Congestion Control in Communication Networks

Size: px
Start display at page:

Download "Congestion Control in Communication Networks"

Transcription

1 Congestion Control in Communication Networks

2 Introduction Congestion occurs when number of packets transmitted approaches network capacity Objective of congestion control: keep number of packets below level at which performance drops off dramatically

3 Queuing Theory Data network is a network of queues If arrival rate > transmission rate (λ >μ) queue size grows without bound and packet delay goes to infinity ( )

4 At Saturation Point, 2 Strategies Discard any incoming packet if no buffer available Saturated node exercises flow control over neighbors May cause congestion to propagate throughout network

5 Ideal Network Performance I.e., infinite buffers and no overhead for packet transmission or congestion control Throughput increases with offered load until full capacity Packet delay increases with offered load approaching infinity at full capacity Power = throughput / delay

6

7 Practical Performance I.e., finite buffers and non-zero packet processing overhead With no congestion control, increased load eventually causes moderate congestion: throughput increases at slower rate than load Further increased load causes packet delays to increase and eventually throughput to drop to zero

8

9 Congestion Control Approaches Backpressure Request from destination to source to reduce rate Choke packet: ICMP Source Quench Implicit congestion signaling Source detects congestion from transmission delays and discarded packets and reduces flow

10 Explicit congestion signaling Direction Backward Forward Categories Binary Credit-based rate-based

11

12 Traffic Management Issues Fairness Last-in-first-discarded (i.e. drop-tail) may not be fair Quality of Service (QoS) provision of service differentiation Voice, video: delay sensitive, loss insensitive File transfer, mail: delay insensitive, loss sensitive Interactive computing: delay and loss sensitive Reservations Policing: excess traffic discarded or handled on best-effort basis T M C C

13 Discard policies Sometimes, you gain by throwing away

14 Proactive Packet Discard Congestion management by proactive packet discard Before buffer full Used on single FIFO queue or multiple queues for elastic traffic E.g. Random Early Detection (RED)

15 Random Early Detection (RED) Motivation Surges fill buffers and cause discards On TCP this is a signal to enter slow start phase, reducing load Lost packets need to be resent Adds to load and delay Global synchronization Traffic burst fills queues so packets lost Many TCP connections enter slow start Traffic drops so network under utilized Connections leave slow start at same time causing burst Bigger buffers do not help Try to anticipate onset of congestion and tell one connection to slow down

16 RED Design Goals Congestion avoidance Global synchronization avoidance Current systems inform connections to back off implicitly by dropping packets Avoidance of bias to bursty traffic Discard arriving packets will do this Bound on average queue length Hence control on average delay

17 RED Algorithm Overview Calculate average queue size avg if avg < THmin queue packet else if Thmin < avg < Thmax calculate probability Pa with probability Pa discard packet else with probability 1-Pa queue packet else if avg THmax discard packet

18 RED Buffer

19 RED Algorithm Detail

20 Discard Probability Why the conversion from Pb to Pa? Using Pb directly tends to penalize bursty traffic prematurely proportional to F=(avg-THmin)/(THmax-THmin) Pa remains low and then rises quickly when count approaches 1/(F Pmax)-1 Result: number of packets allowed to join queue between discards is uniformly distributed in [1,2,...,1/P b]

21

22

23 Traffic Shaping In order to make stochastic process more deterministic: Determine total_capacity for aggregated flows Divide flows into classes (voice, video, data etc.) For each flow: if used_capacity + new flow < total_capacity, admit; else no admission; end; During transfer, force compliance by controlling rates Token bucket system common mechanism

24 Token Bucket System Max # cells departing = R = ρt + β from UPC

25 Transport (TCP) performance TCP has many mechanisms for optimising utility, let s look at a few How does TCP perform Flow Control? Understand the need for TCP Congestion Control Dynamic Window Management

26 TCP Flow Control Uses a form of sliding window Differs from mechanism used in LLC, HDLC and others: Decouples acknowledgement of received data units from granting permission to send more TCP s flow control is known as a credit allocation scheme (i.e. credit-based): And each transmitted octet has a sequence number

27 TCP Header Fields for Flow Control Sequence number (SN) of first octet/byte in data segment Acknowledgement (ACK) number (AN) next octet to receive, (if any) Window (W) If ACK contains AN = i, W = j: Octets through SN = i 1 acknowledged Permission is granted to send W = j more octets, i.e., from octets i through i+j-1

28 Chapter 12 TCP Traffic Control 5

29 Credit Allocation is Flexible Suppose last message B issued was AN = i, W = j: To increase credit to k (k > j) when no new data, B issues AN = i, W = k To acknowledge a segment containing m octets (m < j) without allocating more credit, B issues AN = i + m, W = j m

30 Credit Policy Receiver needs a policy for how much credit to give sender Conservative approach: grant credit up to limit of available buffer space May limit throughput in long-delay situations Optimistic approach: grant credit based on expectation of freeing space before data arrives Dangerous if gamble fails, lots of discard

31 Effect of Window Size W = TCP window size (octets) R = Data rate (bps) at TCP source D = Propagation delay (seconds) After TCP source begins transmitting, it takes D seconds for first octet to arrive, and D seconds for acknowledgement to return TCP source could transmit at most 2RD bits, or RD/4 octets (i.e. rate-delay product)

32 Normalized Throughput S (b/s) 1 W >= 2RD W 2RD W < 2RD S =

33 MSS (16-bit) Wnd Scale Factor (max 14) Timestamp Performance Options Default max wnd size = Scaled Wnd size = 216*24 1 = 220 1

34 Complicating Factors Multiple TCP connections are multiplexed over same network interface, reducing available R and efficiency For multi-hop connections, D is the sum of delays across each link plus delays at each router If source data rate R exceeds data rate on one of the hops, that hop will be a bottleneck Lost segments are retransmitted, reducing throughput Impact depends on retransmission policy

35 Retransmission Strategy TCP relies exclusively on positive ACKs and retransmission on ACK timeout There is no explicit negative ACK Retransmission required when: 1. Segment arrives damaged, as indicated by checksum error, causing receiver to discard segment 2. Segment fails to arrive, lost!

