BHARTI VIDYAPEETH’S

JAWAHARLAL NEHRU INSTITUTE OF TECHNOLOGY

SUB: CAN(22520) CLASS:CM5I

ASSSIGNMENT 5: APPLICATION LAYER PROTOCOL

*1) WRITE SHORT NOTE ON:

a) URL b) STATIC DOCUMENT c) DYNAMIC
DOCUMENT d) WWW
--a) URL: A Uniform Resource Locator (URL),
colloquially termed a web address is a reference to
a web resource that specifies its location on
a computer network and a mechanism for retrieving it.
A URL is a specific type of Uniform Resource
Identifier (URI) ,although many people use the two
terms interchangeably. URLs occur most commonly to
reference web pages (http), but are also used for file
transfer (ftp), email (mailto), database access (JDBC),
and many other applications.

--b)STATIC DOCUMENT: A static web document resides

in a file that it is associated with a web server. The
author of a static document determines the contents at
the time the document is written. Because the
contents do not change, each request for a static
document results in exactly the same response.

--c)DYNAMIC DOCUMENT: A dynamic web document

does not exist in a predifined form. When a request
arrives the web server runs an application program
that creates the document. The server returns the
output of the program as a response to the browser
that requested the document. Because a fresh
document is created for each request, the contents of a
dynamic document can vary from one request to
another.
--d)WWW: The World Wide Web (WWW), commonly
known as the Web, is an information system where
documents and other web resources are identified
by Uniform Resource Locators which may be
interlinked by hypertext, and are accessible over
the Internet. The resources of the Web are transferred
via the Hypertext Transfer Protocol (HTTP), may be
accessed by users by a software application called
a web browser, and are published by a software
application called a web server. The World Wide Web
is not synonymous with the Internet, which pre-
existed the Web in some form by over two decades
and upon whose technologies the Web is built.

*2) WHAT IS FILE TRANSFER PROTOCOL(FTP)?

--The File Transfer Protocol (FTP) is a
standard network protocol used for the transfer
of computer files between a client and server on
a computer network.
FTP is built on a client-server model architecture
using separate control and data connections between
the client and the server.FTP users may authenticate
themselves with a clear-text sign-in protocol, normally
in the form of a username and password, but can
connect anonymously if the server is configured to
allow it. For secure transmission that protects the
username and password, and encrypts the content,
FTP is often secured with SSL/TLS (FTPS) or replaced
with SSH File Transfer Protocol (SFTP).

*3)EXPLAIN THE CONCEPT OF TELNET.

--Telnet is an application protocol used on
the Internet or local area network to provide a
bidirectional interactive text-oriented communication
facility using a virtual terminal connection.
The term telnet is also used to refer to the software
that implements the client part of the protocol. Telnet
client applications are available for virtually
all computer platforms. Telnet is also used as
a verb. To telnet means to establish a connection using
the Telnet protocol, either with a command line client
or with a graphical interface.

*4) EXPLAIN SSH AND ITS PACKET FORMAT.

--SSH(secure shell) is a software package that
enables secure system administration and file
transfers over insecure networks. It is used in nearly
every data center and in every large enterprise.
The SSH protocol uses encryption to secure the
connection between a client and a server. All user
authentication, commands, output, and file transfers
are encrypted to protect against attacks in the
network.
*5) WHAT IS THE DIFFERENCE BETWEEN HTTP
AND HTTPS?
--Beloware some of the main differences between the
HTTP and HTTPS protocols:
 1. HTTP URL in your browser's address bar
is http:// and the HTTPS URL is https://.
2. HTTP is unsecured while HTTPS is secured.
3. HTTP sends data over port 80 while HTTPS uses
port 443.
4. HTTP operates at application layer, while HTTPS
operates at transport layer.
5. No SSL certificates are required for HTTP, with
HTTPS it is required that you have an SSL
certificate and it is signed by a CA.
6. HTTP doesn't require domain validation, where
as HTTPS requires at least domain validation and
certain certificates even require legal document
validation.
7. No encryption in HTTP, with HTTPS the data is
encrypted before sending.

*6)EXPLAIN THE EMAIL ARCHITECTURE AND

SERVICES.
--The architecture mainly consist of two subsystems:
the user agents, which allow people to read and send
e-mail, and the message transfer agents, which move
the messages from the source to the destination. The
user agents are local programs that provide a
command-based, menu-based, or graphical method for
interacting with the e-mail system. The message
transfer agents are typically system daemons, that is,
processes that run in the background. Their job is to
move e-mail through the system.

