List and Describe Four Methods That Are Used to Connect to the Internet ? NETWORK TYPES ?

 NETWORK TYPES

List & Describe Four Methods That Are Used to Connect to the Internet :
What are network types ?
First :After defining networks and physical structure of computer network 

• defining networks
• physical structure of computer network

What are criteria of distinguishing one type of network from another is:

• difficult and sometimes confusing.
• We use a few criteria such as size, geographical coverage, and ownership to make this distinction.

What are the Different Ways to Connect to the Internet?

types of networks :
1__Local Area Network:
What is Local Area Network ?

• A local area network (LAN) is usually privately owned and connects some hosts in a single office,building, or campus.
• Depending on the needs of an organization,
• a LAN can be as simple as two PCs and a printer in someone’s home office, or it can extend throughout a company and include audio and video devices.

Each host in a LAN has :

•  an identifier
• an address
• that uniquely defines the host in the LAN.

NOTE:

• A packet sent by a host to another host carries both the source host’s and the destination host’s addresses.
• In the past, all hosts in a network were connected through a common cable :
• which meant that a packet sent from one host to another was received by all hosts.
• The intended recipient kept the packet; the others dropped the packet.
• Today, most LANs use a smart connecting switch, which is able to recognize the destination address of the packet and guide the packet to its destination without sending it to all other hosts.
• The switch alleviates the traffic in the LAN and allows more than one pair to communicate with each other at the same time if there is no common source and destination among them.
• When LANs were used in isolation they were designed to allow resources to be shared between the hosts.
• LANs today are connected to each other and to WANs to create communication at a wider level.

2__Wide Area Network :
What is Wide Area Network (WAN)?What is WAN?
A wide area network (WAN) is also an interconnection of devices capable of communication.

What is the difference between a LAN and a WAN ?there are some differences between a LAN and a WAN :

• A LAN is normally limited in size.
•  spanning an office, a building, or a campus.
• A LAN interconnects hosts .
• A LAN is normally privately owned by the organization that uses it.

• a WAN has a wider geographical span, spanning a town, a state, a country, or even the world.
• a WAN interconnects connecting devices such as switches, routers, or modems.
• a WAN is normally created and run by communication companies and leased by an organization that uses it.

We see two distinct examples of WANs today:
 point-to-point WANs and switched WANs.

Types of network WAN :
1__Point-to-Point WAN :
What is Point-to-Point WAN ?
A point-to-point WAN is a network that connects two communicating devices through a transmission media (cable or air).
an example of a point-to-point WAN :

2__Switched WAN
What is Switched WAN ?

• A switched WAN is a network with more than two ends.
• used in the backbone of global communication today.
• We can say that a switched WAN is a combination of several point-to-point WANs that are connected by switches.

an example of a switched WAN :

Internetwork

What is Internetwork?
Today, it is very rare to see a LAN or a WAN in isolation; they are connected to one another.
 When two or more networks are connected, they make an internetwork, or internet.
NOTE:
As an example, assume that an organization has two offices, one on the east coast and the other on the west coast.
 Each office has a LAN that allows all employees in the office to communicate with each other.
To make the communication between employees at different offices possible, the management leases a point-to-point dedicated WAN from a service provider, such as a telephone company, and connects the two LANs.
Now the company has an internetwork, or a private internet (with lowercase i).
Communication between offices is now possible.

3__Switching :
What is Switching ?
An internet is a switched network in which a switch connects at least two links together.
A switch needs to forward data from a network to another network when required.

Network Switching: Definition & Types :
The two most common types of switched networks are :
1__circuit-switched networks :
What is circuit-switched networks?
What is the difference between a circuit-switched and a packet-switched networks ?

In a circuit-switched network,

• a dedicated connection, called a circuit, is always available between the two end systems.
• the switch can only make it active or inactive.
• circuit switching was very common in telephone networks in the past, although part of
• the telephone network today is a packet-switched network.

Example_1_circuit-switched network :
A circuit-switched network

OR

Example_2_circuit-switched network :

• the four telephones at each side are connected to a switch. 
• The switch connects a telephone set at one side to a telephone set at the other side.
• The thick line connecting two switches is a high capacity communication line that can handle
• four voice communications at the same time.
• the capacity can be shared between all pairs of telephone sets.
• The switches used in this example have forwarding tasks but no storing capability.
• Let us look at two cases.

In the first case :

• all telephone sets are busy.
• four people at one site are talking with four people at the other site .
• the capacity of the thick line is fully used.

In the second case :

• only one telephone set at one side is connected to a telephone set at the other side;
• only one-fourth of the capacity of the thick line is used.
• This means that a circuit-switched network is efficient only when it is working at its full capacity; most of the time, it is inefficient because it is working at partial capacity.

