Communication Circuit

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Chapter 9

Communication Circuits


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Agenda

Definition

Types

Media

Ownership

Error conditions, prevention, and correction


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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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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


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Point-to-Point Circuits

Only two points or nodes

Between two telephones or terminal to

computer

More expense

Necessary & high volume of traffic


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Multipoint circuits

Multidrop circuit or a network

Low volume of traffic

Less expensive


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Two-wire and Four-wire circuits

Two-wire circuits

Half-duplex circuits

Frequency division multiplexing for full-duplex dataflow

Standard dial-up telephone

Less expensive

Four-wire circuits

Full-duplex circuits

Leased lines

More expensive


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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, & Teletypewriterusage

Use Amplifier for long distance


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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


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Integrated Services Digital Network

(ISDN) - I

Types of channels

B (bearer) channel: 64kbps data

D (delta) channel: 16kbps signal

Broadband ISDN (BISDN): a full-duplexcircuit or two asymmetrical simplex channel forhigh speed

Access methodsBasic rate interface: 2B+D

Primary rate interface: 23B+D

Broadband ISDN (B-ISDN)


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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 standardsHigh cost

Not active marketed service


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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 DifferentialPulse Code Modulation (ADPCM)

Multiplexing equipment needed Flexible to reconfiguration, low cost for high quality

and volume

Fractional T1 (any multiple of 64kbps)


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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 betweencentral offices

Benefit: less expensive


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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


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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 to1,000 feet


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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


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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, and7 (data grade starting Cat 3)

Punchdown block


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Shielded Twisted Pair

Pros:

Less interference

Faster speed

Cons:

More expensive

Physically larger and difficult to connect to aterminating block


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Coaxial Cable

Pros:

Large bandwidth (400 - 600 MHz)

High capacity

Less interference

Good for noise environment

Cons:Tapped easy (security problem)

Bulky to install


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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


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Optical Fiber - II

Pros:

High bandwidth

No interferenceNo crosstalk

Small physical size and light weight for installation

Very secure

Cons:

Repeater for long distance

Expansive


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Microwave Radio - I

Characteristics

Long distance

Straight line transmission

20-30 miles between transmission towers

Radio license by FCC

Private microwave links connecting officein a city


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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


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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 (3001,000 m)

Usages Direct broadcast satellite (DBS) system for TV broadcasting

Digital satellite service (DSS) for high speed Internet receive-only

access

Global telephone systems


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Satellite - II

Pros:

Analog or digital signals

For voice, data and television signals

Long distance

Cons:

Security and encryption

Propagation delay


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Infrared

Light waves

Line of sight

Wireless communication between nearby

equipment


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Circuit Ownership

Private circuits

Leased circuits

Bypass Switched (dial-up) circuits

Selection criteria

Cost, speed, availability, reliability,maintenance, users requirements

Others?


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Circuit Identification

Blue prints and document circuit and

equipment

Circuit number to each circuit foridentification


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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


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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


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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


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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


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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


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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)


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Guidelines for Wiring

25% more capacity

Internet usage

Two Cat 5 at each desk

Fiber optic cable for backbone

Good wiring contractor

Others?


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Future

High-speed digital service

Bandwidth-on-demand


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Points to Remember

Definition

Types Media

Ownership

Error conditions, prevention, and correction


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Discussion

Design the communications circuits needs

for a bank and state you reasons to insure

the security and accuracy

Documents

Communication Circuit