Chapter 3 Chapter 3: Transport Layer Transport Layer

1

Transport Layer 3-1

Chapter 3Transport Layer

A note on the use of these ppt slidesThe notes used in this course are substantially based on powerpoint slides developed and copyrighted by JF Kurose and KW Ross 1996-2007

Computer Networking A Top Down Approach 4th edition Jim Kurose Keith RossAddison-Wesley July 2007

Transport Layer 3-2

Chapter 3 Transport LayerOur goals

Understand principles behind transport layer services

MultiplexingdemultiplexingReliable data transferFlow controlCongestion control

Learn about transport layer protocols in the Internet

UDP connectionless transportTCP connection-oriented transportTCP congestion control

Transport Layer 3-3

Chapter 3 Outline

31 Transport-layer services32 Multiplexing and demultiplexing33 Connectionless transport UDP34 Principles of reliable data transfer

35 Connection-oriented transport TCP

Segment structureReliable data transferFlow controlConnection management

36 Principles of congestion control37 TCP congestion control

Transport Layer 3-4

Transport Services and ProtocolsProvide logical communicationbetween app processes running on different hostsTransport protocols run in end systems

Send side breaks app messages into segments passes to network layerRcv side reassembles segments into messages passes to app layer

More than one transport protocol available to apps

Internet TCP and UDP

applicationtransportnetworkdata linkphysical


networkdata linkphysical



networkdata linkphysicalnetwork

data linkphysical

logical end-end transport

2

Transport Layer 3-5

Transport vs Network Layer

Network layerLogical communication between hosts

Transport layerLogical communication between processesRelies on enhances network layer services

Transport Layer 3-6

Internet Transport-Layer Protocols

Reliable in-order delivery (TCP)

Congestion control Flow controlConnection setup

Unreliable unordered delivery UDP

No-frills extension of ldquobest-effortrdquo IP

Services not available Delay guaranteesBandwidth guarantees







data linkphysical


Transport Layer 3-7

Chapter 3 Outline





Transport Layer 3-8

MultiplexingDemultiplexing

host 1

= process= socket

1 host 1 or more processes1 process 1 or more socketsTransport layer interacts with socket

bull Demultiplexing at rcv hostbull Multiplexing at send host

application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1

host 1 host 2 host 3

3

Transport Layer 3-9

How Demultiplexing WorksHost receives IP datagrams

Each datagram has source IP address destination IP addressEach datagram carries 1 transport-layer segmentEach segment has source destination port number (recall well-known port numbers for specific applications)

Host uses IP addresses amp port numbers to direct segment to appropriate socket

source port dest port

32 bits

applicationdata

(message)

other header fields

TCPUDP segment format

Transport Layer 3-10

Connectionless Demultiplexing

Create sockets with port numbers

DatagramSocket mySocket1 = new DatagramSocket(12534)


UDP socket identified by two-tuple

(dest IP address dest port number)

When host receives UDP segment

Checks destination port number in segmentDirects UDP segment to socket with that port number

IP datagrams with different source IP addresses andor source port numbers directed to same socket


Connection-Oriented Demux

TCP socket identified by 4-tuple

Source IP addressSource port numberDest IP addressDest port number

Recv host uses all four values to direct segment to appropriate socket

Server host may support many simultaneous TCP sockets

Each socket identified by its own 4-tuple

Web servers have different sockets for each connecting client

Non-persistent HTTP will have different socket for each request


Chapter 3 Outline





4


UDP User Datagram Protocol [RFC 768]

ldquoNo frillsrdquo ldquobare bonesrdquoInternet transport protocolldquoBest effortrdquo service UDP segments may be

LostDelivered out of order to app

ConnectionlessNo handshaking between UDP sender receiverEach UDP segment handled independently of others

Why is there a UDPNo connection establishment (which can add delay)Simple no connection state at sender receiverSmall segment headerNo congestion control UDP can blast away as fast as desired


UDP moreOften used for streaming multimedia apps

Loss tolerantRate sensitive

Other UDP usesDNSSNMP

Reliable transfer over UDP add reliability at application layer

Application-specific error recovery


32 bits

Applicationdata

(message)

UDP segment format

length checksumLength in

bytes of UDPsegmentincluding

header


UDP Checksum

SenderTreat segment contents as sequence of 16-bit integersChecksum addition (1rsquos complement sum) of segment contentsSender puts checksum value into UDP checksum field

ReceiverCompute checksum of received segmentCheck if computed checksum equals checksum field value

NO - error detectedYES - no error detected But maybe errors nonetheless More later

Goal detect ldquoerrorsrdquo (eg flipped bits) in transmitted segment


Internet Checksum ExampleNote

When adding numbers a carryout from the most significant bit needs to be added to the result

Example add two 16-bit integers

wraparound

sumchecksum

1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

5


Chapter 3 Outline






Principles of Reliable Data TransferImportant in app transport link layersTop-10 list of important networking topics



Characteristics of unreliable channel will determine complexity of reliable data transfer protocol (rdt)




6


Reliable Data Transfer Getting Started

sendside

receiveside

rdt_send() called from above (eg by app) Passed data to

deliver to receiver upper layer

udt_send() called by rdtto transfer packet over

unreliable channel to receiver

rdt_rcv() called when packet arrives on rcv-side of channel

deliver_data() called by rdt to deliver data to upper


Reliable Data Transfer Getting StartedWersquoll

Incrementally develop sender receiver sides of reliable data transfer protocol (rdt)Consider only unidirectional data transfer

But control info will flow on both directionsUse finite state machines (FSM) to specify sender receiver

state1

state2

event causing state transitionactions taken on state transition

state when in this ldquostaterdquo next state

uniquely determined by next event

eventactions


Summary of the Protocols

Rdt10 all packets arrive correctlyRdt20 all packets arrive with possible errors only in data packets and introducing ACK and NAK (no error)Rdt21 corrupted ACKsNAKsRdt22 similar to rdt21 remove NAKsRdt30 Allows packets to be lost and errors


