The Data Link Layer allows Upper Layer Protocols to access the Physical Layer Media.

It encapsulates Layer 3 packets (IPv4 and IPv6) into Layer 2 Frames.

Layer 3 - Network

Layer 2 - Data Link

The Data Link Layer does not perform error detection and accepts corrupts frames.

IEEE 802 LAN/MAN standards are not specific to the type of network (Ethernet, WLAN, WPAN, etc).

These are Layer 2 Devices:

What is the size allowed for the frame to be accepted in the receiving node?

_____ to _____ bytes

The Data Link Layer consists of two sublayers:

Communicates between the networking software at the upper layers and the device hardware at the lower layers.

Is responsible for data encapsulation and media access control.

- Responsible in getting the packet from the Network Layer.

- It places information in the frame allowing multiple Layer 3 protocols to use the same network interface and media.

- Responsible in transferring from frame to bits in Layer 2.

_______ exchanged between nodes may experience numerous data link layers and media transitions.

At each hop along the path, a router performs four basic Layer 2 functions:

Data link layer protocols are defined by engineering organizations:

The __________ of a network is the arrangement and relationship of the network devices and the interconnections between them.

2 types of topologies used when describing networks:

Shows physical connections and how devices are interconnected.

Identifies the virtual connections between devices using device interfaces and IP addressing schemes.

3 Common Physical WAN Topologies:

The simplest and most common WAN topology.

Consists of a permanent link between two endpoints.

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

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

Physical point-to-point topologies directly connect three nodes.

In Point-to-Point WAN Topology, the nodes may not share the media with other hosts.

Because all frames on the media can only travel to or from the two nodes, Point-to-Point WAN protocols can be very complex.

A source and destination node may be indirectly connected to each other over some geographical distance using multiple intermediary devices.

But, it is still Point-to-Point WAN Topology.

End devices on LANs are typically interconnected using __________________.

Are easy to install, very scalable and easy to troubleshoot.

Early Ethernet and Legacy Token Ring technologies provide two additional topologies:

All end systems chained together and terminated on each end.

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

What is this topology?

What is this topology?

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

- Used on WLANs and legacy bus topologies with Ethernet hubs.

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

Ethernet switches operate in full-duplex mode.

What are the 2 Access Control Methods?

All nodes operating in half-duplex, competing for use of the medium.

- Shared medium

Ex: CSMA/CD (Carrier sense multiple access with collision detection) and CSMA/CA (Carrier sense multiple access with collision avoidance)

Used on legacy bus-topology Ethernet. (Ethernet 802.3)

Used on Wireless LANs. (Ethernet 802.11)

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

Ex: Allotted time of 10 secs to send and the other medium as well.

Ex: Used on legacy networks such as Token Ring and ARCNET.

Used by legacy Ethernet LANs.

CSMA/CD collision detection process:

a. Devices wait a random period of time and retransmit data.

b. Devices detect the collision.

c. Devices transmitting simultaneously will result in a signal collision on the shared

media.

Used by IEEE 802.11 WLANs.

Both CSMA/CA and CSMA/CD:

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

- Uses a process to govern when a device can send and what happens if multiple devices send at the same time.

[CSMA/CA collision avoidance]

When transmitting, devices don't include the time duration needed for the

transmission.

[CSMA/CA collision avoidance]

Other devices on the shared medium receive the time duration information and know how long the medium will be unavailable.

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

A data link frame has three parts:

[Data Link Frame]

The Header's encapsulated information include:

[Data Link Frame]

The Trailer's encapsulated information include:

Is the payload.

The fields of the header and trailer do not vary according to data link layer protocol.

Identifies beginning and end of frame.

Indicates source and destination nodes.

(Done by the MAC Sublayer or the lower layer of the Data Link Layer)

Identifies encapsulated Layer 3 protocol.

(if IPV4 or IPv6 or both)

Identifies flow control services.

(Dependent on the type of data that is being delivered to the destination — if text, audio or voice)

Contains the frame payload.

Used for determine transmission errors.

(Is there tampering? etc. and will be discarded.

If size changed from source and destination, means it was tampered.)

What is the sequence of the frame fields in the Data Link Frame?

1. Frame Start

2. Addressing

3-4. ?????????????

5-6. ?????????????

7. Frame Stop

Also referred to as a physical address.

The Layer 2 (Data Link) Address is contained in the frame header.

Layer 2 (Data Link) Addresses are used only for local delivery of a frame on the link.

The Layer 2 (Data Link) Addresses are not updated by each device that forwards the frame.

The logical topology and physical media - determine the data link protocol used: