2. Session Layer uses the services provided by The transport layer and enables applications to
establish and maintain sessions.
Following are some of the functions which are performed by Session Layer –
• Session Layer works as a dialog controller through which it allows systems to communicate
in either half-duplex mode or full duplex mode of communication.
• This layer is also responsible for token management, through which it prevents two users to
simultaneously access or attempting the same critical operation.
• This layer allows synchronization by allowing the process of adding checkpoints, which are
considered as synchronization points to the streams of data.
• This layer basically provides a mechanism of opening, closing and managing a session
between the end-user application processes.
• This layer also controls single or multiple connections for each-end user application and
directly communicates with both Presentation and transport layers.
• Session Layer uses checkpoints to enable communication sessions which are to be resumed
from that particular checkpoint at which communication failure has occurred.
6. Data Representation
The presentation layer (data presentation layer, data provision level) sets
the system-dependent representation of the data (for example, ASCII,
EBCDIC) into an independent form, enabling the syntactically correct
data exchange between different systems.
11. What are the different types of encryption?
The two main kinds of encryption are symmetric encryption and asymmetric
encryption. Asymmetric encryption is also known as public key encryption.
In symmetric encryption, there is only one key, and all communicating
parties use the same (secret) key for both encryption and decryption.
In asymmetric, or public key, encryption, there are two keys: one key is used
for encryption, and a different key is used for decryption. The decryption key is
kept private (hence the "private key" name), while the encryption key is shared
publicly, for anyone to use (hence the "public key" name).
31. SNMP
1. SNMP stands for Simple Network Management Protocol.
2. SNMP is a framework used for managing devices on the internet.
3. It provides a set of operations for monitoring and managing the internet.
32.
33. SNMP CONCEPT
SNMP has two components Manager and agent.
• The manager is a host that controls and monitors a set of
agents such as routers.
• It is an application layer protocol in which a few manager
stations can handle a set of agents.
• The protocol designed at the application level can monitor the
devices made by different manufacturers and installed on
different physical networks.
• It is used in a heterogeneous network made of different LANs
and WANs connected by routers or gateways.
34. Managers & Agents
• A manager is a host that runs the SNMP client program while the agent is a
router that runs the SNMP server program.
• Management of the internet is achieved through simple interaction between
a manager and agent.
• The agent is used to keep the information in a database while the manager is
used to access the values in the database. For example, a router can store the
appropriate variables such as a number of packets received and forwarded
while the manager can compare these variables to determine whether the
router is congested or not.
• Agents can also contribute to the management process. A server program on
the agent checks the environment, if something goes wrong, the agent sends
a warning message to the manager.
35. Management with SNMP has three basic ideas:
1. A manager checks the agent by requesting the information that reflects the
behavior of the agent.
2. A manager also forces the agent to perform a certain function by resetting
values in the agent database.
3. An agent also contributes to the management process by warning the
manager regarding an unusual condition.
Management Components
Management is not achieved only through the SNMP protocol but also the use
of other protocols that can cooperate with the SNMP protocol. Management is
achieved through the use of the other two protocols: SMI (Structure of
management information) and MIB(management information base).
Management is a combination of SMI, MIB, and SNMP. All these three
protocols such as abstract syntax notation 1 (ASN.1) and basic encoding rules
(BER).
36.
37. SMI
The SMI (Structure of management information) is a component used in network management. Its
main function is to define the type of data that can be stored in an object and to show how to encode
the data for the transmission over a network.
MIB
The MIB (Management information base) is a second component for the network management.
Each agent has its own MIB, which is a collection of all the objects that the manager can manage.
MIB is categorized into eight groups: system, interface, address translation, ip, icmp, tcp, udp, and
egp. These groups are under the mib object.
38. SNMP defines five types of messages: GetRequest, GetNextRequest,
SetRequest, GetResponse, and Trap.
GetRequest: The GetRequest message is sent from a manager (client)
to the agent (server) to retrieve the value of a variable.
GetNextRequest: The GetNextRequest message is sent from the
manager to agent to retrieve the value of a variable. This type of
message is used to retrieve the values of the entries in a table. If the
manager does not know the indexes of the entries, then it will not be
able to retrieve the values. In such situations, GetNextRequest message
is used to define an object.
