Ch 1.3 - OSI Model

Question 1

OSI Layer 1: Physical Layer

Answer 1

Signals and Media

Examples: NICs, twisted-pair cable, fiber

Long Explanation: Provides the electrical and mechanical connection to the network. Examples of technologies working in this layer are Electronic Industries Alliance/Telecommunications Industry Association (EIA/TIA) related technologies, UTP, fiber, and network interface cards (NICs).

Question 2

OSI Layer 2: Data Link

Answer 2

Provides for the flow of data

Examples: MAC addresses

Long: Handles error recovery, flow control (synchronization), and sequencing (which terminals are sending and which are receiving). It is considered the “media access control layer” and is where Media Access Control (MAC) addressing is defined. The Ethernet 802.3 standard is defined in this area, which is why the MAC address is sometimes called the Ethernet address.

Question 3

OSI Layer 3: Network Layer

Answer 3

Provides routing decisions

Examples: IP, IPX

Long: Accepts outgoing messages and combines messages or segments into packets, adding a header that includes routing information. It acts as the network controller. Examples of protocols working in this layer are Internet Protocol (IP) and Internetwork Packet Exchange (IPX).

Question 4

OSI Layer 4: Transport

Answer 4

Ensures error-free packets

Examples: TCP, UDP

Long: Is concerned with message integrity between source and destination. It also segments/reassembles (the packets) and handles flow control. Examples of protocols working in this layer are Transmission Control Protocol (TCP) and User Datagram Protocol (UDP).

Question 5

OSI Layer 5: Session

Answer 5

Establishes, manages, and terminates sessions

Examples: NFS, SQL

Long: Provides the control functions necessary to establish, manage, and terminate the connections as required to satisfy the user request. Examples of technologies working in this layer are Network File System (NFS) and Structured Query Language (SQL).

Question 6

OSI Layer 6: Presentation

Answer 6

Protocol conversion, data translation, Encryption

Examples: ASCII, JPEG

Accepts and structures the messages for the application. It translates the message from one code to another if necessary. This layer is responsible for data compression and encryption. Examples of technologies working in this layer are American Standard Code for Information Interchange (ASCII) and Joint Photographic Experts Group (JPEG).

Question 7

OSI Layer 7: Application layer

Answer 7

Support for applications

Examples: HTTP, FTP, SMTP (email)

Long: Interacts with application programs that incorporate a communication component such as your Internet browser and email. This layer is responsible for logging the message in, interpreting the request, and determining what information is needed to support the request. Examples are Hypertext Transfer Protocol (HTTP) for web browsing, File Transfer Protocol (FTP) for transferring files, and Simple Mail Transfer Protocol (SMTP) for email transmission.