Telecommunications Chapter 6 Updated January 2009
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Transcript of Telecommunications Chapter 6 Updated January 2009
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-1
Raymond Panko’sBusiness Data Networks and Telecommunications, 7th edition
May only be used by adopters of the book
Telecommunications
Chapter 6Updated January 2009
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-2
The Public Switched Telephone Network (PSTN)
Carriers
Telephony
Television
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-3
6-1: Elements of the Public Switched Telephone Network (PSTN)
1. Customer PremisesEquipment
1. Customer Premises Equipment
Customer premisesEquipment (CPE) consists
Of telephones, wires,And other infrastructure
on the customer premises.
It is owned by the customer.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-4
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 this 4-pair UTP used for data.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-5
6-1: Elements of the PSTN
2. & 3. End OfficeSwitch (Class 5)
2.Access Line(Local Loop)
2.Access Line(Local Loop)
The Access System consists ofthe access line to the customer
(called the local loop)and termination equipment at the end office
(nearest telephone office switch).
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-6
6-1: Elements of the PSTN
3. Transport Core
3. TrunkLine
3.Switch
The Transport Core connects end officeswitches and core switches.
Trunk lines connect switches.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-7
6-1: Elements of the PSTN
• Telephone Company Switch
© 2009 Pearson Education, Inc. Publishing as Prentice Hall 6-8
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
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-9
Transport Versus Signaling
• Transport
– 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.
A frequent point of confusion
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-10
6-3: Points of Presence (POPs)
Local, long-distance, and internationalcarriers connect at POPs
(points of presence)
This permits their subscribersto call one another.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-13
6-5: Voice and Data Traffic
Full-Duplex (Two-Way) Circuit
Voice Traffic:Fairly Constant Use;Circuit Switching Is
Fairly Efficient
Data Traffic:Short Bursts,
Long Silences;Circuit Switching Is
Inefficient
Full-Duplex (Two-Way) Circuit
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.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-14
6-6: Dial-Up Circuits Versus Leased Line Circuits
Dial-Up Circuits Leased Line Circuits
Is it a circuit with reserved capacity?
Yes, by definition Yes, by definition
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 Simultaneous Voice Calls per Circuit
One Several due to multiplexing
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-15
6- 7: Time Division Multiplexing (TDM) in T1 Lines
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-16
6- 7: Time Division Multiplexing (TDM) in T1 Lines
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6- 7: Time Division Multiplexing (TDM) in T1 Lines
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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
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-19
6-8: Local Loop Technologies
Technology Use Status
1-Pair Voice-Grade UTP
Residences Already installed, so no installation cost
2-Pair Data-Grade UTP
Businesses for high-speed access lines
Must be pulled to the customer premises. (This is expensive)
Optical Fiber Businesses for high-speed access lines
Must be pulled to the customer premises. (This is expensive)
Note: Within buildings, corporate telephony uses 4-pair UTP
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-21
6-9: Analog Telephone Transmission
Speaking creates pressure waves, which hit the microphone in the handset.
The microphone generates an analogous electrical signal.
This is called an analog signal.
Handset
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-22
6-10: The PSTN: Mostly Digital with Analog Local Loops
The PSTN today is almost entirely digital.
This includes switches (3) and trunk lines (4).
It also includes digital leased access lines to businesses (5).
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-23
6-10: The PSTN: Mostly Digital with Analog Local Loops
Only the residential telephone (1) and the1-pair voice-grade UTP line going to residences (2)
are analog today.
Digital subscriber lines (which we will see later)Send digital signals over these 1-pair VG UTP lines.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-24
6-11: Codec at the End Office Switch
A codec at the end office switch translates between theanalog customer signals and digital signals in the PSTN core
ADC is analog to digital conversion.
DAC is digital to analog conversion.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-25
6-12: Frequency Division Multiplexing (FDM) in Microwave Transmission
Box
Microwave providesPoint-to-point
Terrestrial Transmission
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-26
6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Box
For telephone transmission, a filter at the end office switch
Bandpass filters the voice to fit into 4 kHz channels.Even when microwave is not used, this saves capacity
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-27
6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Box
More precisely, it cuts off all signal below about 300 Hzand above about 3,400 Hz
This gives “guard bands” below 300 HzAnd from 3,400 Hz to 4 Hz
Voice still sounds good because most energy is 30 Hz to 3,400 Hz
0 to 4 kHz
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-28
6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Box
The signal isSampled 8,000
Times per second.
