1. Telecommunications Chapter 6
Panko’s Business Data Networks and Telecommunications, 7th edition © 2009 Pearson Education, Inc.  Publishing as Prentice Hall
May only be used by adopters of the book
So far, we have looked at wired and wireless communication WITHIN the company’s premises, that is, in LANs.
In this chapter, we will begin moving outside the firm’s walls.
First, we will look at the telephone network, which wide area networks use for some, most, or all of their transmission.
Second, we will look at Internet access alternatives from residences and businesses.

2. The Public Switched Telephone Network (PSTN)
The telephone network is officially the “Public Switched Telephone Network”.
It is available to the public—that, is, anyone.
It uses switches to link subscribers together.

3. 6-1: Elements of the Public Switched Telephone Network (PSTN)
Customer premises
Equipment (CPE) consists
Of telephones, wires,
And other infrastructure
on the customer premises.
It is owned by the customer.
Customer premises equipment, as the name suggests, is equipment on the customer’s site—residential homes and apartments and business buildings.
This equipment is owned by the customer.
[Actually, until the 1970s and 1980s, the telephone company owned the telephones and wires in homes and business buildings.]
1. Customer Premises
Equipment
1. Customer Premises Equipment

4. 6-2: Customer Premises Equipment at a Business Site
Most businesses have a PBX (private branch exchange).
It acts like an internal switchboard
Businesses use 4-pair UTP for in-building telephone wiring.
Have long used 4-pair UTP for telephony.
Only recently was 4-pair UTP used for data.
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5. 6-1: Elements of the PSTN The Access System consists of
the access line to the customer (called the local loop)
and termination equipment at the end office (nearest telephone office switch). 2.
Access Line
(Local Loop) 2.
Access Line
(Local Loop)
2. & 3. End Office
Switch (Class 5)
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6. 6-1: Elements of the PSTN 3. Transport Core 3. Switch 3. Trunk Line
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The Transport Core connects end office
switches and core switches.
Trunk lines connect switches.

7. 6-1: Elements of the PSTN Telephone Company Switch
Here is a picture of a telephone company switch.

8. 6-1: Elements of the PSTN 4. Signaling System
Transport is the actual transmission of voice.
Signaling is the control of calling (setup, teardown, billing, etc.).
SS7 in the United States, C7 in Europe
Here is a distinction that students tend to forget easily.
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9. Transport versus Signaling
The carriage of voice during a conversation
Signaling
Supervisory communication to set up a connection, monitor connection quality, collect billing information, closing a connection, etc.
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A point of frequent confusion

10. 6-3: Points of Presence (POPs)
Local, long-distance, and international
carriers connect at POPs
(points of presence)
This permits their subscribers
to call one another.
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11. Circuits Data networks use packet switching to deliver messages.
Telephone networks traditionally have used something simpler, called circuit switching.

12. 6-4: Circuit Switching
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13. 6-5: Voice and Data Traffic
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Voice uses about 30% of capacity, on average.
Data only uses about 5% of capacity, on average.
Circuit switching is not too wasteful for voice,
But it is very wasteful for data transmission.

14. 6-6: Dial-Up Circuits versus Leased Line Circuits
Is it a circuit with reserved capacity?
Yes
Operation
Dial-up. Separate circuit for each call.
Permanent circuit, always on
Speed for Carrying Data
Up to 33.6 kbps
56 kbps to gigabit speeds
Number of Voice Calls
One
Several due to multiplexing
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15. 6- 7: Time Division Multiplexing (TDM) in T1 Lines
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16. 6- 7: Time Division Multiplexing (TDM) in T1 Lines
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17. 6- 7: Time Division Multiplexing (TDM) in T1 Lines
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18. 6- 7: Time Division Multiplexing (TDM) in T1 Lines
Calculation
Each conversation gets an 8-bit time slot in each frame.
There are 8,000 frames per second
So each conversation gets 64 kbps
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19. Analog and Digital Transmission
In this book, we have been looking primarily at digital transmission, in which different states represent 1s and 0s.
The PSTN was created to use a much older form of transmission called analog transmission.

20. 6-9: Analog Telephone Transmission
Speaking creates pressure waves, which hit the microphone.
The microphone generates an analogous electrical signal.
This is called an analog signal.
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21. 6-10: The PSTN: Mostly Digital with Analog Local Loops
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The PSTN today is almost entirely digital.
This includes switches and trunk lines.
It also includes digital leased access lines to businesses.

22. 6-10: The PSTN: Mostly Digital with Analog Local Loops
Only the residential telephone and the
1-pair voice-grade UTP line going to residences
are analog today.
Digital subscriber lines (which we will see later)
Send digital signals over these 1-pair VG UTP lines.
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23. 6-11: Codec at the End Office Switch
A codec at the end office switch translates between the
analog customer signals and digital signals in the PSTN core
ADC is analog to digital conversion.
DAC is digital to analog conversion.
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24. 6-12: Frequency Division Multiplexing (FDM) in Microwave Transmission
Box
Microwave provides
Point-to-point
Terrestrial Transmission
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25. 6-14: Digital-to-Analog Conversion (DAC)
Box
So far, we have been looking at how analog-to-digital conversion works.
In the other direction, the codec has to do digital-to-analog conversion.
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Signals arriving from the PSTN are digital.
The DAC converts the 8 bits of each sample into a loudness level.
Not smooth, but sounds smooth at 8,000 samples/second.