36 Timers A timer is associated with each segment as it is sent, i.e. retransmission timer (RTO) If timer expires before segment ACKed, sender must retransmit Key Design Issue: Find a suitable value of retransmission timer?? Too small: many unnecessary retransmissions, wasting network bandwidth Too large: delay in handling lost segment

37 Two Strategies Timer should be longer than round-trip time (RTT) (send segment, receive ACK) Also, remember delay is variable Strategies: 1. Fixed timer 2. Adaptive

38 Some problems with Adaptive Schemes Peer TCP entity perform cumulative acknowledgements and not acknowledge immediately For retransmitted segments, can t tell whether ACK is response to original transmission or retransmission Network conditions may change suddenly However, adaptive is still better than fixed timer!

39 First try: Adaptive Retransmission Timer Average Round-Trip Time (ARTT) Each term given same weight [1/(K+1)] May not adjust properly to recent changes as this more likely reflect future behaviour Give more weight to recent values!

40 RFC 793 Exponential Averaging Smoothed Round-Trip Time (SRTT) SRTT(K + 1) = α SRTT(K) + (1 α) RTT(K + 1) To see the effect of α, lets see SRTT expansion: SRTT(K + 1) = (1 α) RTT(K + 1) + α(1 α) RTT(K) + α2(1 α) RTT(K-1) + + αk(1 α) RTT(1) E.g., if α = 0.8: SRTT(K + 1) = 0.2 RTT(K + 1) RTT(K) RTT(K-1) The older the observation, the less it is counted in the average (0 < α < 1)

41 Exponential Smoothing Coefficients

42 Figure 12.5 Exponential Averaging

43 RFC 793 Retransmission Timeout RTO should be set slightly > current SRTT RTO(K + 1) = Min(UB, Max(LB, β SRTT(K + 1))) UB, LB: pre-chosen fixed upper and lower bounds Example values for α, β: 0.8 < α < < β < 2.0

44 Variance causes problems

45 How to battle high variability? Van Jacobson s algorithm Extend ERTT Algorithm with variance sampling: As above for SRTT and ERTT Estimate Deviation (DRTT) as: DRTT(K + 1) = (1-α) DRTT(K) + α (SRTT - ERTT) TimeOut (RTO) = ERTT + 4*DRTT

46 Figure 12.8 Jacobson s RTO Calculations Chapter 12 TCP Traffic Control

47 Two Other Factors Jacobson s algorithm can significantly improve TCP performance, but: What RTO to use for retransmitted segments? ANSWER: exponential RTO backoff algorithm Which round-trip samples to use as input to Jacobson s algorithm? ANSWER: Karn s algorithm

48 Exponential RTO Backoff Increase RTO each time the same segment retransmitted backoff process Multiply RTO by constant: RTO = q RTO When q = 2 is called binary exponential backoff (similar to Ethernet backoff)

49 Which Round-trip Samples? If an ack is received for retransmitted segment, there are 2 possibilities: 1. Ack is for first transmission 2. Ack is for second transmission TCP source cannot distinguish these 2 cases No valid way to calculate RTT: From first transmission to ack, or From second transmission to ack?

50 Karn s Algorithm Do not use measured RTT of retransmitted segments to update SRTT and SDEV Calculate backoff RTO when a retransmission occurs Use backoff RTO for segments until an ACK arrives for a segment that has not been retransmitted Then Jacobson s algorithm is reactivated to calculate RTO

Tutorial 8 : Congestion Control

Tutorial 8 : Congestion Control Lund University ETSN01 Advanced Telecommunication Tutorial 8 : Congestion Control Author: Antonio Franco Emma Fitzgerald Tutor: Farnaz Moradi December 18, 2015 Contents I Before you start 3 II Exercises

More information

What Is Congestion? Effects of Congestion. Interaction of Queues. Chapter 12 Congestion in Data Networks. Effect of Congestion Control

What Is Congestion? Effects of Congestion. Interaction of Queues. Chapter 12 Congestion in Data Networks. Effect of Congestion Control Chapter 12 Congestion in Data Networks Effect of Congestion Control Ideal Performance Practical Performance Congestion Control Mechanisms Backpressure Choke Packet Implicit Congestion Signaling Explicit

More information

ADVANCED COMPUTER NETWORKS

ADVANCED COMPUTER NETWORKS ADVANCED COMPUTER NETWORKS Congestion Control and Avoidance 1 Lecture-6 Instructor : Mazhar Hussain CONGESTION CONTROL When one part of the subnet (e.g. one or more routers in an area) becomes overloaded,

More information

Resource allocation in networks. Resource Allocation in Networks. Resource allocation

Resource allocation in networks. Resource Allocation in Networks. Resource allocation Resource allocation in networks Resource Allocation in Networks Very much like a resource allocation problem in operating systems How is it different? Resources and jobs are different Resources are buffers

More information

What Is Congestion? Computer Networks. Ideal Network Utilization. Interaction of Queues

What Is Congestion? Computer Networks. Ideal Network Utilization. Interaction of Queues 168 430 Computer Networks Chapter 13 Congestion in Data Networks What Is Congestion? Congestion occurs when the number of packets being transmitted through the network approaches the packet handling capacity

