Modern Computer Network

Transcription

1 Modern Computer Network An Open Source Approach Chapter 6. Internet QoS

2 Content 6.1 Issues: Requirements for the QoS Network Signal Protocol QoS Routing Admission Control Packet Classification Policing Scheduling 6.2 Integrated Service Concept Service Types Resource ReserVation Protocol (RSVP) QoS Routing Admission Control Flow Identification Packet Scheduling 6.3 Differentiated Service Concept and Difference with IntServ) DS Field Per Hop Behaviors A packet life in the DiffServ Domain Packet Classification Packet Discard 9/13/2008 Copyright Reserved

3 Problem Statement There is no QoS in Internet currently (Only Best Effort is supported) However, the Internet architecture (Ethernet/IP) is popular And QoS is required for many applications (Bounded delay and fixed sending rate requirement) So.. What is the QoS Internet Architecture? The first kind of model is Integrated Services. (It is intuition, iti but is difficult to implement and scale) The Second kind of model is Differentiated Services. (A simple solution for implementation and deployment) 9/13/2008 Copyright Reserved

4 6.1 Issues Signal Protocol QoS Routing Admission Control Packet Classification Policing Scheduling 9/13/2008 Copyright Reserved

5 Requirements for the QoS Network Requirements for the QoS Network Control Plane Signal Protocol QoS Routing Admission Control Admission Control Data Plane Classification Policing Scheduling QoS Routing Taipei: i 90 mins -> <- HsinChu: 30 mins packet 9/13/2008 Copyright Reserved

6 Basic Code Components of TC Open Source Implementation Input Device Upper Layers Process IP Forwarding Output Queuing Traffic Control Without QoS Output Device Output Device Filter Policing i Class Queuing Disciplinei Filter Class Queuing Discipline Queuing Discipline 9/13/2008 Copyright Reserved

7 The General Model of a Queuing Discipline Open Source Implementation arrival packets Enqueue Queuing Discipline Black Pipe Dequeue departure packets FIFO Queue Single FIFO Queue C FIFO Queue S FIFO Queue 9/13/2008 Copyright Reserved

8 Functions invoked when enqueue and dequeue Open Source Implementation dev_queue_xmit qdisc_enqueue Timer qdisc _ wakeup qdisc_restart qdisc_run_queues qdisc_dequeue hard_start_xmit net_bh 9/13/2008 Copyright Reserved

9 6.2 Integrated Service Concept Provided Service Types Resource ReserVation Protocol (RSVP) QoS Q S Routing Admission Control Flow Identification Packet Scheduling 9/13/2008 Copyright Reserved

10 Concept of IntServ Network A flow is the basic management unit Supporting accurate quality control. Resource reservation is dynamic. Allt traffic control lfunctions are embedded din one router. All routers in the network must be IntServ aware. 9/13/2008 Copyright Reserved

11 Simple IntServ Operating Model Sender RSVP Admission Control IntServ router RSVP (signal protocol) QoS Routing Traffic Source Traffic Policing (Regulator) Flow Identification Packet Scheduling control pkts data pkts 9/13/2008 Copyright Reserved

12 How to Support QoS under IntServ? Before transmitting data packets. STEP 1. Resource Reservation Before getting g the resource, to request it is the first step. Sender A B C Receiver IntServ Network Traffic Info. Signal (TSpec) Reservation Signal (Rspec) IntServ Aware Router 9/13/2008 Copyright Reserved

13 How to Support QoS under IntServ? Before transmitting data packets. STEP 2. Admission Control The router needs to decide whether to admit the request according to it s load and the request. A path with 3 MB/s Bandwidth B d Constraint t is required Packet Loss Constraint A BW Max Support BW 10MB Current BW TIME 9/13/2008 Copyright Reserved

14 How to Support QoS under IntServ? Before transmitting data packets. STEP 2a. QoS Routing A path must be selected so that it is likely to have enough resource to satisfy the user s requirement. Sender A? B Bandwidth Constraint Packet Loss Constraint C Receiver? QoS Network D QoS -aware NE 9/13/2008 Copyright Reserved

15 How to Support QoS under IntServ? As transmitting data packets. STEP 3. Flow Identification Examining each incoming packet and decide if the packet belongs to one of the reserved flow. Src IP Dest. IP Protocol ID Src Port Dest Port Fq 1 Flow Identification Fq 2 Fq n Best Effort q scheduling Flow Queue 9/13/2008 Copyright Reserved

16 How to Support QoS under IntServ? As transmitting data packets. STEP4 4. Scheduling Deciding packets transmitting sequence so that it can satisfy the QoS constraints of all reserved flows QoS-aware NE Fq 1 Fq 2 Fq n Best Effort q scheduling S Bandwidth Constraint Max Delay Constraint 9/13/2008 Copyright Reserved

17 Service Types Provided by IntServ Service Types Guaranteed Control Load Best Effort Parameters RSpec >TSpec TSpec None Provide QoS Guaranteed BW Emulate a lightly None E2E * Delay Bound loaded network for AP RFC RFC 2212 RFC 2211 None Common Traffic Description Parameters: *) E2E implies End-to-End Peak rate p Description Specification: Average rate r TSpec : Traffic descriptor specification Burst size b RSpec : Reservation specification 9/13/2008 Copyright Reserved

18 Traffic Description Model Traffic Regulator & Traffic Policing Objective: Conforming the incoming traffic for each flow to it s traffic specification described as resource reserved. Flow Queue Token Bucket Token Stream with average rate r Bucket depth b Peak Rate p Incoming Packets Rate Permitted Packets 9/13/2008 Copyright Reserved

19 Input Police Filter (police.c) Open Source Implementation rsvp_session no match th rsvp_filter pktlen<mtu Y tcp_policepolice N toks = calculate overlimits++ current accumulated tokens in this step Result code Description toks>burst Y toks=burst N toks-=pktlen TC_POLICE_ SHOT TC_POLICE_ RECLASSIFY TC_POLICE_ OK Pkt was selected by filter, but violate the bound such that it should be discarded Pkt was selected by filter, but it exceeds certain bound and should be reclassify Conform the policy TC_POLICE_ UNSPEC Without matching any filter 9/13/2008 Copyright Reserved

20 The enqueue function of TBF Open Source Implementation euque a packet from sk_buff skb->len > q->max_size kfree_skb(skb) skb_queue_tail 9/13/2008 Copyright Reserved

21 The dequeue function of TBF get one packet from skb queue calculate the current tx time toks with avg rate calculate the interval between last query and current both ptoks and toks >=0 reinsert into the head of the skb queue is there peak rate setting? admitted the packet to be tx and update the value of tbf_sched calculate the current tx time ptoks with peak rate 9/13/2008 Copyright Reserved

22 Basic Features of Resource ReserVation Protocol (RSVP) Just a signal protocol It neither makes nor enforces the decision Soft State for maintaining a reservation state Policy Independent Control Parameters is packaged in the opaque with RSVP message Simplex Reservation Receiver Oriented 9/13/2008 Copyright Reserved

23 RSVP Operation Block Diagram 9/13/2008 Copyright Reserved

24 Traffic Flow of the RSVP messages RSVP PATH Message = Previous Hop + Sender Template + Sender Tspec + Adspec RSVP RSVP Message = Reservation Style + flow spec object + Filter Spec RSVP PATH R receiver RSVP RESV R R R RSVP PATH sender RSVP RESV IntServ Domain R RSVP aware Router Control Plane Packet Data Plane Packet 9/13/2008 Copyright Reserved

25 Objectives and Issues of Admission Control Objectives Provide a mechanism to admit users resource reserved request according to 1) Current Resource Usage 2) The User s Requirement Major Issues 1) How to get the information about link resource usage efficiently? 2) How to know the residual resource is enough to satisfy a user s s request under OVERBOOKING? 9/13/2008 Copyright Reserved

26 Basic Approaches of Admission Control Statistical-Based Apply to the Specific traffic Model Detail ilversion: - Average/Peak Rate Combinatory - Additive Effective Bandwidths - Engineering the loss Curve - Maximum-Variance-Based Approaches Drawbacks Sometimes, it is difficult to give a accurate and tight traffic model. It may cause low utilization of network in order to meet the worst-case requirements. 9/13/2008 Copyright Reserved

27 Basic Approaches of Admission Control Measurement-Based Apply to the non-specific traffic Model - Exponential averaging over consecutive measurement estimation new =(1-w) X estimation old + w X measurement new - Time Window Estimated rate=max[c1,c2,c3.cn] Drawbacks It can not be used to provide tight guarantee constraints Measurement is expensive. 9/13/2008 Copyright Reserved

28 Introduction to QoS Routing Major Issues How to collect the state information of all nodes? How to find a feasible path for the specific requriement? Keywords Clarification Optimization VS. Constrainted Link VS Path Link Path Optimization Constrainted Link BW>10KB BW=10 Path Delay< 10ms Delay=10ms 9/13/2008 Copyright Reserved

29 How to QoS Routing? QoS Rouer Major Issues Local Maintenance of State Information Local State: Each Node maintain its up-to-date local state Routing Strategies Distributed Routing: Routing is done on a hop-by-hop basis Global l Global l State: Source Routing: Every node is able to maintain global state by exahanging the local state of every node. A feasible path is locally computed at the source node Hier Aggregated Global State: Hierarchical Routing: archical Containing detail state info. About the nodes in Scalability, but there is a the same group and aggregate state info. About significant negative the other groups impact on QoS routing 9/13/2008 Copyright Reserved

30 The Complexity of QoS Routing Polynomical Complexity Basic Routuing Problems Apply to Example LO Link Optimization Delay, Cost BW-optimization routing LC Link Constrained BW-constrained routing PO Path Optimization Bandwidth Least-cost routing PC Path Constrained Delay-constrained routing Link Optimization LO LC PO PC Constrained Path Composite Comp- Example Routing lexity LC + PC PN BW-Delay-constrained routing PC + LO PN Delay-constrainted BW-optimization routing PC + PO NP Delay-constrained least-cost routing PC + PC NP Delay-delayjitter- constrainted routing 9/13/2008 Copyright Reserved

31 Objectives and Issues of Flow Identification Objectives Identify a packet to decide whether it belongs to one reserved flow or nothing. Major Issues Search Speed Low Storage requirement Fast Update Scalability S l Number Fields Flow Numbers Identified Fields in a IP pkt Source IP, Port Dest IP, Port Protocol ID 104 bits SPACE VS. SPEED Binary Search Tree Direct Memory Lookup 9/13/2008 Copyright Reserved

32 rsvp_classify of CLS_RSVP.h Open Source Implementation skb h1=ha ash_dst() rsvp_sessionsession dstaddr protocol id tunnelid rsvp_filter h1 rsvp_session RF X RF rsvp_filter rsvp_filter src tcf_result tcp_police return value rsvp_session h2=hash_src() h2 RF RF RF srcaddr tcf_result tcf_police info. RF 9/13/2008 Copyright Reserved

33 rsvp_classify & rsvp_change of CLS_RSVP.h Open Source Implementation hash_dst() sequential search in the rsvp_session list N Has rsvp_filter assigned? create modify adjust classid hash_src() src() Has rsvp_session existed itd? Y sequential search in the rsvp_filter list N N insert a rsvp_ session Y match nomatch insert a rsvp_filter The flowchart of function rsvp_classify The flowchart of function rsvp_change 9/13/2008 Copyright Reserved

34 Objectives and Issues Objective of Packet Scheduling Provide a mechanism to divide the bandwidth and guarantee that each flow can get the allocated resource Issues Isolation of Flows Low End-to-End Delays Utilization Fairness Simplicity of Implementation Scalability Work-conserving or Non Work-conserving 9/13/2008 Copyright Reserved

35 Basic Type of Scheduling: Round Robin (Frame Based) Flow Queue 1 credit S Flow Queue N Deficit Round Robin: A Practical Scheduler It is simple, but not very fair within a small time interval 9/13/2008 Copyright Reserved