26. Cellular Telephony Nearly everyone today has a cellular telephone.
In this section, we will look at how your mobile phone works.

27. 6-15: Cellular Technology
Customer has a mobile phone.
A city is divided into small
geographic regions called cells.
Each cell has a cellsite
with an antenna and equipment
to serve mobile phones in the cell
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28. 6-15: Cellular Telephony Cellsites
Here are some pictures of cellular telephone towers.
The antennas are the rectangular metal boxes.
They are not as strongly directional as dish antennas, but they are still strongly direction.

29. 6-15: Cellular Technology
A mobile telephone switching office (MTSO)
coordinates activity among the cellsites.
The MTSO also connects mobile customers
with wired PSTN customers via a POP.
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30. 6-15: Cellular Technology
New
Cellsites connect to the MTSO using a landline or a point-to-point radio system called microwave.
Here is a microwave dish.
It is covered with cloth, which does not interfere with radio transmission.
Here is something that was not in the book.
Obviously, cellsites need to connect to the MTSO.
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31. 6-15: Cellular Technology
Channels can be reused in different cells.
This permits more customers to be served.
Serving more customers through channel reuse
Is the whole reason for cellular service.
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32. 6-15: Cellular Technology
GSM cellular technology cannot use the
same channel in adjacent cells
CDMA can use the same channel in adjacent
cells, providing more channel reuse
and so more customers.
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33. 6-15: Cellular Technology
When a mobile phone travels between cells,
it is handed off to the cellsite in the new cell.
In this figure, there is handoff between
the cellsite in Cell O and the cellsite in Cell P.
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34. 6-15: Cellular Technology
In handoff, a mobile moves from one cell
to another cell in the same city.
In roaming, a mobile is taken to a different city.
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35. 6-16: Handoff and Roaming in 802
6-16: Handoff and Roaming in Wireless Networking and Cellular Telephony
WLANs
Cellular Telephony
Relationship
Handoff and roaming mean the same thing
Handoff and roaming mean different things
Handoffs (means the same in both)
Wireless host travels between access points in an organization
Mobile phone travels between cellsites in the same cellular system
Roaming (means different things)
Mobile phone travels to a different cellular system
We have seen handoffs and roaming in both wireless LANs and cellular telephony.
Sadly, these two terms are not used consistently in the two contexts.
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36. Voice over IP (VoIP)
You may use Skype or some other program to talk over the Internet at low cost or even no cost.
This is called voice over IP, because you are using an IP network, namely the Internet.
Companies also use VoIP, both within their buildings and outside their buildings.
They do not always use the Internet for transmission.

37. 6-17: Voice over IP (VoIP) In voice over IP (VoIP),
calls are transported over an IP network:
either an internal IP network or the Internet.
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In VoIP, sound is digitized and sent in packets.

38. 6-17: Voice over IP (VoIP) The user either has a
PC with multimedia hardware
and VoIP software or
An IP telephone that can be
plugged into an IP network
via a wall jack.
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39. 6-17: Voice over IP (VoIP) A media gateway connects
a VoIP network to the PSTN.
This gives VoIP users access
To PSTN users.
The media gateway must translate
between both signaling technology
and transport technology.
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40. VoIP
VoIP means that a firm does not have to maintain two networks—an IP network for data and a circuit- switched voice network.
This should reduce costs considerably by only requiring the maintenance of a single network.
In addition, VoIP’s packet switching should be more efficient than the PSTN’s circuit switching.
But companies have concerns about sound quality and the high availability expected of telephone service.
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41. Wired “Last Mile” Services
Telephone Modems
ADSL Modem Service
Cable Modem Service
You need to get to the Internet from your home or apartment.
Businesses need to get to the Internet from their sites.
We will begin looking at three traditional ways to connect to the Internet.
All of them used wired transmission.

42. 6-20: “Traditional” Technologies for the Last Mile
The access line to your home
Traditionally, a 1-pair VG UTP line from the telephone company
In the 1960s, a few businesses started getting 2-pair data-grade UTP and optical fiber
Given the cost of upgrading the 1-pair VG UTP plant, it seemed eternal
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43. 6-20: “Traditional” Technologies for the Last Mile
Telephone Service and Cable TV
1950s brought cable television
Used coaxial cable with a central wire and a coaxial conductive ring or mesh
Thick coax trunk lines past homes
Thin coax drop lines to homes
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44. 6-20: “Traditional” Technologies for the Last Mile
Telephone Service and Cable TV
Television services soon went beyond delivering over- the-air signals
A static situation emerged
Telephone companies controlled telephone service
Cable companies controlled television delivery service
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45. 6-20: “Traditional” Technologies for the Last Mile
Telephone modems
Convert digital computer signals to analog and send these over the telephone access line
They also convert incoming analog signals into digital signals for the computer
Digital
Computer
Signal:
Analog
Telephone
Signal:
Telephone
Modem
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Telephone Line

46. 6-20: “Traditional” Technologies for the Last Mile
Telephone modems
Limited to 33.6 kbps sending / 56 kbps receiving
Cannot use your telephone for calls while using the telephone modem
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47. 6-21: Asymmetric Digital Subscriber Line (ADSL)
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Like telephone modems,
ADSL also uses the existing 1-pair voice-grade
UTP line going to the home;
But it offers higher speeds than telephone modems.