More information

Congestion in Data Networks. Congestion in Data Networks

Congestion in Data Networks. Congestion in Data Networks Congestion in Data Networks CS420/520 Axel Krings 1 Congestion in Data Networks What is Congestion? Congestion occurs when the number of packets being transmitted through the network approaches the packet

More information

Lecture 4 Wide Area Networks - Congestion in Data Networks

Lecture 4 Wide Area Networks - Congestion in Data Networks DATA AND COMPUTER COMMUNICATIONS Lecture 4 Wide Area Networks - Congestion in Data Networks Mei Yang Based on Lecture slides by William Stallings 1 WHAT IS CONGESTION? congestion occurs when the number

More information

Reliable Transport II: TCP and Congestion Control

Reliable Transport II: TCP and Congestion Control Reliable Transport II: TCP and Congestion Control Stefano Vissicchio UCL Computer Science COMP0023 Recap: Last Lecture Transport Concepts Layering context Transport goals Transport mechanisms and design

More information

UNIT IV -- TRANSPORT LAYER

UNIT IV -- TRANSPORT LAYER UNIT IV -- TRANSPORT LAYER TABLE OF CONTENTS 4.1. Transport layer. 02 4.2. Reliable delivery service. 03 4.3. Congestion control. 05 4.4. Connection establishment.. 07 4.5. Flow control 09 4.6. Transmission

More information

Transport Protocols and TCP: Review

Transport Protocols and TCP: Review Transport Protocols and TCP: Review CSE 6590 Fall 2010 Department of Computer Science & Engineering York University 1 19 September 2010 1 Connection Establishment and Termination 2 2 1 Connection Establishment

More information

Lecture 14: Performance Architecture

Lecture 14: Performance Architecture Lecture 14: Performance Architecture Prof. Shervin Shirmohammadi SITE, University of Ottawa Prof. Shervin Shirmohammadi CEG 4185 14-1 Background Performance: levels for capacity, delay, and RMA. Performance

More information

Quality of Service. Traffic Descriptor Traffic Profiles. Figure 24.1 Traffic descriptors. Figure Three traffic profiles

Quality of Service. Traffic Descriptor Traffic Profiles. Figure 24.1 Traffic descriptors. Figure Three traffic profiles 24-1 DATA TRAFFIC Chapter 24 Congestion Control and Quality of Service The main focus of control and quality of service is data traffic. In control we try to avoid traffic. In quality of service, we try

More information

Computer Networks. Wenzhong Li. Nanjing University

Computer Networks. Wenzhong Li. Nanjing University Computer Networks Wenzhong Li Nanjing University 1 Chapter 5. End-to-End Protocols Transport Services and Mechanisms User Datagram Protocol (UDP) Transmission Control Protocol (TCP) TCP Congestion Control

More information

TCP: Flow and Error Control

TCP: Flow and Error Control 1 TCP: Flow and Error Control Required reading: Kurose 3.5.3, 3.5.4, 3.5.5 CSE 4213, Fall 2006 Instructor: N. Vlajic TCP Stream Delivery 2 TCP Stream Delivery unlike UDP, TCP is a stream-oriented protocol

More information

Transmission Control Protocol. ITS 413 Internet Technologies and Applications

Transmission Control Protocol. ITS 413 Internet Technologies and Applications Transmission Control Protocol ITS 413 Internet Technologies and Applications Contents Overview of TCP (Review) TCP and Congestion Control The Causes of Congestion Approaches to Congestion Control TCP Congestion

More information

Overview. TCP & router queuing Computer Networking. TCP details. Workloads. TCP Performance. TCP Performance. Lecture 10 TCP & Routers

Overview. TCP & router queuing Computer Networking. TCP details. Workloads. TCP Performance. TCP Performance. Lecture 10 TCP & Routers Overview 15-441 Computer Networking TCP & router queuing Lecture 10 TCP & Routers TCP details Workloads Lecture 10: 09-30-2002 2 TCP Performance TCP Performance Can TCP saturate a link? Congestion control

More information

Congestion control in TCP

Congestion control in TCP Congestion control in TCP If the transport entities on many machines send too many packets into the network too quickly, the network will become congested, with performance degraded as packets are delayed

More information

Transport Layer. -UDP (User Datagram Protocol) -TCP (Transport Control Protocol)

Transport Layer. -UDP (User Datagram Protocol) -TCP (Transport Control Protocol) Transport Layer -UDP (User Datagram Protocol) -TCP (Transport Control Protocol) 1 Transport Services The transport layer has the duty to set up logical connections between two applications running on remote

More information

Transport Protocols & TCP TCP

Transport Protocols & TCP TCP Transport Protocols & TCP CSE 3213 Fall 2007 13 November 2007 1 TCP Services Flow control Connection establishment and termination Congestion control 2 1 TCP Services Transmission Control Protocol (RFC

More information

Protocol Overview. TCP/IP Performance. Connection Types in TCP/IP. Resource Management. Router Queues. Control Mechanisms ITL

Protocol Overview. TCP/IP Performance. Connection Types in TCP/IP. Resource Management. Router Queues. Control Mechanisms ITL Protocol Overview TCP/IP Performance E-Mail HTTP (WWW) Remote Login File Transfer TCP UDP ITL IP ICMP ARP RARP (Auxiliary Services) ATM Ethernet, X.25, HDLC etc. 2/13/06 Hans Kruse & Shawn Ostermann, Ohio

More information

8. TCP Congestion Control

8. TCP Congestion Control 8. TCP Congestion Control 1 TCP Congestion Control Slow-start increase Multiplicative decrease Congestion avoidance Measurement of variation Exponential timer backoff 2002 Yanghee Choi 2 Congestion Control

More information

Chapter 24 Congestion Control and Quality of Service 24.1

Chapter 24 Congestion Control and Quality of Service 24.1 Chapter 24 Congestion Control and Quality of Service 24.1 Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 24-1 DATA TRAFFIC The main focus of congestion control

