Topic 5 (Data Link Layer)

Data Link Layer

Prepares network data for the physical network.

Data Link Layer

Is responsible for network interface card (NIC) to NIC communications.

Frames

Exchanges ________ between endpoints over the network media.

Data Link Layer

Controls how data is placed and received on the media.

Data Link Layer

Performs error detection and rejects any corrupt frame.

Layer 2 Ethernet destination and source NIC information (address)

The data link layer adds ________________________ to a Layer 3 packet.

IEEE 802 LAN/MAN standards

are specific to the type of network (Ethernet, WLAN, WPAN, etc.).

Logical Link Control (LLC)

Communicates between: Networking Software and Device hardware

Networking software

At the upper layers

Device Hardware

at the lower layers

Media Access Control (MAC)

Sublayer provides: Data Encapsulation and Media Access Control

Data Encapsulation

provides addressing and error detection

Addressing

source and destination addressing for transporting the Layer 2 frame between devices on the same shared medium.

Error Detection

includes a trailer used to detect transmission errors.

Media Access Control

to allow multiple devices to communicate over a shared medium.

Point-to-point, Hub and spoke, Mesh

There are three common physical WAN topologies.

Point-to-point

the simplest and most common WAN topology. Consists of a permanent link between two endpoints.

Hub and spoke

similar to a star topology where a central site interconnects branch sites through point-to point links.

Mesh

provides high availability but requires every end system to be connected to every other end system.

Point-to-point

Hub and spoke

Mesh

Star and extended star

Typically used to interconnect end devices on LANs

Star and extended star

Very scalable and easy to install and troubleshoot

Star

Extended Star

Legacy LAN topologies

Consists of Early Ethernet Bus and Legacy Token Ring.

Early Ethernet Bus

All end systems chained together with coaxial cable and terminated on each end.

Legacy Token Ring

Each end system is connected to its respective neighbors to form a ring.

Bus

Ring

Half-duplex communication

Only allows one device to send or receive at a time on a shared medium.

Half-duplex communication

Used on WLANs and legacy bus topologies with Ethernet hubs.

Full-duplex communication

Allows both devices to simultaneously transmit and receive on a shared medium.

Ethernet

________ switches operate in full-duplex mode.

multiaccess network

is a network that can have two or more end devices attempting to access the network simultaneously. Examples: Ethernet LANs and WLANs.

Contention-based access and Controlled access

What are the access control methods

Contention-based access

• Carrier sense multiple access with collision detection (CSMA/CD) - used on legacy bus-topology Ethernet.

• Carrier sense multiple access with collision avoidance (CSMA/CA) - used on Wireless LANs.

Carrier sense multiple access with collision detection (CSMA/CD)

used on legacy bus-topology Ethernet.

Carrier sense multiple access with collision avoidance (CSMA/CA)

used on Wireless LANs.

Controlled Access

Deterministic access, where each node has its own time on the medium.

Carrier sense multiple access with collision detection (CSMA/CD)

Used by legacy Ethernet LANs.

Carrier sense multiple access with collision detection (CSMA/CD) and Carrier sense multiple access with collision avoidance (CSMA/CA) - used on Wireless LANs.

Operates in half-duplex mode where only one device sends or receives at a time.

Carrier sense multiple access with collision detection (CSMA/CD)

Uses a collision detection process to control when a device can send and what happens if multiple devices send at the same time.

Carrier sense multiple access with collision avoidance (CSMA/CA)

Used by IEEE 802.11 WLANs.

Frame

Data is encapsulated by the data link layer with a header and a trailer to form a ______.

Header, Data, Trailer

a frame has three parts

Frame Start and Stop

Identifies beginning and end of frame

Addressing

Indicates source and destination nodes

Type

Identifies encapsulated Layer 3 protocol

Control

Identifies flow control services such as quality of service (QoS).

Data

Contains the frame payload

Error Detection

Used to determine transmission errors

Layer 2 Addresses

• Referred to as a physical address.

• Contained in the frame header.

• Used only for local delivery of a frame on the link.

• Updated by each device that forwards the frame.