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# Nt1210 Midterm Review

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NT1210 Introduction to Networking

Unit 1:
Mid-Term
Mid Term Review

1

Nibble, Byte, Word, Double Word

Nibble, Byte, Word, Double Word

Figure 1-2
2

Kilobyte, Megabyte, Gigabyte, Terabyte
Size (2N
Bytes)

Term

Size (Bytes)

Kilobyte
Megabyte
Gigabyte
Terabyte

1024
1,048,576
1,073,741,824
1,099,511,627,776

Kilobyte, Megabyte, Gigabyte, Terabyte

210
220
230
240

Rounded by
Size (Bytes)
1,000
1,000,000
1,000,000,000
1,000,000,000,000

Table 1-1
3

Random Access Memory (RAM)
Physically exists as set of microchips installed on plastic card (memory module)
Central Processing Unit (CPU) uses RAM like people g (
)
Stores binary value so can use it later
Can read data from RAM to recall value stored earlier

CPU sends electrical signal over bus (electrical pathway) to communicate with RAM

4

Random Access Memory (RAM) (cont.)
RAM uses address for each unique memory location where byte can be stored
To write to RAM: CPU sends signal to RAM over the bus g to write (store) value into byte of RAM
Value to be written

To read from RAM: CPU uses similar process (see example in Figure 1-3 on next slide)

5

CPU Reads Byte 4 from RAM
The CPU uses the same bus to read the current value of a byte in RAM as it does to send a message to RAM. The read request lists the address of the particular byte, asking for its value. RAM returns the binary value stored at that address.

CPU Reads Byte 4 from RAM

6

Figure 1-3

Writing Individual Bits in Byte 4 of RAM
RAM circuitry sends a slightly different electrical input to the bits that need to store a 1 versus a 0 to control the capacitors . Essentially, RAM chooses one of two inputs to each bit, which results in either a full or partial charge in the capacitor, which in turn represents either a 1 or 0, respectively.

Writing Individual Bits in Byte 4 of RAM

7

Figure 1-4

Converting Binary 01111011 to Decimal 123
1.
1 Multiply the decimal digit value times the binary value in each of the eight columns.
2. Add the eight numbers found from the previous step (bottom row in the table).
)

Converting Binary 01111011 to Decimal 123
8

Figure 1-7

Converting Decimal 123 to Binary 01111011
1) If countdown > decimal digit value:
a. Write a 0 for the binary digit b. Copy the countdown
(unchanged) to the next bit position
2) If the countdown <= decimal digit value:
a. Write a 1 for the binary digit b. Subtract the decimal digit value from the countdown, countdown and place in the next bit position
Example of Converting from Decimal 123 to 8-bit Binary 01111011
9

Figure 1-8

Unsigned Integers in Computers, Various Sizes
Size of
Storage
g

Range,
From 0 to 2N – 1

Number of Bits

Byte

8

0 - 255

28 - 1

Word
W d

16

0 – 65 535
65,535

216 - 1

Doubleword

32

0 – 4,294,967,296

32

2

-1

NOTE: Appendix B, Numeric Reference Tables, includes a table of decimal numbers 0-255, along with their 8-bit binary equivalent values. values
10

Table 1-2

Permanent Storage for Bits, Bytes
File Systems – Allow computer to store bytes of single file in many locations, while still keeping track of them
Files – Named set of related bytes of data that OS stores as single entity (b i l tit (based on name) t easily refer t d t d ) to il f to data
Unique name for each file
Keep bytes in order
Can be stored on any kind of physical storage device
Can be copied or moved to other devices and stored there as well

File types examples
Song (.mp3, .wav)
( mp3 wav)
Text file (.txt, .rtf)
This PowerPoint presentation ( ppt .pptx)
(.ppt., pptx)
High-resolution image from space telescope (.png, .jpg)
11

The Process of Storing Files
1. Application knows
1 A li ti k addresses in
RAM that hold contents of document 2. When user clicks save and names the file, OS sends file contents over bus to storage location (drive)
3. Drive stores file

Creating a File on Disk

12

Figure 1-9

File Systems and Directories
Directory - Part of file system used to organize files into hierarchy, keeping similar files together.

Directory Structure: Disk Drive (C:) and DVD Drive (D:)
13

Figure 1-10

Mapping Files and Directories to File Content

File System with Pointers to Actual Files

14

Figure 1-12

Mapping Files and Directories to File Content
(cont.)
1.
1 CPU attempts to read file /notes/mydoc (file mydoc i / t f ld ) tt t t d fil / t / d (fil d in /notes folder)
2. File System supplies file information from directory, including pointer to location on disk where file physically resides
3. CPU reads file’s contents from location discovered in previous step; i.e.,
CPU gets copy of bytes held at that particular place on disk
4. Disk drive transfers bytes of entire 1 KB file to CPU (CPU stores file in RAM so application can work with it

General Conceptual Steps to Find a File Location and Then Read its Contents
15

Figure 1-13

File System Miscellany
File system secures data; particularly useful for f f computers that have multiple users
OS may be able to assign rights per subdirectory or per file
Rights typically give user right to read, write (to modify file’s contents), and/or to delete file

OS defines file system so type of physical storage device does not matter
All file system concepts apply whether storage device is disk drive, drive with removable media (e.g., DVD drive or a flash drive), or any kind of storage media
Important to take time to look more closely at those devices

16

Hard Disk Drives
Most
M t common long-term computer storage devices today l t t t d i t d
Store a lot of data
Do not cost a lot of money
Make data available all the time
Storage topics
Hard Disks vs. Floppy Disks ppy Hard Disk Drive Internals
Writing Data to Sectors, Tracks
Using Bus to Communicate

17

Writing Data to Sectors, Tracks
A platter has many locations that can hold g g magnetic charges.
Physically, these locations exist in concentric circles, with circles each circle called a track. A sector refers to a subset of a track, as b t f t k shown in the figure.

Tracks and Sectors in a Single Disk Drive Platter
18

Figure 1-15

Writing Data to Sectors, Tracks (cont.)
The OS (running on the CPU) has already discovered four currently-unused currently unused sectors on a platter of a hard disk. The OS next tells the drive to prepare to write the file by reserving those sectors so no other application or process tries to use them. The CPU then delivers the file contents to be written in those reserved sectors. Four sectors of 256 bytes each will hold the entire
1KB file.

General Concept: Reserving Sectors, and Then Writing a File to Disk
19

Figure 1-16

Other Permanent Storage Devices
Many competing types of permanent storage devices
Different devices use different mechanisms to read and write data
USB Flash Drives
CD and DVD Drives

20

Key Comparison Points USB Flash and Hard
Points,
Disk Drives
Short Description
Internal or External?
Removable Media? bl di
Solid State?
Read/Write Speed vs. Internal HDD p Hard Disk
Both
No
No
N/A

Price/GB, at Publication, vs. HDD

N/A

*

USB Flash
Drive
External
Yes*
Yes
Slower
More
Expensive

Media cannot be removed from the drive, but the entire drive can be removed from the
,
computer.