More information

Lecture 21: Congestion Control" CSE 123: Computer Networks Alex C. Snoeren

Lecture 21: Congestion Control CSE 123: Computer Networks Alex C. Snoeren Lecture 21: Congestion Control" CSE 123: Computer Networks Alex C. Snoeren Lecture 21 Overview" How fast should a sending host transmit data? Not to fast, not to slow, just right Should not be faster than

More information

Lecture 14: Congestion Control"

Lecture 14: Congestion Control Lecture 14: Congestion Control" CSE 222A: Computer Communication Networks George Porter Thanks: Amin Vahdat, Dina Katabi and Alex C. Snoeren Lecture 14 Overview" TCP congestion control review Dukkipati

More information

6.033 Spring 2015 Lecture #11: Transport Layer Congestion Control Hari Balakrishnan Scribed by Qian Long

6.033 Spring 2015 Lecture #11: Transport Layer Congestion Control Hari Balakrishnan Scribed by Qian Long 6.033 Spring 2015 Lecture #11: Transport Layer Congestion Control Hari Balakrishnan Scribed by Qian Long Please read Chapter 19 of the 6.02 book for background, especially on acknowledgments (ACKs), timers,

More information

Communication Networks

Communication Networks Communication Networks Spring 2018 Laurent Vanbever nsg.ee.ethz.ch ETH Zürich (D-ITET) April 30 2018 Materials inspired from Scott Shenker & Jennifer Rexford Last week on Communication Networks We started

More information

Internet Transport Protocols UDP and TCP

Internet Transport Protocols UDP and TCP Outline Internet Transport Protocols UDP and TCP Transport Layer Review UDP Protocol UDP Characteristics UDP Functionalities TCP Protocol TCP Characteristics Connection Management TCP Flow and Congestion

More information

Unit 2 Packet Switching Networks - II

Unit 2 Packet Switching Networks - II Unit 2 Packet Switching Networks - II Dijkstra Algorithm: Finding shortest path Algorithm for finding shortest paths N: set of nodes for which shortest path already found Initialization: (Start with source

More information

Lecture 14: Congestion Control"

Lecture 14: Congestion Control Lecture 14: Congestion Control" CSE 222A: Computer Communication Networks Alex C. Snoeren Thanks: Amin Vahdat, Dina Katabi Lecture 14 Overview" TCP congestion control review XCP Overview 2 Congestion Control

More information

ETSF10 Internet Protocols Transport Layer Protocols

ETSF10 Internet Protocols Transport Layer Protocols ETSF10 Internet Protocols Transport Layer Protocols 2012, Part 2, Lecture 2.1 Kaan Bür, Jens Andersson Transport Layer Protocols Process-to-process delivery [ed.4 ch.23.1] [ed.5 ch.24.1] Transmission Control

More information

TCP/IP Performance ITL

TCP/IP Performance ITL TCP/IP Performance ITL Protocol Overview E-Mail HTTP (WWW) Remote Login File Transfer TCP UDP IP ICMP ARP RARP (Auxiliary Services) Ethernet, X.25, HDLC etc. ATM 4/30/2002 Hans Kruse & Shawn Ostermann,

More information

Computer Networking. Queue Management and Quality of Service (QOS)

Computer Networking. Queue Management and Quality of Service (QOS) Computer Networking Queue Management and Quality of Service (QOS) Outline Previously:TCP flow control Congestion sources and collapse Congestion control basics - Routers 2 Internet Pipes? How should you

More information

ETSF05/ETSF10 Internet Protocols Transport Layer Protocols

ETSF05/ETSF10 Internet Protocols Transport Layer Protocols ETSF05/ETSF10 Internet Protocols Transport Layer Protocols 2016 Jens Andersson Transport Layer Communication between applications Process-to-process delivery Client/server concept Local host Normally initialiser

More information

Bandwidth Allocation & TCP

Bandwidth Allocation & TCP Bandwidth Allocation & TCP The Transport Layer Focus Application Presentation How do we share bandwidth? Session Topics Transport Network Congestion control & fairness Data Link TCP Additive Increase/Multiplicative

More information

Priority Traffic CSCD 433/533. Advanced Networks Spring Lecture 21 Congestion Control and Queuing Strategies

Priority Traffic CSCD 433/533. Advanced Networks Spring Lecture 21 Congestion Control and Queuing Strategies CSCD 433/533 Priority Traffic Advanced Networks Spring 2016 Lecture 21 Congestion Control and Queuing Strategies 1 Topics Congestion Control and Resource Allocation Flows Types of Mechanisms Evaluation

More information

Congestion Control End Hosts. CSE 561 Lecture 7, Spring David Wetherall. How fast should the sender transmit data?

Congestion Control End Hosts. CSE 561 Lecture 7, Spring David Wetherall. How fast should the sender transmit data? Congestion Control End Hosts CSE 51 Lecture 7, Spring. David Wetherall Today s question How fast should the sender transmit data? Not tooslow Not toofast Just right Should not be faster than the receiver

More information

Advanced Computer Networks

Advanced Computer Networks Advanced Computer Networks QoS in IP networks Prof. Andrzej Duda duda@imag.fr Contents QoS principles Traffic shaping leaky bucket token bucket Scheduling FIFO Fair queueing RED IntServ DiffServ http://duda.imag.fr

More information

CS457 Transport Protocols. CS 457 Fall 2014

CS457 Transport Protocols. CS 457 Fall 2014 CS457 Transport Protocols CS 457 Fall 2014 Topics Principles underlying transport-layer services Demultiplexing Detecting corruption Reliable delivery Flow control Transport-layer protocols User Datagram

