Information Technology Reference
In-Depth Information
As an interesting side note, the seven-layer model actually came about after TCP/IP. DARPA used a
four-layer model instead, which the OSI later expanded to seven layers. This is why TCP/IP doesn't
generally fit all that well into the seven-layer OSI model.
Figure7-1
The Internet Protocol Suite and the OSI Reference Model
OSI reference model
Internet Protocol suite
7
Application
NFS
FTP, Telnet,
SMTP, SNMP
6
Presentation
XDR
5
Session
RPC
4
Transport
TCP, UDP
Routing protocols
IP
ICMP
3
Network
ARP, RARP
2
Data link
Not specified
1
Physical
Creation and documentation of the Internet Protocol suite closely resemble an academic research
project. The protocols are specified and refined in documents called Requests For Comments (RFCs),
which are published, reviewed, and analyzed by the Internet community. Taken together, the RFCs
provide a colorful history of the people, companies, and trends that have shaped the development of what
is today the world's most popular open-system protocol suite.
The Network Layer
IP is the primary Layer 3 protocol in the TCP/IP suite. IP provides the logical addressing that enables
communication across diverse networks. IP also provides fragmentation and reassembly of datagrams
and error reporting. Along with TCP, IP represents the heart of the Internet Protocol suite. The IP packet
format is shown in Figure 7-2.
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