Socket UDP

Socket UDP
H. Fauconnier
M2-Internet Java
1-1
UDP
H. Fauconnier
M2-Internet Java
2
Socket programming with UDP
UDP: no “connection” between
client and server
 no handshaking
 sender explicitly attaches
IP address and port of
destination to each segment
 OS attaches IP address and
port of sending socket to
each segment
 Server can extract IP
address, port of sender
from received segment
H. Fauconnier
application viewpoint
UDP provides unreliable transfer
of groups of bytes (“datagrams”)
between client and server
Note: the official terminology
for a UDP packet is “datagram”.
In this class, we instead use “UDP
segment”.
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Running example
 Client:
User types line of text
 Client program sends line to server

 Server:
 Server receives line of text
 Capitalizes all the letters
 Sends modified line to client
 Client:
 Receives line of text
 Displays
H. Fauconnier
M2-Internet Java
4
Client/server socket interaction: UDP
Server (running on hostid)
create socket,
port= x.
serverSocket =
DatagramSocket()
read datagram from
serverSocket
write reply to
serverSocket
specifying
client address,
port number
H. Fauconnier
Client
create socket,
clientSocket =
DatagramSocket()
Create datagram with server IP and
port=x; send datagram via
clientSocket
read datagram from
clientSocket
close
clientSocket
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Example: Java client (UDP)
in p ut
s tre am
Client
process
m o nitor
inF ro m U ser
k ey b oa rd
P ro c e ss
Input: receives
packet (recall
thatTCP received
“byte stream”)
UDP
p ac k et
receiveP acket
packet (recall
that TCP sent
“byte stream”)
sendP acket
Output: sends
UDP
p ac k et
client
UDP
c lien tS o c k et
socket
to n etw ork
H. Fauconnier
UDP
s oc k et
fro m n etw o rk
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Example: Java client (UDP)
import java.io.*;
import java.net.*;
class UDPClient {
public static void main(String args[]) throws Exception
{
Create
input stream
Create
client socket
Translate
hostname to IP
address using DNS
BufferedReader inFromUser =
new BufferedReader(new InputStreamReader(System.in));
DatagramSocket clientSocket = new DatagramSocket();
InetAddress IPAddress = InetAddress.getByName("hostname");
byte[] sendData = new byte[1024];
byte[] receiveData = new byte[1024];
String sentence = inFromUser.readLine();
sendData = sentence.getBytes();
H. Fauconnier
M2-Internet Java
7
Example: Java client (UDP), cont.
Create datagram
with data-to-send,
length, IP addr, port
Send datagram
to server
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress, 9876);
clientSocket.send(sendPacket);
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
Read datagram
from server
clientSocket.receive(receivePacket);
String modifiedSentence =
new String(receivePacket.getData());
System.out.println("FROM SERVER:" + modifiedSentence);
clientSocket.close();
}
}
H. Fauconnier
M2-Internet Java
8
Example: Java server (UDP)
import java.io.*;
import java.net.*;
Create
datagram socket
at port 9876
class UDPServer {
public static void main(String args[]) throws Exception
{
DatagramSocket serverSocket = new DatagramSocket(9876);
byte[] receiveData = new byte[1024];
byte[] sendData = new byte[1024];
Create space for
received datagram
Receive
datagram
H. Fauconnier
while(true)
{
DatagramPacket receivePacket =
new DatagramPacket(receiveData, receiveData.length);
serverSocket.receive(receivePacket);
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Example: Java server (UDP), cont
String sentence = new String(receivePacket.getData());
Get IP addr
port #, of
sender
InetAddress IPAddress = receivePacket.getAddress();
int port = receivePacket.getPort();
String capitalizedSentence = sentence.toUpperCase();
sendData = capitalizedSentence.getBytes();
Create datagram
to send to client
DatagramPacket sendPacket =
new DatagramPacket(sendData, sendData.length, IPAddress,
port);
Write out
datagram
to socket
serverSocket.send(sendPacket);
}
}
}
H. Fauconnier
End of while loop,
loop back and wait for
another datagram
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UDP observations & questions
 Both client server use DatagramSocket
 Dest IP and port are explicitly attached to
segment.
 What would happen if change both clientSocket
and serverSocket to “mySocket”?
 Can the client send a segment to server without
knowing the server’s IP address and/or port
number?
 Can multiple clients use the server?
H. Fauconnier
M2-Internet Java
11
DatagramPacket
 Un paquet contient au plus 65,507 bytes
 Pour construire les paquet


