UNIX Network Programming

UNIX Network Programming

1

UNIX Network Programming

2nd Edition




UNIX Network Programming

2

Chapter 1. Introduction



•
Contents

–
Introduction

–
A Simple Daytime Client

–
Error Handling: Wrapper Functions

–
A Simple Daytime Server

–
OSI Model

–
Unix Standards

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1.1 Introduction

•
Client / Server


Client

Server

Communication link

Figure 1.1

Network application : client and server

Client

Client

Client

Server

...

...

Figure 1.2

Server handling multiple clients at the same time.

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1.1 Introduction
(continued)

•
Example : Client and Server on the same Ethernet
communication using TCP

Web

Client

TCP

IP

Ethernet

driver

Web

server

TCP

IP

Ethernet

driver

TCP protocol

Application protocol

IP protocol

Ethernet protocol

Actual flow between client and server

Ethernet

Application layer

transport layer

network layer

datalink layer

User

process

Protocol stack

within kernel

Figure 1.3

Client and server on the same Ethernet communicating using TCP

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1.1 Introduction
(continued)

•
Example : Client and Server on different LANs connected
through WAN.

client

application

Host

with

TCP/IP

server

application

Host

with

TCP/IP

router

router

router

router

router

router

LAN

LAN

WAN

Figure 1.4

Client and server on different LANs connected through a WAN

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1.2 A Simple Daytime Client

#include “unp.h”


int

main (int argc, char **argv)

{


int

sockfd, n;


char

recvline[MAXLINE+1];


struct sockaddr_in servaddr;



if ( argc != 2) err_quit(“usage: a.out <IPaddress>”);



if ( (sockfd = socket(AF_INET, SOCK_STREAM, 0)) < 0)



err_sys(“socket error”);




bzero( &servaddr, sizeof(servaddr));


servaddr.sin_family = AF_INET;


servaddr.sin_port = htons(13);

/* daytime server */


if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)



err_quit(“inet_pton error for %s”,argv[1]);




if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) < 0)



err_sys(“connect error”);



while ( (n = read(sockfd, recvline, MAXLINE)) > 0 ) {



recvline[n] = 0;


/* null termicate */



if ( fputs(recvline, stdout) == EOF)




err_sys(“fputs error”);


}


if ( n < 0 ) err_sys ( “read error “);

exit(0);

}

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2

3

4

5

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•
#include

"unp.h"

•
int main(int argc, char **argv)

•
{

•

int


sockfd, n;

•

struct sockaddr_in6

servaddr;

•

char


recvline[MAXLINE + 1];


•

if (argc != 2)


err_quit("usage: a.out <IPaddress>");


•

if ( (sockfd = socket(AF_INET6, SOCK_STREAM, 0)) < 0)

•

err_sys("socket error");


•

bzero(&servaddr, sizeof(servaddr));

•

servaddr.sin6_family = AF_INET6;

•

servaddr.sin6_port = htons(13);

/* daytime server */

•

if (inet_pton(AF_INET6, argv[1], &servaddr.sin6_addr) <= 0)

•


err_quit("inet_pton error for %s", argv[1]);


•

if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) < 0)

•


err_sys("connect error");


•

while ( (n = read(sockfd, recvline, MAXLINE)) > 0) {

•


recvline[n] = 0;

/* null terminate */

•


if (fputs(recvline, stdout) == EOF)

•



err_sys("fputs error");

•

}

•

if (n < 0)

•


err_sys("read error");


•

exit(0);

•
}


1.3 protocol Independence

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1.4 Error Handling: Wrapper Functions

•
Since terminating on an error is the common case, we can shorten our program
by defining a
wrapper function

that performs the actual function call, tests the
return value, and terminates on an error.


•
sockfd = Socket(AF_INET, SOCK_STREAM, 0);


int

Socket(int family, int type, int protocol)

{


int n;


if( (n = socket( family, type, protocol)) < 0 )



err_sys(“socket error”);


return (n);

}


•
Unix
errno

Value

Figure 1.7

Our wrapper function for the
socket
function

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1.5 A Simple Daytime Server

#include “unp.h”

#include <time.h>


int

main(int argc, char **argv)

{


int

listenfd, connfd;


struct sockaddr_in servaddr;


char

buff[MAXLINE];


time_t

ticks;



listenfd = Socket(AF_INET, SOCK_STREAM, 0);



bzero(&servaddr, sizeof(servaddr));


servaddr.sin_family = AF_INET;


servaddr.sin_addr.s_addr = htonl(INADDR_ANY);


servaddr.sin_port = htons(13);

/* daytime server */



Bind(listenfd, (SA *) *servaddr, sizeof(servaddr) );



Listen(listenfd, LISTENQ);



for( ; ; ) {



connfd = Accept(listenfd, (SA *) NULL, NULL) ;




ticks = time(NULL);



snprintf(buff, sizeof(buff), “%.24s
\
r
\
n”, ctime(&ticks) );



Write(connfd, buff, strlen(buff) );




Close(connfd);


}

}

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2

3

4

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1.7 OSI Model

–
Why do both sockets and XTI provide the interface from the upper three layers of
the OSI model into the transport layer?

