Lecture 13: Traffic Engineering

Transcription

1 Lectre 13: Traffic Engineering CSE 222A: Compter Commnication Networks Alex C. Snoeren Thanks: Mike Freedman, Nick Feamster, and Ming Zhang

2 Lectre 13 Overview Dealing with mltiple paths Mltihoming Entact discssion Intro to congestion control CSE 222A Lectre 13: Traffic Engineering 2

3 Mltiple Paths Establish mltiple paths in advance Good se of bandwidth, withstand failres Disseminate link-congestion information Flood thr network, piggyback on data, direct to controller CSE 222A Lectre 13: Traffic Engineering 3

4 Adjst Traffic Splitting Sorce roter adjsts the traffic Changing traffic fraction, e.g. based on congestion Often se hash-based splitting to prevent packet reordering within a flow 35% 65% CSE 222A Lectre 13: Traffic Engineering 4

5 Mlti-Homing Reliability Redced fate sharing Srvive ISP failre Performance Mltiple paths Select the best Financial Provider 1 Provider 2 Leverage throgh competition Game 95 th -percentile billing model Stb: an Atonomos System that does not provide transit CSE 222A Lectre 13: Traffic Engineering 5

6 Otbond Traffic: Pick a BGP Rote Easier to control than inbond traffic IP roting is destination based Sender determines where the packets go Control only by selecting the next hop Border roter can pick the next-hop AS Cannot control selection of the entire path Provider 1 Provider 2 (1, 3, 4) (2, 7, 8, 4) CSE 222A Lectre 13: Traffic Engineering 6

7 Inbond Traffic: Inflencing Others Harder to control than otbond traffic Sender determines where the packets go Control only by inflencing others decisions Static configration of the providers BGP rote attribtes sent by the stb Selective advertising of destination prefixes Provider 1 Provider 2 CSE 222A Lectre 13: Traffic Engineering 7

8 Inbond Traffic: Mltiple Addresses Mltiple external addresses for a service One IP address for each entry point Use DNS to adjst mapping of name to address Give different answers to different clients Adjst over time to performance, cost, traffic, etc. Provider 1 Provider / / CSE 222A Lectre 13: Traffic Engineering 8

9 Online Service Providers CSE 222A Lectre 13: Traffic Engineering 9

10 Rote Injection CSE 222A Lectre 13: Traffic Engineering 10

11 Entact CSE 222A Lectre 13: Traffic Engineering 11

12 Entact Benefits CSE 222A Lectre 13: Traffic Engineering 12

13 Congestion Control Overview Challenge: how do we efficiently share network resorces among billions of hosts? Today: TCP Hosts adjst rate based on packet losses Alternative soltions Fair qeing, RED (roter spport) Vegas, packet pair (add fnctionality to TCP) Rate control, credits CSE 222A Lectre 13: Traffic Engineering 13

14 Qeing Disciplines How to distribte bffers among sers/flows When bffer overflows, which packet to drop? Simple soltion: FIFO First in, first ot If packet comes along with no available bffer space, drop it CSE 222A Lectre 13: Traffic Engineering 14

15 Fair Qeing Goals: Allocate resorces eqally among all sers/flows Low delay for interactive sers Protection against misbehaving sers Approach: simlate general processor sharing (from OS world) Bitwise rond robin Need to compte nmber of competing flows at each instant CSE 222A Lectre 13: Traffic Engineering 15

16 TCP Congestion Problems Original TCP sent fll window of data When links become loaded, qees fill p, leading to: Congestion collapse: when rond-trip time exceeds retransmit interval this can create a stable condition in which every packet is being retransmitted many times Synchronized behavior: network oscillates between loaded and nloaded» Feedback loop CSE 222A Lectre 13: Traffic Engineering 16

17 Jacobson s Soltion Transport protocols shold obey conservation of packets Use ACKs to clock injection of new packets Modify retransmission timer to adapt to variations in delay Infer network bandwidth from packet loss Drops è congestion è redce rate No drops è no congestion è increase rate Limit send rate based on minimm of congestion window and advertised window CSE 222A Lectre 13: Traffic Engineering 17

18 Tracking Bottleneck Bandwidth Throghpt = window size/rtt Mltiplicative decrease Timeot è dropped packet è ct window size in half Additive increase ACK arrives è no drop è increase window size by one packet/window CSE 222A Lectre 13: Traffic Engineering 18

19 TCP Sawtooth Oscillates arond bottleneck bandwidth Adjsts to changes in competing traffic Additive Increase/Mltiplicative Decrease window (in segs) rond-trip times CSE 222A Lectre 13: Traffic Engineering 19

20 Slow Start How do we find bottleneck bandwidth? Cannot se ACKs to clock withot reaching eqilibrim Start by sending a single packet Start slow to avoid overwhelming network Mltiplicative increase ntil get packet loss Qickly find bottleneck Ct rate by half Shift into linear increase/mltiplicative decrease CSE 222A Lectre 13: Traffic Engineering 20

21 Slow Start Qickly find the bottleneck bandwidth 300 Slow Start window (in segs) rond-trip times CSE 222A Lectre 13: Traffic Engineering 21

22 Slow Start Problems Slow start sally overshoots bottleneck Leading to many lost packets in window Can lose p to half of window size Brsty traffic sorce Will case brsty losses for other flows Short flows Can spend entire time in slow start Especially for large bottleneck bandwidth Consider repeated connections to the same server E.g., for web connections CSE 222A Lectre 13: Traffic Engineering 22

23 For Next Class Read XCP paper Project checkpoint de TONIGHT 1-2 page smmary to me CSE 222A Lectre 13: Traffic Engineering 23