{[ promptMessage ]}

Bookmark it

{[ promptMessage ]}

F-TransportAndVoIP - Mobile Networks Module F Transport...

Info icon This preview shows pages 1–12. Sign up to view the full content.

View Full Document Right Arrow Icon
Module F Transport Layer over Wireless Networks + Voice over IP (VoIP) JP Hubaux, P. Papadimitratos and M. Poturalski Mobile Networks http://mobnet.epfl.ch Some slides addapted from Jochen H. Schiller, Nitin Vaidya, and James Kurose & Keith Ross
Image of page 1

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Outline o TCP in Mobile Networks P Real-time traffic in Mobile Networks 2
Image of page 2
Reminder: Transmission Control Protocol o Reliable, in-order data delivery P Flow control P Congestion avoidance and control P End-to-end semantics Host A Host B SYN, Seq_no = x SYN, Seq_no = y, ACK, Ack_no = x+1 Seq_no = x +1, ACK, Ack_no = y+1 3
Image of page 3

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
TCP basic operation Send buffer Segments Receive buffer Application writes bytes in send buffer ACKs Sender Receiver Application reads bytes from receive buffer Application layer Transport layer Write 45 bytes Write 15 bytes Write 20 bytes Read 40 bytes Read 40 bytes Internet 4
Image of page 4
TCP flow control o Flow control is a speed-matching service P Sender adjusts the transmission rate to the receiver P Receiver advertises the remaining buffer space ( rwnd) to the sender P The sender keeps unacknowledged data below rwnd LastByteSent – LastByteAcked ≤ rwnd 5
Image of page 5

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Congestion Light traffic o Arrival Rate << R P Low delay P Can accommodate more Congestion onset o Arrival rate approaches R P Delay increases rapidly P Throughput begins to saturate Saturation o Arrival rate > R P Large delays, packet loss P Useful application throughput drops Throughput (bps) Delay (sec) R R Arrival Rate Arrival Rate 6
Image of page 6
TCP congestion control o Keeps TCP off the congestion collapse cliff P Congestion window mechanism LastByteSent – LastByteAcked ≤ min{cwnd, rwnd} a Slow Start phase P Increase congestion window size ( cwnd ) by one segment for each received ACK P Congestion window increases exponentially ACK Segment RTTs cwnd 7
Image of page 7

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
TCP congestion control o Congestion Avoidance phase P Congestion threshold ssthresh w When cwnd > ssthresh , increase cwnd slowly P cwnd++ per round-trip-time (RTT) Each time an ACK arrives, cwnd is increased by 1/ cwnd In one RTT, cwnd segments are sent, so total increase in cwnd is cwnd x 1/ cwnd = 1 cwnd grows linearly RTTs cwnd ssthresh 8
Image of page 8
TCP congestion control o Congestion detection: P Timeout or P Receipt of duplicate ACKs (Fast Retransmit) P Assumption: current cwnd corresponds to available bandwidth P TCP Tahoe P ssthresh = ½ cwnd P cwnd = 1 P Go back to Slow Start P Over several cycles expect to converge to ssthresh equal to about ½ the available bandwidth Congestion window 0 Slow Start Congestion Avoidance Time-out ssthresh 9 Time (expressed in RTTs)
Image of page 9

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
TCP congestion control o Fast Retransmit mechanism P If a segment is dropped, subsequent segments trigger duplicate ACKs P Sender retransmits segment instantly (without waiting for a timeout) when duplicate ACKs are received (typically 3) P Improves performance P Faster reaction to packet loss P Implemented in TCP-Reno (more recent than TCP-Tahoe) SEQ=1 ACK=2 ACK=2 ACK=2 ACK=2 SEQ=2 SEQ=3 SEQ=4 SEQ=5 10
Image of page 10
Wireless and Mobile Networks Mobile Host (1) Access Point Internet Base Station Mobile Host (2) Wire-line Communication Wire-less Communication 11
Image of page 11

Info icon This preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 12
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern