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CHAPTER Modems. Chapter Objectives. Discuss basic modem related issues Standards, Hayes compatibility etc. Describe the different types of practical modems available Internal, external, null, short-haul modems etc. Present the profile of sample practical modems

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chapter objectives
Chapter Objectives
  • Discuss basic modem related issues
    • Standards, Hayes compatibility etc.
  • Describe the different types of practical modems available
    • Internal, external, null, short-haul modems etc.
  • Present the profile of sample practical modems
    • Asynchronous and synchronous modems
  • Show the establishment of a fiber-optic communication link using the fiber-optic interface
chapter modules
Chapter Modules
  • Modem Functional Considerations
  • Internal, External and Portable Modems
  • A Modem Profile
  • Modem Software Installation
  • A Practical Asynchronous/Synchronous Modem
  • Faster Modem Standards
  • Fiber-optics Connection
  • Null Modem and Short-haul Modem
  • Cable Modem
  • DSL Modem
module

MODULE

Modem Functional Considerations

module objectives
Module Objectives
  • List the two types of modem standards
  • Describe the features that are standardized in modem communication
    • Modulation, data compression etc.
  • Explain the relevance of standards to speed
  • Discuss Hayes compatibility
  • List a few common modem features
major modem standards
Major Modem Standards
  • ITU standard
    • Universal standard
    • Currently in use
  • Bell standard
    • Earlier low speed modem standard
    • No more in use
standards in modem communication
Standards in Modem Communication
  • Modulation standard
  • Data compression standard
  • Error correction Standard
speed and modulation standards
Speed and Modulation Standards
  • Each speed is associated with a modulation standard
  • V.34 is an example standard for the communication speed of 28,800 bps
  • Higher speed modems can operate at lower speeds as well
    • E.G 28,800 bps modem can communicate at 14,400 bps
understanding hayes compatibility
Understanding Hayes Compatibility
  • IBM is to micros what Hayes is to modems
  • Hayes compatibility
    • Ensured by adherence to the Hayes command set known as the AT command set
    • Ensures wide availability of software
command translation for pcs and modems
Command Translation for PCs and Modems
  • Commands for the PC
    • Translated into machine language and executed
      • E.G. Identifying a file for transmission
  • Commands for the modem
    • Generated in Hayes AT command set form and transmitted to the modem for execution
      • E.G. Command instructing the modem to dial
command translation
Command Translation

Intel Machine Code

Software

Intel Micro

Modem

Hayes AT Command

modem features
Modem Features
  • Auto-dial
  • Auto-answer
  • Reverse calling
  • All the above features are standard in today’s Modems
module1

MODULE

Internal, External and Portable Modems

overview of internal and external modems
Overview of Internal and External Modems
  • Internal modem
    • Installed in the expansion slot
    • Usually cheaper
    • Occupies one expansion slot
  • External modem
    • Connects to the serial port of the computer
    • More expensive
    • Does not occupy an expansion slot
    • But, it does utilize one of the available communication ports
internal modems
Internal Modems

Source: Black Box

external modems
External Modems

Source: Black Box

external modem ports and connection
External Modem Ports and Connection

To Com2

Port

To Phone

Jack RJ 11

Connection

modems for the notebooks or pc card modem
Modems for the Notebooks or PC Card Modem
  • Credit card size
  • Connects to the PCMCIA slot
    • Currently, known as PC card slots
  • PC cards have undergone major refinements
    • Efficient in their operation
    • Support high-speed communication devices
pc card modems
PC Card Modems