Rdt10 Reliable Transfer over a Reliable Channel

Underlying channel perfectly reliableNo bit errorsNo loss of packets

Separate FSMs for sender receiverSender sends data into underlying channelReceiver read data from underlying channel

packet = make_pkt(data)udt_send(packet)

Wait for call from above

rdt_send(data)

sender

extract (packetdata)deliver_data(data)

Wait for call from

below

rdt_rcv(packet)

receiver

7


Rdt20 Channel with Bit Errors

Underlying channel may flip bits in packetChecksum to detect bit errors

The question how to recover from errorsAcknowledgements (ACKs) receiver explicitly tells sender that pkt received OKNegative acknowledgements (NAKs) receiver explicitly tells sender that pkt had errorsSender retransmits pkt on receipt of NAK

New mechanisms in rdt20 (beyond rdt10)Error detectionReceiver feedback control msgs (ACKNAK) rcvr-gtsender


Rdt20 FSM specification


extract(rcvpktdata)deliver_data(data)udt_send(ACK)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt)

udt_send(sndpkt)

rdt_rcv(rcvpkt) ampampisNAK(rcvpkt)

udt_send(NAK)

rdt_rcv(rcvpkt) ampamp corrupt(rcvpkt)

Wait for ACK or

NAK

Wait for call from

below

sender

receiversnkpkt = make_pkt(data checksum)udt_send(sndpkt)

rdt_send(data)

rdt_rcv(rcvpkt) ampamp isACK(rcvpkt)Λ


Rdt20 Operation with No Errors


snkpkt = make_pkt(data checksum)udt_send(sndpkt)



rdt_rcv(rcvpkt) ampamp isACK(rcvpkt)

udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

sender

receiver


Rdt20 Error Scenario






udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

8


Rdt20 Has a Fatal Flaw

What happens if ACKNAK corruptedSender doesnrsquot know what happened at receiverCanrsquot just retransmit possible duplicate

Handling duplicates Sender retransmits current pkt if ACKNAK garbledSender adds sequence number to each pktReceiver discards (doesnrsquot deliver up) duplicate pkt

Sender sends one packet then waits for receiver response

stop and wait


Sender whenever sender receives control message it sends a packet to receiver

A valid ACK Sends next packet (if exists) with new sequence A NAK or corrupt response resends old packet

Receiver sends ACKNAK to senderIf received packet is corrupt send NAKIf received packet is valid and has different sequence as prev packet send ACK and deliver new data upIf received packet is valid and has same sequence as prev packet ie is a retransmission of duplicate send ACK

Note ACKNAK do not contain sequence


Rdt21 Sender Handles Garbled ACKNAKs

Wait for call 0 from

above

sndpkt = make_pkt(0 data checksum)udt_send(sndpkt)

rdt_send(data)

Wait for ACK or NAK 0 udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||isNAK(rcvpkt) )


rdt_send(data)

udt_send(sndpkt)


Wait forcall 1 from

above

Wait for ACK or NAK 1

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp isACK(rcvpkt)

Λ


Λ


Rdt21 Receiver Handles Garbled ACKNAKs

Wait for 0 from below

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp has_seq1(rcvpkt)

extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(ACK chksum)udt_send(sndpkt)




sndpkt = make_pkt(NAK chksum)udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp (corrupt(rcvpkt)

rdt_rcv(rcvpkt) ampamp not corrupt(rcvpkt) ampamphas_seq0(rcvpkt)

sndpkt = make_pkt(ACK chksum)udt_send(sndpkt)





9


Rdt21 Discussion

SenderSeq added to pktTwo seq rsquos (01) will suffice WhyMust check if received ACKNAK corrupted Twice as many states

State must ldquorememberrdquowhether ldquocurrentrdquo pkt has 0 or 1 seq

ReceiverMust check if received packet is duplicate

State indicates whether 0 or 1 is expected pkt seq

Note receiver can notknow if its last ACKNAK received OK at sender


Rdt22 a NAK-free Protocol

Same functionality as rdt21 using ACKs onlyInstead of NAK receiver sends ACK for last pkt received OK

Receiver must explicitly include seq of pkt being ACKed

Duplicate ACK at sender results in same action as NAK retransmit current pkt


Rdt22 Sender Receiver Fragments


above


rdt_send(data)

udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||

isACK(rcvpkt1) )Wait for ACK

0sender FSM

fragment



extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(ACK1 chksum)udt_send(sndpkt)

rdt_rcv(rcvpkt) ampamp (corrupt(rcvpkt) ||

has_seq1(rcvpkt))

udt_send(sndpkt)receiver FSM

fragment

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp isACK(rcvpkt0)

Λ


Rdt30 Channels with Errors and Loss

New assumptionUnderlying channel can also lose packets (data or ACKs)

Checksum seq ACKs retransmissions will be of help but not enough

Q how to deal with loss

Sender waits until certain data or ACK lost then retransmitsAny drawbacks

Approach sender waits ldquoreasonablerdquo amount of time for ACK Retransmits if no ACK received in this timeIf pkt (or ACK) just delayed (not lost)

Retransmission will be duplicate but use of seq rsquos already handles thisReceiver must specify seq of pkt being ACKed

Requires countdown timer

10


Rdt30 Sendersndpkt = make_pkt(0 data checksum)udt_send(sndpkt)start_timer

rdt_send(data)

Wait for

ACK0


above

sndpkt = make_pkt(1 data checksum)udt_send(sndpkt)start_timer

rdt_send(data)

rdt_rcv(rcvpkt) ampamp notcorrupt(rcvpkt) ampamp isACK(rcvpkt0)stop_timer


udt_send(sndpkt)start_timer

timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)

rdt_rcv(rcvpkt) ampamp ( corrupt(rcvpkt) ||isACK(rcvpkt1) )

Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action


Performance of rdt30

Rdt30 works but performance stinksExample 1 Gbps link 15 ms e-e prop delay 1KB packet

Ttransmit = 8kbpkt109 bsec = 8 microsec

U sender utilization ndash fraction of time sender busy sending

U sender =

008 30008

= 000027 L R RTT + L R

=

L (packet length in bits)R (transmission rate bps) =

1KB pkt every 30 msec -gt 33kBsec thruput over 1 Gbps linkNetwork protocol limits use of physical resources

11


Rdt30 Stop-and-Wait Operation

first packet bit transmitted t = 0

sender receiver

RTT

last packet bit transmitted t = L R

first packet bit arriveslast packet bit arrives send ACK

ACK arrives send next packet t = RTT + L R

U sender =

008 30008

= 000027 L R RTT + L R

=


Pipelined ProtocolsPipelining sender allows multiple ldquoin-flightrdquo

yet-to-be-acknowledged pktsRange of sequence numbers must be increasedBuffering at sender andor receiver


Pipelined Protocols

Advantage much better bandwidth utilization than stop-and-waitDisadvantage More complicated to deal with reliability issues eg corrupted lost out of order data

Two generic approaches to solving thisbull Go-Back-N protocolsbull Selective repeat protocols

Note TCP is not exactly either


Pipelining Increased Utilization

first packet bit transmitted t = 0sender receiver

RTT

last bit transmitted t = L R



last bit of 2nd packet arrives send ACKlast bit of 3rd packet arrives send ACK

U sender =

024 30008

= 00008 3 L R RTT + L R

=

Increase utilizationby a factor of 3

12


Go-Back-NSender

K-bit seq in pkt headerldquoWindowrdquo of up to N consecutive unackrsquoed pkts allowed

ACK(n) ACKs all pkts up to including seq n - ldquocumulative ACKrdquoMay receive duplicate ACKs (see receiver)

Timer for each in-flight pktTimeout(n) retransmit pkt n and all higher seq pkts in windowCalled a sliding-window protocol


GBN Sender

rdt_Send() called checks to see if window is full No send out packetYes return data to application level

Receipt of ACK(n) cumulative acknowledgement that all packets up to and including n have been received Updates window accordingly and restarts timer

Timeout resends ALL packets that have been sent but not yet acknowledged

This is only event that triggers resend


GBN Sender Extended FSM

Wait start_timerudt_send(sndpkt[base])udt_send(sndpkt[base+1])hellipudt_send(sndpkt[nextseqnum-1])

timeout

rdt_send(data)

if (nextseqnum lt base+N) sndpkt[nextseqnum] = make_pkt(nextseqnumdatachksum)udt_send(sndpkt[nextseqnum])if (base == nextseqnum)

start_timernextseqnum++

elserefuse_data(data)

base = getacknum(rcvpkt)+1If (base == nextseqnum)

stop_timerelsestart_timer



base=1nextseqnum=1

Λ


GBN Receiver Extended FSM

If expected packet receivedSend ACK and deliver packet upstairs

If out-of-order packet received Discard (donrsquot buffer) -gt no receiver bufferingRe-ACK pkt with highest in-order seq May generate duplicate ACKs

Wait

udt_send(sndpkt)default

rdt_rcv(rcvpkt)ampamp notcurrupt(rcvpkt)ampamp hasseqnum(rcvpktexpectedseqnum)

extract(rcvpktdata)deliver_data(data)sndpkt = make_pkt(expectedseqnumACKchksum)udt_send(sndpkt)expectedseqnum++

expectedseqnum=1sndpkt = make_pkt(expectedseqnumACKchksum)

Λ

13


More on Receiver

ACK-only the receiver always sends ACK for last correctly received packet with highest in-order seq Receiver only sends ACKS (no NAKs)Need only remember expectedseqnumCan generate duplicate ACKs


GBN InAction


GBN is easy to code but might have performance problems

In particular if many packets are in pipeline at one time (bandwidth-delay product large) then one error can force retransmission of huge amounts of data

Selective Repeat protocol allows receiver to buffer data and only forces retransmission of required packets


Selective Repeat

Receiver individually acknowledges all correctly received pkts

Buffers pkts as needed for eventual in-order delivery to upper layer

Sender only resends pkts for which ACK not received

Sender timer for each unACKed pktCompare to GBN which only had timer for base packet

Sender windowN consecutive seq rsquosAgain limits seq s of sent unACKed pktsImportant Window size lt seq range

14


Selective Repeat Sender Receiver Windows


Selective Repeat

Data from above If next available seq in window send pkt

Timeout(n)Resend pkt n restart timer

ACK(n) in [sendbasesendbase+N]

Mark pkt n as receivedIf n smallest unACKed pkt advance window base to next unACKed seq

senderpkt n in [rcvbase rcvbase+N-1]

Send ACK(n)Out-of-order bufferIn-order deliver (also deliver buffered in-order pkts) advance window to next not-yet-received pkt

pkt n in [rcvbase-Nrcvbase-1]

ACK(n)Otherwise

Ignore

receiver


Selective Repeat In Action


Selective RepeatDilemma

Example seq rsquos 0 1 2 3window size=3

Receiver sees no difference in two scenariosIncorrectly passes duplicate data as new in (a)

Q what relationship between seq size and window size

15


GBN vs Selective Repeat

Selective repeat is more complicated as it needs buffering at the receiver but only retransmit packets required for retransmission

GBN is simpler but can lead to large number of unnecessary retransmission


Chapter 3 Outline






TCP Overview RFCs 793 1122 1323 2018 2581

Full duplex dataBi-directional data flow in same connectionMSS maximum segment size

Connection-orientedHandshaking (exchange of control msgs) initrsquos sender receiver state before data exchange

