Module 6 Flashcards
The ______ is responsible for
communications between end-device
network interface cards.
Data Link Layer
Data Link Layer allows upper layer protocols to access
the physical layer media and
encapsulates Layer 3 packets (IPv4
and IPv6) into _____
layer 2 Frames
_____ also performs error detection and
rejects corrupts frames.
Data Link Layer
The Data Link Layer consists of two
sublayers.
- Logical Link Control (LLC)
- Media Access Control (MAC)
_____ sublayer communicates
between the networking software at the
upper layers and the device hardware at
the lower layers.
LLC (Logical Link Control)
______ sublayer is responsible for
data encapsulation and media access
control.
MAC (Media Access Control)
______ exchanged between nodes may experience numerous data
link layers and media transitions.
Packets
At each hop along the path, a router performs four basic Layer 2
functions:
- Accepts a frame from the network medium
- De-encapsulates the frame to expose the encapsulated packet
- Re-encapsulates the packet into a new frame
- Forwards the new frame on the medium of the next network segment
Data link layer protocols are
defined by engineering
organizations:
- Institute for Electrical and Electronics Engineering (IEEE)
- International Telecommunications Union (ITU)
- International Organizations for Standardization (ISO)
- American National Standards Institute (ANSI)
The ______ is the arrangement and relationship of the network
devices and the interconnections between them.
topology of a network
There are two types of topologies used when describing networks:
- Physical Topology
- Logical Topology
shows physical connections and how devices are
interconnected.
Physical Topology
– identifies the virtual connections between devices
using device interfaces and IP addressing schemes
Logical Topology
There are three common physical WAN topologies:
- Point-to-point
- Hub and Spoke
- Mesh
– the simplest and most common WAN topology. Consists of
a permanent link between two endpoints.
point-to-point
similar to a star topology where a central site
interconnects branch sites through point-to-point links
Hub and Spoke
provides high availability but requires every end system to be
connected to every other end system.
Mesh
____- topologies directly connect two nodes.
Physical point-to-point
The nodes may not share the media with other hosts.
Point-to-Point WAN Topology
Because all frames on the media can only travel to or from the two
nodes, _____ protocols can be very simple.
Point-to-Point WAN
_____ on LANs are typically
interconnected using a star or extended
star topology.
End devices
_____
topologies are easy to install, very scalable
and easy to troubleshoot.
Star and extended star
Early Ethernet and Legacy Token Ring
technologies provide two additional
topologies:
- Bus
- Ring
All end systems chained
together and terminated on each end.
Bus
– Each end system is connected
to its respective neighbors to form a
ring.
ring
- 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.
Half-duplex communication
- Allows both devices to simultaneously transmit and receive on a shared medium.
- Ethernet switches operate in full-duplex mode.
Full-duplex communication
All nodes operating in half-duplex, competing for use of the medium. Examples are:
- Carrier sense multiple access with collision detection (CSMA/CD) as used on legacy
bus-topology Ethernet. - Carrier sense multiple access with collision avoidance (CSMA/CA) as used on
Wireless LANs.
Contention-based access
- Deterministic access where each node has its own time on the medium.
- Used on legacy networks such as Token Ring and ARCNET.
Controlled Access
- Used by legacy Ethernet LANs.
- Operates in half-duplex mode where only one device sends or receives at a time.
- Uses a collision detection process to govern when a device can send and what
happens if multiple devices send at the same time.
CSMA/CD
- Devices transmitting simultaneously will result in a signal collision on the shared
media. - Devices detect the collision.
- Devices wait a random period of time and retransmit data.
CSMA/CD collision detection process
- Used by IEEE 802.11 WLANs.
- Operates in half-duplex mode where only one device sends or receives at a time.
- Uses a collision avoidance process to govern when a device can send and what
happens if multiple devices send at the same time.
CSMA/CA
- When transmitting, devices also include the time duration needed for the
transmission. - Other devices on the shared medium receive the time duration information and know
how long the medium will be unavailable.
CSMA/CA collision avoidance process
_____ is encapsulated by the data link layer with a header and a trailer to form a frame
Data
A data link frame has three parts:
- Header
- Data
- Trailer
Identifies beginning and end of frame
Frame Start and Stop
Indicates source and destination nodes
Addressing
Identifies encapsulated layer 3 protocol
Type
Identifies flow control services
Control
Contains the frame payload
Data
Used for determine transmission errors
Error Detection
- Also 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
Layer 2 Addresses
The logical topology and physical media determine the data link
protocol used:
- Ethernet
- 802.11 Wireless
- Point-to-Point (PPP)
- High-Level Data Link Control (HDLC)
- Frame-Relay
