Transcript Basic Concepts - Ray Panko Classes Spreadsheet Error and

Telecommunications
Chapter 6
Updated January 2007
Panko’s
Business Data Networks and Telecommunications, 6th edition
Copyright 2007 Prentice-Hall
May only be used by adopters of the book
Telecommunications
• From Chapter 1:
– Data communications
– Telecommunications: Voice and Video Communications
6-2
Technical Elements of
the Public Switched
Telephone Network
Figure 6-1: Elements of the Public Switched
Telephone Network (PSTN)
1. Customer Premises
Equipment
1. Customer Premises Equipment
6-4
Figure 6-2: Customer Premises Equipment
Site
Handset
PBX
4-Pair UT P
T elephone Wiring
PST N
A typical business site.
The private branch exchange is an internal switch for the site.
4-pair UTP was created for business premises telephone wiring
Company is essentially its own telephone company that connects to the
outside PSTN
6-5
Figure 6-1: Elements of the Public Switched
Telephone Network (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)
6-6
Figure 6-1: Elements of the Public Switched
Telephone Network (PSTN)
3. Transport Core
3.
Switch
3. Trunk
Line
The Transport Core connects end office
switches and core switches.
Trunk lines connect switches.
6-7
Figure 6-1: Elements of the PSTN
• Telephone Company Switch
6-8
Figure 6-1: Elements of the Public Switched
Telephone Network (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
6-9
Figure 6-3: Points of Presence (POPs)
Local Access and Transport Area (LAT A)
Local
Carrier 1
Switch
POP
Other Local Area
Long-Distance
Carrier A
POP
International
Carrier X
Local
Carrier 2
Switch
Local
Carrier 1
Customer
Other Country
Local
Carrier 2
Customer
In the U.S., competing
carriers connect at
points of presence (POPs).
6-10
Figure 6-4: Circuit Switching
T he PSTN
has traditionally used
circuit switching.
A circuit is an end-to-end
connection between two subscribers.
Capacity is reserved on all
trunk lines and switches along the way.
Capacity must be paid for even if it is not used.
6-11
Figure 6-5: Voice and Data Traffic
Full-Duplex (Two-Way ) Circuit
Voice Traf f ic:
Fairly Constant Use;
Circuit Switching Is
Fairly Ef f icient
Full-Duplex (Two-Way ) Circuit
Data Traf f ic:
Short Bursts,
Long Silences;
Circuit Switching Is
Inef f icient
The reserved capacity of circuit switching
is OK for voice, but not for bursty data transmission.
6-12
Figure 6-6: Dial-Up Circuits Versus Leased Line
Circuits
Operation
Speed for Carrying
Data
Number of Voice
Calls Multiplexed
Dial-Up Circuits
Leased Line Circuits
Dial-Up. Separate
circuit for each call.
Permanent circuit,
always on.
Up to 56 kbps
Residence can only
Send up to 33.6 kbps
56 kbps to gigabit
speeds
One
Several due to
multiplexing
There are two types of circuits between customer premises:
ordinary dial-up circuits and leased line circuits.
6-13
Figure 6-7: Local Loop Technologies
Technology
Use
Status
1-Pair Voice-Grade
UTP
Residences
Already installed
2-Pair Data-Grade
UTP
Businesses for
Lowest-speed
access lines
Must be pulled to the
customer premises
(this is expensive)
Optical Fiber
Businesses for
higher-speed
access lines
Must be pulled to the
customer premises
(this is expensive)
Residential 1-pair voice-grade UTP is already installed.
This makes it inexpensive to use
Business 2-pair data-grade UTP and fiber for leased lines
must be installed; this is expensive.
6-14
Figure 6-8: Analog Telephone Transmission
Analog
(Analogous)
Electrical Signal
Sound
Wav e
Analog signals rise and fall in intensity with the human voice.
No resistance to errors as there is in digital transmission.
Initially, the entire PSTN was analog.
6-15
Figure 6-9: The PSTN: Mostly Digital with Analog
Local Loops
Today 's Telephone Network: Predominantly Digital
Local
Loop
(Analog)
Residential
Telephone
(Analog)
Local
Loop
(Digital)
Switch
(Digital)
Switch
(Digital)
Trunk Line
(Digital)
Switch
(Digital)
PBX
(Digital)
Today, everything is digital except for the
local loop access line and residential telephones.