Flow controlledSender will not overwhelm receiver

Point-to-pointOne sender one receiver

Reliable in-order byte steam

No ldquomessage boundariesrdquoPipelined

TCP congestion and flow control set window size

Send amp receive buffers

socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment

applicationwrites data

applicationreads data


More TCP DetailsMaximum Segment Size (MSS)

Depends upon implementation (can often be set)The Max amount of application-layer data in segment

Application Data + TCP Header = TCP Segment

Three way HandshakeClient sends special TCP segment to server requesting connection No payload (Application data) in this segmentServer responds with second special TCP segment

(again no payload)Client responds with third special segment

This can contain payload

16


More TCP Details (cont)

A TCP connection between client and server creates in both client and server

(i) Buffers(ii) Variables and

(iii) A socket connection to process

TCP only exists in the two end machinesNo buffers and variables allocated to the connection in any of the network elements between the host and server


TCP Segment Structure


32 bits

applicationdata

(variable length)

sequence numberacknowledgement number

Receive windowUrg data pnterchecksum

FSRPAUheadlen

notused

Options (variable length)

URG urgent data (generally not used)

ACK ACK valid

PSH push data now(generally not used)

RST SYN FINconnection estab(setup teardown

commands)

bytes rcvr willingto accept

countingby bytes of data(not segments)

Internetchecksum

(as in UDP)


TCP Seq rsquos and ACKsSeq rsquos

Byte stream ldquonumberrdquo of first byte in segmentrsquos data

ACKsSeq of next byte expected from other sideCumulative ACK TCP only acknowledge bytes up to the first missing byte in the stream

Host A Host B

Bytes [0~535]

Seq=XX1 ACK=536 data = lsquoYYYYrsquo

helliphellip

Bytes [0~535]

[9001000]Seq=XXN ACK=536 data = lsquoZZZZrsquo

Q how receiver handles out-of-order segmentsA TCP spec doesnrsquot say - up to implementer


TCP Seq rsquos and ACKs

Host A Host B

Seq=42 ACK=79 data = lsquoCrsquo


Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt

of echoedlsquoCrsquo

host ACKsreceipt oflsquoCrsquo echoes

back lsquoCrsquo

time

Simple telnet scenario

17


TCP Round Trip Time and Timeout

Q how to set TCP timeout valueLonger than RTT

But RTT variesToo short premature timeout

Unnecessary retransmissions

Too long slow reaction to segment loss

Q how to estimate RTTSampleRTT measured time from segment transmission until ACK receipt

Ignore retransmissions

SampleRTT will vary want estimated RTT ldquosmootherrdquo

Average several recent measurements not just current SampleRTT



EstimatedRTT= (1- α)EstimatedRTT + αSampleRTT

Exponential weighted moving averageInfluence of past sample decreases exponentially fastTypical value α = 0125


Example RTT EstimationRTT gaiacsumassedu to fantasiaeurecomfr

100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)

SampleRTT Estimated RTT



Setting the timeoutEstimtedRTT plus ldquosafety marginrdquo

Large variation in EstimatedRTT -gt larger safety margin

First estimate of how much SampleRTT deviates from EstimatedRTT

TimeoutInterval = EstimatedRTT + 4DevRTT

DevRTT = (1-β)DevRTT +β|SampleRTT-EstimatedRTT|

(typically β = 025)

Then set timeout interval

18


Chapter 3 Outline






TCP Reliable Data Transfer

TCP creates rdtservice on top of IPrsquos unreliable servicePipelined segmentsCumulative acksTCP uses single retransmission timer

Retransmissions are triggered by

Timeout eventsDuplicate acks

Initially consider simplified TCP sender

Ignore duplicate acksIgnore flow control congestion control


TCP Sender EventsData rcvd from app

Create segment with seq Seq is byte-stream number of first data byte in segmentStart timer if not already running (think of timer as for oldest unacked segment)Expiration interval TimeOutInterval

TimeoutRetransmit segment that caused timeoutRestart timer

Ack rcvdIf acknowledges previously unackedsegments

Update what is known to be ackedStart timer if there are outstanding segments


TCP Sender(simplified)

NextSeqNum = InitialSeqNumSendBase = InitialSeqNum

loop (forever) switch(event)

event data received from application above create TCP segment with sequence number NextSeqNumif (timer currently not running)

start timerpass segment to IP NextSeqNum = NextSeqNum + length(data)

event timer timeoutretransmit not-yet-acknowledged segment with

smallest sequence numberstart timer

event ACK received with ACK field value of y if (y gt SendBase)

SendBase = yif (there are currently not-yet-acknowledged segments)

start timer

end of loop forever

Commentbull SendBase-1 last cumulatively ackrsquoed byte

Examplebull SendBase-1 = 71y= 73 so the rcvrwants 73+ y gt SendBase sothat new data is acked

19


TCP Retransmission ScenariosHost A

Seq=100 20 bytes data

ACK=100

time premature timeout

Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100


TCP Retransmission Scenarios (more)Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

Cumulative ACK scenario

Host B

X


ACK=120

time

SendBase= 120


TCP ACK Generation [RFC 1122 RFC 2581]

Event at Receiver

Arrival of in-order segment withexpected seq All data up toexpected seq already ACKed

Arrival of in-order segment withexpected seq One other segment has ACK pending

Arrival of out-of-order segmenthigher-than-expect seq Gap detected

Arrival of segment that partially or completely fills gap

TCP Receiver action

Delayed ACK Wait up to 500msfor next segment If no next segmentsend ACK

Immediately send single cumulative ACK ACKing both in-order segments

Immediately send duplicate ACK indicating seq of next expected byte

Immediate send ACK provided thatsegment startsat lower end of gap


More on Sender Policies

Doubling the Timeout IntervalUsed by most TCP implementationsIf timeout occurs then after retransmisison Timeout Interval is doubledIntervals grow exponentially with each consecutive timeoutWhen Timer restarted because of (i) new data from above or (ii) ACK received then Timeout Interval is reset as described previously using Estimated RTT and DevRTTLimited form of Congestion Control

