Construction d Applications Réparties / Master MIAGE

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1 Construction d Applications Réparties / Master MIAGE Networking Giuseppe Lipari CRiSTAL, Université de Lille January 26, 2016

2 Outline Introduction Networking Transport Protocols TCP and UDP Addressing Java Implementation TCP UDP Multicast IP

3 Outline Introduction Networking Transport Protocols TCP and UDP Addressing Java Implementation TCP UDP Multicast IP

4 Introduction Distributed Programming = Programming + Networking Software programs run in different nodes They communicate each other exchanging messages Protocol = Rules that dictate how to communicate Format of message Possible (legal) sequences of messages What to do in case of errors etc. Without a protocol, it is impossible to understand each other

5 ISO-OSI Model Network stack: the ISO-OSI model

6 Examples of protocols Application: HTPP, SMTP, FTP Internet level communication Transport: TCP, UDP end-to-end communication Network: IP routing between different LANs Link: Ethernet, IEEE communication within a LAN also called MAC protocol Physical: bits on the cable

7 Communication Protocol Set of formal rules for exchanging data messages between two or more parties Syntax: content and format of messages Semantic: what a message means Synchronization: order of messages requests and responses Protocols are defined in technical standards RFC: (Request for comments) Set of documents that describe the technical aspects of Internet protocols, published by IETF (Internet Engineering Task Force) Some of them became standards

8 Connection and packets Connection-oriented protocol e.g. TCP Establish a "connection" between sender and receiver, then send data flow-oriented Connection-less protocol e.g. UDP just send the data in packets without opening a connection before packet oriented

9 State Stateless protocol Each request is an independent transaction that is unrelated to any previous one the communication consists of independent pairs of request and response. Examples: IP, HTTP The server does not need to store state about the client Stateful protocol Each request depends on the previous one the server needs to maintain the state of the client to understand future requests Examples: TCP, FTP

10 Outline Introduction Networking Transport Protocols TCP and UDP Addressing Java Implementation TCP UDP Multicast IP

11 TCP Objective: safe and reliable transfer of data Connection Oriented initial handshaking for establishing the connection receiver sends acknowledgement of receipt if some packet is lost, it is retransmitted even if packets arrive in the wrong order, they are re-ordered by the receiver flow control: adjusts sending speed to receiving speed and to traffic congestion Advantages: reliable Disadvantages: not adequate for real-time communication (because of retransmission)

12 Example: Connection with TCP 3-way handshake to establish a connection Server is always listening (function listen()) on a port client connects (function connect() sends packet SYN) server responds with an SYN-ACK, but continues to wait when client receives the SYN-ACK, sends the ACK and continues with next instruction after connect() when the server receives the ACK unblocks from the listen() and finally establishes the connection.

13 UDP Objective: fast and efficient transmission of packets Connection-less No need to contact the other party before starting the communication Packets can be lost and are not re-transmitted (unreliable) Packets can arrive in out-of-order late packets can be discarded safely No flow control, no congestion control Advantages: fast, useful for soft real-time data Disadvantages: unreliable

14 IPv4 address 32 bits, grouped into 4 bytes example: In the past, addresses were classified into 4 classes, depending on the first leading bits this method was not scalable and it is now considered obsolete After 1993, IETF introduced the classless inter-domain routing network masks can have an arbitrary number of bits Two parts: MSB: network address LSB: host identifier Notation: /24 it means: network address is the first 24 bits of the remaining bits are used for host address

15 IPv6 address 128 bits, 8 groups of four hexadecimal digits example: 2001:0db8:85a3:0042:1000:8a2e:0370: bits for network subnet mask, 64 bits for the host Advantages wrt IPv4 A much large addressing space security embedded in the protocol stateless autconfig easier mobility etc. Slow adoption Not interoperable with IPv4 As of June 2014, the percentage of users reaching Google services with IPv6 surpassed 4% for the first time

16 IP address and port number Each network card has its own IP If a PC has two network interfaces, it has 2 IP addresses E.g. Ethernet and WiFi How to address one specific application in a host? there could be several running process, each one wants to communicate TCP and UDP both use a port to indicate the service application a 16bit number

