Cis81 E1 4 TransportLayer Rick

8/14/2019 Cis81 E1 4 TransportLayer Rick

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Chapter 4

Transport Layer

CIS 81 Networking Fundamentals

Rick ra!ianiCa"rillo College

gra!iani#ca"rillo$edu

Last %pdated& '('()**+


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Note

This presentation is not in the order o, the "ook or online curriculum$ This presentation also contains in,ormation "eyond the curriculum$


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Transport Layer -.er.iew


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4

Transport Layer

Transport Layer&

Responsi"le ,or creating and maintaining a logical connection

"etween the endpoints

/hat are the two protocols at the transport layer0 TCP Transmission Control 2rotocol

UDP %ser 3atagram 2rotocol

TCP UDP


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Application

Header + data

TCP Header UDP Header

or

23%& Segment

23%& Data

What is the application

PDU called?

What is the transport

PDU called?


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UDP

TCP

TCP/UDP TCP/UDP

The Layer 4 data stream is a& Logical connection "etween the endpoints

2ro.ides transport ser.ices

End-to-end service


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DataHTTPHeader

TCP

Header

P

Header

Data !in"

Header

Data !in"

Trailer

P Pac"etData !in"

Header

Data !in"

TrailerP Pac"etData !in"

Header

Data !in"

Trailer

P Pac"etData !in"Header

Data !in"

TrailerP Pac"etData !in"Header

Data !in"

Trailer

P Pac"etData !in"

Header

Data !in"

TrailerP Pac"etData !in"

Header

Data !in"

Trailer

DataHTTP

Header

TCP

Header

P

Header

Data !in"

Header

Data !in"

Trailer

Reminder o, encapsulation(decapsulation


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Focus on Transport Layer

TCP

TCP


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2rimary responsi"ilities&

Tracking the indi.idual communication "etween applications

/ho is the client0 /hich application0 /hich process0

Identi,ying the di,,erent applications 7TT29 FT29 etc$:

Segmenting data

;anaging each segment

Reassem"ling the segments

Transport Layer

www$cisco$com

TCP Segment

TCP Segment

TCP Segment

TCP Segment


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/hat two protocols are at the Transport Layer0 TCP

UDP

Pis a "est


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11

TC2 .s$ %32

TC2 pro.ides&

Relia"le deli.ery

Brror checking

Flow control

Congestion control

-rdered deli.ery

Connection esta"lishment

pplications&

TT2

FT2

Telnet

;SN messenger

%32 pro.ides&

%nrelia"le deli.ery

No error checking

No ,low control

No congestion control

No ordered deli.ery

No connectionesta"lishment

pplications

3NS 7usually:

S;T2

3C2

RT2 7Real


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1)

single clientmay ha.e multiple transport connections with multipleser.ers$

Notice that TCP is a connection-orientedser.ice 7two


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2ort Num"ers& TC2 and %32


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14

3oth TCP and UDPuse ports 7or sockets: num"ers to pass in,ormation to the

upper layers$

0 15 16 31

16-bit Source Port Number 16-bit Destination Port Number

32-bit Sequence Number

32 bit Acknowledgement Number

-bit !eader

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tions $i4 an'

Data $i4 an'

TCP Header

HTTP is Port 45

UDP Header


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The application this TCP

segment came (rom


segment is going to


segment came (rom


segment is going to
http://www.apache.org/http://www.apache.org/


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Application

Header + dataPort n%m)ers are %sed )#

the receiver so it "no$s

$hich application it sho%ld

send the &Data' to

Application

Header + dataPort n%m)ers are %sed to

)# the sender to tell the

receiver $hich net$or"

application it sho%ld %se

(or the &Data'

Port 6%m)er

Port 6%m)er


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http&((www$iana$org(assignments(port


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Well 7no$n Ports 6%m)ers 5 to 859:

Reser.ed ,or common ser.ices and

applications

Client& TC2 destination port

Server& TC2 source port

Well 7no$n or ;egistered

Port 6%m)er


Port 6%m)er


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Well 7no$n or ;egisteredPort 6%m)er


Port 6%m)er

;egistered Ports 6%m)ers 859< to 8

ssigned to user processes orapplications$

Non


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D#namic or Private Ports 6%m)ers 9 to >>:>

lso known as Bphemeral 2orts

%sually assigned dynamically to client applications when initiating a

connection$

Client& TC2 source port

Server& TC2 destination port

;ay also include the range o, Registered 2orts 7Num"ers 1*)4 to

4+11:


