Congestion Control & Resource Allocation. Issues in Resource Allocation Queuing Discipline TCP Congestion Control
|
|
- Barbara McCormick
- 6 years ago
- Views:
Transcription
1 Congestion Control & Resource Allocation Issues in Resource Allocation Queuing Discipline TCP Congestion Control Reacting to Congestion Avoiding Congestion QoS Issues 1 Issues in Resource Allocation RA & Congestion Control are two sides of the same coin pre-allocate resources so as to avoid congestion, precise allocation is difficult control congestion if (and when) is occurred Bottleneck router RA: by which NEs try to meet the competing demands the appl. have for resource Link bandwidth & buffer space Two points of RA implementation (end user using signaling protocol to convey) hosts at the edges of the network (transport protocol) routers inside the network (queuing discipline) Underlying service model of our discussion best-effort (assume for now) multiple qualities of services (later) 2 Framework Our focus: IP connectionless datagram + TCP end-to-end connection abstraction, not X.25 (resource reservation at each router) Connectionless flows (host-to host, or process-to-process) sequence of packets sent between source/destination pair following the same path maintain soft state at the routers to make RA (queuing discipline) decision about the flow Soft vs. hard state: soft state need not always be explicitly created or removed by signaling; It is the middle ground between purely connectionless & purely connection-oriented network ; the correct operation of the network does not depend on soft state being present. 3 It can be implicitly defined (router inspects the address in the header, and treat the packets as belonging to the same flow for the purpose of congestion control) or explicitly established (source sends a flow setup message), little diff from connection-oriented network, it exists for the purpose of resource allocation. Taxonomy for resource allocation mechanisms classification (reading assignment: p ) router-centric vs. host-centric (non exclusive) reservation-based vs. feedback-based: reservation-based implies a router-centric resource allocation mechanism; feedback-based can be either router- or host-centric window-based (e.g. TCP) vs. rate-based (an open area of research): for both flow control & congestion control Note: rate-based could be used to support video; it is a logical choice in a reservation based system that supports different QoS. More on Soft State 4
2 Evaluation Criteria Effectiveness: Throughput: allow as many packets into the network as possible, increase network resource utilization. However, longer queue -> larger delay Power (ratio of throughput to delay) assumption1: M/M/1 queue; assumption2: for a single connection, not clear how to extend it to multi-flow (n-dimensional?) Better metric? Fairness: fair equal (quantification is difficult) Ideal Performance Ideal goal of network utilization: infinite buffer throughput = full capacity traffic load = full capacity Normalized by the maximum theoretical throughput Power = thrupt/delay Queuing Discipline The queuing policy can be thought of as allocating both bandwidth (which packets get transmitted) and buffer space (which packets get discarded) First-In-First-Out (FIFO) : scheduling discipline + drop policy does not discriminate between traffic sources variation: priority queue via IP TOS, routers maintain multiple FIFO queues, one for each priority -> pushback by economic; Fair Queuing (FQ) explicitly segregates traffic based on flows ensures no flow captures more than its share of capacity To be used in conjunction with an end-to-end congestion control mechanism variation: weighted fair queuing (WFQ) (e.g. DiffServ), Problem? packet-by-packet round-robin vs. bit-by-bit round-robin (not feasible to implement, why??) 7 FQ Algorithm (packet-by-packet): approximating bit-by-bit round-robin For Single Flow Suppose clock ticks each time a bit is transmitted Let P i denote the length of packet i Let S i denote the time when start to transmit packet i Let F i denote the time when finish transmitting packet i F i = S i + P i When does router start transmitting packet i? if it arrives before router finishes packet i - 1 from this flow, then immediately after last bit of i -1 (F i-1 ) if no current packets for this flow, then start transmitting when arrives (call this A i ) Thus: F i = MAX (F i -1, A i ) + P i 8
3 FQ Algorithm (cont) For multiple flows (w/ slower clock) calculate F i for each packet that arrives on each flow treat all F i s as timestamps next packet to transmit is one with lowest timestamp Another version of Fair Queuing byte-by-byte A Packet Finishing-Time C 8 B B 16 C 3 8 D E D 17 E 18 A 20 Ref: book by Tanenbaum 9 FQ Algorithm (cont) FQ is work-conserving link never left idle if queue is not empty If the link is fully loaded with n flows sending data, no one can use more than 1/n of the link bandwidth 10 TCP Congestion Control Flow Control: a sender to avoid overrunning a slow receiver; Congestion Control: a set of senders to avoid overrunning the network of resource General Congestion Control: to prevent or respond network overload condition; commonly with fairness concerns TCP strategy: w/o reservation, react to observable events that occur assumes best-effort network (may have FIFO or