17 Port ranges Well-known ports (0 1024) assigned by IANA (Internet Assigned Numbers Authority) to well-known internet services examples: FTP (20), HTTP (80), SSH (22), SMTP (25), etc. you shouldn t use them Registered ports ( ) still assigned by IANA, but not always official examples: OpenVPN (1194), Kazaa (1214), MySQL (3306), etc. you can use them, but of course at your own risk Ephemeral ports ( ) dynamically assigned by the OS, cannot rely on them

18 Client/Server model Two-party communication One party acts as a server, it provides a service to the other parties The others act as clients that request the service provided by the server

19 Client/Server communication 1. The server is listening for new requests 2. The client sends a request to the server 3. The server receives the request as well as the address of the client 4. The server processes the request 5. The server sends back the response to the client 6. return to 1. In connection-oriented communication (TCP), step 2 is used to establish a connection between the client and the server The connection remains valid until step 5 If the client needs to ask many different services, the connection can remain active

20 Synchronization Send synchronous: the sender blocks waiting for the message to arrive at the destination before continuing execution asynchronous: after sending the message, the sender continues execution without blocking Receive synchronous: the receiver blocks waiting for a message to arrive before it can continue executing asynchronous: if the message did not arrived yet, the receive returns an error, and processing continues Typical configuration: asynchronous send and synchronous receive.

21 Outline Introduction Networking Transport Protocols TCP and UDP Addressing Java Implementation TCP UDP Multicast IP

22 Address representation Addresses are represented by interface InetAddress Examples InetAddress host = InetAddress.getLocalHost(); InetAddress host = InetAddress.getByName(" InetAddress host[] = InetAddress.getAllByName("

23 Sockets A socket is the basic entity for sending/receiving messages at the OS level It was proposed as part of the UNIX interface, now available in all OS Almost all languages provide an interface to the OS socket layer Two types of sockets: passive socket is used by the server to wait for incoming connections from clients when a connection request arrives and the 3-way handshake is completed, two active sockets are created, one on the server, the other on the client both client and server use the active sockets to exchange data

24 Sequence of messages

25 Java TCP Server code A simple server that accepts a string, and returns the same string capitalized ServerSocket ps = null; try { ps = new ServerSocket(4000); while (true) { Socket as = ps.accept(); System.out.println("Connection established"); BufferedReader in = new BufferedReader( new InputStreamReader(as.getInputStream())); DataOutputStream out = new DataOutputStream(as.getOutputStream()); String msg = in.readline(); System.out.println("Message received: " + msg); String resp = msg.touppercase() + \n ; out.writebytes(resp); System.out.println("Response has been sent."); } } catch (IOException ex) { System.exit(-1); }

26 Java TCP Client code The corresponding client Socket as = null; try { as = new Socket(InetAddress.getLocalHost(), 4000); System.out.println("Client: Connection established"); DataOutputStream out = new DataOutputStream(as.getOutputStream()); BufferedReader in = new BufferedReader( new InputStreamReader(as.getInputStream())); String sentence = "Vive la France!\n"; out.writebytes(sentence); System.out.println("Message sent"); String response = in.readline(); System.out.println("Message received: " + response); as.close(); } catch (UnknownHostException ex) { System.exit(-1); } catch (IOException ex) { System.exit(-1); }

27 TCP Server code The ServerSocket constructor requires a port this is a public information that must be given to the clients to allow them to contact the server Cannot read/write from/to a ServerSocket, only accept() new connection the accept() blocks the server until a new request for connection arrives Upon creation of a connection, a new active socket is created and the server can use it to receive/send data from/to the client readline() blocks the server if there is not enough data to read pay attention to the new-line character! The active socket has: the IP address of the host where the server is running an ephemeral port chosen by the OS

28 TCP Client code The client creates an active socket by calling connect() this function requires an IP address and a port It blocks the client until the connection is established The active socket has: the IP address of the host where the client is running an ephemeral port chosen by the OS There is a timeout: if the connection is not established before the timeout expires, the connect() raises an UnknownHostException The readline() blocks the client until a response has been received from the server it reads until a new-line is found, and then returns the string. pay attention to always terminate the messages with a new-line character!