NOTE:

The reason that we need to make the capacity of the thick line four times the capacity of each voice line is that we do not want communication to fail when all telephone sets at one side want to be connected with all telephone sets at the other side. 

2__packet-switched networks:
What is packet-switched networks?
In a computer network, the communication between the two ends is done in blocks of data called packets.
In other words, instead of the continuous communication we see between two telephone sets when they are being used, we see the exchange of individual data packets between the two computers. 

This allows us to make the switches function for both storing and forwarding because a packet is an independent entity that can be stored and sent later.

Example_1_packet-switched networks :
A packet-switched network

OR

Example_2_packet-switched network :

• small packet-switched network that connects four computers at one site to four computers at the other site.
• A router in a packet-switched network has a queue that can store and forward the packet.
• Now assume that the capacity of the thick line is only twice the capacity of the data line connecting the computers to the routers.
• If only two computers (one at each site) need to communicate with each other, there is no waiting for the packets.
• However, if packets arrive at one router when the thick line is already working at its full capacity,
• the packets should be stored and forwarded in the order they arrived.
• The two simple examples show that a packet-switched network is more efficient than a circuit switched network, but the packets may encounter some delays.

4__The Internet :

What is Internet network ?
 Is two or more networks that can communicate with each other.
The most notable internet is called the Internet,

and is composed of thousands of interconnected networks.

shows a conceptual (not geographical) view of the Internet. 

The figure shows the Internet as several backbones, provider networks, and customer networks. At the top level.
What is a backbones ?
backbones are large networks owned by some communication companies such as Sprint, Verizon (MCI), AT&T, and NTT.

What is peering points ?
The backbone networks are connected through some complex switching systems, called peering points.
At the second level, there are smaller networks, called provider networks .

What is provider networks ?
that use the services of the backbones for a fee.
The provider networks are connected to backbones and sometimes to other provider networks.

What is customer networks ?
The customer networks are networks at the edge of the Internet that actually use the services provided by the Internet.
They pay fees to provider networks for receiving services.

What is Internet Service Providers (ISPs) ?
Backbones and provider networks are also called Internet Service Providers (ISPs).
The backbones are often referred to as international ISPs;
the provider networks are often referred to as national or regional ISPs. 

5__Accessing the Internet :
What is Accessing the Internet ?
The Internet today is an internetwork that allows any user to become part of it.
The user, however, needs to be physically connected to an ISP.
How can I access Internet for free?
How do you create a physical connection?
The physical connection is normally done through a point-to-point WAN.

In this section, we briefly describe how this can happen.

List & Describe Four Methods That Are Used to Connect to the Internet =
What are ways to access the Internet?
1__Using Telephone Networks:
What is Telephone Networks ?
How does a computer connect to Internet with a telephone network ?
Today most residences and small businesses have telephone service, which means they are connected to a telephone network.
Since most telephone networks have already connected themselves to the Internet, one option for residences and small businesses to connect to the Internet is to change the voice line between the residence or business and the telephone center to a point-to-point WAN.

what is the difference between dial up and DSL Service =
difference between dial up and DSL:
How can you connect the Internet through telephone?
This can be done in two ways :
1_Dial-up service :
What is Dial-up service ?
The first solution is to add to the telephone line a modem that converts data to voice.
The software installed on the computer dials the ISP and imitates making a telephone connection. Unfortunately ,the dial-up service:
 is very slow, and when the line is used for Internet connection, it cannot be used for telephone (voice) connection.

2__DSL Service :
What is DSL Service ?
Since the advent of the Internet, some telephone companies have upgraded their telephone lines to provide higher speed Internet services to residences or small businesses.
The DSL service also allows the line to be used simultaneously for voice and data communication.
Difference Between Dial-Up Modem and DSL .

3__Using Cable Networks :
What is Cable Networks ?
More and more residents over the last two decades have begun using cable TV services instead of antennas to receive TV broadcasting.
The cable companies have been upgrading their cable networks and connecting to the Internet.
 A residence or a small business can be connected to the Internet by using this service.
It provides a higher speed connection, but the speed varies depending on the number of neighbors that use the same cable.

Dial-Up vs. DSL vs. Cable ?

4__Using Wireless Networks :
What is Wireless Networks ?
Wireless connectivity has recently become increasingly popular.
A household or a small business can use a combination of wireless and wired connections to access the Internet.
With the growing wireless WAN access, a household or a small business can be connected to the Internet through a wireless WAN.

5__Direct Connection to the Internet :
What is Direct Connection to the Internet ?
A large organization or a large corporation can itself become a local ISP and be connected to the Internet.
This can be done if the organization or the corporation leases a high-speed WAN from a carrier provider and connects itself to a regional ISP.
For example, a large university with several campuses can create an internetwork and then
connect the internetwork to the Internet.

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