More information

Introduction to IP QoS

Introduction to IP QoS Introduction to IP QoS Primer to IP Quality of Service Aspects Queuing, Shaping, Classification Agenda IP QoS Introduction Queue Management Congestion Avoidance Traffic Rate Management Classification and

More information

TCP and Congestion Control (Day 1) Yoshifumi Nishida Sony Computer Science Labs, Inc. Today's Lecture

TCP and Congestion Control (Day 1) Yoshifumi Nishida Sony Computer Science Labs, Inc. Today's Lecture TCP and Congestion Control (Day 1) Yoshifumi Nishida nishida@csl.sony.co.jp Sony Computer Science Labs, Inc 1 Today's Lecture Part1: TCP concept Part2: TCP detailed mechanisms Part3: Tools for TCP 2 1

More information

Transport Protocols and TCP

Transport Protocols and TCP Transport Protocols and TCP Functions Connection establishment and termination Breaking message into packets Error recovery ARQ Flow control Multiplexing, de-multiplexing Transport service is end to end

More information

Flow Control. Flow control problem. Other considerations. Where?

Flow Control. Flow control problem. Other considerations. Where? Flow control problem Flow Control An Engineering Approach to Computer Networking Consider file transfer Sender sends a stream of packets representing fragments of a file Sender should try to match rate

More information

Programming Assignment 3: Transmission Control Protocol

Programming Assignment 3: Transmission Control Protocol CS 640 Introduction to Computer Networks Spring 2005 http://www.cs.wisc.edu/ suman/courses/640/s05 Programming Assignment 3: Transmission Control Protocol Assigned: March 28,2005 Due: April 15, 2005, 11:59pm

More information

Random Early Detection (RED) gateways. Sally Floyd CS 268: Computer Networks

Random Early Detection (RED) gateways. Sally Floyd CS 268: Computer Networks Random Early Detection (RED) gateways Sally Floyd CS 268: Computer Networks floyd@eelblgov March 20, 1995 1 The Environment Feedback-based transport protocols (eg, TCP) Problems with current Drop-Tail

More information

Reliable Transport I: Concepts and TCP Protocol

Reliable Transport I: Concepts and TCP Protocol Reliable Transport I: Concepts and TCP Protocol Brad Karp UCL Computer Science CS 3035/GZ01 29 th October 2013 Part I: Transport Concepts Layering context Transport goals Transport mechanisms 2 Context:

More information

Congestion Avoidance and Control. Rohan Tabish and Zane Ma

Congestion Avoidance and Control. Rohan Tabish and Zane Ma Congestion Avoidance and Control Rohan Tabish and Zane Ma TCP is self-clocking Self-clocking systems should be robust Congestion collapse Internet had first of what became a series of congestion collapses

More information

"Filling up an old bath with holes in it, indeed. Who would be such a fool?" "A sum it is, girl," my father said. "A sum. A problem for the mind.

Filling up an old bath with holes in it, indeed. Who would be such a fool? A sum it is, girl, my father said. A sum. A problem for the mind. We were doing very well, up to the kind of sum when a bath is filling at the rate of so many gallons and two holes are letting the water out, and please to say how long it will take to fill the bath, when

More information

CS321: Computer Networks Congestion Control in TCP

CS321: Computer Networks Congestion Control in TCP CS321: Computer Networks Congestion Control in TCP Dr. Manas Khatua Assistant Professor Dept. of CSE IIT Jodhpur E-mail: manaskhatua@iitj.ac.in Causes and Cost of Congestion Scenario-1: Two Senders, a

More information

ETSF05/ETSF10 Internet Protocols. Performance & QoS Congestion Control

ETSF05/ETSF10 Internet Protocols. Performance & QoS Congestion Control ETSF05/ETSF10 Internet Protocols Performance & QoS Congestion Control Quality of Service (QoS) Maintaining a functioning network Meeting applications demands User s demands = QoE (Quality of Experience)

More information

Congestion. Can t sustain input rate > output rate Issues: - Avoid congestion - Control congestion - Prioritize who gets limited resources

Congestion. Can t sustain input rate > output rate Issues: - Avoid congestion - Control congestion - Prioritize who gets limited resources Congestion Source 1 Source 2 10-Mbps Ethernet 100-Mbps FDDI Router 1.5-Mbps T1 link Destination Can t sustain input rate > output rate Issues: - Avoid congestion - Control congestion - Prioritize who gets

More information

Congestion Control. Daniel Zappala. CS 460 Computer Networking Brigham Young University

Congestion Control. Daniel Zappala. CS 460 Computer Networking Brigham Young University Congestion Control Daniel Zappala CS 460 Computer Networking Brigham Young University 2/25 Congestion Control how do you send as fast as possible, without overwhelming the network? challenges the fastest

More information

CHAPTER 3 EFFECTIVE ADMISSION CONTROL MECHANISM IN WIRELESS MESH NETWORKS

CHAPTER 3 EFFECTIVE ADMISSION CONTROL MECHANISM IN WIRELESS MESH NETWORKS 28 CHAPTER 3 EFFECTIVE ADMISSION CONTROL MECHANISM IN WIRELESS MESH NETWORKS Introduction Measurement-based scheme, that constantly monitors the network, will incorporate the current network state in the

More information

Transport Layer TCP / UDP

Transport Layer TCP / UDP Transport Layer TCP / UDP Chapter 6 section 6.5 is TCP 12 Mar 2012 Layers Application Transport Why do we need the Transport Layer? Network Host-to-Network/Physical/DataLink High Level Overview TCP (RFC

