Modern Telecommunications Systems

1
Chapter 6

• Modern Telecommunications Systems

2
Introduction

• Telematique the integration of computers and
  telecommunications systems
• Computers are changing roles from computing
  machines into communications machines

3
Telecommunications

• The science and technology of communication by
  electronic transmission of impulses through
  telegraphy, cable, telephony, radio, or
  television either with or without physical media
• Tele is Greek for distance
• Communicate has its roots in the Latin word to
  impart

4
Voice Networks

• Interactive - Bidirectional networks that provide
  on-demand communication
• The first telephone networks were deployed widely
  following World War II
• By the late 1950s in the United States,
  telephones were a permanent fixture in most homes

5
Circuit Switched Networks

• Telephone networks use circuit switching that
  creates a complete, dedicated, end to end
  connection before voice data begins to flow
• Circuit creation results in exclusive allocation
  of specific data transmission resources for the
  duration of the call

6
Circuit Switching

• Guarantees that each successful connection owns
  all the resources necessary to deliver a high
  quality link
• When the call ends, the circuit is torn down, and
  the resources are freed these resources can then
  be utilized for a new connection

7
Switched Network

• It is the capacity of the network to interconnect
  any two endpoints

8
Legacy

• The telephone network is one of the largest
  legacy systems ever created and maintained
• Phone handsets over 50 years old can still
  interoperate seamlessly with current equipment
• Some basic design specifications date back to the
  early 1900s

9
Telephone Signals

• Original telephone specifications were based on
  analog signal technology
• Analog signals vary in amplitude (signal
  strength) and in frequency (pitch)
• The telephone handset converts sound into
  continuously varying electrical signals with the
  microphone
• The speaker at the other end converts electrical
  signals back to sound

10
Analog Signal
11
Digital Signals

• These signals are discrete and discontinuous
• They exist in predetermined states
• Binary signals are digital signals limited to
  only two states, 0 and 1

12
Digital Signal
13
Multiplexing

• Multiplexing is subdividing the physical media
  into two or more channels
• Telephone lines use frequency multiplexing to
  carry both voice and DSL signals simultaneously
• The frequencies between 0 and 4000 Hz carry
  voice, and those between 25 kHz and 1.5 MHz carry
  DSL

14
Digitizing Voice Signals

• By converting analog voice signals into a digital
  format, voice can then be processed like other
  digital data by computers
• The economies of Moores law and semiconductor
  economics can be brought to bear on voice
  applications

15
Pulse Amplitude and Pulse Code Modification
16
Analog to Digital Conversion

• Generally a two step process
• First, the analog signal is sampled at regular
  intervals measurements taken at these periods
  are converted to a discrete value
• Second, the discrete values are converted to a
  binary format this is called pulse code
  modulation

17
Fidelity

• Translating a signal from analog to digital
  format results in loss of data. By increasing
  the number of discrete values produced per second
  (sampling more often) and increasing the range of
  discrete values produced by sampling, the
  digitized waveform more closely represents the
  analog original. This is fidelity.

18
Nyquists Theorem

• A mathematical formula that will quantify the
  fidelity of the signal given the rate and
  resolution of sampling
• For a 4000 Hz signal, fidelity will be acceptable
  if the signal is sampled 8000 times per second
  with a resolution of 8 bits per sample
• A 4000 Hz signal is equivalent to a 64000 bit per
  second data stream

19
The Digital Telephone

• When a voice signal enters the local switch, it
  is digitized
• The local switch is located physically close to
  the end users of the telephone line (usually
  within 10000 ft)
• The switch is capable of handling 500 to 1000
  copper lines
• It is connected via high speed digital links back
  to the central office

20
Central Office

• Handles the telephone traffic for a number of
  small communities or a small city
• Commonly central offices are responsible for
  100000 lines

21
Central Office Network Configuration
22
Customer Premise Equipment

• CPE is the device found at the customer
  termination of a telephone connection (fax,
  telephone, modem, etc.)

