Transcript Chapter 12

Chapter Twelve
Voice and Data Delivery Networks
Introduction
•
General, we used to go into either
–
•
data communications or voice communications
Today, the two fields are merging
Reasons:
1. Voice systems transfer computer data and
2. data networks support voice
•
Thus, we need to the basic of voice
telecommunications too!
– Basic concept (to p3)
2
Basic concept
It has:
• The local loop is the telephone line that runs from the telephone
company’s central office to your home or business
(to p4)
• Central office – building that houses the telephone company’s switching equipment and provides a local dial tone on
your telephone
•
•
(to p7)
(to p5)
For a local call, it has such a layout
If you place a long-distance call, the central office passes your
telephone call off to a long-distance provider, a nation wide (to p6)
telephone system
•
Trunk – special telephone line that runs between central offices and
other telephone switching centers
– Usually digital, high-speed, and carries multiple telephone
circuits
– Typically a 4-wire circuit, while a telephone line is a 2-wire
circuit
•
How to classify a call is a long distance or local call?
– LATA concept
(to p8)
3
FIGURE 5-8
to each other.
It is more efficient to connect telephones to a central office switch and then connect the central office switches together than to connect all telephones
building that houses the telephone company’s switching
Equipment and provides a local dial tone on your telephone
A Local Environment
(to p3)
4
FIGURE 5-11 Residential telephone cabling.
(to p3)
5
FIGURE 5-10 The connection of the central offices in the nationwide telephone network.
(to p3)
Local Central Offices
A nation-wide environment
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FIGURE 5-7
Diagram of a telephone call involving toll trunks and toll offices.
(to p3)
Note: can be replaced
by a switch office
7
LATA concept
• The country is divided into a few hundred local
access transport areas (LATAs)
– If your call goes from one LATA to another, it is a
long-distance call and is handled by a longdistance telephone company
– If your call stays within a LATA, it is a local call
and is handled by a local telephone company
– (note: This concept applied in USA only and not
HK)
Installing a telephone system/line
(to p9)
8
Telephone System/Line
• When telephone company installs a line, it must
not proceed any further than 12 inches into the
building
– This point is the demarcation point, or demarc
• Modular connectors, such as the RJ-11, are
commonly used to interconnect telephone lines
and the telephone handset to the base
• When handset is lifted off base (off-hook), an offhook signal is sent to the central office
(to p10)
9
Telephone System/Line (continued)
• When off-hook signal arrives at central office, a
dial tone is generated and returned to telephone
• When user hears the dial tone, they dial (or
press) number
• The central office equipment collects dialed
digits, and proceeds to place appropriate call
• Types of telephone systems
(to p11)
10
Types of telephone systems
•
•
•
•
•
Private Branch Exchange (PBX) (to p12)
Automated Attendant (to p15)
Automatic Call Distributor (to p16)
Interactive Voice Response (to p18)
Key Telephone System (to p20)
• Basic Telephone Systems Services
(to p21)
– That offered by local operators
(to p24)
• Other Players in the Market
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PBX
• Private Branch Exchange (PBX) – common
internal phone switching system for medium- to
large-sized businesses
– Provides advanced intelligent features to users,
such as:
• 4-digit internal dialing
• Special prefixes for WATS, FX, etc (private dialing
plans)
• PBX intelligently decides how to route a call for
lowest cost
(to p13)
12
PBX (continued)
• More PBX features:
– Voice mail
– Routes incoming calls to the best station set
(automatic call distribution)
– Provides recorded messages and responds to
touch-tone requests (automated attendant)
– Access to database storage and retrieval
(interactive voice response)
– VoIP
(to p14)
13
PBX (continued)
• PBX components:
–
–
–
–
–
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CPU, memory, telephone lines, trunks
Switching network
Supporting logic cards
Main distribution frame
Console or switchboard
Battery back-up system
(to p11)
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Automated Attendant
• Plays a recorded greeting and offers a set of
options
• Lets the caller enter an extension directly (touch
tone or voice) and bypass an “operator”
• Forwards the caller to a human operator if the
caller does not have a touch tone phone
• Available as an option on a PBX
(to p11)
15
Automatic Call Distributor
• When you call a business and are told all operators /
technicians / support staff / etc. are busy and that
your call will be answered in the order it was
received
• Used in systems where incoming call volume is
large, such as customer service, help desk, order
entry, credit authorization, reservations, and catalog
sales
• Early systems used hunt groups
– Original systems routed call to first operator in line
(kept person very busy!)