public DatagramPacket(byte[] buffer, int length)
public DatagramPacket(byte[] buffer, int offset, int length)
 Pour construire et envoyer




public DatagramPacket(byte[] data, int length,
InetAddress destination, int port)
public DatagramPacket(byte[] data, int offset,
int
length, InetAddress destination, int
port)
public DatagramPacket(byte[] data, int length,
SocketAddress destination, int port)
public DatagramPacket(byte[] data, int offset,
int
length, SocketAddress destination, int
port)
H. Fauconnier
M2-Internet Java
12
Exemple
String s = "On essaie…";
byte[] data = s.getBytes("ASCII");
try {
InetAddress ia =
InetAddress.getByName("www.liafa.jussieu.fr
");
int port = 7;// existe-t-il?
DatagramPacket dp = new DatagramPacket(data,
data.length, ia, port);
}
catch (IOException ex)
}
H. Fauconnier
M2-Internet Java
13
Méthodes
 Adresses
 public InetAddress getAddress( )
 public int getPort( )
 public SocketAddress
getSocketAddress( )
 public void setAddress(InetAddress
remote)
 public void setPort(int port)
 public void setAddress(SocketAddress
remote)
H. Fauconnier
M2-Internet Java
14
Méthodes (suite)
 Manipulation des données:
 public byte[] getData( )
 public int getLength( )
 public int getOffset( )
 public void setData(byte[] data)
 public void setData(byte[] data, int
offset, int length )
 public void setLength(int length)
H. Fauconnier
M2-Internet Java
15
Exemple
import java.net.*;
public class DatagramExample {
public static void main(String[] args) {
String s = "Essayons.";
byte[] data = s.getBytes( );
try {
InetAddress ia = InetAddress.getByName("www.liafa.jussieu.fr");
int port =7;
DatagramPacket dp = new DatagramPacket(data, data.length, ia,
port);
System.out.println(" Un packet pour" + dp.getAddress( ) + " port
" +
dp.getPort( ));
System.out.println("il y a " + dp.getLength( ) +
" bytes dans le packet");
System.out.println(
new String(dp.getData( ), dp.getOffset( ), dp.getLength( )));
}
catch (UnknownHostException e) {
System.err.println(e);
}
}
}
H. Fauconnier
M2-Internet Java
16
DatagramSocket
 Constructeurs
 public DatagramSocket( ) throws
SocketException
 public DatagramSocket(int port) throws
SocketException
 public DatagramSocket(int port, InetAddress
interface) throws SocketException
 public DatagramSocket(SocketAddress
interface) throws SocketException
 (protected DatagramSocket(DatagramSocketImpl
impl) throws SocketException)
H. Fauconnier
M2-Internet Java
17
Exemple
java.net.*;
public class UDPPortScanner {
public static void main(String[] args) {
for (int port = 1024; port <= 65535; port++) {
try {
// exception si utilisé
DatagramSocket server = new DatagramSocket(port);
server.close( );
}
catch (SocketException ex) {
System.out.println("Port occupé" + port + ".");
} // end try
} // end for
}
}
H. Fauconnier
M2-Internet Java
18
Envoyer et recevoir
 public void send(DatagramPacket dp)
throws IOException
 public void receive(DatagramPacket dp)
throws IOException
H. Fauconnier
M2-Internet Java
19
Un exemple: Echo
 UDPServeur

UDPEchoServeur
 UDPEchoClient
• SenderThread
• ReceiverThread
H. Fauconnier
M2-Internet Java
20
Echo: UDPServeur
import java.net.*;
import java.io.*;
public abstract class UDPServeur extends Thread {
private int bufferSize;
protected DatagramSocket sock;
public UDPServeur(int port, int bufferSize)
throws SocketException {
this.bufferSize = bufferSize;
this.sock = new DatagramSocket(port);
}
public UDPServeur(int port) throws SocketException {
this(port, 8192);
}
public void run() {
byte[] buffer = new byte[bufferSize];
while (true) {
DatagramPacket incoming = new DatagramPacket(buffer, buffer.length);
try {
sock.receive(incoming);
this.respond(incoming);
}
catch (IOException e) {
System.err.println(e);
}
} // end while
}
public abstract void respond(DatagramPacket request);
}
H. Fauconnier
M2-Internet Java
21
UDPEchoServeur
public class UDPEchoServeur extends UDPServeur {
public final static int DEFAULT_PORT = 2222;
public UDPEchoServeur() throws SocketException {
super(DEFAULT_PORT);
}
public void respond(DatagramPacket packet) {
try {
byte[] data = new byte[packet.getLength()];
System.arraycopy(packet.getData(), 0, data, 0, packet.getLength());
try {
String s = new String(data, "8859_1");
System.out.println(packet.getAddress() + " port "
+ packet.getPort() + " reçu " + s);
} catch (java.io.UnsupportedEncodingException ex) {}
DatagramPacket outgoing = new DatagramPacket(packet.getData(),
packet.getLength(), packet.getAddress(), packet.getPort());
sock.send(outgoing);
} catch (IOException ex) {
System.err.println(ex);
}
}
}
H. Fauconnier
M2-Internet Java
22
Client: UDPEchoClient
public class UDPEchoClient {
public static void lancer(String hostname, int port) {
try {
InetAddress ia = InetAddress.getByName(hostname);
SenderThread sender = new SenderThread(ia, port);
sender.start();
Thread receiver = new ReceiverThread(sender.getSocket());
receiver.start();
}
catch (UnknownHostException ex) {
System.err.println(ex);
}
catch (SocketException ex) {
System.err.println(ex);
}
}
// end lancer
}
H. Fauconnier
M2-Internet Java
23
ReceiverThread
class ReceiverThread extends Thread {
DatagramSocket socket;
private boolean stopped = false;
public ReceiverThread(DatagramSocket ds) throws SocketException {
this.socket = ds;
}
public void halt() {
this.stopped = true;
}
public DatagramSocket getSocket(){
return socket;
}
public void run() {
byte[] buffer = new byte[65507];
while (true) {
if (stopped) return;
DatagramPacket dp = new DatagramPacket(buffer, buffer.length);
try {
socket.receive(dp);
String s = new String(dp.getData(), 0, dp.getLength());
System.out.println(s);
Thread.yield();
} catch (IOException ex) {System.err.println(ex); }
}
}
}
H. Fauconnier
M2-Internet Java
24
SenderThread
public class SenderThread extends Thread {
private InetAddress server;
private DatagramSocket socket;
private boolean stopped = false;
private int port;
public SenderThread(InetAddress address, int port)
throws SocketException {
this.server = address;
this.port = port;
this.socket = new DatagramSocket();
this.socket.connect(server, port);
}
public void halt() {
this.stopped = true;
}
//…
H. Fauconnier
M2-Internet Java
25
SenderThread
//…
public DatagramSocket getSocket() {
return this.socket;
}
public void run() {
}
try {
BufferedReader userInput = new BufferedReader(new
InputStreamReader(System.in));
while (true) {
if (stopped) return;
String theLine = userInput.readLine();
if (theLine.equals(".")) break;
byte[] data = theLine.getBytes();
DatagramPacket output
= new DatagramPacket(data, data.length, server, port);
socket.send(output);
Thread.yield();
}
} // end try
catch (IOException ex) {System.err.println(ex); }
} // end run
H. Fauconnier
M2-Internet Java
26
Autres méthodes










