1. DC 5 - 1 DATACOMM John Abbott College JPC Efficiency of Communications M. E. Kabay, PhD, CISSP Director of Education, ICSA President, JINBU Corp Copyright © 1998 JINBU Corp. All rights reserved

2. DC 5 - 2 Increasing Efficiency of Datacomm l Front-End Processors l Port-Sharing Devices l Line Splitters & Remote Intelligent Controllers l Multiplexers l Data Compression l Inverse Muxes l Multidrop

3. DC 5 - 3 Front-End Processors (FEPs) l Handles interrupts from DTEs l Sends complete communications to CPU l Allows more efficient use of host

4. DC 5 - 4 Port-Sharing Devices l AKA concentrator l Allows DTEs to share ports sequentially l Can therefore support more terminals

5. DC 5 - 5 Line Splitters & Remote Intelligent Controllers l Line splitters used to put multiple terminal sessions through a single modem l Remote Intelligent Controllers poll DTE and send only meaningful data through modems

6. DC 5 - 6 Multiplexers l Combine multiple lines into single data stream l Allow major cost savings on long-distance lines

7. DC 5 - 7 Multiplexers l Time-Division Muxes l Character and Bit Interleaving l Statistical Time Division Muxes l Frequency Division Muxes

8. DC 5 - 8 Multiplexers Time-Division Multiplexing (TDM) l Share larger bandwidth among slower devices – E.g., 4 terminals running at 2400 bps can MUX the branch ports through a single 9600 bps trunk line – Pure TDM has sum of DTE bps = trunk bps l Wastes bandwidth because very rare to have all terminals active at same time

9. DC 5 - 9 Multiplexers Character and Bit Interleaving l How are branch data streams sent through trunk? l Character interleaving – one character per branch port sent through trunk – always same order – if nothing to send, waste the slot l Bit interleaving – similar idea but breaks data into bits

10. DC 5 - 10 Multiplexers Statistical Time Division Muxes l Usually known as stat muxes l Does not use fixed time slots l Send data + address to indicate which channels data are being sent l Calculates how much time to reserve as function of previous activity per channel l Can buffer I/O l Effectively link many terminals at high speed even though they cannot all simultaneously exchange data with host

11. DC 5 - 11 Multiplexers Frequency Division Multiplexing l Many different frequency carriers simultaneously l Each frequency carries a specific channel l Cost of FDM rises as number of channels in trunk l Variation is Statistical Frequency Division Multiplexing (SFDM) which requires expensive equipment

12. DC 5 - 12 Data Compression l Data compression is adjunct to multiplexing l Many proprietary methods for reducing number of bits sent through trunk l Thus more information sent at higher speed without having to pay for more lines or faster trunk

13. DC 5 - 13 Inverse Muxes l If speed is more important than cost, can split data stream using inverse multiplexers l Use multiple lines in parallel to multiply effective throughput

14. DC 5 - 14 Multidrop l Every message addressed to specific DTE l If terminals close together can simplify cabling l Can even be routed through phone lines l Is a very simple form of Local Area Network

15. DC 5 - 15 Homework l Read Chapter 5 of your textbook in detail, adding to your workbook notes as appropriate. l Review and be prepared to define or expand all the terms listed at the end of Chapter 5 of your textbook (no hand-in required) l Answer all the exercises on pages 110 of the textbook using a computer word-processing program or absolutely legible handwriting (hand in after quiz tomorrow morning) l Scan Chapters 6, 7 & 8 in preparation for tomorrows class