FQ in routers), each source determines available network capacity for itself uses implicit feedback (timeout, retransmission) ACKs pace transmission (self-clocking) Challenges determining the available capacity in the first place adjusting to changes in the available capacity (dynamically) 11 Additive Increase/Multiplicative Decrease Objective: adjust to changes in the available capacity New state variable per connection: CongestionWindow limits how much data source has in transit MaxWin = MIN(CongestionWindow, AdvertisedWindow) EffWin = MaxWin - (LastByteSent - LastByteAcked) Unlike AdvertisedWindow, CongestionWindow set by TCP source based on the observed congestion level Idea: increase CongestionWindow when congestion goes down decrease CongestionWindow when congestion goes up Question: how does the source determine whether or not the network is congested? Answer: a timeout occurs timeout signals that a packet was lost packets are seldom lost due to transmission error lost packet implies congestion 12
4 Algorithm AIMD (cont) increase CongestionWindow by one packet per RTT (linear increase) divide CongestionWindow by two whenever a timeout occurs (multiplicative decrease) In practice: increment a little for each ACK Increment = MSS*(MSS/CongestionWindow) = MSS*(1/# of ACKs Per RTT) CongestionWindow += Increment 13 Trace: sawtooth behavior AIMD (cont) Reason of being conservative: consequences of having too large a window are much worse than those of it being too small: e.g., dropped packets have to be retransmitted->more cong. Note: the accurate timeout mechanism is desirable, which is a function of RTT in TCP (Karn/Partridge algorithm, and Jacobson/Karels algorithm) Problem: it takes too long to ramp up a connection when it is starting from scratch (cold start) 14 Slow Start Slow start increase the congestion window exponentially rather than linearly. Idea: begin with CongestionWindow = 1 packet double CongestionWindow each RTT (increment by 1 packet for each ACK). Slow Start (cont) Exponential growth, slower than all at once (original TCP) Used when first starting connection when connection goes dead waiting for timeout (more knowledge) Trace of TCP CongestionWindow: interplay of slow start & AIMD Packet trans. Packet retrans. later(no ACK) timeout Why slow? compare with the original behavior of TCP (advertised window), not compare with linear growth of AIMD. 15 Problem: lose up to half a CongestionWindow s worth of data Idea of so called packet pair : gap between the ACKs 16
5 Fast Retransmit and Fast Recovery Problem: coarse-grain TCP timeouts lead (flat part in previous figure) to idle periods EffWin = MaxWin - (LastByteSent - LastByteAcked) Too aggressive, once lost, all lost, no enough duplicated ACKs to trigger fast retransmission Results Fast retransmit: use duplicate ACKs to trigger retransmission, until the sender sees some # of duplicated ACKs, it then retransmits the missing packet. In TCP, sender waits till three duplicated ACKs Fast Recovery reading assignment: p Note: For a small window size, there will not be enough packets in transit to cause enough duplicate ACKs to be delivered; Given the current 64KB maximum advertised window size, TCP s fast retransmit mechanism is able to detect up to three dropped packets per window in practice. AIMD -> Slow Start -> Fast Retransmit Fast Recovery: improvement 18 Congestion Avoidance TCP s strategy control congestion once it happens repeatedly increase load in an effort to find the point at which congestion occurs, and then back off Alternative strategy predict when congestion is about to happen reduce rate before packets start being discarded call this congestion avoidance, instead of congestion control Two possibilities router-centric: put a small amount of additional functionality into the router to assist the end node in the prediction. e.g., DECbit and RED Gateways host-centric: effort purely from end nodes. e.g., TCP Vegas 19 DECbit Add binary congestion bit to each packet header Router monitors average queue length over last busy+idle cycle+current cycle The router set congestion bit if average queue length > 1 attempts to balance throughput against delay -> optimize the power function 20
6 End Hosts Destination copies and echoes bit back to source Source records how many packets resulted in set bit If less than 50% of last window s worth had bit set increase CongestionWindow by 1 packet If 50% or more of last window s worth had bit set decrease CongestionWindow by times previous value 21 Random Early Detection (RED) Similar to DECbit: each router monitor its own queue length, and notify the source once it senses congestion Notification is implicit (diff from DECbit) just drop the packet (TCP will timeout, or duplicate ACKs) Be used in conjunction with TCP, which currently detects congestion by timeout or duplicate ACKs could make explicit by marking the packet like DECbit Early random drop rather than wait for queue to become full, drop each arriving packet with some drop probability whenever the queue length exceeds some drop level 22 RED Details 1) Compute average queue length dynamically AvgLen=(1 - Weight) * AvgLen + Weight * SampleLen 0 < Weight < 1 (usually 0.002) SampleLen is queue length at each time a packet arrives Note: use average instead of instantaneous because the bursty nature of Internet traffic RED Details (cont) 2) Two queue length thresholds if AvgLen <= MinThreshold then queue the packet if MinThreshold < AvgLen < MaxThreshold then calculate probability P drop arriving packet with probability P if MaxThreshold <= AvgLen then drop arriving packet MaxThreshold MinThreshold MaxThreshold MinThreshold AvgLen 23 AvgLen 24