20


Fast Retransmit

Time-out period often relatively long

Long delay before resending lost packet

Detect lost segments via duplicate ACKs

Sender often sends many segments back-to-backIf segment is lost there will likely be many duplicate ACKs

If sender receives 3 ACKs for the same data it supposes that segment after ACKeddata was lost

Fast retransmit resend segment before timer expires




start timer

else increment count of dup ACKs received for yif (count of dup ACKs received for y = 3)

resend segment with sequence number y

Fast Retransmit Algorithm

a duplicate ACK for already ACKed segment

fast retransmit


TCP GBN or Selective Repeat

Basic TCP looks a lot like GBN

Many TCP implementations will buffer received out-of-order segments and then ACK them all after filling in the range

This looks a lot like Selective Repeat

TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control

Sender should not overwhelm receiverrsquos capacity to receive dataIf necessary sender should slow down transmission rate to accommodate receiverrsquos rateDifferent from Congestion Controlwhose purpose was to handle congestion in networkBut both congestion control and flow control work by slowing down data transmission

low capacity receiver

fast network

flow control problem


TCP Flow Control

Receive side of TCP connection has a receive buffer

Speed-matching service matching the send rate to the receiving apprsquos drain rateApp process may be

slow at reading from buffer

sender wonrsquot overflowreceiverrsquos buffer by

transmitting too muchtoo fast

flow control


TCP Flow Control How it Works

(Suppose TCP receiver discards out-of-order segments)Spare room in buffer

= RcvWindow= RcvBuffer-[LastByteRcvd -

LastByteRead]

Rcvr advertises spare room by including value of RcvWindow in segmentsSender limits unACKeddata to RcvWindow

Guarantees receive buffer doesnrsquot overflow


Technical IssueSuppose RcvWindow=0 and that receiver has already ACKrsquod ALL packets in bufferSender does not transmit new packets until it hears RcvWindowgt0Receiver never sends RcvWindowgt0 since it has no new ACKS to send to SenderDEADLOCK

Solution TCP specs require sender to continue sending packets with one data byte while RcvWindow=0 just to keep receiving ACKS from receiverAt some point the receiverrsquos buffer will empty and RcvWindowgt0 will be transmitted back to sender

22


Note on UDP

UDP has no flow control

UDP appends packets to receiving socketrsquos buffer If buffer is full then packets are lost


Chapter 3 Outline






TCP Connection Management

Recall TCP sender receiver establish ldquoconnectionrdquo before exchanging data segmentsInitialize TCP variables

Seq sBuffers flow control info (eg RcvWindow)

Client connection initiatorSocket clientSocket

= new Socket(hostname port number)

Server contacted by clientSocket connectionSocket = welcomeSocketaccept()


TCP Connection Management (Cont)

Three way handshakeStep 1 client host sends TCP SYN

segment to serverSpecifies client initial seq No application data

Step 2 server host receives SYN replies with SYNACK segment

Server allocates buffersSpecifies server initial seq

Step 3 client receives SYNACK replies with ACK segment which may contain data

client

Connection request (SYN=1 seq=client_isn)

server

Connection granted (SYN=1 server_isn

ACK (SYN=0 seq=client_isn+1)

ack=client_isn+1)

ack=server_isn+1

23


TCP Connection Management (cont)

Closing a connection

client closes socketclientSocketclose()

Step 1 client end system sends TCP FIN control segment to server

Step 2 server receives FIN replies with ACK Closes connection sends FIN

client

FIN

server

ACK

FIN

close

close



Step 3 client receives FIN replies with ACK

Enters ldquotimed waitrdquo -will respond with ACK to received FINs

Step 4 server receives ACK Connection closed

Note with small modification can handle simultaneous FINs

client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed



TCP client lifecycle

TCP server lifecycle


A few Special Cases

Have not discussed what happens if both client and server decide to close down connection at same time

It is possible that first ACK (from server) and second FIN (also from server) are sent in same segment

24


Chapter 3 Outline






Principles of Congestion Control

CongestionInformally ldquotoo many sources sending too much data too fast for network to handlerdquoDifferent from flow controlManifestations

Lost packets (buffer overflow at routers)Long delays (queueing in router buffers)

A top-10 problem

high capacity receiver

congested network

congestion control problem


CausesCosts of Congestion

Examine 3 scenarios in which congestion occursLook at

Why congestion occursThe cost of congestion (resource utilization and performance at the end system)

Not focus onHow to react to or avoid congestion


CausesCosts of Congestion Scenario 1

Two senders two receiversOne router infinite buffers No retransmission

Large delays when congestedMaximum achievable throughput

unlimited shared output link buffers

Host Aλin original data

Host B

λout

Throughput and delay as a function of host sending rate

25



One router finite buffers Sender retransmission of lost packet

finite shared output link buffers

Host A λin original data

Host B

λout

λin original data plus retransmitted data

Offered Load



Always λin = λout (goodput)Case (a) magic transmission

Only send when therersquos space in buffer and no packet lossCase (b) ldquoperfectrdquo retransmission only when loss λrsquoin gt λout

Case (c) retransmission of delayed (not lost) packet makes λout

larger (than perfect case) for same λrsquoin



Brief summary of the ldquocostsrdquo of congestion so farLarge queuing delays as the packet-arrival rate nears the link capacitySender perform retransmissions to compensate the lost packets due to buffer overflowUnneeded retransmissions in the face of large delays

Link carries multiple copies of pkt


CausesCosts of Congestion Scenario 3 Four sendersMultihop pathsTimeoutretransmit

λin

Q what happens as and increase λ

in



Host B

λout


Host C

Host D

26



Another ldquocostrdquo of congestionWhen packet dropped any ldquoupstream transmission capacityrdquo used for that packet was wasted

Host A

Host B

λou

t


Approaches towards Congestion Control

End-end congestion controlNo explicit feedback from networkCongestion inferred from end-system observed loss delayApproach taken by TCP