Port 6%m)er

Private/D#namic Port

6%m)er


Port 6%m)er

Private/D#namic Port

6%m)er


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)1

Client Server

Telnet


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))

Client sends TC2 segment with&

3estination 2ort& )'7/ell known port num"er:

Source 2ort& 1*)873ynamic 2ort assigned "y client:

Client TCP Header0 15 16 31




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9:8594

Data (or Telnet

Client Server


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Ser.er responds with TC2 segment with&

3estination 2ort& 1*)873ynamic 2ort assigned "y client:

Source 2ort& )'7/ell known port num"er:

Server TCP Header0 15 16 31




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85949:

Data (or Telnet

Client Server


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Notice the di,,erence in how source and destination port num"ers areused with clients and ser.ers&

Client initiating Telnet service@

3estination 2ort E )' 7telnet: Source 2ort E 1*)8 7dynamically assigned:

Server responding to Telnet service@

3estination 2ort E 1*)8 7source port o, client:

Source 2ort E )' 7telnet:


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Same client to same ser.er < Two di,,erent TT2 sessions

Client& Same destination port

Client& 3i,,erent source ports to uniuely identi,y this we" session$


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C:\Users\rigrazia>netstat -n

Active Connections

Proto Local Address Foreign Address State

TCP 192.16.1.1!1:"9 19.1##.219.2$:! T%&'()A%T

TCP 192.16.1.1!1:"99! 19.1##.219.2$:! T%&'()A%T

C:\Users\rigrazia>

TCP

or

UDP

So%rce Port

Destination P

Destination Port Connection State

So%rce P


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What makes each connection unique? How does the server knowwhich source port 49888 is who?

Connection de,ined "y the pair o, num"ers& So%rce P address9 So%rce port 7From Client to Ser.er: Destination P address9 Destination port7From Ser.er to

Client: 3i,,erent connections can use the same destination port on ser.er

host as long as the source ports or source I2s are di,,erent$

8=9848858

898>>

Destination

Port

45

45

45

So%rce

Port


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6ote@ /hen downloading a we" document and its o"Gects it is common that

there will "e se.eral TC2 sessions created$

netstat Bn$$$ciscocom$$$googlecom

TCP

or

UDP So%rce Port

Destination P

Destination Port

Connection StateSo%rce P


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%sing NetStat

-pen a we" "rowser$

-pen a command prompt window 7Start


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Connectionless Transport& %32


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UDP

/hat do you notice looking at the %32 protocol0

No ,rills9 "are"ones transport protocol$

3estination and Source 2orts

Length and Checksum 7used ,or error checking:

RFC 658

Connectionless transport

No >handshaking? 7no connection esta"lishment: as with TC2 7coming:

%nrelia"le deli.ery

No error checking

No ,low control

No congestion control

No ordered deli.ery

0 15 16 31


16-bit (DP "engt# 16-bit (DP *#ecksum

Data $i4 an'?


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%32

so%rce port


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''

%32

Why would an application developer choose UDP rather than TP? 0iner application-la#er control

TC2 will continue to resend segments that are not acknowledged$

pplications that use %32 can tolerate some data loss&

Streaming .ideo

DoI2 7Doice o.er I2:

pplication decides whether or not to resend entire ,ile& TFT2

0 15 16 31



Data $i4 an'


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%32

6o connection esta)lishment

TC2 uses a three


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'

%32

6o connection state

%32 does not maintain connection state as does TC2 7coming:

%sed ,or relia"ility and ,low control$

Ser.er can support more acti.e clients when not maintaining state

in,ormation

Small pac"et header overhead

TC2 header has )* "ytes o, o.erhead$

%32 header has only 8 "ytes o, o.erhead

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Data $i4 an'

Time

%32segment

%32segment

%32segment

%32segment

Client Server


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Note on %32

6ote@ 1%ltimedia Applications and UDP

There is an issue 7contro.ersy: with multimedia applications o.er%32$

%32 o,,ers no congestion control 7as we will see with TC2:

Congestion control is needed to pre.ent the network ,rom entering andstaying in a congested state$

I, all applications were using %329 "ecause o, congestion9 .ery ,ew%32 packets would "e deli.ered and this would also cause TC2 tra,,icrates to dramatically decrease$