7 RED Details (cont) 3) Computing probability P TempP = MaxP * (AvgLen - MinThreshold)/ (MaxThreshold - MinThreshold) = MaxP/(MaxThreshold - MinThreshold) * (AvgLen - MinThreshold) P = TempP/(1 - count*tempp) Note: count keeps track of how many newly arriving packets have been queued (not dropped) while AvgLen has been between the two thresholds Reading Assignment: P487-P492 4) Drop Probability Curve Tuning RED- A Research Area (reading assignment: p492-p493 - skipped) Probability of dropping a particular flow s packet(s) should be roughly proportional to the share of the bandwidth that flow is currently getting -> fairness concern MaxP is typically set to 0.02, meaning that when the average queue size is halfway between the two thresholds the gateway drops roughly one out of 50 packets. If traffic is bursty, then MinThreshold should be sufficiently large to allow link utilization to be maintained at an acceptably high level Difference between two thresholds should be larger than the typical increase in the calculated average queue length in one RTT setting MaxThreshold to twice MinThreshold is reasonable for traffic on today s Internet Source-Based Congestion Avoidance: TCP Vegas Idea: source watches for some sign that router s queue is building up and congestion will happen too; e.g., RTT grows for each successive packet Average sending rate (average throughput) flattens Bottleneck router Algorithm Let BaseRTT be the minimum of all measured RTTs (commonly the RTT of the first packet) If not overflowing the connection, then ExpectRate = CongestionWindow/BaseRTT Source calculates sending rate (ActualRate) once per RTT Source compares ActualRate with ExpectRate (Note: β > α > 0) Diff = ExpectedRate - ActualRate if Diff < α (means real RTT is small->no congest.) increase CongestionWindow linearly else if Diff > β (means real RTT big ->congestion) decrease CongestionWindow linearly else leave CongestionWindow unchanged 27 28
8 Parameters α = 1 packet/sec β = 3 packets/sec Trace of TCP Vegas When actual rate below shaded area, decrease CW When actual rate above shaded area, increase CW Algorithm (cont) Expected Rate Actual Rate Although (early) linear decrease in the above algorithm; once timeout occurs (hopefully not), it does multiplicative decrease. 29 Quality of Service Application Requirements Real-time Audio Example Taxonomy of Real-Time Application Approaches to QoS Support Integrated Services (RSVP) Service Classes Overview of Mechanisms Flowspecs Admission Control Packet Classifying & Scheduling Reservation Protocol Differentiated Services 30 Realtime Applications Require deliver on time assurances must come from inside the network Playback Buffer Microphone Sampler, A D converter Buffer, D A Speaker Example application (audio) sample voice once every 125us (8000HZ) each sample has a playback time : a time at which the sample is playback packets experience variable delay in network: Jitter add a constant offset to playback time: playback point Question: How much? Answer: < 300ms Sequence number Packet generation Network delay Time Buffer Packet arrival Playback 31 32
9 Example Distribution of Delays for an Internet Connection Taxonomy of Applications 3 90% 97% 98% 99% Applications Real time Elastic Packets (%) 2 1 Delay/ bit rate Adaptive Tolerant Nonadaptive Occasional loss Rate-adaptive Intolerant Interactive Nonadaptive Interactive bulk Asynchronous Delayadaptive Rateadaptive Delay (milliseconds) Reading assignment: p Approaches to QoS Support Fine-grained approach: provide QoS to individual applications or Flows (e.g. Integrated Service, associated with RSVP) Coarse-grained approaches: provide QoS to large classes of data or aggregated traffic (e.g. Differentiated Services) Integrated Services (RSVP): IntServ (defined by IETF around 95-97) Service Classes Delay Guaranteed: for intolerant applications to guarantee the maximum delay controlled-load: for tolerant/adaptive applications, which run well on networks that are not heavily loaded, e.g., audio application vat. Mechanisms for QoS implementation Flowspec: a set of information about the flow (within a single application, share common requirements) admission control (say no when necessary) signaling protocol: by which user & network components exchange information such as requests of service, flowspecs, admission decision. in ATM, it is called signaling, in Internet, it is called resource reservation. packet scheduling: how routers and switches behave based on admission control decision 35 Flowspec Rspec: describes service requested from network controlled-load guaranteed: delay target/bound Tspec: describes flow s traffic characteristics (varies with time) average bandwidth + burstiness: token 2 bucket filter token bucket rate r : a long term average rate 1 bucket depth B must have a token to send a byte must have n tokens to send n bytes accumulate tokens at rate of r per second start with no tokens can accumulate no more than B tokens (big B corresponding to big variant) Bandwidth (MBps) Flow A Flow B time 36