The actual local loop line can carry either analog or digital signals,
but the equipment at both ends is analog.
6-16
Figure 6-10: Codec at the End Office Switch
Analog Signal
Telephone
Home
Local Loop
ADC
Digital
Signal
Codec
DAC
Digital Switch
End Of f ice
A codec at the end office translates between
residential analog and PSTN digital signaling.
ADC = analog to digital conversion
DAC = digital to analog conversion
6-17
Figure 6-11: Frequency Division Multiplexing
(FDM) in Microwave Transmission
Box:
Codec Operation
Microwave uses
radio transmission
for PSTN trunk lines
Channel 1 / Circuit A
Channel 2 / Circuit D
Channel 3 / Circuit C
Channel 4 / Unused
Channel 5 / Circuit E
Each circuit is sent in a separate channel.
If channel bandwidth is large,
there will be f ewer channels.
Voice uses 4 kHz-wide channels
to allow more channels.
6-18
Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass
Filtering and Pulse Code Modulation (PCM)
Step 1: Bandpass Filtering
Analog Voice
Signal
Subscriber
Box:
Codec
Operation
Analog Electrical
Signal
Filteratat
Filter
End Of f ice Switch
End Office Switch
At the end office, the voice signal is bandpass-filtered
to limit its bandwidth to 4 MHz.
This permits more calls to be multiplexed on trunk lines
6-19
Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass
Filtering and Pulse Code Modulation (PCM)
Box:
Codec Operation
Step 1: Bandpass Filtering
Signal
0 Hz
Energy Distribution of
Human Speech Along the
Frequency Spectrum
300 Hz
3,400 Hz (3.4 kHz)
20 kHz
Frequency
Bandwidth (3.1 kHz)
Actually, to provide a safety margin, the signal
is filtered to between about 300 Hz and 3.4 kHz
instead of from 0 Hz to 4 kHz.
6-20
Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass
Filtering and Pulse Code Modulation (PCM)
Step 2: Pulse Code Modulation (PCM) Sampling
255 (maximum)
Analog
Signal
Duration
of Sample
(1/8000 sec.)
Box:
Codec Operation
Signal
Amplitude
0
Nyquist found that signals must be
sampled at twice their highest frequency.
Sample
For a top frequency of 4 kHz,
Intensity
ofmust
Sample
there
be 8,000 samples per second.
(125/255 or 01111101)
Each sample is 1/8000 second.
Time
6-21
Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass
Filtering and Pulse Code Modulation (PCM)
Step 2: Pulse Code Modulation (PCM) Sampling
255 (maximum)
Analog
Signal
Signal
Amplitude
Duration
of Sample
(1/8000 sec.)
In each sampling
period, the intensity
of the signal is
measured.
In pulse code
modulation, the
signal is measured
as one of 256
intensity levels.
Box:
Codec Operation
0
Sample
Intensity of Sample
(125/255 or 01111101)
Time
One byte stores
one sample.
6-22
Figure 6-12: Analog-to-Digital Conversion (ADC): Bandpass
Filtering and Pulse Code Modulation (PCM)
Step 2: Pulse Code Modulation (PCM) Sampling
255 (maximum)
Analog
Signal
Duration
of Sample
(1/8000 sec.)
Signal
Amplitude
0
Sample
Intensity of Sample
(125/255 or 01111101)
Pulse Code
Modulation (PCM)
produces
8,000 one-byte
samples per second.
This is 64 kbps
of data.
Time
Box:
Codec Operation
6-23
ADC Recap
Box:
Codec Operation
• First, Bandpass-Filter the Incoming Signal to 4 kHz
– Really about 300 Hz to 3.4 kHz
– To reduce transmission requirements
• The Codec then Uses PCM for the Conversion
– Samples at twice the highest frequency (4 kHz so 8,000
samples/second)
– Loudness is recorded with 8 bits per sample (to give 256
loudness levels)
– Generates 64 kbps of traffic (8 bits/sample times 8,000
samples per second)
6-24
Figure 6-13: Digital-to-Analog Conversion (DAC)
Box:
Codec Operation
One 8-Bit
Sample
One 8-Bit
Sample
00000100 00000011 00000111
To Customer:
Generated “analog” signal
(Sounds smooth because
the sampling rate
is very high)
DAC
at End
Office
Switch
From digital PSTN network:
Arriving digital signal
from the PSTN Core
(8,000 Samples/Second)
6-25
Figure 6-14: Cellular Telephony
Mobile Telephone Switching Of f ice
Cellsite
G
PSTN
D
Channel
47
B
A
K
H
E
C
N
L
I
In cellular technology, the region
F
is divided into smaller cells.