36 Advanced Concept of Scheduling: Smallest Selection (Sorted-Based) Generalized Processor Sharing (GPS) An ideal fair queuing based on the fluid model. It provides perfect fairness in bandwidth allocation For a traffic source LB(b,r), it can guarantee - a delay bound of b/r φi R V - the received BW >= =1 φ j However, it s impossible to be implemented!! j Flow A Flow B A1 A2 A3 B1 B2 Fluid Model A1 B1 A2 B2 A3 Packetized Model 9/13/2008 Copyright Reserved

37 Packet-by-Packet GPS (PGPS) Try to emulate a GPS by calculating the departure time of a packet (finish time) and give a virtual timestamp for each packets. Finish time is a number representing the order of sending out the packets. ( not is a real departure time ) If there are packets in the flow queue i, the finish i time of fkth k-th k packet is k k 1 Li Fi = Fi + φ i If the flow queue i is empty, the finish time of k-th packet is k 1 [ F, V ( t ) ] k k Li F i = max i + φ Virtual Time Implementation t j is the time where the j th event occurs. i V V ( t 1 ) = 0 ( t 1 + τ ) = V ( t 1 ) j τ t t, j j j 1 = j + 2,3,... τ i B φ i, 9/13/2008 Copyright Reserved

38 Arrival-Departure Curve 9/13/2008 Copyright Reserved

39 Round Robin and Sorted-Based will be similar as. Assume the credits got by all flows in one round is decrease to infinitesimal with a fixed ratio. Assume it spends no time to decide whether there are packets allowed to be send out in one flow. Then, the order of packet transmitting will be similar. In fact, Sorted-Based may be regarded as a ingenious implementation of Round Robin 9/13/2008 Copyright Reserved

40 The enqueue function of sch_csz.c Open Source Implementation csz_classify():get the flow id drop the pkt full check the len. of flow queue csz_update(): update VST calculated new VFT based on the VST csz_insert_finish() : Wake up the flow N Is the flow active? Y calculated new VFT based on the last VST csz_insert_start() : Wake up the flow skb_queue_tail() 9/13/2008 Copyright Reserved

41 The VFT calculation function of sch_csz.c Open Source Implementation get the csz_flow where the headed packet with the smallest VFT skb_dequeue(): get the headed packet of the flow if the flow is non empty N Return the packet for sending out Y recalculate the min VFT in the flow csz_insert_start() 9/13/2008 Copyright Reserved

42 The dequeue function of sch_csz.c Open Source Implementation Get the time interval, delay, between now and the time where last packet arrived Assume all flows are active and calculate the current VST by delay and last VST If exist any flow actively F>VST Get the minimum VFT, F, from the tail packet of headed item in the list f The flow pointed by the headed item in the list f is no longer active Assume the time A means the non active flow sends out the least packet. Then, Get the VST at the time A and adjust delay to the time interval between now and the time A. All residual flows are still active and the VST, F, calculated just now is right. 9/13/2008 Copyright Reserved

43 6.3 Differentiated t Service Concept and the Difference with IntServ DS Field Per Hop Behaviors A Packet Life in the DiffServ Domain Packet Classification Packet Discard 9/13/2008 Copyright Reserved

44 Concept of DiffServ Network Objective: Define a simple and coarse methods of providing differentiated classes of service for Internet traffic. 1. If You want to get QoS, You must have be signed the contracts with SP 2. Only support the aggregated traffic resource allocation 3. Only provide a better behavior and provision (no accurate bandwidth reservation ) Ingress Router Police, Mark, Shape, Drop Packets Core Routers Forward Packet Egress Router DiffServ Domain Core Router Edge Router 9/13/2008 Copyright Reserved

45 Basic Elements Tree of DiffServ 9/13/2008 Copyright Reserved

46 Major Difference between DiffServ and IntServ Compared Items DiffServ IntServ Manageable Unit Class Flow Router s Capability Edge and Core All in One Defined in the Standard Forwarding behavior Service Type Guarantee Required Provisioning Reservation Work Region Domain End-to-end 9/13/2008 Copyright Reserved

47 Differentiated Services (DS) Field Redefine the existing IP TOS field to DS field Some level of backward compatibility to IP TOS No use IP TOS Precedence D T R DS DSCP = 64 behaviors 12 AF PHBs 1 EF PHB 1 Best Effort PHB 8 Class Selector PHBs 9/13/2008 Copyright Reserved