10 QoS Mechanisms (reading:p ) Admission Control: Based on Tspec & Rspec decide if a new flow can be supported answer depends on service class not the same as policing (e.g. priority when resource available) Packet Processing: how the router deliver the packet after network decides to admit the traffic and made the reservation on routers classification: associate each packet with the appropriate reservation (check src/dest addrs/ports, and protocol number) scheduling: manage queues so each packet receives the requested service 37 Reservation Protocol Called signaling in ATM Proposed Internet standard: RSVP Consistent with robustness of today s connectionless model Uses soft state (refresh periodically w/ timeout) Designed to support multicast Receiver-oriented Two messages: PATH and RESV Source transmits PATH messages every 30 seconds Destination responds with RESV message Merge requirements in case of multicast Can specify number of speakers 38 RSVP Example: skipped Sender 2 Sender 1 PATH R PATH R RSVP vs. ATM (Q.2931): skipped RSVP receiver generates reservation soft state (refresh/timeout) separate from route establishment QoS can change dynamically receiver heterogeneity RESV (merged) R R R RESV RESV Receiver B Receiver A ATM sender generates connection request hard state (explicit delete) concurrent with route establishment QoS is static for life of connection uniform QoS to all receivers 39 40
11 Differentiated Services (Diffserv) Problem with Integrated Services: scalability of flow-based Idea: support a small number of classes of packets. e.g., premium P(drop) best-effort 1.0 Mechanisms: packets: in and out bit e.g., edge routers: tag packets DSCP (6 bits) indicates the MaxP AvgLen PHB(per-hop behavior): e.g. EF; AF Min out Min in Max out Max in RIO (RED with In and Out) (at the intermediate router) is the root of AF (assured forwarding): for two classed, can generalize 41
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 informationCS 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 informationTCP Congestion Control. Housekeeping. Additive Increase/Multiplicative Decrease. AIMD (cont) Pick up folders for exam study Exam next Friday, Nov.
Fall 01 CptS/EE 555 3 Fall 01 CptS/EE 555 4 TCP Congestion Control Idea assumes best-effort network (FIFO or FQ routers)each source determines network capacity for itself uses implicit feedback ACKs pace
More informationCongestion Control 3/16/09
Congestion Control Outline Resource Allocation Queuing TCP Congestion Control Spring 009 CSE3064 Issues Two sides of the same coin pre-allocate resources so at to avoid congestion control congestion if
More informationCongestion. 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 informationCongestion Control. Resource allocation and congestion control problem
Congestion Control 188lecture8.ppt Pirkko Kuusela 1 Resource allocation and congestion control problem Problem 1: Resource allocation How to effectively and fairly allocate resources among competing users?
More informationChapter 6 Congestion Control and Resource Allocation
Chapter 6 Congestion Control and Resource Allocation Congestion-Avoidance Mechanisms Congestion avoidance is to predict when congestion is about to happen and then to reduce sending rate of source host
More informationCongestion Control and Resource Allocation
Problem: allocating resources Congestion control Quality of service Congestion Control and Resource Allocation Hongwei Zhang http://www.cs.wayne.edu/~hzhang The hand that hath made you fair hath made you
More informationWhat is Congestion? Congestion: Moral of the Story. TCP Approach. Transport Layer: TCP Congestion Control & Buffer Management
Transport Layer: TCP Congestion Control & Buffer Management Congestion Control What is congestion? Impact of Congestion Approaches to congestion control TCP Congestion Control End-to-end based: implicit
More informationChapter 6 Congestion Avoidance. Networking CS 3470, Section 1
Chapter 6 Congestion Avoidance Networking CS 3470, Section 1 Congestion Avoidance TCP s strategy control congestion once it happens repeatedly increase load in an effort to find the point at which congestion
More informationTCP Congestion Control. Lecture 16. Outline. TCP Congestion Control. Additive Increase / Multiplicative Decrease (AIMD)
Lecture 16 TCP Congestion Control Homework 6 Due Today TCP uses ACK arrival as a signal to transmit a new packet. Since connections come-and-go TCP congestion control must be adaptive. TCP congestion control
More informationADVANCED 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 informationC 6. Congestion Control and Resource Allocation. Copyright 2010, Elsevier Inc. All rights Reserved
C 6 Congestion Control and Resource Allocation Copyright 2010, Elsevier Inc. All rights Reserved Congestion Control and Resource Allocation Resources Bandwidth of the links Buffers at the routers and switches
More informationCongestion Control in TCP
Congestion Control in TCP Outline Overview of RENO TCP Reacting to Congestion SS/AIMD example CS 640 1 TCP Congestion Control The idea of TCP congestion control is for each source to determine how much
More informationUNIT IV. UDP TCP Adaptive Flow Control-Adaptive Retransmission Congestion Control Congestion avoidance QoS.
