1. Justin Andrews<br />ACSG 520<br />1. The OSI model is an ISO standard, and one that covers all aspects of network communications. <br />2. a. Route determination is handled by the Network Layer.<br />b. Flow control is handled by the Data Link and Transport Layers.<br />c. The Physical Layer deals with the Interface to transmission media.<br />d. The Application Layer provides access for the end user.<br />3. a. The Transport Layer ensures a reliable process-to-process message delivery.<br />b. Route selection is handled by the Network Layer.<br />c. The Data Link Layer defines frames.<br />d. The Application Layer provides user services such as e-mail and file transfer.<br />e. The Physical Layer deals with the transmission of a bit stream across physical medium.<br />4. a. The Application Layer communicates directly with a user's application program.<br />b. The Data Link Layer handles error correction and retransmission.<br />c. The Physical Layer uses a mechanical, electrical, and functional interface.<br />d. The Physical Layer has the responsibility for carrying frames between adjacent nodes.<br />5. a. The Presentation Layer handles the format and code conversion services.<br />b. The Session Layer established, manages, and terminates session.<br />c. The Data Link Layer ensures reliable transmission of data.<br />d. The Application Layer uses log-in and log-out procedures.<br />e. The Presentation Layer provides independence from differences in data representation.<br />6. Sender(Application -> Transport -> Network -> Data Link -> Physical) -> Link -> Receiver(Physical -> Data Link -> Network -> Transport -> Application)<br />The Network Layer isn't necessarily needed in this instance.<br />7. Sender(Application -> Transport -> Network -> Data Link -> Physical) -> Link -> Router(Physical -> Data Link -> Network -> Data Link -> Physical) -> Link -> Receiver(Physical -> Data Link -> Network -> Transport -> Application)<br />8. 100:150 bytes<br />9. Minimum header size at the transport layer is 8 bytes.<br />10. Minimum header size at the network layer is 12 bytes.<br />11. Minimum header size at the data link layer is 12 bytes.<br />12. In a way we encapsulate the message of a regular letter as we place it in an envelope, which consists of both the message it contains, and the address of the person sending and receiving it. A post card is not encapsulated, as the message is only found with the addresses in question.<br />13. We do not need addresses at the physical layer because that layer is simply the means of transporting the message, similar to a road being a means from a car going from point A to point B. Addresses can be found on it, but it is not the message itself.<br />14. A radio station does not need addresses when using a broadcast, as the message is going out to every single address possible, making the information unnecessary.<br />15. I think the sender and receiver addresses are needed in the Internet due primarily to the sheer size it has reached. In order for a message to reach its destination, the receiver address is a must, and the sender address is necessary in the event of errors, notifying the receiver, and to firmly set up the path a message will take.<br />16. I think the reason the Internet needs four levels of addresses as opposed to one for a telephone network is due to the fact that errors are more prominent when dealing with messages over the Internet. There are also the many different manners in which a message can be sent, and the system of sending a message through routers works in a more automated manner, as opposed to a telephone network, requiring further depth.<br />