1.1 – The OSI Model

Question 1

OSI Layers

Answer 1

Physical > Data Link > Network > Transport > Session > Presentation >Application

Question 2

Physical Layer

Answer 2

Layer 1:

• It is responsible for the actual physical connection between the devices
• contains information in the form of bits
• responsible for transmitting individual bits from one node to the next
• When receiving data, this layer will get the signal received and convert it into 0s and 1s and send them to the Data Link layer, which will put the frame back together

Question 3

Bit synchronization

Answer 3

The physical layer provides the synchronization of the bits by providing a clock. This clock controls both sender and receiver thus providing synchronization at bit level.

Question 4

Bit rate control

Answer 4

The Physical layer also defines the transmission rate i.e. the number of bits sent per second.

Question 5

Physical topologies

Answer 5

Physical layer specifies the way in which the different, devices/nodes are arranged in a network i.e. bus, star, or mesh topology.

Question 6

Transmission mode

Answer 6

Physical layer also defines the way in which the data flows between the two connected devices. The various transmission modes possible are Simplex, half-duplex and full-duplex.

Question 7

Physical Layer devices

Answer 7

Hub, Repeater, Modem, Cables

Question 8

Data Link Layer

Answer 8

Layer 2: “Switching Layer”

• main function of this layer is to make sure data transfer is error-free from one node to another
• When a packet arrives in a network, it is the responsibility of DLL to transmit it to the Host using its MAC address
• Packet in Data Link layer is referred to as Frame

Question 9

Framing

Answer 9

Framing is a function of the data link layer. It provides a way for a sender to transmit a set of bits that are meaningful to the receiver. This can be accomplished by attaching special bit patterns to the beginning and end of the frame.

Question 10

Physical addressing

Answer 10

After creating frames, the Data link layer adds physical addresses (MAC address) of the sender and/or receiver in the header of each frame.

Question 11

Error control

Answer 11

Data link layer provides the mechanism of error control in which it detects and retransmits damaged or lost frames.

Question 12

Flow Control

Answer 12

The data rate must be constant on both sides else the data may get corrupted thus, flow control coordinates the amount of data that can be sent before receiving acknowledgement.

Question 13

Access control

Answer 13

When a single communication channel is shared by multiple devices, the MAC sub-layer of the data link layer helps to determine which device has control over the channel at a given time.

Question 14

Data Link Layer devices

Answer 14

Switch & Bridge

Question 15

The packet received from the Network layer

Answer 15

further divided into frames depending on the frame size of NIC(Network Interface Card). DLL also encapsulates Sender and Receiver’s MAC address in the header.

Question 16

LLC
MAC
NIC
ARP

Answer 16

Logical Link Control
Media Access Control
Network Interface Card
Address Resolution Protocol

Question 17

Network Layer

Answer 17

Layer 3: “routing layer”

• works for the transmission of data from one host to the other located in different networks
• It also takes care of packet routing i.e. selection of the shortest path to transmit the packet, from the number of routes available
• The sender & receiver’s IP addresses are placed in the header by the network layer.
• Segment in Network layer is referred to as Packet.

Question 18

Routing

Answer 18

The network layer protocols determine which route is suitable from source to destination. This function of the network layer is known as routing.

Question 19

Logical Addressing

Answer 19

In order to identify each device on internetwork uniquely, the network layer defines an addressing scheme.
The sender & receiver’s IP addresses are placed in the header by the network layer.
Such an address distinguishes each device uniquely and universally.