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Batchprocessingsystems

Centralizedsystembasedonmainframe

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MultiterminalSystems

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MainEvents

1969:ARPANET

Early

1980s:

TCP/IP 1980:Ethernet

1985:TokenRing,FDDI

1994:Yahoo

1998:Google

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Sharingresources

Data

Computation

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Sharingresources

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Socket

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Whatisasocket?

Aninterfacebetweenapplicationandnetwork eapp ca oncrea esasoc e

Thesockettypedictatesthestyleof reliablevs.besteffort

connectionorientedvs.connectionless

Onceconfiguredtheapplicationcanpassdatatothesocketfornetworktransmission

receivedatafromthesocket(transmittedthroughthenetworkbysomeotherhost)

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Twoessentialtypesofsockets

SOCK_STREAM

a.k.a.TCP SOCK_DGRAM

a.k.a.UDP re a e e very

inorderguaranteed

connectionoriented

unreliabledelivery

noorderguarantees

nonotionofconnection app bidirectional indicatesdest.foreachpacket

cansendorreceive

3 2 1

App D1

Dest.

socket3 2 1 D2

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D3

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SocketCreationinC:socket()

int s = socket(domain, type, protocol); ,

domain:integer,communicationdomain e.g.,PF_INET (IPv4protocol) typicallyused

type:communicationtype SOCK_STREAM:reliable,2way,connectionbasedservice

SOCK_DGRAM:unreliable,connectionless,

othervalues:needrootpermission,rarelyused,orobsolete

protocol:specifiesprotocol(seefile/etc/protocols fora

NOTE:socket calldoesnotspecifywheredatawillbecomingfrom,norwhereitwillbegoingto itjustcreatestheinterface!

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Ports

Eachhosthas65,536orts

Port1 Someportsarereserved ors eci ic

Port65535apps

20,21:FTP23:Telnet

80:HTTP

Asocketprovidesaninterfacetosenddatato/fromthenetworkthroughaport

2000portsarereserved)

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Addresses,PortsandSockets

Likeapartmentsandmailboxes

Yourapartmentbuildingaddressistheaddress

Thepostofficeisthenetwork

Thesocketisthekeythatgivesyouaccesstotherightmailbox(onedifference:assumeoutgoingmailisplacedbyyouinyourmailbox)

Q:Howdoyouchoosewhichportasocketconnectsto?

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Thebind() function

associatesand(canexclusively)reservesaportfor

int status = bind(sockid, &addrport, size);

,

sockid:integer,socketdescriptor

addr ort: struct sockaddr the IP address and ort ofthemachine(addressusuallysettoINADDR_ANYchoosesalocaladdress)

s ze:t es ze n ytes o t ea rpor structure

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ConnectionSetup(SOCK_STREAM)

Recall:noconnectionsetupforSOCK_DGRAM

connec onoccurs e ween wo n so participants

connection

active:initiatesconnectionrequesttopassiveside

Onceconnectionisestablished,passiveandactive

participantsaresimilar

bothcansend&receivedata

eithercanterminatetheconnection

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Connectionsetupcontd

Passiveparticipant Active artici ant step1:listen (forincoming

requests)

step3:accept (arequest) step2:request&establish

step4:datatransfer

Theacceptedconnectionisonanewsocket

step4:datatransfer

Theoldsocketcontinuestolistenforotheractive

PassiveParticipant

lsockasock1 asock2

Why?

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Active1soc e

Active2soc e

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Connectionsetup: listen &accept

Calledbypassiveparticipant

int status = listen(sock, queuelen); status:0iflistening, 1iferror

sock:integer,socketdescriptor queuelen:integer,#ofactiveparticipantsthatcanwaitfora

listen isnonblocking:returnsimmediately

int s = accept(sock, &name, &namelen); s:inte er thenewsocket usedfordatatransfer sock:integer,theorig.socket(beinglistenedon) name:struct sockaddr,addressoftheactiveparticipant namelen:sizeof(name): value/resultparameter

must

e

set

appropriate y

e ore

ca adjustedbyOSuponreturn

accept isblocking:waitsforconnectionbeforereturning

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connect call

int status = connect(sock, &name,name en ;

status:0ifsuccessfulconnect, 1otherwise

sock:integer,sockettobeusedinconnection

name:struct sockaddr:addressofpassiveparticipant

namelen:integer,sizeof(name)

connect isblocking

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Sending/ReceivingData

Witha connection(SOCK_STREAM): , , ,

count:#bytestransmitted(1iferror) buf:char[], buffertobetransmitted len:integer,lengthofbuffer(inbytes)totransmit flags:integer,specialoptions,usuallyjust0

