CS457/557 - Computer Networks: Chapter 3 - Personal Computer Connectivity

Objectives

Understand alternatives to connect two or more computers and/or peripherals (without a LAN)
Understand modem operation, comparative modem features, modem standards
understand comparative features of communications software
understand implications of use of digital rather than analog carrier services

Introduction

Business Model	Faster Cheaper More reliable More secure
Data Model	Faster New modem standards Data compression digital transmission Cheaper Modem sharing compatibility with older modems More reliable error prevention error detection error corrrection backup for leased line failure More secure Unauthorized access prevention encryption

Business Model	Data and Network Model
Faster	New Modem Standards V.90 (56 Kbps download / 33.6 upload [ISP and all intermediate links must be digital]) Enhanced V.34 (33.6 Kbps) V.34 & V.Fast (28.8 Kbps) V.32 & V.32bis (9600 bps / 14.4 Kbps) Fast retrain echo cancellation Data Compression V.42bis & MNP Class 5 (upto 4:1) Digital Transmission DDS Services (digital data service) CSU/DSU (customer service unit / data service unit)
Cheaper	Modem sharing Modem & port sharing devices Line sharers and splitters compatibility with Older Modems Handshaking fallback compatibility Hayes AT command set
Reliable	Error Prevention Line Conditioning Repeaters and Amplifiers Adaptive Protocols (ex. MNP Class 4) Error Detection Parity Checksums LRC (Longitudinal Redundancy Checks) CRC (Cyclic Redundancy Checks) Error Correction ARQ (Automatic Retransmission Request) ACK/NAK sliding window protocols (Continuous ARQ) Forward error correction (V.42 & MNP classes 2,3,4) Backup for Leased Line Failure Autodial backup Auto restoral (Standalone & integral)
Secure	Unauthorized Access Protection Password protection Callback security (standalone and integral) Encryption Standards (standalone or integeral)

Principle of Shifting Bottlenecks:

as modems get faster, the bottleneck has shifted to the serial port (19.2 or 38.4 Kbps)
One Solution - use alternative bus: USB (Universal serial bus) [upto 12 Mbps)

Modem Trends

56K modems
Digital simultaneous voice data (DSVD) [28.8]
Analog simultaneous voice data (ASVD) [28.8] {actually switches between voice and data}
Cable modems [10-60 Mbps] (may only be one-way)
Cellular modems [2-3 Kbps]
Wired/wireless modems [POTS 28.8; wireless 8-19.2Kbps]
Asymetmetric digital subscriber line (ADSL) [upto 8 Mbps one way; 640 K return]
ISDN modem [128 Kbps]
CSU/DSU [56Kbps - 45 Mbps] (requires switched or leased digital service)

Communications Software

must be easy to use
must maximize the efficient use of available hardware and circuit technology
must be cost effective
must support business objectives

Uses

connect to a remote mainframe / minicomputer
transfer files
connect to a value-added information service
connect to the Internet

Technical Features

GUI
UART Support
Hayes ESP(enhanced serial port) Board Support
Terminal Emulation (VT100, VT220, IBM 3270)
Modem Access via a Network
Information Service Access
Scripting Languages
Memory and CPU Requirements
Security Features (passwords, dial-back)
Multiple Platform File Transfers
- X-modem
- Y-modem (X-modem 1K)
- Y-modem batch
- Z-modem
- Kermit
- ftp

Non-LAN PC Connectivity

peripheral sharing devices: modem pools, manual A/B switches for printers

Activities [e-mail your answers to summers_wayne@ColumbusState.edu before 4 p.m. on Thurs., Sept. 17, 1998]: #2, 4
Note: This assignment may be completed by groups of two students