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Day 7

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There would be different printers for Macs and Windows and Unix ... Auto call back. You dial ISP, it answers authenticates and then hangs up to call you back ... – PowerPoint PPT presentation

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Title: Day 7


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
  • Youd have to buy a DELL modem, or an HP sound
    card.
  • Standards are good for everyone
  • Manufacturers only make one thing
  • Consumers dont 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 -gt 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
  • 88000 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 (2464,000)
  • 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 _at_.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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