23
Local Loop

• Also known as the access line
• Identified by the last four digits of the
  telephone number
• It is the physical connection between the CPE and
  the local switch
• The first three digits of a seven digit telephone
  number identify the local switch to the central
  office

24
Local Switch

• A local switch is a smart router. It can
  independently connect calls from any two lines
  terminating directly into it.
• This helps to keep local calls confined to the
  local switch
• It identifies and routes outbound calls quickly
  to the central office

25
Topology

• Topology is the configuration of elements in a
  network
• The local exchange (local switch and all attached
  CPE and trunks) form a switched star network
• This is an effective arrangement when most of the
  lines are idle at any one time
• At peak hours 15 of a given set of lines are in
  use

26
Regional Connections

• A Central Office is connected to other Central
  Offices by high speed links it also has
  connections to other higher level centers and
  long distance networks
• These links in the US form a network of 150
  million lines

27
Regional Telephone Switching Networks
28
Call Setup

• When the handset is raised, the local switch
  issues a dial tone
• When the user inputs the destination phone
  number, the local exchange uses it to set up the
  circuit
• A leading 1 signals the local switch that the
  call is long distance and routes the call
  immediately to the Central Office

29
T-Services

• T-services are high speed digital links using
  time-division multiplexing (TDM) to move multiple
  signals
• TDM successively allocates time segments on a
  transmission medium to different users
• It combines multiple low speed streams into one
  high speed stream

30
T-1

• The T-1 line is capable of carrying 1.544 Mbps
• The T-1 frame is composed of 24 time slices.
  Each time slice is a channel. Each channel is
  capable of carrying one phone circuit.

31
Time-Division Multiplexing and the T-1 Frame
32
T-1 Frame

• Multiplexing equipment aggregates the incoming
  individual channels and constructs a frame
• Each channel can transmit 8 bits per frame
• Each frame contains 24 channels and one framing
  or start bit
• 8000 frames are transmitted per second yielding
  1.544 Mbps

33
The T-Service Hierarchy

• The T-1 connection is composed of 24 channels
  called B channels
• They are able to carry the digitized audio data
  for one voice circuit
• A T-1 connection can carry 24 Bs
• A T-3 connection can carry 672 Bs (45 Mbps)

34
T-Services
35
E-Services

• Europeans use a slightly different standard
  called the E series
• 8000 frames per second with each frame composed
  of 32 channels
• Only 30 of the channels can be used for data, the
  other two are reserved for signaling information
  and signaling the framing start sequence
• Carries 2.048 Mbps

36
Corporate Use of T-Services

• T-services are available to customers
• T-lines can be configured to create a high speed
  private point-to-point network
• Internally, data and voice can be mixed, so that
  a T-1 line can be provisioned to carry 12 voice
  circuits and 12 data circuits
• T-1s allow rapid connection of fixed locations
  with high speed private links

37
Data Communication Networks

• Voice networks have hard requirements for network
  latency (the amount of time needed for data to
  move from one end to the other)
• Data that arrives late or out of order is
  worthless
• Pure data networks have looser time constraints
  opening the door to different topologies and
  technologies

38
Packet Switching

• In traditional voice networks, circuits are
  established that provide for a continuous stream
  of data packet switching takes outgoing data and
  aggregates it into segments called packets
• Packets carry up to 1500 bytes at a time
• Packets have a header prepended onto the front of
  the packet that contains the destination address
  and sequence number

39
Packet Routing

• In circuit switched networks, the entire data
  pathway is created before data transmission
  commences in packet networks, the packet travels
  from router to router across the network
• At each router, the next hop is chosen, slowly
  advancing the packet toward its destination

40
Packet Routing

• Given moment to moment changes in network loading
  and connections, packets may or may not take the
  same route
• In taking different routes, packets may arrive in
  a different order than the order they were
  transmitted
• The destination uses the sequence number in the
  header to reassemble the incoming data in the
  correct order

41
Local Area Networking

• Until the 1990s, local area networking used
  vendor specific protocols that made
  interoperability difficult
• With widespread deployment of personal computers,
  networking to the desktop became more imperative
  for companies, so that they could fully leverage
  their IT infrastructure investments

42
Metcalfes Law

• Robert Metcalfe is the patent holder for Ethernet
  networking
• He asserted that the value of a network increases
  as a square function to the number of attached
  nodes

43
OSI Model

• OSI was the Open System Interconnection model
  that attempted to modularize and compartmentalize
  networking interfaces
• The result was a seven layer model
• As data passes down from layer 7 to layer 1 it is
  broken into smaller pieces and encapsulated with
  wrappers of additional information used at the
  corresponding layer by the recipient to
  reconstruct the original data and destination