UNIT IV UDP TCP Adaptive Flow Control-Adaptive Retransmission Congestion Control Congestion avoidance QoS. Transport Layer Introduction The following are some of the common properties that a transport
More informationCS519: Computer Networks. Lecture 5, Part 5: Mar 31, 2004 Queuing and QoS
: Computer Networks Lecture 5, Part 5: Mar 31, 2004 Queuing and QoS Ways to deal with congestion Host-centric versus router-centric Reservation-based versus feedback-based Window-based versus rate-based
More informationCongestion Control & Resource Allocation
Congestion Control & Resource Allocation Proper Use of Networks Congestion A system is loaded beyond its capacity In a lightly loaded network, network throughput and delay increase linearly as offered
More informationCS 356: Computer Network Architectures Lecture 19: Congestion Avoidance Chap. 6.4 and related papers. Xiaowei Yang
CS 356: Computer Network Architectures Lecture 19: Congestion Avoidance Chap. 6.4 and related papers Xiaowei Yang xwy@cs.duke.edu Overview More on TCP congestion control Theory Macroscopic behavior TCP
More informationCSE 123b Communications Software
CSE 123b Communications Software Spring 2002 Lecture 10: Quality of Service Stefan Savage Today s class: Quality of Service What s wrong with Best Effort service? What kinds of service do applications
More informationCongestion Control and Resource Allocation
Congestion Control and Resource Allocation Lecture material taken from Computer Networks A Systems Approach, Third Edition,Peterson and Davie, Morgan Kaufmann, 2007. Advanced Computer Networks Congestion
More informationTCP Congestion Control
TCP Congestion Control Lecture material taken from Computer Networks A Systems Approach, Third Ed.,Peterson and Davie, Morgan Kaufmann, 2003. Computer Networks: TCP Congestion Control 1 TCP Congestion
More informationOverview. Lecture 22 Queue Management and Quality of Service (QoS) Queuing Disciplines. Typical Internet Queuing. FIFO + Drop tail Problems
Lecture 22 Queue Management and Quality of Service (QoS) Overview Queue management & RED Fair queuing Khaled Harras School of Computer Science niversity 15 441 Computer Networks Based on slides from previous
More informationLecture 21. Reminders: Homework 6 due today, Programming Project 4 due on Thursday Questions? Current event: BGP router glitch on Nov.
Lecture 21 Reminders: Homework 6 due today, Programming Project 4 due on Thursday Questions? Current event: BGP router glitch on Nov. 7 http://money.cnn.com/2011/11/07/technology/juniper_internet_outage/
More informationOverview Computer Networking What is QoS? Queuing discipline and scheduling. Traffic Enforcement. Integrated services
Overview 15-441 15-441 Computer Networking 15-641 Lecture 19 Queue Management and Quality of Service Peter Steenkiste Fall 2016 www.cs.cmu.edu/~prs/15-441-f16 What is QoS? Queuing discipline and scheduling
More informationAdvanced 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 informationCS/ECE 438: Communication Networks Spring Problem Set 7. Title: Congestion control and Performance Analysis
Problem Set 7 Title: Congestion control and Performance Analysis Due: start of class, Wednesday, May 2 nd Recommended Reading: Section 6. All problems carry equal weight. To receive full credit, show all
More informationAdvanced Lab in Computer Communications Meeting 6 QoS. Instructor: Tom Mahler
Advanced Lab in Computer Communications Meeting 6 QoS Instructor: Tom Mahler Motivation Internet provides only single class of best-effort service. Some applications can be elastic. Tolerate delays and
More informationComputer 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 informationCS321: 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 informationQuality of Service (QoS)
Quality of Service (QoS) The Internet was originally designed for best-effort service without guarantee of predictable performance. Best-effort service is often sufficient for a traffic that is not sensitive
More informationUnit 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 informationReal-Time Applications. Delay-adaptive: applications that can adjust their playback point (delay or advance over time).
