Communication Circuits

1
Chapter 9

• Communication Circuits

2
Agenda

• Definition
• Types
• Media
• Ownership
• Error conditions, prevention, and correction

3
Definitions

• Telecommunication circuit
• Link
• Data link
• Channel
• Data circuit
• Forward channel (high speed for data)
• Reverse channel (low speed for control)
• Node

4
Type of Circuits

• Point-to-point circuits
• Multipoint circuits or multidrop circuits
• Two-wire circuits and four-wire circuits
• Analog
• Digital circuits
• ISDN
• T-carrier systems

5
Point-to-Point Circuits

• Only two points or nodes
• Between two telephones or terminal to computer
• More expense
• Necessary high volume of traffic

6
Multipoint circuits

• Multidrop circuit or a network
• Low volume of traffic
• Less expensive

7
Two-wire and Four-wire circuits

• Two-wire circuits
• Half-duplex circuits
• Frequency division multiplexing for full-duplex
  data flow
• Standard dial-up telephone
• Less expensive
• Four-wire circuits
• Full-duplex circuits
• Leased lines
• More expensive

8
Analog Circuits

• Voice grade circuits
• Low speed but up to 56,00bps
• Noise
• Error
• Low-speed circuits or subvoice-grade circuits
• Subdivide voice grade circuit to 12 or 24
  circuits
• Speed ranges between 45 to 200 bps
• Burglar alarm, fire alarm, telegraph,
  Teletypewriter usage
• Use Amplifier for long distance

9
Digital Circuits

• Low error rate, noise, high speed
• Data service unit/channel service unit (DSU/CSU)
• Shape and time the pulses
• Less complicated
• Less expensive
• Need repeater for long distance

10
Integrated Services Digital Network (ISDN) - I

• Types of channels
• B (bearer) channel 64kbps data
• D (delta) channel 16kbps signal
• Broadband ISDN (BISDN) a full-duplex circuit or
  two asymmetrical simplex channel for high speed
• Access methods
• Basic rate interface 2BD
• Primary rate interface 23BD
• Broadband ISDN (B-ISDN)

11
Integrated Services Digital Network (ISDN) - II

• Benefits
• Efficient
• Integrated voice and data
• Programmable to meet users need
• Robust signaling channel for network management
• International defined open system interface
• Problems in US
• Difficulty in agreeing on precise standards
• High cost
• Not active marketed service

12
T-carrier Systems

• T1, T2, T3, T4
• T2 and T4 for carriers
• T1 and T3 for carriers and customers
• T1 Line
• Repeater for every mile
• 24 circuits of 64,000 bps
• Pulse Code Modulation (PCM) or Adaptive
  Differential Pulse Code Modulation (ADPCM)
• Multiplexing equipment needed
• Flexible to reconfiguration, low cost for high
  quality and volume
• Fractional T1 (any multiple of 64kbps)

13
Switched Multimegabit Data Service (SMDS)

• High-speed switched digital service from carrier
• Two speeds
• T1 speed (1.544 Mbps)
• T3 speed (44.736 Mbps)
• Configuration
• Lease line from organization to central office
• Normal, shared communication facilities between
  central offices
• Benefit less expensive

14
Digital Subscriber Line (DSL) - I

• Deliver digitized signals over telephone lines
• Higher data communication speed for Internet
  usage
• xDSL for dedicated, point-to-point, public
  network access over twisted pair copper wire
• More bandwidth downstream than upstream
• More for individual customer than business
  organization

15
Digital Subscriber Line (DSL) - II

• Asymmetric digital subscriber line (ADSL)
• Standard voice band
• Medium speed upstream band
• High speed downstream band
• New offerings
• G.Lite ADSL lower bandwidths for less cost
• SDSL (symmetric digital subscriber line) equal
  speed in both direction
• VDSL (very-high-rate digital subscriber line)
  high speed over short twisted pair telephone
  lines up to 1,000 feet

16
Circuit Media

• Conducted or guided media
• Twisted pair or unshielded twisted pair (UTP)
• Shield twisted pair
• Coaxial cable
• Optical fiber
• Radiated or unguided media (wireless)
• Microwave radio
• Satellite
• Infrared

17
Twisted Pair

• 22, 24, 26 gauge
• Twisted pair or unshielded twisted pair (UTP)
• Electrical noise other interference
• Electrical Industries Association (EIA) Category
  1, 2, 3, 4, 5,5E (extended), 6, and 7 (data grade
  starting Cat 3)
• Punchdown block

18
Shielded Twisted Pair

• Pros
• Less interference
• Faster speed
• Cons
• More expensive
• Physically larger and difficult to connect to a
  terminating block