44
Open System Interconnection Model
45
OSI is a Model

• OSI was intended to be the final structure and
  framework for global networking
• Widespread implementation of the entire OSI model
  has never taken place
• It took years to develop
• It was the product of a committee
• It was extremely rigid

46
ARPANET

• In the early 1970s, the Department of Defense saw
  the need to make heterogeneous networks of
  information systems communicate seamlessly
• They needed networks that were self healing and
  had a distributed intelligence
• ARPA (Advanced Research Projects Agency) took the
  OSI layering concept and built an operational
  system with layers 3, 4, and 5 only

47
The Internet

• From this nucleus of networked machines grew the
  Internet
• ARPA called the OSI layer 4 protocol TCP
  (Transmission Control Protocol) and layer 3 IP
  (Internet Protocol), hence the Internet
  networking standard TCP/IP
• This has become the de facto global standard, and
  OSI has been relegated to a reference model

48
Internetworking Technology

• The Internet Protocol Suite is a group of helper
  applications that standardizes interactions
  between systems and assists users in navigating
  the Internet
• These helper applications work at many different
  levels of the OSI model from seven all the way
  down to two

49
Internet Protocol Suite

• Layer seven applications include
• FTP File Transfer Protocol
• HTTP HyperText Transfer Protocol
• SMTP Simple Mail Transfer Protocol
• Layer two protocols include
• ARP Address Resolution Protocol

50
Internet Protocol

• The Layer three protocol is responsible for the
  standard dotted decimal notation used for
  computer addressing
• Each machine has a unique address specified by a
  set of four numbers ranging from 0 to 255
• These numbers are separated by decimal points in
  the format 216.39.202.114

51
DNS

• Domain Name System
• A distributed database that contains the mappings
  between IP numbers and human readable naming
• DNS is also a Internet Protocol Suite helper
  application
• DNS takes a request for www.yahoo.com and returns
  the corresponding IP address

52
Domain Names

• Composed of a hierarchical naming database
• Moves from general to specific in a right to left
  manner
• The rightmost element of the name is called the
  Top Level Domain (TLD)
• TLDs can be country codes, organizations (.org),
  commercial (.com), and others

53
Communication Between Networks

• Layers 1 and 2 are used for the transmission of
  data packets between routers
• Layer 1 The Physical Layer
• Specifies voltage parameters, timing signaling
  rates, and cable specifications
• Layer 2 The Data Link Layer
• Describes how data is formatted for transmission
  across a specific type of Physical Layer link

54
Physical Layer Technologies

• Transmission links can be built using either
  conducting or radiating media
• Conducting media create a direct physical
  connection between network components like copper
  wire or fiber optics
• Radiating media uses radio waves to link stations
  together

55
10 Base T

• The most common Ethernet based wiring standard
• Uses 8 stranded wire links
• These wires are similar in size to telephone wire
  and use slightly larger modular plugs
• Carries data signals at 10 Mbps to 1000 Mbps over
  distances up to several hundred meters

56
Coaxial Cable

• Useful to carry signals over distances up to
  several miles
• Diameter of coax ranges from 1/4th inch to one
  inch
• Inner wire surrounded by a foam insulator,
  wrapped by a metal shield and covered with an
  external insulator

57
Coaxial Cable Construction
58
Optical-Fiber Media

• Used in new installations instead of coax
• Capable of carrying extremely high rates of data
  over distances exceeding 100 miles
• Constructed of a glass core covered with plastic
  cladding and bundled with a tough external sheath

59
Construction of Optical-Fiber Cable
60
Transmission Modes

• Multimode uses internal reflectivity of the
  cladding to propagate the signal down the fiber
• Graded Index the glasss refractive index
  varies from the center to the edge, causing the
  light to bend back toward the center
• Single Mode no reflection or refraction, light
  travels down the center of the fiber like a wave
  guide

61
Wavelength Division Multiplexing

• Multiple different data streams are sent at the
  same time down the same fiber. Each stream is on
  a distinct color of light.
• A wavelength is also called a lambda
• Multiplexing hundreds or thousands of wavelengths
  down a single fiber is called Dense Wavelength
  Division Multiplexing (DWDM)