Real-Time Applications Tolerant: can tolerate occasional loss of data. Intolerant: cannot tolerate such losses. Delay-adaptive: applications that can adjust their playback point (delay or advance over
More informationLecture 24: Scheduling and QoS
Lecture 24: Scheduling and QoS CSE 123: Computer Networks Alex C. Snoeren HW 4 due Wednesday Lecture 24 Overview Scheduling (Weighted) Fair Queuing Quality of Service basics Integrated Services Differentiated
More informationPriority 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 informationImproving QOS in IP Networks. Principles for QOS Guarantees
Improving QOS in IP Networks Thus far: making the best of best effort Future: next generation Internet with QoS guarantees RSVP: signaling for resource reservations Differentiated Services: differential
More information514 CHAPTER 6 Congestion control and resource allocation
514 CHAPTER 6 Congestion control and resource allocation The HighSpeed TCP proposal, now an experimental RFC, makes TCP more aggressive only when it is clearly operating in a very high bandwidthdelay product
More informationInternet Services & Protocols. Quality of Service Architecture
Department of Computer Science Institute for System Architecture, Chair for Computer Networks Internet Services & Protocols Quality of Service Architecture Dr.-Ing. Stephan Groß Room: INF 3099 E-Mail:
More informationCS551 Router Queue Management
CS551 Router Queue Management Bill Cheng http://merlot.usc.edu/cs551-f12 1 Congestion Control vs. Resource Allocation Network s key role is to allocate its transmission resources to users or applications
More information6.3 TCP congestion control 499
6.3 TCP congestion control 499 queue each time around. This results in each flow getting 1/nth of the bandwidth when there are n flows. With WFQ, however, one queue might have a weight of 2, a second queue
More informationLecture 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 informationChapter III: Transport Layer
Chapter III: Transport Layer UG3 Computer Communications & Networks (COMN) Mahesh Marina mahesh@ed.ac.uk Slides thanks to Myungjin Lee and copyright of Kurose and Ross Principles of congestion control
More informationChapter 6: Congestion Control and Resource Allocation
Chapter 6: Congestion Control and Resource Allocation CS/ECPE 5516: Comm. Network Prof. Abrams Spring 2000 1 Section 6.1: Resource Allocation Issues 2 How to prevent traffic jams Traffic lights on freeway
More informationRSVP 1. Resource Control and Reservation
RSVP 1 Resource Control and Reservation RSVP 2 Resource Control and Reservation policing: hold sources to committed resources scheduling: isolate flows, guarantees resource reservation: establish flows
More informationResource Control and Reservation
1 Resource Control and Reservation Resource Control and Reservation policing: hold sources to committed resources scheduling: isolate flows, guarantees resource reservation: establish flows 2 Usage parameter
More informationLecture 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 informationCSE 461 Quality of Service. David Wetherall
CSE 461 Quality of Service David Wetherall djw@cs.washington.edu QOS Focus: How to provide better than best effort Fair queueing Application Application needs Transport Traffic shaping Guarantees IntServ
More informationComputer 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 informationTransmission 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 informationCongestion 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 informationReal-Time Protocol (RTP)
Real-Time Protocol (RTP) Provides standard packet format for real-time application Typically runs over UDP Specifies header fields below Payload Type: 7 bits, providing 128 possible different types of
More informationCS519: 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 informationQuality of Service II
Quality of Service II Patrick J. Stockreisser p.j.stockreisser@cs.cardiff.ac.uk Lecture Outline Common QoS Approaches Best Effort Integrated Services Differentiated Services Integrated Services Integrated
More informationCS557: Queue Management
CS557: Queue Management Christos Papadopoulos Remixed by Lorenzo De Carli 1 Congestion Control vs. Resource Allocation Network s key role is to allocate its transmission resources to users or applications
More informationQuality of Service in the Internet
Quality of Service in the Internet Problem today: IP is packet switched, therefore no guarantees on a transmission is given (throughput, transmission delay, ): the Internet transmits data Best Effort But:
More informationCongestion Control in TCP
Congestion Control in TCP Antonio Carzaniga Faculty of Informatics University of Lugano May 6, 2005 Outline Intro to congestion control Input rate vs. output throughput Congestion window Congestion avoidance
More informationResource 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 informationNetwork 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 informationPart1: Lecture 4 QoS
Part1: Lecture 4 QoS Last time Multi stream TCP: SCTP Multi path TCP RTP and RTCP SIP H.323 VoIP Router architectures Overview two key router functions: run routing algorithms/protocol (RIP, OSPF, BGP)
More informationLast time! Overview! 14/04/15. Part1: Lecture 4! QoS! Router architectures! How to improve TCP? SYN attacks SCTP. SIP and H.