19
Coaxial Cable

• Pros
• Large bandwidth (400 - 600 MHz)
• High capacity
• Less interference
• Good for noise environment
• Cons
• Tapped easy (security problem)
• Bulky to install

20
Optical Fiber - I

• Types
• Single mode more expensive high capacity
• Multimode less expensive and less capacity
• Inexpensive plastic
• Expensive glass
• Standard
• Synchronous optical network (SONET) in US

21
Optical Fiber - II

• Pros
• High bandwidth
• No interference
• No crosstalk
• Small physical size and light weight for
  installation
• Very secure
• Cons
• Repeater for long distance
• Expansive

22
Microwave Radio - I

• Characteristics
• Long distance
• Straight line transmission
• 20-30 miles between transmission towers
• Radio license by FCC
• Private microwave links connecting office in a
  city

23
Microwave Radio - II

• Pros
• Analog or digital signals
• For voice, data and television signals
• Long distance
• Cons
• Interference by heavy rain
• Straight line transmission
• Security
• Vendors
• Motorola
• Rockwell Communication Systems

24
Satellite - I

• Characteristics
• Geosynchronous orbit
• Microwave radio transmission
• Uplink and downlink
• Types
• Geosynchronous satellites (22,300 m)
• Medium earth orbit (MEO) satellites (6,000 m)
• Low earth orbit (LEO) satellite (300 1,000 m)
• Usages
• Direct broadcast satellite (DBS) system for TV
  broadcasting
• Digital satellite service (DSS) for high speed
  Internet receive-only access
• Global telephone systems

25
Satellite - II

• Pros
• Analog or digital signals
• For voice, data and television signals
• Long distance
• Cons
• Security and encryption
• Propagation delay

26
Infrared

• Light waves
• Line of sight
• Wireless communication between nearby equipment

27
Circuit Ownership

• Private circuits
• Leased circuits
• Bypass
• Switched (dial-up) circuits
• Selection criteria
• Cost, speed, availability, reliability,
  maintenance, users requirements
• Others?

28
Circuit Identification

• Blue prints and document circuit and equipment
• Circuit number to each circuit for identification

29
Multiplexing and Concentrating

• Time division multiplexing (TDM)
• Bit, character, or entire message
• Statistical time division multiplexing (STDM)
  using address field
• Frequency division multiplexing (FDM)
• Concentrator using buffering and intelligence
• Circuit multiplexer
• Concentration
• Inverse concentration

30
Circuit Error Conditions

• Background noise (electrical phenomenon)
• Impulse Noise (spike)
• Attenuation
• Attenuation distortion
• Envelope delay distortion (different propagation
  delay)
• Phase jitter (by carrier signal)
• Echo
• Crosstalk
• Dropouts

31
Error Prevention

• Line conditioning for leased lines reduce
• Attenuation (class C)
• Envelope delay distortion (class C)
• Noise (class D)
• Distortion (class D)
• Methods
• Shielding
• Improving connection for cables and connectors
• Electronic versus mechanical equipment
• Quality
• Trouble-free

32
Error Detection

• Echo checking every character
• Vertical redundancy checking (VRC) or parity
  checking
• Longitudinal redundancy checking (LRC) or block
  check character (BCC)
• Cyclic redundancy checking (CRC-16) of polynomial
  error checking

33
Parity Check Example

• Parity BCC
• 1 1 1 1 1 1 0
• 0 0 0 0 0 0 0
• 1 0 1 0 1 1 0
• 0 0 0 1 0 1 0
• 0 0 0 0 1 0 1
• 0 0 1 0 0 0 1
• 0 1 0 1 0 1 1
• 0 0 1 1 1 0 1 VRC

34
Error Correction

• Equipment and circuit requirement
• Buffer
• Reverse channel or channel turn around
• Retransmission - automatic repeat request (ARQ)
• Methods
• Stop and wait ARQ - ACK and NAK long data block
  , low error rate, having a reverse channel
• Continuous ARQ long propagation time
• Forward error correction (FEC) simplex
  transmission
• using Hamming code, Hagelbarger code,
  Bose-Chaudhuri code
• High cost (extra bits codes)

35
Guidelines for Wiring

• 25 more capacity
• Internet usage
• Two Cat 5 at each desk
• Fiber optic cable for backbone
• Good wiring contractor
• Others?

36
Future

• High-speed digital service
• Bandwidth-on-demand

37
Points to Remember

• Definition
• Types
• Media
• Ownership
• Error conditions, prevention, and correction

38
Discussion

• Design the communications circuits needs for a
  bank and state you reasons to insure the security
  and accuracy