S.3 Dion Training Network+ (N10-009)

Section 3 OSI Model

What is the OSI model used for?

Categorizing network functions and aiding troubleshooting.

What model do modern networks primarily use?

The TCP/IP model.

Name the 7 OSI layers in order.

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

What are the data names at each OSI layer?

Bits (L1), Frames (L2), Packets (L3), Segments (L4), Data (L5–L7).

What happens at the Physical Layer?

Transmission of bits across the network using physical/electrical characteristics

What is the data type at Layer 1?

Bits (1s and 0s).

How does copper wire represent bits?

Voltage levels (0V for 0, +5V/−5V for 1).

How does fiber optic represent bits?

Light on = 1, light off = 0.

What connector is used for CAT5/CAT6 cables?

RJ‑45.

What are the two Ethernet wiring standards?

TIA/EIA‑568A and TIA/EIA‑568B.

What is a crossover cable?

568A on one end, 568B on the other.

What is a straight‑through cable?

568B on both ends.

Name the common physical topologies.

Bus, Ring, Star, Hub‑and‑Spoke, Full Mesh, Partial Mesh.

What is asynchronous communication?

Uses start/stop bits for out‑of‑sync transmission.

What is synchronous communication?

Real‑time communication using a common time source.

What is broadband?

Divides bandwidth into separate channels (e.g., cable TV).

What is baseband?

Uses the entire frequency of the cable all the time (e.g., telephone).

What is multiplexing?

Efficiently sharing a limited resource so multiple users can access it.

What is TDM?

Time Division Multiplexing — dedicated time slots.

What is StatTDM?

Dynamically allocates time slots based on demand.

What is FDM?

Frequency Division Multiplexing — divides medium into channels.

Name common Layer 1 media types.

Fiber optic, Ethernet, Coaxial.

Name wireless Layer 1 media.

Bluetooth, Wi‑Fi, NFC.

Name Layer 1 infrastructure devices.

Hubs, Access Points, Media Converters.

What logic do Layer 1 devices perform?

None — they simply repeat what they receive.

What is the primary job of the Data Link Layer?

Packaging bits from Layer 1 into frames and transmitting them across the network.

What key functions does Layer 2 perform?

Error detection/correction, MAC addressing, and flow control.

What is the data type at Layer 2?

Frames.

What is a MAC address?

A unique 48‑bit physical address assigned to every NIC.

How is a MAC address written?

In hexadecimal.

What do the first 24 bits of a MAC address represent?

The manufacturer (OUI).

What do the last 24 bits of a MAC address represent?

The specific device identifier.

Why are MAC addresses important?

Unique identifiers for devices on a network

What does LLC provide?

Connection services and message acknowledgment.

What is LLC’s basic form of flow control?

Limiting data sent to prevent receiver overwhelm.

How does LLC detect corrupted frames?

Using a checksum.

What is isochronous communication?

Uses a common reference clock with time slots and less overhead.

What is synchronous communication at Layer 2?

Devices share the same clock and use control characters for frame boundaries.

What is asynchronous communication at Layer 2?

Devices use their own clocks with no strict timing control.

Name common Layer 2 devices.

NICs, Bridges, Switches.

What makes switches “intelligent”?

They learn MAC addresses and forward frames selectively.

What table do switches use to map MAC addresses to ports?

Content Addressable Memory table.

What does selective forwarding enable?

Sending data only to the intended destination port.

What is the main responsibility of the Network Layer?

Routing and forwarding traffic using logical addresses.

What is the data type at Layer 3?

Packets.

What are the two IP variants used for logical addressing?

IPv4 and IPv6.

How is IPv4 written?

Dotted‑octet notation (e.g., 172.16.254.1).

What older protocols were replaced by IP?

AppleTalk and IPX.

What is packet switching?

Dividing data into packets and forwarding them independently.

What is circuit switching?

Establishing a dedicated communication link between two devices.

What is message switching?

Sending data as messages that may be stored and forwarded.

What do routers maintain to determine the best path?

Routing tables.

What do dynamic routing protocols like RIP and OSPF do?

Share and update route information between routers.

What do routing protocols decide?

How data flows across the network and how routers communicate path info.

What does Layer 3 add to Layer 2 services?

Flow control and packet reordering.

Why is packet reordering needed?

To ensure packets arrive and reassemble in the correct order.

What is ICMP (Internet Control Message Protocol) used for?

Sending error messages and operational information.

What does PING do?

Tests connectivity and response times.

What does traceroute do?

Traces the path a packet takes through the network.

Name common Layer 3 devices.

Routers and multi‑layer switches.

When is a switch considered a Layer 3 device?

Only when specifically identified as a multi‑layer switch.

Name common Layer 3 protocols.

IPv4, IPv6, ICMP.

What is the Transport Layer responsible for?

Providing end‑to‑end communication between devices and dividing upper vs. lower OSI layers.

What is the data type at Layer 4?

Segments (TCP) and Datagrams (UDP).

Is TCP connection‑oriented or connectionless?

Connection‑oriented.

What makes TCP reliable?

Acknowledgments, sequencing, retransmissions, and flow control.

What is the TCP three‑way handshake?

SYN → SYN‑ACK → ACK.

What does TCP use for flow control?

Windowing.

When is TCP used?

When data must be guaranteed to reach its destination.

Is UDP connection‑oriented or connectionless?

Connectionless.

Is UDP reliable?

No — no acknowledgments, sequencing, or retransmissions.

What is UDP commonly used for?

Audio and video streaming.

What is the data type for UDP?

Datagram.

List key TCP characteristics.

Reliable, connection‑oriented, sequencing, acknowledgments, windowing, retransmissions.

List key UDP characteristics.

Unreliable, connectionless, no sequencing, no acknowledgments, no windowing.

What does windowing allow?

Adjusting the amount of data sent before requiring an acknowledgment.

Why adjust the window size?

To optimize throughput and bandwidth.

What is buffering?

Allocating memory to store segments when bandwidth isn’t available.

What is a buffer?

Temporary storage for segments.

Why is buffering important?

Prevents overflow by clearing stored segments.

What protocols operate at Layer 4?

TCP and UDP.

What devices operate at Layer 4?

WAN accelerators, load balancers, and firewalls.

What is the main purpose of the Session Layer?

Managing sessions and keeping conversations separate so data doesn’t intermingle.

What happens when a session is set up?

User credentials are checked and session numbers are assigned.

What does maintaining a session involve?

Continuous data transfer and acknowledging data.

What happens if a connection breaks?

The session must be re‑established.

How is a session terminated?

By mutual agreement or when one party disconnects.

What is H.323 used for?

Setting up, maintaining, and tearing down voice/video connections over RTP.

What is NetBIOS used for?

File sharing between computers, commonly in Windows environments.

Are there specific hardware devices for Layer 5?

No — Layer 5 issues involve software and protocols, not physical devices.

What is the main purpose of the Presentation Layer?

Formatting data for exchange and securing it through encryption.

Why does Layer 6 format data?

To ensure compatibility between different devices.

What does ASCII provide?

A text‑based language ensuring data is readable and properly structured.

What does Layer 6 negotiate for Layer 7?

Data transfer syntax.

Name common text formats.

ASCII, Unicode, EBCDIC.

Name common image formats.

GIF, JPEG, TIFF, SVG, PNG.

Name common movie/video formats.

MP4, MPEG, MOV.

Why is encryption used at Layer 6?

To scramble data and provide confidentiality during transit and storage.

What is TLS used for?

Creating an encrypted tunnel for secure data transfer.

What older encryption protocol did TLS replace?

SSL.