Joseph Faber Wonderful Talking Machine (1845)

Transcription

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2 Joseph Faber Wonderful Talking Machine (1845)

3 Connected World Human-to-Human communication Human-Machine interaction Machine-to-Machine communication (M2M) Internet-of-Things (IOT)

4 Internet of Things

5 How Do Machines Communicate? 1. Internet Elements 2. Client-Server Model 3. Sockets in Java

6 1. Internet Elements TCP/IP Protocol Stack Types of Communication TCP and UDP Protocol

7 Internet structure The Internet is all about connecting machines together

8 TCP/IP Protocol Stack Advantages Modularity Protocols easier to manage and maintain Abstract functionality Lower layers can be changed without affecting the upper layers Reusability Upper layers can reuse the functionality provided by lower layers Disadvantages Information hiding inefficient implementations Application (HTTP, FTP, telnet, ) ) Transport ( TCP, UDP,... ) Network ( IP, ) Data Link Physical

9 TCP/IP Protocol Stack 5. Application HTTP Message 4. Transport HTTP Message TCP Hdr TCP segment 3. Network HTTP Message TCP Hdr IP Hdr IP packet DL HTTP TCP IP DL 2. Data Link frame Trlr Message Hdr Hdr Hdr 1. Physical Converts bits of frame into signals

10 TCP/IP Protocol Stack 5. Application HTTP Message 4. Transport HTTP Message UDP Hdr datagram 3. Network HTTP Message UDP Hdr IP Hdr IP packet DL HTTP UDP IP DL 2. Data Link frame Trlr Message Hdr Hdr Hdr 1. Physical Converts bits of frame into signals

11 What Does a Router Do? A B 5 R1 R

12 Interprocess Communication Interprocess communication (IPC) is the backbone of distributed computing Process = runtime representation of a program IPC refers to the ability of two processes to communicate P1 Sender data P2 Receiver Protocol = set of rules that must be respected during communication

13 Types of Communication Unicast data is sent from one process to another single process Multicast data is sent from one process to more than one process at the same time Broadcast data is sent from one process to every node in the network P2 P2 P3 P4 m m m m P1 P1

14 Types of Communication Multicast is not multiple unicasts Packet duplicated Multiple Unicasts Multicast

15 Types of Communication Applications Unicast HTTP, FTP, telnet Multicast Networked TV channels Multi-users network games Broadcast ARP protocol

16 TCP and UDP Protocol TCP Connection-oriented protocol Provides reliable flow of data order delivery Applications: HTTP and FTP UDP Protocol that sends independent packets of data (datagrams) No guarantee about arrival and sequencing Applications: multimedia streaming, VoIP

17 TCP and UDP Protocol TCP and UDP use the ports to map incoming data to a particular running process Ports are divided in three ranges: Well-known ports used by major applications HTTP=80, SMTP=25 Registered ports for any application Dynamic/private ports used by clients app app app port port port TCP or UDP data port# IP packet or datagram 5 4

18 Network Architectures Client-Server P2P

19 P2P Model Direct communication between the nodes of the network Nodes are dynamically connected for traffic routing processing bandwidth-intensive tasks Advantages Scalability Low cost Applications Kazaa, Napster (file sharing) Skype (the name was derived from sky and peer)

20 2. Client-Server Model Client and Server Sockets Types of Servers

21 Client and Server Standard model for developing network applications Notion of client and server A server is a process that offers some service A client is a process that requests a service Server and client typically run on different machines Server waits for requests from clients Client Server Client Client

22 Client and Server Server process Starts Initializes itself Goes to sleep waiting for a client request Server port Possibly, client process Starts Server port Client How to connect them?

