__1_Chap I -- Intro to Networking

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Network programming:Network programming:Chap 1: Introduction to networking Chap 1: Introduction to networking

Dr. Mohamad Chaitou – LIU

Mohamad Chaitou2

Course contentsCourse contents

Basic Concepts, Protocols and Terminology (1 week)

Client/server scheme, TCP connection, UDP connectionless, Port,

Socket

Manipulating Internet Addresses (1 week)

DNS System, Local/Remote IP Finder Application

TCP/UDP Sockets (3 weeks)

Echo, Ping, Simplex Chat, Port Scanner, IP Scanner

Network Programming with GUIs (2.5 weeks)

Chat through GUI, Browsing Web Pages

Multithreading (1.5 weeks)

Chat with Multiple Clients, Full Duplex Chat



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Course contentsCourse contents

File Handling, Serialisation (2 weeks)

File transfer

Remote Method Invocation (2 weeks)

Banking Application

Projects’ Demos (1 week)

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AssessmentAssessment

Assignments & Participations: Weekly assignments due every

Wednesday at the beginning of class time. (10 percent)

Tests & Final Examination: Each test takes place according to the

following table:

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Test Number Date Duration Weight

Assg & Part 10%

MID I December 1st, 2010 90 minutes 25%

Project JAN 14th, 2011 25%

Final Exam* TBA 3 hours 40%



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Network definition and advantagesNetwork definition and advantages

Definition:

A network is a set of nodes interconnected together via physical links

in order to exchange information and share resources. These nodes can

be a computer, a phone, or other network equipment such as a router

or firewall.

Advantages:

Resource sharing, e.g. Printers, memory space ( file server ), processor

( Application server or distributed application). Data exchange and communication: Networks provide new ways of

communication and of data exchange, for example, teleconference, e-mail services…etc.

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Network classificationNetwork classification

By size:

PAN, LAN, MAN, WAN

By topology:

Mesh, bus, ring, star,etc.

By performance:

Bandwidth and delay

By the type of terminals:

Telephony network

Computer network

Home network6



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Classification by size: PAN, LAN, MAN, WANClassification by size: PAN, LAN, MAN, WAN

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1 m 10 m 100 m 1 Km 10 Km 100 Km

LAN

Local area networks

WAN

Wide area networkMAN

Metropolitan

area networks

PAN

1m: connection between a (mouse,

keyboard,printer, etc.) and

a computer)

10m/1km: building,

campus, etc: Use of Ethernet LAN or Wireless

LAN

10km: city, town Use of simple

architecture (ring): xDSL

Fiber To The Home

>100km: Internet (network inter-

connexion),Planet:

Fiber optic,satellite

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By topologyBy topology

Mesh:

Full:

each node is connected to all other nodes

Rarely used because it need n(n-1)/2 cables!

Partial mesh:

Each node is connected to a few number of nodes

Use of routing/switching protocols to go from node to node

BUS or Ring:

Each node is connected to a shared bus or ring

Used in Ethernet LAN

Star:

All nodes are connected to a central node

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By performanceBy performance

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Public switched telephony network (PSTN)Public switched telephony network (PSTN)

Used for voice transmission:

Data can be transmitted by

using a numeric to analog

modem (56kbit/s)

Data and voice cannot betransmitted simultaneously

Resources are reserved for a

call:

64 Kbit/s per channel

Multiplexing is performed

by the telephony switches

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Computer network Computer network

A set of computer connected

between them by the same

technology

Many computer network can

be connected between them:

This is the example of the

internet

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Wireless networksWireless networks

Multiple technologies:

GSM, 3G, 3G+, 4G

Wireless LAN (standard IEEE 802.11): up to 54 Mbit/s for several meters

Example: WIFI, ADHOC, BLUETOOTH

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StandarizationStandarization

IETF (Internet Engineering Task Force):

Regroups: constructors, network operators and researchers from all the

world

It aims to produce standards called RFC (Request For Comments) for

protocols covered by the technology TCP/IP. It aims also to ensure a

long-term development of the Internet

IEEE(Institute of Electrical and Electronics EngineersInstitute of Electrical and Electronics Engineers):

IEEE has started the standardization of local networks in 1979.

