the process of delivery. (Through CRC)

· Network- This layer would be equivalent to postal workers checking the address and making sure it took the fastest route as possible. Primarily the routing through Paris and then to the smaller town.

· Transport – The transport layer would make sure that the letters would arrive at a time that the other spy could receive them. As well as taking the pages and separating the orders and reassembling them at the other spy location.

· Session – This would be the knowledge that the letters were to be sent. Then that they were sent, and received via the return receipt.

· Presentation – The Presentation layer would handle the encryption and decryption of the letter.

· Application – This would be the writing and reading of the finished documents.

2. Compare the parts of the addressed and stamped letter to a data frame.

- The preamble would be the flag on the mailbox to let the mail man know that there is mail going out.

- The Start of Frame Delimiter (SFD) Is where the address’s are in the appropriate spots.

- The destination address would be the same as the receiving spies address.

- The source address would be the same as the sending spies address.

- The Length would indicate that 3 letters were being sent out. (or the weight of the letters so that the correct stamp would have to be purchased and placed on the envelope.

- The data would be the letters them selves.

- The pad would be the anything extra placed in the envelopes to through people off from thinking it was a secret document.

- The Frame check sequence (FCS) would be just making sure that the document was physically legible.

Note: This assignment will be delivered via oral team presentation to the class.