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VOIP and the “Last Mile”
1
Voice over IP (VoIP)
2
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.
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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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VoIP
• VoIP means that a firm does not have to maintain
two networks—an IP network for data and a circuitswitched 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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VoIP Signaling and Transport
Again, signaling is the transmission
of supervisory messages.
Transport is the actual
transmission of voice.
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VoIP Signaling and Transport
VoIP transport consists of a stream of VoIP packets.
Each VoIP packet contains a short amount codec-encoded voice.
There is no time to wait for error correction, so UDP is used.
The Real Time Protocol (RTP) header “fixes” weaknesses of UDP.
First, the RTP has a sequence number to place packets in order.
Second, RTP has a time stamp so that the voice steam
can be played back at the correct time.
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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 must
use the same codec
to encode and
decode voice.
They must agree on
one of several standard
codec protocols
through negotiation.
Generally,
more compression
gives lower
sound quality but
lowers transmission cost
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Wired “Last Mile” Services
Telephone Modems
ADSL Modem Service
Cable Modem Service
Fiber to the Home
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“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, 1pair VG UTP seemed eternal
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“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
• Telephone companies controlled broadcast telephone service
• Cable companies controlled television delivery service
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“Traditional” Technologies for the Last
Mile
• Telephone modems obsolete(I hope nobody uses it
anymore)
– Limited to 33.6 kbps sending / 56 kbps receiving
– Cannot use your telephone for calls while using the
telephone modem
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Asymmetric Digital Subscriber Line (ADSL)
+ADSL2
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
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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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Asymmetric Digital Subscriber Line (ADSL)
Unlike telephone modem services,
ADSL provides simultaneous voice and data.
The phone line is not tied up
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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.
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Speeds are increasing rapidly in both directions.
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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Cable Modem Service
Optical fiber brings signals to and from the neighborhood.
Thick coaxial cables carry signals in the neighborhood.
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ADSL Versus Cable Modem Service
• Generally, cable modem service is somewhat
faster and not 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
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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 vary. See Verizon FIOS.
• Not more expensive than DSL service.
• See FIOS and COMCAST comparison.
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Wireless Access Service
Wireless Technologies for the Last
Mile
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Wireless for the Last Mile
• 3G Cellular Data Transmission
– 3G cellular was created to send data faster
• current services offer DSL speeds at higher prices
• 2 Mbps to 3 Mbps speeds are even more
expensive
• Consumer usage is dominating with downloading
music, videos, and games
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Wireless for the Last Mile
• Cellular companies are still using many 3G
technologies
• Cellular companies are introducing faster 4G
service
– 100 Mbps or more
– Using Long-Term Evolution (LTE)
– Which is IP-based
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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
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Wireless for the Last Mile
• WiMAX Metropolitan Area Networks
– Promised to be faster than 3G service at lower cost
• Mobile subscribers with omnidirectional antennas
could receive speeds at the lower end
• Fixed subscribers in homes with directional antennas
could receive at the higher end
• The largest WiMAX network was created by Clearwire
in the US.
• Sprint acquired Clearwire and converted their users
for LTE and will shutdown WiMAX in 2015.
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4G LTE Services
• Standards are the same as for cellular 4G LTE
• Evolving market offerings
– Verizon 4G LTE Internet (Installed)
• a variety of Internet and routers providing wireless connection to
home and office.
• see link at bottom of the page.
– AT&T Wireless Home Phone & Internet
• prices vary based on data usage.
• see link at bottom of the page.
– Mobile hotspots
• an alternative to have Internet connection for devices without a
4G LTE antenna (e.g. Laptops, tablets, etc).
• Cost of the device, plus provider monthly fee.
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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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The Market Situation
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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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The Market Situation
• The International Situation
– United States ranks 9th internationally in broadband
speed and availability
– Korea and Japan provide 500 Mbps speeds or faster at
prices comparable to U.S. prices (for lower speeds)
– Leadership in speed brings leadership in applications
– See link at the bottom of the page for a recent report.
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