1

What is the Internet?

• Hosts or end-systems• PCs, workstations, servers

• PDAs, phones, toasters

• Communication links• fiber, copper, radio, satellite

• Routers• forward packets

• Protocols• TCP, IP, HTTP, FTP, SMTP

• Internet• Network of networks

• Applications• WWW, email, games, e-

commerce, database, voting, file (MP3) sharing

local ISP

companynetwork

regional ISP

router workstation

servermobile

2

Network Equipment

Ethernet Switches

Wiring Closet

Ethernet

3

Network Equipment

Wireless LAN base station

Cisco Routers

Cable Modem

4

What is a Protocol?

Human Protocol

Hi

Hi

Got thetime?

2:00

connection req.

connectionreply.

<file>

time

Network Protocol

5

Network Structure

• Core Networks• Routers• Network of networks

• End systems (hosts):• Run application programs• E.g., WWW, email• At “edge of network”

• How is data transferred through networks?• Routing• Forwarding

6

Delays and Routes in the Internet

1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms17 * * *18 * * *19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms

Traceroute in Unix

7

Air Travel Organization

ticket (purchase)

baggage (check)

gates (load)

runway takeoff

airplane routing

ticket (complain)

baggage (claim)

gates (unload)

runway landing

airplane routing

airplane routing

Is there a way to organize structure of network?

8

Internet Protocol Stack

• Application: supporting network applications• ftp, smtp, http

• Transport: host-host data transfer• tcp, udp

• Network: routing of datagrams from source to destination• ip, routing protocols

• Link: data transfer between neighboring network elements• ppp, ethernet

• Physical: bits “on the wire”

application

transport

network

link

physical

9

Internet Layering

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical application

transportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

10

Data Communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

data

11

Protocol Layering and Data

Each layer takes data from above• adds header information to create new data unit• passes new data unit to layer below

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

source destination

M

M

M

M

Ht

HtHn

HtHnHl

M

M

M

M

Ht

HtHn

HtHnHl

message

segment

frame

12

The TCP/IP Protocol Suite

ARP RARPHardwareInterface

ICMP IGMPIP

TCP UDP

UserProcess

UserProcess

UserProcess

UserProcess

application

transport

network

link

13

IP: Internet Protocol

• IP provides an unreliable, connectionless, datagram delivery service.

• Addressing• IP addresses are 32-bit numbers and are divided into two

components: the host address and the network address.• Example: 129.21.38.169• Who assigns the IP addresses? InterNIC, IANA, ICANN

14

Routing

Graph abstraction for routing algorithms:

• Graph nodes are routers

• Graph edges are physical links• Link cost: delay, $ cost,

or congestion level

Goal: determine “good” path(sequence of routers) thru

network from source to dest.

Routing protocol

A

ED

CB

F

2

2

13

1

1

2

53

5

• “Good” path:• Typically means

minimum cost path• Other def’s possible

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TCP: Transmission Control Protocol

• TCP provides a connection-oriented, reliable, byte stream service (RFC793).

• A stream of 8-bit bytes is exchanged across a TCP connection.

• TCP uses congestion control via congestion windows and acknowledgments.

• TCP uses protocol port numbers to identify the ultimate destination within a machine.

16

Internet Service Provider (ISP)

Sprint US backbone network

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Socket Programming

• In the early 80s, UCB developed the UNIX BSD versions supporting TCP/IP.

• Berkeley sockets are one of the most widely used communication APIs.

• A socket is an object from which messages are sent and received.

• Two types of transfer• connection-oriented vs. connectionless

The “Network”

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Connection-oriented Transfer

Create Socket

Accept

Read/Write

Create Socket

Connect

Read/Write

Server

Client

Connection Establishment

Communication

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Connectionless Transfer

Create Socket

Read/Write

Create Socket

Read/Write

Server

Client

Communication

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java.net.*

• Classes• InetAddress• Socket• ServerSocket• DatagramSocket• DatagramPacket

• Exceptions– BindException– ConnectException– MalformedURLException– NoRouteToHostException– ProtocolException– SocketException– UnknownHostException – UnknownServiceException

The java.net package provides networking support.

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Class InetAddress

public byte[] getAddress();public static InetAddress[] getAllByName(String host);public static InetAddress getByName(String host);public String getHostAddress();public String getHostName();public static InetAddress getLocalHost();

This class represents an Internet Protocol (IP) address.

