CS457/557 - Computer Networks: Chapter 2 - Indtroductory Concepts

Objectives

Distinguish between:
- analog - digital
- synchronous - asynchronous
- full-duplex - half-duplex - simplex
- two-wire - four-wire
- serial - parallel
- bps - baud rate
- leased line - dial-up/switched line
understand importance of standards and RS-232
Understand three components of any data comm system (hardware, software, media)
Apply I-P-O frame to technology analysis
Understand concept of modularity of design
Illustrate use of OSI model as a frame of reference
Understand basic structure of public phone network
understand impact and limitation of various modulation techniques

Introduction

Practice the vocabulary

Getting the bits and pieces of data from here to there

Receive the bits and pieces of data
Examine the bits and pieces of data
Decide how to process the data
Send the data to its proper destination

Encoding

ASCII (American Standard Code for Information Interchange) (ex. A - 11000001)
EBCDIC
Unicode & ISO 10646 (16 bit code)

Serial vs. Parallel

Most data communications is serial

	Serial	Parallel
Transmission	one bit after another	all bits simultaneously
Speed	slower	faster
Distances	farther	shorter
Application	between two computers	within the computer
	to lower speed printers
	to data comm equipment
Cable	all bits travel down one wire	each bit travels down its own wire

Parallel to Serial

requires a UART (Universal Asynchronous Receiver Transmitter)

Communcations Software

takes data from PC's serial port -> modem cable -> modem -> phone line -> modem -> serial port
can store phone numbers and auto dial
can initiate, monitor, resume and terminate transfer of files

Serial Port

DB-25, DB-9 uses RS-232-C standards established by EIA(Electrical Industries Association)

Serial Cable or Modem Cable

modem cable typically uses 12 pins
DTE - data terminal equipment
DCE - data communications equipment
RS-232 communications (see Fig. 2-7)

MODEM

modulator-demodulator (converts input from digital to output of analog signal) data transmission is over a switched or dial-up line via the POTS analog transmission - uses bandwidth from 300 Hz to 3300 Hz)

Modulation/Demodulation

Carrier Wave - typical sine wave can be modulated by:

amplitude
frequency
phase

Baud Rate - signalling events per second (number of signal changes pers second)
bps - bits per second

method of data movement

asynchronous - requires start & stop bits (cheaper but slower)
synchronous - requires a clock (data sent in large blocks)

More than one bit per baud

dibit - represents two bits with one phase shift
QAM (Quadrature Amplitude Modulation) - uses 8 phase angles and two different amplitudes for 16 different events (or 4 bits at a time)

Characteristics/Questions		Node 1	Compatibility Issues with Other Notes
Hardware	Modem: Manufacturer: Baud rate: bps: Interface: Error detection standard: Error correction standard: Data compresion standard: PC: Operating System Operating System version:
Software:	Communications Software: File transfer protocol: error dectection standard: error correction standard:
Media	Phone Network: Switched or leased line: Analog or digital: 2-wire or 4-wire: Async or sync: half or full duplex Modem cable from PC to modem:

Importance of Standards

V. standards (CCITT) MNP (Microcom Networking Protocol) (defacto standard)

OSI Model Concepts

phone network (OSI layer 1 - physical layer) requires RJ-11 interface

Service Name	Dial-up/ Leased	Analog/ Digital	Async/Sync	2-wire/4-wire	Flat/Usage	Trans. Rate
Analog
POTS	D	A	Depends	2	U	V.90 (56 Kbps download / 33.6 upload)
Voice Grade Lease	L	A	S	4	F	V.90 (56 Kbps download / 33.6 upload)
Narrowband Digital
DDS	L	D	S	4	F	56K
DS-0	L	D	S	4	F	64K
Wideband/Broadband Digital
T-1	L	D	S	4	F	1.544 Mbps
T-3	L	D	S	Fiber	F	44.836
Digital Dial-up
ISDN	D	D	S	4	U	144Kbps
Switched ISDN	D	D	S	4	U	56kBPS

Two-wire versus Four-wire

simplex vs. half-duplex vs. full duplex
two-wire typically only supports half-duplex which requires "handshaking"

Narrowband Digital Services

DDS (Digtal Data Service) requires a CSU/DSU (customer service unit / data service unit) instead of a modem and requires that the speed be specified beforehand

Broadband Digital Services

T-1, T-3, ISDN

Slides

Review Questions: [e-mail your answers (where possible) to summers_wayne@ColumbusState.edu before 4 p.m. on Thurs., Sept. 10, 1998]

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