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Unformatted text preview: ication layer determines
whether a remote communication
partner is available and accessible.
It also ensures that sufficient resources
are available to support Lthe requested 27 Application Layer …cont.
Numerous application-specific protocols
are found within this layer,
Hypertext Transfer Protocol (HTTP)
File Transfer Protocol (FTP)
Line Print Daemon (LPD)
Simple Mail Transfer Protocol (SMTP)
Trivial File Transfer Protocol (TFTP)
Electronic Data Interchange (EDI)
Post Office Protocol version 3
28 Application Layer …cont.
There is a network device (or service)
that works at the Application layer,
namely the gateway.
However, an Application layer gateway
is a very specific type of component.
Serves as a protocol translation tool.
For example, an IP-to-IPX gateway
takes inbound communications from
TCP/IP and translates them over to
IPX/SPX for outbound transmission.
Lecture-3 29 TCP/IP Model
The TCP/IP model (also called the
DARPA or the DOD model) consists of
only four layers, as opposed to the OSI
Reference Model’s seven.
These four layers can be compared to
the seven layers of the OSI model.
The four layers of the TCP/IP model are
Application, Host-to-Host, Internet, and
The TCP/IP protocol suite was
developed before the OSI Reference TCP/IP Model … cont.
The TCP/IP model’s Application layer
corresponds to layers 5, 6, and 7 of the
The TCP/IP model’s Host-to-Host layer
corresponds to layer 4 from the OSI
model. The TCP/IP model’s Internet
layer corresponds to layer 3 from the
The TCP/IP model’s Network Access
layer corresponds to layers 1 and 2 from
the OSI model. TCP/IP Model … cont. Lecture-3 32 Communications and Network Security Network Cabling: The type of connectivity media
employed in a network is important to
the network’s design, layout, and
capabilities. Without the right cabling, a network
may not be able to span your entire
enterprise or it may not support the
necessary traffic volume. The most common causes of network
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- Winter '08