KEY Concept D325 Networks - OSI Model Overview and Networking Concepts
Notes 2025 new update version Western Governors University
OBJECTIVES - NETWORK +
https://partners.comptia.org/docs/default-source/resources/comptia-network-n10-008-exam-objectives-(2- 0)
OSI Model LAYERS
LAYER 1-PHYSICAL
,The physical layer (PHY) of the OSI model (layer 1) is responsible for the transmission and receipt of the
signals that represent bits of data from one node to another node. Different types of transmission media can
be classified as cabled or wireless:
■ Cabled-A physical signal conductor is provided between two nodes. Examples include cable
types such as copper or fiber optic cable. Cabled media can also be described as bounded
media.
■ Wireless-Uses free space between nodes, such as microwave radio. Wireless media can also be
described as unbounded media.
The Physical layer specifies the following:
, ■ Physical topology-The layout of nodes and links as established by the transmission media. An area
of a larger network is called a segment. A network is typically divided into segments to cope with
the physical restrictions of the network media used, to improve performance, or to improve
security. At the Physical layer, a segment is where all the nodes share access to the same media.
■ Physical interface-Mechanical specifications for the network medium, such as cable specifications,
the medium connector and pin-out details (the number and functions of the various pins in a
network connector), or radio transceiver specifications.
■ Signaling—The process of transmitting and receiving encoded data over the network
medium, including modulation schemes and timing/synchronization.
Devices that operate at the Physical layer include:
■ Transceiver-The part of a network interface that sends and receives signals over the network
media.
■ Repeater-A device that amplifies an electronic signal to extend the maximum allowable
distance for a media type.
■ Hub-A multiport repeater, deployed as the central point of connection for nodes.
■ Media converter-A device that converts one media signaling type to another.
■ Modem-A device that performs some type of signal modulation and demodulation, such as
sending digital data over an analog line.
, DATA ENCAPSULATION AND DECAPSULATION
A network protocol is a set of rules for exchanging data in a structured format. A network protocol has two
principal functions:
■ Addressing-Describing where data messages should go. At each layer, there are different
mechanisms for identifying nodes and rules for how they can send and receive messages.
■ Encapsulation-Describing how data messages should be packaged for transmission.
Encapsulation is like an envelope for a letter, with the distinction that each layer requires its
own envelope. At each layer, the protocol adds fields in a header to whatever data (payload) it
receives from an application or other protocol.
LAYER 2-DATA LINK
The data link layer (layer 2) is responsible for transferring data between nodes on the same logical segment. At
the Data Link layer, a segment is one where all nodes can send traffic to one another using hardware
addresses, regardless of whether they share access to the same media. A layer 2 segment might include
multiple physical segments. This is referred to as a logical topology.
Notes 2025 new update version Western Governors University
OBJECTIVES - NETWORK +
https://partners.comptia.org/docs/default-source/resources/comptia-network-n10-008-exam-objectives-(2- 0)
OSI Model LAYERS
LAYER 1-PHYSICAL
,The physical layer (PHY) of the OSI model (layer 1) is responsible for the transmission and receipt of the
signals that represent bits of data from one node to another node. Different types of transmission media can
be classified as cabled or wireless:
■ Cabled-A physical signal conductor is provided between two nodes. Examples include cable
types such as copper or fiber optic cable. Cabled media can also be described as bounded
media.
■ Wireless-Uses free space between nodes, such as microwave radio. Wireless media can also be
described as unbounded media.
The Physical layer specifies the following:
, ■ Physical topology-The layout of nodes and links as established by the transmission media. An area
of a larger network is called a segment. A network is typically divided into segments to cope with
the physical restrictions of the network media used, to improve performance, or to improve
security. At the Physical layer, a segment is where all the nodes share access to the same media.
■ Physical interface-Mechanical specifications for the network medium, such as cable specifications,
the medium connector and pin-out details (the number and functions of the various pins in a
network connector), or radio transceiver specifications.
■ Signaling—The process of transmitting and receiving encoded data over the network
medium, including modulation schemes and timing/synchronization.
Devices that operate at the Physical layer include:
■ Transceiver-The part of a network interface that sends and receives signals over the network
media.
■ Repeater-A device that amplifies an electronic signal to extend the maximum allowable
distance for a media type.
■ Hub-A multiport repeater, deployed as the central point of connection for nodes.
■ Media converter-A device that converts one media signaling type to another.
■ Modem-A device that performs some type of signal modulation and demodulation, such as
sending digital data over an analog line.
, DATA ENCAPSULATION AND DECAPSULATION
A network protocol is a set of rules for exchanging data in a structured format. A network protocol has two
principal functions:
■ Addressing-Describing where data messages should go. At each layer, there are different
mechanisms for identifying nodes and rules for how they can send and receive messages.
■ Encapsulation-Describing how data messages should be packaged for transmission.
Encapsulation is like an envelope for a letter, with the distinction that each layer requires its
own envelope. At each layer, the protocol adds fields in a header to whatever data (payload) it
receives from an application or other protocol.
LAYER 2-DATA LINK
The data link layer (layer 2) is responsible for transferring data between nodes on the same logical segment. At
the Data Link layer, a segment is one where all nodes can send traffic to one another using hardware
addresses, regardless of whether they share access to the same media. A layer 2 segment might include
multiple physical segments. This is referred to as a logical topology.