So each sampleIs 1/8000 second
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-29
6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Box
In eachsampling period,
only the amplitudeof the signalIs sampled
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-30
6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Box
The filter candistinguish 256loudness levels.
Each loudnesslevel is representedas a binary numberbetween 0 and 255.
0 = 000000001 = 00000001
255=11111111
This requires oneoctet of storage
per sample.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-31
6-13: Analog-to-Digital Conversion (ADC): Bandpass Filtering and Pulse Code Modulation (PCM)
Box
This sampling method,which is called pulse
code modulation (PCM),produces 8 bits
per sample.
Times 8,000samples per second –
this means64 kbps per conversation
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-32
6-14: Digital-to-Analog Conversion (DAC)
Box
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.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-34
6-15: Cellular Technology
Customer has a mobile phone.
A city is divided into smallgeographic regions called cells.
Each cell has a cellsitewith an antenna and equipment
to serve mobile phones in the cell
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-36
6-15: Cellular Technology
A mobile telephone switching office (MTSO)coordinates activity among the cellsites.
The MTSO also connects mobile customerswith wired PSTN customers via a POP.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-37
6-15: Cellular Technology
• 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.
New
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-38
6-15: Cellular Technology
Channels can be reused in different cells.
This permits more customers to be served.
Serving more customers through channel reuseIs the whole reason for cellular service.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-39
6-15: Cellular Technology
GSM cellular technology cannot use thesame channel in adjacent cells.
CDMA can use the same channel in adjacentcells, providing more channel reuse
and so more customers.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-40
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 betweenthe cellsite in Cell O and the cellsite in Cell P.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-41
6-15: Cellular Technology
In handoff, a mobile phone moves from one cellto another cell in the same city.
In roaming, a mobile phone is taken to a different city.
In handoff, a mobile phone moves from one cellto another cell in the same city.
In roaming, a mobile phone is taken to a different city.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-42
6-16: Handoff and Roaming in 802.11 Wireless Networking and Cellular Telephony
802.11 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 city
Roaming (means different things)
Wireless host travels between access points in an organization
Mobile phone travels to a different city
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-44
6-17: Voice over IP (VoIP)
In voice over IP (VoIP),calls are digitized, packetized, and
transported over an IP network:either an internal IP network or the Internet.
In voice over IP (VoIP),calls are digitized, packetized, and
transported over an IP network:either an internal IP network or the Internet.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-45
6-17: Voice over IP (VoIP)
The user either has aPC with multimedia hardware
and VoIP softwareor
an IP telephone that can beplugged into an IP network
via a wall jack.
Either must have a codec
The user either has aPC with multimedia hardware
and VoIP softwareor
an IP telephone that can beplugged into an IP network
via a wall jack.
Either must have a codec
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-46
6-17: Voice over IP (VoIP)
A media gateway connectsa VoIP network to the PSTN.
This gives VoIP users accessTo PSTN users.
The media gateway must translatebetween both signaling technology
and transport technology.
A media gateway connectsa VoIP network to the PSTN.
This gives VoIP users accessTo PSTN users.
The media gateway must translatebetween both signaling technology
and transport technology.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-47
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.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-48
6-18: VoIP Signaling and Transport
The most popular SIGNALING protocol in VoIP is SIP.This figure shows how a sender initiates a connection using SIP.The initiator sends a SIP INVITE message to its SIP proxy server.
The initiator’s SIP proxy server passes the INVITE to the receivers’ server.The receiver’s SIP proxy server passes the INVITE to the receiver.
If the receiver accepts the INVITE, the conversation begins.
The most popular SIGNALING protocol in VoIP is SIP.This figure shows how a sender initiates a connection using SIP.The initiator sends a SIP INVITE message to its SIP proxy server.