(to p17)
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Automatic Call Distributor (continued)
• Modern systems perform more advanced
functions, such as:
– Prioritize the calls
– Route calls to appropriate agent based on the
skill set of the agent
– If all agents busy, deliver call to waiting queue
and play appropriate message (like how long they
may have to wait)
– Forward calls to another call center, or perform
automatic return call
(to p11)
17
Interactive Voice Response
• IVR is similar to automated attendant except:
– IVR incorporates a connection to a database (on
a mainframe or server)
– IVR allows caller to access and/or modify
database information
– IVR can also perform fax on demand
(to p19)
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Interactive Voice Response (continued)
• Common examples of IVR include:
– Call your bank to inquire about an account
balance
– University online registration system
– Brokerage firm taking routine orders from
investors
– Investment fund taking routine requests for new
account applications
– A company providing employees with info about
their benefit plans
(to p11)
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Key Telephone System
• Used within a small office or a branch office, a
key telephone system (KTS) is an on-premise
resource sharing device similar to a PBX
• Example – key system might distribute 48
internal telephone sets over 16 external phone
lines
– The business would pay for the 16 individual lines
but have 48 telephone sets operating
• User selects outside line by pressing
corresponding line button on key set (phone)
(to p11)
20
Basic Telephone Systems Services
• Foreign exchange service (FX) - customer calls
a local number which is then connected to a
leased line to a remote site
– It can serve as discounted IDD for service agents
(to p22)
• Wide area telecommunications services (WATS)
– discount volume calling to local- and longdistance sites
• Off-premises extensions (OPX) – dial tone at
location B comes from the PBX at location A
(to p11)
21
Wide Area Telecomm Services
• Wide Area Telecomm Services (WATS)
– offers quantity discounts to high volumes of calls
– there are 3 basic categories:
– a) call direction (that is in-WATS or out-WATS)
• In-WATS (only allow users to call in to company)
• Out-WATS(only allows users to call out to
company)
(to p23)
22
– b) Coverage
• The charges depends on band zone to which
company has prescribed.
• In USA, it has 5 bands (1-5)
– c) Geographic regions
• three types
• 1) Intra-state (service provides on either in or
out WATS, within subscriber’s home state)
• 2) Inter-state (applies to outside state boundary
but within the country)
• 3) International (applies similar to IDD calls)
(to p21)
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Other Players in the Market
• Alternate operator services
– Pay phones, hotel phones
• Aggregator
– pulls a bunch of small companies together and goes
after phone discounts
• Reseller
– rents or leases variety of lines from phone
companies, then resells to customers
• Specialized mobile radio carriers – mobile
communication services to businesses and
individuals, including dispatch, paging, and data
services
HK Telecomm Revolution !
(to p25)
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Telecomm and Deregulation in HK Environment
• Prior 1995, all telecomm services in HK are
franchised (why need to cater for franchising?)
• HK Government opens up the telecomm markets of
fixed network services in 1995.
• Franchised right to HK telecomm (now PCCW)
expired on 1995.
• New operators fixed line tel line registered in 1995
• HK telecom (PCCW) licensed on June 29, 1995
• Hutchison Telecomm Ltd licensed on June 30,
1995
• New World licensed on June 20, 1995
•
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(to p26)
Telecomm and Deregulation in HK Environment (cont.)
• Deregulation of Mobile comm services
– In 23 Feb 1999, OFTA (Office for Telecomm
Authority) announced the regulation of MNP
(Mobile number portability) started on 1 March
1999, that a customer could retain of his/her
mobile phone number as personal identity.
• Worldwide Regulatory agencies
• Limitations of voice telecomm!
(to p27)
(to p28)
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Worldwide regulatory agency
USA
Hong Kong
Federal Communications Commission (FCC)
Office for Telecommunications Authority
(OFTA)
(to p26)
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Limitations of Telephone Signals
• POTS lines were designed to transmit the
human voice, which has a bandwidth less than
4000 Hz
• A telephone conversation requires two channels,
each occupying 4000 Hz
• A 4000 Hz analog signal can only carry about
33,600 bits per second of information while a
4000 Hz digital signal can carry about 56,000
bits per second – ie the use of mulltiplexing (to p29)
• How to make it faster? (to p30)
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Limitations of Telephone Signals (continued)
(to p28)
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Limitations of Telephone Signals (continued)
• If you want to send information faster, you need
a signal with a higher frequency or you need to
incorporate more advanced modulation
techniques
• POTS cannot deliver faster signals
– What will?
