Wilamowski B.M., Irwin J.D. The Industrial Electronics Handbook. Second Edition: Industrial Communication Systems

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IV-1

Internet

Programming

60 User Datagram Protocol—UDP. Aleksander Malinowski

andBogdanM.Wilamowski

......................................................................................60-1

Introduction. •. Protocol.Operation. •. Programming.Samples. •. References

61 Transmission Control Protocol—TCP. Aleksander Malinowski

andBogdanM.Wilamowski

...........................................................................................61-1

Introduction. •. Protocol.Operation. •. State.Diagram. •. Programming.

Sam

ples

. •. Ref

erences

62 Development of Interactive Web Pages. Pradeep Dandamudi ..................................62-1

Introduction. •. Installations. •. Introduction.to.PHP. •. MySQL. •. Creating.Dynamic.

WebS

ites

.Us

ing

.PH

.and.My

SQL

. •. Ref

erences

63 Interactive Web Site Design Using Python Script. Hao Yu and Michael Carroll .....63-1

Introduction. •. Soware.Installation. •. Database-Driven.Web.Site.

Des

ign

. •. Con

clusion

. •. Ref

erences

64 Running Soware over Internet. Nam Pham, Bogdan M. Wilamowski,

andAleksander Malinowski

............................................................................................64-1

Introduction. •. Most.Commonly.Used.Network.Programming.

Too

. •. Exa

mples

. •. Sum

mary

.and.Co

nclusion

. •. Ref

erences

65 Semantic Web Services for Manufacturing Industry. Chen Wu

andaramS.Dillon

................................................................................................. 65-1

Background. •. Aims. •. Approach. •. Conclusion. •. References

66 Automatic Data Mining on Internet by Using PERL

ScriptingLanguage

. NamP

ham andBogdanM. Wilamowski

...................................66-1

Introduction. •. Examples. •. Summary.and.Conclusion. •. References

60-1

60.1 Introduction

User.datagram.protocol.(UDP).is.a.part.of.TCP/IP.suite.[STD6,C02-1,F10,GW03,PD07]..It.provides.

full.tran

sport

.laye

.serv

ices

.to.appl

ications.

.It.belo

ngs

.to.the.tran

sport

.laye

.in.the.TCP/

.suit

.mode

as.show

.in.Figu

.60.1

.UDP.prov

ides

.a.conn

ection

.betw

een

.two.proc

esses

.at.both.ends.of.tran

smis-

sion.

. is.conn

ection

.is.prov

ided

.with.mini

mal

.over

head,

.with

out

.ow.cont

rol

.or.ackn

owledgment

.of.

rece

ived

.data

. e.mini

mal

.erro

.cont

rol

.is.prov

ided

.by.igno

ring

.(dro

pping)

.rece

ived

.pack

ets

.that.fail.

the.che

cksum

.tes

.UDP.is.stan

dardized

.by.Inte

rnet Society,

.whic

.is.an.inde

pendent

.inte

rnational

.not-

for-prot

orga

nization.

.A.comp

lete

.info

rmation

.abou

.UDP-

.stan

dards

.is.publ

ished

.by.RFC Ed

itor

.[RFC

Seve

ral

.rel

evant

.RFC.art

icles

.as.wel

.as.fur

ther

.rea

ding

.mat

erials

.are.lis

ted

.at.the.end.of.thi

.art

icle.

60.2 Protocol Operation

Underlying.IP.provides.data.transport.through.the.network.between.two.hosts..UDP.allows.addressing.

part

icular

.proc

esses

.at.each.host.so.that.inco

ming

.data.is.hand

led

.by.a.part

icular

.appl

ication.

.Whil

unde

rlying

.IP.prov

ides

.logi

cal

.addr

essing

.and.is.resp

onsible

.for.data.tran

smission

.thro

ugh

.netw

orks

[STD

5],

.UDP.prov

ides

.addi

tional

.addr

essing

.that.allo

.sett

ing

.up.conn

ections

.for.mult

iple

.appl

ica-

tions

.and.serv

ices

.on.the.same.end..Addr

essing

.the.proc

esses

.is.impl

emented

.by.assig

ning

.a.numbe

to.each.conn

ection

.to.the.netw

ork,

.whic

.is.call

.a.port.numbe

.Figu

.60.2.illu

strates

.the.conc

ept

.of.

port.numbe

.and.show

.the.die

rence

.betw

een

.IP.and.UDP.addr

essing.