Source: Black Box

multi purpose pc cards
Multi-Purpose PC Cards

Source: Black Box

module2

MODULE

A Modem Profile

module objectives1
Module Objectives
  • Examine the profile of an actual commercial modem
  • Discuss the standards as they relate to speed, data compression and error correction
  • Describe the FAX related communication details of the modem
profile of a modem black box modem 288 standards
Profile of a Modem : Black Box Modem 288 Standards
  • Standards
    • ITU V.92, ITU V.90, ITU V.34, v.32bis, v.23, v.22bis, v.22, v.21, Bell 101 and Bell 212a
  • Protocols
    • Asynchronous and synchronous
  • Speed
    • V.90 ------ 56Kbps
    • V.34 -------> 28.8 Kbps
    • Others up to 14.4 Kbps
    • Possible up to 115.2 Kbps
profile operation interface and connectors
Profile: Operation, Interface and Connectors
  • Operation
    • 2 wire dial-up
  • Interface
    • RS-232C
  • Connectors
    • 1 DB25 female
    • 2 RJ11 female
profile speed and compression standards
Profile: Speed and Compression Standards
  • V.90
    • Supports 56 Kbps
  • V.34
    • Supports 28.8 Kbps
  • V.32
    • Supports 14.4 Kbps
  • V.42bis
    • Data compression standards
    • Up to 4 to 1 compression is possible
profile error correction and other data compression standards
Profile: Error Correction and Other Data Compression Standards
  • MNP 2-4 and 10
    • Error correction
  • MNP 5
    • Data compression
combined effect of speed and compression standards
Combined Effect of Speed and Compression Standards
  • Combined effect of v.34 and v.42bis data compression
    • 115.2 Kbps
    • This is only a theoretical reality
    • Practical speeds can be considerably slow
effect of compression on file transfer
Effect of Compression on File Transfer
  • Highest transfer speeds cannot be achieved in the case of already compressed files
    • Example: jpg, mp3 etc.
    • Because the above files are already compressed
profile fax communication
Profile: Fax Communication
  • Fax details
    • 14.4 Kbps speed
    • Class 1 and 2 fax software support
    • Works with class 3 fax machines
module3

MODULE

Modem Software Installation

module objectives2
Module Objectives
  • Demonstrate the step-by-step installation of a modem in the Windows 95 operating system
installation overview
Installation Overview
  • The task is to install a Hayes Accura 28.8 modem on Com2 port
  • Overview of the Steps
    • Open the control panel
    • Choose the Modem icon
    • Proceed with the installation as instructed and finally specify the properties of the installed modem
selecting the modem
Selecting the Modem

Load the driver from the disk

If the modem is not found in

the List.

non mainstream modem
Non-Mainstream Modem
  • If the modem is not of a popular type, then the driver must be loaded from a location on the disk
  • In the above case, select the option that says “Have Disk”
module4

MODULE

A Practical Asynchronous/Synchronous Modem

module objectives3
Module Objectives
  • Examine briefly the profile of an asynchronous/synchronous modem
  • Discuss speed related factors
  • Give an illustration of the typical use of a synchronous modem
profile of an asynchronous synchronous modem
Profile of an Asynchronous/Synchronous Modem
  • Blackbox 32fast modem
  • Claimed speed
    • 72k bps synchronous
      • Uses sync. Data compression to send data under HDLC/SDLC
    • 115.2k bps asynchronous
  • Best compression is automatically chosen
    • Between v.42 bis and MNP 5
profile of asynchronous synchronous modem
Profile of Asynchronous/Synchronous Modem
  • Other features
    • Trellis-coded modulation
    • MNP 4 error correction
  • Suggested lines
    • 2 or 4 wired leased lines
    • Switched phone lines may not provide optimum performance
  • UART connection
    • For effective high-speed transmission
typical use of a synchronous modem
Typical Use of a Synchronous Modem

