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Pertemuan 2Socket Introduction

Matakuliah : T0483 / Bahasa rakitan

Tahun : 2005

Versi : 1.0

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Learning Outcomes

Pada akhir pertemuan ini, diharapkan mahasiswa

akan mampu :

• menjelaskan konsep-konsep Sockets pada Unix, Linux dan Windows

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Outline Materi

• Port

• IPv4 Socket address structure

• Generic Socket address structure

• Byte Ordering function

• Byte manipulation function.

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<<PORT>>

• PORT Numbers– Each TCP/IP machine has multiple logical

communication channels called ports– Setiap saat banyak proses bisa menggunakan UDP

atau TCP. – TCP atau UDP menggunakan 16-bit positip integer

Port Number untuk proses-proses yg berbeda tsb.– Nomor Ports mulai dari 0 – 65536.– Well known Port : 0 s/d 1023 dikontrol oleh IANA

(Internet Assigned Numbers Authority) . Contoh:

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<<Port>>

• Contoh:– Port 21 untuk FTP– Port 69 untuk TFTP– Port 7 untuk echo server– Port 9 untuk discard server– Port 13 untuk day time server– Port 19 untuk chargen server

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<<Port>>

• A connection between two machines is uniquely defined by:– the protocol (TCP or UDP) – the IP address of local machine – the port number used on the local

machine – the IP address of remote machine – the port number used on the remote

machine

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<<Network API >>

• Network Application Programming Interface (Network API).– Network Application Programming Interface

(Network API) : The services provided by the operating system that provide the interface between application and protocol software

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<< Network API >>

• Network API– Generic Programming Interface.– Support for message oriented and connection

oriented communication.– Work with existing I/O services – Operating System independence.

• Generic Programming Interface– Support multiple communication protocol suites

(families).– Address (endpoint) representation

independence.– Provide special services for Client and Server ?

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<<Network API>>

• TCP/IP– TCP/IP does not include an API definition.– There are a variety of APIs for use with TCP/IP:

• Sockets• TLI, XTI• Winsock• MacTCP

Functions Needes– Specify local and remote communication endpoints– Initiate a connection– Wait for incoming connection– Send and receive data– Terminate a connection – Error handling

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<<Sockets>>

• SOCKETS– A socket is an abstract representation of a

communication endpoint.– Sockets work with Unix I/O services just like

files, pipes & FIFOs.– Sockets have special needs:

• establishing a connection• specifying communication endpoint addresses

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<<Sockets>>

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<<Sockets>>

• Creating a Socket– family specifies the protocol family (PF_INET

for TCP/IP).– type specifies the type of service

(SOCK_STREAM, SOCK_DGRAM).– protocol specifies the specific protocol

(usually 0, which means the default). Protocol yang digunakan seperti tabel dibawah.

– Menggunakan System call Socket(). Contoh :– fd = socket(AF_INET, SOCK_STREAM, 0);

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<<Sockets>>

• Protocol Family Description

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<<Sockets>>

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<< Sockets>>

• Socket() system call– The socket() system call returns a socket

descriptor (small integer) or a -1 on error.– socket() allocates resources needed for a

communication endpoint – TCP/IP requires an IP address and a port

number for each endpoint address.

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<< Sockets>>

POSIX Data Type

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<< Sockets>>

Generic Socket Address Structure• Serupa dgn void * (generic pointer type pada

ANSI C)

<sys/socket.h>

struct sockaddr {

uint8_t sa_len;

sa_family_t sa_family;

char sa_data[14];

};

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<< Sockets>>

Dimana:• sa_family specifies the address type.• sa_data specifies the address value.• socket address structure selalu di-pass “by

reference” jika sebagai argument pada socket functions.

• Contoh: int bind(int, struct sockaddr*, socklen_t)

struct sockaddr_in server; /* IP4 */

bind(sockfd, (struct sockaddr *) &server, sizeof(server));

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<< Sockets>>

• IP4 Socket Address Structurestruct sockaddr_in {

uint8_t sin_len;sa_family_t sin_family;in_port_t sin_port;

struct in_addr sin_addr; char sin_zero[8];

};struct in_addr {

in_addr_t s_addr; };– Alamat IP4 dan Nomor Port TCP atau UDP selalu

disimpan dalam stuktur network byte order.

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<< Sockets>>

Network Byte Order– Nilai yg disimpan pada “sockaddr_in” harus

dalam “network byte order”, seperti :

– sin_port : untuk menyimpan TCP atau UDP port number.

– sin_addr : untuk menyimpan 32-bit IP4 address.

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<< Sockets>>

Network Byte Order Function– Ada dua cara untuk menyimpan 2-byte data di

memori: little-endian and big-endian.– Fungsi-fungsi untuk meng-konversi dari host

byte order ke network byte order umumnya diawali dengan huruf:

• ‘h’ : host byte order • ‘n’ : network byte order• ‘s’ : short (16bit)• ‘l’ : long (32bit)

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<< Sockets>>

• Contoh Fungsi yg mengembalikan Network Byte Order :– uint16_t htons(uint16_t);– uint32_t htonl(uint32_t);

• Contoh Fungsi yg mengembalikan Host Byte Order :- uint16_t ntohs(uint16_t);

- uint32_t ntohl(uint32_t);

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<< Sockets>>

Byte Manipulation Functions#include <string.h>void bzero(void *dst, size_t nbytes);void bcopy(const void *src, void *dest, size_t nbytes);int bcmp(const void *ptr1, const void *ptr2, size_t nbytes);

Contoh:#include <string.h>#include <sys/errno.h>main(){

char x[10];int i;

for(i=0; i<10;i++) x[i]=65+i; bzero(x,4);

for(i=0;i<10;i++) printf("%c\n",x[i]);}

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<< Sockets>>

IPv4 Address Conversion

int inet_aton( char *, struct in_addr *);

• Fungsi inet_aton() berfungsi untuk mengkonversi “ASCII dotted-decimal IP address” menjadi nilai 32-bit dalam format “network byte order”. Fungsi ini mengembalikan nilai 1 jika sukses, dan mengembalikan nilai 0 jika ada error.

char *inet_ntoa(struct in_addr);

• Fungsi inet_ntoa() berfungsi untuk mengkonversi nilai “network byte ordered” menjadi string yg berisi “ASCII dotted-decimal IP address”.