Socket UDP

1
Socket UDP
2
UDP
3
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

Note the official terminology for a UDP packet
is datagram. In this class, we instead use
UDP segment.
4
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

5
Client/server socket interaction UDP
Server (running on hostid)
create socket, port x.
serverSocket DatagramSocket()
6
Example Java client (UDP)
Client process
Input receives packet (recall thatTCP received
byte stream)
Output sends packet (recall that TCP sent byte
stream)
client UDP socket
7
Example Java client (UDP)
import java.io. import java.net. class
UDPClient public static void main(String
args) throws Exception
BufferedReader inFromUser new
BufferedReader(new InputStreamReader(System.in))
DatagramSocket clientSocket new
DatagramSocket() InetAddress IPAddress
InetAddress.getByName("hostname")
byte sendData new byte1024 byte
receiveData new byte1024 String
sentence inFromUser.readLine() sendData
sentence.getBytes()
Create input stream
Create client socket
Translate hostname to IP address using DNS
8
Example Java client (UDP), cont.
Create datagram with data-to-send, length, IP
addr, port
DatagramPacket sendPacket new
DatagramPacket(sendData, sendData.length,
IPAddress, 9876) clientSocket.send(send
Packet) DatagramPacket receivePacket
new DatagramPacket(receiveData,
receiveData.length) clientSocket.receiv
e(receivePacket) String
modifiedSentence new
String(receivePacket.getData())
System.out.println("FROM SERVER"
modifiedSentence) clientSocket.close()

Send datagram to server
Read datagram from server
9
Example Java server (UDP)
import java.io. import java.net. class
UDPServer public static void main(String
args) throws Exception
DatagramSocket serverSocket new
DatagramSocket(9876) byte
receiveData new byte1024 byte
sendData new byte1024 while(true)
DatagramPacket
receivePacket new
DatagramPacket(receiveData, receiveData.length)
serverSocket.receive(receivePacket)
Create datagram socket at port 9876
Create space for received datagram
Receive datagram
10
Example Java server (UDP), cont
String sentence new
String(receivePacket.getData())
InetAddress IPAddress receivePacket.getAddress()
int port receivePacket.getPort()
String
capitalizedSentence sentence.toUpperCase()
sendData capitalizedSentence.getBytes()
DatagramPacket sendPacket
new DatagramPacket(sendData,
sendData.length, IPAddress,
port) serverSocket.send(s
endPacket)
Get IP addr port , of sender
Create datagram to send to client
Write out datagram to socket
End of while loop, loop back and wait for another
datagram
11
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 servers IP address and/or port
  number?
• Can multiple clients use the server?

12
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)

13
Exemple

• String s "On essaie"
• byte data s.getBytes("ASCII")
• try
• InetAddress ia InetAddress.getByName("www.li
  afa.jussieu.fr")
• int port 7// existe-t-il?
• DatagramPacket dp new DatagramPacket(data,
  data.length, ia, port)
• catch (IOException ex)

14
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)

15
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)

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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)

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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)

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Exemple

• java.net.
• public class UDPPortScanner
• public static void main(String args)
• for (int port 1024 port lt 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

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Envoyer et recevoir

• public void send(DatagramPacket dp) throws
  IOException
• public void receive(DatagramPacket dp) throws
  IOException

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Un exemple Echo

• UDPServeur
• UDPEchoServeur
• UDPEchoClient
• SenderThread
• ReceiverThread

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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 bytebufferSize
• while (true)
• DatagramPacket incoming new
  DatagramPacket(buffer, buffer.length)
• try
• sock.receive(incoming)

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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 bytepacket.getLengt
  h()
• System.arraycopy(packet.getData(), 0,
  data, 0, packet.getLength())
• try
• String s new String(data,
  "8859_1")
• System.out.println(packet.getAddre
  ss() " port "
• packet.getPort() "
  reçu " s)
• catch (java.io.UnsupportedEncodingEx
  ception ex)
• DatagramPacket outgoing new
  DatagramPacket(packet.getData(),
• packet.getLength(),
  packet.getAddress(), packet.getPort())
• sock.send(outgoing)
• catch (IOException ex)
• System.err.println(ex)

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Client UDPEchoClient

• public class UDPEchoClient
• public static void lancer(String hostname, int
  port)
• try
• InetAddress ia InetAddress.getByName(hostn
  ame)
• 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

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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 byte65507
• while (true)
• if (stopped) return
• DatagramPacket dp new
  DatagramPacket(buffer, buffer.length)
• try
• socket.receive(dp)

