The Internet and Java Sockets ICW Lecture 5 Tom Chothia

Reminder of Last Time: Encryption can be public key or symmetric. Use a Cipher Object in Java to encrypt and decrypt. Keep your keys in a KeyStore

This Time: How the Internet works. –Some History –TCP/IP –DNS How to make socket connections between computers using Java. How to send Strings and Objects.

Before the Internet Life was solitary, poor, nasty, brutish and short. Computer Networks: –local networks, –telephone line connections, –leased line.

The Start 1969 The US Defense Advanced Research Projects Agency (then ARPA now DARPA) gives research grants to universities to buy computers. The decide to link their computers. But how?

The Problem With Leased Lines A BD C

A BD C

If A and D use the line, then C and B can't A BD C

But if everyone just sends a small packet of data, they can both use the line at the same. A BD C

The Internet Protocol Packet

IP Addresses Every computer has an IP address. e.g Every router on the Internet keeps a list of which connection it should use for which addresses.

Transmission Control Protocol 1974: daily traffic more than 3 million packets a day. Many are getting lost. TCP is a protocol than runs on top on IP, if an IP packet gets lost. It requests that it is resent. TCP/IP becomes allows Inter network connections. So in 1977:

The ARPAnet 1969 the birth of the ARPAnet the ARPAnet becomes a Inter-network first Spam message send. Admin assures users this will never happen again

The Internet 1982 :-) 1983 TCP/IP becomes standard. By 1990 most of Europe, India and South Africa have joined.

Domain Name Servers (DNS) Remembering IP address is to hard. So people associate names with addresses. e.g. news.bbc.com → A hierarchy of servers list handle requests The route for most of Europe is RIPE based in Amsterdam.

The Internet 1988 The Morris Worm, CERT formed The Web: HTTP and HTML The first ISPs and Mosaic the first web browser Yahoo

Today All computers on the Internet have an IP address. Key Internet Protocols: TCP/IP DNS to turn names into numbers.

The Internet Protocol Stack Application Transport Network Link/Hardware Internet communication uses a stack of protocols. Each protocol uses the protocol below it to sent data.

Using the Stack to Send Data Application Transport Network Link/Hardware Application Transport Network Link/Hardware Data H T (Data) H N (H T (Da) H N (H T (ta)) H L H N (H T (Da), H L H N (H T (ta)) Computer 2Computer 1 H N (H T (Da) Data H T (Data) H L H N (H T (Da) ),H L H N (H T (ta)) H T (Da) Lost

The Stack, Most of the Time: Stuff that you write TCP or UDP IP Ethernet or Application Transport Network Link/Hardware

Sockets A computer is Identified by an IP address. To allow multiple connections each computer has a port number. WWW runs on port 80, ssh on port 22, dns on 53, (free wifi). A simple connection between two computers is called a socket. Sockets are uniquely identified by (IP sender, port sender,IP receiver,port receiver).

Our View of the Stack in Java Application Java Program Sockets

Sockets in Java Use java.io.Socket to make a socket that connects to a remote computer. Use java.io.ServerSocket to make a socket that listens for an incoming connection. Sockets just give bytes, so then need a wrapper.

Code Demo Simple socket connections

Multi-Threaded Servers To receive multiple connections you can use threads. See demo. More on Threads in Lecture 11.

Sending an Object Java lets you send an object over a socket. The Object must be Serializable and have a UID (see demo). Use the ObjectStream wrapper to send Objects.

Conclusion The Internet uses a packet based routing system IP. Sockets are an easy way to connect between machines. Use the Socket and ServerSocket Class. Use a wrapper for the socket for different data types.

Next Time: All the data send was total insecure. Next lecture I will show you how how to make encrypted sockets, how to know who your talking to. i.e. what exactly does the little padlock main in my web browser?