Front End

Processor

Leased Line

Terminal

Cluster

Controller

Synchronous

Modem

Mainframe

module5

MODULE

Faster Modem Standards

faster modem standards
Faster Modem Standards
  • The current fastest analog modem operates at a speed of 56 Kbps
  • Standards
    • ITU V.90
    • X2
    • K56flex
  • X2 was introduced by US Robotics that has been acquired by 3 Com
  • K56flex standard was introduced by Rockwell and Lucent Technologies
practical speed considerations
Practical Speed Considerations
  • 56 Kbps has not been achieved in many tests in practice
  • Speed is usually in the region of 45k bps or less
  • FCC restriction on download speed
    • Currently the speed limitation is 53 Kbps
56 kbps v 90 information
56 Kbps /V.90 Information
  • Cedric Walravens’ web site is a good source of information on 56K /V.90 modems and communication
data compression limitations
Data Compression Limitations
  • High speed modems use compression to increase the throughput
  • Files such as image files are already compressed
    • There is little leeway for further compression
    • Results in a drop in the communication speed
quality of the phone lines
Quality of the Phone Lines
  • Certain phone lines cannot support 56K bps speed
  • Central office that services a particular area may not have the latest switching equipment
  • Testing the line for 56K bps support
    • X2.usr.com/linetest1.html
bonding of telephone lines to achieve higher speeds 112 kbps
Bonding of Telephone Lines to Achieve Higher Speeds (112 Kbps)

Modem with

Bonding

Capability

Computer

Phone Lines

Bonding of two phone lines can provide a

total bandwidth of 112K bps.

module6

MODULE

Fiber-Optics Connection

module objectives4
Module Objectives
  • Examine a fiber-optic connection used for extending the length of the communication link
  • Give an illustration of a practical fiber-optic link
fiber optic connection for rs 232c
Fiber-optic Connection for RS-232C
  • Extends RS-232C connection to nearly 2 . 5 miles
  • Fiber interface (line driver) specifications
    • Transfer mode
      • Synchronous and asynchronous
    • Speed
      • 56 K bps for sync.
      • 64 K bps for aysnc.
      • Selectable depending on the connection
some fiber optic connections fiber modems
Some Fiber-optic Connections :Fiber Modems

2.5 miles

Host

RS 232

Terminal

Fiber Line Drivers

fiber optic line drivers
Fiber-optic Line Drivers

Building 1

Building 2

T1

Router,

Bridge.

(Support

Videoconferencing)

Fiber-optic Line Driver

module7

MODULE

Null Modems and Short-Haul Modems

null modem

Send

Send

Comp 1

Null

Modem

Comp 2

Receive

Receive

Null Modem
  • Use for connecting two computers together
    • Communicate through their respective serial ports
  • Digital signals are not modulated
characteristics of the null modem
Characteristics of the Null Modem
  • Cross-over connection
    • Enables the sending and receiving of signals to facilitate communication
  • Instead of a null-modem, one may also use a crossover cable
  • In the past, null modems were used with software like lap-link
    • The primary purpose was for file transfer
  • Null modem is being replaced by a simple null modem cable
null modem cable connection
Null Modem Cable Connection

Comp 1

Null

Modem

Comp 2

Cable 1

Cable 2

Past

Comp 1

Comp 2

Null Modem Cable

Present

other ways to connect two computers network
Other Ways to Connect Two Computers (Network)

NIC

RJ 45Cross-over Cable

Comp 2

Comp 1

other ways to connect two computers network1
Other Ways to Connect Two Computers (Network)

Infrared Port Device

Infrared Connection

Comp 2

Comp 1

crossover cable use
Crossover Cable Use
  • Laplink
    • A software that is used for transferring information between computers
  • The Laplink cable that is used to connect computers together is indeed a crossover cable
    • In this case, the computers are connected either over the serial, parallel or USB ports
  • Nowadays, a popular method of exchanging information between computers is to use Infrared
short haul modem
Short-Haul Modem
  • Purpose
    • Extend the length of a RS-232 serial connection
  • Signals are not modulated
    • The term modem is a misnomer
  • Signals are boosted so that they may be carried over a longer distance
short haul modem1
Short-Haul Modem

SHM

Term.

Asynchronous.

Host

SHM

Term.

SHM

SHM

Term.