Last time Part1: Lecture 4 QoS How to improve TCP? SYN attacks SCTP SIP and H.323 RTP and RTCP Router architectures Overview two key router functions: run routing algorithms/protocol (RIP, OSPF, BGP) forwarding
More informationCSCI-1680 Transport Layer III Congestion Control Strikes Back Rodrigo Fonseca
CSCI-1680 Transport Layer III Congestion Control Strikes Back Rodrigo Fonseca Based partly on lecture notes by David Mazières, Phil Levis, John Jannotti, Ion Stoica Last Time Flow Control Congestion Control
More informationTCP 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 informationEECS 122: Introduction to Computer Networks Resource Management and QoS. Quality of Service (QoS)
EECS 122: Introduction to Computer Networks Resource Management and QoS Computer Science Division Department of Electrical Engineering and Computer Sciences University of California, Berkeley Berkeley,
More informationCS 349/449 Internet Protocols Final Exam Winter /15/2003. Name: Course:
CS 349/449 Internet Protocols Final Exam Winter 2003 12/15/2003 Name: Course: Instructions: 1. You have 2 hours to finish 2. Question 9 is only for 449 students 3. Closed books, closed notes. Write all
More informationQuality of Service in the Internet
Quality of Service in the Internet Problem today: IP is packet switched, therefore no guarantees on a transmission is given (throughput, transmission delay, ): the Internet transmits data Best Effort But:
More informationMulticast and Quality of Service. Internet Technologies and Applications
Multicast and Quality of Service Internet Technologies and Applications Aims and Contents Aims Introduce the multicast and the benefits it offers Explain quality of service and basic techniques for delivering
More informationCSCD 433/533 Advanced Networks Spring Lecture 22 Quality of Service
CSCD 433/533 Advanced Networks Spring 2016 Lecture 22 Quality of Service 1 Topics Quality of Service (QOS) Defined Properties Integrated Service Differentiated Service 2 Introduction Problem Overview Have
More informationRSVP and the Integrated Services Architecture for the Internet
RSVP and the Integrated Services Architecture for the Internet N. C. State University CSC557 Multimedia Computing and Networking Fall 2001 Lecture # 20 Roadmap for Multimedia Networking 2 1. Introduction
More informationComputer Network Fundamentals Fall Week 12 QoS Andreas Terzis
Computer Network Fundamentals Fall 2008 Week 12 QoS Andreas Terzis Outline QoS Fair Queuing Intserv Diffserv What s the Problem? Internet gives all flows the same best effort service no promises about
More informationIntegrated and Differentiated Services. Christos Papadopoulos. CSU CS557, Fall 2017
Integrated and Differentiated Services Christos Papadopoulos (Remixed by Lorenzo De Carli) CSU CS557, Fall 2017 1 Preliminary concepts: token buffer 2 Characterizing Traffic: Token Bucket Filter Parsimonious
More informationMultimedia Networking
CMPT765/408 08-1 Multimedia Networking 1 Overview Multimedia Networking The note is mainly based on Chapter 7, Computer Networking, A Top-Down Approach Featuring the Internet (4th edition), by J.F. Kurose
More informationCongestion Avoidance
COMP 631: NETWORKED & DISTRIBUTED SYSTEMS Congestion Avoidance Jasleen Kaur Fall 2016 1 Avoiding Congestion: Strategies TCP s strategy: congestion control Ø Control congestion once it occurs Repeatedly
More informationBasics (cont.) Characteristics of data communication technologies OSI-Model
48 Basics (cont.) Characteristics of data communication technologies OSI-Model Topologies Packet switching / Circuit switching Medium Access Control (MAC) mechanisms Coding Quality of Service (QoS) 49
More informationThe Transport Layer Congestion control in TCP
CPSC 360 Network Programming The Transport Layer Congestion control in TCP Michele Weigle Department of Computer Science Clemson University mweigle@cs.clemson.edu http://www.cs.clemson.edu/~mweigle/courses/cpsc360
More informationBandwidth 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 informationChapter 3 outline. 3.5 Connection-oriented transport: TCP. 3.6 Principles of congestion control 3.7 TCP congestion control
Chapter 3 outline 3.1 Transport-layer services 3.2 Multiplexing and demultiplexing 3.3 Connectionless transport: UDP 3.4 Principles of reliable data transfer 3.5 Connection-oriented transport: TCP segment
More informationChapter 3 Transport Layer
Chapter 3 Transport Layer 1 Chapter 3 outline 3.1 Transport-layer services 3.2 Multiplexing and demultiplexing 3.3 Connectionless transport: UDP 3.4 Principles of reliable data transfer 3.5 Connection-oriented
More informationOutline 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 informationOverview. 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 informationTutorial 9 : TCP and congestion control part I
Lund University ETSN01 Advanced Telecommunication Tutorial 9 : TCP and congestion control part I Author: Antonio Franco Course Teacher: Emma Fitzgerald January 27, 2015 Contents I Before you start 3 II
More informationCongestion 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 informationLecture 13. Quality of Service II CM0256
