TCP/IP Programming - Opus One&#174 Programming Terms and Concepts Joel Snyder Opus1 Slide 5 Portions Copyright © 1996, Opus1, Process Software, TGV Terms and Concepts Overview What

TCP/IP ProgrammingTCP/IP Programming

Joel Snyder, Opus1Geoff Bryant, Process Software

Portions Copyright © 1996 TGV Software, Inc., Copyright © 1996 Process Software Corp. Copyright © 1996 Opus1

Slide 2 Portions Copyright © 1996, Opus1, Process Software, TGV

Course Roadmap

NM055 (11:00-12:00) Important Terms andConcepts

TCP/IP and Client/Server ModelSockets and TLIClient/Server in TCP/IP

NM056 (1:00-2:00) Socket RoutinesNM057 (2:00-3:00) Library RoutinesNM058 (3:00-4:00) Sample Client/ServerNM059 (4:00-5:00) VMS specifics (QIOs)NM067 (6:00-7:00) Clinic - Q&A


TCP/IP Programming

Slides and Source Code available via anonymous FTP:

Host:: ftp.process.comDirectory: [pub.decus]Slides: DECUS_F96_PROG.PSExamples: DECUS_F96_PROG_EXAMPLES.TXT

Host: ftp.opus1.comSlides: DECUS_F96_PROG.PSExamples: DECUS_F96_PROG_EXAMPLES.TXT

Session NM055Session NM055

TCP/IP ProgrammingTCP/IP ProgrammingTerms and ConceptsTerms and Concepts

Joel SnyderJoel SnyderOpus1Opus1


Terms and ConceptsOverview

What is the TCP/IP model?What is the client/server model?What are sockets and TLI?What is network byte order?What is encapsulation? Multiplexing?Demultiplexing? Fragmentation?What are addresses?


Networks are layered tosimplify construction

Data Link

Physical

Network

Transport

Session

Presentation

Application

Data Link

Physical

Network

Data Link

Physical

Network

Transport

Session

Presentation

Application

The FamousOSI 7-Story

ApartmentBuilding with

attachedParking Garage


The OSI Model(similar to the Holy Grail)

Physical

Data Link

Network

Transport

Session

Presentation

Application

Transmission of binary data of a medium

Transfer of units of information, framing, and error checking

Delivery of packets of information, which includes routing

Provision for end-to-end reliable and unreliable delivery

Establishment and maintenance of sessions

Data formatting and encryption

Network applications such as file transfer and terminalemulation

OSI layer Function provided


TCP/IP is (usually) slicedup into four layers

DataLink/Physi

cal

Network

Transport

Application

Network Network

Transport

Application

There are actuallymore layers to

TCP/IP than this setof four, but from theprogramming pointof view, this will do

just fine.Data

Link/Physical

DataLink/Physi

cal


We care most about thetwo center layers

Application

TCP

(Transmission Control Protocol)

UDP

(User Datagram Protocol)

IP

(Internet Protocol)

hardwareinterface

Application ApplicationApplication

Transport

Network

Physical/Data Link


TCP

Transmission Control Protocol is defined byRFC-793TCP provides connection-oriented transportserviceEnd-to-end transparent byte-stream


UDP

User Datagram Protocol is defined by RFC-768UDP provides datagram serviceConnectionless


Client/Server isapplication-to-application

TCP/IP and DECnet are client/servernetworksA client/server application has two parts

One which runs on one side of the networkOne which runs on the other side of the network

Differentiate this from a terminal-basednetwork or most Netware applications


Clients and Servers useIPC to talk to each other

Inter-Process Communication mechanismslet two cooperating applicationscommunicateThere are LOTS of IPC mechanisms forlocal communicationsThe two popular TCP/IP based IPCs areSockets (Berkeley Unix) and TLI (AT&T UnixSystem V)


Sockets is the standard APIfor TCP/IP IPC

Normally, you’d have an operating systemspecific routine set to talk to the networkIn the world of standardized APIs, you wouldhave an operating system independent setof routinesSockets takes it one step further: it makesthe network look much like a file system


TCP/IP is a file system?

Routines to openup a file

Routines to closean open file

Routines to openup a connection

Routines to close anopen connection

Read

Write

Yes, sockets treatsTCP/IP as if it were a

file system(with some added complexity

in the open and closeroutines)


It looks like a file, but it’sreally a network interface

ApplicationApplication

write()

read()

write()

read()


Life was easy whenmachines had 8-bit words

Welcome to the concept of “network byteorder”Remember that “network byte order” is notthe same as “host byte order”You have to convert to network byte order!


There are two ways to storemulti-byte integers

high order byte

high order byte

low order byte

low order byte

Address n

Address n

Address n+1

Address n+1

big endian

little endian


VMS systems are littleendian architectures

Big-endian architectures Little-endian architectures

Motorola 68xxx

IBM 370

Intel 80x86

VAX & Alpha (VMS)

PDP-11(sort of)

0 1 2 3 3 2 1 0


Relax: you could be doingEthernet and Token Ring

. . . .

