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Day 7

Day 7. Connections. Standards. Unless we had connection standards nothing would be interchangeable. There would be different printers for Macs and Windows and Unix You’d have to buy a DELL modem, or an HP sound card. Standards are good for everyone Manufacturers only make one thing

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Day 7

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  1. Day 7 Connections

  2. Standards • Unless we had connection standards nothing would be interchangeable. • There would be different printers for Macs and Windows and Unix • You’d have to buy a DELL modem, or an HP sound card. • Standards are good for everyone • Manufacturers only make one thing • Consumers don’t have to worry about it

  3. 2 Sides • DTE • Data Terminal Equipment • Your computer • DCE • Data Communication Equipment • Your modem

  4. Who makes standards? • IEEE • Institute for Electrical and Electronics Engineers • ISO • International Organization of Standardization • ANSI • American National Standards Institute • ITU • International Telecommunication Union • EIA • Electronics Industries Association

  5. Interface standards are made of: • Mechanical • Size, Shape of connector, Number of Pins • Electrical • Voltage, Resistance etc. • Functional • How each pin is used • Procedural • Describes how a plug and connector work together

  6. RS232 - Serial • One of the first connectors on computers • Officially called EIA-232F • Electric: ITU – V.28 • Mechanical: ISO 2110 • Functional & Procedural: ITU V.24 • Used to connect computer to modem

  7. RS232 Standards • Electrical – ITU V.28 Standard: • 0 is sent by having a voltage difference of -3v or more • 1 is sent by having a voltage difference of +3 or more • Mechanical – ISO 2110 • DB 25 Original standard • Now more common to use DB 9 • Most commonly used wires

  8. Functional Specification

  9. Procedural Sequence

  10. Bell & Hayes Standards • Communicating over a modem has had many standards • Bell • 209A • 9600bps • quadratic amplitude modulation • Hayes • AT command set • Supports all modem functionality • Replaced need for setting parameters by switches • AT D 123-4567 • +++

  11. Modems • Digital Signal -> Analogue • Modulate/Demodulate • Use phase, amplitude and frequency shift keying • Speeds up to 56K (56,000 bits per second) • Speed dynamically decided by both modems to ensure compatibility and max speed • Compression and Error Correction • Handled by modem

  12. The 56K myth • POTS transmit an 8K sample 8,000 times per second • 8*8000 = 64,000bits/second • Some of that speed is reserved for phone use • FCC standards require lower power for modems which allows noise • 53,000 is max possible • V.90 and V.92 are 2 standards • V.92 includes call waiting

  13. Other Modem Features • Auto call back • You dial ISP, it answers authenticates and then hangs up to call you back • Fax • All modern modems can act as fax machines.

  14. Connection of modem • Internal • PCI, ISA, On board • External • RS232, USB • Laptop • PCMCIA

  15. Modem pool • 100 employees • Only 20 online at any time • Buy 20 modems • Have computer shuffle connections to modems • Reasons • Cheaper • Less maintenance • Problems • What if more than 20 want to use at once

  16. Replacements for RS232 • RS499 • Faster, built in testing ability (loopback) • Never caught on • X11 • Fewer pins (15) • Primarily used for connection to ISDN modems

  17. Faster Alternatives • T1 Line • CSU/DSU required on both ends • 1.544Mb/s = 24 phone lines (24*64,000) • Cable Modem • Download speed can be as high as 16Mbps, upload typically 128k or 256k • Actual speed depends on how busy the network is • ISDN modem • Digital phone connection end to end. • 64K/channel 2 B channels + D channel • DSL • Asynchronous or Synchronous • All digital use of unused frequencies on phone wires

  18. Newer standards • USB • Can connect up to 128 devices • Supplies 2.5W of power per segment (5v @.5A) • 1.0 • 12Mb/s • 2.0 • 480Mb/s • Firewire • Can connect up to 63 devices • Supplies 45W of power • (400) • 393 Mb/s • 4.5 meters, 16 cable daisy chain • (800) • 786Mb/s

  19. SCSI, iSCSI, Fiberchannel • SCSI • Allows connection of hard drives • Up to 16 on a dual channel • Speeds up to 320MB/s (2.56Gbps) depending on protocol • iSCSI • Connection using TCP/IP instead of serial connectors • SATA • 1.5Gb/s or 2.4Gb/s • Fiber Channel • Connects hard drives at high speeds • 400MB/s (3.2Gb/s)

  20. Data link layer • Asynchronous • Character by character • Start bit • Data • Stop bit • Sometimes a parity bit • High overhead for large transmissions • Synchronous communication • Many characters at once

  21. Duplex • Half • Only one side can talk at any given moment • Think CB Radio • Full • Both sides can talk at once • Think Phone • Simplex • Only one side can ever talk • Think Radio

  22. Point to Point vs Multipoint • Point to point • Each computer is directly connected to mainframe and each connection is handled directly • Multipoint • All computers and mainframe connect via a common backbone • Requires polling

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