23 Establishing a connection Before start of communication, a connection has to be established between the two machines (hosts) Five components in a connection - Protocol used (TCP, UDP) - Source IP address - Source port number - Destination IP address - Destination port number

24 Sockets A socket is an endpoint of the connection between two hosts Exists on both sides of the connection Identified by protocol used, IP address and port number Protocol Source IP address Source port number Protocol Destination IP address Destination port number On top of Transport layer Application Socket Transport Network Data Link Physical

25 Client and Server A client makes a connection request to the server Server port Connection request Client Session established with dynamic ports used for two ways communication Server port port Client port Connection

26 Types of Sockets Stream Sockets Connection oriented Rely on TCP to provide reliable two-way connected communication Applications: HTTP, FTP (file transfer) Datagram Sockets Rely on UDP Connection is unreliable Applications: multimedia streaming, game protocols, VoIP

27 Types of Sockets Push technology In several application there is a need for the server to send data to the client when new data is available (push) Long polling Create illusion of a server initiated connection Client opens an HTTP connection to the server which keeps it open until sending a response Widely used nowdays Overhead of HTTP, not suited for low latency (time delay) applications: see online games with realtime component

28 Types of Sockets WebSockets Bringing sockets to the Web Single TCP socket connection established between the client and server Allows for bi-directional, full duplex, messages to be instantly distributed Little overhead resulting in a low latency connection Becoming a cross platform standard for realtime communication between client and server Not only Web browsers technology

29 Types of Servers Iterative Servers Used when the server knows in advance how long it will take to handle each request Time to provide the client request is not too large (within a reasonable time limit) Single copy of the server runs A client must wait if the server is busy Concurrent Servers Used when the amount of work required to handle a request is unknown or large The server starts a new process to handle each request As many copies of the server as there are clients All the copies run concurrently

30 3. Sockets in Java Stream Sockets Iterative Server Concurrent Server Datagram Sockets Multicast Communication

31 Java Sockets Part of the java.net.* package Provides two classes of sockets for TCP Socket (client side) ServerSocket (server side) Provides one socket type for UDP DatagramSocket

32 Stream Sockets C Socket connect write read S ServerSocket bind listen accept read write ServerSocket performs functions: bind, fix to a certain port number listen, wait for incoming requests on the port Socket performs function: connect (begins TCP session) close

33 Iterative Server ISAServer.java and ISAClient.java Based on TCP protocol connection-oriented transfer Provides reliable, bidirectional, point-to-point, stream based connection between two hosts C:\> javac ISAServer.java C:\> java ISAServer C:\> javac ISAClient.java C:\> java ISAClient > abc You sent this to server: ABC

34 Concurrent Server Can handle multiple client requests at the same time Implemented via Java threads - Everytime a client establish a connection with the server, the accept call will return - At this time a new thread is created to handle the client connection - The main thread will go back and wait for the next connection

35 Concurrent Server summationserver.java and summationclient.java Run the server and then two clients The second client will terminate before first client C:\> javac summationserver.java C:\> java summationserver 3400 C:\> javac summationclient.java C:\> java summationclient localhost sum = 666 Time consumed for receiving the feedback from the server: 7414 milliseconds C:\> javac summationclient.java C:\> java summationclient localhost sum = 15 Time consumed for receiving the feedback from the server: 1033 milliseconds

36 Datagram Sockets Java also supports connectionless transfers using datagrams Based on UDP protocol Used in situations where optimal performance is required Java implements datagrams on top of the UDP protocol using two classes: DatagramPacket acts as the data container to prepare the UDP packets that have to be sent DatagramSocket used for sending and receiving datagrams

37 Datagram Sockets Datagram packets are created by using one of the constructors DatagramPacket(byte buf[],int size) DatagramPacket(byte buf[],int size,inetaddr addr,int port) The first form is used to receive data The second form is used to send data

38 Datagram Sockets C S ServerSocket Socket bind bind write read close read write close

39 Datagram Sockets datagramreceiversender.java and datagramsenderreceiver.java Start first datagramreceiversender C:\> javac datagramreceiversender.java C:\> java datagramreceiversender 3400 aaa bbb C:\> javac datagramsenderreceiver.java C:\> java datagramsenderreceiver localhost 3400 bbb aaa

40 Multicast Communication multicastsender.java and multicastreceiver.java Start a couple of multicast receivers in separate command windows C:\> javac multicastreceiver.java C:\> java multicastreceiver -->/ Hello How are you? C:\> java multicastreceiver -->/ Hello How are you? C:\> javac multicastsender.java C:\> java multicastsender