Foundation Summary

The "Foundation Summary" is a condensed collection of material for a convenient review of key concepts in this chapter. If you are already comfortable with the topics in this chapter and decided to skip most of the "Foundation Topics" material, the "Foundation Summary" will help you recall a few details. If you just read the "Foundation Topics" section, this review should help further solidify some key facts. If you are doing your final preparation before the exam, the "Foundation Summary" offers a convenient and quick final review.

Table 2-17 OSI Model

OSI Name and Layer Number


Application layer (Layer 7)

The application layer is closest to the end user, which means that the application is being accessed by the end user. This layer's major function is to provide services to end users. Examples of application layer services include the following:

File Transfer Protocol (FTP)



Trace route SMTP Mail clients

Presentation layer (Layer 6)

The Presentation layer handles data formats and code formatting. This layer's functions are normally transparent to the end user because it takes care of code formats and presents them to the application layer (Layer 7), where the end user can examine the data. Examples of presentation layer protocols include the following:







Session layer (Layer 5)

The session layer performs several major functions, including managing sessions between devices and establishing and maintaining sessions. Examples of session layer protocols include the following:

Database SQL NetBIOS Name Queries H.323

Real Time Control Protocol

continues continues

Table 2-17 OSI Model (Continued)

OSI Name and Layer Number


Transport layer (Layer 4)

The transport layer is responsible for segmenting upper-layer applications and establishing end-to-end connections between devices. Other transport layer functions include providing data reliability and error-free delivery mechanisms. Information being processed at this layer is commonly known as segments. Examples of transport layer protocols include Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

Network layer (Layer 3)

The network layer determines the best path to a destination. Device addressing, packet fragmentation, and routing all occur at the network layer. Information being processed at this layer is commonly known as packets. Examples of network layer protocols include the following:

Internet Protocol (IP)

Open Shortest Path First (OSPF)

Cisco's EIGRP routing protocol

Data Link layer (Layer 2)

The data link layer focuses on getting data reliably across any particular kind of link. Flow control and error notifications are other data link layer functions. The data link layer applies to all access methods, whether they are LAN or WAN methods. Information being processed at this layer is commonly known as frames. Example include the following:


Frame Relay Spanning tree protocol NetBEUI

Physical layer (Layer 1)

The physical layer consists of standards that describe bit ordering, bit transmission rates, connector types, and electrical and other specifications. Information at Layer 1 is transmitted in binary (1s and 0s; for example, the letter A is transmitted as 00001010). Examples of physical layer standards include the following:









Gigabit Ethernet

Table 2-18 Ethernet Media Formats

Media Type



Maximum length 500 m. Maximum stations are 1024. Speed is 10 Mbps.

Minimum distance between devices is 2.5 m.


Maximum length 185 m, using RG58 cable types, T connectors on all end stations.

Minimum distance between devices is 0.5 m.

Maximum devices per 185 m segment is 30 stations.

Speed is 10 Mbps.

End points need termination.

Up to 100 m (longer for better category cables). One device per cable.

Typically only one device per segment with hubs or switches connecting all devices together.

Speed is 10 Mbps.

Physical topology is star, logical topology is liner.


Same characteristics as 10baseT but operates faster, at 100 Mbps. Can be fibre, as well (100BaseFx). Defined in IEEE 802.3U.

1000 GE

Gigabit Ethernet operating at 1000 Mbps. Can run over Fibre or UTP.

Frame formats and CSMA/CD identical to Ethernet standards.

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