•
First, the upper three layers handle all the details of the application and The lower four
layers handle all the communication details.

•
Second, the upper three layers is called a user process while the lower four layers are
provided as part of the operating system kernel.

Application

Session

Presentation

Transport

Network

Datalink

Physical

7

6

5

4

3

2

1

OSI Model

Application

TCP | | UDP

IPv4, IPv6

Device driver

and Hardware

Internet protocol
suite

Sockets

XTI

user

process

kernel

application

details

communication

details

Figure 1.14

Layers on OSI model and Internet protocol suite

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1.10 Unix Standards

•
POSIX

–
Potable Operating System Interface

–
a family of standards being developed by IEEE

•
The Open Group

–
an international consortium of vendors and end
-
user
customers from industry, government, and academia.

•
IETF (Internet Engineering Task Force)

–
a large open international community of network designers,
operators, vendors, and researchers concerned with the
evolution of the Internet architecture and the smooth
operation of the internet.

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Chapter 2. The Transport Layer :







TCP and UDP

•
Contents


–
Introduction

–
The Big Picture

–
UDP: User Datagram Protocol

–
TCP: Transmission Control Protocol

–
TCP Connection Establishment and Termination

–
TIME_WAIT State

–
Port Numbers

–
TCP Port Numbers and Concurrent Servers

–
Buffer Sizes and Limitations

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2.1 Introduction

•
Overview of the TCP / IP protocol

•
Transport layer : TCP & UDP


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2.2 The Big Picture

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2.3 UDP : User Datagram Protocol


•
The application writes a
datagram

to a UDP socket, which is
encapsulated as either a IPv4 of a IPv6 datagram, which is sent to
its destination.

•
UDP provides a
connectionless

service.

•
Each UDP datagram has a length and we can consider a datagram
as a
record
.

•
RFC 768[Postel 1980]

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2.4 TCP: Transmission Control Protocol


•
Provides
connections

between clients and servers.

•
Provides
reliability
.

–
RTT (
round
-
trip
-
time
)

•
TCP also
sequences

the data by associating a sequence number
with every byte that it sends.

•
TCP provides
flow control
.

–
window

•
A TCP connection is also
full
-
duplex
.

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2.5 TCP
Connection Establishment and Termination

•
Three
-
Way Handshake










•
SYN segment

•
ACK

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TCP Header

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Encapsulation

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2.5 TCP
Connection Establishment and Termination
(cont)


•
TCP Options

–
MSS option

•
With this option the TCP sending the SYN announces its
maximum segment
size
, the maximum amount of data that it is willing to accept in each TCP
segment, on this connection.


–
Window Scale option


–
Timestamp option

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•
TCP Connection Termination











•
half
-
close
: Between steps 2 and 3 it is possible for data to flow from the end
doing the passive close to the end doing active close.

2.5 TCP
Connection Establishment and Termination
(cont)

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2.5 TCP
Connection
Establishment
and
Termination
(cont)


-

State

transition

diagram

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•
Watching the Packets

2.5 TCP
Connection Establishment and Termination
(cont)

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2.6
TIME_WAIT

State

•
The end that performs the active close is the end that remains in
the TIME_WAIT state=>because that end is the one that might
have to retransmit the final ACK.


•
There are two reason for TIME_WAIT state

–
to implement TCP’s full
-
duplex connection termination
reliably

–
to allow old duplicate segments to expire in the network

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2.7 Port Numbers

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2.8
TCP port Numbers




and Concurrent Servers

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2.8
TCP port Numbers




and Concurrent Servers

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2.9 Buffer Sizes and Limitations

•
Maximum size of IPv4 => 65535 byte

•
Maximum size of IPv6 => 65575 byte

•
MTU(maximum transmit unit) => fragmentation

•
DF (don’t fragment)

•
IPv4 and IPv6 define a minimum reassembly buffer size.

•
TCP has MSS(maximum segment size)

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TCP output

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UDP output

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2.10 standard internet service

Notice:

TCP and UDP port number is same.

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2.11protocol usage by common internet Application