More information

CS 5520/ECE 5590NA: Network Architecture I Spring Lecture 13: UDP and TCP

CS 5520/ECE 5590NA: Network Architecture I Spring Lecture 13: UDP and TCP CS 5520/ECE 5590NA: Network Architecture I Spring 2008 Lecture 13: UDP and TCP Most recent lectures discussed mechanisms to make better use of the IP address space, Internet control messages, and layering

More information

A Survey on Quality of Service and Congestion Control

A Survey on Quality of Service and Congestion Control A Survey on Quality of Service and Congestion Control Ashima Amity University Noida, U.P, India batra_ashima@yahoo.co.in Sanjeev Thakur Amity University Noida, U.P, India sthakur.ascs@amity.edu Abhishek

More information

II. Principles of Computer Communications Network and Transport Layer

II. Principles of Computer Communications Network and Transport Layer II. Principles of Computer Communications Network and Transport Layer A. Internet Protocol (IP) IPv4 Header An IP datagram consists of a header part and a text part. The header has a 20-byte fixed part

More information

TCP Congestion Control

TCP Congestion Control TCP Congestion Control What is Congestion The number of packets transmitted on the network is greater than the capacity of the network Causes router buffers (finite size) to fill up packets start getting

More information

TCP Congestion Control

TCP Congestion Control What is Congestion TCP Congestion Control The number of packets transmitted on the network is greater than the capacity of the network Causes router buffers (finite size) to fill up packets start getting

More information

CS419: Computer Networks. Lecture 10, Part 3: Apr 13, 2005 Transport: TCP performance

CS419: Computer Networks. Lecture 10, Part 3: Apr 13, 2005 Transport: TCP performance : Computer Networks Lecture 10, Part 3: Apr 13, 2005 Transport: TCP performance TCP performance We ve seen how TCP the protocol works But there are a lot of tricks required to make it work well Indeed,

More information

Data Link Control Protocols

Data Link Control Protocols Protocols : Introduction to Data Communications Sirindhorn International Institute of Technology Thammasat University Prepared by Steven Gordon on 23 May 2012 Y12S1L07, Steve/Courses/2012/s1/its323/lectures/datalink.tex,

More information

TCP. CSU CS557, Spring 2018 Instructor: Lorenzo De Carli (Slides by Christos Papadopoulos, remixed by Lorenzo De Carli)

TCP. CSU CS557, Spring 2018 Instructor: Lorenzo De Carli (Slides by Christos Papadopoulos, remixed by Lorenzo De Carli) TCP CSU CS557, Spring 2018 Instructor: Lorenzo De Carli (Slides by Christos Papadopoulos, remixed by Lorenzo De Carli) 1 Sources Fall and Stevens, TCP/IP Illustrated Vol. 1, 2nd edition Congestion Avoidance

More information

Outline Computer Networking. TCP slow start. TCP modeling. TCP details AIMD. Congestion Avoidance. Lecture 18 TCP Performance Peter Steenkiste

Outline Computer Networking. TCP slow start. TCP modeling. TCP details AIMD. Congestion Avoidance. Lecture 18 TCP Performance Peter Steenkiste Outline 15-441 Computer Networking Lecture 18 TCP Performance Peter Steenkiste Fall 2010 www.cs.cmu.edu/~prs/15-441-f10 TCP congestion avoidance TCP slow start TCP modeling TCP details 2 AIMD Distributed,

More information

Advanced Network Design

Advanced Network Design Advanced Network Design Organization Whoami, Book, Wikipedia www.cs.uchicago.edu/~nugent/cspp54015 Grading Homework/project: 60% Midterm: 15% Final: 20% Class participation: 5% Interdisciplinary Course

More information

Toward a Reliable Data Transport Architecture for Optical Burst-Switched Networks

Toward a Reliable Data Transport Architecture for Optical Burst-Switched Networks Toward a Reliable Data Transport Architecture for Optical Burst-Switched Networks Dr. Vinod Vokkarane Assistant Professor, Computer and Information Science Co-Director, Advanced Computer Networks Lab University

More information

Flow and Congestion Control

Flow and Congestion Control CE443 Computer Networks Flow and Congestion Control Behnam Momeni Computer Engineering Department Sharif University of Technology Acknowledgments: Lecture slides are from Computer networks course thought

More information

RED behavior with different packet sizes

RED behavior with different packet sizes RED behavior with different packet sizes Stefaan De Cnodder, Omar Elloumi *, Kenny Pauwels Traffic and Routing Technologies project Alcatel Corporate Research Center, Francis Wellesplein, 1-18 Antwerp,

More information

Flow and Congestion Control (Hosts)

Flow and Congestion Control (Hosts) Flow and Congestion Control (Hosts) 14-740: Fundamentals of Computer Networks Bill Nace Material from Computer Networking: A Top Down Approach, 6 th edition. J.F. Kurose and K.W. Ross traceroute Flow Control

More information

EC1009 HIGH SPEED NETWORKS (ELECTIVE) (2 marks Questions and answers)

EC1009 HIGH SPEED NETWORKS (ELECTIVE) (2 marks Questions and answers) DEPARTMENT OF ECE EC1009 HIGH SPEED NETWORKS (ELECTIVE) (2 marks Questions and answers) FINAL YEAR 7 th SEMESTER UNIT I HIGH SPEED NETWORKS 1) What is common channel signaling? The data s and control signals

More information

TCP Congestion Control : Computer Networking. Introduction to TCP. Key Things You Should Know Already. Congestion Control RED

TCP Congestion Control : Computer Networking. Introduction to TCP. Key Things You Should Know Already. Congestion Control RED TCP Congestion Control 15-744: Computer Networking L-4 TCP Congestion Control RED Assigned Reading [FJ93] Random Early Detection Gateways for Congestion Avoidance [TFRC] Equation-Based Congestion Control

