Chapter 2. Protocols TCP/IP

Chapter 2. Protocols TCP/IP


TCP/IP Model

Although the TCP/IP protocol can be fit into the OSI model, it actually uses its own model,
which is slightly different. Remember that the OSI model is intended to be a standardized framework, and TCP/IP was originated as a proprietary Department of Defense protocol. It stands to reason that there will be some variances from the official OSI stack. The following section describes these differences.

The TCP/IP model has only four layers:

• Application
• Transport
• Internet
• Network interface
  
  
  OSI Layers 5, 6, and 7 have been amalgamated into a single layer called the application layer. The Application layer features all the same protocols as found in OSI Layer 7: Telnet, FTP, TFTP, SMTP, SNMP, and so on. The transport layer is equivalent to OSI Layer 4. TCP and UDP are located here.
  
  The Internet layer corresponds to OSI Layer 3. IP, ARP, and ICMP are the primary protocols here.
  
  Layer 1 and 2 are fused into the network interface layer. This is confusing because it is illogical to have a protocol software stack define a physical interface; just remember that the TCP/IP model is a logical framework, and the fact that physical standards are included is necessary because it must connect to the media at some point. The TCP/IP model uses the same definitions for Network Interface standards as the OSI model does for data link and physical layers.

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Exam Questions

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1. Which protocols use TCP? Choose all that apply.

A. DNS

B. SNMP

C. SMTP

D. FTP

E. TFTP

F. POP3

Answers A, C, D, and F are correct. DNS uses both TCP and UDP; B and E use UDP only.

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2. Which layer of the TCP/IP model is responsible for interhost data movement, using either connection-oriented or connectionless protocols?

A. Network

B. Internet

C. Transport

D. Network interface

Answer C is correct; connectionless and connection-oriented protocols are found at Layer 4 (transport). Answer A is incorrect because it is an OSI layer name; Answers B, D, and E are incorrect because those layers do not use connection-oriented or connectionless protocols.

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