Network-assisted congestion controlRouters provide feedback to end systems

Single bit indicating congestion (SNA DECbit TCPIP ECN ATM)Explicit rate sender should send at

Two broad approaches towards congestion control


Two Ways for Providing Feedback


Case study ATM ABR Congestion Control

ABR available bit rateldquoElastic servicerdquoIf senderrsquos path ldquounderloadedrdquo

Sender should use available bandwidth

If senderrsquos path congested

Sender throttled to minimum guaranteed rate

RM (resource management) cellsSent by sender interspersed with data cellsBits in RM cell set by switches (ldquonetwork-assistedrdquo)

NI bit no increase in rate (mild congestion)CI bit congestion indication

RM cells returned to sender by receiver with bits intact

27



Two-byte ER (explicit rate) field in RM cellCongested switch may lower ER value in cellSenderrsquo send rate thus maximum supportable rate on path

EFCI bit in data cells set to 1 in congested switchIf data cell preceding RM cell has EFCI set sender sets CI bit in returned RM cell


Chapter 3 Outline






TCP Congestion ControlEnd-to-end control (no network assistance)Transmission rate limited by congestion window size Congwin over segments

Congwin dynamically modified to reflect perceived congestion

w segments each with MSS bytes sent in one RTT

throughput = w MSSRTT Bytessec

Congwin


To simplify presentation we assume that RcvBuffer is large enough that it will not overflow Tools are ldquosimilarrdquo to flow controlsender limits transmission usingLastByteSent-LastByteAcked le CongWin

How does sender perceive congestionloss event = timeout or 3 duplicate ACKsTCP sender reduces rate (CongWin) after loss event

CongWin incrementACK arrives at slow rate -gt CongWin be increased at a slow rateACK arrives at high rate -gt CongWin be increased at a high rate

Self-ClockingTCP uses ACK to trigger (clock) its increase in congwin

28


Three mechanismsAIMD = Additive Increase Multiplicative DecreaseSlow start = CongWin set to 1 and then grows exponentially

Conservative after timeout events

TCP Congestion Control Algorithms


TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow

Multiplicative decreasecut CongWin in half after loss event

Additive increase increase CongWin by 1 MSS every RTT in the absence of loss events probing also known as congestion avoidance

Long-lived TCP connection


TCP Slow Start

When connection begins CongWin = 1 MSS

Example MSS = 500 bytes amp RTT = 200 msecInitial rate = 20 kbps

Available bandwidth may be gtgt MSSRTT

Desirable to quickly ramp up to respectable rate

When connection begins increase rate exponentially fast until first loss event

Slow Start is NOT really Slow


TCP Slow Start (more)

When connection begins increase rate exponentially until first loss event

Double CongWin every RTTDone by incrementing CongWin for every ACK received

Summary initial rate is slow but ramps up exponentially fast

one segment

RTT

two segments

Host A Host B

time

four segments

29


So FarSlow-Start ramps up exponentiallyFollowed by AIMD sawtooth patternQ When should the exponential increase switch to linear

Reality (TCP Reno)Introduce new variable threshold initially very largeSlow-Start exponential growth stops when reaches threshold and then switches to AIMDTwo different types of loss events

bull 3 dup ACKS cut CongWin in half and set threshold=CongWin (now in standard AIMD)

bull Timeout set threshold=CongWin2 CongWin=1 and switch to Slow-Start


Reason for treating 3 dup ACKS differently than timeout is that

3 dup ACKs indicates network capable of delivering some segments while Timeout before 3 dup ACKs is ldquomore alarmingrdquo

Note that older protocol TCP Tahoe treated both types of loss events the same and always goes to slow-start with Congwin=1 after a loss event

TCP Renorsquos skipping of the slow start for a 3-DUP-ACK loss event is known as fast-recovery


Summary TCP Congestion Control

When CongWin is below Threshold sender in slow-start phase window grows exponentially

When CongWin is above Threshold sender is in congestion-avoidance phase window grows linearly

When a triple duplicate ACK occurs Thresholdset to CongWin2 and CongWin set to Threshold(only in TCP Reno)

When timeout occurs Threshold set to CongWin2 and CongWin is set to 1 MSS (TCP Tahoe does this for 3 Dup Acks as well)


The Big Picture

30


TCP Sender Congestion Control

Duplicate ACK

Timeout

Loss event detected by triple duplicate ACK

ACK receipt for previously unacked data


Event

SS or CA

SS or CA

SS or CA

CongestionAvoidance (CA)

Slow Start (SS)

State

CongWin and Threshold not changed

Increment duplicate ACK count for segment being acked

Enter slow startThreshold = CongWin2 CongWin = 1 MSSSet state to ldquoSlow Startrdquo

Fast recovery implementing multiplicative decrease CongWin will not drop below 1 MSS

Threshold = CongWin2 CongWin = ThresholdSet state to ldquoCongestion Avoidancerdquo

Additive increase resulting in increase of CongWin by 1 MSS every RTT

CongWin = CongWin+MSS (MSSCongWin)

Resulting in a doubling of CongWin every RTT

CongWin = CongWin + MSS If (CongWin gt Threshold)

set state to ldquoCongestion Avoidancerdquo

CommentaryTCP Sender Action


TCP Throughput

Whatrsquos the average throughout of TCP as a function of window size and RTT

Ignore slow startLet W be the window size when loss occursWhen window is W throughput is WRTTJust after loss window drops to W2 throughput to W2RTTAverage throughout 75 WRTT


TCP Futures TCP over ldquoLong Fat Pipesrdquo

Example 1500 byte segments 100ms RTT want 10 Gbps throughputRequires window size W = 83333 in-flight segmentsThroughput in terms of loss rate

L = 210-10 Wow

New versions of TCP for high-speed needed

LRTTMSSsdot221


Fairness goal if K TCP sessions share same bottleneck link of bandwidth R each should have average rate of RK