This process consists of applying the principles of layers 1 and 2 of the

OSI model on the varieties of LAN and MAN networks This working group has taken the name of IEEE 802.X in 1980

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OSI model (1)OSI model (1)

Open System Interconnexion:

based on a principle stated by Julius Caesar 'divide and rule‘

description of networks as a set of layers superimposed on each other:

their number, their name, their function varies depending on the network

the goal of each layer is to provide services to higher layers:

– the latter do not know the implementation of these services

The study of the network is reduced to that of its parts, the whole

becomes easier to manipulate

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7 functional layers divided into 2 groups:

lower layers:

transport functions

information transfer between terminals via a telecommunication network

layers 1-4

upper layers:

application management

applications taken over by the terminal

layers 5-7

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Layer 1 - Physical: transmission of bits on physical support. Also, it

determines the voltage of each bit level, length of bits, modulation, etc.

Layer 2 - Link: transfer of information in the form of frames, detection and

correction of errors.

Layer 3 - Network: establishment and release of communications, routing

through the network: Internet protocol (IP)

Layer 4 - Transport: transports information reliably from one end of theconnection to the other end, connection procedure: TCP or UDP

Layer 5 - Session: organization of the exchange and structure of dialogue

between applications (example: negociate if half-duplex or full duplex)

Layer 6 - Presentation: syntax for the exchange of information (alphabet,

presentation graphics, etc..). Representing data independently from usedplatforms or OS. The security mechanism to access information

Layer 7 - Application: contains the mechanism that can be activated for

different services (applications). The user accesses OSI by this service. The

applications are not parts of this layer: HTTP, FTP, SMTP, etc.16



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OSI Model (8)OSI Model (8)

There are three key concepts for the OSI model:

SAP (SERVICE ACCESS POINT):

identifies the interfaces between adjacent layers in the equipment. The

interface between Layer 1 (Physical) and layer 2 is named PH-SAP, between

layer 2 and 3 is DL-SAP, between layer 3 and 4 N-SAP, etc.

Primitives:

constitute the basis of dialogue between the adjacent layers in the

equipment. There are 4 types: request, indication, response and

confirmation. They are used by the layer n requesting a service from layern-1 and offering the service to layer n +1.

Protocols rules defining the dialogue between the layers of the same level for two

terminals in communication. The precise specification of protocols impliesthat there is a detailed division of functions between the terminals.

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Introduction to InternetIntroduction to Internet

A little history on the Internet:

Research from the DARPA

Defense Advanced Research Projects Agency

ARPANET network

– first network packet (beginning 1970)

– point to point links (terrestrial, radio, satellite) 1980: TCP / IP implemented on the DARPA network

this is the beginning of the Internet!

DARPA will require that all machines of ARPANET have to use TCP / IP

TCP / IP is then integrated into the UNIX world

Entering into the academic world

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What is the Internet?

virtual network constructed by interconnecting physical networks

through gateways: Routers

need for a universal communication service

TCP / IP allows the use of applications without knowing the technology andarchitecture of the Internet

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Network 1 network 2 Network 3 3

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InternetInternet

Users view of the Internet



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Reality of the Internet

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The IP layerThe IP layer

IP: Internet Protocol (RFC 791)

comparable to the layer 3 of OSI model (Network)

IP is operating over everything it is the convergence protocol

It works on all existing level 2 protocols:

Ethernet (RFC 894)

Token-Ring (RFC 1469)

Serial connexion: SLIP (RFC 1055), PPP (RFC 1353), X25 (RFC 877), FR (RFC

1294)

FDDI (RFC 1188)

ATM (RFC 1483, RFC 1577, LANE)

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The IP layerThe IP layer

The TCP/IP model and the OSI model

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The IP datagramThe IP datagram

The format of the IP datagram

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Options (+ padding)Options (+ padding)

