Transcript Introduction to Networking ITT Version

NT1210 Introduction to Networking
Unit 2:
Chapter 2, Introduction to
Computer Networking
1
Objectives
 Identify the major needs and stakeholders for computer
networks and network applications.
 Identify the classifications of networks and how they are
applied to various types of enterprises.
 Explain the functionality and use of typical network protocols.
 Use preferred techniques and necessary tools to troubleshoot
common network problems.
2
Objectives
 Define a computer network.
 Identify the primary needs for computer networks and
network applications.
 Draw the four major physical network topologies: bus, star,
ring, and mesh.
3
Computer Networking
 Use large variety of components that must work
together.
 Move bits from one device to another.
 Bit: Smallest unit of data, binary 1 or 0.
 Focuses on copying bits on one device to another.
 Computing devices include computers, gaming
systems, televisions, phones, tablets, GPS navigation
systems, watches, etc.
4
Defining a Network with User Applications
 Examples: Digital advertising, online/video games, text
messages, websites, social media, and email.
 Network diagrams often use cloud to identify what part
of network to ignore for a particular discussion.
 LAN vs WAN
5
Defining a Network with User Applications
Computer Networks: Cloud Representing Hidden Parts of the Network
6
Figure 2-1
An Informal General Definition of a
Computer Network
 Telecom: Short for telephone communications
 Primarily focuses on role of traditional telephone companies.
 Datacom: Short for data communications
 Older synonym for computer networking.
7
User Actions and the User Devices
 Users use network devices via applications (apps).
 Application: Why we use networks.
 Example: Would you use a phone that did not allow phone
calls? Maybe, but what if it also did not allow texting? Or email?
Or posting to social media? Or web surfing? Or anything that
used a network?
 Key common feature for many apps: Need to send bits.
 Focus of this chapter: Email, voice calls, and video
downloads.
8
Email
 Electronic Mail: One of oldest networking applications.
 Sends mail electronically with bits.




Write (type) email.
Identify (type) sender’s and receiver’s email addresses.
Give messages to email service.
Email service delivers email to destination email address.
9
Email
 Users typically access email using email software or web
browser.
 Email software apps gives users way to create, send,
and receive email.
 Common email apps:
 Microsoft Outlook
 Microsoft Windows Mail
 Mozilla Thunderbird
 Apple Mail
 Many built-in mail apps on phone/tablet
10
Email
Example: Apple’s
Mail application
Sample Window on Email Software: Barney Types Email to Fred
11
Figure 2-2
Sending Email: Sender’s Computer
Perspective
 Step 1: Start email application and click icon or menu
item to cause “create message” window to open.
 Step 2: Type destination’s email address and message.
 Step 3: Behind the scenes:
1. Application stores and processes bits and bytes of message and
addresses in RAM and (sometimes) on hard disk.
2. Application uses some kind of character set to represent text.
3. Application uses email addresses to identify sender and
recipient of email.
4. Application works with other parts of computing device to send
email.
12
Email
The Operating System (OS) on the
computer typically plays a big role,
because every modern OS includes
lots of networking features, and the
applications rely on the OS to do
part of the work. The email client
essentially asks the OS to send the
email. However, the OS, being
software, cannot physically send
the bits. So the OS asks for help
from the NIC. Figure 2-3 shows the general idea.
General Process of Sending an Email on Barney’s Computer
13
Figure 2-3
Sending Email: Network’s Perspective
 Network sits between user devices and physically moves
bits between devices.
 Networks must provide services that help clients
(devices that use network) to do tasks they want to do.
 Example: using “snail mail”:
 To send mail, could go to different post office or drop.
 When receiving mail, must go to particular place to pick it up.
(e.g., box by house door, common area in apartment complex)
 Each mailing address must be known by both post office
and people who live at address.
14
Sending Email: Network’s Perspective
Example: Barney sends a letter to Fred’s postal address. Barney drops
the letter in the mailbox for outgoing mail at his apartment complex
(step 1). The postal service moves the letter towards Fred (step 2), and
eventually, the postal service leaves the letter in Fred’s mailbox (step
3). Then the letter sits in Fred’s mailbox until he next checks his mail.