The initiator’s SIP proxy server passes the INVITE to the receivers’ server.The receiver’s SIP proxy server passes the INVITE to the receiver.
If the receiver accepts the INVITE, the conversation begins.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-49
6-19: VoIP Codecs
Codec Transmission Rate
G.711 64 kbps
G.721 32 kbps
G.722 48, 56, 64 kbps
G.722.1 24, 32 kbps
G.723 5.33, 6.4 kbps
G.723.1A 5.3, 6.3 kbps
G.726 16, 24, 32, 40 kbps
G.728 16 kbps
G.729AB 8 kbps
The two phones mustuse the same codec
to encode anddecode voice.
They must agree onone of several standard
codec protocolsthrough negotiation.
Generally,more compression
gives lowersound quality but
lowers transmission cost
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-50
Wired “Last Mile” Services
Telephone Modems
ADSL Modem Service
Cable Modem Service
Fiber to the Home
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-51
6-20: “Traditional” Technologies for the Last Mile
• 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, 1-pair VG UTP seemed eternal
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-52
6-20: “Traditional” Technologies for the Last Mile
• Telephone Service and Cable TV
– 1950s brought cable television service
• Used coaxial cable with a central wire and a coaxial conductive ring or mesh
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-53
6-20: “Traditional” Technologies for the Last Mile
• Telephone Service and Cable TV
– A static situation emerged
– Telephone companies controlled broadcast telephone service
– Cable companies controlled television delivery service
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-54
6-20: “Traditional” Technologies for Data Transmission in 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
TelephoneModem
Telephone Line
DigitalComputer
Signal:1011001101010
AnalogTelephone
Signal:
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-55
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
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-56
6-21: Asymmetric Digital Subscriber Line (ADSL)
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
ADSL
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-57
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)
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-58
6-21: Asymmetric Digital Subscriber Line (ADSL)
Unlike telephone modem services,ADSL provides simultaneous voice and data.
The phone line is not tied up
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-59
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.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-60
6-21: Asymmetric Digital Subscriber Line (ADSL)
Home user needsa splitter for eachtelephone outlet
Connects a phoneto the splitter voice port
Connects anADSL modem
To the splitter data port
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-61
6-21: Asymmetric Digital Subscriber Line (ADSL)
End office switchneeds a DSLAM
(DSL access multiplexer)
Connects voice callsto the PSTN
Connects data callsto a data network
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-62
6-22: Cable Modem Service
Cable modem service is providedby the cable television company,
not by a telephone company
Generally is faster than ADSLbut also more expensive
CableModem
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-63
6-22: Cable Modem Service
Optical fiber brings signalsto and from the neighborhood.
Thick coaxial cables carry signalsin the neighborhood.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-64
6-22: Cable Modem Service
Thin coaxial drop cables carrysignals from the trunk cable
to individual residences.
Subscriber needs a cable modemto receive data service.
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-65
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, which are encrypted
© 2009 Pearson Education, Inc. Publishing as Prentice Hall
Fiber to the Home
• Some carriers are beginning to replace their 1-pair voice grade UTP residential wiring with optical fiber
• This is called fiber to the home or fiber to the premises
• Download speeds of 100 Mbps or more
• Substantially more expensive than DSL service
6-66
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Wireless Access Service
Figure 6-23: Wireless Technologies for the Last Mile
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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
© 2009 Pearson Education, Inc. Publishing as Prentice Hall
6-23: Wireless for the Last Mile
• Cellular companies are using many 3G technologies
• Cellular companies will eventually introduce faster 4G service
– 100 Mbps or more
– Beginning to converge on Long-Term Evolution (LTE)
– Which is IP-based
6-69
New
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6-23: Wireless for the Last Mile
• WiMAX Metropolitan Area Networks
– Designed to compete with DSL, cable modem service, and 3G and 4G cellular service
– Designed to serve a metropolitan area
– Users can get service anywhere,not just at hotspots
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-71
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 televisiondelivery, is not tooexpensive
• Two-way datatransmission is complexand therefore expensive
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-73
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
© 2009 Pearson Education, Inc. Publishing as Prentice Hall6-74
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