Note: Table information may change over time, but as of publication, USB flash drives work well for convenience, portability, and low price; but are too slow and too small to be used to replace a hard disk drive.
Key Comparison Points, USB Flash and Hard Disk Drives
21

Table 1-4

CD and DVD Drives – A Short History (cont.)
DVDs followed similar history as CDs but with video
VHS tape first popular format to buy movies to view at home Analog magnetic tape technology

Video world migrated from VHS tapes to DVDs (like CDs but for movies)
DVDs used many of same ideas as CDs but with more storage capacity
CDs and DVDs store bits by using optics (light)
Optical Disc Drives p 22

Input and Output (I/O)
Input : Creating information in computer
Typing at keyboard
Clicking with mouse
Talking into computer microphone
Recordings from video security camera connected to computer
Statistics gathered by website
Sales data from grocery store scans

Output: Presents information to users and for other purposes Computer display showing image or some video
Computer speakers playing sound
Printers printing images
23

Keyboard
Two general categories of actions
Input text and numeric data into application
Control computer’s actions

Some keys on keyboard tell computer actions to take
Function key: Tells either current application the OS to take action
Key Combination Example: In Microsoft OS pressing Control Alt
OS,
Control-AltDelete tells OS to bring up window that lets you reboot or shutdown, or to stop specific tasks

Other k
Oth keys input data i td t
Example: In word processing program, keyboard lets you type letters and numbers and then puts those into document

24

How Keyboards Send Bits to Represent Letters
To physically send bits to the computer, the p y y p
,
keyboard varies the electrical signal over time.
Fro example, to send a binary 1, the keyboard might use a positive voltage (the current flows in one direction), and to send a 0, use a negative voltage (the current flows in the opposite direction). Wired Keyboard Connection to a PC System Unit
25

Figure 1-20

How Keyboards Send Bits to Represent Letters
(cont.)
Imagine the user has opened a text editor and is ready to practice typing
“The quick brown fox jumped over the lazy river.” The graphic here illustrates what happens when the “T” is pressed (requires 2 keys, the Shift and “t” keys).

Keyboard, Character Map, Bit Transmission, and Storing the Typed Character
26

Figure 1-21

The Mouse
Allows control of computer’s actions but in much different way than keyboard: Point-and-click
When user moves mouse pointer OS has list of actions to pointer, take depending on mouse action
Single click of left mouse button causes OS application window to b t become active ti Double click of left mouse button when pointing at icon or file causes OS to start application or open file
Single click of right mouse button causes app or OS to display contextual menu based on where pointer was when click occurred

27

The Computer Display
Provides output
Also called computer monitor or screen
Shines light so user can see information on screen
Sits outside system unit, connecting to system using cable
When system powered off, display either shows nothing or y p p y g some kind of error message

28

Early Analog Voice Calls
To
T create the call, the T l creates an electrical circuit all the way f t th ll th Telco t l t i l i it ll th 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
29

Figure 2-7

Digital Voice Calls
The two home phones create an electrical circuit i t th T l
Th t h h t l t i l i it into the Telco, b t th but the analog circuit does not extend from phone-to-phone.

Analog to the Phones, Digital in the Telco
30

Figure 2-8

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. 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.
Beach

31

World Wide Web
The
Th web browser (client) and web server cooperate so that th web bb ( li t) d b t th t the b 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 page, web page back to the web browser.

Web Browser Requesting and Receiving a Web Page from a Web Server
32

Figure 2-12

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. 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 network. 33

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). 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.

34

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 i id image as still i till 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 code. 35

Video Compression
Example of th overall fl
E
l f the ll flow: Th video producer – th person who
The id d the h 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
3) Later
4,

Producing and Posting Smaller Compressed Video Files
36

Figure 2-11

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. 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.
Beach

37

Web address: Identifies specific web page to display display. Formal name: Universal Resource Locator (URL).
Identifies web server and specific web p g ( ) on p page (file) 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)
38

Figure 2-16

Can l
C also access web pages via h b i hyperlinks. li k
,
g button. Browser will list menu that typically shows options to either display linked web address or copy.

39

Uncovering the Network Between the
Application Endpoints
Internet: I t
I t t Interconnected Networks t dN t k Internet core looks like one big network but is network, 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
40

Figure 2-33

Uncovering the Network Between the
Application Endpoints
Internet Core is huge 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 billi t d billions of i di id l f individuals.

Internet Core: Three ISPs and One Mobile Service Provider
41

Figure 2-34

Defining the Rules for a TCP/IP Network:
Product Standards and Rules
Transmission C t l Protocol (TCP) / Internet Protocol
T
i i Control P t l I t tP t l (IP).
Requests for Comment (RFC): Documents created by network stakeholders to comment and improve ideas for standards. Define how products work.
Used by network designers.
Open source.

42

Defining the Rules for a TCP/IP Network
Hardware and software work t
H d d ft k together t create usable th to t bl network. Protocols (network software): Hypertext Transfer
Protocol (HTTP), Simple Mail Transfer Protocol
(SMTP), Post Office Protocol (POP), etc.
Used on networked devices (hardware): Phones, game systems, televisions, tablets, computers, software, networking devices cables etc devices, cables, etc.

43

Defining the Rules for a TCP/IP Network
TCP/IP identifies b th stuff and how it works t id tifi both t ff d h k together: th Defines protocols.
Defines concepts of Local A
D fi t fL l Area N t
Networks (LAN ) and Wid k (LANs) d Wide
Area Networks (WANs).
Defines concept of links and nodes the functions of each.

Definition of TCP/IP network: Network built using
TCP/IP standards and rules.

44

Defining the Rules for a TCP/IP Network:
Standards
Record d t il of exactly what new t h l i d and
R
d details f tl h t technologies do d how they do it.
Help everyone agree to how something works so that it works well within network.
Important feature: Documentation of ideas that matter to anyone creating networking products or designing networks. Example: Brief history of Web browsers and servers as envisioned by Web creator Tim Berners-Lee. http://bit.ly/vd0pWE http://bit ly/vd0pWE
45

Defining the Rules for a TCP/IP Network:
HTTP Example
HTTP began life as idea and d t il of h b lif id d details f how it was t work to k had to be determined:
What byte values does browser use to send HTTP GET?
What byte value does server use to send HTTP REPLY?
Is // required before name of server in web address?
How does server tell browser when it can’t find requested object? How does server tell browser where object’s bytes begin and end? 46

Defining the Rules for a TCP/IP Network:
Hardware
Standards
St d d apply t b th h d l to both hardware and software. d ft
Example: NICs connectors.
Without standards, not all cables would fit NIC’s port
(proprietary configurations).
Fixes size and shape standards for connectors and other networking gear set.

