TRANSPORT AND
NETWORK LAYERS
• HTTP, FTP, and Remote Desktop are all
examples of client-server applications.
• When a client or server application runs on a
computer, it is assigned a port number at the
transport layer of the OSI model.
• This port is used to identify the application
when multiple applications run on the same
computer
The transmission control protocol (TCP)
is used at the transport layer of the OSI
model.
• TCP is responsible for guaranteeing data is
received and in the correct order.
The Internet protocol (IP) is used at the
network layer of the OSI model and is
responsible for breaking down messages
into packets small enough to travel through
the network.
• The network layer uses IP addresses to
locate a computer or other device on the
network.
• IP addresses function much like mailbox
addresses used by the postal service.
Two versions of IP addresses are used
today.
• IP version 4 (IPv4) uses 32 bits in an
address, which is divided into 4 octets of 8
bits each.
• The newer version of IP addresses is IP
version 6 (IPv6).
• IPv6 uses 128 bits and these bits are
divided into blocks of 16 bits each.
The service that controls the translation
from words to numbers is called the
domain name service (DNS).
• The DNS resolves domain names into the
IP address that the network understands to
reach the correct computer on the intranet
or Internet.
• The DNS runs in the background on a
computer, and a user does not need to be
aware that it is running.