VersionVersion IHLIHL TypeType--ofof--serviceservice Total lengthTotal length

Fragement OffsetFragement OffsetIdentificationIdentification FlagsFlags

TimeTime--toto--livelive ProtocolProtocol Header checksumHeader checksum

Source addressSource address

Destination addressDestination address

Data (variable)Data (variable)

1717 3232191911 44 55 88 99 1616 2020

IP headerIP header DataData

Minimum 20Minimum 20 bytesbytes



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The IP datagram:The IP datagram: demultiplexingdemultiplexing by using theby using the“protocol” field of the header“protocol” field of the header

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IP ModuleIP Module

DatagramDatagram arrivalarrival

ICMPICMP UDPUDPTCPTCP

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The IP datagramThe IP datagram

Source @ field (32 bits): @ IP of the transmitter

Destination @ field (32 bits): @ IP of the destination

These are the addresses of the end machines and not those of

intermediate equipments!

Options field (variable size): Allows extensions

option code (1 byte) + length of option (1 byte) + data associated

Padding field (variable size)

Complete the Options field so that the length of the header is a

multiple of 32 bits

Note: size of the IP header ≥≥≥≥ 20 bytes

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ICMPICMP

Internet Control Message Protocol (RFC 792)

Protocol of 'management' of the network

error reporting mechanisms

Implemented on all IP devices

ICMP is contained in the IP datagram

Protocol field = 1

Sent by the destination device or an intermediate router:

if there is a problem with the IP datagram

to notify the transmitter to change its behavior

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ICMPICMP

Using ICMP: PING (Packet INternet Groper)

To verify IP connectivity equipment with other network equipment

By default: sending 4 queries and waiting for 4 answers

Example:

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IP addressing, DNSIP addressing, DNS

The IP addresses:

consists of 4 bytes (32 bits)

notation "dotted decimal" : X.X.X.X with 0 <= X <= 255

Example: 130.190.57.12

2 distinct parts:

network address: network ID

assigned by an authority, identifies the network

machine address: host ID

assigned by the administrator, identifies the machine (host)

It must be unique (@ public)

Software configurable

associated with each network interface

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IP addresses and DNSIP addresses and DNS

Normally, human beings will use domain names in preference to IP

addresses, but they can just as well use the corresponding IP

addresses (if they know what they are!). The Domain Name System

provides a mapping between IP addresses and domain names and is

held in a distributed database. The IP address system and the DNS

are governed by ICANN (the Internet Corporation for Assigned

Names and Numbers), which is a non-profitmaking organisation.When a URL is submitted to a browser, the DNS automatically

converts the domain name part into its numeric IP equivalent.

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IP addressingIP addressing

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TNA - 28/08/02

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. . .10101010 01010101 00110011 11001100

170 85 51 204

Binary notation

Decimal notation

32 bits

Network id Host id

8 bits 8 bits 8 bits 8 bits

. . .

.

.

. .

.

. ...

Classe A16 777 214 machines

Classe B65 534 machines

Classe C254 machines

1 to 126 host host host

128 to 191 0 to 255 host host

192 to 223 0 to 255 0 to 255 host

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The concept of sub-networks (subnetting)

pure classes -> limited flexibility, waste places

Cutting the network into smaller entities:

decided by the network administrator

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@ hôte@ network

@initial host id

@ host@ subnet

@final net id @final host id

@initial network id

This division may be unknown to the outside

All network devices must use the notion of sub-networks (PC,routers, printers, ...)

Interconnection of subnets by routers



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The division is made possible by using a subnet mask :

same notation as the IP address (32 bits): X.X.X.X

X values: 0, 128, 192, 224, 240, 248, 252, 255

bit 1 -> designate the network portion

bit 0 -> means the party host

CIDR: Classless Routing InterDomain

address format: @ IP / x, where x is the number of bits in the network

address (the rest designating the host part)

ex: Class B: 130.190.0.0

default mask: 255.255.0.0 -> 130.190.0.0/16

255.255.255.0 mask if dividing into 256 subnets of class C ->

130.190.0.0/24

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Subnetting IP Address (1st method)

IP: 170.85.51.204

Subnet Mask: 255.255.248.0 or / 21

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.