47

Defining the Rules for a TCP/IP Network:
Hardware
Example: Thi cable h an RJ
E
l This bl has
RJ45 connector. (RJ-45 is the name of the standard for the connector). connector)
The NIC has an RJ-45 port of the same size. size The RJ-45 has 8 pins and looks much like the RJ-11 which is commonly know as a “Phone
Connector,” but is half the size of the RJ-45.
Example of Physical Standard: RJ-45 Connector (on Cable) and Socket (on NIC)
48

Figure 3-1

Defining the Rules for a TCP/IP Network:
Types of Standards, Part 1
National: St d d approved b a national government
N ti l Standard d by ti l t which then appoints an organization to oversee it.
Example: Electrical p p power outlets’ size, shape, electrical current,
,
p ,
,
voltage.

International: Standard approved by a group of nations that typically relates to functions that benefit from consistency among the participating nations.
Vendor (proprietary): Standard approved by a single vendor which allows the vendor to keep control yet allows other vendors to use them so they are interoperable. interoperable
49

Defining the Rules for a TCP/IP Network:
Types of Standards, Part 2
Vendor Group: St d d approved b a group of
V d G
Standard
d by f vendors (vendor consortium, vendor alliance, vendor forum). )
Wants their standards to become national/international standards. Can move quicker than national/international standards groups groups. Works to get compatible products to market quicker, while working with formal standards groups.

De Facto: Standard that exists because it is what is currently in use, usually not written down.
Example: MS-Word has become de facto standard of most offices. 50

Defining the Rules for a TCP/IP Network
Not all protocols and hardware specs are standardized; however, most used today happen to be standards.

Networking Standards Compared to Protocols and Hardware Specs
51

Figure 3-2

Defining the Rules for a TCP/IP Network:
TCP/IP Model
Defines l
D fi large set of standards i l t f t d d implemented t t d together t th to create safe and useful network.
Model name has many variations but all refer to same idea. TCP/IP network architecture, TCP/IP networking model, TCP/IP networking blueprint blueprint. Organizes standards into layers so…
Humans can understand what networks do.
Easier to divide work among different products.
Devices can be interoperable.

52

Defining the Rules for a TCP/IP Network:
TCP/IP Model
Commonly-used version of
C
l d i f TCP/IP model has five layers.
Original TCP/IP model had four layers: Bottom two layers of model y combined into Network Interface layer (or Network Access layer).

TCP/IP Model

Figure 3-3
53

Defining the Rules for a TCP/IP Network:
TCP/IP Model
Includes standards created for TCP/IP as well as some
TCP/IP,
created by other standards groups.
Each standards-setting g p follows some kind of p g group process: Repeated experimentation
Documentation
Review

Example: Internet Engineering Task Force (IETF) acts as primary standards group for TCP/IP model, so model includes standards created by both IETF and other standards groups.
54

Defining the Rules for a TCP/IP Network:
Organizations Useful to TCP/IP

Sources of Standards in the TCP/IP Model

Figure 3-4
55

Defining the Rules for a TCP/IP Network:
IETF (www.ietf.org)
Works
W k as standard-setting group for TCP/IP. t d d tti f TCP/IP
Decides:
What needs to be updated
What new standards need to be added

Organized around working groups made up of volunteers who work on new standards (create “internet drafts”).
Experiments, changes details, improves how new technology works, then shares changes.
Submits findings into standards process.
Document created by group can become informational or experimental RFC if draft not submitted. p 56

Defining the Rules for a TCP/IP Network:
IETF Working Groups Process

Standard and Non-Standard TCP/IP RFCs

Figure 3-5
57

Defining the Rules for a TCP/IP Network:
IEEE (www.ieee.org)
Institute f El t i l d El t i Engineers (IEEE)
I tit t of Electrical and Electronics E i
(IEEE).
Plays huge role in networking and for TCP/IP in general.
World s
World’s largest professional organization. organization IEEE standards for TCP/IP define LANs (including Ethernet, y gy) most commonly used wired and wireless LAN technology).
Not agency of any particular government or agency.
US government appoints ANSI to manage US standards across i d t i industries. ANSI certifies standards by certifying other standards groups.

58

Defining the Rules for a TCP/IP Network:
ITU
International Telecommunications Union
Union.
International standards body that focuses on standards for telecom and WAN networking technologies. g g
Example: ITU standards define country codes for international phone calls.

Enables worldwide digital voice communications by standardizing voice codecs.
TCP/IP model uses ITU standards for same reasons it uses IEEE standards.

59

Defining the Rules for a TCP/IP Network:
Vendor Consortia & Other Groups
Vendor Group/Consortium: Vendors team up to get quick and broad acceptance in marketplace.
Group agrees on standardized version of new technology
BEFORE formal standards group sets standards.
Example: Wi-Fi Alliance (www.wi-fi.org) helped get new wireless technology to market q gy quicker than formal IEEE standards p process would have.
Tested products to certify (confirm) they worked together.
Created pre-standard rules. pre standard
Allowed vendors to brand products as “Wi-Fi certified”.
Worked with IEEE to help overall standards process.

60

Defining the Rules for a TCP/IP Network
Overall process: No matter whether a person with good ideas works through the Wi-fi Alliance or IEEE, when those two groups cooperate, products get to market sooner, and the standards happen.

Vendor Groups Impact on Speed to Market
61

Figure 3-6

Defining the Rules for a TCP/IP Network:
LAN/WAN Standards

TCP/IP Using Other Standards for LAN and WAN
62

Figure 3-7

Comparing TCP/IP to Other Networking
Models: Standards
While a single standard typically focuses on one protocol or hardware spec, the TCP/IP model collects all the standards needed to do everything required to make a complete modern network into one handy model. Each device in the network and each component follows a subset of the TCP/IP standards, p g depending on its role.
Conceptual View of TCP/IP Model

Figure 3-8
63

Comparing TCP/IP to Other Networking
Models: History of Networking Models
First
Fi t commercial computers hit market i 1950 and i l t k t in 1950s d became more common in larger companies by 1960s.
Personal computers hit market in late 1970s and became common in 1980s.
Networks didn’t exist yet. didn t
Eventually computer vendors saw need to create network between computers.
Individual vendors created their own proprietary networking products and networking models.

64

Comparing TCP/IP to Other Networking
Models: History of Networking Models
Typical enterprise network from the 1980s used 3 different
1980s—used
models to operate:
IBM networking model.
DEC networking model.
Other vendor that could connect them together.

Typical Mix of Corporate Networks over Three Decades
65

Figure 3-9

Comparing TCP/IP to Other Networking
Models: History of Networking Models
What h
Wh t happened in typical enterprise networks from the 1980 into the di t i l t i t k f th 1980s i t th early 21st century? Enter TCP/IP…

Typical Migration of Enterprise Networks from Vendor Models to TCP/IP
66

Figure 3-10

Comparing TCP/IP to Other Networking
Models: OSI Model
Open Systems Interconnection (OSI)
O
S t
I t ti model.
ISO began work on OSI model following timeline that was close to TCP/IP’s:
Started in 1970s.
Progressed on individual standards in 1980s.
Allowed standards-based vendor products to start appearing by early 1990s.

The OSI Model

Figure 3-11
67

Comparing TCP/IP to Other Networking
Models: OSI Model
The biggest differences between the TCP/IP and OSI models exist at the top.
The TCP/IP model defines many functions as part of the application layer while the OSI layer, model split those functions into multiple layers.

