1.3.2: OSI Model Facts // 1.3.3: OSI Model Layers
Mnemonic for OSI (from top to bottom)
All people seem to need data processing
protocols associated with the application layer include
HTTP, FTP, TFTP, and SMTP
OSI layers are theoretical and do not actually perform real functions, a particular protocol implementation may not represent every OSI layer, industry implementations rarely have layer-to-layer correspondence with the OSI layers
OSI model limitations
Mnemonic for OSI (bottom to top)
Please do not throw sausage pizza away
connection-oriented protocol that takes advantage of sequencing, error correction, and flow control to assure that data sent from upper layers is received at the receiving device
TCP
two specific protocols that are used at the transport layer
TCP and UDP
referred to as a connectionless protocol because it is more concerned with moving data through the network, without necessarily ensuring that everything arrives at the destination device
UDP
the data that comes down to the physical layer is just
a series of bits or radio signals
benefits of the OSI model
aids in troubleshooting, allows specialization of features at different levels, provides modularity
the top layers (layers five, six, and seven) in the three-layer OSI grouping are called the
application layers
the bottom layers (layers one and two) in the three-layer OSI grouping are called the
architecture layers
one very important thing that happens at the networking layer is the
assignment of IP addresses
when grouping the OSI model layers, the _________________ because the bottom layers are related to the network architecture
bottom two layers are separated from the top five layers
a mathematical value that helps the receiving device identify any errors that may have occurred during transmission
cyclic redundancy check (CRC)
responsible for interfacing between the physical transmission media - the physical devices - and the network layer
data link layer
where the MAC address is assigned after a packet arrives from the network layer
data link layer
the bottom layers of the OSI model
dictate how devices are connected and how data is transmitted
the transport layer is also responsible for ___________________ (data being sent too fast or too slow)
flow control between two hosts
the presentation layer can be thought of as the ________________ - it deals with ______________________
formatting layer, syntax, encryption, and compression
data at the data link layer is called a
frame
the network layer packet with the MAC address of the source and destination devices added, as well as a cyclic redundancy check (CRC)
frame
each service (ex. HTTP, SMTP) ____________ so that the transport layer can identify the upper layer protocol that the data is intended for
is assigned a port number
provides the interface between the lower and upper layers in the data link layer
logical link control layer (LLC)
the data link layer also defines the
logical topology of the network (how devices access the media)
responsible for identifying how devices can access the physical medium - part of the data link layer
medium access control sublayer (MAC)
the middle (transport) layers handle how
messages get from one device to another through the network
although we associate protocols with the application layer, __________________ because programmers create protocols and services that function through multiple layers
most of the protocols extend down to the session layer
the bottom two layers of the OSI model are related to the
network architecture or physical hardware
responsible for moving data between systems throughout the internetwork; where routing happens
network layer
the top five layers of the OSI model are the
networking protocols, such as TCP/IP
where we work with physical hardware; also includes protocols that identify the cables, connectors, and devices that can be used on the network (ex. using the CAT6 protocol to define the types of cables used in the network, and using the RJ-45 protocol to define the connectors to use)
physical layer
a number which identifies an upper layer service running on a server (ex. installing a web server and an email server on the same physical system - information from lower levels needs to be directed up to the higher levels, which is done using these numbers)
port number
the transport layer assigns
port numbers
ex. when the SSL encrypts data on a website that is using the HTTP protocol
presentation layer
takes a message sent from a device to a router to another router until it reaches the destination device
routing
specify how each router identifies destination networks and the path data should take to arrive at that destination network
routing protocols
another common way to group the OSI model is to ___________________, creating three layers
separate the two middle layers (layers three and four) from the top
the application layers handle
service protocols like HTTP and DNS
ex. multiple clients connects to a web server (each client has its own ID and is called a session)
session layer
responsible for creating sessions (client connections) between communication devices and terminating session
session layer
the top five layers of the OSI model are concerned with
software and applications
responsible for integrating network services with the operating system; provides an interface between the application running on the system and the rest of the network
the application layer
what are the two sub layers of the data link layer?
the logical link control layer (LLC) and media access control sublayer (MAC)
when a segment is passed off to the network layer,
the source and destination IP addresses are added to the segment, and the data then becomes a packet
ex. divides the data of a file you need to download into smaller segments so the data can be passed
transport layer
responsible for delivering data on a network - receives data from the upper layers and segments it
transport layer
the middle layers (layers three and four) in the three-layer OSI grouping are called the
transport layers