P
O
M
Handof f
J
In each cell, a cellsite serves
cellphones in the cell.
6-26
Figure 6-14: Cellular Telephony
• Cellsites
6-27
Figure 6-14: Cellular Telephony
Of f ice
ChannelsMobile
can beTelephone
reused inSwitching
different cells.
Channel reuse supports more customers.
This is the reason for using cells.
(Channel 47 is reused in cells
A, D, and F)
Cellsite
G
PSTN
D
Channel
47
B
A
K
H
E
C
N
L
I
O
M
F
P
Handof f
J
6-28
Figure 6-14: Cellular Telephony
Mobile Telephone Switching Of f ice
Cellsite
G
PSTN
When a subscriber moves from one
D
cell to another
Channelin a cellular system,
B
this 47
is called a handoff.
A
E
When a subscriber moves from
one city to another, this is C
roaming.
K
H
L
I
P
O
M
F
(In WLANs, handoffs and roaming
mean the same thing.)
N
Handof f
J
6-29
Figure 6-14: Cellular Telephony
Mobile Telephone Switching Of f ice
Cellsite
G
PSTN
Channel
47Mobile Telephone
B
The
D
Switching Office
A (MTSO) E
coordinates the cellsites and
implements signaling andChandoffs.
F
The MTSO also connects
cellphones to the PSTN
(called the wireline network).
K
H
N
L
I
P
O
M
Handof f
J
6-30
Cellular Technologies
• GSM is the worldwide standard for cellular voice
–
–
–
–
–
Uses time division multiplexing (TDM)
Uses 200 kHz channels
Divides each second into many frame periods
Divides each frame into 8 slots
Gives same slot in each frame to a conversation
Time Frame 1
Slot 1
Slot 2
Conversation Conversation ……
A
B
Frame 2
Slot 8
Slot 1
Conversation Conversation
H
A
6-31
Cellular Technologies
• Cannot use the same channel in adjacent cells
– So can only reuse a channel about every 7 cells
– For example, suppose there are 50 cells
• Channel can be reused 50 / 7 times
• This is 7 (not precise, so round things off)
• So each channel can support 7 simultaneous
customers in these 7 cells
6-32
Cellular Technologies
• Code Division Multiple Access (CDMA)
– Also used in the United States
– A form of spread spectrum transmission
– Unlike traditional spread spectrum technology, multiple
users can transmit simultaneously
– 1.25 MHz channels
– Can support many users per channel
• Can use the same channel in adjacent cells
– So can only reuse a channel in every cell
6-33
Figure 6-15: Voice over IP (VoIP)
VoIP carries telephone calls over
LANs and the Internet
PC with
Multimedia Hardware
and VoIP Sof tware
With IP, there is no wasted capacity
as there is with circuit switching.
This reduces cost.
Internet
Media
Gateway
IP Telephone
with
Codec and
TCP/IP Functionality
PSTN
6-34
Figure 6-15: Voice over IP (VoIP)
Stations can be special IP telephones
with IP functionality
PC with
Multimedia Hardware
and VoIP Sof tware
Or a PC with multimedia hardware
and VoIP software
IP phones need a codec to convert
Internet
voice analog signals from the microphone
into digital IP signals
Media
Gateway
IP Telephone
with
Codec and
TCP/IP Functionality
PSTN
6-35
Figure 6-15: Voice over IP (VoIP)
A media gateway connects a
VoIP network to the PSTN
Handles transport and signaling differences
PC with
Multimedia Hardware
and VoIP Sof tware
Internet
Media
Gateway
IP Telephone
with
Codec and
TCP/IP Functionality
PSTN
6-36
Figure 6-16: Speech Codes
Codec
G.711
G.721
G.722
G.722.1
G.723.1A
Transmission Rate
64 kbps (pulse code modulation)
32 kbps (adaptive PCM)
46, 56, or 64 kbps
24, 32 kbps
5.3, 6.3 kbps
There are several codec standards.