Mapping the Layers of the TCP/IP and OSI Models
68

Figure 3-12

Comparing TCP/IP to Other Networking
Models: OSI Model

Three Example Standards, and the Phrases to Use
69

Figure 3-13

Understanding How a TCP/IP Network
Works: LANs vs. WANs
When defining LANs and
WANs, always consider the Data Link and
Physical layers as local versus remote—or owned versus leased.

The Terms LAN and WAN in the TCP/IP Model
70

Figure 3-14

Understanding How a TCP/IP Network
Both the
B th th sender and receiver must agree on th rules of h d d i t the l f how t use th to the electrical circuit. The sending NIC sends the bits over the loop to create the electrical signal. Signal varies over time to encode different bits.
The receiving NIC must know what rules the sender uses so it can interpret the circuit changes into the correct 0s and 1s (bits).

NICs on Both Ends of a Cable Creating a Loop
71

Figure 3-15

Understanding How a TCP/IP Network
Works: LAN Switches
Every Eth
E
Ethernet LAN d i connects t th LAN using a cable. Th t device t to the i bl The cable installers run a cable from each device to a central place on that floor, usually to a switch that sits in a locked room called a wiring room. room By connecting all the cables to the switch all are connect to the switch, LAN—and each other.

Using a LAN Switch to Physically Connect Devices to a LAN
72

Figure 3-16

Defining the Rules for a TCP/IP Network:
The Eth
Th Ethernet Data Link layer/standards define the rules (protocols) that t D t Li k l
/ t d d d fi th l ( t l ) th t tells the devices how and when to use the Ethernet Physical layer.

Using an Address to Send Data to the Right LAN Device
73

Figure 3-17

Defining the Rules for a TCP/IP Network:
Data Communication over Layers 1 & 2
1.
1 The server sends the data over the physical link but only after the link, sever adds the destination MAC (physical) address of
1111.1111.1111 to the data.
2.
2 The switch sees the destination address and switches the data to
PC1—and PC1 only.
3. The data arrives at PC1, and PC1 knows the data is meant for it because of the MAC address address. Using an Address to Send Data to the Right LAN Device
74

Figure 3-17

Defining the Rules for a TCP/IP Network:
Many protocols use h d
M
t l headers and/or t il d/ trailers t store to t bytes of info that control data flow through network.
75

Figure 3-18

Defining the Rules for a TCP/IP Network:
WANs
WAN physical links created by service provider (usually h i l li k t db i id ( ll Telco) used by customer company in its corporate network.
Example: Fred buys house three miles from
Barney’s house.

Defining the Rules for a TCP/IP Network:
WANs
WANs
WAN create li k b t t link between sites of corporate network it f t t k when company could not physically cable between sites itself. Example: Company has two sites 3 miles apart; although
Ethernet LAN standards allow for 3-mile-long cables to connect LAN s itches at both sites compan can’t switches sites, company legally lay cable over other people’s land between sites.
Solution: Contract with 3rd party company that has right to run cables near existing roads.
Links are leased (rented) from 3rd party company by customers.

77

Defining the Rules for a TCP/IP Network:
WAN Examples
Telco h
T l has phone line i t most h h li into t houses.
Electric company has power lines into most buildings.
Cable TV company has cable lines into most buildings buildings. Government lets utility companies y p dig up road to install cables or hang cables from poles above ground. 78

Defining the Rules for a TCP/IP Network:
Leased Lines
Creates
C t equivalent of cable di tl b t i l t f bl directly between t two remote t sites.
Enterprises lease lines to connect remote sites sites. Leased lines create 2-way path to transmit data at predetermined speed (for pre-determined price!).

79

Defining the Rules for a TCP/IP Network:
Leased Lines
Enterprises use Layer 3 devices called routers to connect to the WAN leased line at each site.
The Telco connects the ends of the leased line directly into the enterprise’s routers in their WAN interfaces (ports) on each end of the link.

Physical Cabling of a Leased Line, from Each Customer Site to Central Office (CO)
80

Figure 3-21

Defining the Rules for a TCP/IP Network:
Leased Lines
Two leased lines:
One connecting
Miami to Atlanta.
One connecting
Miami to Boston.
The length of the leased line could literally run across the street in a c ty o thousands of city or t ousa ds o miles across a country.
(WAN lines that look like lightning bolts represent leased lines.)
Leased Line, Cabling View, with Routers Connecting LAN and WAN
81

Figure 3-22

Defining the Rules for a TCP/IP Network:
Data Link Protocols for Leased Lines
High-level
High level Data Link Control (HDLC standardized by
(HDLC—standardized
ISO).
Point-to-Point Protocol (PPP—defined by TCP/IP in RFC
(
y
1661).
When router sends data over leased line, data can only go to router o ot e e d o link. oute on other end of
Every Data Link protocol focuses on particular Physical layer technology.
Routers typically sit at border between different data links.
82

Defining the Rules for a TCP/IP Network:
Routers strip off old Data Link h d
R t t i ff ld D t Li k headers no l longer needed and d d d replace them with new Data Link headers needed for next leg (hop) of the data’s journey to its destination.

Encapsulation and De-encapsulation

Figure 3-23
83

Defining the Rules for a TCP/IP Network:
Encapsulation Example
2, 3. Border router removes Ethernet header/trailer and adds new WAN one (e.g., PPP) then sends data over WAN link.
4, 5. Destination border router discards

84

Defining the Rules for a TCP/IP Network:
Similar to t
Si il t steps you t k when you t k a long trip: take h take l ti 1.Start by taking subway train to airport.
2.Take
2 Take plane to another city.
3.Rent car at destination. 4.Drive car to final destination.
None of above vehicles accomplished entire trip from start to finish; takes planes, trains, and automobiles!

Routers Separate a Network into Separate Data Links
85

Figure 3-24

Defining the Rules for a TCP/IP Network:
Identifies device in TCP/IP network.
Every device must have unique IP address.
IP address has 32 bits written in dotted decimal notation (DDN) of four sets of eight bits each with dot
(period) between each number.
Networking devices see decimal numbers as binary binary. Binary IP Address
00000001
01010101
00001010
01111110
00100001

00001000
10101010
00000101
10000001
01000001

00010000
00001111
00011010
01010101
10000001

00100000
11110000
00010101
11111000
00010001

Example IP Addresses, Binary and DDN Formats
86

Equivalent Decimal
1.8.16.32
1 8 16 32
85.170.15.240
10.5.26.21
126.129.85.248
126 129 85 248
33.65.129.17
Table 3-1

Defining the Rules for a TCP/IP Network:
Each
E h PC with a connection i t th TCP/IP network has a ith ti into the t kh unique IP address.

IP Addresses in a Network Diagram

Figure 3-25
87

Defining the Rules for a TCP/IP Network:
Routers play a bi role with th IP protocol i th t th route (f
R t l big l ith the t l in that they t (forward)
d)
data based on the destination IP address. To do that, a router must connect using multiple interfaces to multiple data links.
Example: Each router has 2 interfaces:
One for WAN link and one for LAN.

