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 What sort of technologies are needed to support such applications?

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 –Both include text and graphics

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 high compression rates

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 Is data communication ever “fast enough”?