Description
1) Consider a connection with a transmission rate of 16 Mbps where the distance between the sender and the receiver is 5000 km. Assume that the delay for the connection is propagation delay and the speed of propagation is 2×10
5 km/s. We will transfer a verylargefileover this connection. Each segment has a maximum size of 1000 Bytes includinga40Bytesheader and ACK segments have negligible size. Assume no segments experience errors or losses,and that the processing time at the receiver is negligible. a) What is the minimum window size in segments that should be used for this connectionsothatthe throughput for this file transfer is maximized?
b) If we will use the FTP protocol for this file transfer, can we achieve the maximumpossiblethroughput? Justify your answer. 2) Consider the above connection where the file to be transferred contains 12,000 Bytes. Assumethatthe communication between the sender and receiver is full duplex, i.e., sender cansenddatasegments while receiving an ACK segment. We use the Selective Repeat protocol for thefiletransfer with a window size of N = 10 segments. The initial sequence number is 1. Assumethat thefirst transmissions of the ACK segments with acknowledgment numbers 3 and8areerrored,whereas all other data and ACK segments are received correctly. The timeout for eachdatasegment is set to 60 msec starting from the end of the transmission of the segment. Howmuchtime is required to complete the transfer of the whole file and receive the final ACKat thesender?3) Calculate the transfer time for the file transfer in 2) when Go-Back-N protocol is usedwithawindow size of N = 10 segments. Each window of the sender has a timeout of 60 msecstartingfrom the time when the window is set by the sender. 4) Four TCP connections are sharing a link with capacity of 110 Mbps. Assume that the bandwidthbottleneck for all four connections is this shared link. The roundtrip times for the connectionsare10 ms, 10 ms, 20 ms and 40 ms, respectively. Calculate the maximumthroughputs achievedbyeach connection. 5) Suppose that a file transfer requires delivery of 9 segments each with size 1250 Bytes over aTCPconnection with a round-trip delay of 5 msec and transmission rate of 10 Mbps. The retransmissiontimeout for the TCP connection is set to 15 msec. Assume that the receive windowis 10,000Bytesduring the entire file transfer. The fourth data segment transmitted is lost in its first transmissionand no other data or ACK segments are lost or errored during the file transfer. We assumethat out-of-order segments are buffered at the receiver. Further assume that the slowstart threshold(ssthresh) at the beginning of the TCP connection is 10 segments. How long does it takeaftertheTCP connection is established until the final ACK is received?
6) At time t, a TCP connection has CongWin=4000 Bytes, ssthresh=7000, nextSequenceNumber=500and there are no unacknowledged segments. The sender sends three more segments betweent ands(s > t), each containing 1000 Bytes. TCP sender receives three ACK segments betweent andswithacknowledgement numbers 1500, 2500, and 2500. Assume that the maximumsegment size(MSS)for the TCP connection is 1000 Bytes. a) What are the sequence numbers of the three segments transmitted by the sender?
b) Assume that the last ACK segment contains a Receive Window of 8,000 Bytes. Howmanymore bytes is the TCP sender allowed to send at time s?
c) Answer the question in b) if the last ACK segment contains a Receive Windowof 4,000Bytes.
7) Assume that a modification is made in the TCP header such that the Receive Windowfieldisextended to 3 Bytes. Consider a TCP connection with a transmission rate of 10 Gbps androundtrip delay of 20 ms. What is the maximum possible limit for the sender’s utilizationforthisconnection assuming that TCP window scaling factor is not used?
8) Assume that there is a TCP connection between two processes, one running at Host Aandtheother at Host B in order to transfer a very large file from Host A to Host B. The slowest linkinthenetwork along this connection has a transmission rate of 100 Mbps. The applicationrunningatHost A can write data to its TCP send buffer at a rate of 70 Mbps, whereas the applicationrunningat Host B can read data from its TCP receive buffer at a rate of 60 Mbps. a) What is the average rate of data transfer from the application at Host Ato the applicationatHost B? Justify your answer. b) Which of the TCP flow control and congestion control algorithms limits the data transferratein your answer above? How does this algorithm limit the transfer rate?
c) Now assume that the slowest link along this connection has a transmission rate of 50Mbps.Which of the TCP flow control and congestion control algorithms nowlimits the datatransferrate? How does this algorithm limit the transfer rate?
9) Assume that a TCP connection is experiencing timeouts as the only loss event whenthewindowsize is W = 2
n
, for some n. Similar to the derivation that we made in class, find an expressionforthe average throughput as a function of MSS, RTT and L. Assume that W>> 1. 10) Suppose that a TCP connection currently has the values of EstimatedRTT = 32 ms andDevRTT=4 ms. The next segment transmitted over the TCP connection experiences a timeout andtheacknowledgment for that segment arrives 40 ms after the retransmission. The SampleRTTforthesegment transmitted next over the TCP connection is measured as 16 ms. Calculate thelast valueof the Timeout obtained for this TCP connection.