Short-

Haul

Modem

Rack

UNIX

Computer

SHM

Term.

practical implementation
Practical Implementation

Source: Black Box

in summary
In Summary
  • Traditional modems
    • Perform modulation
  • Nontraditional modems
    • Do not perform any modulation
module8

MODULE

Cable Modems

cable modem
Cable Modem
  • A modem that is used for connecting a computer to the cable TV line
  • The purpose is to facilitate high speed access to the Internet
  • Cable modem is a broadband technology device
    • The cable carries multiple channels including TV channels and upstream and downstream data channels
typical cable modem connection single ip address
Typical Cable Modem Connection (Single IP Address)

Coaxial Cable

Cable

Modem

UTP (Cat 3 – 5)

Computer

NIC

sharing single ip address with multiple computers 10base2
Sharing Single IP Address with Multiple Computers (10base2)

Source:

Tim Higgins

Site

1

2

  • A proxy server can be used.
  • Windows 2000.
  • Windows 98 Second edition supports the sharing of
  • one PC for multiple PC access to the Internet.

1

sharing single ip address with multiple computers 10baset
Sharing Single IP Address with Multiple Computers (10baseT)

Source:

Tim Higgins

Site

1

2

  • A proxy server can be used.
  • Windows 2000.
  • Windows 98 Second edition supports the sharing of
  • one PC for multiple PC access to the Internet.

1

two computers sharing one ip without a hub
Two Computers Sharing One IP without a Hub

1

Source:

Tim Higgins

Site

2

2

3

  • A proxy server can be used.
  • Windows 2000.
  • Windows 98 Second edition supports the sharing of
  • one PC for multiple PC access to the Internet.

2

cable modem lan connection multiple ip addresses
Cable Modem LAN Connection (Multiple IP Addresses)

Coaxial

Cable

UTP (Cat 3 – 5)

Crossover Cable?

Hub

Cable

Modem

UTP (Cat 3 – 5)

Computer

Computer

Computer

NIC

NIC

NIC

cable modem customer connections
Cable Modem Customer Connections

Cable Service

Provider

CMTS

Customer

CM

Customer

CM

Customer

CM

CM: Cable Modem

CMTS: Cable Modem Termination System

cable modem limitation
Cable Modem Limitation
  • Each cable drop is shared by a number of customers
  • As the number of customers increases in a trunk the bandwidth available per customer decreases
cable modem types
Cable Modem Types
  • Internal Modems
    • Installed into a PC’s expansion slot
  • External Modems
    • An external box connected to the computer’s NIC
  • External Web TV Box
    • Used with Web TV setups
    • A return channel may be provided through a POTS line
cable modem standards
Cable Modem Standards
  • The current versions are known as the second generation modems
  • US Standards
    • MCNS/DOCSIS 1.0/1.1
    • A de facto standard
    • IEEE is yet to propose or approve a standard
  • European
      • DVB/DAVIC 1.3/1.4/1.5
the tutorial for cable modems
The Tutorial for Cable Modems
  • www.cable-modems.org
    • Contains useful information on cable modems
  • Access to the tutorial
    • http://www.cable-modems.org/tutorial/
  • Access to Q and A
    • http://www.cable-modems.org/Q&A/
  • Appreciation and credit
    • Some of the slides used in this chapter are from the above web site as acknowledged in the appropriate slides
    • Also, visit the site for a description of some of the technical terms associated with cable modems
additional sites
Additional Sites
  • www.cablemodemdatacom.com
    • Extensive information with good graphics
modulation and demodulation frequencies
Modulation and Demodulation Frequencies

Source: http://www.cable-modems.org/tutorial/01.htm

speed and bandwidth
Speed and Bandwidth
  • Shannon’s Law
    • Speed is proportional to bandwidth
  • In most cases, downstream speed is higher than upstream speed
  • Higher upstream speed is desired in certain cases
    • Hosting of a web server
  • Symmetric streams are desired for video conferencing
maximum bandwidth
Maximum Bandwidth
  • Upstream
    • Lower frequencies are used
    • Up to 3Mbps
  • Downstream
    • Higher frequencies are used
    • Between 27-56 Mbps
  • Note that communication speed is proportional to available bandwidth
downstream communication characteristics
Downstream Communication Characteristics