Byte 0 Byte 1 Byte 5

Byte 0 Byte 1 Byte 5Source address

Bit 0

Bit 0

Bit 7Transmitted first

Bit 7Transmitted first

Destination address

Type field

6 bytes

6 bytes

2 bytes

46 - 1500 bytes

4 bytes

Multicast bit

LSB MSB

M

. . . .

TransmissionsequenceDestination

address

Sourceaddress

Datafield

FrameCheck

Sequence

Bits within bytes are transmitted left to right


Encapsulation adds controlinformation to data

Trailers HeadersNow is the time for all good

File serverClient workstation

Headers TrailersRequest block of data

Request

Response

Data field

Data from user program such as an applicationprogram or session control information

Networkheaders

Networktrailers

men to come to the aid of

Response

of their country

Response

Headers

Headers

Trailers

Trailers

Now is the timefor all good mento come to theaid of theircountry


Each layer encapsulatesthe layer below it

Physical

Data Link

Network

Transport

Session

Presentation

Application

Data linkheader

Network layerheader

Transport layer header

Session layer header

Presentation and Application layer

header

OSI model

Network packet

Data linktrailers


Things can be added onand peeled off at the ends

ApplicationLayer Data





Look at your averageWWW query

HTTPheader

HTTPheader

HTTPheader

HTTPheader

TCPheader

TCPheader

TCPheader

IPheader

IPheader

Ethernetheader

Ethernettrailer

14 20 20 192 4


Make sure you memorizeall of this encapsulation info

Destinationaddress

Source address

Type field Data field CRC

Destinationaddress

Source address

Length field Data field CRC

Destinationaddress

Source address

Length field DSAP SSAP CTRL Data field CRC

SNAP header

Destinationaddress

Source address

Length field Data field CRCFFFF

Destinationaddress

Source address

Length field DSAP SSAP CTRL Data field CRCOUI

Ethernet V2.0

IEEE 802.3

IEEE 802.3 with IEEE 802.2

IEEE 802.3 SNAP

Novell proprietary

6 bytes 2 bytes Up to 1500 bytes 4 bytes

Up to 1496 bytes

6 bytes

6 bytes 6 bytes 4 bytes

4 bytes

2 bytes 4 bytes6 bytes 6 bytes 1 byte 1 byte *

4 bytes2 bytes6 bytes 6 bytes Up to 1500 bytes

6 bytes 6 bytes 2 bytes 1 byte 1 byte 3 bytes 2 bytes 1492 bytes

FDDI

Token Ring

Destinationaddress

Source address

Length field DSAP SSAP CTRL Data field

4 bytes6 bytes 6 bytes 2 bytes 1 byte 1 byte 4472 bytes

EtherType

Preamble SD FC FCS FSED

1 byte 1 byte

Destinationaddress

Source address DSAP SSAP CTRL Data field CRC

4 bytes6 bytes 6 bytes 1 byte 1 byte 4472 (4 Mbps or 17800 (16 Mbps) bytes

RIFSD AC FC FS


Multiplexing andDemultiplexing

ApplicationProcess

ApplicationProcess

ApplicationProcess

TCP UDP

IP

Ethernetinterface

Ethernetinterface

IPX DECnet


Segmentation andReassembly

Application DataMessage

TCP

IP

TCP

IP

TCP Segments

IP Packets


Addressing identifiesentities in the network

Each layer in a TCP/IP stack has an addressmade up of two parts

The address of everything below itThe address of itself

In some cases, lower-level addresses areimplied and do not have to be stated

For example, Ethernet MAC addresses are tieddirectly to IP addresses, so they can be omited


Three addresses areimportant: IP, Protocol, Port

Application-leveladdresses

Transport-leveladdresses

Network-leveladdresses


IP addresses are 32-bitintegers




IP Address: 192.245.12.2


Transport addresses are8-bit protocol numbers




ProtocolNumber:

TCP = 6

UDP=17


Port Numbers are16-bit integers




PortNumber:

SMTP = 25


The triplet (IP,Proto,Port)identifies a process

1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1

versionheader length total length (in 8-bit bytes)

protocol id

source IP address

destination IP address

IP number(network address)

Protocol number(transport address)

Port number(application address)


Two triplets identify aconnection

Now we have a socket!(sometimes called a “socket pair”)

Application number 1117

on protocol number 6 (TCP)

at IP address 192.245.12.2

Application number 25

on protocol number 6 (TCP)

at IP address 128.196.128.233


A socket maps oneapplication to another

ApplicationProcess

ApplicationProcess

TCP UDP

IP

Ethernetinterface

ApplicationProcess

TCP UDP

IP

Ethernetinterface

1117 25

6 6

192.245.12.2 128.196.128.233


Addresses are assigned bydifferent entities

IP addresses are assigned by the InterNICand are managed by the local networkmanagerProtocol numbers are assigned by the IANA(Internet Assigned Number Authority) andare fixed across the Internet (RFC 1700)Application port numbers come from twosources