TCP Fairness

TCP connection 1

bottleneckrouter

capacity RTCP connection 2

31


Why is TCP fairTwo competing sessions

Additive increase gives slope of 1 as throughout increasesmultiplicative decrease decreases throughput proportionally

R

R

equal bandwidth share

Connection 1 throughput

Conn

ecti

on 2

thr

ough

put

congestion avoidance additive increaseloss decrease window by factor of 2



Fairness (more)Fairness and UDP

Multimedia apps often do not use TCP

Do not want rate throttled by congestion control

Instead use UDPpump audiovideo at constant rate tolerate packet loss

Research area TCP friendly

Fairness and parallel TCP connectionsNothing prevents app from opening parallel connections between 2 hostsWeb browsers do this Example link of rate R supporting 9 cnctions

New app asks for 1 TCP gets rate R10New app asks for 11 TCPs gets R2


Chapter 3 SummaryPrinciples behind transport layer services

Multiplexing demultiplexingReliable data transferFlow controlCongestion control

Instantiation and implementation in the Internet

UDPTCP

NextLeaving the network ldquoedgerdquo (application transport layers)Into the network ldquocorerdquo

2

Transport Layer 3-5

Transport vs Network Layer

Network layerLogical communication between hosts

Transport layerLogical communication between processesRelies on enhances network layer services

Transport Layer 3-6

Internet Transport-Layer Protocols

Reliable in-order delivery (TCP)

Congestion control Flow controlConnection setup

Unreliable unordered delivery UDP

No-frills extension of ldquobest-effortrdquo IP

Services not available Delay guaranteesBandwidth guarantees







data linkphysical


Transport Layer 3-7

Chapter 3 Outline





Transport Layer 3-8

MultiplexingDemultiplexing

host 1

= process= socket

1 host 1 or more processes1 process 1 or more socketsTransport layer interacts with socket

bull Demultiplexing at rcv hostbull Multiplexing at send host

application

transport

network

link

physical

P1 application

transport

network

link

physical

application

transport

network

link

physical

P2P3 P4P1

host 1 host 2 host 3

3

Transport Layer 3-9





32 bits

applicationdata

(message)

other header fields






















Chapter 3 Outline





4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP Checksum









wraparound

sumchecksum

1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

5


Chapter 3 Outline













6



sendside

receiveside











state1

state2




eventactions










rdt_send(data)

sender


Wait for call from

below

rdt_rcv(packet)

receiver

7











udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

sender


rdt_send(data)









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

sender

receiver








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

8






stop and wait









above


rdt_send(data)




rdt_send(data)

udt_send(sndpkt)


Wait forcall 1 from

above



Λ


Λ

















9


Rdt21 Discussion














above


rdt_send(data)

udt_send(sndpkt)



0sender FSM

fragment





has_seq1(rcvpkt))


fragment


Λ










10



rdt_send(data)

Wait for

ACK0


above


rdt_send(data)




timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)


Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action






U sender =

008 30008

= 000027 L R RTT + L R

=



11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


3

Transport Layer 3-9





32 bits

applicationdata

(message)

other header fields






















Chapter 3 Outline





4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP Checksum









wraparound

sumchecksum

1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

5


Chapter 3 Outline













6



sendside

receiveside











state1

state2




eventactions










rdt_send(data)

sender


Wait for call from

below

rdt_rcv(packet)

receiver

7











udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

sender


rdt_send(data)









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

sender

receiver








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

8






stop and wait









above


rdt_send(data)




rdt_send(data)

udt_send(sndpkt)


Wait forcall 1 from

above



Λ


Λ

















9


Rdt21 Discussion














above


rdt_send(data)

udt_send(sndpkt)



0sender FSM

fragment





has_seq1(rcvpkt))


fragment


Λ










10



rdt_send(data)

Wait for

ACK0


above


rdt_send(data)




timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)


Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action






U sender =

008 30008

= 000027 L R RTT + L R

=



11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


4














32 bits

Applicationdata

(message)

UDP segment format



header


UDP Checksum









wraparound

sumchecksum

1 1 1 1 0 0 1 1 0 0 1 1 0 0 1 1 01 1 1 0 1 0 1 0 1 0 1 0 1 0 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 1 0 01 0 1 0 0 0 1 0 0 0 1 0 0 0 0 1 1

5


Chapter 3 Outline













6



sendside

receiveside











state1

state2




eventactions










rdt_send(data)

sender


Wait for call from

below

rdt_rcv(packet)

receiver

7











udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

sender


rdt_send(data)









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

sender

receiver








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

8






stop and wait









above


rdt_send(data)




rdt_send(data)

udt_send(sndpkt)


Wait forcall 1 from

above



Λ


Λ

















9


Rdt21 Discussion














above


rdt_send(data)

udt_send(sndpkt)



0sender FSM

fragment





has_seq1(rcvpkt))


fragment


Λ










10



rdt_send(data)

Wait for

ACK0


above


rdt_send(data)




timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)


Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action






U sender =

008 30008

= 000027 L R RTT + L R

=



11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


5


Chapter 3 Outline













6



sendside

receiveside











state1

state2




eventactions










rdt_send(data)

sender


Wait for call from

below

rdt_rcv(packet)

receiver

7











udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

sender


rdt_send(data)









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

sender

receiver








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

8






stop and wait









above


rdt_send(data)




rdt_send(data)

udt_send(sndpkt)


Wait forcall 1 from

above



Λ


Λ

















9


Rdt21 Discussion














above


rdt_send(data)

udt_send(sndpkt)



0sender FSM

fragment





has_seq1(rcvpkt))


fragment


Λ










10



rdt_send(data)

Wait for

ACK0


above


rdt_send(data)




timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)


Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action






U sender =

008 30008

= 000027 L R RTT + L R

=



11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


6



sendside

receiveside











state1

state2




eventactions










rdt_send(data)

sender


Wait for call from

below

rdt_rcv(packet)

receiver

7











udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

sender


rdt_send(data)