.UDP.pack

ets

.are.also.call

data

grams.

.Each.data

gram

.is.char

acterized

.by.four.para

meters—the

.IP.addr

ess

.and.the.port.numbe

at.each.end.of.the.conn

ection

.[STD

6].

.Cert

ain

.clas

.of.dest

ination

.IP.addr

esses

.may.not.desc

ribe

.indi

vidual

.comp

uters

.but.a.grou

.of.proc

esses

.on.mult

iple

.host

.that.are.to.rece

ive

.the.same.data

gram

[STD

2,RFC3171].

.Comp

uters

.that.need.to.rece

ive

.mult

icast

.mess

ages

.must.“join

”

.the.mult

icast

.grou

asso

ciated

.wit

.a.par

ticular

.mul

ticast

.IP.add

ress.

Although

.the.term.conn

ection

.is.used.here

.unli

.in.case.of.tran

smission

.cont

rol

.proto

col

.(TCP

there.is.no.persistent.connection.between.the.two.processes.. e.data.exchange.may.follow.certain.

User Datagram

Protocol—UDP

60.1. Introduction.....................................................................................60-1

60.2

. Proto

col

.Ope

ration..........................................................................60-1

UDP.Datagram. •. Port.Number.Assignments. •. Connectionless.

Service—Flow.and.Error.Control

60.3. Programming.Samples...................................................................60-8

References...................................................................................................60-10

Aleksander

Malinowski

Bradley University

Bogdan M.

Wilamowski

Auburn University

60-2 Industrial Communication Systems

pattern.or.protocol.but.there.is.no.guarantee.that.all.data.reach.the.destination.and.that.the.order.of.

their.receiving.would.be.the.same.as.the.order.they.were.sent.. e.client–server.approach,.which.is.

usually.used.to.describe.interaction.between.two.processes,.still.can.be.used.. e.process.that.may.be.

identied.as.waiting.for.the.data.exchange.is.called.the.server.. e.process.that.may.be.identied.as.one.

that.initializes.that.exchange.is.called.the.client.

60.2.1 UDP Datagram

Datagram.have.a.constant.size.8.byte.header.prepended.to.the.transmitted.data,.as.shown.in.Figure.60.3.

[STD6].. e.meaning.of.each.header.eld.is.described.below:

•

. Source port address:. is.is.a.16.bit.eld.that.contains.a.port.number.of.the.process.that.sends.

options.or.data.in.this.segment.

•

. Destination port address:. is.is.a.16.bit.eld.that.contains.a.port.number.of.the.process.that.is.

supposed

.to.receive.options.or.data.carried.by.this.segment.

Application layer

Transport layer

Network layer

SMTP FTP DNS SNMP BOOTP

UDPTCP

ARP RARP

Underlying LAN or WAN technology

ICMPIGMP

Data link layer

Physical layer

FIGURE 60.1 UDP.and.TCP/IP.in.the.TCP/IP.suite.model.

Processes

(running application program)

Processes

(running application program)

Internet

Domain of IP protocol

Domain of UDP protocol

FIGURE 60.2 Comparison.of.IP.and.UDP.addressing.

User Datagram Protocol—UDP 60-3

•. Total length:. is.is.a.16.bit.eld.that.contains.the.total.length.of.the.packet..Although.the.num-

ber

.could.be.in.the.range.from.0.to.65,535,.the.minimum.length.is.8.bytes.that.correspond.to.the.

packet.with.the.header.and.no.data.. e.maximum.length.is.65,507.because.20.bytes.are.used.by.

the.IP.header.and.8.bytes.by.the.UDP.header.. us,.this.information.is.redundant.to.the.packet.

length.stored.in.the.IP.header..An.extension.to.UDP.that.allows.for.transmission.of.larger.data-

grams

.over.IPv6.packets.has.been.standardized.[RFC2675,RFC2147]..In.such.a.case,.the.UDP.

header.specied.total.length.is.ignored.