They differ in transmission rate, sound quality, and latency.
Both sides must use the same codec standard.
6-37
Figure 6-17: VoIP Protocols
Signaling: SIP or H.323
(Call setup, breakdown, accounting, and other supervisory tasks)
VoIP Transport Packet
Codec Data
Stream
PC with Multimedia and
VoIP Software
RTP
Hdr
UDP
Hdr
IP
Hdr
T ransport
(Voice transmission)
IP T elephone
Transport is the transmission of voice
(carries codec data).
Signaling is call supervision.
6-38
Figure 6-17: VoIP Protocols
1. VoIP transport packets use UDP at the transport layer.
Signaling: SIP or H.323
(There
is
no
time
for
to repair
errors.)
(Call setup, breakdown,retransmissions
accounting, and other
supervisory
tasks)
The receiver puts in fill sounds for lost packets.
3.
The application
message is a
codec data
stream
PC with Multimedia and
VoIP Software
VoIP Transport Packet
Codec Data
Stream
RTP
Hdr
UDP
Hdr
T ransport
(Voice transmission)
IP
Hdr
IP T elephone
2. The UDP header is followed by a
Real Time Protocol (RTP) header, which contains
a sequence number and timing information.
Receiver uses timing information to smooth out sound playback.
6-39
Figure 6-17: VoIP Protocols
Signaling: SIP or H.323
(Call setup, breakdown, accounting, and other supervisory tasks)
VoIP Transport Packet
Codec Data
Stream
RTP
Hdr
UDP
Hdr
IP
Hdr
T ransport
Signaling
is call
supervision.
(Voice
transmission)
PC with Multimedia and
H.323 signaling
VoIP The
Software
IP T elephone
standard came first for VoIP signaling.
SIP is simpler and now dominates VoIP signaling
6-40
Video over IP
• The Other VoIP
– It’s not just voice over IP
– Video Telephones
– Video Conferencing
• PC to PC
• Multiparty
• Sometimes room-to-room
– Video Downloads on Demand
6-41
Figure 6-18: Residential Internet
Access Services
• Telephone Modems
• Broadband Internet Access
Note:
Speeds and Prices
Change Rapidly
• Asymmetric Digital Subscriber Line (ADSL)
• Cable Modem Service
• 3G Cellular Data Service
• WiMAX (802.16d and 802.16e)
• Broadband over Power Lines
• Fiber to the Home (FTTH)
6-42
Figure 6-19:
Telephone Modem Connection to an ISP
Telephone modems
convert digital computer
signals to analog
telephone signals.
PSTN (Digital)
Analog
Digital
33.6 kbps
Client A
Telephone Telephone
Modem
Analog
Access
Line
56 kbps
6-43
Figure 6-19:
Telephone Modem Connection to an ISP
PSTN (Digital) Digital Leased Line
(No Modem)
Digital
56 kbps
ISP does not have a modem.
It has a digital leased line so
can send at 56 kbps.
(There is no bandpass
filtering on digital leased lines.)
33.6 kbps
ISP
6-44
Figure 6-19:
Telephone Modem Connection to an ISP
PSTN (Digital)
Analog
Digital
33.6 kbps
Client A
Analog
Access
Line
Telephone Telephone
Modem
56 kbps
Digital Access Line
(No Modem)
Digital
56 kbps
33.6 kbps
ISP
Circuit
Dial-up circuits connect the client with the ISP.
56 kbps downstream, 33.6 kbps upstream
6-45
Telephone Modem Limitations
• Very low transmission speeds
– Long delays in downloading webpages
• Subscriber cannot simultaneously use the
telephone line for voice calls
• Still used by 30% to 40% of Internet users.
6-46
Figure 6-20: Amplitude Modulation
Binary Data
Modulated Analog
Signal
PSTN
Client A
Serial
Cable
Modem Telephone Telephone
Cable
Amplitude Modulation
Modulation is the conversion of binary computer signals
into analog signals that can travel over an ordinary access line.
