When the receiver
replies with a clear-to-send (CTS) message, the sender proceeds. This approach results in fewer collisions and
less wasted time on retransmissions.
Many other data-link standards exist. FDDI is a standard for computers linked with fiber-optic connections
instead of wires. Token Ring is a standard that IBM popularized in the 1980s. Because the network protocols
are layered, improvements in techniques for link-level connections can be adopted without disrupting the
protocols that provide higher-level services.
INTERNET (NETWORK) LAYER PROTOCOL
An important higher-level service is that for the routing of messages between networks. When I send a message
from my computer to my friend in the UK, the message must pass through many networks. Starting from my
home network, the message must go to my internet service provider (ISP), which maintains connections with
other ISPs and networks to enable my worldwide access. The routing of a message is the responsibility of the
internet (network) layer protocol.
The internet layer protocol is responsible for transporting a ???packet??? of data from one computer to another
over possibly many intervening networks. When one computer sends a message to another, the internet layer
protocol breaks the message into pieces (packets), and appends a header to each packet that identifies the
destination computer as well as the source.
Pages:
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363