7] NETWORKING 131
132 NETWORKING [CHAP. 7
insure reliable communication over the inherently unreliable IP network layer. The end-to-end (transport)
layer protocol performs this magic every day.
END-TO-END (TRANSPORT) LAYER PROTOCOL
The transport layer protocol of the internet is transmission control protocol (TCP). TCP uses the IP layer
to send messages through the internet, and TCP adds a whole set of services that together insure that complete
messages always arrive, uncorrupted, in order, without duplication of data, at the intended destination, regardless
of hardware or network failures or changes during the time the many datagrams comprising the message are
being sent.
TCP is a connection-oriented protocol, which means that the two computers first establish a connection
with one another before either begins sending data. To do this, one computer, the server, reserves a port for
communication. Some writers call this the ???passive open??? of a connection, for nothing happens outside of the
server; the server simply makes itself ready to communicate.
When another computer, the client, wishes to communicate with the server, the client contacts the server
requesting a connection. This step is sometimes called the ???active open.
Pages:
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366