48. Telephone Modems and ADSL
Both use the 1-pair VG UTP line running to the subscriber’s home
Already installed, so no extra cost of running a new line
Telephone modems send analog signals
This is what the traditional telephone system expects
ADSL
Send digital signals for data (digital subscriber line)
Requires special equipment at the end office switch (DSLAM)
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49. 6-21: Asymmetric Digital Subscriber Line (ADSL)
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Unlike telephone modem services,
ADSL provides simultaneous voice and data.
The phone line is not tied up

50. 6-21: Asymmetric Digital Subscriber Line (ADSL)
Speed is asymmetric.
Faster downstream (to home) speed
than upstream (from the home) speed.
This is ideal for World Wide Web downloads.
Speeds are increasing rapidly in both directions.
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51. 6-21: Asymmetric Digital Subscriber Line (ADSL)
Home user needs
a splitter for each
telephone outlet.
Connects a phone
to the splitter voice port.
Connects an
ADSL modem
To the splitter data port
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52. 6-21: Asymmetric Digital Subscriber Line (ADSL)
End office switch
needs a DSLAM
(DSL access multiplexer)
Connects voice calls
to the PSTN
Connects data calls
to a data network
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53. Cable Modem 6-22: Cable Modem Service Cable modem service is provided
by the cable television company,
not by a telephone company.
Generally is faster than ADSL
but also more expensive
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54. 6-22: Cable Modem Service Optical fiber brings signals
to and from the neighborhood.
Thick coaxial cables carry signals in the neighborhood.
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55. 6-22: Cable Modem Service Thin coaxial drop cables carry
signals from the trunk cable
to individual residences.
Subscriber needs a cable modem
to receive data service.
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56. ADSL versus Cable Modem Service
Generally, cable modem service is somewhat faster and more expensive than ADSL service
However, price and performance ranges overlap
And performance is increasing rapidly
In cable modem service, all subscribers in a neighborhood must share the speed
However, cable modem speed to the neighborhood is very high, so cable modem subscribers usually still get higher-than-ADSL speeds
And other subscribers cannot read a subscriber’s transmissions
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57. Wireless Access Service
Figure 6-23: Wireless Technologies for the Last Mile
We have looked at wired access to the Internet.
We will no look at wireless access technologies to get you to the Internet.

58. 6-23: Wireless for the Last Mile
3G Cellular Data Transmission
2G cellular service is for voice, texting, and photographs
Can send data via a cellular modem, but only at 10 kbps
3G cellular was created to send data faster
Most current services offer low DSL speeds at higher prices
2 Mbps to 3 Mbps speeds are arriving but will be even more expensive
Consumer usage is dominating with downloading music, videos, and games
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59. 6-23: Wireless for the Last Mile
WiMAX Metropolitan Area Networks
Designed to compete with DSL and cable modem service
Designed to serve a metropolitan area
Users can get service anywhere, not just at hotspots.
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60. 6-23: Wireless for the Last Mile
WiMAX Metropolitan Area Networks
Promises to be faster than 3G service at lower cost
Beginning with 1 to 4 Mbps and will be faster
Mobile subscribers with omnidirectional antennas will receive speeds at the lower end
Fixed subscribers in homes will have directional antennas and speeds will be at the higher end
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61. 6-23: Wireless for the Last Mile
Satellite Access Service
Very expensive because of long transmission distance to satellites
Hundreds to thousands of miles from the user site
One-way transmission, which is used in television delivery, is not too expensive
Two-way data transmission is complex and therefore expensive
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62. The Market Situation
Having looked at technologies, we need to turn the situation in the marketplace for services.

63. 6-24: The Market Situation
The Triple Play
The goal of access carriers
Telephony companies
Cable television companies
Wireless access companies
Provide telephony, data, and video in a package
Video is the hardest
People want multiple incoming TV signals
They also want HDTV
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64. 6-24: The Market Situation
Very High Speed Access Is Coming
Fiber to the home (FTTH)
Speeds of up to 100 Mbps or more
The backhaul issue: the entire network must be upgraded in capacity
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65. 6-24: The Market Situation
The International Situation
United States ranks 16th internationally in broadband speed and availability
Korea and Japan provide 50 Mbps speeds or faster at prices comparable to U.S. prices (for lower speeds)
Leadership in speed brings leadership in applications.
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