•

. Checksum:. is.16.bit.eld.contains.the.checksum.. e.checksum.is.calculated.by

•

. Initially.lling.it.with.0s.

•

. Adding.a.pseudoheader.with.information.from.IP,.as.illustrated.in.Figure.60.4.

•

. Treating. the. whole. segment. with. the. pseudoheader. prepended. as. a. stream. of. 16. bit.

numbers..If.the.number.of.bytes.is.odd,.0.is.appended.at.the.end.

•

. Adding.all.16.bit.numbers.using.1s.complement.binary.arithmetic.

•

. Complementing.the.result.. is.complemented.result.is.inserted.into.the.checksum.eld.

•

. Checksum verication:. e.receiver.calculates.the.new.checksum.for.the.received.packet.that.

includes.the.original.checksum,.aer.adding.the.so-called.pseudoheader.(see.Figure.60.4)..If.the.

new.checksum.is.nonzero,.then.the.datagram.is.corrupt.and.is.discarded.

8 bytes

Header

Data

Source port number

16 bits

Total length

16 bits

Checksum

16 bits

Destination port number

16 bits

FIGURE 60.3 User.datagram.format.

32 bit source IP address

32 bit destination IP address

16 bit UDP total length

Destination port address

16 bits

Source port address

16 bits

All 0s

8 bit

protocol

UDP total length

16 bits

Checksum

16 bits

Data

(padding must be added to make the data

a multiple of 16 bits)

Header Pseudoheader

FIGURE 60.4 Pseudoheader.added.to.the.UDP.datagram.

60-4 Industrial Communication Systems

In.case.of.UDP,.the.use.of.checksum.is.optional..If.it.is.not.calculated.then.the.eld.is.lled.with.0s..

 e.rece

iver

.can.dete

rmine

.whet

her

.chec

ksum

.was.calc

ulated

.by.insp

ecting

.the.eld

.Even.in.case.the.

chec

ksum

.is.0.the.eld.does.not.cont

ain

.0.as.the.calc

ulated

.chec

ksum

.is.comp

lemented

.at.the.end.of.the.

proc

ess

.and.neg

ative

.0.(th

.el

.ll

.wit

.1s).is.stor

ed.

60.2.2 Port Number assignments

In.order.to.provide.platform.for.an.independent.process.addressing.on.a.host,.each.connection.of.the.

proc

ess

.to.the.netw

ork

.is.assig

ned

.a.16.bit.numbe

. ere.are.thre

.cate

gories

.of.port.numbe

rs:

.well

known

.(0-1

,023),

.regi

stered

.(1,0

24-49,151),

.and.ephe

meral

.(49,

152-6,553).

.Well

-known ports

.have.been.

histo

rically

.assig

ned

.to.comm

.serv

ices.

.Tabl

.60.1.show

.well

-known

.port

.comm

only

.used.by.UDP..

Some.oper

ating

.syst

ems

.requ

ire

.that.the.proc

ess

.that.util

izes

.thes

.port

.must.have.admi

nistrative

.priv

ileges.

. is.requ

irement

.was.histo

rically

.crea

ted

.to.avoi

.hack

ers

.runn

ing

.serv

.impo

sters

.on.mult

iuser

syst

ems.

.Well

-known

.port

.are. regi

stered

.and. cont

rolled

.by.Inte

rnet

.Assig

ned

.Numbe

. Auth

ority

(IAN

.[IAN

.[STD

2].

.Regi

stered ports

.are.also.regi

stered

.by.IANA.to.avoi

.possi

ble

.con

icts

.amon

die

rent

.appl

ications

.atte

mpting

.to.use.the.same.port.for.list

ening

.to.inco

ming

.conn

ections.

.Ephe

meral

port

.are.also.call

.dyna

mic

.port

. ese.port

.are.used.by.outg

oing

.conn

ections

.that.are.typi

cally

assig

ned

.to.the.rst.avai

lable

.port.abov

.49,1

51.

.Some.oper

ating

.syst

ems

.may.not.foll

.IANA.rec-

mmendations

.and.trea

.the.regi

stered

.port

.rang

.as.ephe

meral.

