chap 11 modified pp2003

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TCP/IP Protocol Suite 1

Chapter 11Chapter 11

Upon completion you will be able to:

User DatagramUser DatagramProtocolProtocol

Be able to explain process-to-process communication

Know the format of a UDP user datagram

Be able to calculate a UDP checksum

Understand the operation of UDP

Know when it is appropriate to use UDP

Understand the modules in a UDP package

Objectives


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Figure 11.1 Position of UDP in the TP!"P protocol suite


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11.1 PROCESS-TO-PROCESS

COMMUNICATION

Before we examine UDP# we must first understand host-to-hostBefore we examine UDP# we must first understand host-to-hostcommunication and process-to-process communication and thecommunication and process-to-process communication and the

difference between them$difference between them$

The topics discussed in this section include:The topics discussed in this section include:

Port %umbersPort %umbers

&ocket 'ddresses&ocket 'ddresses


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Figure 11.2 UDP (ersus "P

UDP (User Datagram Protocol) creates atransport layer connection between two

processes.

user !atagram is encapsulate! in an IP!atagram.

The port number i!enti"es the process# orrunning application program. So using the pnumber# UDP !irects the pac$et to the correctlocation.

UDP !oes little else. %o &ow control. %o ac$o' receie! pac$ets. nly error control is i'a chec$sum error is !etecte!# it *uietly !rops

the pac$et.


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UDP is a connectionless# unreliable transportprotocol.

It !oes not a!! anything to the serices o' IPe+cept 'or proi!ing process,to,processcommunication# instea! o' host,to,host.

!antages- inimal oerhea! 'aster

UDP wor$s well with apps that hae their ownerror an! &ow control wor$s well withmulticasting# S%P# T0TP (triial 0TP)#(but not 0TP)# an! IP.


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0or communication# 2 pieces o' in'o are nee!e!3

1.local host (IP a!!r)# 4.local process (port 5)#6.remote host (IP a!!r)# 2. remote process (port 5).7ocal process port 5 can be 8ust about any number(between 9 an! :;#;6;)# but remote process port 5has

to be "+e!# otherwise who woul! $now what it is-


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Figure 11.3 Port numbers


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Figure 11.4 "P addresses (ersus port numbers


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ICANN ranges

Well-known ports 0 -> 1023 (assigne an !ontrolle "# ICANN$%

&egistere ports 1024 -> 4'151 &egistere wit ICANN to pre)ent *pli!ation%

+#na,i! ports

4'152 -> 65535 e# !an "e *se as te,porar# or pri)ate port

n*,"ers%

TCP/IP Protocol Suite '


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Figure 11.5 "'%% ranges


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Table ))$)Table ))$) *ell-known ports used with UDP*ell-known ports used with UDP

>ell,$nown port 5s are ? 1942.


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Figure 11.6 &ocket address

In Uni+# the socket addressis the combination o'IP a!!ress an! UDP/TCP port number.


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11.2 USER DATAGRAM

UDP packets are called user datagrams and ha(e a fixed-si+e header of ,UDP packets are called user datagrams and ha(e a fixed-si+e header of ,bytes$bytes$


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Figure 11.7 User datagram format


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UDP length "P length . "P header/s length

Note:Note:


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.+/ pro)ies a connectionless service. Thismeans that each *ser atagra, sent "#.+/ is an inepenent atagra,%

ere is no relationsip "etween teierent *ser atagra,s e)en i te# are!o,ing ro, te sa,e so*r!e pro!ess angoing to te sa,e estination progra,%

e *ser atagra,s are not n*,"ere%



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11.3 CHECKSUM

UDP checksum calculation is different from the one for "P and "0P$UDP checksum calculation is different from the one for "P and "0P$1ere the checksum includes three sections: a pseudoheader# the UDP1ere the checksum includes three sections: a pseudoheader# the UDP

header# and the data coming from the application layer$header# and the data coming from the application layer$


hecksum alculation at &enderhecksum alculation at &ender

hecksum alculation at 2ecei(erhecksum alculation at 2ecei(er

3ptional Use of the hecksum3ptional Use of the hecksum


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Figure 11.8 Pseudoheader for checksum calculation

Psue!ohea!er an! pa!!ing are only use! to calculatchec$sum. 'ter chec$sum is calculate!# they are

!roppe!.