Routers: Multiple Interfaces, Multiple IP Addresses
88

Figure 3-26

Defining the Rules for a TCP/IP Network:
To
T make IP routing work, addresses grouped using rules. k ti k dd d i l IP groups addresses in different ways: Classful networks and subnetting .
Rules give network engineers flexibility in how they assign addresses, but still allow IP routing g to work efficiently.

Five Classful IP Networks

Figure 3-27
89

Defining the Rules for a TCP/IP Network:
IP Classful N t
Cl
f l Networks k Class

IP Range

Designed for

A

1.0.0.0 – 126.255.255.255

Large enterprises, government agencies, etc.

B

128.0.0.0 191.255.255.255
128 0 0 0 – 191 255 255 255

C

192.0.0.0 – 223.255.255.255

For small entities and home networks D

224.0.0.0 – 239.255.255.255

Multicast

E

240.0.0.0 – 255.255.255.255

Experimental, research

Five Classful IP Networks
90

Defining the Rules for a TCP/IP Network:
IP version 4 addresses no longer issued out (all used).
Based on 32-bit addresses 192.168.3.5, dotted decimal.

IP version 6 is new IP addressing scheme scheme. Based on 128-bit address.
Expressed in 8 sets of 4 hexadecimal numbers, for example: p p
2001:0db8:85a3:0000:0000:8a2e:0370:7334.
Creates billions and billions of IP addresses: 2128, or approximately 3.4×1038 (a number with 37 zeros). pp y
(
)

For all practical purposes, eliminates classful networks and need for subnetting.
World IPv6 Launch took place on 6 June 2012.
Five Classful IP Networks
91

Defining the Rules for a TCP/IP Network:
IP Routing
IP routing defines exactly how routers f ti d fi tl h t forward data in dd t i network. Each router connects to multiple physical links so has multiple physical interfaces (ports).
Router has rules that tell it how to make routing decisions. IP routing relies on two ideas:
Routers forward data based on destination IP address.

92

Defining the Rules for a TCP/IP Network:
IP Routing
Moving data on network relies on routers to forward data to correct destination host.
Routers talk to each other (using protocols) to learn about IP addresses in network.
Routers keep routing information in their RAM in IP routing tables.

Routing Tables on R1 and R2, for Network 12.0.0.0
93

Figure 3-29

Defining the Rules for a TCP/IP Network:
IP Routing
PC11 sends an IPv4 packet to PC21 by adding an IP header that includes d IP 4 k tt b ddi h d th t i l d its address and the destination’s IPv4 address to the data (payload).

Web Client Host PC11 Puts 12.1.1.21 into the IP Header Destination IP Address Field
94

Figure 3-28

Defining the Rules for a TCP/IP Network:
IP Routing
1. PC11 sends data with destination IPv4 address 12.1.1.21 (PC21) to R1.
2. R1 compares destination
IP address listed in header with its routing table. R1 finds matching table entry that tells
R1 to send data14.1.1.2
(R2).
(R2)
3. R21sends packet to router R2.
4, 5. R2’s routing table says that network IPv4 12.0.0.0 is local so R2 forwards data over LAN directly to PC21.

95

Defining the Rules for a TCP/IP Network:
Forwarding Packets

Encapsulation on the Sending Host: Frame and Packet
96

Figure 3-30

Defining the Rules for a TCP/IP Network:
Forwarding Packets
Frame: E
F
Encapsulated d t th t i l d D t Li k l t d data that includes Data Link header and trailer—plus everything in between (including
)
Encapsulation/de-encapsulation process continues until
IP packet delivered to destination.
97

Defining the Rules for a TCP/IP Network:
Routing IP Packets

Routers: Remove Packet from Frame, Send Packet inside a New Frame
98

Figure 3-31

Defining the Rules for a TCP/IP Network:
Routing IP Packets
1.
1 Sending host sends Ethernet frame to router router. 2. Router:
a. Removes IP packet from inside frame and discards old Data Link header/trailer. h d /t il
b. Decides where to route IP packet (to next router across WAN link).
c. Encapsulates packet in new PPP frame and sends across link.

3. PPP frame holds original IP packet as it crosses WAN link to destination router.
4.
4 Destination router repeats same three steps as sending router. 5. Ethernet frame (with original IP packet) crosses LAN and arrives at d ti ti d i i t destination device.
99

Defining the Rules for a TCP/IP Network:
Transport Protocols
Transport layer protocols provide th connection t network
T
tl t l id the ti to t k applications (apps).

Widening Scope of Higher TCP/IP Layers

Figure 3-32
100

Defining the Rules for a TCP/IP Network:
Transport Protocols TCP and UDP
Transport layer connects source and destination
T
tl t d d ti ti applications. Port number: Used by transport protocol to identify each destination app.
Transmission Control Protocol (TCP) – ConnectionConnection oriented. User Datagram Protocol (UDP) – Connectionless.

101

Defining the Rules for a TCP/IP Network:
TCP/IP Roles Summary, Part 1
TCP/IP network delivers bits f t k d li bit from one d i t another device to th and from one application to another.
Applications run on various devices devices. Application vendors use protocols that let apps communicate through network.
Application layer protocols rely on Transport layer protocols to connect sending app to destination app.

102

Defining the Rules for a TCP/IP Network:
TCP/IP Roles Summary, Part 2
Each
E h application’s writer chooses t use TCP UDP or li ti ’ it h to TCP, UDP, some other less common Transport protocol.
TCP and UDP use port numbers (specified in header) that identify destination app.
Transport layer protocols rely on IP to deliver packets from sending host to destination host.

103

Defining the Rules for a TCP/IP Network:
TCP/IP Roles Summary, Part 3
IP defines details t make network communication d fi d t il to k t k i ti possible, including logical IP addressing and routing.
IP relies on Data Link and Physical layers to deliver frames across LANs and WANs.
Physical layer defines how to encode bits over cable or wirelessly. 104

Defining the Rules for a TCP/IP Network:
TCP/IP Roles Summary, Part 4
Host or
Network

Layer Name Key Functions
Physical parts that communicate, and energy
Physical
Network over those parts (electricity light, radio).

Network

Network
(Network) of the physical links); routing.
Communications functions useful to apps, pp ,
Transport
T
Host
H but likely useful to many apps.
Communication functions specific to a
Host
Application particular app. app TCP/IP Model Summary

Device Focus
LAN Switch
Router
Any endpoint y p device Any endpoint device Table 3-2

105

Transmitting Bits: Communication Analogy
When two f i d t lk one t lk while other listens and
Wh t friends talk, talks hil th li t d understands (we hope!).
Speaker makes sounds that travel through air to listener’s ears.
Sounds have no meaning unless each person’s brain person s works to interpret those sounds.
In networks, nodes send data to each other over link:
Sending node acts like person talking; receiving node acts like person listening.

106

Transmitting Bits: Communication Analogy
General id of how a TCP/IP network forwards IP packets from one
G
l idea f h t kf d k t f host to another: Nodes (routers in this example) each make a choice of where to send the packet next so the data arrives at the correct destination. destination Always keep the big goal of the network in mind: Delivering data from the source to the destination.