• The 56k Dial-Up Modem (to p31)
• Other High speed data networks
(to p36)
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The 56k Dial-Up Modem
• A 56k modem (56,000 bps) achieves this speed
due to digital signaling as opposed to analog
signaling used on all other modems
• Would actually achieve 64k except:
– Local loop is still analog, thus analog signaling
(to p32)
– Analog to digital conversion at the local modem
introduces noise/error (to p33) (to p34)
– Combined, these shortcomings drop the speed to
at best 56k
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The 56k Dial-Up Modem (continued)
(to p31)
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The 56k Dial-Up Modem (continued)
(to p31)
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The 56k Dial-Up Modem (continued)
• In reality, it does not achieve 56k either
– FCC will not let modem transmit at power level
necessary to support 56k, so the best modem
can do is approximately 53k
• Will not even achieve 53k if connection between
your modem and remote computer contains an
additional analog to digital conversion, or if there
is significant noise on line
• Two standards in the market
(to p35)
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The 56k Dial-Up Modem (continued)
• Based upon one of two standards:
– V.90
• Upstream speed is maximum 33,600 bps
– V.92
• Newer standard
• Allows maximum upstream speed of 48 kbps
(under ideal conditions)
• Can place a data connection on hold if the
telephone service accepts call waiting and a voice
telephone call arrives
(to p30)
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High Speed data networks
•
•
(to p44)
•
•
Digital Subscriber Line (DSL)
Cable Modems (to p42)
T-1 Leased Line Service
Frame Relay (to p48)
(to p37)
– Committed Information Rate (CIR)
• Asynchronous Transfer Mode (ATM)
– Comparison
• Convergence
(to p60)
(to p64)
(to p65)
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Digital Subscriber Line
• Digital subscriber line (DSL) is a relative
newcomer to the field of leased line services
• DSL can provide very high data transfer rates
over standard telephone lines
• Unfortunately, less than half the telephone lines
in the U.S. are incapable of supporting DSL
– And there has to be a DSL provider in your region
(to p38)
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DSL Basics
• DSL, depending on the type of service, is capable of
transmission speeds from 100s of kilobits into
single-digit megabits
• Because DSL is highly dependent upon noise levels,
a subscriber cannot be any more than 5.5 kilometers
(2-3 miles) from the DSL central office
• DSL service can be:
– Symmetric – downstream and upstream speeds are
identical
– Asymmetric – downstream speed is faster than the
upstream speed
(to p39)
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DSL Basics (continued)
• DSL service
– Often connects a user to the Internet
– Can also provide a regular telephone service (POTS)
• The DSL provider uses a DSL access multiplexer
(DSLAM) to split off the individual DSL lines into
homes and businesses
– A user then needs a splitter to separate the POTS line
from the DSL line, and then a DSL modem to convert
the DSL signals into a form recognized by the
computer
(to p40)
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DSL Basics (continued)
(to p41)
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DSL Formats
• A DSL service comes in many different forms:
– ADSL (Asymmetric DSL)
– CDSL (Consumer DSL)
• Trademarked version by Rockwell
– DSL Lite
• Slower form than ADSL
– HDSL (High bit-rate DSL)
– RADSL (Rate-adaptive DSL)
• Speed varies depending on noise level
(to p36)
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Cable Modems
• Allow high-speed access to wide area networks
such as the Internet
• Most are external devices that connect to the
personal computer through a common Ethernet
card
• Can provide data transfer speeds between 500
kbps and 25 Mbps
(to p43)
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Cable Modems (continued)
(to p36)
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T-1 Leased Line Service
• T-1 – digital service offered by the telephone
companies that can transfer data as fast as
1.544 Mbps (both voice and computer data)
• To support a T-1 service, a channel service unit /
data service unit (CSU/DSU) is required at the
end of the connection
(to p45)
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T-1 Leased Line Service (continued)
• A T-1 service
– Is a digital, synchronous TDM stream used by
businesses and telephone companies
– Is always on and always transmitting
– Can support up to 24 simultaneous channels
• These channels can be either voice or data (PBX
support)
– Can also be provisioned as a single channel
delivering 1.544 Mbps of data (LAN to ISP
connection)
(to p46)
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T-1 Leased Line Service (continued)
