Section 3: OSI Model (aka Stack)

Question 1

Pneumonic For OSI Model (Layer 1 to Layer 7)

Answer 1

Please - Do - Not - Throw - Sausage - Pizza - Away

Question 2

OSI Model Layer 1 / Data Type

Answer 2

Physical Layer / Bits
(Transmitted as binary data)

▪ Transmission of bits across the network
▪ Physical and electrical characteristics
▪ Examples: Cables (Ethernet, Fiber); RF (Wi-Fi, Bluetooth); Infrastructure Devices (Hubs, Wireless Access Point (WAP), Media Converter)

Question 3

OSI Model Layer 2 / Data Type

Answer 3

Data Link Layer / Frames

(Header adds Source and Destination MAC Addresses)

▪ Packages data into frames, perform error detection/correction, and uniquely identifying network devices with an address (MAC), and flow control

Examples: Network Interface Cards (NIC), Bridges, Switches

Question 4

OSI Model Layer 3 / Data Type

Answer 4

Network Layer / Packets

(Header adds Source and Destination IP addresses)

Examples:
▪ Routers
▪ Multilayer switches
▪ IPv4 protocol
▪ IPv6 protocol
▪ Internet Control Message Protocol (ICMP)

Question 5

OSI Model Layer 4 / Data Type

Answer 5

Transport Layer /
Segments for TCP;
Datagrams for UDP

(Header Adds Source and Destination Ports)

Examples:
▪ TCP
▪ UDP
▪ WAN Accelerators
▪ Load Balancers
▪ Firewalls

Question 6

OSI Model Layer 5 / Data Type

Answer 6

Session Layer / Data:

Responsible for Interhost Communication - [aka Session Management]

(Setup, Maintain and Tear-down Session between end-user application processes.)

Protocol Examples:
▪ H.323 - Voice/Video Sessions - Setup, maintain, and tear down
▪ NetBIOS - Used by computers to share files over a network

Question 7

OSI Model Layer 6 / Data Type

Answer 7

Presentation Layer / Data:

Responsible for the delivery and formatting of information to the Application Layer.

Examples:
▪ HTML, XML, PHP, JavaScript, …
▪ ASCII, EBCDIC, UNICODE, …
▪ GIF, JPG, TIF, SVG, PNG, …
▪ MPG, MOV, …
▪ TLS, SSL, …

Question 8

OSI Model Layer 7 / Data Type

Answer 8

Application Layer / Data:

Responsible for displaying data to the user.

▪ Provides application-level services (Not Word or Notepad)
▪ Layer where the users communicate with the computer
▪ Functions:
● Application services - File Transfer and Sharing, eMail, Remote Access, Network Management, Client-Server processes,
● Service advertisement - Printers, file servers
Examples:
▪ E-mail (POP3, IMAP, SMTP)
▪ Web Browsing (HTTP, HTTPS)
▪ Domain Name Service (DNS)
▪ File Transfer Protocol (FTP, FTPS)
▪ Remote Access (TELNET, SSH)
▪ Simple Network Management Protocol (SNMP)

Question 9

Pneumonic for OSI Model Data-Types (Layer 7 to Layer 1)

Answer 9

Do [Data - Layers 5, 6, & 7]
Some [Segments - Layer 4]
People [Packets - Layer 3]
Fear [Frames - Layer 2]
Birthdays [Bits - Layer 1]

Question 10

TCP

Answer 10

Transmission Control Protocol
▪ Connection-oriented protocol
▪ Reliable transport of segments

● If segment is dropped, protocol detects it and resends segment
▪ Acknowledgements received for successful communications

Question 11

UDP

Answer 11

User Datagram Protocol
▪ Connectionless protocol
▪ Unreliable transport of segments

● If dropped, sender is unaware, no retransmission
▪ Lower overhead for increased performance - good for audio/video streaming

Question 12

Each Layer’s Data Type in the OSI Model (1-7)

Answer 12

Layer 1 (Physical) = Bits
Layer 2 (Data Link) = Frames
Layer 3 (Network) = Packets
Layer 4 (Transport) = Segments
Layer 5 (Session) = —-.
Layer 6 (Presentation) = —+- Data
Layer 7 (Application) = —.

Question 13

PDU

Answer 13

Protocol Data Unit (PDU) -
Protocol-specific control information and user data added or removed by a peer layer of the OSI model.

Question 14

MAC Address

Answer 14

Media Access Control Address -

A 48-bit Hexadecimal address assigned to a network interface card (NIC) to uniquely identify a network card on a local area network.

The first 24 bits (1st three octets) represent a vendor code and the second 24 bits (2nd three octets) are NIC unique value.
OUI NIC
1a:32:4b : cc:78:d5

Question 15

LLC

Answer 15

Logical Link Control - sublayer of Data Link (Layer 2) that controls synchronization, multiplexing, flow control and error-checking.