.For.exam

ple,

.BSD.uses.port

.1,02

thro

ugh

.4,99

.as.ephe

meral

.port

.many.Linu

.kern

els

.use.32,76

8–61,000,

.Windo

.use.1,02

5–5,000,

whil

.Fre

eBSD

.fol

lows

.IAN

.por

.ran

ge.

60.2.3 Connectionless Service—Flow and Error Control

As.it.was.already.outlined,.UDP.provides.connectionless.communication..Each.datagram.is.not.related.

to.anot

her

.data

grams

.comi

.earl

ier

.or.late

.from.the.same.sour

ce.

. e.data

grams

.are.not.numbe

red.

 ere.is.no.need.for.esta

blishing

.or.tear

ing

.down.the.conn

ection.

.In.the.extr

eme

.case

.just.one.data

gram

migh

.be.sen

.in.the.pro

cess

.of.dat

.exc

hange

.bet

ween

.the.two.pro

cesses.

UDP

.does.not.prov

ide

.any.ow.cont

rol.

. e.rece

iving

.side.may.be.over

owed

.with.inco

ming

.data

Unli

.in.TCP,.whic

.has.a.wind

owing

.mech

anism,

.ther

.is.no.way.to.cont

rol

.the.send

er.

. ere.is.no.

TABLE 60.1 Common.Well-Known.Ports.Used.with.UDP

Port Protocol Description RFC/STD.#

7 Echo Echoes

.a.recei

ved

.dat

agram

.back.to.its.sender S

TD20

9 Discard Discards

.any.dat

agram

.tha

.is.recei

ved STD21

13 Daytime Returns

.the.dat

.and.the.time.in.ASCII.str

ing

.for

mat STD25

19 Chargen Returns

.a.str

ing

.of.cha

racters

.of.rando

.length.0.to.512.cha

racters STD22

37 Time Returns

.the.curr

ent

.time.in.seco

nds

.since.1/1/1900.in.a.32.bit.for

mat STD26

53 Nameserver Domain

.Nam

.Serv

ice STD13

67 DHCP Dynamic

.Host.Congura

tion

.Pro

tocol

.Serv

er RFC2131

68 DHCP Dynamic

.Host.Congura

tion

.Pro

tocol

.Client RFC2131

TFTP Trivial

.File.Tran

sfer STD33

111 RPC SUN

.Remo

.Pro

cedure

.Cal

l RFC5531

123 NTP Network

.Time.Protocol STD12

161 SNMP Simple

.Netw

ork

.Man

agement

.Pro

tocol STD62

162 SNMP Simple

.Netw

ork

.Man

agement

.Pro

tocol

.(trap) S

TD62

213 IPX Internetwork

.Pack

.Exc

hange

.Netw

ork

.Lay

.Pro

tocol

.over.IP RFC1234

520 RIP

Routing

.Info

rmation

.Pro

tocol SDT56

546 DHCPv6 DHCPv6

.client RFC3315

547

DHCPv6 DHCPv6

.serv

er RFC3315

User Datagram Protocol—UDP 60-5

FIGURE 60.5 Sample.C.program.that.illustrates.a.UDP.server.

60-6 Industrial Communication Systems

FIGURE 60.6 Sample.C.program.that.illustrates.a.UDP.client.

User Datagram Protocol—UDP 60-7

FIGURE 60.7 Sample.C.program.that.illustrates.a.UDP.server.utilizing.multicasting.

(continued)

60-8 Industrial Communication Systems

other.error.control.than.the.checksum.discussed.above.. e.sender.cannot.be.requested.to.resend.any.

data

gram.

.Howe

ver,

.an.uppe

.leve

.proto

col

.that.util

izes

.UDP.may.impl

ement

.some.kind.of.cont

rol.

.In.

that.case

.unli

.in.TCP,.no.data.is.repe

ated

.by.rese

nding

.the.same.data

gram.

.Inst

ead,

.the.comm

unicat-

ing

.proc

ess

.send

.a.requ

est

.to.send.some.info

rmation

.agai

.Triv

ial

.le.tran

sfer

.proto

col

.(TFT

.is.a.

very.good.exam

ple

.of.that.situa

tion

.[STD

33].