.

.

.

.

.

@ IP

Mask11111111 11111111 11111 000 00000000

10101010 01010101 00110011 11001100

170 85 51 204

255 255 248 0

. . . @ network10101010 01010101 00110 000 00000000

170 85 48 0

. . . @ host00000000 00000000 00000 011 11001100

0 0 3 204

2 046 possible host



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Subnetting (2nd method): “complement to 255“

IP address: 170.85.51.204

Subnet Mask: 255.255.248.0 or / 21

what is the @ Network and the @ of the host?

(255 - 248) + 1 = 8 (the value used for sub-network partitioning)

subnet 1 : 170.85.0.x to 170.85.7.x

subnet 2 : 170.85.8.x to 170.85.15.x

subnet 3 : 170.85.16.x to 170.85.23.x

subnet 4 : 170.85.24.x to170.85.31.x

subnet 5 : 170.85.32.x to 170.85.39.x

subnet 6 : 170.85.40.x to 170.85.47.x

subnet 7 : 170.85.48.x to 170.85.55.x

etc … until 170.85.255.x 39

@ network:@ network:

170.85.48.0170.85.48.0

@ host(51@ host(51--48 = 3) :48 = 3) :0.0.3.2040.0.3.204

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The transport layerThe transport layer

Two protocols are used for communication between applications:

UDP: User Datagram Protocol

Connectionless

the sending machine sends data without notifying the receiving machine,

and the receiving machine receives the data without sending a receipt tothe sending machine

TCP: Transmission Control Protocol

Connection-oriented

the receiving machine sends acknowledgments during the communication

and the sending machine guarantees the validity of the data it sends

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Need for identifying an application:

the identification is made by a port number

abstract value used only by the transport protocol to designate an

application

Combination (IP address - port number):

necessary to identify the processes on a machine : it is called "demon“

ex: 130.190.5.1 - port 23 is the telnet demon on the station 130.190.5.1

The combination of two (IP address - port number) completely

defines a TCP or UDP flow:

ex: 130.190.5.1 - 23 and 147.171.150.2 – 1094

User 147.171.150.2 took a telnet in 130.190.5.1

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Pre-defined Ports (RFC 1060 "Assigned Numbers") for standard

services:

Ports are coded on 16 bits: 65536 possibilities

Ports 0-1023: Well Known Ports

assigned by the IANA: only to be used by system processes or programs

executed by privileged users

ports 1024-49151: registered ports (Registered)

Ports 49152 to 65535: dynamic or private ports

All equipment TCP / IP must respect this allocation

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port 21port 21 --> FTP> FTP port 23port 23 --> Telnet> Telnetport 25port 25 --> SMTP> SMTP port 69port 69 --> TFTP> TFTPport 53port 53 --> DNS (Domain Name Server)> DNS (Domain Name Server) port 80port 80 --> HTTP> HTTP



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UDPUDP

User Datagram Protocol

connectionless service, no warranty, using IP to transport messages

between machines

UDP segment is contained in an IP datagram

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Source PortSource Port Destination PortDestination Port

ChecksumChecksumLengthLength

1717 323211 1616

IP headerIP header DataData

8 octets8 octets

UDP headerUDP header

IP dataIP data

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UDPUDP

Compared to IP, UDP adds information indicating the service used:

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UDPUDP multiplexingmultiplexing

IP layerIP layer

Port 161Port 161 Port 69Port 69Port 123Port 123

DatagramDatagram UDPUDP

ntpntpsnmpsnmp tftptftp



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UDPUDP

UDP does not:

connected mode

packet retransmission if errors or losses

sequencing of packets

Flow Control -> very easy to saturate a LAN or router! (Streaming

audio / video)

It is an unreliable transport protocol:

used by NFS (Network File System)

used for broadcasting:

TFTP (Trivial File Transfer Protocol)

NTP (Network Time Protocol)

more generally: when the multicast is required

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TCP protocolTCP protocol

Transmission Control Protocol

The TCP / IP is enabled on all network devices with

IP (routers, workstations, ...)