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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
• //

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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

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Autres méthodes

• public void close( )
• public int getLocalPort( )
• public InetAddress getLocalAddress( )
• public SocketAddress getLocalSocketAddress( )
• public void connect(InetAddress host, int port)
• public void disconnect( )
• public void disconnect( )
• public int getPort( )
• public InetAddress getInetAddress( )
• public 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

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Multicast
30
Broadcast Routing

• Deliver packets from srce to all other nodes
• Source duplication is inefficient

• Source duplication how does source determine
  recipient addresses

31
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
  hasnt 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

32
Spanning Tree

• First construct a spanning tree
• Nodes forward copies only along spanning tree

33
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

3
4
2
5
1

• Stepwise construction of spanning tree

(b) Constructed spanning tree
34
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

35
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)

36
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

Shared tree
37
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
38
Shortest Path Tree

• mcast forwarding tree tree of shortest path
  routes from source to all receivers
• Dijkstras algorithm

S source
LEGEND
R1
R4
router with attached group member
R2
router with no attached group member
R5
link used for forwarding, i indicates order
link added by algorithm
R3
R7
R6
39
Reverse Path Forwarding

• rely on routers 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

40
Reverse Path Forwarding example
S source
LEGEND
R1
R4
router with attached group member
R2
router with no attached group member
R5
datagram will be forwarded
R3
R7
R6
datagram will not be forwarded

• result is a source-specific reverse SPT
• may be a bad choice with asymmetric links

41
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
router with no attached group member
R2
P
P
R5
prune message
links with multicast forwarding
P
R3
R7
R6
42
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

43
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

44
Center-based trees an example
Suppose R6 chosen as center
LEGEND
R1
router with attached group member
R4
3
router with no attached group member
R2
2
1
R5
path order in which join messages generated
R3
1
R7
R6
45
Internet Multicasting Routing DVMRP

• DVMRP distance vector multicast routing
  protocol, RFC1075
• flood and prune reverse path forwarding,
  source-based tree
• RPF tree based on DVMRPs 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

46
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

47
Tunneling

• Q How to connect islands of multicast routers
  in a sea of unicast routers?

logical topology
physical 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

48
PIM Protocol Independent Multicast

• not dependent on any specific underlying unicast
  routing algorithm (works with all)
• two different multicast distribution scenarios

• Dense
• group members densely packed, in close
  proximity.
• bandwidth more plentiful

• Sparse
• networks with group members small wrt
  interconnected networks
• group members widely dispersed
• bandwidth not plentiful

49
Consequences of Sparse-Dense Dichotomy

• Dense
• group membership by routers assumed until routers
  explicitly prune
• data-driven construction on mcast tree (e.g.,
  RPF)
• bandwidth and non-group-router processing
  profligate

• Sparse
• no membership until routers explicitly join
• receiver- driven construction of mcast tree
  (e.g., center-based)
• bandwidth and non-group-router processing
  conservative

50
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

51
PIM - Sparse Mode

• center-based approach
• router sends join msg to rendezvous point (RP)
• intermediate routers update state and forward
  join
• after joining via RP, router can switch to
  source-specific tree
• increased performance less concentration,
  shorter paths

R1
R4
join
R2
join
R5
join
R3
R7
R6
all data multicast from rendezvous point
rendezvous point
52
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!

R1
R4
join
R2
join
R5
join
R3
R7
R6
all data multicast from rendezvous point
rendezvous point
53
Multicast

• Géré par les routeurs
• Pas de garantie
• Importance du ttl
• (Évaluation)
• Local0
• Sous-réseau local1
• Pays48
• Continent64
• Le monde255

54
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

55
Sockets multicast

• Extension de DatagramSocket
• public class MulticastSocket extends
  DatagramSocket
• Principe
• Créer une MulticastSocket
• Rejoindre un group joinGroup()
• Créer DatagramPacket
• Receive()
• leaveGroup()
• Close()

56
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
  )

57
Création

• try
• MulticastSocket ms new MulticastSocket(null)
• ms.setReuseAddress(false)
• SocketAddress address new InetSocketAddress(4
  000)
• ms.bind(address)
• // receive datagrams...
• catch (SocketException ex) System.err.println(
  ex)

58
Rejoindre

• try
• MulticastSocket ms new MulticastSocket(4000)
• InetAddress ia InetAddress.getByName("224.2.2.2
  ") ms.joinGroup(ia)
• byte buffer new byte8192
• 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)
  

59
send

• try
• InetAddress ia InetAddress.getByName("experime
  nt.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)