Voice and Data Delivery Networks

1
Voice and Data Delivery Networks
2
Telephone Lines, Trunks, and Numbers

• The local loop is the telephone line that runs
  from the telephone companys central office to
  your home or business
• Central office building that houses the
  telephone companys switching equipment and
  provides a local dial tone on your telephone
• If you place a long-distance call, the central
  office passes your telephone call off to a
  long-distance provider

3
Telephone Lines, Trunks, and Numbers (continued)

4
Telephone Lines, Trunks, and Numbers (continued)

• 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
  long-distance telephone company
• If your call stays within a LATA, it is a local
  call and is handled by a local telephone company

5
Telephone Lines, Trunks, and Numbers (continued)

• 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

6
Telephone Lines, Trunks, and Numbers (continued)

• A trunk is not associated with a single telephone
  number like a line is
• A telephone number consists of an area code, an
  exchange, and a subscriber extension
• The area code and exchange must start with the
  digits 2-9 to separate them from long distance
  and operator services

7
Telephone Lines, Trunks, and Numbers (continued)

• 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
  off-hook signal is sent to the central office

8
Telephone Lines, Trunks, and Numbers (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

9
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

10
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

11
PBX (continued)

• PBX components
• CPU, memory, telephone lines, trunks
• Switching network
• Supporting logic cards
• Main distribution frame
• Console or switchboard
• Battery back-up system

12
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

13
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!)

14
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

15
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

16
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

17
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)

18
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
• Wide area telecommunications services (WATS)
  discount volume calling to local- and
  long-distance sites
• Off-premises extensions (OPX) dial tone at
  location B comes from the PBX at location A

19
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
• ARDIS and RAM Mobile Data two good examples

20
The Telephone Network Before and After 1984

• In 1984, U.S. government broke up ATT
• Before then, ATT owned large majority of all
  local telephone circuits and all the
  long-distance service
• With Modified Final Judgment of 1984, ATT had to
  split off local telephone companies from
  long-distance company
• The local telephone companies formed seven
  Regional Bell Operating Companies
• Today, there are only 4 left BellSouth, SBC,
  Qwest (US West), and Verizon (Bell Atlantic)

21
The Telephone Network Before and After 1984
(continued)

22
The Telephone Network Before and After 1984
(continued)

• Another result of the Modified Judgment was
  creation of LATA (local access and transport
  area)
• Local telephone companies became known as local
  exchange carriers (LECs), and long distance
  telephone companies became known as interexchange
  carriers (IEC, or IXC)
• Calls that remain within LATA are intra-LATA, or
  local calls
• Calls that pass from one LATA to another are
  inter-LATA, or long distance

23
The Telephone Network Before and After 1984
(continued)

• Before 1984, telephone networks in the U.S.
  resembled a large hierarchical tree, with Class 5
  offices at the bottom and Class 1 offices at the
  top
• Users were connected to Class 5 offices
• The longer the distance of a telephone call, the
  further up the tree the call progressed
• Todays telephone structure is a collection of
  LECs, POPs, and IECs

24
Telephone Networks After 1996

• Another landmark ruling affecting the telephone
  industry was the Telecommunications Act of 1996
• Opened up local telephone market to competitors
• Now cable TV companies (cable telephony),
  long-distance telephone companies, or anyone that
  wants to start a local telephone company can
  offer local telephone service
• Local phone companies that existed before the Act
  are known as incumbent local exchange carriers
  (ILEC) while the new companies are competitive
  local exchange carriers (CLEC)

25
Telephone Networks After 1996 (continued)

• LECs are supposed to allow CLECs access to all
  local loops and switching centers / central
  offices
• If a local loop is damaged, the LEC is
  responsible for repair
• The LEC is also supposed to provide the CLEC with
  a discount to the dial tone (17-20)
• LECs can also provide long-distance service if
  they can show there is sufficient competition at
  the local service level

26
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

27
Limitations of Telephone Signals (continued)

28
Limitations of Telephone Signals (continued)

• 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
• 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?

29
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
• Analog to digital conversion at the local modem
  introduces noise/error
• Combined, these shortcomings drop the speed to at
  best 56k

30
The 56k Dial-Up Modem (continued)

• 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

31
The 56k Dial-Up Modem (continued)

32
The 56k Dial-Up Modem (continued)

33
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

34
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

35
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

36
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

37
DSL Basics (continued)

38
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

39
Cable Modems (continued)

40
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

41
T-1 Leased Line Service

Data
Loopback control
DSX-1 Interface
T-1 Mux
T-1 Line
DSU
CSU
Customer Supplied
?
From Telco
42
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)

43
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

44
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)

45
CSU (Channel Service Unit)

• First (last) piece of equipment on a T-1 line
• Can perform various loop-back tests
• CSU can also generate keep alive signal when
  the attached DTE fails to deliver a valid stream
  of data or DTE is disconnected
• CSU can also collect error statistics for the
  phone company

46
DSU (Digital Service Unit)

• Shapes the T-1 signal being sent
• Prepares the customer data to meet the
  requirements of the DSX-1 interface
• Suppresses long strings of zeros with special
  coding
• Provides the terminal (user) with remote and
  local loopback tests
• DSU if often built into the terminal equipment or
  multiplexor and should eventually disappear

47
ISDN

• Allows digital transmission of voice and data
  over traditional copper lines
• We have already seen the ISDN frame layout in the
  chapter on Multiplexing
• Three basic types of ISDN
• Basic rate
• Primary rate
• Broadband

48
Basic Rate ISDN

• Entry level service
• 144 kbps service
• 2 64 kbps bearer (data) channels (DS-0) and 1
  16 kbps delta channel (for signaling or data)
  (also known as 2BD)
• User can bond both data channels together for a
  128 kbps channel
• Rarely used in the US some degree of use in
  Japan / England / Europe fairly popular in
  Germany (29 of all subscriber lines as of 2003
  20 of all ISDN lines worldwide)
  (sourceWikipedia)

49
Primary Rate ISDN

• In Europe, this consists of 30 B-channels of 64
  kbps each plus 1 D-channel of 64 kbps and is
  carried over an E-1
• In North America, this service is 23 B-channels
  and 1 D-channel and carried over a T-1 (J-1 in
  Japan)
• PRI-ISDN is popular through-out the world and is
  used to connect PSTN to company PBXs
• In US, PRI-ISDN is used on connection of non-VoIP
  PBXs to PSTN