Using an Outgoing Mail Drop/Box, and an Incoming Mail Box
15
Figure 2-4
Sending Email: Network’s Perspective
 Works similar to snail mail but uses email servers.
 Email servers (software running on computer in network)
must be ready to receive, process, and hold emails for
clients using SMTP (Simple Mail Transfer Protocol).
 To send email: Email application sends mail to outgoing
mail server using POP3 (Post Office Protocol, ver. 3).
 Client must know location of outgoing mail server.
 To receive mail: Email client must get mail from its
incoming mail server also using POP3.
 Email application must know location of incoming mail server.
16
Sending Email: Network’s Perspective
Step 1: Barney sends an email to his outgoing email server.
Step 2: Barney’s outgoing email server must know how to find the
incoming email server used by Fred – more specifically, the incoming
email server used by email address [email protected].
Step 3: Fred’s incoming email server holds the email for Fred, waiting
until he next checks his email.
Using Outgoing and Incoming Email Services
17
Figure 2-5
Voice Telephone Calls
 Modern telephony networks use bits to send telephone
calls (voice calls).
 Modern networks need to be ready to send bits, no
matter whether those bits make up email or represent
voice traffic.
18
Early Analog Voice Calls
 Majority of telephone services in USA for first 100 years
grew from Bell’s original work and business ventures.
 Local telephone company (Telco) ran cable to each
home.
 Inside Telco network, lots of other equipment connect to
create telephone network.
Big Picture View, Two Home Phones and the Telco
Figure 2-6
Early Analog Voice Calls Example
 Barney picks up home phone in New York and dials
Fred’s phone number in California.
 To make Barney’s call work, Telco has to know all phone
numbers and their matching phone lines.
 Telco keeps a list of all phone numbers and knows
which phone line connects to which phone using that
phone number.
 When new call occurs, Telco knows exactly where call
physically needs to go.
20
Early Analog Voice Calls
To create the call, the Telco creates an electrical circuit all the way from
one phone to the other. Once the Telco creates the call by creating an
electrical circuit, the two people can talk.
Electrical Circuit Between Two Phones to Carry the Voice Call
21
Figure 2-7
Early Analog Voice Calls, Part 1
1. Telco creates electrical circuit between phones.
2. Barney speaks, creating sound waves in air.
– When graphed over time, sound waves go up and down just like
waves in the ocean.
3. Microphone near mouth of speaker takes in sound
waves and outputs electrical signal that looks very
similar to graph of caller’s sound waves.
(continued on next slide)
22
Early Analog Voice Calls, Part 2
4. Fred’s phone converts analog electrical signal back to
sound waves using speaker in part of phone near his
ear.
– Speaker takes in analog electrical signal and vibrates air,
creating sound waves that look like analog electrical signal.
– Result: What Barney speaks, Fred hears.
23
Digital Voice Calls, Part 1
 Telco had large networks to support analog voice calls
long before computers became commonplace in
businesses.
 To take advantage of computers and related technology,
Telco replaced analog telephone networks with digital
ones.
 Telco developed analog to digital (A to D—A/D)
process to take electrical signal they already worked with
(the analog signal) and convert it to digital signal (bits).
 A/D paved way for VoIP (Voice over IP): Way to send
digital voice signal over IP network.
24
Digital Voice Calls, Part 2
 Part of A/D process breaks voice into very small time
intervals.
 Voice in calls sampled voice 8000 times per second so each
sound sample was .125 milliseconds long
 Another part of A/D process assigns binary value to each
unique short sound (similar to character map process).
 Original AT&T A/D conversion process used 8-bit code.
 To make use of networks for more efficient, lower cost,
and better calls, Telcos added equipment to do A/D
conversion process on each end of each call.
25
Digital Voice Calls
The two home phones create an electrical circuit into the Telco, but the
analog circuit does not extend from phone-to-phone.
