Network Programming

BTCS703
Chat
Chatting online is talking to someone - or many someones - using the Internet to send typed
messages back and forth. You type your message and send it, other people read it and type
their messages and send them. You read the messages, type your reply and send it back etc.
Each person's messages are identified by the screen name of the person who typed it.

A screen name is the name you are known by to this chat group. You may use the same
screen name each time, or choose a different one for each chat session. For security reasons,
do not use your real name. The people you are chatting to may use different names as well.
You may talk to Rose one session, Wonder Woman the next session and Shyness the next,
and be chatting to the same person in all three sessions. On the other hand, you may talk to
Master Fox in five chat sessions and be talking to a different person each time.

You can chat in two ways: using a channel, or using a direct connection.

A channel is where a lot of people are talking together. It is another name for a chat room.
Each channel has a name that should indicate what the people in the room are talking about.
A direct connection is a private conversation between you and another person using the
Internet.

You join chat groups in different ways, depending on what sort of ISP you have.

If you have a PPP account with your ISP, you use the IRC (Internet Relay Chat) to talk.

If you use a large company (such as CompuServe) you chat with other users of that company.

When you first join a chat group, you will see the screen names of people who are already
chatting and a window that is keeping track of their messages. Everyone in the group will be
notified when you join it, so if it is friendly someone should send you a welcome message.

Writing Your Messages

When you are chatting, you use smileys to express your feelings. Common smileys are listed
in the section on E-Mail. Chatters also use simple abbreviations. Some are easy to understand
(for example, u for you). Others are acronyms. A list of some of these appears in the section
on E-Mail.

Things to remember when you join a chat group:

1. The conversation has already been going for a while. Read a full page of exchanges
(messages) before you type any so you understand what people are talking about. Reading
messages without replying is called lurking. When you do say something, you are de-lurking

2. Start by reading the messages from one person, then another person etc until you get
used to following all the different threads of the conversation.
3. Scroll up to read older messages if you have to, and scroll down to see new messages.

4. Do not hurt anyone's feelings. These are people you are talking to.

5. Be cautious. You have no idea who these people are (and if you ask them, they may
lie to you).

6. Keep your messages short, to the point, and clean.

7. If you like, use the chat system to create a profile about yourself that other chatters
can read (as you can read theirs). Do not include any personal information.

8. If you want to talk to someone in private send them a message saying hello, who you
are and what you want.

9. If you join an offensive group by mistake, leave. Fast.

10. If you have someone in your chat group being offensive either ignore them, go to
another chat room or set your screen so you don't get their messages.

Things to remember to chat safely:

1. Many people lie. About anything. This includes personal information.

2. Do not reveal information that enables someone to find you - name, address, phone
number, place of work, suburb, mailing address etc.

3. Never give your password to anyone. No exceptions.

4. Be very cautious if someone without a profile wants to chat with you.

5. If you ever choose to meet a chat friend in person, be very cautious and plan your
meeting with safety in mind

Email
Email is short for 'electronic mail'. Similar to a letter, it is sent via the internet to a recipient.
An email address is required to receive email, and that address is unique to the user. Some
people use internet-based applications and some use programs on their computer to access
and store emails.
Key benefits and features of using email

 It's quick – your recipient receives your email as soon as they go online and collect
their mail.
 It's secure.
 It's low cost.
 Photos, documents and other files can be attached to an email, so that more
information can be shared.
 One email can be sent to more than one recipient at a time.

Email Basics

 The email message - Instead of using a pen to write a letter on paper, you're using
your keyboard to type an email message in an email program on your computer.

 Sending the email - When the email is finished and has been addressed to the
recipient's email address, press the Send button  to allow the email message to reach the
intended recipient.
 Email transport - Email servers transmit messages from sender to recipient.
 Fetching new mail - If you've got new mail in your mailbox, you simply have to
click on it and open it.

