Suppose TCP is used over a lossy link that loses on average one segment in four. Assume the delay x bandwidth window size is considerably larger than four segments. (a) What happens when we start a connection? Do we ever get to the linear-increase phase of congestion avoidance? (b) Without using an explicit feedback mechanism from the routers, would TCP have any way to distinguish such link losses from congestion losses, at least over the short term? (c) Suppose TCP senders did reliably get explicit congestion indications from routers. Assuming links as above were common, would it be feasible to support window sizes much larger than four segments? What would TCP have to do?

Suppose TCP is used over a lossy link that loses on average one segment in four. Assume the delay x bandwidth window size is considerably larger than four segments. (a) What happens when we start a connection? Do we ever get to the linear-increase phase of congestion avoidance? (b) Without using an explicit feedback mechanism from the routers, would TCP have any way to distinguish such link losses from congestion losses, at least over the short term? (c) Suppose TCP senders did reliably get explicit congestion indications from routers. Assuming links as above were common, would it be feasible to support window sizes much larger than four segments? What would TCP have to do?

Systems Architecture

7th Edition

ISBN:9781305080195

Author:Stephen D. Burd

Publisher:Stephen D. Burd

Chapter9: Computer Networks

Section: Chapter Questions

Problem 10VE

See similar textbooks

Similar questions

Consider one TCP connection on a path with a bottleneck link with capacity L. We have a file of size F(assume F is a very large file size). If TCP segment size is B bytes, the two-way propagation delay is tp and connection is always in congestion avoidance phase, find the following: A. Maximum window size that TCP can achieve B. Average window size and average throughput in this TCP connection C. Time it will take from connection establishment to reaching the maximum window size.
Consider a TCP connection with congestion window size 40 KB, maximum segment size is 2 KB, if time taken by TCP connection to get 37 KB congestion window is 351 ms, round trip time of the connection is __(ms).
Problem 2. Consider a packet of L bits that is sent over a path of Q links (i.e., a source and destination connected by a sequence of (Q-1) routers or switches). Each link transmits at R bps. This packet is the only traffic transmitted by the network (so there are no queuing delays) and the propagation delay and processing delay at routers are negligible. How long does it take to send this packet from source to destination if the network is: a) a packet-switched datagram network b) a circuit-switched network. Assume that bandwidth of R bps on each link is sliced into five individual circuits, so that cach circuit receives (R/5) bandwidth. Also assume that the circuit setup time is t,.. Give an expression for the number of links Q such that the packet delivery from the sender to the receiver will be faster over the packet-switched network, and the expression for the number of links Q such that the circuit-switched network will be faster.
In TCP connection, congestion occurs if the load on the network is greater than the capacity of the network. TCP uses the following algorithm to handle congestion. The algorithm is based on the size of the congestion window (cwnd) which starts with one maximum segment size (MSS). The MSS is determined during connection establishment. At each time the whole window of segments is acknowledged (one transmission), the size of the window grows exponentially. To stop this exponential growth, the sender keeps the track of a threshold. The threshold is set to 16 MSS. After reaching the threshold, the size of the congestion window is increased by 1. After how many transmissions the congestion window size will be 22 MSS?
TCP a. Consider two TCP connections, one between Hosts A (sender) and B (receiver), and another between Hosts C (sender) and D (receiver). The RTT between A and B is half that of the RTT between C and D. Suppose that the senders' (A's and C's) congestion window sizes are identical. Is their throughput (number of segments transmitted per second) the same? Explain. b. Now suppose that the average RTT between A and B, and C and D are identical. The RTT between A and B is constant (never varies), but the RTT between C and D varies considerably. Will the TCP timer values of the two connections differ, and if so, how are they different, and why are they different? Give one reason why TCP uses a three-way (SYN, SYNACK, ACK) handshake rather than a two-way handshake to initiate a connection. a.
Consider four Internet hosts, each with a TCP session. These four TCP sessions share a common bottleneck link - all packet loss on the end-to-end paths for these four sessions occurs at just this one link. The bottleneck link has a transmission rate of R. The round trip times, RTT, for all fours hosts to their destinations are approximately the same. No other sessions are currently using this link. The four sessions have been running for a long time. i) What is the approximate throughput of each of these four TCP sessions? Explain your answer briefly. ii) What is the approximate size of the TCP window at each of these hosts? Explain briefly how you arrived at this answer.
Consider that only a single TCP (Reno) connection uses one 10Mbps link which does not buffer any data. Suppose that this link is the only congested link between the sending and receiving hosts. Assume that the TCP sender has a huge file to send to the receiver, and the receiver's receive buffer is much larger than the congestion window. We also make the following assumptions: each TCP segment size is 1,500 bytes; the two-way propagation delay of this connection is 150 msec; and this TCP connection is always in congestion avoidance phase, that is, ignore slow start. A. What is the maximum window size (in segments) that this TCP connection can achieve? B. What is the average window size (in segments) and average throughput (in bps) Of this TCP connection? C. How long would it take for this TCP connection to reach its maximum window again after recovering from a packet loss?
Assume that a bottleneck connection with a rate of R bps carries two TCP connections. In both cases, there is a big file that must be downloaded (in the same direction over the bottleneck link). The files are all transmitted at the same time How much data will TCP be able to transmit each connection?
Is it the case or not? Consider a TCP connection where the most recent SampleRTT was 1 second. The current TimeoutInterval setting for the connection must be larger than one second.
Additive-Increase, Multiplicative Decrease (AIMD) refers to... a. TCP increases its round-trip time estimate by 1 second with each ACK received, and divides it by two with each loss event. O b. TCP's congestion control mechanism in the congestion-avoidance phase, in which the congestion window is increased by 1 maximum segment size (MSS) every round-trip time (RT), and decreased by 1/2 when there's a loss event indicated by 3 duplicate ACKS. c. TCP's ability to add additional receivers, one-by-one, until there are too many receivers. At this point, TCP reduces the number of receivers by 1/2 by sending those receivers a reset (RST) packet.
Consider the scenario below where 4 TCP senders are connected to 4 receivers. The servers transmit to the receiving hosts at the fastest rate possible (i.e., at the rate at which the bottleneck link between a server and its destination is operating at 100% utilization, and is fairly shared among the connections passing through that link). R =1 Gbps and Rc is 300 Mbps and Rs is 400 Mbps. And that all four senders have data to send, What is the minimum value of Re that will ensure that the connections to Host-1 and Host-2 are not bottlenecked at links with capacity Rc or Re?
as a possible congestion control mechanism in a subnet using virtual circuits internally, a router could refrain from acknowledging a received packet until (1) it knows its last transmission along the virtual circuit was received successfully and (2) it has a free buffer. for simplicity, assume that the routers use a stop-and-wait protocol and that each virtual circuit has one buffer dedicated to it for each direction of traffic. if it takes 7 sec to transmit a packet (data or acknowledgement) and there are n routers on the path, what is the rate at which packets are delivered to the destination host? assume that transmission errors are rare and that the host-router connection is infinitely fast.