The aim is to transport data:

end to end between applications

connected mode: establishement/closure of sessions

without error: control and retransmission if necessary

Lossless: "dial" and retransmission

ordered: sequencing of packets

Acknowledgment system

flow control: emission window

Full Duplex..

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TCP/IP architectureTCP/IP architecture

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Ports and socketsPorts and sockets A port is a logical connection to a computer (as opposed to a

physical connection) and is identified by a number in the range 1-

65535. This number has no correspondence with the number of

physical connections to the computer, of which there may be only

one

Addresses would be all you needed if each computer did no more

than one thing at a time. However, modern computers do many

different things at once. Email needs to be separated from FTPrequests, which need to be separated from web traffic. This is

accomplished through ports.

In most applications, of course, there are likely to be multiple

clients wanting the same service at the same time. A common

example of this requirement is that of multiple browsers (quite

possibly thousands of them) wanting Web pages from the same

server. The server, of course, needs some way of distinguishing

between clients and keeping their dialogues separate from each

other. This is achieved via the use of sockets.48



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Ports and socketsPorts and sockets

When a client wishes to make connection to a server, it will create

a socket at its end of the communication link. Upon receiving the

client's initial request (on a particular port number), the server will

create a new socket at its end that will be dedicated to

communication with that particular client. Just as one hardware

link to a server may be associated with many ports, so too may one

port be associated with many sockets

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Ports and socketsPorts and sockets

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TCPTCP

TCP treats the data from the upper layers as a sequence of bytes

It Cuts this sequence of bytes in TCP segments

maximum size: 64 Kbytes

size depends on the media in face of the sending station

Segments are exchanged to:

open connections

transfer data manage flow control: sends "ACK“

inform the window size

close connections

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TCPTCP

Connected mode: mechanism "Send and Wait“

It transmits a packet, then waits for acknowledgment before sending

the following one:

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TransmitTransmit packetpacket 11

ReceiveReceive packetpacket 11

Transmit ACK 1Transmit ACK 1

ReceiveReceiveACK 1ACK 1

ReceiveReceive PacketPacket 22

TransmitACKTransmitACK 22

TransmitTransmit PacketPacket 22

ReceiveReceiveACK 2ACK 2

SenderSender receiverreceivernetworknetwork



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TCPTCP

If there is no acknowledgment (ACK) at the expiration of the timer,

it retransmits the packet and then waits again, etc.

This technique uses very little network

The network is only used when transmitting

eg transmission time tt =, tp = propagation time , efficiency = tt / (tt + 2 x

tp) = 1 / (1 + 2 x tp / tt)

if the network size increases (ie tp increases), efficiency decreases!

Introduction of the window of anticipation (or transmissionwindow) to maximize the effeciency of TCP exchanges

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TCPTCP

Mechanism of the "sliding window”

The transmitter may send 3 packets before receiving an

acknowledgment

The ack of a packet arrives, the window slides:

The performance depends on the size of the window and the speed

at which the network accepts packets

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Initial windowInitial window

11 22 33 44 55 66 77 88PacketsPackets

SlidingSliding

11 22 33 44 55 66 77 88PacketsPackets



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TCPTCP

If the window is large enough, there is no blockage

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SenderSender destinationdestinationnetworknetwork

Important :Important :•• no blocking because ACK1 received before the end ofthe transmission window

endend rxrx segment 1segment 1-->> txtx ACK 1ACK 1

endend rxrx segment 2segment 2

-->> txtx ACK 2ACK 2


TransmissionTransmission

windowwindow

tttt

tttt

tttt

tptp




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TCPTCP

If he window size is too small, then there is blocking:

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BlockingBlocking zonezone

BlockingBlocking zonezone

SenderSender ReceiverReceiverNetworkNetwork

TransmissionTransmissionwindowwindow

tttt

tttt

tttt






EndEnd rxrx segment 5segment 5



tptp

TransmissionTransmissionwindowwindow

tttt

tttt

tttt



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TCPTCP

Flow Control:

the recipient plays with the space available in its buffers to reduce (or

increase) the transmission window:

