Why sockets are used

These are rarely just byte-sized chunks, although they might be. The network chops that chunk up into packets, and each packet is routed separately over the network. At the other end, the receiver reassembles the packets together into a stream of bytes. The result is a bursty kind of data transmission — the data may already be there when you want to read them, or you may have to wait for them to arrive and be reassembled.

When data arrive, they go into a buffer , an array in memory that holds the data until you read it. You start the server running on port Seuss Did Technical Writing? The data going into or coming out of a socket is a stream of bytes. In Java, InputStream objects represent sources of data flowing into your program. OutputStream objects represent data sinks, places we can write data to.

With sockets, remember that the output of one process is the input of another process. Blocking means that a thread waits without doing further work until an event occurs. We can use this term to describe methods and method calls: if a method is a blocking method , then a call to that method can block , waiting until some event occurs before it returns to the caller.

If data or for write , space is already available in the buffer, the call might return very quickly. The operating system takes care of the details of delaying that thread until read or write can succeed. This statement has the form:. Notice how both ServerSocket. While the client-specific thread is working with that client perhaps blocked in a read or a write , another thread perhaps the main thread is blocked waiting to accept a new connection.

Unfortunately, their multithreaded Knock Knock Server implementation creates that new thread by subclassing Thread. Which of these is it necessary for a client to know in order to connect to and communicate with a server?

In the EchoClient example, which of these might block? And in EchoServer , which of these might block? Since BufferedReader. Now that we have our client and server connected up with sockets, what do they pass back and forth over those sockets? A protocol is a set of messages that can be exchanged by two communicating parties.

You can use a program called Telnet to check them out. You'll be using Telnet on the problem set, so try these out now. The GET command gets a web page. So for many web sites, you might need to speak HTTP 1. This time, your request must end with a blank line. HTTP version 1. You will also more than likely find that telnet does not exit after making this request — this time, the server keeps the connection open so you can make another request right away.

Simple Mail Transfer Protocol SMTP is the protocol for sending email different protocols are used for client programs that retrieve email from your inbox. Because the email system was designed in a time before spam, modern email communication is fraught with traps and heuristics designed to prevent abuse. But we can still try to speak SMTP. Recall that the well-known SMTP port is 25, and dmz-mailsec-scanner When designing a wire protocol, apply the same rules of thumb you use for designing the operations of an abstract data type:.

Keep the number of different messages small. The set of messages must be adequate for clients to make the requests they need to make and for servers to deliver the results. Related Articles. Table of Contents.

Save Article. Improve Article. Like Article. Recommended Articles. If delivery is impossible, the sender receives an error indicator. Data records do not have any boundaries. These sockets are normally datagram oriented, though their exact characteristics are dependent on the interface provided by the protocol. Raw sockets are not intended for the general user; they have been provided mainly for those interested in developing new communication protocols, or for gaining access to some of the more cryptic facilities of an existing protocol.

This interface is provided only as a part of the Network Systems NS socket abstraction, and is very important in most serious NS applications. Sequenced-packet sockets allow the user to manipulate the Sequence Packet Protocol SPP or Internet Datagram Protocol IDP headers on a packet or a group of packets, either by writing a prototype header along with whatever data is to be sent, or by specifying a default header to be used with all outgoing data, and allows the user to receive the headers on incoming packets.

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