CS162 Operating Systems and Systems Programming Lecture 22 Networking IIIReviewTransport ProtocolAutomatic Repeat reQuest (ARQ)Stop-and-Wait PropertiesHow Fast Can Stop-and-Wait Go?AdministriviaSliding WindowThroughputSliding Window Example (This is NOT TCP !)Sliding Window ExampleSlide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Performance with Sliding WindowSliding Window PropertiesCongestionCongestion CollapseTwo Basic Components (TCP)TCP Congestion ControlSizing the WindowsRate AdjustmentAddresses and NamesIP Addresses (IPv4)Hierarchical Addressing: IP PrefixesIP Address and a 24-bit Subnet MaskHierarchical Addressing ExampleIP addresses vs. Host NameSeparating Naming and AddressingScalable (Name Address) MappingsDomain Name System (DNS)Distributed Hierarchical DatabaseUsing DNSExampleRecursive vs. Iterative QueriesSlide 41ConclusionPutting Everything TogetherSlide 44Slide 45CS162Operating Systems andSystems ProgrammingLecture 22Networking IIIApril 22, 2010Ion Stoicahttp://inst.eecs.berkeley.edu/~cs162Lec 22.24/13/10 CS162 ©UCB Spring 2010Review•Link (datalink) layer: Broadcast network; frames sent by one host reaches every other host in same network–Multi-access protocol–(didn’t go over) construct frames, error detection and correction, flow control, … •Network layer: stitch together multiple link layer networks–Deliver a packet to specified network destination–(didn’t go over) segmentation/reassemble, packet scheduling, buffer management•Transport layer–Multiplexing/demultiplexing (two lectures ago)–Flow & congestion control, in-order delivery, reliability (today)Lec 22.34/13/10 CS162 ©UCB Spring 2010Transport Protocol•Flow control keeps one fast sender from overwhelming a slow receiver•Congestion control keeps a set of senders from overloading the network•Reliability makes sure the receiver got all packets sent by sender•In-order delivery makes sure the receiver delivers the packet to application in same order sender sent them•Two protocols:–Stop-and-Wait–Window basedLec 22.44/13/10 CS162 ©UCB Spring 2010Automatic Repeat reQuest (ARQ)TimePacketACKTimeoutAutomatic Repeat RequestReceiver sends acknowledgment (ACK) when it receives packetSender waits for ACK and times out if does not arrive within some time periodSimplest ARQ protocolStop and WaitSend a packet, stop and wait until ACK arrives Sender ReceiverLec 22.54/13/10 CS162 ©UCB Spring 2010Stop-and-Wait Properties•Flow control: yes–Receiver can implicitly slow down sender by acking a packet only if it has room for at lest another packet –Assumption: timeout doesn’t trigger before receiving ack•Congestion control: yes–Sender sends a new packet only after previous one made it–If network is congested packet or ack is lost sender doesn’t send new data•Reliability: yes–If a packet is lost, sender timeouts and resends the packet•In-order delivery: yes–Receiver doesn’t get next packet before receiving (and acking) previous one•So what’s the problem with Stop-and-Wait? Efficiency!Lec 22.64/13/10 CS162 ©UCB Spring 2010How Fast Can Stop-and-Wait Go?•Suppose we’re sending from UCB to New York:–Bandwidth = 1 Mbps (megabits/sec)–RTT = 100 msec–Maximum packet size a.k.a. Maximum Transmission Unit (MTU) = 1500 B = 12,000 b–No other load on the path and no packet loss•What (approximately) is the fastest we can transmit using Stop-and-Wait?–Answer: 12,000b/0.1s = 120 kbps•How about if Bandwidth = 1 Gbps?Lec 22.74/13/10 CS162 ©UCB Spring 2010Administrivia•Keys to access AWS will be sent today•Last two lectures on security•Final Exam–Friday, May 14, 7:00PM-10:00PM–All material from the course»With slightly more focus on second half, but you are still responsible for all the material–Two sheets of notes, both sidesLec 22.84/13/10 CS162 ©UCB Spring 2010Sliding Window•Idea: allow multiple packets in-flight–“In-flight” = un-acked packets•Window size (W): number of packets the sender can send without receiving an ack–E.g., after receiving ack for all packet before and including K, send packets K+1, K+2, …, K+W+1–Stop-and-wait: particular case of sliding window, W=1 •Receiver tells sender W–W cannot be larger than receiver’s buffer!Lec 22.94/13/10 CS162 ©UCB Spring 2010Throughput•Up to W packets (or bytes) per RTT•Throughput = W/RTT•How large should be the window to fully utilize a link with bandwidth B?–W = Bandwidth x RTT (i.e., “Bandwidth-Delay” or “Delay-Bandwidth” product)Lec 22.104/13/10 CS162 ©UCB Spring 2010Sliding Window Example (This is NOT TCP !)Lec 22.114/13/10 CS162 ©UCB Spring 2010Sliding Window ExampleSender Receiver111s2s3s4s5s6s7s8s9s10s11s12s13s14s•Sender, at 1s–Send 1st pktLec 22.124/13/10 CS162 ©UCB Spring 2010Sliding Window ExampleSender Receiver1111s2s3s4s5s6s7s8s9s10s11s12s13s14s•Sender, at 1s–Send 1st pkt•Receiver, at 3s–Get 1st pkt–Deliver 1st pkt to appl.–Send ack=1 to senderack=1Lec 22.134/13/10 CS162 ©UCB Spring 2010Sliding Window Example•Sender, at 2s–Send 2nd pkt, which is lostSender Receiver11ack=11s2s3s4s5s6s7s8s9s10s11s12s13s14s2 12Lec 22.144/13/10 CS162 ©UCB Spring 2010Sliding Window Example1s2s3s4s5s6s7s8s9s10s11s12s13s14sSender Receiver12 13 2 13123ack=1nack=2•Sender, at 3s–Send 3nd pkt•Receiver, at 5s:–Get 3rd pkt; doesn’t deliver it since out of seq.–Send nack=2 (request 2nd pkt)Lec 22.154/13/10 CS162 ©UCB Spring 2010Sliding Window Example1s2s3s4s5s6s7s8s9s10s11s12s13s14sSender Receiver12 13 2 13123ack=1nack=2•Sender, at 4s–Send 4th pkt–Receiver window full!•Receiver, at 6s–Get 4th packet4 3 2 144 3Lec 22.164/13/10 CS162 ©UCB Spring 2010Sliding Window Example1s2s3s4s5s6s7s8s9s10s11s12s13s14sSender Receiver12 13 2 13123ack=1nack=2•Sender, at 5s–Get ack=1–Remove 1st pkt from buffer–Send 5th pkt; now 2, 3, 4, 5 are in flight (window full!)•Receiver, at 7s–Get 5th pkt4 3 2 144 35 4 3 254 35Lec 22.174/13/10 CS162 ©UCB Spring 2010Sliding Window Example1s2s3s4s5s6s7s8s9s10s11s12s13s14sSender Receiver12 13 2 13123ack=1nack=2•Sender, at 7s–Get nack=2–Resend pkt 2•Receiver, at 9s–Get 2nd pkt–Deliver it to appl.–Send ack=24 3 2 144 35 4 3 254 35ack=25 4 3 224 35 2Lec 22.184/13/10 CS162 ©UCB Spring 2010Sliding Window Example1s2s3s4s5s6s7s8s9s10s11s12s13s14sSender Receiver12 13 2 13123ack=1nack=2•Sender, at 11s–Get ack=2–Send pkt 6; pkts 3, 4, 5, 6 are
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