public
public
public
public
public
public
public
public
public
public
H. Fauconnier
void close( )
int getLocalPort( )
InetAddress getLocalAddress( )
SocketAddress getLocalSocketAddress( )
void connect(InetAddress host, int port)
void disconnect( )
void disconnect( )
int getPort( )
InetAddress getInetAddress( )
InetAddress getRemoteSocketAddress( )
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Options
 SO_TIMEOUT
 public synchronized void setSoTimeout(int timeout) throws
SocketException
 public synchronized int getSoTimeout( ) throws IOException
 SO_RCVBUF
 public void setReceiveBufferSize(int size) throws SocketException
 public int getReceiveBufferSize( ) throws SocketException
 SO_SNDBUF
 public void setSendBufferSize(int size) throws SocketException
 int getSendBufferSize( ) throws SocketException
 SO_REUSEADDR (plusieurs sockets sur la même adresse)
 public void setReuseAddress(boolean on) throws SocketException
 boolean getReuseAddress( ) throws SocketException
 SO_BROADCAST
 public void setBroadcast(boolean on) throws SocketException
 public boolean getBroadcast( ) throws SocketException
H. Fauconnier
M2-Internet Java
28
Multicast
H. Fauconnier
M2-Internet Java
29
Broadcast Routing
 Deliver packets from srce to all other nodes
 Source duplication is inefficient:
duplicate
duplicate
creation/transmission
R1
R1
duplicate
R2
R2
R3
R4
source
duplication
R3
R4
in-network
duplication
 Source duplication: how does source
determine recipient addresses
H. Fauconnier
M2-Internet Java
4-30
In-network duplication
 Flooding: when node receives brdcst pckt,
sends copy to all neighbors

Problems: cycles & broadcast storm
 Controlled flooding: node only brdcsts pkt
if it hasn’t brdcst same packet before
Node keeps track of pckt ids already brdcsted
 Or reverse path forwarding (RPF): only forward
pckt if it arrived on shortest path between
node and source

 Spanning tree
 No redundant packets received by any node
H. Fauconnier
M2-Internet Java
4-31
Spanning Tree
 First construct a spanning tree
 Nodes forward copies only along spanning
tree
A
B
c
F
A
E
c
D
F
G
(a) Broadcast initiated at A
H. Fauconnier
B
E
D
G
(b) Broadcast initiated at D
M2-Internet Java
4-32
Spanning Tree: Creation
 Center node
 Each node sends unicast join message to center
node

Message forwarded until it arrives at a node already
belonging to spanning tree
A
A
3
B
c
4
E
F
1
2
B
c
D
F
5
E
D
G
G
(a) Stepwise construction
of spanning tree
(b) Constructed spanning
tree
H. Fauconnier
M2-Internet Java
4-33
Multicast
 Groupe: adresse IP de classe D

Un hôte peut joindre un groupe
 Protocole pour établir les groupes (IGMP)
 Protocole et algorithme pour le routage
H. Fauconnier
M2-Internet Java
4-34
IGMP
 IGMP (internet Group Management
Protocol

Entre un hôte et son routeur (multicast)
• Membership_query: du routeur vers tous les hôtes
pour déterminer quels hôtes appartiennent à quels
groupe
• Membership_report: des hôtes vers le routeur
• Membership_leave: pour quitter un groupe (optionnel)
H. Fauconnier
M2-Internet Java
4-35
Multicast Routing: Problem Statement
 Goal: find a tree (or trees) connecting
routers having local mcast group members



tree: not all paths between routers used
source-based: different tree from each sender to rcvrs
shared-tree: same tree used by all group members
H. Fauconnier
Shared tree
Source-based trees
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1-36
Approaches for building mcast trees
Approaches:
 source-based tree: one tree per source
shortest path trees
 reverse path forwarding

 group-shared tree: group uses one tree
 minimal spanning (Steiner)
 center-based trees
…we first look at basic approaches, then specific protocols adopting these
approaches
H. Fauconnier
M2-Internet Java
1-37
Shortest Path Tree
 mcast forwarding tree: tree of shortest
path routes from source to all receivers

