Network Programming

Network Programming

Eddie Aronovich

mail: eddiea@mta.ac.il

How did it started ?1983 First wide

availiable Tcp/IP(BSD 4.2)

1988 (BSD 4.3)slow start,congestion

avoidence, fastretransmit

1990 (BSD 4.3)fast recovery, TCPheader prediction,

routing tables changes

1993(4.4BSD)multicast,

long fat pipemodification

1989 - Net/1

1991 - Net/2

1994 Net/3

How can we write communication ?

Application Program Interface (API)

– Sockets

– TLI (Transport Layer Interface)

System calls Library functions

What is it for ?

Communication systems provides 3 services:

– Information & resource Sharing

– Distance gapping

– Backup abilities

Fundamentals

Server - An entity which gives services

Client - An entity which requests services

Transport layer - To transfer the data

The 7 layers model

Layer 1Physical

Interface Layer(Ethernet, SLIP, loopback, etc)

Socket Layer

Protocol Layer(TCP/IP, OSI, Unix)

Layer 7Application

Layer 6Presentation

Layer 5Session

Layer 4Transport

Layer 3Network

Layer 2Data Link

Media

Process

The 7 Layer model in real life

Process

Layer 7Application

Layer 6Presentation

Layer 5Session

Layer 1Physical

Media

Socket LayerLayer 4

Transport

Protocol Layer(TCP/IP, OSI, Unix)

Layer 3Network

Interface Layer(Ethernet, SLIP, loopback, etc)

Layer 2Data Link

Function Call

Function CallSocket Queue Socket Queue

Interfacequeue Protocol queue

Interfacequeue

The message is built in one side...Message from

application

Message fromapplication

4th layerheader

Message fromapplication

4th layerheader

3rdlayer

header

Message fromapplication

4th layerheader

3rdlayer

header

2ndlayer

header

2ndlayertrailer

And striped in the dest. side…

Ethernet

Driver

3rd layer3rd layer3rd layer

4th layer 4th layer

ApplicationApplication

From Lynx to Netscapeor chat client

Presentation

InitiatesConnection

Requestsservice

ProcessResponse

Closeconenction

InitiatesConnection

AcceptsRequest

Responseto Request

Closeconenction

Waits forconnection

Client Server

Descriptors

Everything in Unix is a file Descriptor is an index into an array

fd1fd2fd3

.

.

.fdifdj..

proc {}

i-node

file{}

V-node

file{}

i-node

file{}

V-node

socket{}

Memory Buffers

Contains Socket Address Structure

Headers

Data

The Basics of communication

LectureII

Processing Techniques

The Client Server Model

The server roles:– Give service as asked– Wait the client to appeal to him

The client roles:– Start the communication process– Asks the wanted service

Design considerations

Serve single or multiple users

Use reliable or unreliable protocol

Software updates

Client and server roles in UDP

Server roles:– Bind a port– Wait for a message to come– Send reply

Client roles:– Send a message– Get the reply

User Datagram Protocol*

Simple protocol

Connectionless

Unreliable

*{RFC 768}

Socket:={ip_addr, port number}

API, an interface for the program to contact with communication.

Enable usage of regular file commands as read, write and so on.

The sockets are structures passed from kernel to process and vice versa.

What the socket struct contains ?

Socket type {stream, dgram, raw,…} Socket options {broadcast, OOB...} Time to linger wait before close the socket Socket state flags Protocol Control Block Protocol Handle

The socket & address structs

Generalstruct sockaddr {

uint8_t sa_len; /*Len of socket struct */sa_family_t sa_family; /*Addr family as AF_INET */

char sa_data[20]; /*Protocol Address */

IP V4 address socketstruct sockaddr_in {

uint8_t sin_len; /*The socket length*/sa_family_t sin_family; /*AF_INET for IP addresses*/unit16_t sin_port; /*The port id 16-bit

port num */struct in_addr sin_addr; /*The IP address 32-bit */char sin_zero [8]; /* FFU - Must be zero */

How the socket is created

The system call passes identifiers for address family(e.g.AF_UNIX, AF_INET,etc.), socket type and protocol.

Socket data structure is allocated.

Pointer from the fd table to other i-node struct which points to the socket.

User Datagram Protocol (rfc 768)

Data transport layer protocol(Fragment packets to fit local MTU)

Used to make available datagram packet switched mode

Connectionless protocol

Used when RTT is important or no connection needed

UDP header

Source port number

(16 bit)

Destination port number (16 bit)

Length

(16 bit)

UDP Checksum

(16 bit)

Data

UDP by network monitor

Lets do it in UDP - client

C:\TEMP\udp-cli-c.htmC:\TEMP\udp-cli-c.htm

Lets do it in UDP - server

C:\TEMP\udp-srv-c.html

TCP

LectureIII

Transmission Control Protocolrfc 793

Reliability

Sequenced data transfer

Flow control

Full duplex

TCP HeaderSource port number

(16 bit)

Dest port number

(16 bit)

Sequence number (32 bit)

Acknowledgement number (32 bit)

Header length

(4 bit)

F.F.U

(6 bit)

UR

G

AC

K

PS

H

RS

T

SY

N

FIN

Window size

(16 bit)

TCP Checksum

(16 bit)

Urgent Pointer

(16 bit)

Options

Data

Ack & Flow control

Acknowledgements are sent by byte.

The acks can be sent for group of packets (but should arrive before time out of first packet).

Window size is used for flow control and is controlled by receiver.

How connection starts ?

connect(); listen();

connect returns…. accept();

accept returns….

SYN j

SYN k, ACK j+1

Connection Established

ACK k+1

How we do it in C ?

Server Clientsocket(); socket();

bind();

connect();listen();

accept();

{New file descriptor is given}

Ending Sessions

Passive close (FIN arrives) Vs. Active close

FIN_WAIT_1CLOSE_WAIT

FIN_WAIT_2LAST_ACK

TIME_WAIT(2MSL) CLOSED

FIN M

ACK M+1

FIN N

ACK N+1

Internet Protocol

LectureIV

Network Layer

Passing packet from source host to destination host (cross networks if needed)

Independent of the datalink layer

QoS

Flow control

Internet Protocol

Connectionless

Unreliable

Best effort

Address

IP address consist 32bit and is divided into {network id.,host id}

Part of host id can be used for subnet mask

Some special addresses are defined (as: net-addr, broadcast-addr, multicast-addr)

Addresses and Classes

Class A

Addresses: 0-127.X.X.X

Class B

Addresses: 128-191.0-255.X.X

Class C

Addresses: 192-223.0-255.0-255.X

01XXXXXX

10XXXXXX

110XXXXX

Masks

Mask is used to refine network division.

‘1’b in mask symbolize bit belongs to network address.

‘0’b in mask symbolize bit belongs to host address.

Address conventions

Network address filled with ‘0’ in host address.

Broadcast address filled with ‘1’ in host address.

First, last subnet and address aren’t used

How routing is done ?

The router compares destination IP with each Network & subnet address.

Unknown destination is routed to default.

Routers update each other with appropriate algorithms.

VIשיעור I/O Multiplexing

I/O Models

Blocking I/O

Nonblocking I/O

I/O Multiplexing

Signal driven

Asynchronous I/O

Non-Blocking I/O

No blocking is done (Error is returned)

Reading is done in loop (until data arrives)

Polling – costs CPU time

Implementation in real time systems only

Signal Driven I/O

Signal handler should be started