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Chapter 9. Communication Circuits. Agenda. Definition Types Media Ownership Error conditions, prevention, and correction. Definitions. Telecommunication circuit Link Data link Channel Data circuit Forward channel (high speed for data) Reverse channel (low speed for control) Node.

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chapter 9

Chapter 9

Communication Circuits

agenda
Agenda
  • Definition
  • Types
  • Media
  • Ownership
  • Error conditions, prevention, and correction
definitions
Definitions
  • Telecommunication circuit
  • Link
  • Data link
  • Channel
  • Data circuit
    • Forward channel (high speed for data)
    • Reverse channel (low speed for control)
  • Node
type of circuits
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
point to point circuits
Point-to-Point Circuits
  • Only two points or nodes
  • Between two telephones or terminal to computer
  • More expense
  • Necessary & high volume of traffic
multipoint circuits
Multipoint circuits
  • Multidrop circuit or a network
  • Low volume of traffic
  • Less expensive
two wire and four wire circuits
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
analog circuits
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
digital circuits
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
integrated services digital network isdn i
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: 2B+D
    • Primary rate interface: 23B+D
    • Broadband ISDN (B-ISDN)
integrated services digital network isdn ii
Integrated Services Digital Network (ISDN) - II
  • Benefits
    • Efficient
    • Integrated voice and data
    • Programmable to meet user’s 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
t carrier systems
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)
switched multimegabit data service smds
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
digital subscriber line dsl i
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
digital subscriber line dsl ii
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
circuit media
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
twisted pair
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
shielded twisted pair
Shielded Twisted Pair
  • Pros:
    • Less interference
    • Faster speed
  • Cons:
    • More expensive
    • Physically larger and difficult to connect to a terminating block
coaxial cable
Coaxial Cable
  • Pros:
    • Large bandwidth (400 - 600 MHz)
    • High capacity
    • Less interference
    • Good for noise environment
  • Cons:
    • Tapped easy (security problem)
    • Bulky to install
optical fiber i
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
optical fiber ii
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
microwave radio i
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
microwave radio ii
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
satellite i
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
satellite ii
Satellite - II
  • Pros:
    • Analog or digital signals
    • For voice, data and television signals
    • Long distance
  • Cons:
    • Security and encryption
    • Propagation delay
infrared
Infrared
  • Light waves
  • Line of sight
  • Wireless communication between nearby equipment
circuit ownership
Circuit Ownership
  • Private circuits
  • Leased circuits
  • Bypass
  • Switched (dial-up) circuits
  • Selection criteria
    • Cost, speed, availability, reliability, maintenance, users’ requirements
    • Others?
circuit identification
Circuit Identification
  • Blue prints and document circuit and equipment
  • Circuit number to each circuit for identification
multiplexing and concentrating
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
circuit error conditions
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
error prevention
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
error detection
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
parity check example
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
error correction
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)
guidelines for wiring
Guidelines for Wiring
  • 25% more capacity
  • Internet usage
  • Two Cat 5 at each desk
  • Fiber optic cable for backbone
  • Good wiring contractor
  • Others?
future
Future
  • High-speed digital service
  • Bandwidth-on-demand
points to remember
Points to Remember
  • Definition
  • Types
  • Media
  • Ownership
  • Error conditions, prevention, and correction
discussion
Discussion
  • Design the communications circuits needs for a bank and state you reasons to insure the security and accuracy
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