Dijkstra’s algorithm
S: source
LEGEND
R1
1
2
R4
R2
3
R3
H. Fauconnier
router with attached
group member
5
4
R6
router with no attached
group member
R5
6
R7
i
link used for forwarding,
i indicates order link
added by algorithm
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1-38
Reverse Path Forwarding
 rely on router’s knowledge of unicast
shortest path from it to sender
 each router has simple forwarding behavior:
if (mcast datagram received on incoming link
on shortest path back to center)
then flood datagram onto all outgoing links
else ignore datagram
H. Fauconnier
M2-Internet Java
1-39
Reverse Path Forwarding: example
S: source
LEGEND
R1
R4
router with attached
group member
R2
R5
R3
•
R6
R7
router with no attached
group member
datagram will be
forwarded
datagram will not be
forwarded
result is a source-specific reverse SPT
– may be a bad choice with asymmetric links
H. Fauconnier
M2-Internet Java
1-40
Reverse Path Forwarding: pruning
 forwarding tree contains subtrees with no mcast
group members
 no need to forward datagrams down subtree
 “prune” msgs sent upstream by router with no
downstream group members
LEGEND
S: source
R1
router with attached
group member
R4
R2
P
R5
R3
H. Fauconnier
R6
P
R7
P
router with no attached
group member
prune message
links with multicast
forwarding
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1-41
Shared-Tree: Steiner Tree
 Steiner Tree: minimum cost tree
connecting all routers with attached group
members
 problem is NP-complete
 excellent heuristics exists
 not used in practice:
computational complexity
 information about entire network needed
 monolithic: rerun whenever a router needs to
join/leave

H. Fauconnier
M2-Internet Java
1-42
Center-based trees
 single delivery tree shared by all
 one router identified as “center” of tree
 to join:
edge router sends unicast join-msg addressed
to center router
 join-msg “processed” by intermediate routers
and forwarded towards center
 join-msg either hits existing tree branch for
this center, or arrives at center
 path taken by join-msg becomes new branch of
tree for this router

H. Fauconnier
M2-Internet Java
1-43
Center-based trees: an example
Suppose R6 chosen as center:
LEGEND
R1
3
R2
router with attached
group member
R4
2
R5
R3
H. Fauconnier
1
R6
1
router with no attached
group member
path order in which join
messages generated
R7
M2-Internet Java
1-44
Internet Multicasting Routing: DVMRP
 DVMRP: distance vector multicast routing
protocol, RFC1075
 flood and prune: reverse path forwarding,
source-based tree
RPF tree based on DVMRP’s own routing tables
constructed by communicating DVMRP routers
 no assumptions about underlying unicast
 initial datagram to mcast group flooded
everywhere via RPF
 routers not wanting group: send upstream prune
msgs

H. Fauconnier
M2-Internet Java
1-45
DVMRP: continued…
 soft state: DVMRP router periodically (1 min.)
“forgets” branches are pruned:
mcast data again flows down unpruned branch
 downstream router: reprune or else continue to
receive data

 routers can quickly regraft to tree

following IGMP join at leaf
 odds and ends
 commonly implemented in commercial routers
 Mbone routing done using DVMRP
H. Fauconnier
M2-Internet Java
1-46
Tunneling
Q: How to connect “islands” of multicast
routers in a “sea” of unicast routers?
physical topology
logical topology
 mcast datagram encapsulated inside “normal” (non-multicast-
addressed) datagram
 normal IP datagram sent thru “tunnel” via regular IP unicast to
receiving mcast router
 receiving mcast router unencapsulates to get mcast datagram
H. Fauconnier
M2-Internet Java
1-47
PIM: Protocol Independent Multicast
 not dependent on any specific underlying unicast
routing algorithm (works with all)
 two different multicast distribution scenarios :
Dense:
Sparse:
 group members densely
 # networks with group members
packed, in “close” proximity.
 bandwidth more plentiful
H. Fauconnier
small wrt # interconnected networks
 group members “widely dispersed”
 bandwidth not plentiful
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1-48
Consequences of Sparse-Dense Dichotomy:
Dense
 group membership by
Sparse:
 no membership until
routers assumed until
routers explicitly join
routers explicitly prune  receiver- driven
 data-driven construction
construction of mcast
on mcast tree (e.g., RPF)
tree (e.g., center-based)
 bandwidth and non bandwidth and non-groupgroup-router processing
router processing
profligate
conservative
H. Fauconnier
M2-Internet Java
1-49
PIM- Dense Mode
flood-and-prune RPF, similar to DVMRP but
 underlying unicast protocol provides RPF info for incoming
datagram
 less complicated (less efficient) downstream flood than DVMRP
reduces reliance on underlying routing algorithm
 has protocol mechanism for router to detect it is a leaf-node
router
H. Fauconnier
M2-Internet Java
1-50
PIM - Sparse Mode
 center-based approach
 router sends join msg
to rendezvous point
(RP)

