Consider a system as shown in Figure 1, where packets are transferred from Host 1 to Host 2. All transferred packets have the same size of . On the communication path from Host 1 to Host 2, there are two high-speed switches (SW1 and SW2), and it is assumed that no packets generated by other applications or other hosts are being transferred. Let the one-way delay of a packet between Host 1 and Host 2 be , and let the bandwidths of the respective transmission links be and (where ). Answer the following questions.
(1) To provide error-free data transfer between hosts, data transfer is performed while confirming the arrival of data packets. As the simplest method, consider a method where when a packet sent by Host 1 (data packet) arrives at Host 2, Host 2 generates an acknowledgment packet (ACK packet) and sends it back to Host 1. Note that the size of the ACK packet is , where , and the time required for transmitting and receiving packets onto the communication links at the hosts and switches is assumed to be negligible. Furthermore, Host 1 sends the next data packet with zero delay when it receives an ACK packet, and Host 2 sends an ACK packet with zero delay when it receives a data packet from Host 1. In this case, show the maximum value of the data transfer rate from Host 1 to Host 2.
(2) In the system of question (1), if data packets and ACK packets are lost randomly during transmission with a probability , show the average time required for a data packet to be transferred without error from Host 1 to Host 2. Assume that Host 1 retransmits the data packet if an ACK packet does not arrive even after waiting for after sending the data packet, and that ACK packets do not arrive at Host 1 after .
(3) To start communication, we want to perform an information synchronization procedure between Host 1 and Host 2. Assume that the information to be synchronized between Host 1 and Host 2 can be transferred in a single packet. Describe the procedure for cases where packet loss in the transmission path is expected, along with state transition diagrams (or state transition tables) to be executed by Host 1 and Host 2.
(4) In the packet transfer method of question (1), the data transfer rate does not increase when is large. Propose two methods to improve the data transfer rate, and for each method, show the maximum data transfer rate and the conditions necessary to achieve that maximum data transfer rate.
