Information Technology Reference
In-Depth Information
OSI Model
TCP/IP Architecture
TCP/IP Protocols
Application
Application
Telnet, SMTP, SNMP,
FTP, TFTP, HTTPS,
DNS
Presentation
Session
Transport
Host-to-Host Transport
TCP, UDP
Network
Internet
IP, ARP, OSPF, ICMP
Data Link
Network Interface
Use of lower layer
protocols such as
Ethernet and Frame
Relay.
Physical
Figure C-3
The TCP/IP Architecture and the OSI Model
Network Interface Layer
The TCP/IP network interface layer (also known as network access layer) maps to the OSI
data link and physical layers. TCP/IP uses the lower-layer protocols for transport.
Internet Layer
The Internet layer is where IP resides. IP packets exist at this layer. It directly maps to the
network layer of the OSI model. Other TCP/IP protocols at this layer are Internet Control
Message Protocol (ICMP), Address Resolution Protocol (ARP), and Reverse ARP (RARP).
Host-to-Host Transport Layer
The host-to-host transport layer of TCP/IP provides two connection services: TCP and
UDP. TCP provides reliable transport of IP packets, and UDP provides transport of IP
packets without verification of delivery. This layer maps to the OSI transport layer, but the
OSI model only defines reliable delivery at this layer.
Application Layer
The TCP/IP application layer maps to the top three layers of the OSI model: application,
presentation, and session. This layer interfaces with the end user and provides for authen-
tication, compression, and formatting. The application protocol determines the data's for-
mat and how the session is controlled. Examples of TCP/IP application protocols are
Te l n e t , F T P, B G P, a n d H y p e r t e x t Tr a n s fe r P r o t o c o l S e c u r e ( H T T P S ) .
Example of Layered Communication
Suppose that you use a Telnet application. Telnet maps to the top three layers of the OSI
model. In Figure C-4, a user on Host 1 enables the Telnet application to access a remote
host (Host 2). The Telnet application provides a user interface (application layer) to net-
work services. As defined in RFC 854, ASCII is the default code format. No session layer