48 Per-Hop Behavior Group 9/13/2008 Copyright Reserved

49 Ingress of DiffServ Domain DS Domain Packet Classifier Meter DSCP Marker Dropper Shaper DSCP Classifier Class Scheduler Traffic Conditioning Traffic Forwarding 9/13/2008 Copyright Reserved

50 Ingress Router Structure Open Source Implementation 9/13/2008 Copyright Reserved

51 Core Router of DiffServ Domain DS Domain Routing Database DSCP Classifier Class Scheduler Control Plane Data Plane Traffic Forwarding 9/13/2008 Copyright Reserved

52 Core Router Structure Open Source Implementation 9/13/2008 Copyright Reserved

53 DiffServ Resource Manager 9/13/2008 Copyright Reserved

54 Packet Classification: Multi- Dimensional Range Match dest addr Rule B Rule A src addr 9/13/2008 Copyright Reserved

55 Packet Discard(Buffer Management) Tail Drop ( The Natural Method ) : Drop packet as queue is full Drop queue Early Drop : To early drop packets before queue is full Drop with P Queue queue Drop 9/13/2008 Copyright Reserved

56 Longest Tail Drop g p Rerspective Space A A A A B B B B Logic Memory Pool C C C C C Logic Memory Pool A A A A B B B C C C B C C C C C C C queue but has a P to be dropped 9/13/2008 Copyright Reserved queue but has a P to be dropped

57 Random Early Detection (Sally Floyd) To Maintain a variable Qlength avg computed by Qlength g Qlength avg = (1-W)Qlength avg + W * Qlength Rules 1. To Drop or Mark all packets as Qlength avg >max_threshold 2. To Queue all packets as Qlength avg <min_threshold 3. To Drop packets with p as min_threshold < Qlength avg <max_threshold where p = max p * ( Qlength avg min_threshold) / (max_threshold-min_threshold) 9/13/2008 Copyright Reserved

58 Generic RED Open Source Implementation 9/13/2008 Copyright Reserved

59 Pitfalls and Misleading 1. Shaper and Scheduler 2. WFQ and WRR 3. Service and Forwarding Behavior 9/13/2008 Copyright Reserved

60 Further Reading Related RFCs Other text t books Web Site 9/13/2008 Copyright Reserved

61 Hand-on exercise 9/13/2008 Copyright Reserved

62 Written exercises 1. As mentioned in Section 6.1, there are six basic components required by a QoS aware are router. Can you give a block diagram to describe how to design a IntServ router by the components and the operating relationship among them. Of course, adding some components is allowed for demand as designing. 2. Assume a traffic is regulated by a token bucket with parameters ( r, p, B). Can you further discuss the effect caused from the token bucket? For example, what is its expected output result? Or what is the result if one of the parameters are modified? 3. There are two common traffic estimated methods introduced in measured-based admission control. One is EWMA and the other is time window. Can you further compare the difference on estimation between them? 4. There is a 10 7 bits/sec link and WRR is used to schedule. Suppose N flows attemps to share the link and the size of their packets is 125 bytes. If we plan to fair alloc 8*10 6 bits/sec bandwidth for half number of flows and the residual bandwidth for other half. If N-1 flows are backlogged and what is the possible worst delay waitted for sending the first packet by the non-actived flow once its packet arrived. 5. Generally speaking, WRR is suitable for the network whose packet size is fixed length and DRR is a improved version which is able to handle packets with variant length. In fact, due to the simple implementation of DRR, it is more and more popular. However, it still exists the drawback for providing a small worst delay guarantee. Can you further study their abilities about the worst delay guarantee. Does DRR guarantee the smaller worst delay than WRR? 6. A trace on queue length and a calculation on average queue length periodically are required in the original algorithm of RED, which are a large load for implementation. In TC, a better skill is provided to reduce the load. You should observe the source code in the file sch_red.c and try to picture a flowchart and describe how the problem is solved as implementation. 9/13/2008 Copyright Reserved