= count:#bytesreceived(1iferror) buf:void[], storesreceivedbytes

:

y es

rece ve flags:integer,specialoptions,usuallyjust0

Callsareblockin [returnsonl afterdataissent

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(tosocketbuf)/received]

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Sending/ReceivingData(contd)

Withouta connection(SOCK_DGRAM):

int count = sendto(sock, &buf, len, flags, &addr,addrlen);

count, soc , u , en, ags:sameassen

addr:struct sockaddr,addressofthedestination

int count = recvfrom(sock, &buf, len, flags,,

count, sock, buf, len, flags: sameasrecv

name:struct sockaddr,addressofthesource

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namelen:sizeof(name): value/resultparameter

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close

Whenfinishedusingasocket,thesocket

s ou ec ose :

status = close(s);

status:0ifsuccessful, 1iferror

s:thefiledescriptor(socketbeingclosed) Closingasocket

closes a connection for K TREAM _

freesuptheportusedbythesocket

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Socketcommunication

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Thestruct sockaddr

Thegeneric: TheInternets ecific:

u_short sa_family;char sa_data[14];

struct sockaddr_in {short sin_family;u_short sin_port;

sa_family

struct in_addr sin_addr;char sin_zero[8];

}; specifieswhichaddress

familyisbeingused

determineshowthe

sin_family = AF_INET

sin_port:port#(065535)

sin addr:IPaddress

remaining14bytesareused

_

sin_zero:unused

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Addressandportbyteordering

Addressandportarestoredasintegers

_ _

in_addrsin_addr;(32bit)

_u_long s_addr;

};

Problem:

differentmachines/OSsusedifferentwordorderings

littleendian:lowerbytesfirst

bigendian:higherbytesfirst

thesemachinesmaycommunicatewithoneanotheroverthenetwork

12.40.119.128

BigEndianmachine LittleEndian

machine

23

. . .

128 119 40 12 128 119 40 12

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Solution:NetworkByteOrdering

Defs: os y e r er ng: e y eor er nguse y

ahost(bigorlittle)

bythenetwork alwaysbigendian

AnywordssentthroughthenetworkshouldbeconvertedtoNetworkByteOrderpriortotransmission(andbacktoHostByteOrderoncereceived)

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UNIXsbyteorderingfuncs

u lon htonl u lon x u lon ntohl u lon x_ _

u_short htons(u_short x);

_ _

u_short ntohs(u_short x);

Onbigendianmachines,theseroutinesdonothing

Onlittleendianmachines,theyreversethebyteorder

128.119.40.12128.119.40.12

BigEndian

machine LittleEndian

machine128 119 40 121281194012

128 119 40 12 128 119 40 12

n

tohl

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Dealingwithblockingcalls

Manyofthefunctionswesawblockuntilacertainevent

connect:

until

the

connection

is

established recv, recvfrom:untilapacket(ofdata)isreceived

sen , sen o :unt ata spus e ntosoc et s u er

Forsimpleprograms,blockingisconvenient

multipleconnections

simultaneoussendsandreceives

s mu taneous y

o ng

non

networ ng

process ng

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Dealingw/blocking(contd)

Options:

turn

off

the

blocking

feature

(e.g.,

using

the

fcntl file

descriptor

controlfunction)

.

Whatdoesselect do?

canbepermanentblocking,timelimitedblockingornonblocking input:asetoffiledescriptors

output:infoonthefiledescriptorsstatus

socketwillreturnimmediately

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select functioncall

int status = select(nfds, &readfds, &writefds,excep s, meou ;

status:#ofreadyobjects, 1iferror

readfds:listofdescriptorstocheckifreadready

exceptfds:listofdescriptorstocheckifanexceptionisregistered

timeout:timeafterwhichselectreturns,evenifnothingready canbe0or(pointtimeout parametertoNULL for)

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Tobeusedwithselect:

Recallselect usesastructure,struct fd_set

ifbitiissetin[readfds, writefds, exceptfds],selectwillcheckiffiledescriptor(i.e.socket)iisrea y or rea ng,wr t ng,except on

Beforecallingselect: _ : FD_SET(i, &fdvar):tocheckfiledesc.i

int FD_ISSET(i, &fdvar):booleanreturnsTRUE

iffiisready

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Otherusefulfunctions

bzero(char* c, int n): 0snbytesstartingatc

ethostname char *name int len : ets the name of thecurrenthost

gethostbyaddr(char *addr, int len, int type): convertsIP

inet_addr(const char *cp): convertsdotteddecimalchar

stringtolonginteger inet_ntoa(const struct in_addr in): convertslongtodotted

decimalnotation

Warning:checkfunctionassumptionsaboutbyteordering(hostornetwork). Often,theyassumeparameters/return

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