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Chapter 10: Application Layer (Layers of presentation and session (Layers…
Chapter 10: Application Layer
allow us to send and receive information with relative ease
However, for network professionals, it is important to know how an application can format, transmit and interpret messages
Layers of presentation and session
Layers of presentation
Format the data of the source device, or present it, in a compatible manner so that the destination device receives it.
Compress the data in such a way that the target device can decompress it.
Encrypt the data for transmission and decrypt it upon receipt.
Layers of session
create and maintain dialogs between the source and destination applications.
TCP / IP application layer protocols
specify the format and control information necessary for many common Internet communication functions
Client-server model
The client begins the exchange by requesting the data from the server, who responds by sending one or more data flows to the client
protocols
describe the format of requests and responses between clients and servers.
Networks between pairs
In addition to sharing files, a network like this would allow users to enable network games or share an Internet connection.
Applications
allows a device to function as a client and as a server within the same communication
Common applications
eDonkey
G2
BitTorrent
Bitcoin
Hypertext transfer protocol and hypertext markup language
the browser interprets the three parts of the URL
http (the protocol or scheme)
www.cisco.com (the name of the server)
index.html (the specific file name requested)
HTTP y HTTPS
HTTP
specifies the types of messages that are used for that communication. The three types of common messages are GET, POST and PUT
HTTPS
it uses the same client-response request process from the server as HTTP but uses authentication and encryption to protect the data while traveling between the client and the server..
Operation of POP
mail is downloaded from the server to the client and then deleted on the server
Operation of IMAP
The original messages are kept on the server until they are manually deleted.
DNS message format
Some of these types of records are
A: a terminal IPv4 address
NS: a server with an authoritative name
AAAA: a terminal IPv6 address
MX: a mail exchange record
DHCP operation
ensures that all IP addresses are unique (you can not assign the same IP address to two different network devices simultaneously).
File Transfer Protocol
The client establishes the first connection to the server for control traffic through TCP port 21, which consists of client commands and server responses
The client establishes the second connection to the server for the actual data transfer via TCP port 20. This connection is created every time there is data to transfer.
The applications are computer programs with which the user interacts and which initiate the process of data transfer at the request of the user.