Analog to the Phones, Digital in the Telco
26
Figure 2-8
Digital Voice Calls
1. Barney speaks, creating sound waves.
2. Phone creates analog signal representing voice and
sends into Telco network.
3. Telco uses A/D device to convert analog voice to bits.
4. Telco sends bits across its network.
5. Telco converts bits back to analog electrical signal for
transmission to Fred’s home phone.
6. Fred’s home phone uses speaker to convert electrical
signal into sound waves.
NOTE: Devices that perform A/D conversion called codecs (coders/
decoders). G.711—original AT&T codec—used 8,000 8-bit
samples per second to create 64Kbps voice calls.
27
End-to-End Digital Voice with Business and
Mobile Phones
 Modern business telephones and mobile phones only
use digital voice.
 Phone can connect to same network as PCs.
 Send and receive digital signals (bits) directly; A/D
converter built into phone.
 Phones often have computer-like features built-in.
 Display with simple web browser.
 Some phones essentially have built-in tablet computers
so they are mobile.
 Look more like small computers with phone attached; voice
calling feature just one of many features.
28
End-to-End Digital Voice with Business and
Mobile Phones
 Mobile phones have some of same features as business
phones, but no cables.
 Mobile phones (cell phone) use wireless technologies
to send and receive bits for voice calls and data
applications (like text messaging).
Summary: Voice traffic exists as common type of traffic in networks
today. Networks typically support voice traffic as just one of
many applications.
29
Recorded Video
 Networks may need to support live and recorded video.
 Focus: Recorded video
 Digital Video Recordings
 Video Files
 Video Compression
30
Recorded Video
 Modern video cameras
make digital recordings
and store them as bits.
 Camera also has
processors to take
input and convert light
and sound into bits to
store as file on permanent storage.
 Later, user can copy video to PC.
Video Camera Components and Moving the Video Files to a PC
31
Figure 2-9
Video Files
 Digital video revolves around concept of single video
frame (think animation cells).
 Rectangle (width by height) of individual points of light of each
video image as still image.
 When played back, video player software shows one
frame after another.
 Computers cannot store video as points of light or as
motions on screen, but as bits.
 Computer thinks of video frame as pixel grid.
 To represent color of pixel, computer uses table that lists
all colors and matching binary code.
32
Video Files
 Videos files can become very large.
 Example: High definition video with these specifications:
 3-byte code to represent color of each pixel
 Frame size 1920 (wide) by 1080 (high)
 Records 30 frames per second for smooth video
A Somewhat Extreme Example of Uncompressed Video
33
Figure 2-10
Video Compression
 Large video files cause problems: Take long time to
download over network.
 Compression: Stores video file as smaller file.
 Compressed video file often looks just as good as
original (depends on compression ratio used).
 Example: Video originally recorded with frame size of 1920 x
1080 could be compressed by shortening width and height to
25% original size (480 by 270); only requires 1/16th original
number of pixels.
NOTE: To learn many aspects of video and video compression, use
tools built into PC. Check out Real World Video Compression, by
Andy Beach.
34
Video Compression
Example of the overall flow: The video producer – the person who
recorded the video and decided what compressions to use –
compressed and posted the file on a video server on the Internet (steps
1 through 3). Later, at step 4, video users might actually watch the
video because it downloads in a reasonable amount of time.
Producing and Posting Smaller Compressed Video Files
35
Figure 2-11
Break
Take 10
36
A Deeper Look at One Application: World
Wide Web
 World Wide Web (the Web): Web browser software
which allows users access to Web may be single most
commonly used application in world.
 Web works well for learning networking because uses
basic client-server model.
 User sits at computer and uses web browser (Web client).
 “Client” indicates this software receives some type of
service from another device (information from web
server).
37
World Wide Web
The web browser (client) and web server cooperate so that the web
browser can get a copy of the information from a web server. The
server organizes information into pages called web pages. The web
browser asks the web server for a web page, and the server sends the
web page back to the web browser.