router can switch to
source-specific tree
increased performance:
less concentration,
shorter paths
H. Fauconnier
R4
join
intermediate routers
update state and
forward join
 after joining via RP,

R1
R2
R3
join
R5
join
R7
R6
all data multicast
from rendezvous
point
rendezvous
point
M2-Internet Java
1-51
PIM - Sparse Mode
sender(s):
 unicast data to RP,
which distributes down
RP-rooted tree
 RP can extend mcast
tree upstream to
source
 RP can send stop msg
if no attached
receivers

“no one is listening!”
H. Fauconnier
R1
R4
join
R2
R3
join
R5
join
R7
R6
all data multicast
from rendezvous
point
rendezvous
point
M2-Internet Java
1-52
Multicast
 Géré par les routeurs
 Pas de garantie…
 Importance du ttl
• (Évaluation)
– Local:0
– Sous-réseau local:1
– Pays:48
– Continent:64
– Le monde:255
H. Fauconnier
M2-Internet Java
4-53
Multicast
 Un groupe est identifié par une adresse IP
(classe D) entre 224.0.0.0 et
239.255.255.255
 Une adresse multicast peut avoir un nom

Exemple ntp.mcast.net 224.0.1.1
H. Fauconnier
M2-Internet Java
4-54
Sockets multicast
 Extension de DatagramSocket

public class MulticastSocket extends
DatagramSocket
 Principe:
 Créer une MulticastSocket
 Rejoindre un group: joinGroup()
• Créer DatagramPacket
– Receive()
• leaveGroup()

Close()
H. Fauconnier
M2-Internet Java
55
Création
try {
MulticastSocket ms = new MulticastSocket( );
// send datagrams...
}catch (SocketException se){System.err.println(se);}
------try {
SocketAddress address = new
InetSocketAddress("192.168.254.32", 4000);
MulticastSocket ms = new MulticastSocket(address);
// receive datagrams...
}catch (SocketException ex) {System.err.println(ex);}
H. Fauconnier
M2-Internet Java
56
Création
try {
MulticastSocket ms = new MulticastSocket(null);
ms.setReuseAddress(false);
SocketAddress address = new
InetSocketAddress(4000);
ms.bind(address);
// receive datagrams...
}catch (SocketException ex) {
System.err.println(ex);}
H. Fauconnier
M2-Internet Java
57
Rejoindre…
try {
MulticastSocket ms = new MulticastSocket(4000);
InetAddress ia = InetAddress.getByName("224.2.2.2");
ms.joinGroup(ia);
byte[] buffer = new byte[8192];
while (true) {
DatagramPacket dp = new DatagramPacket(buffer,
buffer.length);
ms.receive(dp);
String s = new String(dp.getData( ), "8859_1");
System.out.println(s);
}
}catch (IOException ex) { System.err.println(ex);}
H. Fauconnier
M2-Internet Java
58
send
try {
InetAddress ia =
InetAddress.getByName("experiment.mcast.net
");
byte[] data = "un packet…\r\n".getBytes( );
int port = 4000;
DatagramPacket dp = new DatagramPacket(data,
data.length, ia, port);
MulticastSocket ms = new MulticastSocket( );
ms.send(dp,64);
}catch (IOException ex) {System.err.println(ex);}
H. Fauconnier
M2-Internet Java
59