Sending Data Through a Network of Nodes and Links
107

Figure 4-1

Sending Bits with Electricity and Copper
Wires: Electrical Circuits
Electrical i
El t i l circuit must exist as complete loop of it t i t l t l f material (medium) over which electricity can flow.
Material used to create circuit can’t be just any material; can t must be good electrical conductor (e.g., copper wire).

Simple Direct Current Circuit Using a Battery
108

Figure 4-2

Sending Bits with Electricity and Copper
Wires: Electrical Circuits
Direct Current (DC) electrical circuits
Di t C t l t i l i it
Electrical current: Amount of electricity that flows past single point on circuit (amount of electron flow in circuit).
Current always flows away from negative (-) lead in circuit and towards positive (+) lead.

Powering a Light Bulb with a DC Circuit

Figure 4-3
109

Sending Bits with Electricity and Copper
Wires: Frequency, Amplitude, Phase
DC circuit ( l ft) and AC circuit ( right) b th use 1 volt. i it (on left) d i it (on i ht) both lt DC shows constant +1 volt signal.
AC circuit slowly rises to +1 volt falls to 0 then falls to -1 volt, 1 volt (1 volt, but in opposite direction), repeating over time.
Resulting AC wave: Sine wave g Graphs of 1 Volt (Y-Axis) over time: DC (Left) vs AC (Right)
110

Figure 4-4

Sending Bits with Electricity and Copper
Wires: AC Frequency, Amplitude, Phase
To
T send d t networking Ph i l l d data, t ki Physical layer standards can t d d change amplitude, frequency, phase, period of AC electrical signal g .

Graphs of AC Circuit: Amplitude, Period, Frequency
111

Figure 4-5

Sending Bits with Electricity and Copper
Wires: AC Frequency, Amplitude, Phase
Most
M t commonly used i networking encoding schemes. l d in t ki di h One signal used by encoding scheme means binary 0, other means binary 1
1.

Encoding Options: Frequency, Amplitude, and Phase Shifts
112

Figure 4-6

Sending Bits with Electricity and Copper Wires:
AC Frequency, Amplitude, Phase, Period
Wave
Feature

Electrical Feature it
Represents

Definition of the Graph

Maximum height of the curve over the centerline centerline. Number of complete waves
Frequency
(cycles) per second (in Hertz).

Amplitude

Phase

Period

Voltage

Speed with which current alternates directions.
Voltage jumps, which makes
Vl
j hi h k
Single location in repeating wave. signal graph jump to new phase. Time for voltage to change from maximum positive
Time (width on x-axis) for one p p voltage back to same p g point complete wave to complete. again. Common Features Used by Encoding Schemes
113

Table 4-1

Sending Bits with Electricity and Copper
Wires: Network Cabling
Before a node can send d t it needs t create a circuit
B f d d data, d to t i it between itself and the destination node.
Copper cable has outer plastic cover (jacket) that holds wires (conductors).
Sending/receiving nodes use a pair of wires connected at their ends to create circuit.

Photo of Wires Inside a Networking Cable

Figure 4-7
114

Sending Bits with Electricity and Copper
Wires: Network Cabling Example
Cable has
C bl h 4 pairs of wires: 2 used, 2 unused. i f i d d
Hardware of each node must agree which wires to use and which to ignore ignore. For wires chosen to use, nodes loop ends together to create a circuit.

Physical Components to Create an Electrical Circuit Between Two Nodes
115

Figure 4-8

Sending Bits with Electricity and Copper
Wires: Network Cabling
Loop ( i it) can’t create circuit b it lf something h
L
(circuit)
’t
t i it by itself: thi has to create electrical current.
Transmitting node creates electrical signal changing signal, signal over time to encode different bit values.
Transmitter: Part of node that sends data.
Receiver: Part that listens for signal of incoming bits.

Transmitter Generating a Current to Send; Receiver Sensing Current to Receive Figure 4-9
116

Sending Bits with Electricity and Copper
Wires: Circuit Bit Rates
Bit rate (li k speed): D fi t (link
d) Defines number of bit sent over li k b f bits t link per second (bps).
Impacts how nodes send data over circuit. circuit Example of how bit rate and encoding scheme work together: Bit rate = 10 bps; encoding scheme states that binary 1 should be +2 volts and binary 0 as +1 volts.

Example where Encoder Changes Signal Every Bit Time
117

Figure 4-10

Sending Bits with Electricity and Copper
Wires: Encoding Scheme
Works lik language: D fi
W k like l
Defines electrical equivalent of 1’ l ti l i l t f 1’s and 0’s.
Different frequencies represent binary 1’s and 0’s
1s
0 s.
Example sending 1010: Lower frequency represents binary 1, higher frequency represents binary 0.

Frequency Shift Keying: Low Frequency = 1, High Frequency = 0
118

Figure 4-11

Sending Bits with Electricity and Copper
Wires: Manchester Encoding Scheme
Used
U d on some early Eth l Ethernet networks. t t k Does not choose one electrical signal at beginning of bit time, time instead changes signal in middle of bit time time. Follows this logic:
To encode 0: Start high, and transition low in the middle of bit time.
To encode 1: Start low, and transition high in the middle of bit time.

Manchester Encoding: 0 = High-to-Low, 1 = Low-to-High
119

Figure 4-12

Sending Bits with Electricity and Copper
Wires: Using Multiple Circuits
Simplex transmissions are one way: If encoding scheme works in only one direction (on single circuit):
Devices must take turns using that circuit or …
Devices must use different circuits for each direction.

Half-duplex transmissions take turns: Node1 sends while
Node2 listens; when Node1 finishes, Node2 sends while
Node1 listens.
Full duplex transmissions can send/receive simultaneously: Both endpoints can send at same time because they use multiple wire pairs.
Full Duplex Using Two Pair, One for Each Direction
120

Figure 4-13

Sending Bits with Electricity and Copper
Wires: Using Multiple Circuits

Full Duplex Using Two Pair, One for Each Direction
121

Figure 4-13

Sending Bits with Electricity and Copper
Wires: Problems with Electricity
Noise: El t M
N i
Electro-Magnetic I t f ti Interference (EMI)
Cables help prevent effects of EMI in many ways, including shielding. Twisting of wire pairs creates “cancellation” effect to help stop
EMI effect.

Attenuation: Signals fade away over distance to point where devices can’t interpret individual bits
Ethernet standards li it copper li k t 100 meters.
Eth
t t d d limit links to t Very important when designing network.

122

Sending Bits with Electricity and Copper
Wires: Unshielded Twisted Pair (UTP)
10Base-T, 100Base-T & 1000Base-T uses U hi ld d
10B
T 100B
T 1000B
T
Unshielded
Twisted Pair (UTP).
Cable contains twisted pairs of wires and no added shielding materials.
Twisting reduces EMI effects between pairs in same jacket and in nearby cables.
Lack of shielding makes cables less expensive, lighter, easier to install install. Supports full-duplex.
Note: Twisted pair cables with shielding are called p g
Shielded Twisted Pair (STP).
123

Sending Bits with Electricity and Copper
Wires: LAN Standards Progression
Ethernet h l
Eth
t has long hi t history (d
(developed i 1970 and i l d in 1970s d is still used today).
IEEE standardized Ethernet in 802 3 standard in early
802.3
1980s.
Has added many more Ethernet standards since then.
Each standard took years to grow in marketplace and eventually drive prices down.