Web Browser Requesting and Receiving a Web Page from a Web Server
38
Figure 2-12
Web Browsers (Web Clients)
 Web browser (first one
came out in early 1990s):
Software that allows user to
get and display copy of web
page from web server.
 Once web server sends
content back to browser, it
displays information.
 Example: Apple’s Safari
browser.
Window Created by Apple Safari Web Browser
39
Figure 2-13
Components on the Client Computer
 Web browsers must follow same set of rules that tell
browser how to request web page from server.
 Browsers generally work same way in how they divide
work: browser does some work but also relies on
computer OS for some parts.
1. Client computer requires way to physically connect to network so
bits that make up web page can move from server to client.
2. Client typically uses hardware called Network Interface Card
(NIC) for network access.
Photo of Network Interface Card (NIC)
Figure 2-14
40
Components on the Client Computer: NIC
Each NIC has a circuit board with microchips and circuits (main part of
the board) that is inside the computer case, as well as a port for the
cable to connect to it on the outside of the case.
Photo of Network Interface Card (NIC)
Figure 2-14
41
Components on the Client Computer
 Some NICs exist as separate computer expansion cards.
 Other devices put NIC functions onto some other part of
device.
 Tablet: Has wireless NIC function but doesn’t have NIC as
separate physical card.
 OS controls CPU, RAM, permanent storage, and other
hardware, including NIC.
 OS also manages all applications and provides services to them.
 When user clicks or types something to load new web
page, browser, OS, and NIC all play roles.
42
Components on the Client Computer
Steps when user decides to load web page from
www.example.com web server:
1. Browser creates message to request web page from server and gives
request to OS for help.
2. OS does some work on request, including adding web server’s network
address, then asks NIC to send request.
3. NIC physically sends request as bits into network.
Three Major Steps on Client Computer after the User Requests a Web
43
Figure 2-15
Using Web Addresses (URLs)
 Web address: Identifies specific web page to display.
 Formal name: Universal Resource Locator (URL).
 Identifies web server and specific web page (file) on
server:
 Server name: Name listed between // and /
 Web page: Name after /
 Example: http://www.itt-tech.edu/information-technology
Protocol
Web Server
Web Page
Example of Identifying a Web Page Using a Web Address (URL)
44
Figure 2-16
Using Web Addresses (URLs)
 Can also access web pages via hyperlinks.
 Hyperlinks hide web addresses.
 When hyperlinked item on web page is clicked, the
browser loads web page for web address linked via that
hyperlink.
Note: When using web browsers to see hidden web address
associated with hyperlink, hover over link, and right click mouse
button. Browser will list menu that typically shows options to either
display linked web address or copy.
45
Web Servers (Hardware and Software)
 Store information (text, graphics, video, and audio) that
users see and hear.
 Waits to receive requests for web pages, and sends
page back to browser when requested.
 Is software so must run on computer hardware which
can support many kinds of applications.
46
Web Servers (Hardware and Software)
 Web server software allow web services to happen (e.g.,
storing web pages, listening for requests, and sending
web pages in response to requests).
 Hardware can be almost any computer that has OS that
supports web server software.
 Businesses must consider:
 Number of users requesting same web page at same time.
 Number of pages server must supply per second.
 Speed of connection to network.
 And many other factors.
47
Web Servers (Hardware and Software)
 Many businesses build
or lease space for their
physical servers in a
special type of room:
Data Center (DC).
 Server hardware sits in
racks (see graphic).
 DC also typically
connects each server
to network using
cables.
Data Center with Servers in Racks
Figure 2-17
48
Web Servers (Hardware and Software)
What happens inside the server once it has decided to send a web
page out into the network?
1. Server takes the web page in storage and asks the OS to send it
out (via the network) to the web browser that requested the page.
2. The OS does some work (not shown) and asks the NIC for help.
3. The NIC sends the request physically into the network.
Three Steps: Web Server Sends Web Page into Network
49
Figure 2-18
Web Sites, Pages, and Objects
 Web page: Collection of content (text, images, video,
audio) that server supplies to web browsers.