• A T-1 service (continued)
– Requires 4 wires, as opposed to a 2-wire
telephone line
– Can be either intra-LATA (local) which costs
roughly $350-$400 per month, or inter-LATA (long
distance) which can cost thousands of dollars per
month (usually based on distance)
• A customer may also be able to order a 1/4 T-1 or
a 1/2 T-1
(to p47)
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T-1 Leased Line Service (continued)
• Constantly transmits frames (8000 frames per
second)
– Each frame consists of one byte from each of the 24
channels, plus 1 sync bit (8 * 24 + 1 = 193 bits)
• 8000 frames per second * 193 bits per frame = 1.544
Mbps
– If a channel is used for voice, each byte is one byte of
PCM-encoded voice
– If a channel is used for data, each byte contains 7 bits
of data and 1 bit of control information (7 * 8000 = 56
kbps)
(to p36)
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Frame Relay
• Leased service that can provide a high-speed
connection for data transfer between two points
either locally or over long distances
• A business only has to connect itself to local
frame relay port
– Hopefully this connection is a local telephone call
– Once data reaches local frame relay port, the
frame relay network, or cloud, transmits the data
to the other side
(to p49)
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Frame Relay (continued)
(to p50)
49
Frame Relay (continued)
• Permanent virtual circuit (PVC) – connection
between two endpoints
– Created by the provider of the frame relay service
• The user uses a high-speed telephone line to
connect its company to a port, which is the
entryway to the frame relay network
• The high-speed line, the port, and the PVC
should all be chosen to support a desired
transmission speed
(to p51)
50
Frame Relay (continued)
(to p52)
51
Frame Relay Setup
• Consider a company that has four office
locations and currently has six leased lines
interconnecting the four locations
– To install frame relay, the company would ask for
six PVCs in place of the six leased lines
– The company would also need four high-speed
telephone lines and four ports connecting the four
locations to the frame relay cloud
(to p53)
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Frame Relay Setup (continued)
(to p54)
53
Frame Relay Setup (continued)
Service agreement/ Committed Information Rate (CIR)
(to p55)
54
Committed Information Rate (CIR)
• The user and frame relay service would agree
upon a committed information rate (CIR)
• The CIR states that if the customer stays within
a specified data rate (standard rate plus a burst
rate) the frame relay provider will guarantee
delivery of 99.99% of the frames
• The burst rate cannot be exceeded for longer
than 2 seconds
(to p56)
55
Committed Information Rate (CIR)
(continued)
• Example – if a company agrees to a CIR of 512
kbps with a burst rate of 256 kbps, the company
must stay at or below 512 kbps, with an occasional
burst up to 768 kbps, as long as the burst does not
last longer than 2 seconds
– If the company maintains their end of the agreement,
the carrier will provide something like 99.99%
throughput and a network delay of no longer than 20
ms
– If the customer exceeds its CIR, and the network
becomes congested, the customer’s frames may be
discarded
(to p57)
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Frame Relay vs. the Internet
• Frame relay has many advantages over the
Internet, including guaranteed throughput and
minimum delay, and better security
• Internet has the advantage of being practically
everywhere, cheaper, and simpler to create
connections (no PVCs necessary)
– And Internet tunnels (VPNs) are attractive
(to p58)
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Voice over Frame Relay (VoFR)
• Frame relay is also capable of supporting voice
communications
• The high transfer speeds of frame relay
adequately support the needs of interactive
voice
• If a company requires multiple voice circuits,
frame relay is an interesting solution
(to p59)
58
Frame Relay Switched Virtual Circuits
• Frame relay can also provide switched virtual
circuits (SVC)
– A SVC can be created dynamically by the
customer
– Good for short-term connections, but more
expensive
(to p60)
59
Asynchronous Transfer Mode (ATM)
• Asynchronous Transfer Mode (ATM) – very highspeed packet-switched service, similar in a
number of ways to frame relay
• Both send packets of data over high-speed lines
• Both require a user to create a circuit with a
provider
• One noticeable difference between ATM and
frame relay is speed
– ATM is capable of speeds up to 622 Mbps while
frame relay’s maximum is typically 45 Mbps
(to p61)
60
Asynchronous Transfer Mode (ATM)
(continued)
• Similar to frame relay, data travels over a connection
called a virtual channel connection (VCC)
• To better manage VCCs, a VCC must travel over a
virtual path connection (VPC)
• One of ATM’s strengths (besides its high speeds) is