Typically, e-mail systems support five basic functions.

Let us take a look at them.

Composition refers to the process of creating

messages and answers. Although any text editor can
be used for the body of the message, the system itself
can provide assistance with addressing and the
numerous header fields attached to each message. For
example, when answering a message, the e-mail
system can extract the originator's address from the
incoming e-mail and automatically insert it into the
proper place in the reply.

Transfer refers to moving messages from the

originator to the recipient. In large part, this requires
establishing a connection to the destination or some
intermediate machine, outputting the message, and
releasing the connection. The e-mail system should do
this automatically, without bothering the user.
Reporting has to do with telling the originator what
happened to the message. Was it delivered? Was it
rejected? Was it lost? Numerous applications exist in
which confirmation of delivery is important and may
even have legal significance (''Well, Your Honor, my e-
mail system is not very reliable, so I guess the
electronic subpoena just got lost somewhere'').

Displaying incoming messages is needed so people

can read their e-mail. Sometimes conversion is
required or a special viewer must be invoked, for
example, if the message is a PostScript file or digitized
voice. Simple conversions and formatting are
sometimes attempted as well.

Disposition is the final step and concerns what the

recipient does with the message after receiving it.
Possibilities include throwing it away before reading,
throwing it away after reading, saving it, and so on. It
should also be possible to retrieve and reread saved
messages, forward them, or process them in other
ways.
*7)WRITE SHORT NOTE ON:
a)PROXY SERVER b)TFTP

--a)PROXY SERVER: A proxy server is basically

another computer which serves as a hub through
which internet requests are processed. By connecting
through one of these servers, your computer sends
your requests to the server which then processes your
request and returns what you were wanting.
Moreover, in this way it serves as an intermediary
between your home machine and the rest of the
computers on the internet. Proxies are used for a
number of reasons such as to filter web content, to go
around restrictions such as parental blocks, to screen
downloads and uploads and to provide anonymity
when surfing the internet.
b)TFTP: The Trivial File Transfer Protocol (TFTP)
is a protocol layered on the User Datagram transport
Protocol (UDP) used over the Internet Protocol (IPv4
or IPv6). FTP is a very simple file transfer protocol. It
was first specified in 1980 and provides functions to
copy files across a network (a very basic form of FTP).
It is defined in [RFC2347]. Since it is so simple, it is
easy to implement in a very small amount of memory,
an important consideration at that time it was defined.
TFTP is therefore sometimes useful for booting or
loading the configuration of systems (such as routers,
thin client, and wireless base stations) which do not
have data storage devices. TFTP has no authentication
or encryption mechanisms, and generally provides the
same access to all files in the TFTP directory. Due to
this lack of security, use of TFTP can be dangerous
over the open Internet. Therefore, TFTP is generally
only used on private local area networks for
applications where ftp would be too expensive or
difficult to implement (e.g. down-loading firmware,
software and configuration data to network devices).

*8)EXPLAIN MIME IN DETAIL.

--Multipurpose Internet Mail Extensions (MIME) is
an Internet standard that extends the format
of email messages to support text in character
sets other than ASCII, as well as attachments of audio,
video, images, and application programs. Message
bodies may consist of multiple parts, and header
information may be specified in non-ASCII character
sets. Email messages with MIME formatting are
typically transmitted with standard protocols, such as
the Simple Mail Transfer Protocol (SMTP), the Post
Office Protocol (POP), and the Internet Message Access
*Features of MIME –
1. It is able to send multiple attachments with a
single message.
2. Unlimited message length.
3. Binary attachments (executables, images, audio, or
video files) which may be divided if needed.
4. MIME provided support for varying content types
and multi-part messages.

*9) ENLIST THE APPLICATION LAYER PROTOCOL

ALONG WITH ITS PORT NUMBER.
--
PROTOCOLS
PORTS TRANSPORT
(SERVICE
NUMBERS PROTOCOLS
NAMES)
1.File Transfer
20 and 21 TCP
Protocol (FTP)
2.Secure Shell
22 TCP and UDP
(SSH)
3.Telnet 23 TCP
4.Simple Mail
Transfer
25 TCP
Protocol
(SMTP)
5.Domian
Name System 53 TCP and UDP
(DNS)
6.Trivial File
Transfer
69 UDP
Protocol
(TFTP)
7.Hyper Text
Transfer
80 TCP
Protocol
(HTTP)
8.Dynamic 67 and 68 UDP
Host
Configuration
Protocol
(DHCP)
9.HyperText 443
Transfer Protocol
Secure.

