Section 6 : OSI Model

Question 1

What is the OSI Model Layer 7?

Answer 1

• Layer 7 is called Application Layer
• Part of the Host/Upper layers (Data)
• Acts as an interface bwteen an appication and end-user protocols
• Privides an interface to communicate with the network interface (API)(Outlook,Chrom etc..)
• Applications do not reside i nthe application layer protocol, but instead interfaces with application-layer protocols.
• Some of the common network services / protocols at this layer:
  
  • Simple Message Transfer Protocol (SMTP)
  • Post Office Protocol (POP)
  • Internet Message Access Protocol (IMAP)
  • Hypertext Transfer Protocol (HTTP)
  • Domain Name System (DNS)
  • Secure Shell (SSH)
  • File Transfer Protocol (FTP)

Question 2

What is the OSI Model Layer 6?

Answer 2

• Layer 6 is called the Presentation Layer
• Part of the Host/Upper Layer (Data)
• Ensures that data transferred from one system’s Application Layer(Layer 7) can be read by the Application Layer on another system.
• Provides character code conversion, data compression and data encryption/decryption
• an example:
  
  • HTM converted to ASCII format
  • JPEG
  • TIFF
  • GIF

Question 3

What is the OSI Model Layer 5?

Answer 3

• Layer 5 is called the Session Layer
• Part of the Host/Upper Layers (Data)
• Responsible for setting up, manaing, and then tearing down sessions between network devices.
• Ensures data from different application sessions are kept separate.
• It is on this layer that the devices agree upon the type of communication that’s going to take place including the following:
  
  • Simplex
  • Half-duplex
  • Full-duplex
• The protocols that are supported on this layer include the following:
  
  • RPC
  • SQL
  • NetBIOS
  • Point-to-Point Tunnel Protocol (PPTP)

Question 4

What is the OSI Model Layer 4?

Answer 4

• Layer 4 is called the Transport Layer
• Part of theMedia/Lower Layers (Segment)
• Responsible for host-to-host communication and creating a logical connection between two devices.
• It includes initiating the connection between the devices, flow control between the devices,same-order delivery, and multiplex communication.
• Ensures data is delivered error-free and in sequence
• Segments data and reassembles correctly.
• Considered the “Post Office” layer
• The two main protocols on the transport layer are as follows:
  
  • Transmission Control Protocol(TCP)
  • User Datagram Protocol (UDP)
• Logical ports (21 = FTP, 22 = SSH, 80 = HTTP, 53 = DNS, 23 = Telnet, 67,68 = DHCP, 88 = Kerberos, 110 = POP3, 123 NTP, 143 = IMAP, 161 = SNMP, 389 = LDAP, 443 = HTTPS, 3389 = RDP)
  
  • ​There are 65,536 logical port numbers available (numbered 0 - 65,535). These numbers are allocated by the Internet Assigned Numbers Authority (IANA) and are broken down into ranges:
    
    • Well-known ports (0- 1,023): These are ports that are allocated to commonly used network services.
    • Registered ports (1,024-49,151): These port numbers are allocated to applications or services by IANA, following a request by the developers.
    • Dynamic or ephemeral ports (49,152-65,535): These ports are not allocated by IANA and are usually used by client machines as the source port

Question 5

What is the OSI Model Layer 3?

Answer 5

• Layer 3 is called the Network Layer
• Part of theMedia/Lower Layers (Packet)
• The “Routing” Layer
• Provides logical addressing and routing services.
• Places two addresses in the packet:
  
  • Source Address & Destination IP Address

Question 6

What is the OSI Model Layer 2?

Answer 6

• Layer 2 is called the Data Link Layer
• Part of theMedia/Lower Layers (Frame)
• Provides physical transmission of the data
• Ensures that messages are delivered to the proper device on a LAN using hardware.
  
  • MAC(Media Access Control) address
  • The basic fundamental addressing on network to be able to send traffic from one device to another
• Translates messages from Network layer into bits for physical layer.

Question 7

What is the OSI Model Layer 1?

Answer 7

• Layer 1 is called the Physical Layer
• Part of theMedia/Lower Layers (Bit)
• Defines the physical and electrical medium for network communication
  
  • Sends bits and receives bits (1 or 0)
  • Network cabling , jacks, patch panels
  • Encoded signal types
  • Ethernet IEEE 802.3 Standard