Question

In the last module you learned a formula for calculating bit rate, R = b/t, that is the number of bits divided by the time. This formula expresses the number of bits that are transmitted over a circuit in a given period of time. In practice, however, we are not only concerned with the number bits transmitted, but also with the number of data bits transmitted over a circuit. The data bits are those that the sender decides to send to the receiver, and do not include the overhead bits used by the networking protocols involved. Recall that the protocols that send messages on a circuit use some of the available bits to store metadata (overhead) for protocol communication. From a data perspective, the bit rate on a circuit can be termed the maximum data rate because it calculates the theoretical maximum number of data bits that can be sent over a network circuit if the protocols were to use no overhead bits. Effective data rate is a rate that takes into account the overhead of the protocols involved. In this part, you will perform effective data rate calculations with two scenarios. Each scenario gives you the maximum data rate of the circuit, along with details of the protocol(s) involved, and asks you to calculate the transmission efficiency and effective data rate. For full credit, the calculations you use to derive the answers must be shown. Scenario 1: 7, 500 ASCII characters are being transmitted over a 3 Mbps circuit. The protocol uses 8-bits for each ASCII character, as well as 2 parity bits (used for error detection and correction) for each ASCII character. Calculate the transmission efficiency of sending these characters using this protocol. Determine the effective data rate of sending these characters using this protocol. Scenario 2: A web browser sends an HTTP packet using TCP over IP over Ethernet. The web browser request consists of 145 bytes. The HTTP protocol adds an additional 35 bytes of overhead to the request as part of the HTTP packet. The transmission occurs over a 100 Mbps circuit. Calculate the transmission efficiency of sending this packet using the specified protocol. All protocols involved add some overhead bytes to the request. Unless the scenario otherwise specifies a specific number of bytes, use the nominal header sizes for the protocols. Determine the effective data rate of sending this packet over this circuit. In this module, you learned that some communication protocols implement error correction, which is a mechanism that both detects and corrects errors that occur between the sender and receiver of a message. You also learned that one common method of error correction is automatic repeat request (ARQ), in which the sender and receiver detects potential errors in each protocol data unit (PDU) sent, and retransmits them when appropriate. In this part, you are given different scenarios which begin with the receiver transmitting a single PDU. Each scenario indicates the state of the transmission. For each scenario, indicate a complete and numbered series of steps describing exactly how the sender and receiver ultimately successfully transmit the message, correcting errors where appropriate, using stop-and-wait ARQ. Keep in mind that the last step for each scenario should be the successful acknowledgment from the receiver. Scenario 1: The PDU is transmitted without an error. Scenario 2: The initial transmission of the PDU contains an error. Scenario 3: The initial transmission of the PDU is lost before it arrives at the receiver. Scenario 4: The acknowledgment of successful reception of the PDU, by the receiver, is lost before it arrives at the sender. An organization has written an application that allows all of their employees to send messages instantly or to an inbox to other employees. The application was written to use the UDP transport protocol; however, sometimes messages are lost, or have missing, unreadable, or out-of-order text segments. The project manager is considering having the programmers rewrite the application to use the TCP protocol but has first requested your input. Answer the following questions to help the project manager decide. Why might the application have missing, unreadable, or out-of-order text segments in its messages? What could be done by the application to correct these issues? How might switching to the TCP protocol solve these issues? Other than items mentioned in item c, what would be the advantages of switching to the TCP protocol? What would be the disadvantages of switching to the TCP protocol?

Answer 1

Answer: UDP does not guarantee that the message will reach its destination with a proper sequential order. a) b) To correct these errors we can use TCP protocol. c) If the packets are lost or re-transmitted it does not guarantee that the packets will be receiving in proper order. It is also reliable. d) It provides congestion control protocol. e) It is connection-oriented and slower and the efficiency of TCP decreases.