;any applications gi.e you a choice o, TC2 or %32$


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-nline aming

ame data Ser.er and client need make sure all data 7mo.es9

actions9 etc: reach the other end relia"ly$

Doice chat Some missing data can "e tolerated 7up to a point:$

Retransmission would cause delay$

uestion& 3o the /orld

o, /arcra,t ser.ers

use TC2 or %320

nswer& TC2 ,or game

data9 %32 ,or .oicechat$

/hy0


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%32 Checksum 7FJI:

%32 checksum pro.ides error detection9 any changed "its or missing segments$ Simpli,ied e@planation 7see RFC 1*61 ,or more details:& Sender

%32 adds 15 "it KwordsA keeping a c%m%lative s%m

2er,orms ones complemento, the sum o, all the 15


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%32 Checksum 7FJI:

/hat i, there is an error0 %32 does nothing to reco.er the error$ It is up to the application layer protocol 7e@ample TFT2: to decide what to do9

such as prompt the user to download(upload the entire ,ile again$

0 15 16 31



Data $i4 an'

Time

%32segment

%32segment

%32segment

%32segment

Client Server

Cumulative Sum: 1100101011001010

1s complement: 0011000100110101

Total: 1111101111111111

FinalChecksum


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Connection


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4)

TCP

TC2 pro.ides relia"le deli.ery on top o, unrelia"le I2

TC2 pro.ides&

Relia"le deli.ery

Brror checking

Flow control

Congestion control

-rdered deli.ery

Connection esta"lishment

0 15 16 31




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bi b bi i i b


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TC2

so%rce port


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TCP@ Connection Esta)lishment

0or a connection to )e esta)lished9 the two end stations must synchroni!e

on each others TC2 initial se.%ence n%m)ers S6s

Se.%ence n%m)ers&

Track the order o, packets Bnsure that no packets are lost in transmission$

The initial se.%ence n%m)eris the starting num"er used when a TC2

connection is esta"lished$

B@changing "eginning seuence num"ers during the connection seuence

ensures that lost data can "e reco.ered$

0 15 16 31




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Three


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45

Three


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46

Three


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48 Step 8@ Client sends S6* SEFG4>: last (o%r digits


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4+ Step 9@ Server responds $ith AC7G4>


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Step :@ Client sends AC7G8=


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Client no$ sends HTTP ;e.%est ET to We) Server


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TC2& Connection Termination

1$ /hen the client has no more data to send in the stream9 it sends a segment

with the 06 (lag set$

)$ The ser.er sends an AC7to acknowledge the receipt o, the FIN to terminate

the session ,rom client to ser.er$'$ The ser.er sends a 06to the client9 to terminate the ser.er to client session$

4$ The client responds with an AC7to acknowledge the FIN ,rom the ser.er$

0 15 16 31




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'

2acket Tracer B@ercise& TC2 Connection and

Termination

3ownload the ,ile& 2T


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4

0lo$ Control and ;elia)ilit#

;elia)ilit#

uaranteed deli.ery

0lo$ Control Flow control makes sure these "u,,ers do not recei.e more data than

the connection can handle$

0 15 16 31




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0lo$ Control and ;elia)ilit#

This $indo$ siIespeci,ies the num"er o, "ytes9 starting with the

acknowledgment num"er9 that the recei.ing hosts TC2 layer is currently

prepared to recei.e$

Included in e.ery TC2 segment starting with three


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;eceive Windo$ Sending host can send only that amount o, data "e,ore getting an acknowledgment and

window update ,rom this 7the recei.ing: host$

Send Windo$ not a TCP (ield

The TC2 Recei.e /indow si!e o, the other host$

Client Eample

Recei.e /indow Si!eE9*** "ytes Ser.er can only send 9*** "ytes "e,ore it recei.esan acknowledgement$

Send /indow Si!e E 1*9*** "ytes Ser.er told the client that it can send the ser.er1*9*** "ytes "e,ore recei.ing an acknowledgment$

ClientWindo$SiIeG>*555

ServerWin

do$

SiIeG85*55

5Ser.erAs Send

/indow& 1*9***

;y Recei.e

/indow& 1*9***;y Recei.e

/indow& 9***

ClientAs Send

/indow& 9***I can send 10,000

bytes without hearing

an AC, and I can

only receive !,000

bytes at a time."

I can send !,000

bytes without hearing

an AC, and I can

only receive 10,000

bytes at a time."


