1. COS 125
Day 3

2. Agenda Questions from last Class?? Today’s topics
Connecting to the Internet
Assignment #1 is due on Feb 5
Quiz #1 on Feb 12
Chap 1-26
20 M/C, 4 short essays, One extra credit Question
60 Min, open book, open notes

3. Connecting to the Internet
Lots of ways to connect with more being invented
General rule >>> faster is better
In order of speed
Direct LAN connection
Cable modem or DSL
Telephone modem
Newest way is wireless
WiFi, Cellular WiMAX

4. Where do you get Internet Service
ISPs
St. John Valley Communications
Pivot. net
Earthlink
Bluelight
Online Service
AOL
MSN

5. How a modem works
Modems allow digital signals to go over an analog circuit
Analog Data
Smooth changes among an infinite number of states—like hands going around an analog clock
Digital Data
Few states
In a digital clock, each position can be in one of ten states (the digits 0 through 9)

6. Quiz Which is Analog? Which is Digital? On/Off Switch Number Of
Fingers
Calendar
Clock TV
Now let’s play the which is analog and which is digital game.
What is a calendar? (Digital—it’s the same date all day, and it changes abruptly at midnight)
Wall clock? (This one is analog. There also are digital wall clocks that show seconds, minutes, and hours as digits—0 through 9)
Fingers on a hand? Digital because fingers usually come in whole numbers. <In fact, fingers are called digits, and this is the origin of the term digital.>
The on/off switch? This is binary. Binary is a special case of digital, so it is digital.
Audio CDs are digital songs are digitized and stored on the audio CD in digital format. <Older vinyl records had analog grooves with bumps.>
Audio CD

7. Sending data with a modem
Modulated Analog
Signal
Telephone
Binary Data
PSTN
Modem
Computer
Amplitude (Loudness or Intensity) Modulation
Can you send binary data over an analog line? No problem. But you need a device called a modem to translate between binary data and analog signals.
The modem uses modulation to create analog signals. Here we see amplitude (loudness) modulation. A one is a high amplitude, while a zero is a low amplitude. Here we send 1011, so in the four clock cycles, the modem sends a loud tone, a soft tone, a loud tone, and a loud tone. 1 1 1
1011 becomes loud-soft-loud-loud

8. Getting Data with a modem
Modulated Analog
Signal
Demodulated
Binary Data
Telephone
PSTN
Modem
Computer
Amplitude (Loudness or Intensity) Modulation
Demodulation coverts the analog signal back to binary. It reads loud-soft-loud-loud and generates 1011. 1 1 1
Loud-soft-loud-loud becomes 1011

9. Modems Two types Computers control modems using the Hayes Command Set
Internal
External
Computers control modems using the Hayes Command Set
In the early days of the Internet (early 1990’s) users had to program modem using Hayes command to connect to an ISP

10. Modem Speeds V.34 V.90 Send and receive at up to 33.6 kbps
Fall back in speed if line conditions are not optimal
V.90
Receive at up to 56 kbps
Send at up to 33.6 kbps
Asymmetric speed is good for WWW service.
Other party must have a digital connection to the PSTN
There are several speed standards for modems. Each used a different modulation scheme.
There still are many V.34 modems in use. These modems can send and receive up to 33.6 kbps. However, they will fall back to lower speeds if there are problems with the line conditions.
V.90 modems are the most common today. They can receive at up to 56 kbps, but they can only send at 33.6 kbps. This asymmetric speed is good for WWW service because downloaded webpages are large while HTTP request messages sent upstream tend to be small.
For 56 kbps reception, the other party must have a digital connection to the PSTN, as noted in the previous slide.

11. Modem Speeds V.92 Receive at up to 56 kbps
Send at up to 33.6 kbps or higher if the line permits
Other party must have a digital connection to the PSTN
Modem on hold: can receive an incoming call for a short time without losing the connection
Cuts call setup time in half
The newest modem is the V.92 modem.
This modem can receive at 56 kbps, like V.90 modems. Again, the other party must have a digital connection.
However, it can potentially transmit somewhat faster than 33.6 kbps, although only if the transmission link to the telephone network is a very good one. Another drawback is that if the upstream speed is increased, some downstream speed will be sacrificed.
If the ISP permits it, V.92 modems can provide Modem on Hold—the ability to answer incoming calls for a very brief period of time without losing the Internet connection.
Another welcome thing about V.92 modem is that it cuts the initial call setup time in half.

