Networking and TCP/IP

Networking Basics

• Networking revolutions date back 90 years
• Explosion of the internet required standards and architecture interconnection.
• A Java contradiction is that it strived for universality but ended up controlled by Sun Microsystems.
• Java became a language for distributed environments.

Starting Networking

• Network interoperability involves overcoming hardware, software, and resource diversity challenges.
• Machines with different characteristics can communicate using a common protocol.
• Protocols are indispensable elements for making computer networks viable.

TCP/IP as Universal Language

• TCP/IP protocol facilitates computer communication
• Transmission Control Protocol/Internet Protocol has linked different computers from the internet's inception.
• TCP/IP is functionally simple, making it implementable across systems for wide use.
• Key TCP/IP applications: SMTP, FTP, and HTTP.

TCP/IP Communication Model

• TCP/IP communications permutes packets on a line, unlike phone calls holding a channel.
• When an application transmits, its data splits into packets labeled with control information, creating datagrams, then frames for the network.
• Point-to-point communication utilizes dynamic addressing to uniquely identify and differentiate computers by IP address.

IP Addresses Explained

• An IP address is a 32-bit string with four octets, for example: 11001000 00010011 10111111 00100011
• The equivalent decimal form of the IP address is: 200 019 191 035
• Possible IP address range is 0.0.0.0 to 255.255.255.255, totaling 4,294,967,296 (256^4) addresses.
• IP addresses adhere to a class rule (A, B, C) that organizes communication and routing between networks and subnets.
• Dynamic IP addresses are generated in network connections within Internet Service Providers
• This is in addition to fixed addresses

Basic TCP/IP Communication Steps

• Computer A sends a message, packages it, and converts it into a datagram and a frame
• The Bus transfers the message between Computer A through Router 1 and Router 2 to Computer B
• Computer B converts the packaged components back into Computer B message for the Application

Ports and Multi-Programming Support

• Current systems support multi-programming, enabling communication not just between computers but between applications.
• Logical entity called a communication port identifies each application.
• Ports shouldn't be confused with physical ports used on PCs.
• Ports are identified by 16-bit numbers ranging up to 65535.
• Port 0111 (or 7) is a example port, which is used for echo messages.

Ports in Networking

• Ports are plentiful, but certain points should be noted.
• Ports below 1024 are reserved
• Other ports may be used for other services.
• In Windows, any user can use any port without any privileges;
• Some services default to certain ports
• Echo (Message) uses Port 7
• FTP (File transfer) uses Port 21
• Telnet (remote connection) uses Port 23
• SMTP (email) uses Port 25
• HTTP (web service) uses Port 80
• POP3 (post office) uses Port 110
• RMI (Remote Method Invocation) uses Port 1099

Communication Identification Via IP and Ports

• IP's and ports are used to enable communication identification
• DNS convert IPs into hostnames and vice versa.
• Accessing a website internally communicates its IP and web service port
• For Google, it's 172.217.13.196:80.

Web Standards

• Originated at CERN in 1989, aiming for distributed information among researchers using hypermedia/hypertext.
• The Web, since 1993, exploded due to combining simplicity with versatility.
• Web is based on three standards: HTTP, HTML, and URL.

HTTP Protocol Details

• HTTP defines communication between server and client
• HTTP uses MIME to differentiate and transfer via 7-bit ASCII
• HTTP is a stateless protocol, ensuring no client-server permanence
• Connection process: server waits, client connects via port 80, server replies, and client closes connection.

HTML

• HTML is derived from SGML, created in 1970, for design meaning.
• HTML is based on TAG declarations for displaying information.
• HTML's TAGs can be nested, but must be correctly closed.
• HTML has continuously evolved from text binding to embedding images, tables, and equations.

URLs

• URL, a standard, defines resource locations
• files, email addresses, and CGI programs
• Uniform Resource Identifier, URI, can be: URL and URN
• URL points to resources, a ‘link’
• URN points resources, without reference location

Additional URL Information

• URL structure: ://[:port]//[#
  ]
• Protocol examples: file for files, http for web server, FTP and Telnet
• Host identification can be via IP or DNS
• Default Port: 80, HTTP service
• Path includes path (absolute/relative)
• Web servers often ‘mask’ the path
• Section identifies link points in the file

Java and Networking

• Java enables networking facilities
• The "java.net" package is for classes used in distributed applications
• InetAddress Class handles IP addresses
• URL Class is for Uniform Resource Locators Interface
• Sockets allow system connection for reading/writing data, primarily used on clients;
• The ServerSocket Class manages interfaces server connections
• The DatagramSocket Class is for configuring UDP.

Working with Java Addresses

• The first function that is conducted to use Java networking applications is identifying an address on a given network.
• The class represents an internet address and hosts two fields, including the hostname and IP address.

Addresses in Java Cont.

• A comparison between two hosts is conducted to see if they belong to the same IP.

DNS Lookups and Java

• Java can look up Unix "nslookup" command, used with IP addresses and hostnames.

URL Operations with Java

• Java obtains information easily with URLs
• "java.net.*" URLs follow protocol, host, port, file, and ref (anchor) standards.

Interacting with components from URLs

• Java can display components from any given URL

Reading URLs with Java

• URLs can be loaded in three ways in Java
• URLConnection
• InputStream inputs
• ContentHandler commands

Downloading Pages with a Java URL Cont.

• A code is provided to show the ability for Java to download any given page through the code.

Notes on Downloading with a Java URL

• Data will be pulled and changed to a more readable and accessible format.
• However, specific forms of code cannot be included from a browser for text use.

Error Approaches

• When faced with the possibility of error, options include a retry limit of 3, waiting with default values, raising exceptions, or finding default solution.

Programming with Binary

• Programmed by preparing and sending (1st step) then receiving and checking (2nd step)

Protocols and Communication

• Options include row data text communication, and binary.

Game Architecture and Protocol

• Diagram shown for a server/client game communication including sequence, lists, and connectivity
• Lab testing and examples provided