Servers are assigned by IANA (RFC 1700)Clients are handled by the network kernel


IP Addressing

IP is the Internet Protocol, currently version4IPNG is the Next Generation (also known asIPv6)IP is defined by RFC-791IP uses four octet (8-bit byte) addressesIP takes care of getting packets todestination


Client and Server PortNumbers are coordinated

NORMALLY, Server port numbers are lownumbers in the range 1-1023

Defined in RFC 1700NORMALLY, Client port numbers are highnumbers starting at 1024

These are called “ephemeral ports”


You only pick server ports

A server running on a “well-known port” letsthe operating system know what port itwants to listen onA client simply lets the operating system picka new port (ephemeral) that isn’t already inuse


Well-Known-Servers

Public services (e.g. and email server) areassigned a particular number by IANAThese numbers are stored in the InternetAssigned Numbers RFC (changing number,latest is 1797)These are called Well-Known-ServersExamples of these include TELNET (23),SMTP (25), FINGER (79), HTTP (80),RLOGIN (512) and others

Important TermsKey Concepts

TCP/IP networks are layeredTCP/IP uses a client/server paradigmAddressing triples (IP, protocol, port) identifyapplications in TCP/IPA pair of triples beats a full house

Client/Server in TCP/IPClient/Server in TCP/IP


Client/Server in TCP/IPOverview

What is the server process (INETD)?What are ephemeral ports?How can you have multiple connections?How are processes identified?What is Connection-oriented? Connection-less?


Making the initialconnection to a server

When a connection enters a TCP/IP system,someone has to handle it

Either a running daemon is waiting (yourapplication)or a running daemon is waiting (InetD)

Trade off efficiency for performanceChoose whichever model you want based onindividual application characteristicsSeldom used? InetdConstantly used? True Daemon


Your application can waitfor an incoming connection

This is called the “Daemon” (or Demon)approach

YourApplication

Network Kernel

If anything shouldcome in for Port 25 onTCP, give it to me. I willbe waiting right here.

OK.


Or you can have the InetDdo it for you

YourApplication

Network Kernel

Here’s anincoming call.

Port 25? I will start anew process runningYour Application andhand it this incoming call.

InetD

In Multinet, InetD is known as the Master ServerIn TCPware, InetD is part of NETCPIn UCX, InetD is the Auxilliary Server


Servers low, Clients highServers:

ports1-1023

Clients:

“ephemeralports”above1023


A Server may connect tomultiple clients

Each connection is a pair of triples (IP,protocol, port)The server side may remain the sameacross multiple clientsOf course, the server programmer has tokeep it all straight


Socket-pairs leave noambiguity between 2 clients

Client

TCP

IP

Ethernetinterface

SERVER

TCP

IP

Ethernetinterface

1117 25

6 6

192.245.12.2 128.196.128.233

Client

TCP

IP

Ethernetinterface

5555

6

195.240.3.1


Applications are known bytheir port numbers

A process is identified by its 16-bit portnumberIf a server uses both TCP and UDP, it willoften use the same port number for bothprotocols

Protocol number means no ambiguityThe concept of low-numbered ports as“privileged” disappeared with PCs

Don’t base your security on port numbers!Some services use a meet-me approach


TCP/IP supports CL andCO at transport layer

CO = Connection OrientedTCP“Stream”

CL = ConnectionlessUDP“Datagram”

CL can be provided by pure IPUnusual“Raw”


Connection oriented is likea phone call

Connection oriented data communicationsarrived before connectionless

Used primarily over noisy serial lines in originalintention.

not necessarily an issue with TCPTwo stations must establish a connectionbefore data is transmitted.Connection is strictly maintained usingsequence numbers, acknowledgments, retriesand so on.


Connect, Transfer,Disconnect

Connect Request

Connect Confirm

Data

Disconnect Request

Disconnect ConfirmNote: This is almostlike how it’s done in

TCP. Take theinternals course for

more info.


Connectionless is like apostcard

Connectionless allows data to be transmittedwithout a pre-established connectionbetween two stations.

This type of service flourished with theproliferation of LANs.

LANs tend to have a very low error rate and aconnection need not be established to ensure theintegrity of the data.

This type of service does not provide errorrecovery, flow or congestion control.

upper layer network protocols can accomplish this.It requires less overhead and is implicitly faster.


Nike style datacommunications

Data

Note: This is exactlylike how it’s done in

UDP. Take theinternals course for

more info.

Data

Data

Data


Client/Server in TCP/IPKey Concepts

Servers are handled in one of two ways:resident daemons or InetDServer ports are low-numbers; client portsare high-numbered ephemeral portsA server can talk to many clients if theprogrammer can keep them straightTCP is CO; UDP is CL

Documents

TCP/IP Programming - Opus One&#174 Programming Terms and Concepts Joel Snyder Opus1 Slide 5 Portions Copyright © 1996, Opus1, Process Software, TGV Terms and Concepts Overview What