12. Telephone Modem Communication
Need Modem at Each End Up to 33.6 kbps
Analog Modulated
Signal
Binary Data
Modem
Telephone
33.6
kbps
Modem
Telephone
Server A
Client A
First, we will look at modems up to 33.6 kbps
For modems in this speed range, both the sender and the receiver have modems.
Recall that a modem translates between binary (or digital) data and analog line signals. The data coming from the computer are binary, and the transmission line to the Public Switched Telephone Network is analog.
PSTN

13. Figure 7.2: Telephone Modem Communication
PSTN
Digital Access Line
Server B
56 kbps
Modem
Telephone
For modes that can download at 56 kbps, the situation is different.
The party at the other end does not have a modem.
The party at the other end has a 56 kbps or faster digital access line to the telephone company.
Why? The answer is that modems usually are limited to 33.6 kbps when they transmit, while digital lines can transmit faster. If the party at the other end had a modem, they could only transmit at 33.6 kbps, so the receiver could only receive this fast.
Client B
For 56 kbps Download Speed
Server Must Have a Digital Connection (ISDN PRI), Not a Modem

14. How Internet TV works TV was the first “Information Super highway”
Able to move of lot of info to the user
Problem was User could not interact with the info
Unidirectional
The internet allows Interactive use
Greater bandwidth means TV like performance
Existing TV cable system also can bring you High Speed Internet service
TV and Internet are combined in some services like MSN TV
MSN bought out Web TV

15. Cable Modem Services ISP 2. Optical 4. Coaxial Fiber to Cable to
Neighborhood
4. Coaxial
Cable to
Premises 3.
Neighborhood
Splitter
1. Cable
Television
Head End
Although DSL is popular, there is a competing service for residential users in the United States and some other countries. This is cable modem service, which uses cable television transmission networks to carry data.
The ISP connects to the cable television system’s Head End. All television and data signals come out of this single Head End.
From the head end, optical fiber carries signals to neighborhood splitters.
From each splitter, coaxial cable trunk lines fan out down individual streets. Coaxial cable tap lines carry signals from the coaxial cable trunk line to the individual house.
Users need cable modems, which have two ports. One is a coaxial cable port to connect the drop line to the cable modem. The other is a UTP port going to the user’s PC.
5. Cable
Modem
Subscriber
Premises PC
6. Requires NIC or USB port

16. MSN TV Can watch TV and get on the Internet at the same time
Requires
MSN TV receiver (keyboard & mouse)
Phone access TV
Receiver acts like a PC and TV receiver all at once
Uses a proprietary web browser and lots of proxy web servers

17. Internet Enhanced TV
TV networks send both TV signal and digital information to your homes
A special receiver formats digital signals and overlays that information on the TV image
Digital information is interactive WWW HTML

18. Digital Subscriber Lines
Uses existing Phone lines to get very high speed Internet Access
Up to 55 Mbps (1000 times faster than a V.90 modem)
Normal speeds for ADSL is 384 kbps down/ 96 kbps up
Pivot.net 768 kbps down/128 kbps up
On 24/7 and doesn’t interfere with regular phone usage
The faster the DSL speed the closer you must be to the phone company

19. ASDL with Splitter Subscriber Premises Telephone Company
End Office Switch
Data
WAN 1.
Existing
Single Pair of
Voice-Grade
UTP Wires
ADSL
Modem PC
Here is the type of DSL you are most likely to encounter--Asynchronous DSL or ADSL.
1. It uses the existing voice-grade single UTP pair already going to the customer premises.
2. The user connects a splitter to each telephone outlet. This allows the user to connect an ordinary analog telephone to one splitter jack and a computer with an ADSL modem to the other jack.
3. The carrier needs to add a DSL access multiplexer (DSLAM) to its end-office switch. This sends the voice signal over the PSTN and the data signal over a data network.
DSLAM
Splitter 3.
PSTN 2.
Telephone

20. ASDL with Splitter 1. Data 256 kbps to 1.5 Mbps Subscriber Premises
Telephone Company
End Office Switch
Data
WAN 2.
64 kbps to
256 kbps
ADSL
Modem PC
ADSL provides asynchronous speed--faster downstream than upstream. This is ideal for WWW service with its large page downloads and small upstream requests. It is not as good for IP telephony or other services that need high speed in both directions.
The downstream speed is 256 kbps to Mbps, depending on the price the user is willing to pay. Most vendors offer several speeds at different prices.
The upstream speed is slower--generally 64 kbps to 256 kbps.
DSLAM
Splitter
PSTN
Telephone