Demodulation, at the other ends, converts the modulated
1
0 to digital computer
1
signals back
signals. 1
6-47
Figure 6-20: Amplitude Modulation
Modulated Analog
Signal
Binary Data
In amplitude modulation, there are
two amplitude (loudness levels)—
one for 1 and one for 0
Serial Modem Telephone Telephone
Cable
Cable
Client A
PSTN
Amplitude Modulation
1
0
1
1
1011 is loud-soft-loud-loud
6-48
Figure 6-21: Asymmetric Digital Subscriber Line
(ADSL)
Subscriber
Premises
PC
ADSL
Modem
Splitter
Telephone Company
End Of f ice Switch
Data
WAN
Single Pair of
Voice-Grade
UTP Wires
DSLAM
PSTN
Telephone
ADSL ALSO uses the existing residential local loop technology.
Inexpensive because no need to pull new wires, but
1-pair voice-grade UTP is not designed for high-speed transmission.
6-49
Figure 6-21: Asymmetric Digital Subscriber Line
(ADSL)
1.
Telephone Company
Subscriber
Subscriber needs an ADSL modem.
Premises
Also needs a splitter for each End Of f ice Switch
telephone wall outlet.
PC
ADSL
Modem
Splitter
Data
WAN
Single Pair of
Voice-Grade
UTP Wires
DSLAM
PSTN
Telephone
2.
Telephone carrier needs a digital subscriber line
access multiplexer (DSLAM) to separate the two signals.
6-50
Figure 6-21: Asymmetric Digital Subscriber Line
(ADSL)
Subscriber
Premises
Telephone Company
Downstream Data
Data End Of f ice Switch
Downstream
Up
Mbps
Up to
to 1.5
3 Mbps
Upstream Data
Up to 512 kbps
PC
ADSL
Modem
Single Pair of
Voice-Grade
UTP Wires
DSLAM
Splitter
Telephone
Data
WAN
PSTN
Ordinary Telephone
Serv ice
Unlike telephone modems, ADSL service
provides simultaneous voice and data transmission.
6-51
Figure 6-21: Asymmetric Digital Subscriber Line
(ADSL)
Subscriber
Premises
Telephone Company
Downstream
Downstream Data End Of f ice Switch
Up
Mbps
Uptoto1.5
3 Mbps
Upstream Data
Up to 512 kbps
PC
ADSL
Modem
Telephone
Single Pair of
Voice-Grade
UTP Wires
DSLAM
Speed is asymmetric
Ordinary
Telephone
Faster
downstream
than upstream
Serv ice
(Up to 3 Mbps versus up to 512 kbps)
Ideal for Web access
Acceptable for e-mail
Good for residential use
Splitter
Data
WAN
PSTN
6-52
Figure 6-22: Cable Modem Service
Maximum download
throughput is about 5 Mbps
Coaxial Cable
in Neighborhood
(Shared T hroughput)
ISP
Coaxial Cable
Drop Cable
Optical
Fiber to
Neighborhoods
UTP
or
USB
PC
Cable
Modem
Neighborhood
Splitter
Cable T elevision
Head End
Subscriber Premises
Cable modem service brings high-speed
optical fiber lines to the neighborhood.
6-53
Figure 6-22: Cable Modem Service
In the neighborhood,
thick coaxial cable
brings service to
households.
ISP
Thick Coaxial Cable
in Neighborhood
(Shared Throughput)
Thin
Coaxial Cable
Drop Cable
This bandwidth is
Optical
Fiber to shared by
Neighborhoods
everyone in the
UTP
or
USB
PC
Cable
Modem
Subscriber Premises
neighborhood.
Neighborhood
Splitter
A thinCable
coaxTelevision
line
End
goes toHead
each
home’s
cable modem.
6-54
Figure 6-22: Cable Modem Service
T hick Coaxial Cable
in Neighborhood
(Shared T hroughput)
Maximum download
throughput is about 5 Mbps
ISP
T hin
Coaxial Cable
Drop Cable
Optical
Fiber to
Neighborhoods
UTP
or
USB
PC
Cable
Modem
Subscriber Premises
Neighborhood
Splitter
Cable T elevision
Head End
Downstream speeds up to 5 Mbps.
Upstream speeds up to about 1 Mbps.