Applications should use the methods getLocalHost(),

getByName(), or getAllByName() to create a new InetAddress instance.

22

HostInfo.java

import java.net.*;import java.io.*;import java.util.*;

public class HostInfo { public static void main(String argv[]) { InetAddress ipAddr; try { ipAddr = InetAddress.getLocalHost(); System.out.println("This is "+ipAddr); } catch (UnknownHostException e) { System.out.println("Unknown host"); }}

Can you write a program that identifies the host name and IP address of a specified host?

23

Resolver.java

import java.net.*;import java.io.*;import java.util.*;

public class Resolver { public static void main( String args[] ) { InetAddress ipAddr;

try { ipAddr = InetAddress.getByName( args[0] ); System.out.print("IP address = “ + ipAddr + "\n"); } catch (UnknownHostException e){ System.out.println("Unknown host"); } }

}

24

Daytime Service

Most UNIX servers run the daytime service on TCP port 13.

cobalt> telnet holly.cs.rit.edu 13 Trying 129.21.30.35... Connected to holly. Escape character is '^]'. Fri Feb 6 08:33:44 1998 Connection closed by foreign host. It is easy to write a Java daytime client. All the program needs to do is to establish a TCP connection on port 13 of a remote host.

A TCP style connection is made using the Socket class.

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Class Socket

// Constructors (partial list)public Socket()public Socket(InetAddress address, int port);public Socket(String host, int port);

// Methods (partial list)public void close();

public InetAddress getInetAddress(); public int getLocalPort();

public InputStream getInputStream();public OutputStream getOutputStream();

public int getPort(); public String toString();

26

DayTimeClient.java

import java.net.*; import java.io.*; import java.util.*;

public class DayTimeClient { static int dayTimePort = 13;

public static void main(String argv[]) { try { Socket sock = new Socket(argv[0], dayTimePort); BufferedReader din = new BufferedReader( new InputStreamReader( sock.getInputStream() )); String rTime = din.readLine(); System.out.println(rTime); sock.close(); } catch (exception e) {} }}

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A Java Daytime Server

• It is easy to create a daytime server in Java.• The only real problem is that your Java server will not be

able to use port 13.• The server version of the program will use a

ServerSocket to communicate with a client. • A ServerSocket will open a TCP port and wait for a

connection. • Once a request is detected, a new port will be created,

and the connection will be established between the client's source port and this new port.

• Most servers listen for requests on a particular port, and then service that request on a different port.

• This makes it easy for the server to accept and service

requests at the same time.

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Class ServerSocket

// Constructors (partial list)public ServerSocket(int port);public ServerSocket(int port, int count);

// Methods (partial list)public Socket accept();public void close();

public InetAddress getInetAddress();public int getLocalPort();

public String toString();

29

DayTimeServer

import java.net.*; import java.io.*; import java.util.*;

public class DayTimeServer { public static void main(String argv[]) { try { ServerSocket listen = new ServerSocket(0); System.out.println("Listening on port: "+listen.getLocalPort());

for(;;) { Socket clnt = listen.accept(); System.out.println(clnt.toString()); PrintWriter out = new PrintWriter(clnt.getOutputStream(), true); out.println(new Date()); clnt.close(); } } catch(Exception e) {}}}

30

DayTimeServer in Action

The output from the daytime server looks like this: kiev> java DayTimeServer Listening on port: 36109 Socket[addr=cobalt/129.21.37.176,port=32875,localport=36109] Socket[addr=localhost/127.0.0.1,port=36112,localport=36109]

The client output looks like this:

cobalt> telnet kiev 36109 Trying 129.21.38.145... Connected to kiev. Escape character is '^]'. Fri Feb 06 09:53:00 EST 1998 Connection closed by foreign host.

31

Problem: Client/Server

• Write a client/server application in which the client sends a radius, and the server computes the area and sends it back to the client.

• Write a client program that reads a Web page specified by a given URL (Uniform Resource Locator).• Use class java.net.URL.

32

Multi-Threaded Servers

• It is quite easy, and natural in Java, to make a server multi-threaded.

• In a multi-threaded server a new thread is created to handle each request.

• Clearly for a server such as the daytime server this is not necessary, but for an FTP server this is almost required.