29 Relationship between the two sockets A.getInetAddress() == B.getLocalInetAddress() A.getPort() == B.getLocalPort() A.getLocalInetAddress() == B.getInetAddress() A.getLocalPort() == B.getPort()

30 UDP It is a much simpler protocol no need to open a connection however, you still need to open a socket the client just sends one or more packets (datagrams) the server just waits for packets and replies

31 Java UDP Server code int myport = 4500; int cport; DatagramSocket ss = new DatagramSocket(myport); byte [] rdata = new byte[1024]; byte [] sdata; while(true) { DatagramPacket dp = new DatagramPacket(rData, rdata.length); ss.receive(dp); System.out.println("recv"); InetAddress caddr = dp.getaddress(); cport = dp.getport(); String s = new String(dp.getData()); String r = s.touppercase(); sdata = r.getbytes(); DatagramPacket rp = new DatagramPacket(sData, sdata.length,caddr,cport); ss.send(rp); System.out.println("sent"); }

32 Java UCP Client code DatagramSocket cs = new DatagramSocket(); InetAddress saddr = InetAddress.getByName("localhost"); int port = 4500; String sentence = "Construction d Applications Reparties"; byte[] sdata = sentence.getbytes(); DatagramPacket dp = new DatagramPacket(sData, sdata.length, saddr, port); cs.send(dp); System.out.println("Datagram sent"); byte[] rdata = new byte[1024]; DatagramPacket rp = new DatagramPacket(rData, rdata.length); cs.receive(rp); String response = new String(rp.getData()); System.out.println("Response: " + response);

33 Comments Packet Oriented communication there is no need for new lines to terminate the message communication happens with packets The socket is only for sending out packets, it sets the sender ports Destination address (IP+port) must be specified in each datagram

34 Customisation There are various way to customise the behaviour of sockets it depends on the objective, but also on the usage Modification of transmitted/received data it is possible to filter input/output data with appropriate streaming classes Filtering socket streams in = s.getinputstream(); out = s.getoutputstream(); zin = new GZIPInputStream(in); zout = new GZIPOutputStream(out); now we use zin and zout for reading/writing

35 Factory The second method consists in defining a class that creates sockets according to the desired parameters You can specify this class in the socket interface for creation call the method static Socket.setSocketFactory(SocketImplFactory) specify an object of a class that implements SocketImplFactory: interface SocketImplFactory { SocketImpl createsocket(); } You need to call this function only once in the program (during initialization) You can do the same with ServerSocket.

36 Subclassing The third method consists in subclassing the class Socket and ServerSocket you can redefine accept(), getinputstream(), etc... Advantages: more general and hence more powerful Disadvantages: you are changing the interface, so be careful when passing this object to existing code

37 Multicast Used to send messages to a (large) group of destinations the sender sends a message on a special address the message is received by all recipients that are listening on that address more than one emitter can send messages on the same special address the recipients can join/leave the group at all times The addresses must belong to class D ( ) these addresses are independent from the physical location of the senders/receivers It has the same properties as UDP message oriented no flow control it is possible to lose packets, etc...

38 Multicast Applications Massive on-line games streaming of popular video programs (soccer matches, etc. ) Interesting properties: the service location is independent of the address possibility of having multiple instances of the same service for fault-tolerance, or for load balancing Some class of multicast address has already been assigned see multicast-addresses/multicast-addresses.xhtml

39 Multicast Java API java.net.multicastsocket Constructor MulticastSocket(port) Open a socket on a certain port MulticastSocket() Open a socket on a ephemeral p. Sending send(datagrampacket) sending a packet Receiving receive(datagrampacket) receiving groups joingroup(inetaddress) join a group on a MCast addr. leavegroup(inetaddress) leave the group Control settimetolive(int) 0 (none, the packet is not sent) diffusion 1 (subnet) 128 (world) 1 1 Routers often block multicast packets after a certain number of hops (ignoring the TTL)

Outline of Topics. UDP Socket Java Programming. Multicast in Java. Real-time protocol (RTP) XMPP and Jingle protocols. Java I/O and New IO (NIO)

Outline of Topics. UDP Socket Java Programming. Multicast in Java. Real-time protocol (RTP) XMPP and Jingle protocols. Java I/O and New IO (NIO) Outline Outline of Topics UDP Socket Java Programming Multicast in Java Real-time protocol (RTP) XMPP and Jingle protocols Java I/O and New IO (NIO) UDP Socket Java Programming User Datagram Protocol (UDP)