 Web objects: Parts of Web page stored as separate
files.
 Web page includes links to objects’ locations on server.
 Text in one Web object (file), and each graphic in as different
object (file).
Conceptual View: Web Site, Web Page, Web Object
50
Figure 2-19
The Process to Get One Web Page
 HTTP (HyperText Transfer Protocol): Defines rules
that web browsers use to ask for web pages from web
servers and that web servers use to send web pages
back to browsers.
 GET request/response
 Allows Web browser to get web object (GET request).
 Allows Web server to supply web object (GET response).
 Web pages often contain more than 1 object.
 To get entire Web page, browser may have to do
multiple HTTP GET requests and look for more
instructions in each object it receives.
51
The Process to Get One Web Page, Part 1
1.The Web client issues an
HTTP GET request for the
original object (Main1.html),
based on what the user
clicked or typed.
2.The Web server supplies
the Web object in the HTTP
GET Reply.
3.The Web browser reads the
Main1.html file and sees
directions that tell it to get
three other objects on the
Web page.
Using Four HTTP GET Requests for One Web Page
52
Figure 2-21
The Process to Get One Web Page, Part 2
4.The Web browser issues an
HTTP GET request for the
first extra object
(Object1.jpg).
5.The Web browser issues an
HTTP GET request for the
second extra object
(Object2.jpg).
6.The Web browser issues an
HTTP GET request for the
third extra object
(Object3.jpg).
Using Four HTTP GET Requests for One Web Page
53
Figure 2-21
Refining the Definition of a Network
 Revised definition of computer networking could be:
 Software on client computers (e.g., Web browsers).
 Software on server computers (e.g., Web server software).
 OS on those computers.
 Some hardware to connect computers to network (e.g., NIC).
 Network able to deliver bits from one computer to another.
 Complete set of protocols (rules) that allow devices to work
together to send bits from one computer to another.
54
Refining the Definition of a Network, Part 1
1.The Web browser thinks about the user’s action (a click of a hyperlink),
and creates an HTTP GET request for the Web address.
2.The OS performs some networking tasks that the browser cannot do,
like identifying the correct Web server’s address. The OS then asks the
NIC to transmit the bits.
3.The NIC physically transmits the bits representing the HTTP GET
request into the network.
A Demonstration of Web Components Working Together
55
Figure 2-22
Refining the Definition of a Network, Part 2
4.The network delivers the bits that contain the HTTP GET request to the
server.
5.The server’s NIC receives the bits and gives them to the OS.
6.The OS processes the data, mainly deciding which application should
be given the received data.
7.The Web server thinks about the HTTP GET request and prepares to
respond.
A Demonstration of Web Components Working Together
56
Figure 2-22
Uncovering the Network Between the
Application Endpoints
 Compare Computer Networks to Road Systems
Create a road (link) between 2 places (devices):
Cables, radio waves, etc.
A Road Between Two Houses (and the Network Equivalent)
57
Figure 2-23
Uncovering the Network Between the
Application Endpoints
 Comparing Computer Networks to Road Systems:
Sharing roads (links) between towns (sites)
 Would there be a
road directly from
each house in the
first town to each
house in the other
town?
 No, they would
build one road
between the two
towns and share
the road.
Sharing a Road Between Towns (and the Network Equivalent)
58
Figure 2-24
Uncovering the Network Between the
Application Endpoints
 Network topology: Shows
each device and each cable
between pairs of devices
with little or no detail.
 Cables used to transmit
data.
http://www.cisco.com/en/US/prod/collateral/voicesw/ps6789/ps729
0/ps10589/images/data_sheet_c78-598389-2.jpg
 If connected to multiple cables,
networking device can receive
bits over one cable and send
them out again over another.
http://www.cisco.com/en/US/prod/collateral/switches/ps5718/ps64
06/images/product_data_sheet0900aecd806b0bd8-2.jpg
 Two very common devices:
switches, routers.
http://us.fotolia.com/id/692608
Photos of Routers, Switches, and a LAN Networking Cable
59
Figure 2-25
Uncovering the Network Between the
Application Endpoints
 Links and Nodes
 Link: Any cable between two devices.