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Flow Control and Relia"ility

Application Data 855*555 )#tes

8-8555 8558-9555 9558-:555 :558-


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Se.%ence 6%m)er and Ac"no$ledgements Remote host sends TC2 segments with a Se.%ence 6%m)er$

Note& This is the ,irst "yte in the segment$



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;SS , 1 *** " t


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This is known as a

Stop-and-Waitwindowing protocol$

Ser.er must wait ,or

acknowledgment

"e,ore continuing to

send data$

"etter method0

Sliding Windo$s

3JN;IC

Send /indow =yte&

This is the last "yte

that can "e sent

"e,ore recei.ing anCM

Client

SBE19**1 7to )9***:

We)

Server

SBE)9**1 7to '9***:

SBE'9**1 7to 49***:

SBE49**1 7to 9***:

CME9**1

SBE1 7to 19***:

SBE59**1 7to 69***:

SBE69**1 7to 89***:

SBE89**1 7to +9***:

SBE+9**1 7to 1*9***:

CME1*9**1

SBE9**1 7to 59***:

J/



ServerWindo

$

SiIeG85*555

ServerWindo$

SiIeG85*555

J

J

Send /indow&=yte 1*9***

Send /indow&

=yte 19***

ServerWindo

$

SiIeG85*555

J

SBE1*9**1 7to 119***:

Send

Windo$G>*555

Clienthas a

/indow Si!e o,

9*** "ytes


;SS o, 19*** "ytes

S d


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TCP Windo$ SiIe TC2 pro.ides (%ll-

d%ple service9which means data

can "e ,lowing ineach direction9independent o, theother direction$

Recei.er sendsaccepta"lewindow si!e to

sender duringeach segmenttransmission 7,lowcontrol:

I, too much data"eing sent9accepta"le

window si!e isreduced I, more data can

"e handled9accepta"lewindow si!e isincreased

Client

SBE19**1 )9***

We)

Server

SBE)9**1

'9***SBE'9**1

49***SBE49**1

9***

CME9**1

SBE1 19***1

SBE59**1

69***SBE69**1

89***SBE89**1

+9***SBE+9**1 1*9***

CME1*9**1

SBE9**1

59***

J/



ServerWindo

$

SiIeG85*555

ServerWindo$

SiIeG85*555

J

J

Send /indow&=yte 1*9***

Send /indow&

=yte 19***

ServerWindo

$

SiIeG85*555

J

SBE1*9**1 119***

Send

Windo$G>*555


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Sliding Windo$ Protocol

Sliding window algorithms are a method o, ,low control ,or network data trans,ers usingthe recei.ers /indow si!e$

The sender computes its usa"le window9 which is how much data it can immediatelysend$

-.er time9 this sliding window mo.es to the rights9 as the recei.er acknowledges data$

The recei.er sends acknowledgements as its TC2 recei.e "u,,er empties$

The terms used to descri"e the mo.ement o, the le,t and right edges o, this slidingwindow are&

1$ The le,t edge closes 7mo.es to the right: when data is sent and acknowledged$

)$ The right edge opens 7mo.es to the right: allowing more data to "e sent$ This happenswhen the recei.er acknowledges a certain num"er o, "ytes recei.ed$

'$ The middle edge open 7mo.es to the right: as data is sent9 "ut not yet acknowledged$

Kctets sent6ot AC7ed

Usa)le Windo$Can send ASAP

Wor"ing Windo$ siIe

Usa)le Windo$Can send ASAP

nitial Windo$ siIe

Sliding /indows 73ynamic or Scaling:

0 15 16 31




TCP Header


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5)

8 9 : < > 4 = 85 88 89 8:

9

:

ost = gi.es ost a window si!e o, 5 7octets:$ ost "egins "y sending octets to ost =& octets 19 )9 and ' and slides itAs

window o.er showing it has sent those ' octets$

ost will not increase its usa"le window si!e "y '9 until it recei.es an

CMnowldegement ,rom ost = that it has recei.ed some or all o, the octets$

ost =9 not waiting ,or all o, the 5 octets to arri.e9 a,ter recei.ing the third octet

sends an e@pectational CMnowledgement o, >4? to ost $

AC7 4 = 85 88 89 8: 8 9 : < > 4 = 85 88 89 8:

8 9 : < > 4 = 85 88 89 8:

8

Host A - Sender Host 3 - ;eceiver

g

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Host 3 - ;eceiverHost A - Sender


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5'

8 9 : < > 4 = 85 88 89 8:

8 9 : < > 4 = 85 88 89 8:

9

:

AC7

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Cis81 E1 4 TransportLayer Rick