• Why?

• The code for the multi-threaded version of the server consists of a new class called Connection.

• An instance of this class handles the clients request.

33

TDayTimeServer.java

import java.net.*; import java.io.*; import java.util.*;

public class TDayTimeServer { public static void main(String argv[]) { try { ServerSocket listen = new ServerSocket(0); System.out.println("Listening on: "+listen.getLocalPort());

while(true) { Socket clnt = listen.accept(); System.out.println(clnt.toString()); Connection c = new Connection(clnt); c.start(); } } catch(Exception e) { System.out.println("Server terminated"); } }}

34

Connection.java

import java.net.*; import java.io.*; import java.util.*;

class Connection extends Thread { protected Socket clnt;

public Connection(Socket sock) { clnt = sock; }

public void run() { Date today = new Date(); try { PrintWriter out = new PrintWriter(clnt.getOutputStream(), true); out.println(today); clnt.close(); } catch (IOException e) {} }

}

35

Multi Servers and Clients

• We can also create a new server thread listening to the port every time.

• See MTS.java and MTSclient.java

36

Datagrams

• Datagram packets are used to implement a connectionless, packet based, delivery service.

• Each message is routed from one machine to another based solely on information contained within that packet.

• Multiple packets sent from one machine to another might be routed differently, and might arrive in any order.

• Packets may be lost or duplicated during transit.

• The class DatagramPacket represents a datagram in Java.

37

Class DatagramPacket

//Constructors// For receiving a packet:public DatagramPacket(byte ibuf[], int ilength);// For sending a packet (need address information):public DatagramPacket( byte ibuf[], int ilength, InetAddress iaddr, int iport);

// Methodspublic synchronized InetAddress getAddress();public synchronized int getPort();public synchornized byte[] getData();int getLength();

void setAddress(InetAddress iaddr);void setPort(int iport);void setData(byte ibuf[]);void setLength(int ilength);

38

Class DatagramSocket

• This class represents a socket for sending and receiving datagram packets.

• Addressing information for outgoing packets is contained in the packet header.

• A socket that is used to read incoming packets must be bound to an address (sockets that are used for sending must be bound as well, but in most cases it is done automatically).

• There is no special datagram server socket class.• Since packets can be lost, the ability to set timeouts is

important.

39

Class DatagramSocket

// ConstructorsDatagramSocket() DatagramSocket(int port)DatagramSocket(int port, InetAddress iaddr) // Methodsvoid receive(DatagramPacket p) void send(DatagramPacket p) void setSoTimeout(int timeout)void close() InetAddress getLocalAddress() int getLocalPort() int getSoTimeout()

40

Echo Services• A common network service is an echo server.• An echo server simply sends packets back to the

sender.

• A client creates a packet, sends it to the server, and waits for a response.

• Echo services can be used to test network connectivity and performance.

41

UDPEchoClient.javaimport java.net.*; import java.io.*; import java.util.*;

public class UDPEchoClient { static int echoPort = 7000; static int msgLen = 16; static int timeOut=1000;

public static void main(String args[]) { try { DatagramSocket sock = new DatagramSocket(); DatagramPacket pak; byte msg[] = new byte[msgLen];

InetAddress echoHost = InetAddress.getByName(args[0]); pak = new DatagramPacket(msg,msgLen,echoHost,echoPort);

sock.send(pak); sock.setSoTimeout(timeOut); sock.receive(pak); } catch (InterruptedIOException e) {System.out.println("Timeout");} catch (Exception e) {} }}

42

UDPEchoServer.javaimport java.net.*;import java.io.*;import java.util.*;

public class UdpEchoServer { static int echoPort = 7000; static int msgLen = 1024; public static void main(String args[]) { try { DatagramSocket sock = new DatagramSocket(echoPort); DatagramPacket p, reply; byte msg[] = new byte[msgLen]; p = new DatagramPacket(msg,msgLen);

for (;;) { sock.receive(p); System.out.println(p.getAddress()); reply = new DatagramPacket(p.getData(), p.getLength(), p.getAddress(), p.getPort()); sock.send(reply); } } catch (Exception e) {} }}

43

Problem: UDPDayTime Server and Client

• Write a program that implements a DayTime Server and Client using UDP connections.

• How can I convert my previous tic-tac-toe program to a networked version?