NTA - Lesson 2 - Networking - The Layers of the OSI Model

Encapsulation process

1. User info converted to data at the application layer 2. Data converted to segments and transport layer header is added 3. segments converted to packets or datagrams. Network layer adds a header to each segment and hands them down to the Data Link Layer 4. Packets/datagrams converted to frames for transmission. At the data link layer a frame and MAC header is added to identify the destination. 5. Frames are converted to bits at the physical layer. Digital encoding or signalling method is used to convert data frames into a format that network devices can read.

OSI Model 7 Layers

Application Presentation Session Transport Network Data Link Physical

What layer does DNS operate at?

Application Layer

What layer does FTAM operate at?

Application Layer

What layer does FTP operate at?

Application Layer

What layer does Gopher operate at?

Application Layer

What layer does HTTP operate at?

Application Layer

What layer does NFS operate at?

Application Layer

What layer does NTP operate at?

Application Layer

What layer does SMTP operate at?

Application Layer

What layer does SNMP operate at?

Application Layer

What layer does Telnet operate at?

Application Layer

What layer does X.400 directory services operate at?

Application Layer

Encapsulation

As data moves down the OSI model it is wrapped in protocols.

De-capsulation

As data moves up the OSI model it is unwrapped of the protocols

Application Support

Covers layers Application, Presentation and Session. The primary responsibility of this functional Block is to connect software programs to a network

Network Support

Covers the layers: Transport, network, data link, and physical. The primary responsibility of this block is moving data on a network.

What layer do switches operate at?

DataLink Layer

What layer does Frame Relay operate at?

DataLink Layer

What layer does PPP operate at?

DataLink Layer

What layer does SLIP (Serial Line Internet Protocol) operate at?

DataLink Layer

What layer does SONET (Synchronous Optical Networking) operate at?

DataLink Layer

Application

Highest Layer 7. Provides network services to end user according application being used.

What are the two sublayers of the Data Link Layers?

LLC (Logical Link Control) MAC (Media Access Control)

Data Link

Layer 2 or L2. Handles hardware addresses so that physically linked devices can be located. Its responsible for the transferring and awaiting acknowledgement of packets between adjacent nodes without errors.

Network

Layer 3. Specifies how to route data from hosts on one network to hosts on another network based on the hosts network addresses. Defines how a network is segmented. Network layer protocols are categorized based on the function they perform: Reliability Establish and maintain connection Routing

Transport

Layer 4. End to end transmission occurs on the Transport layer. Implements mechanisms for enduring reliable data transfer and data integrity. Also correcting transmission errors. It manages connections with eh 2 adjacent layers, Network above and session below. Protocols at this layer segment data received and pass it to the network layer in the appropriate size.

Session

Layer 5. Establishes connections between devices and applications, maintains the connection and then terminates it. It also specified the procedures for synchronizing data transfer between different data transmission rates.

Presentation

Layer 6. ensures that data represented by one system can be interpreted by another system. (One language translated to another) Adds data compression and security related services like encryption and decryption.

LLC

Logical Link Layers is responsible for encapsulating protocols in upper layers so that multiple upper layer protocols can share the same media.

Physical

Lowest Layer 1, or L1 defines the physical media and specs a network uses when transferring data. For example it describes cables connectors or frequencies and modulation in wireless networks Protocols at this layer receive fully formatted data frames from the data link layer and places them on physical communication medium. Determines the mode and medium of data transmission which affect the transmission speeds.

MAC

Media Access Control defines how packets are transferred onto media in contention scheme. For instance CSMA (Carrier Sense Multiple Access) or CD (Collision Detection)

What layer does ARP operate at?

Network Layer

What layer does ICMP operate at?

Network Layer

What layer does IGMP operate at?

Network Layer

What layer does IP operate at?

Network Layer

What layer does RIP (Routing information protocol operate at?

Network Layer

What layer do Network Adapters operate at?

Physical Layer

What layer do access points operate at?

Physical Layer

What layer does 802.11 wifi standards operate at?

Physical Layer

What layer does Asynchronous Transfer Mode (ATM-Token Ring) operate at?

Physical Layer

What layer does Ethernet operate at?

Physical Layer

What layer does FDDI (Fiber Distributed Data Interface) operate at?

Physical Layer

What layer does Fast Ethernet operate at?

Physical Layer

What layer does ASN.1 (Abstract Syntax Notation one) operate at?

Presentation Layer

What layer does SSL operate at?

Presentation Layer

What layer does TLS operate at?

Presentation Layer

What layer does the Gif file format operate at?

Presentation Layer

What layer does the JPEG file format operate at?

Presentation Layer

What layer does the TIFF file format operate at?

Presentation Layer

What layer do Sockets operate at?

Session Layer

What layer does Radius operate at?

Session Layer

What layer does TACACS+ operate at?

Session Layer

What layer does TCP operate at?

Session and Transport Layer

What layer does UDP operate at?

Transport Layer