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TCP/IP Protocol Suite 1'

Figure 11.9 hecksum calculation of a simple UDP user datagram


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ptional *se o te

!e!ks*, I te !e!ks*, is not !al!*late teel is lle wit 0s%

I te so*r!e oes !al!*late te!e!ks*, an te res*lt appens to"e all 0s it ,*st "e !o,ple,ente(1s$%



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11.4 UDP OPERATION

UDP uses concepts common to the transport layer$ These concepts willUDP uses concepts common to the transport layer$ These concepts willbe discussed here briefly# and then expanded in the next chapter on thebe discussed here briefly# and then expanded in the next chapter on the

TP protocol$TP protocol$


onnectionless &er(icesonnectionless &er(ices

4low and 5rror ontrol4low and 5rror ontrol

5ncapsulation and Decapsulation5ncapsulation and Decapsulation

6ueuing6ueuing

0ultiplexing and Demultiplexing0ultiplexing and Demultiplexing


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Figure 11.10 5ncapsulation and decapsulation


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Figure 11.11 6ueues in UDP


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Multiplexing and demultiplexingmultiplexing

At te sener site tere ,a# "e se)eral pro!essestat nee to sen *ser atagra,s% owe)ertere is onl# one .+/% is is a ,an#-to-onerelationsip an re*ires ,*ltipleing %

Demultiplexing

At te re!ei)er site tere is onl# one .+/% owe)erwe ,a# a)e ,an# pro!esses tat !an re!ei)e

*ser atagra,s% is is a one-to-,an#relationsip an re*ires e,*ltipleing%



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Figure 11.12 0ultiplexing and demultiplexing


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11.5 USE OF UDP

-UDP is suitable for a process that re7uires simple re7uest-responseUDP is suitable for a process that re7uires simple re7uest-responsecommunication with little concern for flow and error control$communication with little concern for flow and error control$

-UDP is suitable for a process with internal flow and error-controlUDP is suitable for a process with internal flow and error-control

mechanisms 8T4TP9$mechanisms 8T4TP9$

-UDP is suitable transport protocol for multicasting$UDP is suitable transport protocol for multicasting$

-

UDP is used for management processes such as &%0P$UDP is used for management processes such as &%0P$

-UDP is used for some route updating protocols such as 2"P$UDP is used for some route updating protocols such as 2"P$


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11.6 UDP PACKAGE

To show how UDP handles the sending and recei(ing of UDP packets#To show how UDP handles the sending and recei(ing of UDP packets#we present a simple (ersion of the UDP package$ The UDP packagewe present a simple (ersion of the UDP package$ The UDP package

in(ol(es fi(e components: a control-block table# input 7ueues# a control-in(ol(es fi(e components: a control-block table# input 7ueues# a control-

block module# an input module# and an output module$block module# an input module# and an output module$


ontrol-Block Tableontrol-Block Table

"nput 6ueues"nput 6ueuesontrol-Block 0oduleontrol-Block 0odule

"nput 0odule"nput 0odule

3utput 0odule3utput 0odule

Fi 11 13 UDP d i


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Figure 11.13 UDP design

Fi 11 13 UDP d i


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TCP/IP Protocol Suite 2'

Figure 11.13 UDP design

Control,bloc$ table , $eeps trac$ o' the open ports.Table entries inclu!e state ('ree or in,use)# processID# port number# an! correspon!ing *ueue number.

Control,bloc$ mo!ule , manages the entries in thecontrol,bloc$ table. >hen a process starts# it as$s 'oPort number 'rom the operating system.

Input mo!ule , accepts a user !atagram 'rom the IPan! chec$s to see i' there is an e+isting port entryin table. I' yes# *ueue re*uest i' no# generateICP error message.

utput mo!ule , creates an! sen!s user !atagrams.


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Table ))$Table ))$ The control-block table at the beginning of examplesThe control-block table at the beginning of examples

7et@s loo$ at some e+amples. Aelow is the control,bloc$table be'ore the e+amples.


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The first acti(ity is the arri(al of a user datagram with

destination port number ;#


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'fter a few seconds# a process starts$ "t asks the operatingsystem for a port number and is granted port number ;#$

%ow the process sends its "D 8>#?@,9 and the port number to

the control-block module to create an entry in the table$ The

module takes the first 4255 entry and inserts the information

recei(ed$ The module does not allocate a 7ueue at this moment

because no user datagrams ha(e arri(ed for this destination

8see Table ))$=9$

Example3

See Next Slide


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Table ))$=Table ))$= ontrol-block table after 5xample =ontrol-block table after 5xample =


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' user datagram now arri(es for port ;#=9$ &ee Table ))$>$

Example4

See Next Slide


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Table ))$>Table ))$> ontrol-block after 5xample >ontrol-block after 5xample >


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'fter a few seconds# a user datagram arri(es for port ;#$

The input module checks the table and cannot find an entry for

this destination$ The user datagram is dropped and a re7uest is

made to "0P to send an Aunreachable port message to the

source$

Example5

chap 11 modified pp2003

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