Session 3

Objectives: By the end of this session, the student will be able to: Identify a dial-up modem and cite its basic operating characteristics Discuss the advantages of digital modems and recognize why they do not achieve the high transfer speeds advertised List the alternatives to dial-up modems, including T-1 modems, cable modems, ISDN modems and DSL modems Discuss the basic operation of the EIA-232F interface standard Cite the advantages of Firewire, Universal Serial Bus Outline the characteristics of asynchronous and synchronous data link interfaces Recognize the difference between half-duplex, full-duplex and simplex connections

Modem Terms Autoanswer Autodial Autodisconnect Autoredial Fallback Fall forward 3

Modem Terms De facto Standards MNP4 MNP5 FAX Modems Special protocols are used, and are built into the modem. Security Call back Black list Back door 4

Loop Back 5

Modems 6

56K Digital Modem 7 56K Modem is a hybrid of analog and digital signaling

56K Digital Modem 8 Upstream PC – Modem – CO : 33.6Kbps (analog signaling) limited to 33.6Kbps due to analog signaling limitation on phone system Downstream CO – Modem – PC : near 56Kbps (digital signaling) CO – CO at 64Kbps using PCM (8bits at 8KHz) – pure digital signaling As local loop is analog – cannot achieve 64Kbps as quantizing noise is introduced when converting from analog to digital Noise is increased as power level must be lowered (FCC regulations) Noise is increased the further you are from the CO Downstream in high 40Kbps if near a CO

T1 Line 9 T1 DSU – Data Service Unit CSU – Channel Service Unit Carries 1.55Mbps over 56Kbps – 64Kbps leased lines

Cable Modems 10 Cable Modems Speed ranges 300Kbps – 2.5Mbps Asymmetric Upload / download speeds Uses coaxial local loop with fibre between main distribution nodes Data collisions only drawback

ISDN 11 ISDN Integrated Services Digital Network All digital Modem required More detailed examination when we discuss WAN technologies

DSL 12 DSL Digital Subscriber Loop All digital phone service Modem required Speeds from 100sKbps - 1sMbps More detailed examination when we discuss WAN technologies

Modem Pools 13

Interfaces 14 Terminology DTE – Data Terminal Equipment (e.g. computer) DCE – Data Communications Equipment (e.g. Modem) Interchange circuits connect DTE to DCE

Components of an Interface 15 Electrical Component Line voltages Line capacitance Other electrical issues Mechanical Component Connector / plug descriptions Pin configurations Functional Component Describes the function of each pin or circuit Procedural Component Describes how the particular circuits are used to perform an operation

EIA-232F 16

EIA-232F 17

EIA-449 EIA449 Replaced EIA-232F with following improvements: Allow for 2 possible standards (RS-422A and RS-423A) that can be used as the electrical component (both of these standards provide for faster transmission speeds between DTE / DCE) Add 10 additional circuits, including loop-back testing (original RS-232 standard did not include loop-back) Connector changed to 37 PIN connector from 25 PIN connector Never caught on due to widespread use and acceptance of RS

X.21 Also intended to replace RS-232 Uses 15 PIN connector On EIA-232 / RS-449 each signal is carried by its own dedicated line On X.21 4 lines are used to 'encode' various signals 19

Hayes Interface AT–attention D-dial T-touch tone dial P-pulse dial +++-go to command mode A-autoanswer mode E0-do not locally echo characters E1-locally echo characters S0=x-number of rings before answering (auto answer mode) H-hang up ATDT9, ATH 20

Firewire IEEE1394 Digital interface Developed by Apple. 400Mbps 2 types of data connections-asynchronous -iosynchronous (guaranteed data rate for multimedia) 21

USB (Universal Serial Bus) USB Digital interface Daisy chain devices (127 max) USB Mbps USB Mbps 22

Asynchronous Connections 23

Synchronous Connections 24

Connection Types Simplex – one way communication. Similar to car radio. Half-Duplex – two way communication, only one can talk at a time. Similar to a polite conversation or a CB radio Full-Duplex – both sides can talk and listen simultaneously. 25