its ability to offer various classes of service
• If a company requires a high-speed, continuous
connection, they might consider a constant bit rate
service
(to p62)
61
ATM Classes of Service
• A less demanding service is variable bit rate (VBR)
– VBR can also support real-time applications (rt-VBR),
as well as non-real-time applications (nrt-VBR), but
do not demand a constant bit stream
• Available bit rate (ABR) is used for bursty traffic that
does not need to be transmitted immediately
– ABR traffic may be held up until a transmission
opening is available
• Unspecified bit rate (UBR) is for lower rate traffic
that may get held up, and may even be discarded
part way through transmission if congestion occurs
(to p63)
62
Advantages and Disadvantages of ATM
• Advantages of ATM include very high speeds
and the different classes of service
• Disadvantages include potentially higher costs
(both equipment and support) and a higher level
of complexity
(to p36)
63
Comparison of DSL, Cable Modems, Frame
Relay, and ATM
(to p36)
64
Convergence
• Big issue in the voice and data delivery industry
• Phone companies are buying other phone
companies
• Older technologies are falling by the wayside as
newer technologies take over a larger share of the
market
• Newer devices are incorporating multiple
applications
• Computer telephony integration is one large
example of convergence
(to p66)
65
Computer-Telephony Integration (CTI)
• Emerging field that combines more traditional voice
networks with modern computer networks
• Consider a system in which a customer calls a
customer support number
– The customer’s telephone number appears on the
customer support rep’s terminal and immediately pulls
up the customer’s data
– The rep answers the phone by clicking on an icon on
the screen and helps the customer
– The rep transfers the call by clicking on another icon
on the computer screen
(to p67)
66
Computer-Telephony Integration (CTI)
(continued)
• CTI can also integrate voice cabling with data
cabling
• The company PBX talks directly to the LAN
server
– The PBX can direct the LAN server to provide a
telephone operation to the user through the
user’s computer
• The telephones may still be connected to the
PBX or they may be connected to the LAN via
the LAN wiring
(to p68)
67
Computer-Telephony Integration (CTI)
(continued)
• CTI applications could include the following:
–
–
–
–
–
Unified messaging
Interactive voice response
Integrated voice recognition and response
Fax processing and fax-back
Text-to-speech and speech-to-text conversions
(to p69)
68
Computer-Telephony Integration (CTI)
(continued)
• CTI applications could include the following:
(continued)
–
–
–
–
Third-party call control
PBX graphic user interface
Call filtering
Customized menuing systems
69
Telecommunication Systems In Action:
A Company Makes a Service Choice
• Better Box Corporation has offices in Seattle,
San Francisco, and Dallas, with headquarters in
Chicago
• Better Box wants to connect Chicago to each of
the other three offices
• Better Box needs to download 400k byte files in
20 seconds
– This requires a transmission speed of 160,000
bps
70
Telecommunication Systems In Action:
A Company Makes a Service Choice
(continued)
• What could Better Box use for communications?
–
–
–
–
–
–
56kbps dial-up?
DSL?
Cable modem?
T-1?
Frame relay?
ATM?
71
Telecommunication Systems In Action:
A Company Makes a Service Choice
(continued)
• 56 kbps lines are too slow for our application
• DSL and cable modems connect users to the
Internet, not user-to-user as needed in our
application
• T-1s, frame relay, and ATM appear to be viable
choices
72
Telecommunication Systems In Action:
A Company Makes a Service Choice
(continued)
73
Telecommunication Systems In Action:
A Company Makes a Service Choice
(continued)
74
Telecommunication Systems In Action:
A Company Makes a Service Choice
(continued)
• Typical various prices for these services are
shown on the next table
75
Telecommunication Systems In Action:
A Company Makes a Service Choice
(continued)
76
Telecommunication Systems In Action:
A Company Makes a Service Choice
(continued)
• To provide T-1 service to all four offices:
– Seattle to Chicago: $6325 ($1200 + $2.50 per
mile)
– San Francisco to Chicago: $6625
– Dallas to Chicago: $3500
– Total interLATA T-1 costs = $16,450 / month
77
Telecommunication Systems In Action:
A Company Makes a Service Choice
(continued)
• To provide frame relay service:
–
–
–
–
–
Three ports at 256K = 3 x $495
One port at 768K = $1240
Three 256K PVCs = 3 x $230
Four intraLATA T-1s = 4 x $350
Total charge = $4815 / month
78
Telecommunication Systems In Action:
A Company Makes a Service Choice
(continued)
• To provide asynchronous transfer mode service:
–
–
–
–
–
Four ports at 1.544 Mbps ABR = 4 x $1750
Three channels = 3 x $250
Three paths = $2 per mile x 5140 miles = $10,280
Four intraLATA T-1s = 4 x $350
Total ATM charges = $19,430 / month
79