Benefits of Using Email

It's advantageous to use email rather than write a letter, send a text or make a telephone call
for the following reasons:

 Convenience - Emails are quicker in some instances than making a phone call, where
you might be left on hold for an extended period of time or forced to engage in lengthy
conversations. Instead, if you have a quick question for someone, sometimes it's easier to
shoot off an email that can be answered at a speedy pace.
 Speed - Emails typically arrive within seconds or minutes.
 Attachments - You can attach any file on your computer to an email message. It's as
easy to send a long master's thesis around the world as it is to email a spreadsheet, a report or
pictures.

 Accessibility - Emails can be stored conveniently in your email program. Good

programs make it easy to organize, archive and search your emails, so any information
contained in an email is always readily accessible.
 A Record - Email provides a record of a conversation that you don't have if
communicating verbally.

 Unlimited space -- Unlike texting, you have unlimited space to write as much as you
want in an email.
Email Flaws

Unfortunately, email's big problem is unsolicited mail, more commonly known asspam.
With hundreds of these junk emails in your inbox, the occasional good email can get lost.
Fortunately, though, sophisticated filters exist that go through your new messages and sort
out the unwanted ones automatically.
To report spam correctly, do the following:

 Identify the real source of the message.

 Find the ISP responsible for the part of the net where the message originated.
 Identify the correct person to contact at that ISP.

The TCP/IP Reference Model

TCP/IP means Transmission Control Protocol and Internet Protocol. It is the network model
used in the current Internet architecture as well. Protocols are set of rules which govern every
possible communication over a network. These protocols describe the movement of data
between the source and destination or the internet. These protocols offer simple naming and
addressing schemes.
Overview of TCP/IP reference model

TCP/IP that is Transmission Control Protocol and Internet Protocol was developed by
Department of Defence's Project Research Agency (ARPA, later DARPA) as a part of a
research project of network interconnection to connect remote machines.

The features that stood out during the research, which led to making the TCP/IP reference
model were:
 Support for a flexible architecture. Adding more machines to a network was easy.
 The network was robust, and connections remained intact untill the source and
destination machines were functioning.
The overall idea was to allow one application on one computer to talk to(send data packets)
another application running on different computer.

Description of different TCP/IP protocols

Layer 1: Host-to-network Layer

1. Lowest layer of the all.

2. Protocol is used to connect to the host, so that the packets can be sent over it.

3. Varies from host to host and network to network.

Layer 2: Internet layer

1. Selection of a packet switching network which is based on a connectionless

internetwork layer is called a internet layer.

2. It is the layer which holds the whole architecture together.

3. It helps the packet to travel independently to the destination.

4. Order in which packets are received is different from the way they are sent.

5. IP (Internet Protocol) is used in this layer.

Layer 3: Transport Layer

1. It decides if data transmission should be on parallel path or single path.

 2. Functions such as multiplexing, segmenting or splitting on the data is done by
transport layer.

3. The applications can read and write to the transport layer.

4. Transport layer adds header information to the data.

5. Transport layer breaks the message (data) into small units so that they are handled
more efficiently by the network layer.

6. Transport layer also arrange the packets to be sent, in sequence.

Layer 4: Application Layer

The TCP/IP specifications described a lot of applications that were at the top of the protocol
stack. Some of them were TELNET, FTP, SMTP, DNS etc.

1. TELNET is a two-way communication protocol which allows connecting to a remote

machine and run applications on it.

2. FTP(File Transfer Protocol) is a protocol, that allows File transfer amongst computer
users connected over a network. It is reliable, simple and efficient.

3. SMTP(Simple Mail Transport Protocol) is a protocol, which is used to transport

electronic mail between a source and destination, directed via a route.

4. DNS(Domain Name Server) resolves an IP address into a textual address for Hosts
connected over a network.

Merits of TCP/IP model

1. It operated independently.

2. It is scalable.

3. Client/server architecture.

4. Supports a number of routing protocols.

5. Can be used to establish a connection between two computers.

Demerits of TCP/IP

1. In this, the transport layer does not guarantee delivery of packets.

2. The model cannot be used in any other application.

3. Replacing protocol is not easy.

4. It has not clearly separated its services, interfaces and protocols.