WINDOW field in the TCP frame

number of bytes that the receiver can process

– transmission window accordingly modified

Flow control is essential to the Internet

heterogeneous Internet systems

TCP solves the problem with the "Sliding Window“

Machines of the Internet are of different capacities:

TCP solves the problem by the algorithm of "Slow Start“

segment loss interpreted as a sign of congestion

transmission window is reduced sharply

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TCPTCP

A TCP segment is contained in an IP datagram

protocol field of IP datagram = 6

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IP HeaderIP Header DataData

min 20min 20 bytesbytes

TCP headerTCP header

IP dataIP data

WindowWindowReservedReserved

Options (+ padding)Options (+ padding)

Source PortSource Port Destination PortDestination Port

Sequence NumberSequence Number

Acknowledgment NumberAcknowledgment Number

Data OffsetData Offset

ChecksumChecksum

Data (variable)Data (variable)

1717 323211 1616

SSYYNN

FFIINN

AACCKK

UURRGG

PPSSHH

PPSSTT

Urgent PointerUrgent Pointer

44 55 12121313141415151010 1111



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FirewallsFirewalls

The most basic firewall is a packet filter that inspects each packet

coming into or out of a network and uses a set of rules to

determine whether that traffic is allowed.

Filtering is usually based on network addresses and ports. For

example, all traffic coming from the Class C network 193.28.25

may be rejected because you had bad experiences with hackers

from that net in the past.

Outgoing Telnet connections may be allowed, but incoming Telnet

connections may not be. Incoming connections on port 80 (Web)

may be allowed but only to the corporate web server.

The exact configuration of a firewall—which packets of data are

and are not allowed to pass through—depends on the security needs

of an individual site.

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FirewallsFirewalls

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Proxy serversProxy servers

A machine that is prevented from connecting to the external

network by a firewall would make a request for a web page from

the local proxy server instead of requesting the web page directly

from the remote web server.

The proxy server would then request the page from the web server

and forward the response to the original requester.

While firewalls generally operate at the level of the transport or

internet layer, proxy servers operate at the application layer. A

proxy server has detailed understanding of some application level

protocols, like HTTP and FTP.

Packets that pass through the proxy server can be examined to

ensure that they contain data appropriate for their type. For

instance, FTP packets that seem to contain Telnet data can be

rejected.

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Proxy serversProxy servers

Proxy servers can also be used to implement local caching. When a

file is requested from a web server, the proxy server will first

check to see whether the file is in its cache. If the file is in the

cache, then the proxy will serve the file from the cache rather than

from the Internet. If the file is not in the cache, then the proxy

server will retrieve the file, forward it to the requester, and store

it in the cache for the next time it is requested.

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Client/Server modelClient/Server model

A client/server application typically stores large quantities of data

on an expensive, high-powered server, while most of the program

logic and the user interface is handled by client software running

on relatively cheap personal computers.

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Client/server modelClient/server model

Some servers process and analyze the data before sending the

results to the client. Such servers are often referred to as

"application servers" to distinguish them from the more common

file servers and database servers. A file or database server will

retrieve information and send it to a client, but it won't process

that information.

Web servers such as Apache respond to requests from web clients

such as Netscape.

An older service that fits the client/server model is FTP.

Java is a powerful environment in which to write GUI programs that

access many different kinds of servers

Java makes it easy to write clients of all sorts, but it really shines

when you start writing servers.

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Client/server modelClient/server model

Not all applications fit easily into a client/server model. For

instance, in networked games it seems likely that both players will

send data back and forth roughly equally (at least in a fair game).

These sorts of connections are called "peer-to-peer". The telephone

system is the classic example of a peer-to-peer network.

Java does not have explicit peer-to-peer communication in its

networking API. However, applications can easily implement peer-

to-peer communications in several ways, most commonly by acting

as both a server and a client. Alternatively, the peers can

communicate with each other through an intermediate server

program that forwards data from one peer to the other peers.

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