39. GetResponse: The GetResponse message is sent from an
agent to the manager in response to the GetRequest and
GetNextRequest message. This message contains the value of a
variable requested by the manager.
SetRequest: The SetRequest message is sent from a manager
to the agent to set a value in a variable.
Trap: The Trap message is sent from an agent to the manager to
report an event. For example, if the agent is rebooted, then it
informs the manager as well as sends the time of rebooting.
40.
41. HTTP
1. HTTP stands for HyperText Transfer Protocol.
2. It is a protocol used to access the data on the World Wide Web (www).
3. The HTTP protocol can be used to transfer the data in the form of plain text, hypertext, audio, video,
and so on.
4. This protocol is known as HyperText Transfer Protocol because of its efficiency that allows us to use
in a hypertext environment where there are rapid jumps from one document to another document.
5. HTTP is similar to the FTP as it also transfers the files from one host to another host. But, HTTP is
simpler than FTP as HTTP uses only one connection, i.e., no control connection to transfer the files.
6. HTTP is used to carry the data in the form of MIME-like format.
7. HTTP is similar to SMTP as the data is transferred between client and server. The HTTP differs from
the SMTP in the way the messages are sent from the client to the server and from server to the client.
SMTP messages are stored and forwarded while HTTP messages are delivered immediately.
42. Features of HTTP:
• Connectionless protocol: HTTP is a connectionless protocol. HTTP
client initiates a request and waits for a response from the server. When
the server receives the request, the server processes the request and
sends back the response to the HTTP client after which the client
disconnects the connection. The connection between client and server
exist only during the current request and response time only.
• Media independent: HTTP protocol is a media independent as data can
be sent as long as both the client and server know how to handle the data
content. It is required for both the client and server to specify the content
type in MIME-type header.
• Stateless: HTTP is a stateless protocol as both the client and server know
each other only during the current request. Due to this nature of the
protocol, both the client and server do not retain the information between
various requests of the web pages.
43.
44. WWW
• What is World Wide Web?
• World Wide Web, which is also known as a Web, is a collection
of websites or web pages stored in web servers and connected
to local computers through the internet. These websites contain
text pages, digital images, audios, videos, etc. Users can
access the content of these sites from any part of the world over
the internet using their devices such as computers, laptops, cell
phones, etc. The WWW, along with internet, enables the
retrieval and display of text and media to your device.
45. • The building blocks of the Web are web pages which are formatted in HTML and
connected by links called "hypertext" or hyperlinks and accessed by HTTP. These links
are electronic connections that link related pieces of information so that users can access
the desired information quickly. Hypertext offers the advantage to select a word or phrase
from text and thus to access other pages that provide additional information related to that
word or phrase.
• A web page is given an online address called a Uniform Resource Locator (URL). A
particular collection of web pages that belong to a specific URL is called a website, e.g.,
www.facebook.com, www.google.com, etc. So, the World Wide Web is like a huge
electronic book whose pages are stored on multiple servers across the world.
• Small websites store all of their WebPages on a single server, but big websites or
organizations place their WebPages on different servers in different countries so that when
users of a country search their site they could get the information quickly from the nearest
server.
• So, the web provides a communication platform for users to retrieve and exchange
information over the internet. Unlike a book, where we move from one page to another in
a sequence, on World Wide Web we follow a web of hypertext links to visit a web page
and from that web page to move to other web pages. You need a browser, which is
installed on your computer, to access the Web.
47. • The Web works as per the internet's basic client-server format as shown in the following
image. The servers store and transfer web pages or information to user's computers on the
network when requested by the users. A web server is a software program which serves
the web pages requested by web users using a browser. The computer of a user who
requests documents from a server is known as a client. Browser, which is installed on the
user' computer, allows users to view the retrieved documents.
48. • All the websites are stored in web servers. Just as someone lives on rent in
a house, a website occupies a space in a server and remains stored in it.
The server hosts the website whenever a user requests its WebPages, and
the website owner has to pay the hosting price for the same.
• The moment you open the browser and type a URL in the address bar or
search something on Google, the WWW starts working. There are three
main technologies involved in transferring information (web pages) from
servers to clients (computers of users). These technologies include
Hypertext Markup Language (HTML), Hypertext Transfer Protocol (HTTP)
and Web browsers.