Lecture 13 Quality of Service II CM0256 Types of QoS Best Effort Services Integrated Services -- resource reservation network resources are assigned according to the application QoS request and subject
More informationQuality of Service in the Internet. QoS Parameters. Keeping the QoS. Leaky Bucket Algorithm
Quality of Service in the Internet Problem today: IP is packet switched, therefore no guarantees on a transmission is given (throughput, transmission delay, ): the Internet transmits data Best Effort But:
More information15-744: Computer Networking. Overview. Queuing Disciplines. TCP & Routers. L-6 TCP & Routers
TCP & Routers 15-744: Computer Networking RED XCP Assigned reading [FJ93] Random Early Detection Gateways for Congestion Avoidance [KHR02] Congestion Control for High Bandwidth-Delay Product Networks L-6
More informationCongestion Control in TCP
Congestion Control in TCP Antonio Carzaniga Faculty of Informatics University of Lugano November 11, 2014 Outline Intro to congestion control Input rate vs. output throughput Congestion window Congestion
More informationA 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 informationInstitute of Computer Technology - Vienna University of Technology. L73 - IP QoS Integrated Services Model. Integrated Services Model
Integrated Services Model IP QoS IntServ Integrated Services Model Resource Reservation Protocol (RSVP) Agenda Integrated Services Principles Resource Reservation Protocol RSVP Message Formats RSVP in
More informationProject Computer Networking. Resource Management Approaches. Start EARLY Tomorrow s recitation. Lecture 20 Queue Management and QoS
Project 3 15-441 Computer Networking Start EARLY Tomorrow s recitation Lecture 20 Queue Management and QoS Lecture 20: QOS (c) CMU, 2005-10 2 Traffic and Resource Management Resource Management Approaches
More informationCS4700/CS5700 Fundamentals of Computer Networks
CS4700/CS5700 Fundamentals of Computer Networks Lecture 15: Congestion Control Slides used with permissions from Edward W. Knightly, T. S. Eugene Ng, Ion Stoica, Hui Zhang Alan Mislove amislove at ccs.neu.edu
More informationCS Transport. Outline. Window Flow Control. Window Flow Control
CS 54 Outline indow Flow Control (Very brief) Review of TCP TCP throughput modeling TCP variants/enhancements Transport Dr. Chan Mun Choon School of Computing, National University of Singapore Oct 6, 005
More informationEnd-to-End Protocols. Transport Protocols. User Datagram Protocol (UDP) Application Layer Expectations
# # # & *, + & %$ & Transport Protocols End-to-End Protocols Convert host-to-host packet delivery service into a process-to-process communication channel Demultiplexing: Multiple applications can share
More informationDesign Intentions. IP QoS IntServ. Agenda. Design Intentions. L73 - IP QoS Integrated Services Model. L73 - IP QoS Integrated Services Model
Design Intentions Integrated Services Model IP QoS IntServ Integrated Services Model Resource Reservation Protocol (RSVP) The Internet was based on a best effort packet delivery service, but nowadays the
More informationCS3600 SYSTEMS AND NETWORKS
CS3600 SYSTEMS AND NETWORKS NORTHEASTERN UNIVERSITY Lecture 24: Congestion Control Prof. Alan Mislove (amislove@ccs.neu.edu) Slides used with permissions from Edward W. Knightly, T. S. Eugene Ng, Ion Stoica,
More informationMohammad Hossein Manshaei 1393
Mohammad Hossein Manshaei manshaei@gmail.com 1393 Voice and Video over IP Slides derived from those available on the Web site of the book Computer Networking, by Kurose and Ross, PEARSON 2 Multimedia networking:
More informationCSCI Topics: Internet Programming Fall 2008
CSCI 491-01 Topics: Internet Programming Fall 2008 Transport Layer Derek Leonard Hendrix College October 20, 2008 Original slides copyright 1996-2007 J.F Kurose and K.W. Ross 1 Chapter 3: Roadmap 3.1 Transport-layer
More informationCS 344/444 Computer Network Fundamentals Final Exam Solutions Spring 2007
CS 344/444 Computer Network Fundamentals Final Exam Solutions Spring 2007 Question 344 Points 444 Points Score 1 10 10 2 10 10 3 20 20 4 20 10 5 20 20 6 20 10 7-20 Total: 100 100 Instructions: 1. Question
More informationII. 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 informationLecture 8. TCP/IP Transport Layer (2)
Lecture 8 TCP/IP Transport Layer (2) Outline (Transport Layer) Principles behind transport layer services: multiplexing/demultiplexing principles of reliable data transfer learn about transport layer protocols
More informationCS 268: Computer Networking
CS 268: Computer Networking L-6 Router Congestion Control TCP & Routers RED XCP Assigned reading [FJ93] Random Early Detection Gateways for Congestion Avoidance [KHR02] Congestion Control for High Bandwidth-Delay
More informationLecture Outline. Bag of Tricks
Lecture Outline TELE302 Network Design Lecture 3 - Quality of Service Design 1 Jeremiah Deng Information Science / Telecommunications Programme University of Otago July 15, 2013 2 Jeremiah Deng (Information
More informationUNIT IV TRANSPORT LAYER
UNIT IV TRANSPORT LAYER UDP - SIMPLE DEMULTIPLEXER (UDP) The simplest transport protocol is one that extends the host-to-host delivery service of the underlying network into a process-to-process communication
More information