Timeline of the Introduction of Ethernet Standards
124

Figure 4-14

Sending Bits with Electricity and Copper
Wires: RJ-45 Connectors, Ports
Ethernet standards allow use of RJ-45 connectors on
Eth
t t d d ll f RJ 45 t twisted pair cable and matching RJ-45 ports (sockets) on NICs, switch ports, and other devices.
,
p
,
Again, RJ-45 connectors and ports accommodate
8 wires (pins) in single row row. Example RJ-45 Connectors and Sockets

Figure 4-15
125

Sending Bits with Electricity and Copper
Wires: Cable Pinouts
Pinouts: H
Pi
t How each wire i cable should b connected h i in bl h ld be t d to each pin in connector according to Ethernet standards. Wires must be in correct order so correct wires in twisted pair send to correct direction.

Wires, Connector Pin numbers, and Socket Pin Numbers
126

Figure 4-16

Sending Bits with Electricity and Copper
Wires: Cable Pinouts
Straight-through: E h wire connects t th same pin
St i ht th h Each i t to the i number on both ends of the cable.

Conceptual Drawing of Straight-Through Cable
127

Figure 4-17

Sending Bits with Electricity and Copper
Wires: Cable Pinout Standards
Ethernet uses TIA (Telecommunications Industry
Eth
t
(T l i ti
I d t
Association) standards to define specific wires to use for pinouts. UTP cables have four pairs of wires, each using a different color: green, blue, orange, brown.
Each pair has 1 wire with solid color and other one with white stripe. TIA Cable Pinouts – T568A On Each End Creates a Straight-Through Cable
128

Figure 4-18

Sending Bits with Electricity and Copper
Wires: Cable Pinout Standards—568A/568B

NOTE: 568B switches green and orange wires.

TIA Cable Pinouts – T568A On Each End Creates a Straight-Through Cable
129

Figure 4-18

Sending Bits with Electricity and Copper
Wires: Cable Pinout Standards
UTP cable with f bl ith four pairs (8 wires) can support f i i ) t four circuits. i it
10Base-T and 100Base-T only use two pairs.
NOTE: 1000BaseT uses all 4 wire pairs pairs. Ethernet uses following rules for creating circuits:
One pair at pins 1 and 2
One pair at pins 3 and 6

PC NIC Transmitting on Pair at 1,2, Receiving on Pair 3,6
130

Figure 4-19

Sending Bits with Light and Fiber Optic
Cables
Fiber bl
Fib cables contain several parts th t wrap around t i l t that d glass or plastic fiber core.
Core is about as thin as human hair.
Fiber breaks easily without some type of support.
Core and cladding have direct effect on how light travels down cable.
Optical transmitter (laser or LED) shines light into core to t t transmit data. it d t
Components of a Fiber Optic Cable

Figure 4-21
131

Sending Bits with Light and Fiber Optic
Cables
Cladding surrounds core for entire length of cable cable. Reflects light back into core
Light waves reflect off cladding back into core until light waves reach other end of cable

Fiber optic cables work well to send light in one direction at time, but not two.
Cable acts like dark tunnel so nodes can easily see light coming through cable cable. If both ends try to shine light and look for light at same time, couldn’t tell whether light is coming from local or remote node.

Cladding Reflecting the Light Back into the Fiber Optic Cable’s Core
132

Figure 4-22

Sending Bits with Light and Fiber Optic
Cables
Instead of using one fiber cable for half-duplex communication, most fiber links use pair of cables so can use full-duplex.
Each fiber NIC, port, interface, etc., has interface with two sockets: One for send cable, one for receive cable.
Each node’s transmit socket must connect to same cable as other node’s receive socket. node s
NOTE: In addition to sending data using light over cables, fiber technology also includes free space optics (e.g., TV remote) which sends light through air; requires line of sight line-of-sight. Two Fiber Optic Cables, with Connectors

Figure 4-23
133

Sending Bits with Light and Fiber Optic
Cables: Transmitters
Key technical difference between LEDs and lasers: LEDs shine light in multiple directions; lasers shine in one direction. direction
Fiber cables come in two major categories: Multimode
(
(MM), single mode (SM).
)
g
( )
Multimode have larger cores and work best with LED transmitters.
Single
Si l mode h d have smaller ll diameter cores and work best with laser transmitters.
LEDs with Multiple Modes (Angles), and Lasers, with a Single Mode (Angle)
134

Figure 4-24

Sending Bits with Light and Fiber Optic
Cables: Ethernet LANs
Fiber bl do t
Fib cables d not create EMI t EMI.
Example: Typical campus
LAN has employees in two buildings in office park that sit 150 meters apart, which exceeds Ethernet standards for copper pp cabling. However, multimode links can run past 200 meters.
Typical Use of Fiber Optics in a LAN: Links Between Neighboring Buildings
135

Figure 4-25

Sending Bits with Light and Fiber Optic
Telcos and ISPs that support WAN services use fiber optics because they service businesses that sit far apart. To do this, Telco/ISP must have a link from the customer to the Telco central office (CO) or ISP
Point of Presence (POP)
(POP).

Two Perspectives on a Leased Line

Figure 4-26
136

Sending Bits with Light and Fiber Optic
Example: Fib th t connects equipment i CO t other
E
l Fiber that t i t in to th
Telco sites (called core sites).
COs sit at edge sites of Telco network and have links to core g sites.
Physical locations include office buildings with server rooms.
CO to customer router which use copper.

Fiber Links Used to Help Create a Telco Network
137

Figure 4-27

Sending Bits with Light and Fiber Optic
Synchronous O ti l N t
S
h
Optical Network (SONET) O of longerk (SONET): One f l established standards for WAN links.
SONET defines series of Physical layer standards for data transmission over
Name
(Rounded) Line Speed optical links. p OC-1
52 Mbps
Uses hierarchy of speeds
OC-3
155 Mbps that are multiples of base
OC-12
622 Mbps speed ( p (51.84 Mbps) p p ) plus
OC-24
OC-48
2488 Mbps
OC-96
OC-192
OC 192

4976 Mbps
9952 Mb
Mbps

SONET Optical Carrier (OC) Names and (Rounded) Line Speeds
138

Table 4-2

Sending Bits with Radio Waves and No
More electrical power creates stronger radio waves that can travel longer distances distances. Radio tower sends signals upward because radio waves bounce off ionosphere (one of layers of Earth’s atmosphere). Bouncing radio waves off ionosphere lets radio waves reach wider area area. A Radio Station Broadcasting a Radio Signal to a Car Radio
139

Figure 4-28

Sending Bits with Radio Waves and No

140

Figure 4-28

Sending Bits with Radio Waves and No
El t ti di ti (ER) Described using ib d i electromagnetic spectrum conceptual model
These types of energy travel as waves so have specific waves, wavelength.
Spectrum categorizes energy based on wavelength.
Radio waves make up one category in EM spectrum.
Other parts include visible light, X-rays, microwaves.