6-55
ADSL versus Cable Modem Service
• Do Not Over-Stress the Importance of Sharing
– Cable modem service usually is still faster than ADSL
service
– DSLAM sharing can slow ADSL service too
• The Bottom Line Today:
– Cable modem service usually is faster
– ADSL service usually is cheaper
• ADSL offers more speed-price options
• Both are improving rapidly in terms of speed and
(sometimes) price
6-56
Figure 6-23: Third-Generation (3G)
Cellular Data Services
• Cellphone connects to computer via a cellphone
modem or USB
• Traditional GSM and CDMA
– Limited to only about 10 kbps
– Far too slow for usability
6-57
Figure 6-23: Third-Generation (3G) Cellular
Data Services
• Both GSM and CDMA are evolving
• Second Generation (now dominant)
– Only 10 kbps data transmission
• Third Generation
– Low end: comparable to telephone modem service
– High end: comparable to low-speed DSL service
• Future
– Speeds comparable to high-end DSL or cable modem
service
– 100 Mbps or more (fast enough for good video)
6-58
Figure 6-18: Residential Internet
Access Services
• WiMax (802.16)
– Wireless Internet access for metropolitan areas
– Basic 802.16d standard: ADSL speeds to fixed locations
• Will use dish antennas
• Just reaching the market
– 802.16e will extend the service to mobile users
• Will use omnidirectional antennas
6-59
Figure 6-18: Residential Internet
Access Services
New
• Satellite Internet
Access
– Very expensive
– Often needed to
serve rural areas
6-60
Figure 6-18: Residential Internet
Access Services
• Broadband over Power Lines
– Broadband data from your electrical company
– It already has transmission wires and access to
residences and businesses
– It can modulates data signals over electrical power
lines
– It works, but has very limited availability and is slow
– Especially promising for rural areas
6-61
Figure 6-18: Residential Internet
Access Services
• Fiber to the Home (FTTH)
– Carrier runs fiber to the home
– Provides speeds of tens of megabits per second for highspeed video, etc.
• Less if fiber only goes to the curb (FTTC)
• Or to the neighborhood (FTTN)
– Much faster than other residential internet access
services
– Could dominate residential (and business) Internet
access in the future
6-62
Internet Access and VoIP
• Most ISPs are Planning to or Already Provide VoIP
Telephone Service
– An alternative to the local telephone company service
– Media gateways will interconnect with the PSTN
– Should be less expensive that traditional phone service
– Questions remain
• Voice quality and reliability
• 911 and 911 location discovery
• Regulation and taxation
• Laws that require wiretapping with warrants
6-63
Topics Covered
Telecommunications
• Data Communications versus Telecommunications
• The PSTN’s Technical Elements
– Customer premises equipment (PBX and 4-pair UTP)
– Access system (local loop)
– Transport core
– Signaling (call setup and management)
• POP to interconnect carriers
6-65
Telecommunications
• Access Lines
– For residences, 1-pair voice-grade UTP
• DSL uses existing residential access lines to carry data
by changing the electronics at each end (DSL modem in
the home and DSLAM at the end office switch)
• DSL is cheap because 1-p VG UTP is already in place
– For businesses,
• 2-pair data-grade UTP for speeds up to a few Mbps
• Optical fiber for faster speeds
• Usually must be pulled into place, so expensive
– Eventually, fiber to the home (FTTH), FTTC, FTTN
6-66
PSTN Transmission
• Circuit Switching
– Reserved capacity end-to-end
– Acceptable for voice, but not for bursty data transmission
– Dial-up and leased line circuits
• Analog and Digital Transmission
– Analog signals on the local loop
– ADC and DAC at the end office switch
– ADC: bandpass filtering and sampling for 64 kbps
– DAC: sample values are converted to sound levels
6-67
Cellular Telephony
• Cells Allow Channel Reuse
– Channel reuse allows more customers to be served with
a limited number of channels
• GSM: most widely used technology for cellular
telephony
• CDMA for greater channel reuse
• Handoffs and Roaming
6-68
VoIP
• To allow voice to be carried over data networks
• Converge voice and data networks
• Phone needs a codec
• Transport: UDP header followed by RTP header
• Signaling: H.323 and SIP
• Video over IP
6-69
Residential Internet Access
Services
• Telephone Modems
• Asymmetric Digital Subscriber Line (ADSL)
• Cable Modem Service
• 3G Cellular Data Service
• WiMAX (802.16 and 802.16e)
• Broadband Over Power Lines
• Fiber to the Home (FTTH)
6-70