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

sender

receiver








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

8






stop and wait









above


rdt_send(data)




rdt_send(data)

udt_send(sndpkt)


Wait forcall 1 from

above



Λ


Λ

















9


Rdt21 Discussion














above


rdt_send(data)

udt_send(sndpkt)



0sender FSM

fragment





has_seq1(rcvpkt))


fragment


Λ










10



rdt_send(data)

Wait for

ACK0


above


rdt_send(data)




timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)


Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action






U sender =

008 30008

= 000027 L R RTT + L R

=



11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


7











udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

sender


rdt_send(data)









udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

sender

receiver








udt_send(sndpkt)


udt_send(NAK)


Wait for ACK or

NAK

Wait for call from

below

rdt_send(data)

Λ

8






stop and wait









above


rdt_send(data)




rdt_send(data)

udt_send(sndpkt)


Wait forcall 1 from

above



Λ


Λ

















9


Rdt21 Discussion














above


rdt_send(data)

udt_send(sndpkt)



0sender FSM

fragment





has_seq1(rcvpkt))


fragment


Λ










10



rdt_send(data)

Wait for

ACK0


above


rdt_send(data)




timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)


Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action






U sender =

008 30008

= 000027 L R RTT + L R

=



11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


8






stop and wait









above


rdt_send(data)




rdt_send(data)

udt_send(sndpkt)


Wait forcall 1 from

above



Λ


Λ

















9


Rdt21 Discussion














above


rdt_send(data)

udt_send(sndpkt)



0sender FSM

fragment





has_seq1(rcvpkt))


fragment


Λ










10



rdt_send(data)

Wait for

ACK0


above


rdt_send(data)




timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)


Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action






U sender =

008 30008

= 000027 L R RTT + L R

=



11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


9


Rdt21 Discussion














above


rdt_send(data)

udt_send(sndpkt)



0sender FSM

fragment





has_seq1(rcvpkt))


fragment


Λ










10



rdt_send(data)

Wait for

ACK0


above


rdt_send(data)




timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)


Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action






U sender =

008 30008

= 000027 L R RTT + L R

=



11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


10



rdt_send(data)

Wait for

ACK0


above


rdt_send(data)




timeout


timeout


above

Wait for

ACK1

Λrdt_rcv(rcvpkt)


Λrdt_rcv(rcvpkt)Λ


Λ


Rdt30 In Action


Rdt30 In Action






U sender =

008 30008

= 000027 L R RTT + L R

=



11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


11




sender receiver

RTT




U sender =

008 30008

= 000027 L R RTT + L R

=





Pipelined Protocols







RTT





U sender =

024 30008

= 00008 3 L R RTT + L R

=


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


12


Go-Back-NSender





GBN Sender








timeout

rdt_send(data)








base=1nextseqnum=1

Λ





Wait





Λ

13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


13


More on Receiver



GBN InAction






Selective Repeat






14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


14




Selective Repeat








ACK(n)Otherwise

Ignore

receiver








15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


15






Chapter 3 Outline















socketdoor

TCPsend buffer

TCPreceive buffer

socketdoor

segment










16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


16










32 bits

applicationdata

(variable length)



FSRPAUheadlen

notused



ACK ACK valid



commands)



Internetchecksum

(as in UDP)





Host A Host B

Bytes [0~535]


helliphellip

Bytes [0~535]





Host A Host B



Seq=43 ACK=80

Usertypes

lsquoCrsquo

host ACKsreceipt



back lsquoCrsquo

time


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


17

















100

150

200

250

300

350

1 8 15 22 29 36 43 50 57 64 71 78 85 92 99 106time (seconnds)

RTT

(mill

iseco

nds)











18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


18


Chapter 3 Outline




























start timer

end of loop forever



19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


19




ACK=100


Host B

Seq=92 8 bytes data

ACK=120

Seq=92 8 bytes data

Seq=

92 t

imeo

ut

ACK=120

Host A

Seq=92 8 bytes data

ACK=100

loss

tim

eout

lost ACK scenario

Host B

X

Seq=92 8 bytes data

ACK=100

time

Seq=

92 t

imeo

ut

SendBase= 100

SendBase= 120

SendBase= 120

Sendbase= 100



Seq=92 8 bytes data

ACK=100

loss

tim

eout


Host B

X


ACK=120

time

SendBase= 120



Event at Receiver





TCP Receiver action








20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


20


Fast Retransmit










start timer





fast retransmit






TCP is a hybrid


Chapter 3 Outline





21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


21


TCP Flow Control



fast network



TCP Flow Control






flow control





LastByteRead]






22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


22


Note on UDP




Chapter 3 Outline



















client


server



ack=client_isn+1)

ack=server_isn+1

23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


23







client

FIN

server

ACK

FIN

close

close







client

FIN

server

ACK

ACK

FIN

close

closing

closed

tim

ed w

ait

closed






A few Special Cases



24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


24


Chapter 3 Outline









A top-10 problem


congested network













Host B

λout


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


25






Host B

λout


Offered Load













λin


in



Host B

λout


Host C

Host D

26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


26




Host A

Host B

λou

t


















27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


27






Chapter 3 Outline










Congwin






28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


28






TCP AIMD

8 Kbytes

16 Kbytes

24 Kbytes

time

congestionwindow





TCP Slow Start












one segment

RTT

two segments

Host A Host B

time

four segments

29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


29


















The Big Picture

30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


30



Duplicate ACK

Timeout




Event

SS or CA

SS or CA

SS or CA


Slow Start (SS)

State













TCP Throughput






L = 210-10 Wow


LRTTMSSsdot221



TCP Fairness

TCP connection 1

bottleneckrouter


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


31




R

R



Conn

ecti

on 2

thr

ough

put















UDPTCP


Chapter 3 Chapter 3: Transport Layer Transport Layer

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