*10)DESCRIBE SMTP WITH ITS COMMANDS.

--Simple Mail Transfer Protocol (SMTP)
Email is emerging as one of the most valuable services
on the internet today. Most of the internet systems use
SMTP as a method to transfer mail from one user to
another. SMTP is a push protocol and is used to send
the mail whereas POP (post office protocol) or IMAP
(internet message access protocol) are used to retrieve
those mails at the receiver’s side.

HELO
It’s the first SMTP command: is starts the conversation
identifying the sender server and is generally followed
by its domain name.
EHLO
An alternative command to start the conversation,
underlying that the server is using the Extended SMTP
protocol.
MAIL FROM
With this SMTP command the operations begin: the
sender states the source email address in the “From”
field and actually starts the email transfer.
RCPT TO
It identifies the recipient of the email; if there are more
than one, the command is simply repeated address by
address.
SIZE
This SMTP command informs the remote server about
the estimated size (in terms of bytes) of the attached
email. It can also be used to report the maximum size
of a message to be accepted by the server.
DATA
With the DATA command the email content begins to
be transferred; it’s generally followed by a 354 reply
code given by the server, giving the permission to start
the actual transmission.
VRFY
The server is asked to verify whether a particular email
address or username actually exists.
*11)STATE THE USE OF POP.
--A point of presence (PoP) is an
artificial demarcation point or interface point between
communicating entities. A common example is
an Internet point of presence, the local access point
that allows users to connect to the Internet with
their Internet service provider (ISP). A PoP typically
houses servers, routers, network switches,
multiplexers, and other network interface equipment,
and is typically located in a data center. ISPs typically
have multiple PoPs. PoPs are often located at Internet
exchange points and colocation centres.
*12)WHAT IS IMAP?
--In computing, the Internet Message Access
Protocol (IMAP) is an Internet
standard protocol used by email clients to
retrieve email messages from a mail server over
a TCP/IP connection. IMAP is defined by RFC 3501.
IMAP was designed with the goal of permitting
complete management of an email box by multiple
email clients, therefore clients generally leave
messages on the server until the user explicitly deletes
them. An IMAP server typically listens on port
number 143. IMAP over SSL (IMAPS) is assigned the
port number 993.
Virtually all modern e-mail clients and servers support
IMAP, which along with the earlier POP3 (Post Office
Protocol) are the two most prevalent standard
protocols for email retrieval Many webmail service
providers such as Gmail, Outlook.com and Yahoo!
Mail also provide support for both IMAP and POP3.
*13)WRITE A SHORT NOTE ON SNMP.
--The SimpleNetworkManagement Protocol
(SNMP) is a framework for managing devices in
an internet using the TCP/IP protocol suite. It
provides a set of fundamental operations for
monitoring and maintaining an internet.
SNMP uses the concept of manager and agent. That is,
a manager, usually a host, controls and monitors a set
of agents, usually routers.
SNMP is an application-level protocol in which a few
manager stations control a set of agents. The protocol
is designed at the application level so that it can
monitor devices made by different manufacturers and
installed on different physical networks. In other
words, SNMP frees management tasks from both the
physical characteristics of the managed devices and
the underlying networking technology. It can be used
in a heterogeneous internet made of different LANs
and WANs connected by routers or gateways made by
different manufacturers.

*14)DRAW AND EXPLAIN DNS IN DETAIL.

--DNS is a host name to IP address translation service.
DNS is a distributed database implemented in a
hierarchy of name servers. It is an application layer
protocol for message exchange between clients and
servers.

Requirement:
Every host is identified by the IP address but
remembering numbers is very difficult for the people
and also the IP addresses are not static therefore a
mapping is required to change the domain name to IP
address. So DNS is used to convert the domain name of
the websites to their numerical IP address.

*15)DRAW AND EXPLAIN DHCP(DYNAMIC HOST

CONFIGURATION PROTOCOL) IN DETAIL.
--Dynamic Host Configuration Protocol(DHCP) is an
application layer protocol which is used to provide:
1. Subnet Mask
2. Router Address
3. DNS Address
4. Vendor Class Identifier/
 5. DHCP is based on a client-server model and based
on discovery, offer, request, and ACK.
DHCP port number for server is 67 and for the client
is 68. It is a Client server protocol which uses UDP
services. IP address is assigned from a pool of
addresses. In DHCP, the client and the server exchange
mainly 4 DHCP messages in order to make a
connection, also called DORA process, but there are 8
DHCP messages in the process.