Business data communications 5e by stallings chapter 02

Analog Data• Continuous signal • Expressed as an oscillation sine wave format of frequency • Information rate and channel capacity are measured in hertz Hz of bandwidth 1 Hz = 1 cycle

Chapter 2 : Business Information

Business Data Communications, 5e

Analog Data

• Continuous signal

• Expressed as an oscillation (sine wave

format) of frequency

• Information rate and channel capacity are measured in hertz (Hz) of bandwidth (1 Hz

= 1 cycle per second).

Basic Analog Terms

• Wave frequency: Number of times a cycle occurs in given time period

• Wave amplitude: Height of a wave cycle

• Hertz (Hz): The number of times a wave cycle occurs in one second (commonly

used measure of frequency)

Types of Information

• Audio

• Data

• Image

• Video

Understanding Audio

• What makes sound? Vibration of air

• How can we record that vibration?

• How can we convert that to an electrical signal?

Digital Audio

• For good representation, must sample amplitude

at a rate of at least twice the maximum frequency

• Measured in samples per second, or smp/sec

• Telephone quality: 8000smp/sec, each sample

using 8 bits

– 8 bits * 8000smp/sec = 64kbps to transmit

• CD audio quality: 44000smp/sec, each sample using 16 bits

– 16 bits * 44000smp/sec = 1.41mbps to transmit clearly

Networking Implications

for Voice Communication

• Requires powerful, flexible intralocation facility, and access to outside services (e.g telcos)

• In-house alternatives

– PBX (perform switching in the customer side) – Centrex (perform switching in the telcos)

Digital Data

• Represented as a sequence of discrete symbols from a finite “alphabet” of text and/or digits

• Rate and capacity of a digital channel measured

in bits per second (bps)

• Digital data is binary: uses 1s and 0s to represent everything

• Data encoded in strings

– ASCII, IRA, UTF, etc

• Data is often redundant (why?)

Data Networking Implications

• Vary significantly based on application and data types

– Example: Transferring financial transactions data from CitiBank-Taipei to CitiBank-NY (Not just real-time, but also )

– Daily reports vs monthly reports

– DHL parcel tracking

• Response time often a key component

Understanding Images

• Vector graphics

– Collection of straight and curved line segments

– Image described as a collection of segments

• Raster graphics

– Two-dimensional array of “spots” (pixels)

– Also called “bitmap” image

• In terms of memory, which kind of graphic needs more memory?

Image and Document Formats

• Common Raster Formats

– JPEG

– GIF

• Common Document Formats

– PDF

– Postscript

Networking Implications

for Image Data

• More pixels=better quality=larger size

• More compression=reduced quality=increased speed

– “Lossy” gives from 10:1 to 20:1 compression

– “Lossless” gives less than 5:1

• Format (vector vs bitmapped/raster) affects size and therefore bandwidth requirements

• Choices in imaging technology, conversion, and communication all affect end-user’s satisfaction

Video Communication

• Sequences of images over time

• Same concept as image, but with the

dimension of time added

• Significantly higher bandwidth

requirements in order to send images

(frames) quickly enough

• Similarity of adjacent frames allows for

Performance Measure:

Response Time

• User response time

• System response time

• Network transfer time (throughput)

Bandwidth Requirements

• Review Figure 2.7

• What happens when bandwidth is

insufficient?

• How long does it take to become impatient?

– Let us feel about that

– YouTube