More information

Advanced Networking TCP

Advanced Networking TCP Advanced Networking TCP Renato Lo Cigno Content Some details on window protocols TCP hearders and formats TCP Options TCP flow control TCP Congestion control (most bulky!) Advanced Networking TCP 2 Basic

More information

Network Management & Monitoring

Network Management & Monitoring Network Management & Monitoring Network Delay These materials are licensed under the Creative Commons Attribution-Noncommercial 3.0 Unported license (http://creativecommons.org/licenses/by-nc/3.0/) End-to-end

More information

EE122 MIDTERM EXAM: Scott Shenker, Ion Stoica

EE122 MIDTERM EXAM: Scott Shenker, Ion Stoica EE MITERM EXM: 00-0- Scott Shenker, Ion Stoica Last name Student I First name Login: ee- Please circle the last two letters of your login. a b c d e f g h i j k l m n o p q r s t u v w x y z a b c d e

More information

Multiple unconnected networks

Multiple unconnected networks TCP/IP Life in the Early 1970s Multiple unconnected networks ARPAnet Data-over-cable Packet satellite (Aloha) Packet radio ARPAnet satellite net Differences Across Packet-Switched Networks Addressing Maximum

More information

Communications Software. CSE 123b. CSE 123b. Spring Lecture 3: Reliable Communications. Stefan Savage. Some slides couresty David Wetherall

Communications Software. CSE 123b. CSE 123b. Spring Lecture 3: Reliable Communications. Stefan Savage. Some slides couresty David Wetherall CSE 123b CSE 123b Communications Software Spring 2002 Lecture 3: Reliable Communications Stefan Savage Some slides couresty David Wetherall Administrativa Home page is up and working http://www-cse.ucsd.edu/classes/sp02/cse123b/

More information

CS519: Computer Networks. Lecture 5, Part 4: Mar 29, 2004 Transport: TCP congestion control

CS519: Computer Networks. Lecture 5, Part 4: Mar 29, 2004 Transport: TCP congestion control : Computer Networks Lecture 5, Part 4: Mar 29, 2004 Transport: TCP congestion control TCP performance We ve seen how TCP the protocol works Sequencing, receive window, connection setup and teardown And

More information

Contents. CIS 632 / EEC 687 Mobile Computing. TCP in Fixed Networks. Prof. Chansu Yu

Contents. CIS 632 / EEC 687 Mobile Computing. TCP in Fixed Networks. Prof. Chansu Yu CIS 632 / EEC 687 Mobile Computing TCP in Fixed Networks Prof. Chansu Yu Contents Physical layer issues Communication frequency Signal propagation Modulation and Demodulation Channel access issues Multiple

More information

Congestion Control. Queuing Discipline Reacting to Congestion Avoiding Congestion. Issues

Congestion Control. Queuing Discipline Reacting to Congestion Avoiding Congestion. Issues Congestion Control Outline Queuing Discipline Reacting to Congestion Avoiding Congestion Issues Two sides of the same coin pre-allocate resources to avoid congestion (e.g. telephone networks) control congestion

More information

CS 640 Introduction to Computer Networks Spring 2009

CS 640 Introduction to Computer Networks Spring 2009 CS 640 Introduction to Computer Networks Spring 2009 http://pages.cs.wisc.edu/~suman/courses/wiki/doku.php?id=640-spring2009 Programming Assignment 3: Transmission Control Protocol Assigned: March 26,

More information

Computer Networking Introduction

Computer Networking Introduction Computer Networking Introduction Halgurd S. Maghdid Software Engineering Department Koya University-Koya, Kurdistan-Iraq Lecture No.11 Chapter 3 outline 3.1 transport-layer services 3.2 multiplexing and

More information

Congestion Control In The Internet Part 2: How it is implemented in TCP. JY Le Boudec 2014

Congestion Control In The Internet Part 2: How it is implemented in TCP. JY Le Boudec 2014 1 Congestion Control In The Internet Part 2: How it is implemented in TCP JY Le Boudec 2014 Contents 1. Congestion control in TCP 2. The fairness of TCP 3. The loss throughput formula 4. Explicit Congestion

More information

image 3.8 KB Figure 1.6: Example Web Page

image 3.8 KB Figure 1.6: Example Web Page image. KB image 1 KB Figure 1.: Example Web Page and is buffered at a router, it must wait for all previously queued packets to be transmitted first. The longer the queue (i.e., the more packets in the

More information

ECE 333: Introduction to Communication Networks Fall 2001

ECE 333: Introduction to Communication Networks Fall 2001 ECE 333: Introduction to Communication Networks Fall 2001 Lecture 28: Transport Layer III Congestion control (TCP) 1 In the last lecture we introduced the topics of flow control and congestion control.

More information

Congestion / Flow Control in TCP

Congestion / Flow Control in TCP Congestion and Flow Control in 1 Flow Control and Congestion Control Flow control Sender avoids overflow of receiver buffer Congestion control All senders avoid overflow of intermediate network buffers

More information

User Datagram Protocol (UDP):

User Datagram Protocol (UDP): SFWR 4C03: Computer Networks and Computer Security Feb 2-5 2004 Lecturer: Kartik Krishnan Lectures 13-15 User Datagram Protocol (UDP): UDP is a connectionless transport layer protocol: each output operation

More information

Congestion Control In The Internet Part 2: How it is implemented in TCP. JY Le Boudec 2014

Congestion Control In The Internet Part 2: How it is implemented in TCP. JY Le Boudec 2014 1 Congestion Control In The Internet Part 2: How it is implemented in TCP JY Le Boudec 2014 Contents 1. Congestion control in TCP 2. The fairness of TCP 3. The loss throughput formula 4. Explicit Congestion