21. ASDL with Splitter Subscriber Premises Telephone Company
End Office Switch
Data
WAN
ADSL
Modem PC
In addition, the line carriers ordinary telephone service.
This means that the user can use his or her telephone while connected to the Internet or to their corporate network.
DSLAM
Splitter
PSTN 1.
Ordinary Telephone
Service
Telephone

22. Old Online services
Available prior to public internet service (ISPs ~ 1995)
BBS (bulletin board service)
AOL, Prodigy, CompuServe
Some local BBS’s
Gave you & chat only with other users of the same online service
Allowed file transfers up and down
Applications, pictures, music
Required subscription fees and phone access
Never really popular in rural areas

23. Modern Online Services
Internet Plus
Gives access to all (or most) of the Internet through gateways
Several Propriety applications
Lost of data “firewalled” away from the Internet
“Walled gardens”
Most common is AOL and MSN
Both use TCP/IP
Great for Internet Novices
Much greater control over Spam, viruses

24. How Wireless works All sorts of devices Many types of wireless Laptops
PDA
Cell phones
Peripherals
Many types of wireless
WiFi
Satellite
Bluetooth
Cellular

25. WiFi
standards
802.11b
2.4 GHz
802.11a
54 5 GHz
802.11g
GHz
Devices must have a WiFi card and they connect to Wireless Access Points (Hot spots)

26. WiFi

27. Typical 802.11 Wireless LAN Operation with Access Points
Industry
Standard
Coffee
Cup
Wireless
Notebook
NIC
Here is an access point with a UTP connection to an Ethernet switch.
Here also is a wireless NIC that fits inside a notebook’s PC Card slot.
Antenna
(Fan)
To Ethernet
Switch
PC Card
Connector

28. Typical 802.11 Wireless LAN Operation with Access Points
CSMA/CA+ACK
Switch
UTP
Radio Link
Access
Point A
Notebook
UTP
Handoff
If mobile computer
moves to another
access point,
it switches service
to that access point
Access
Point B
Now we’ll look at wireless LANs—WLANs
The dominant WLAN standards are the standards from the IEEE 802 Committee’s Working Group. (Ethernet standards are created by the sister working group.)
Wireless stations, such as notebook computers and personal digital assistants communicate with wireless access points. Two access points are shown here. In real WLANs, there may be quite a few more.
As a station moves away from one access point and toward another, the station will be “handed off” to the other access point.
Notice that the access points are also connected by UTP to the main wired LAN, because that is where the servers are that the wireless clients need to use.
Client PC
Server
Large Wired LAN

29. Wardriving

30. War Drive How To Equipment needed
Car
Another person (prevents accidents!)
Laptop with wireless access
Wireless antenna optional
Netstumbler software
GPS unit
Drive around till Netstumbler detects an access point
Analyze access point
Record coordinates using GPS
Mark on Electronic Map
Chalk mark sidewalk
Why?
Most access points are not secure (no WEP)
Allows free internet access
Hackers use as entry points to get to other more secure networks

31. Chalk Symbols

32. Satellite Internet

33. Orbits

34. GEO Satellite System 1. Geosynchronous Satellite 2. Point-to-Point
Uplink 3.
Broadcast
Downlink
A potential competitor for both DSL and cable modem service is satellite service. A satellite is a big repeater in the sky.
Some satellites have a geosynchronous orbit that allows them to orbit at the same speed as the earth’s rotation. This makes them appear to be stationary in the sky.
Users transmit to the satellite using point-to-point radio connections.
However, the satellite transmits outgoing signals over a broad area known as its footprint.
Each user needs an earth station. Because the satellite is far away (36,000 km or 22 miles), a dish antenna is needed on the earth station. 4.
Footprint
5. Earth Station A
Earth Station B
Satellite appears stationary in sky (35,785 km or 22,236 mi)
Far, so earth station needs dish antenna
At speed of light takes 250 ms to travel distance

