IT427 Network Programming Seminar - Lecture 3, Oct. 26, 2000

ARP (Address Resolution Protocol)

ARP maps Internet addresses to physical addresses.
 

Problem:

given 2 machines A, B, connected to the same physical network.
Each has    IPAddress -- Ia, Ib
                   physical adderess -- Pa, Pb

Goal:

given machine A wants to send IP packet to address Ib, how does it determine which physical address Pb to use.

Solution:

ARP:

1) A sends request for Pb to P broadcast. ARP request

2) B replies with mapping: ARP reply

ARP Message format:

 
 
 

Client Server Model of Interaction Paradigm:
 
 
• Pattern of Interaction among cooperating application programs
• Basic building block for network communications on which distributed algorithms are built.

Server:
• program that offers a service that can be reached over a network
• accepts requests, performs its service, returns the result to the requester
Client:
• progran that sends a request to a server and waits for a response

If a computer's primory purpose is to support and run a particular server program, the term "server" is often applied to the computer as well. Ex: web server, file server,...

Server starts execution before interaction begins, continually accepts connections and sends responses without terminating. This is where the infinite loop is needed.
 

Protocol + Services:

 
 
 

Objects of interest:
 

• Internet Addresses

http://java.sun.com/products/jdk/1.1/docs/api/java.net.InetAddress.html
 
• Ports(sockets)    //separate port spaces for UDP and TCP

At any given time, a "connection" can be identified by:
 
• source address
• sourse port
• destination address
• destination port
• protocols
• Sockets: Communication endpoint or "heart of networked IPC." Sockets enable connectionless, best-effort communications: UDP or connection oriented service: TCP.

          http://java.sun.com/products/jdk/1.1/docs/api/java.net.Socket.html

• Server Sockets:

http://java.sun.com/products/jdk/1.1/docs/api/java.net.ServerSocket.html