.Sinc

.it.has.its.own.high

.leve

.ow.and.erro

.cont

rol,

.it.

can.use.UDP.as.a.tran

sport

.laye

.proto

col

.inst

ead

.of.TCP..Othe

.exam

ples

.of.UDP.util

ization

.are.simpl

netw

ork

.mana

gement

.proto

col

.(SNM

.[STD

62]

.or.any.othe

.proto

col

.that.requ

ires

.only.simpl

.shor

requ

est-response

.com

munication.

60.3 Programming Samples

Figures.60.5.and.60.6.contain.two.C.programs.that.demonstrate.use.of.UDP.for.communication.using.

clie

nt–server

.para

digm

.[C02

-3].

.Sock

.appl

ication

.prog

ramming

.inte

rface

.(API

)

.is.a.de.fact

.stan

dard.

Prog

rams

.use.cond

itional

.comp

ilation

.dire

ctives

.that.incl

ude

.mino

.vari

ations

.in.the.libr

ary

.head

ers

need

.for.oper

ation

.unde

.Unix

/Linux

.and.Wind

ows.

.Func

tion

.call

.shou

.be.modi

ed,

.if.desi

red,

to.run.unde

.othe

.oper

ating

.syst

ems

.or.with.prop

rietary

.oper

ating

.syst

ems

.for.embe

dded

.devi

ces.

Mino

. modi

cations

. need. to. be. perf

ormed

. when. utili

zing

. unde

rlying

. IPv6. API,. as. desc

ribed

. in.

[RFC

3493].

.Figu

.60.5.show

.the.serv

.prog

ram

.that.wait

.for.inco

ming

.data

gram

.from.the.clie

prog

ram

.list

.in.Figu

.60.6

.Beca

use

.UDP.is.conn

ectionless,

.the.serv

.is.capa

ble

.of.serv

icing

.data.

from.seve

ral

.clie

nts

.almo

.simu

ltaneously.

.In.case.a.dist

inction

.is.need

.amon

.clie

nts,

.this.must.be.

impl

emented

.in.the.code.of.the.serv

.prog

ram.

.Prog

rams

.show.all.step

.nece

ssary

.to.set.up,.use,.and.

tear.down.a.UDP-

based

.exch

ange

.of.data

Figures

.60.7.and.60.8.cont

ain

.anot

her

.pair.of.C.prog

rams

.that.demo

nstrate

.the.use. of.UDP.for.

comm

unication

.using.mult

icasting.

.Seve

ral

.serv

.prog

rams

.list

.in.Figu

.60.7.rece

ive

.one.mess

age

sent.by.the.clie

.prog

ram

.list

.in.Figu

.60.8

. e.serv

.must.subs

cribe

.to.the.mult

icast

.IP.addr

ess,

i.e.,.“join.the.mult

icast

.grou

p”

.in.orde

.to.rece

ive

.data

.In.case.of.a.clie

.that.only.send

.mult

icast

.data.

this.ste

.may.be.omi

tted.

FIGURE 60.7 (continued)

User Datagram Protocol—UDP 60-9

Internet.socket.is.an.end.point.of.a.bidirectional.interprocess.communication.ow.across.an.IP-based.

com

puter

.net

work.

.Int

erface

.to.the.soc

ket

.lib

rary

.is.sta

ndardized

.onl

.on.Uni

x/Linux

.and.Win

dows.

.Oth

ope

rating

.sys

tems

.inc

luding

.var

ious

.emb

edded

.sys

tems

.may.emp

loy

.di

erent

.fun

ctions

.to.car

.out.the.sam

fun

ctionality.

.Pro

grams

.of.the.sam

.fun

ctionality

.imp

lemented

.in.oth

.lan

guages

.may.com

bine

.sev

eral

ste

.int

.cal

ling

.a.sin

gle

.fun

ction.

. is.is.esp

ecially

.tru

.for.the.soc

ket

.ini

tialization

.and.conn

ection

.set.up.

FIGURE 60.8 Sample.C.program.that.illustrates.a.UDP.client.utilizing.multicasting.

(continued)