62
Advanced Fiber Transport

• Due to low installation costs and high data
  capacity, optical fiber is the medium of choice
  for new buildings
• Fiber has the flexibility to carry voice, data,
  and video with no change to the installed fiber
  base

63
FDDI

• OSI layer 1 and 2 specification
• Used when building high speed redundant
  metropolitan area data networks
• Employs two unidirectional rings so that any
  cable cut can be healed by looping data back
  onto the other ring

64
FDDI Network Configuration
65
SONET

• Synchronized Optical NETwork
• Set of standard rates for high speed data
  transmission
• STS stands for Synchronous Transport Signal
  (SONET over copper)
• OC stands for Optical Connection (SONET over
  fiber)
• STS-1 and OC-1 rates are identical

66
OC Line Rates
67
OC-1 SONET Framing

• A SONET frame is made up of a 9 bit x 90 byte
  block of data (6,480 bits total)
• The frame rate is 8000 per second yielding a data
  rate of 51.84 Mbps
• For higher OC or STS levels, the frame rate is
  multiplied by the trailing number (i.e. OC-3 is
  8000 x 3, OC-12 is 8000 x 12)

68
Frame Relay, ATM, and Gig-E

• These technologies represent newer frame based
  networking standards that are able to deliver
  high speed, low latency connections
• Use frame-based protocols and star topologies

69
ATM Cells and Frame Relay Packets
70
The Last Mile

• High speed global networks are of little value if
  individual access is unavailable
• WANs terminate locally at POPs (Points of
  Presence)
• For businesses, T-1 connections are a common
  solution to the last mile T-1s are expensive to
  setup and require long term contracts

71
Digital Subscriber Lines

• DSL enables regional phone providers to deliver
  digital connectivity to customers over existing
  copper connections
• At the local switch, an additional network unit
  is installed called a DSLAM (Digital Subscriber
  Local Access Multiplexer)
• The DSLAM injects and extracts the DSL
  information into the copper line

72
DSL

• On the customer side, a modem/router is attached
  to the line, injecting and extracting the DSL
  signals
• DSL connections from the customer to the local
  switch is limited to 3.5 miles
• 80 of phone subscribers in the US are currently
  within these boundaries

73
Digital Cable

• 60 of US homes and businesses are accessible to
  cable broadcasters
• Cable initially was designed for one way content
  delivery
• In the 1990s, systems were upgraded to deliver
  interactive programming and digital data access

74
Digital Cable

• The highest margin, fastest growth sector of the
  cable industry is cable-based Internet access
• Cable providers piggyback a 5 10 Mbps digital
  backbone onto existing broadcast spectrum
• Home users attach specially constructed Cable
  Modems (routers) to interface home systems to
  the cable data feed

75
Voice Over Cable

• Cable operators want to bundle more services for
  customers
• Delivery of telephone connectivity over cable
  systems is an additional service they can provide
• This service will require additional capital
  outlays to provision customers at a time when
  growth at any cost is not a viable business
  strategy

76
Wireless Systems

• Licensed wireless Includes cellular voice and
  data networks
• Unlicensed wireless ad hoc networking
  technologies like 802.11b and 802.11g
• Both these technologies enable consumers to have
  untethered, mobile connectivity bringing
  networking to the consumer instead of making the
  consumer find the network

77
Licensed Wireless

• Cellular service first began in the early 1980s
• It has grown at a 30 compounded rate over the
  last decade with penetration of 50 across the US
• Cellular systems are dense networks of low power
  broadband radio transmitters and receivers

78
Cellular Network Architecture
79
Cellular Standards

• 1 G Systems
• AMPS Advanced Mobile Phone System
• 2 G Systems
• CDMA Code Division Multiple Access
• TDMA Time Division Multiple Access
• GSM Global System for Mobile Communications
• 3 G
• W-CDMA
• IMT-2000

80
Unlicensed Wireless

• 802.11.b An Ethernet networking standard that
  replaces layers 1 and 2 with a wireless
  equivalent
• 11 Mbps network connectivity over a 50m radius
• No transmitter license is necessary so it is
  inexpensive for consumers with little setup or
  administration costs

81
Summary

• Advances in semiconductor technology have enabled
  enormous advances in telecommunications systems
• Rapid change is occurring in this field, and
  seems set to change how individuals and
  organizations grow, act, and react