Radio waves work well for networking because can be changed (modulated) over time to send data.

141

Figure 4-28

Sending Bits with Radio Waves and No
Th
facts i k i t b t h di be used to wirelessly send data.
1. Radio waves have energy level that moves up and down over gy p time, so when graphed, waves look like sine wave.
2. Radio waves can be changed and sensed by networking devices, including changes to frequency, amplitude, p
,
g g q y, p
, phase,
,
period, wavelength.
3. EM energy does not need physical medium to move.

142

Figure 4-28

Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Voice
Mobile t
M bil network provider creates k id t its own network.
But most phone users want to communicate with more phones than just those on same mobile company’s network, as well as landline phones.
Enter the Public Switched
Telephone Network (PSTN)

Major Components in the Mobile Phone Network Model
143

Figure 4-29

Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Voice
Most
M t mobile phones act as di it l phones. bil h t digital h
Send and receive digits (bits) that represent voice traffic.

To transmit bits phones use wireless radio technology bits, technology.
Phone sends bits encoded as radio waves to nearby radio antenna on tower owned by mobile phone company. Connecting a Mobile Phone Call through a Radio Tower to the Telco Network
144

Figure 4-30

Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Voice
Steps t place call on mobile phone:
St
to l ll bil h
1. Person speaks creating sound waves (as usual).
2. Phone converts sound waves into bits (as with all digital phones).
3. Phone sends
(encodes) bits as radio waves through air towards cell tower. 4. Radio equipment at tower receives (decodes) radio waves back into original bits.
5.
5 Rest of trip uses various technology (details not included here) here). 145

Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Data
R di li k on phone supports d t service j t as it h t data i just does for voice.
When sending or receiving data phone passes bits data, using radio waves between itself and radio tower.
Phone encapsulates data.
To support data applications, mobile network connects to Internet and any other networks that support data apps requested by user user. Mobile network forwards data to correct destination in Internet, not through PSTN.

Smart Phone: Using Radio to Forward Bits to the Tower, and then to the Internet Figure 4-31
146

Sending Bits with Radio Waves and No
Cables: WANs—Mobile Phones & Data
Steps i accessing I t
St
in i Internet via mobile phone: t i bil h
1. Person types URL or taps hyperlink.
2. Phone encapsulates HTTP request into IP packet, then Data Link layer frame.
3. Phone sends (encodes) frame’s bits as radio waves towards cell tower. 4. Radio equipment at tower receives
(decodes) radio waves back into original bits.
5.
5 Equipment near cell tower forwards bits into Internet as for any IP packet. 147

Sending Bits with Radio Waves and No
Cables: WANs—Other Mobile Devices
Laptops, t bl t can connect to same network as
L t tablets tt t k mobile phone.
Laptops typically need wireless NIC that supplies radio to connect to network radio towers.
Also need contract with mobile provider for connectivity to wireless network.

Using the Wireless WAN (Mobile Network) from Computers Instead of Phones
148

Figure 4-32

Sending Bits with Radio Waves and No
Cables: WAN Standards
Gen
2G
3G

4G

Other Terms
Standards
Related to
Body
Generation

Umbrella Standard

GSM (Global System for
TDMA, CDMA
Mobile Communications)
IMT-2000 (International
Mobile Telecommunications- UTMS
2000)
(International Mobile
LTE, Wi-Max

Mobile Wireless Standards and Terms

ETSI
ITU

ITU, ETSI,
IEEE

Table 4-3
149

Sending Bits with Radio Waves and No
Cables: WLANs—Devices & Topology
Wireless LAN d i
Wi l devices need d WLAN Network Interface Card
(
(NIC).
)
Gives PC ability to connect WLAN

Most WLANs use Access Points (AP) which are small devices that acts like small radio tower tower. All wireless user devices communicate through AP.

A Small Wireless LAN with One Access Point (AP)
150

Figure 4-33

Sending Bits with Radio Waves and No
Cables: WLANs—Devices & Topology
WLAN with AP creates a WLAN B i Service Set (BSS). I a BSS, ith t
Basic S i S t (BSS) In BSS all communications happen with the AP, much like it does in the wireless WAN model.

A WLAN AP Bridges Between the WLAN and an Ethernet LAN
151

Figure 4-34

Sending Bits with Radio Waves and No
Cables: WLANs—Sending Data
For
F most WLAN standards, the encoding scheme uses some f t t d d th di h form of f amplitude shift keying or phase shift keying, which changes the amplitude or phase (respectively) to represent a 0 or 1.

Amplitude and Phase Shift Basic Examples
152

Figure 4-35

Sending Bits with Radio Waves and No
Cables: WLANs—Typical Problems
AP sits under metal d k ( di waves d not pass it d t l desk (radio do t through metal very well).
AP sits next to other equipment and cables that interfere (EMI).
AP sits on wrong side of interior wall away from end user devices.

A WLAN with Possible Sources of Interference
153

Figure 4-36

Sending Bits with Radio Waves and No
Cables: WLANs—Transmission
Wireless LANs t k t
Wi l
LAN take turns by using rules called C i Sense Multiple b i l ll d Carrier S
M lti l
Access with Collision Avoidance (CSMA/CA). This technology is similar to wired Ethernet’s CSMA/CD.

CSMA/CA Process

Figure 4-37
154

Sending Bits with Radio Waves and No
Cables: WLANs—Transmission
Step 1
St 1: All d i devices use i d independent random wait ti d t d it time if they have data to send.
Step 2: When particular device completes its wait timer it timer, sends data.
Sender lists time it estimates is needed to send data (in
(
milliseconds) so other devices know how long WLAN will be in use. Step 3: Receiving device shows required ACK
Step 4: ACK triggers silence on WLAN.
CSMA/CA Process

Figure 4-37
155

Sending Bits with Radio Waves and No
Cables: WLAN IEEE Standards
IEEE WLAN
Standard

Maximum
Stream Rate
(Mbps)

Number of NonFrequency overlapping Range
Channels

802.11b

11

2.4 GHz

3

802.11a

54

5 GHz

23

802.11g

54

2.4 GHz

3

802.11n

72

5 GHz

21

802.11n*

150

5 GHz

9

802.11ac**

1000 Plus

5 GHz

12

• * When using bonded 40 MHz channel, instead of 20 MHz channel (as used by other
)
standards outlined in table).

WLAN Standards and Speeds

Table 4-4
156

Sending Bits with Radio Waves and No
Cables: Example Enterprise
Many corporate campus LANs have both wired and wireless LAN support on each floor. The WLAN connects to the same Ethernet network as the wired network does so all devices in the two building can communicate.

Campus LAN: Wireless Devices, Wired Desktops, and Fiber Trunks
157

Figure 4-38

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