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Data Communication & Networks
G22.2262-001
Session 10 - Main Theme
Java Sockets
Dr. Jean-Claude Franchitti
New York University
Computer Science Department
Courant Institute of Mathematical Sciences
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Java Sockets and Socket Programming with TCP, Lecture notes of Data Communication Systems and Computer Networks
The use of Java sockets and socket programming with TCP in data communication and networks. The document covers topics such as internet transport-layer protocols, multiplexing/demultiplexing, and connection-oriented demux. It also explains how demultiplexing works and provides examples of socket programming with TCP. likely to be useful as study notes or lecture notes for university courses related to computer science, networking, or data communication. It could be associated with the typology of lecture notes and is most likely to belong to a course on computer networks or data communication. The document could be useful for both university and high school students as well as lifelong learners. The document succeeded in providing meaningful information about the title, description, related university topics, correlated university topics, rate, typology, academic course, academic year, user type, and succeeded fields.
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2021/2022
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Data Communication & Networks
G22.2262-
Session 10 - Main Theme
Java Sockets
Dr. Jean-Claude Franchitti
New York University
Computer Science Department
Courant Institute of Mathematical Sciences
Agenda
Internet Transport-Layer Protocols
Multiplexing / Demultiplexing
Socket Programming
Internet Transport-Layer Protocols
- Reliable, in-order
delivery TCP
- congestion control
- flow control
- connection setup
- Unreliable, unordered
delivery: UDP
- no-frills extension of “best-effort” IP
- Services not available:
- delay guarantees
- bandwidth guarantees
application transport data link^ network physical
application transport data link^ network physical
data link^ network physical
data link^ network physical
data link^ network physical
data link^ network data linknetwork physical physical
Part II
Multiplexing / Demultiplexing
How Demultiplexing Works
- Host receives IP datagrams
- each datagram has source IP address, destination IP address
- each datagram carries 1 transport-layer segment
- each segment has source, destination port number (recall: well-known port numbers for specific applications)
- Host uses IP addresses & port numbers to direct segment to appropriate socket
source port # dest port #
32 bits
application data (message)
other header fields
TCP/UDP segment format
Connectionless Demultiplexing
- Create sockets with
port numbers:
DatagramSocket mySocket1 = new DatagramSocket(99111) ; DatagramSocket mySocket2 = new DatagramSocket(99222) ;
- UDP socket identified by two-tuple:
(dest IP address, dest port number)
- When host receives UDP
segment:
- checks destination port number in segment
- directs UDP segment to socket with that port number
- IP datagrams with
different source IP
addresses and/or source
port numbers directed to
same socket
Connection-Oriented Demux
- TCP socket identified
by 4-tuple:
- source IP address
- source port number
- dest IP address
- dest port number
- recv host uses all four
values to direct
segment to appropriate
socket
- Server host may support
many simultaneous TCP
sockets:
- each socket identified by its own 4-tuple
- Web servers have different
sockets for each
connecting client
- non-persistent HTTP will have different socket for each request
Connection-Oriented Demux (cont.)
Client IP:B
P
client IP: A
P4 P2^ P
server IP: C
SP: 9157 DP: 80
SP: 9157 DP: 80
P5 P6^ P
D-IP:C
S-IP: A D-IP:C
S-IP: B
SP: 5775 DP: 80
D-IP:C
S-IP: B
13
Socket Programming
Socket API
- introduced in BSD4. UNIX, 1981
- explicitly created, used, released by apps
- client/server paradigm
- two types of transport service via socket API: - unreliable datagram - reliable, byte stream- oriented
Goal: learn how to build client/server application that communicate using sockets
a host-local, application-created, OS-controlled interface (a “door”) into which application process can both send and receive messages to/from another application process
socket
Socket Programming Using TCP
Socket: a door between application process and end-end-
transport protocol (UCP or TCP)
TCP service: reliable transfer of bytes from one process
to another
process
TCP with buffers, variables
socket
controlled by application developer controlled by operating system
host or server
process
TCP with buffers, variables
socket
controlled by application developer controlled by operating system
host or server
internet
Stream Jargon
- A stream is a sequence of
characters that flow into or
out of a process
- An input stream is attached
to some input source for
the process (e.g., keyboard
or socket)
- An output stream is
attached to an output
source (e.g., monitor or
socket)
Socket Programming With TCP
Example client-server app:
client reads line from standard input ( inFromUser stream) , sends to server via socket ( outToServer stream)
server reads line from socket
server converts line to uppercase, sends back to client
client reads, prints modified line from socket ( inFromServer stream)
outToServer
to network from network
inFromServer
inFromUser
keyboard monitor
Process
clientSocket
streaminput
streaminput
streamoutput
socketTCP
Client process
client TCP socket
Example: Java Client (TCP)
import java.io.; import java.net.; class TCPClient {
public static void main(String argv[]) throws Exception { String sentence; String modifiedSentence;
BufferedReader inFromUser = new BufferedReader(new InputStreamReader(System.in)); Socket clientSocket = new Socket("hostname", 6789);
DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());
Create input stream Create client socket, connect to server Create output stream attached to socket
Example: Java Client (TCP), cont.
BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream())); sentence = inFromUser.readLine(); outToServer.writeBytes(sentence + '\n'); modifiedSentence = inFromServer.readLine(); System.out.println("FROM SERVER: " + modifiedSentence);
clientSocket.close(); } }
Create input stream attached to socket
Send line to server Read line from server