Transcript Project #1 - How Data Flows - Alexandra Mikolai`s ePortfolio

How Data Flows Across a
Network
Alexandra Mikolai
This presentation will cover the following
concepts:
Local Network Connectivity to the Internet
Router and Switch Functions
MAC Addresses
 Use of Layers to View Data Flow
Data Flow Across Networks
Protocol (HTTP and TCP) Usage
Processing IP
What exactly is the internet?
• Basically, the internet is a network of networks.
• It’s a global system of interconnected computers that
use a standard internet protocol suite to serve
billions of users.
Hypothetical Example
To understand how data flows across networks
we’re going to use the example of Rebecca:
Rebecca prefers to shop from our
website at home using her laptop.
Some components need to be in
place before Rebecca can open her
Internet browser:
1. Internet Connection
2. Network Interface Card
1. Internet Connection
• There are various ways to connect to the
internet:
– Dial up
– Ethernet
– Wireless (Wi-Fi)
• For our example, let’s say that Rebecca has a
Wireless Local Area Network (WLAN) set up in
her home.
What does Rebecca’s WLAN consist of?
The router is plugged into the
modem with an Ethernet
cable. The router converts the
signal into radio waves.
Internet
Service
Provider
(ISP)
Modem
The modem is plugged
into the wall with a
coaxial cable.
Router/Switch
Laptop
iPad
Side note on Switches
• This is a switch:
• Since Rebecca has a small
home network, she most likely has one switch
built into her router.
• On larger networks though, switches like the one
above will be used to connect all of the devices to
the network.
• The switch attaches with an Ethernet to the
modem.
• Switches connect devices to a network, whereas
routers connect networks to other networks.
What does Rebecca’s WLAN consist of?
The router is plugged into the
modem with an Ethernet
cable. The router converts the
signal into radio waves.
Internet
Service
Provider
(ISP)
Modem
The modem is plugged
into the wall with a
coaxial cable.
Router/Switch
Laptop
iPad
The network interface
cards (NICs) pick up the
radio wave signal from
the router.
2. Network Interface Card (NIC)
• A Network Interface Card, or NIC, is a device
located on the motherboard of most
computers that allows for the sending and
receiving of data.
• Every NIC has it’s own unique serial number
called the MAC Address.
• The MAC Address is the physical
address of the hardware
The MAC Address
• MAC = media access control
• 48-bit serial number
• The MAC is used as an identifier in the
sending and receiving of data.
Progress Report:
Local Network Connectivity to the Internet
Router and Switch Functions
MAC Addresses
 Use of Layers to View Data Flow
Data Flow Across Networks
Protocol (HTTP and TCP) Usage
Processing IP
So exactly how does data flow
through a network?
• There are rules, called protocols, which
determine how data passes through a network.
• There are two important protocol models that
you should know:
– The OSI model
– TCP/IP Model
• The TCP/IP model is the standard protocol suite
used, however, it’s basically just a condensed
version of the OSI model which is why you should
know the components of both.
The Open Systems Interconnection
(OSI) Model:
OSI model
establishes seven
protocol layers that
allow for
communication
over networks.
Physical Layer
• The physical layer consists of the hardware
that is used to send and receive data between
networks.
– The best example of the hardware used at the
physical layer is unshielded twisted pair cabling
Data Link Layer
• The data link layer provides the means for how
data enters and leaves the physical layer.
• The Network Interface Card (NIC) operates on the
data link layer.
– To send data, the NIC first breaks the data up into
chunks called frames.
– The frame consists of the destination MAC Address,
the source MAC Address, the data itself, and
something called a frame check sequence, or FCS.
• An FCS is used to verify that the data arrived intact.
Frame
Destination
MAC Address
Source
MAC Address
Data
FCS
Network Layer
• The network layer includes the switch and router.
• Internet Protocol (IP) packets are created.
– The packets use IP addresses to insure that the data
reaches the right place on the network.
– The router uses the IP address to forward the data to it’s
correct location.
– The IP Packet is located inside the frame that was created
during the data link layer
IP Packet
Destination
IP Address
Source
IP Address
Data
Transport Layer
• The transport layer is involved with the
assembly and disassembly of of data.
• The transport layer breaks the data into
chunks and then places the chunks into TCP
segments.
– TCP = transfer control protocol. It is a connectionoriented protocol which means the client and
server both have to verify a good connection
before data can be sent/received.
Session Layer
• The session layer handles all of the sessions
for a system.
– It initiates sessions, accepts incoming sessions,
and opens and closes existing sessions.
Presentation Layer
• The presentation layer converts data into
formats that are readable by the system.
Application Layer
• The Application layer consists of the software
applications that you use on your computer.
• For example, to access a website you would
need to use your internet browser.
Progress Report:
Local Network Connectivity to the Internet
Router and Switch Functions
MAC Addresses
 Use of Layers to View Data Flow
Data Flow Across Networks
Protocol (HTTP and TCP) Usage
Processing IP
Now let’s get back to our example
with Rebecca:
We’ve established that she does have a good
internet connection so she’s going to try and
access our webserver from her home
network
First Rebecca needs to open her web
browser
I personally prefer
Google Chrome, but
other popular web
browsers include
Mozilla FireFox, Safari,
and Internet Explorer.
Next Rebecca should type the URL of
our website into the address bar
Let’s take a closer look at the URL
• URL = uniform resource locator
• We can break the URL into 3 parts:
– The protocol being used
• http (hypertext transfer protocol)
– The server name
– The requested file name
URLs and IP Addresses
• Once Rebecca clicks enter on her URL, the
domain name system (DNS) is used to locate
the server which finds the IP address that
matches the company’s web address.
• The IP address is used to connect to the server
machine.
• You could just enter the IP address instead of
the URL but typically URLs are easier to
remember.
Components of an IP address
• IP = internet protocol
• 4 numbers, each containing up to three digits
separated by periods
– Example: 24.248.9.71
• Allows for communication between different
devices that are connected to the internet.
After a connection to the server has
been established
• The browser must form a connection to the
server at the IP address on port 80.
– Port 80 is the port number that HTTP uses.
• The browser then sends a GET request to the
server
– The request asks for the file and the webserver.
• The requested page is then returned and the
browser renders the screen to display the
company page.
Progress Report:
Local Network Connectivity to the Internet
Router and Switch Functions
MAC Addresses
 Use of Layers to View Data Flow
Data Flow Across Networks
Protocol (HTTP and TCP) Usage
Processing IP
Please let me know if you have any further
questions.