 Node: Any device.
 Link acts like road between two towns; node acts like
intersection.
Network Nodes (Like Intersections) and Links (Like Roads)
60
Figure 2-26
Uncovering the Network Between the
Application Endpoints
 You arrive at node 1 with “Node 10” on your sign.
 The policeman for node 1 tells you to take the lower path.
 You travel over the link to node 4.
 The node 4 policeman tells you to take the link towards
node 7.
 You travel over the
link to node 7.
Road Network with Policemen at Every Intersection (Node)
61
Figure 2-27
Uncovering the Network Between the
Application Endpoints
Small Lab Networks: Devices typically all sit in the same room. The
network does not need to be sophisticated at all. In fact, with just two
computers, just connect the two computers by connecting a cable to
the NIC in each computer.
A Simple Lab Network: One Cable
Figure 2-28
62
Uncovering the Network Between the
Application Endpoints
A more convenient way to connect multiple devices into the same small
network uses a device called a Local Area Network (LAN) switch.
The term Local Area Network simply refers to the idea that the
computers sit near each other (local). To create this kind of small
network, connect each computer’s NIC to a cable, and connect the
other end of the cable to the LAN switch.
A Simple Lab Network: All Computers Connect to One Switch (Node)
63
Figure 2-29
Uncovering the Network Between the
Application Endpoints
 Wireless networking: Uses radio waves to communicate.
 Example: Home-based network with
multiple devices.
 Each device creates link to
switch using cables (wires)
or radio frequency (wireless)
to send bits to each other.
 Bits first go to switch, then to
receiving device.
A Home Network Using Wired (Cabled) and Wireless
64
Figure 2-30
Uncovering the Network Between the
Application Endpoints
 Enterprise Networks
 Small/Medium Business (SMB)
 Enterprise: Businesses larger
than SMBs
 Example: physical topology for
multi-floor business.
A Single Site in an Enterprise with LAN Switches
65
Figure 2-31
Uncovering the Network Between the
Application Endpoints
 Enterprise Networks: Use Wide Area Networks (WANs)
to connect various remote
sites together.
 Network designers prefer
routers to connect sites
using WAN links, as routers
can connect to both WAN
links and LAN switches.
Bits that represent the customer account number
flow over the LAN link to the Boston switch, then over the
LAN link to the Boston router, then over the WAN link to the headquarters
router, then over the short LAN link to the first floor switch, and so on.
Multiple Sites in an Enterprise with Routers
66
Figure 2-32
Uncovering the Network Between the
Application Endpoints
 Internet: Interconnected Networks
 Internet core looks like
one big network, but is
many networks.
 Internet Service Providers
(ISPs) build networks that
combine to create Internet
core.
All Who Care to Use the Internet Connect to the Internet
67
Figure 2-33
Uncovering the Network Between the
Application Endpoints
 Internet Core is huge.
 Some ISPs have
thousands of
sites with many
network devices
at each site.
 Worldwide, thousands
of ISPs exist with millions of business
customers and billions of individuals.
Internet Core: Three ISPs and One Mobile Service Provider
68
Figure 2-34
Summary: This chapter…
 Began by focusing on the parts of networking that the
average person uses: apps on typical consumer
electronics and computing devices.
 Introduced the hidden concepts and terms of networking
while using those familiar topics to ease the process.
 Sketched out how web protocols work so that a user’s
Web browser requests a Web page, and how the Web
server responds to supply that Web page.
 Explained how Web server software, running on some
computer hardware, uses the network between the
computers to send a Web page to a user’s computer.
69
Summary: This chapter…
 Used a “road” scenario to compare the functions in a
computer network to transportation systems (roads and
intersections).
 Used common terms to describe networks of different
sizes, from small home networks to the worldwide
Internet.
 Described network topology as a set of nodes and links.
70
Questions? Comments?
71