OSI Model

Question 1

What is the OSI model?

Answer 1

Open Systems Interconnection Model.

Question 2

What is a network protocol and what are its two principal functions?

Answer 2

It is a set of rules for exchanging data in a structured format.
Addressing- Describing where data messages should go.
Encapsulation- Describing how data messages should be packaged for transmission.

Question 3

What is the difference between same layer interaction and adjacent layer interaction?

Answer 3

The communication between nodes at the same layer is described as a same layer interaction, a peer to peer interaction.
Adjacent Layer interaction is how each layer interacts with each other, each layer above uses the services of the layer below.

Question 4

Tell me about the physical layer.

Answer 4

Layer 1.
Responsible for the transmission and receipt of the signals that represent bits of data.
Transmission media can be classified as cabled or wireless.
Specifies: Physical topology, Physical Interface (types of cables or radio transceivers and antenna specifications), and Signaling (transmitting and receiving data).
PDU=bits

Question 5

What are devices that operate at the physical layer?

Answer 5

Transceiver- Receives signals over the network media.
Repeater- Amplifies the electronic signal to extend the maximum allowable distance for media type.
Hub- A multiport repeaters deployed as the central point of connection for nodes.
Media Converter- Device that converts one media signaling type to another.

Question 6

Tell me about the data link layer.

Answer 6

Layer 2.
Responsible for transferring data between nodes on the same network.
Performs encapsulation, and basic error checks.
Uses MAC/hardware addresses.
PDU=frames

Question 7

What devices operate at the data link layer?

Answer 7

Network adapter/ NIC- Allows a host to communicate over the network by assembling and disassembling frames (can be cabled or wireless).
Bridge- Joins physical network segments.
Switch- An advanced type of bridge with many ports, creates links between large numbers of nodes more efficiently.
Wireless Access Point (AP)- Allows nodes with wireless NICs to communicate and creates a bridge between wireless networks and wired ones.

Question 8

Tell me about the network layer.

Answer 8

Layer 3.
Responsible for moving data around different networks.
Uses IP addresses.
PDU= packets or datagrams

Question 9

What are the devices that operate at the network layer?

Answer 9

Router- links dissimilar networks and forwards packets.
Firewalls- enforces ACL.

Question 10

Tell me about the transport layer.

Answer 10

Layer 4.
AKA the end to end or host to host layer.
This layer is responsible for ensuring reliable data delivery.
Identifies each type of network application by assigning it a port number.
PDU=segments

Question 11

What devices work at the transport layer?

Answer 11

Multilayer switches (that usually work as load balancers)
Security appliances (like more advanced firewalls and IDS )

Question 12

Tell me about the Session layer.

Answer 12

Layer 5.
Administers the process of establishing dialog, managing data transfer, and then ending the session.

Question 13

Tell me about the Presentation Layer.

Answer 13

Layer 6.
Transforms data between the format required for the network and the format required for the application.
Supports data compression and encryption.

Question 14

Tell me about the Application Layer.

Answer 14

Layer 7.
Provides an interface for software programs on network hosts.
The layer we see.

Question 15

What is a PDU?

Answer 15

Protocol Data Unit.
Describes the form that data takes at each layer of the OSI model.