19.1 Java4620: general information  (Page 3/8)

• IP
• TCP
• UDP

IP

IP , which stands for Internet Protocol , is the protocol that will be involved below the Application Layer to move our data between a client and a server. Beyond knowing that it exists, we probably don't need toconcern ourselves with the fact that IP is being used

In fact, in some situations, some other protocol could be used to move our data between a client and a server. As long as it works, we really don't care toomuch.

In a nutshell, IP is a network protocol that moves packets of data from a source to a destination. As the name implies, this is the protocol normally usedon the Internet.

TCP

It is sometimes important to be able to have confidence that all packets that make up a message arrive at the destination undamaged and in proper order.

The Transmission Control Protocol ( TCP ) was added to IP to give each end of a connection the ability to acknowledge receipt of IP packets and to request retransmission of corrupted or lost packets. Also TCP makes it possible to put the packets back together at the destination in the same order that they were sent.

Therefore, you will often hear people using both acronyms in the same breath, as in TCP/IP . The two work together to provide a reliable method of encapsulating a message into data packets, sending the packets to adestination, and reconstructing the message from the packets at the destination.

UDP

Sometimes it may not be critically important that all the packets arrive at the destination or that they arrive in the proper order. Further, sometimes, you maynot want to incur the time delays and overhead cost associated with those guarantees.

For example, if one computer is sending date and time information to another computer every 100 milliseconds, and the data in the packets is displayed on adigital clock as it is received, you might prefer that each packet make the trip as quickly as possible even if that means that occasionally a packet will belost or damaged.

The User Datagram Protocol ( UDP) is available to support this type of operation. UDP is often referred to as an unreliable protocol because there is no guarantee that a series of packets will arrive inthe right order, or that they will arrive at all.

As Java programmers, we have the choice of TCP or UDP , and we need to know enough about the characteristics of each to be able to makeinformed choices between them.

IP Addresses

We don't really need to know very much about IP to be able to use it, but we do need to know about the addressing scheme used in IP .

Every computer attached to an IP network has a unique address, typically consisting of four bytes or 32 bits ( IPv4 ) .

Thirty-two bits are sufficient to define a large number of unique addresses, but the manner in which addresses are allocated is wasteful, and many of theaddresses that have been allocated are not being used.

Efforts are underway to expand the number of possible unique addresses to a much larger number. The planned number is the number of unique addresses thatcan be represented with a 128-bit address. The new scheme is known as IPv6 .