35. Wireless Internet Access for small devices
Cell phones and PDA do not have big enough screens for full size Web Pages
WAP
Wireless access protocol
WML
Wireless markup language
WAP gateways converts regular HTML to WML and vice versa

36. WAP

37. BlueTooth Wireless networks for peripherals Personal Area Network
Does not provide Internet Access
Limited range

38. Personal Area Networks (PANs)
Connect Devices On or Near a Single User’s Desk
PC, Printer, PDA, Notebook Computer, Cellphone
Connect Devices On or Near a Single User’s Body
Notebook Computer, Printer, PDA, Cellphone
The Goal is Cable Elimination
Personal area networks (PANs) connect devices on or near a single user’s desk or around their bodies. Read them off.
The goal is to eliminate cables between all these devices.

39. Personal Area Networks (PANs)
There May be Multiple PANs in an Area
May overlap
Also called piconets
There may be multiple PANs in an area.
PANs are officially called piconets. (In the metric system, pico is smaller than micro)

40. 802.11 versus Bluetooth LANs 802.11 Bluetooth Focus Large WLANs
Personal Area Network
Speed
11 Mbps to 54 Mbps
In both directions
722 kbps with back
channel of 56 kbps.
May increase.
Distance
100 meters for b
(but shorter in reality)
10 meters
(may increase)
While was created for large LANs with multiple access points and fairly long transmission distances, the Bluetooth wireless technology was created for PANs.
Bluetooth is much slower and more limited in distance than , but this may increase.
In addition, Bluetooth can only have eight devices per piconet and only 10 piconets in an overlapping area.
Number
of Devices
Limited in practice only
by bandwidth and traffic
Only 10 piconets,
each with
8 devices maximum

41. multiple access points
versus Bluetooth LANs
802.11
Bluetooth
Scalability
Good through having
multiple access points
Poor
(but may get
access points)
Cost
Probably higher
Probably Lower
Battery Drain
Higher
Lower
So on the plus side, is much more scalable than Bluetooth. You can add access points to increase distance.
On the other hand, drains batteries faster and costs more, so Bluetooth should find a good niche for small devices.
One really neat thing about Bluetooth is that nearby devices can discover one another automatically, making setup easier. They learn of one another’s presence and automatically exchange set-up information, for instance, allowing a notebook computer to print to a printer without having to load device drivers.
Discovery No
Yes
Discovery allows devices to figure out how to work together automatically

42. Figure 5.11: Bluetooth Operation
Notebook
Master
File Synchronization
Client PC
Slave
Printing
Printer Slave
Piconet 1
Here we have Piconet 1 with a notebook, a printer, and a client PC. The notebook actually is the master, controlling the “slave” client PC and the “slave” printer.
Cellphone
Telephone

43. Figure 5.11: Bluetooth Operation
Notebook
Client PC
Printing
Printer Slave
Call Through Company
Phone System
Here is another Piconet with a cell phone as the master.
The cell phone master can print short messages on the nearby slave printer and place long-distance calls through the slave office telephone.
Cellphone
Master
Telephone Slave
Piconet 2

44. Figure 5.11: Bluetooth Operation
Notebook
Master
File Synchronization
Client PC
Slave
Printing
Printer Slave
Piconet 1
Call Through Company
Phone System
Note that the printer is a slave in both piconet. Here, at least, a slave can have multiple masters.
Cellphone
Master
Telephone Slave
Piconet 2

45. Home Networks
Many Homes have more than one computer or Internet Device
Don’t want to provide Internet to each device independently
Connect all device to a network and provide Internet access to the Home networks
Sometimes called SOHO networks
SOHO >> small office/home office

46. Needed to build home Networks
Internet Access
Broadband DSL or Cable modem
A way to connect all devices
Wired with Ethernet
Hub or Switch
Expensive
Wireless (WiFi)
Easier & Cheaper
A network Address Scheme
Most broadband device provide DHCP
Use Microsoft Internet Connection Sharing
ME, XP, Windows NT
Firewall
Keep hackers out

47. WiFi Home network

48. Smart House If your home has a network then can get Places to check
Internet enabled appliance
Control systems that you can access from anywhere
Security systems
Places to check

49. For next class Read through chapter 26 (page 187)
Extra Credit Question on Next exam
How many Hackers have been arrested in Maine?
Can you name any successful prosecutions of Hackers in the state of Maine?
What is the problem in catching and prosecuting Hackers in Maine?