3.5-4 TCP sequence numbers and ACKS (2). Suppose that as shown in the figure below, a TCP sender is sending segments with 100 bytes of payload. The TCP sender sends five segments with sequence numbers 100, 200, 300, 400, and 500. Suppose that the segment with sequence number 300 is lost. The TCP receiver will buffer correctly-received but not-yet-in-order segments for later delivery to the application layer (once missing segments are later received). sender - receiver send (seq=100) send (seq=200) send (seq=300) send (seq=400) send (seq=500) Reply (ACK=??) Reply (ACK=??) X/oss Reply (ACK=??) Reply (ACK=??) re-send (seq=300) Reply (ACK=??) Complete the sentences below. After receiving segment 100, the receiver responds with an ACK A. 200 with value: B. 300 | After receiving segment 200, the receiver responds with an ACK C. 300, a duplicate ACK with value: D. 600 After receiving segment 500, the receiver responds with an ACK with value: | After receiving the retransmitted segment 300, the receiver responds with an ACK with value:

Consider transferring an enormous file of L bytes from Host A to Host B. Assume an MSS of 536 bytes. a. What is the maximum value of L such that TCP sequence numbers are not exhausted? Recall that the TCP sequence number field has 4 bytes. b. For the L you obtain in (a), find how long it takes to transmit the file. Assume that a total of 66 bytes of transport, network, and data-link header are added to each segment before the resulting packet is sent out over a 155 Mbps link. Ignore flow control and congestion control so A can pump out the segments back to back and continuously.

Compare GBN, SR, and TCP (no delayed ACK). Assume that the timeout values for all three protocols are sufficiently long such that 5 consecutive data segments and their corresponding ACKs can be received (if not lost in the channel) by the receiving host (Host B) and the sending host (Host A) respectively. Suppose Host A sends 5 data segments to Host B, and the 3rd segment (sent from A) is lost. In the end, all 5 data segments have been correctly received by Host B. How many segments has Host A sent in total and how many ACKs has Host B sent in total? What are their sequence numbers? Answer this question for all three protocols.   The previous expert did the wrong question and the answer was incorrect. The 3rd packet is lost not the 2nd packet

1. What is the difference between packet fragmentation (i.e., at network layer) and frame frag- mentation (i.e., at link layer) in terms of purpose? 2. Suppose that host A is connected to a router R1, R1 is connected to another router, R2, and R2 is connected to host B. Suppose that a TCP message that contains 800 bytes of data and 20 bytes of TCP header is passed to the IP function at host A for delivery to B. Show the Total length, DF, MF, and Fragment offset fields of the IP header in each packet transmitted over the three links. (Assume that link A-R1 can support a maximum frame size of 1024 bytes including a 14-byte frame header, link R1-R2 can support a maximum frame size of 512 bytes, including an 8-byte frame header, and link R2-B can support a maximum frame size of 432 bytes including a 12-byte frame header.) (*hint: the Fragment offset field is denominated by 8-bytes, not bytes) 3. What is the purpose of the path MTU discovery process (see textbook Figure 5-42) and why does…

Networking & Data Communcations

Assume the maximum transmission unit (or MTU) of an IP packet on 100 Mbps Ethernet is set at 1500 bytes. Also, assume we are sending our file using IPv6 at the Network layer and UDP at the Transport layer. A typical IPv6 header consists of 40 bytes, a UDP header consists of 8 bytes. Answer the following three questions based on the information provided above. For all answers, enter a decimal integer value without formatting (no commas). 1. How many packets do we have to send in order to transfer a file of 24KB over 100 Mbps Ethernet? packets 2. How many bytes do we have to send at the network layer in order to transfer the above file entirely? bytes 3. How many bytes do we have to send at the data link layer in order to transfer the above file entirely? Assume that the Ethernet header is 14 bytes and the frame checksum is 4 bytes. bytes

13. The following figures plot the timeline for sending TCP segments by host A and TCP ACKS by host B, where “seq #” is the value of the sequence number in the TCP header, and "ACK #” is the value of the acknowledge number in the TCP header. Assume that every segment always includes 500 bytes of data, excluding the TCP header. A seg #: 1000 seq #: 1500 seq #: 2000 seq #: 2500 (1) B ACK #: a ACK #: b ACK #: c ACK #: d A seq #: 1000 seq #: 1500 seq #: 2000 seq #: 2500 (2) B ACK #: r ACK #: s TACK 1) In Figure (1), the second ACK sent out by host B gets lost in the network. a) What are the acknowledge numbers a, b, c, and d? b) Will sender A think the segment with seq#=1500 was lost because it never receives the acknowledgement from B containing ACK# = b? 2) In Figure (2), the second TCP segment from host A to host B gets delayed in the network but later arrives at B. What should be the value for the ACK number r, s and t?