More information

CSE 123A Computer Networks

CSE 123A Computer Networks CSE 123A Computer Networks Winter 2005 Lecture 14 Congestion Control Some images courtesy David Wetherall Animations by Nick McKeown and Guido Appenzeller The bad news and the good news The bad news: new

More information

MAHALAKSHMI ENGINEERING COLLEGE TIRUCHIRAPALLI

MAHALAKSHMI ENGINEERING COLLEGE TIRUCHIRAPALLI MAHALAKSHMI ENGINEERING COLLEGE TIRUCHIRAPALLI 621 213 UNIT IV INTEGRATED AND DIFFERENTIATED SERVICES Part A (2 Marks) 1. What are the two types of traffic on internet? Traffic on network or internet is

More information

Lecture 4: Congestion Control

Lecture 4: Congestion Control Lecture 4: Congestion Control Overview Internet is a network of networks Narrow waist of IP: unreliable, best-effort datagram delivery Packet forwarding: input port to output port Routing protocols: computing

More information

Flow and Congestion Control Marcos Vieira

Flow and Congestion Control Marcos Vieira Flow and Congestion Control 2014 Marcos Vieira Flow Control Part of TCP specification (even before 1988) Goal: not send more data than the receiver can handle Sliding window protocol Receiver uses window

More information

Lecture 22: Buffering & Scheduling. CSE 123: Computer Networks Alex C. Snoeren

Lecture 22: Buffering & Scheduling. CSE 123: Computer Networks Alex C. Snoeren Lecture 22: Buffering & Scheduling CSE 123: Computer Networks Alex C. Snoeren Lecture 23 Overview Buffer Management FIFO RED Traffic Policing/Scheduling 2 Key Router Challenges Buffer management: which

More information

Network Protocols. Transmission Control Protocol (TCP) TDC375 Autumn 2009/10 John Kristoff DePaul University 1

Network Protocols. Transmission Control Protocol (TCP) TDC375 Autumn 2009/10 John Kristoff DePaul University 1 Network Protocols Transmission Control Protocol (TCP) TDC375 Autumn 2009/10 John Kristoff DePaul University 1 IP review IP provides just enough connected ness Global addressing Hop by hop routing IP over

More information

TCP Performance. EE 122: Intro to Communication Networks. Fall 2006 (MW 4-5:30 in Donner 155) Vern Paxson TAs: Dilip Antony Joseph and Sukun Kim

TCP Performance. EE 122: Intro to Communication Networks. Fall 2006 (MW 4-5:30 in Donner 155) Vern Paxson TAs: Dilip Antony Joseph and Sukun Kim TCP Performance EE 122: Intro to Communication Networks Fall 2006 (MW 4-5:30 in Donner 155) Vern Paxson TAs: Dilip Antony Joseph and Sukun Kim http://inst.eecs.berkeley.edu/~ee122/ Materials with thanks

More information

Reliable Transport II: TCP and Congestion Control

Reliable Transport II: TCP and Congestion Control Reliable Transport II: TCP and Congestion Control Brad Karp UCL Computer Science CS 3035/GZ01 31 st October 2013 Outline Slow Start AIMD Congestion control Throughput, loss, and RTT equation Connection

More information

Congestion Control In The Internet Part 2: How it is implemented in TCP. JY Le Boudec 2015

Congestion Control In The Internet Part 2: How it is implemented in TCP. JY Le Boudec 2015 1 Congestion Control In The Internet Part 2: How it is implemented in TCP JY Le Boudec 2015 Contents 1. Congestion control in TCP 2. The fairness of TCP 3. The loss throughput formula 4. Explicit Congestion

More information

ETSF05/ETSF10 Internet Protocols. Performance & QoS Congestion Control

ETSF05/ETSF10 Internet Protocols. Performance & QoS Congestion Control ETSF05/ETSF10 Internet Protocols Performance & QoS Congestion Control Quality of Service (QoS) Maintaining a functioning network Meeting applications demands User s demands = QoE (Quality of Experience)

More information

CSE 461. TCP and network congestion

CSE 461. TCP and network congestion CSE 461 TCP and network congestion This Lecture Focus How should senders pace themselves to avoid stressing the network? Topics Application Presentation Session Transport Network congestion collapse Data

More information

CS CS COMPUTER NETWORKS CS CS CHAPTER 6. CHAPTER 6 Congestion Control

CS CS COMPUTER NETWORKS CS CS CHAPTER 6. CHAPTER 6 Congestion Control COMPUTER NETWORKS CS 45201 CS 55201 CHAPTER 6 Congestion Control COMPUTER NETWORKS CS 45201 CS 55201 CHAPTER 6 Congestion Control P. Farrell and H. Peyravi Department of Computer Science Kent State University

More information

Impact of transmission errors on TCP performance. Outline. Random Errors

Impact of transmission errors on TCP performance. Outline. Random Errors Impact of transmission errors on TCP performance 1 Outline Impact of transmission errors on TCP performance Approaches to improve TCP performance Classification Discussion of selected approaches 2 Random

More information

Connection-oriented (virtual circuit) Reliable Transfer Buffered Transfer Unstructured Stream Full Duplex Point-to-point Connection End-to-end service

Connection-oriented (virtual circuit) Reliable Transfer Buffered Transfer Unstructured Stream Full Duplex Point-to-point Connection End-to-end service 최양희서울대학교컴퓨터공학부 Connection-oriented (virtual circuit) Reliable Transfer Buffered Transfer Unstructured Stream Full Duplex Point-to-point Connection End-to-end service 1 2004 Yanghee Choi 2 Addressing: application

More information

Network Support for Multimedia

Network Support for Multimedia Network Support for Multimedia Daniel Zappala CS 460 Computer Networking Brigham Young University Network Support for Multimedia 2/33 make the best of best effort use application-level techniques use CDNs

More information