OSI Model

Question 1

1. Physical Layer

Answer 1

Concerned with transmission and reception of the unstructured raw bit stream over the physical medium.

Physical structure:

• Cables
• Hubs

Primary device - hub

Question 2

2. Data Link Layer

Answer 2

Provides node-to-node data transfer over the physical layer.

Frame - primary protocol data unit, container for single n/w packet and contains MAC address.

2 sublayers:

1. Medium Access Control (MAC) Layer - controls a device’s access to n/w and permission to transmit data.
2. Logical Link Control (LLC) Layer - identifies and encapsulates n/w layer protocols

Central devices: Switch, Bridge, WAP

Central protocols: PPP/SLIP

Question 3

3. Network Layer

Answer 3

Controls the operations of the subnet, deciding which physical path the data takes.

Provides functional and procedural means to xfr packets from one node to another network’s node.

Central device: Router

Central protocol: IP/IPX/ICMP

Question 4

4. Transport Layer

Answer 4

Ensures that messages are delivered error-free, in sequence, and with no lossess or duplications.

TCP - Host to Host, Flow Control

Central protocols: TCP/SPX/UDP

Question 5

5. Session Layer

Answer 5

Controls dialogue between computers

Establishes, manages and terminates connections between a local and remote machine

Synch & send to ports (logical ports)

Central device: logical ports

Central Protocols: RPC/SQL/NFS/NetBIOS names

Question 6

6. Presentation Layer

Answer 6

Formats the data to be presented to the Application layer. Viewed as the translator for the network.

Syntax layer - encrypt & decrypt (if needed)

Central protocols: JPEG/ACII/EBDIC/TIFF/GIF/PICT

Question 7

7. Application Layer

Answer 7

Serves as the window for users and application processes to access the network service.

End User Layer - program that opens what was sent or creates what will be sent.

Protocols: (E)SMTP/Telnet/FTP/DNS/DHCP/SNMP

Question 8

OSI Model

Answer 8

Open Systems Interconnection model

Conceptual model that standardizes communications functions of telecom or computing systems.

Goals:

• Interoperability of diverse systems
• Standardized communications protocols

Comprised of 7 layers

Question 9

OSI Model Layers

Answer 9

7. Application layer
8. Presentation layer
9. Session layer
10. Transport layer
11. Network layer
12. Data layer
13. Physical layer