Source: http://www.cable-modems.org/tutorial/08.htm

upstream communication characteristics
Upstream Communication Characteristics

Source: http://www.cable-modems.org/tutorial/09.htm

osi iso reference model and cable modem communication
OSI-ISO Reference Model and Cable Modem Communication

Source: http://www.cable-modems.org/tutorial/02.htm

sample cable modem companies
Sample Cable Modem Companies
  • 3Com
  • CISCO Systems
  • Toshiba
  • Sony
  • More DOCSIS compatible Cable Modems
    • A gallery of selected cable modems from cable-modems.org
sample product demonstration
Sample Product Demonstration
  • 3Com Cable Modem CMX product demonstration
    • Explore the purpose of the different status lights on the modem
    • Try this to see the product feature and rotate the modem to view the different sides of the modem
possible downside
Possible Downside
  • Potential downsides to the cable modem are discussed in this ZDnet article
advantages and disadvantages
Advantages and Disadvantages
  • Advantages
    • Higher speeds compared to analog connections
    • The connection is always on
    • Possible assignment of static IP addresses
  • Disadvantages
    • Speed drops with an increase in the number of customers on a cable drop
    • Higher costs compared to analog connections
slide112
FAQs
  • A collection of 100 FAQs from cable-modems.org
    • Includes FAQs for DSL as well
other cable modem links
Other Cable Modem Links
  • ZDnet home page on cable modem
  • Cable modem help web site
  • Cable modem net information site
  • Tom Higgins’ cable modem site
    • Recommended
  • Cable modem books
    • A listing of selected books from cable-modems.org
module9

MODULE

DSL Modems

dsl modem
DSL Modem
  • A modem that is used for connecting a computer to the Digital Subscriber Line (DSL)
  • The purpose is to facilitate high speed access to the Internet
  • DSL modem is a broadband technology device
    • The regular telephone line carries the DSL line as well
    • Therefore, there are multiple channels present on the POTS line delivering the DSL connection
simple dsl line drop
Simple DSL Line Drop

Source: xDSL Technology Web Site

typical dsl modem connection single ip address
Typical DSL Modem Connection(Single IP Address)

POTS line

DSL

Modem

UTP (Cat 3 – 5)

10/100 Mbps

(*Cat 5 is recommended)

Computer

NIC

dsl resources
DSL Resources
  • DSL Reports itself is a good DSL web site
  • A good reference to DSL Resources from DSL reports
  • A good page that shows graphically the speed comparison of DSL with other technologies
typical adsl connection
Typical ADSL Connection

Source: ADSL Tutorial from adsl.com

cable modem limitation1
Cable Modem Limitation
  • Each cable drop is shared by a number of customers
  • As the number of customers increase in a trunk the bandwidth available per customer decreases
asdl modem types
ASDL Modem Types
  • Internal Modems
    • Installed into a PC’s modem
  • External Modems
    • An external box connected to the computer’s NIC
cable modem standards1
Cable Modem Standards
  • The current versions are known as the second generation modems
  • US Standards
    • MCNS/DOCSIS 1.0/1.1
    • A de facto standard
    • IEEE is yet to propose or approve a standard
  • European
      • DVB/DAVIC 1.3/1.4/1.5
the tutorial for cable modems1
The Tutorial for Cable Modems
  • www.cable-modems.org
    • Contains useful information on cable modems
  • Access to the tutorial
    • http://www.cable-modems.org/tutorial/
  • Access to Q and A
    • http://www.cable-modems.org/Q&A/
  • Appreciation and credit
    • Some of the slides used in this chapter are from the above web site as acknowledged in the appropriate slides
    • Also, visit the site for a description of some of the technical terms associated with cable modems
modulation and demodulation frequencies1
Modulation and Demodulation Frequencies

Source: http://www.cable-modems.org/tutorial/01.htm

maximum bandwidth1
Maximum Bandwidth
  • Upstream
    • Lower frequencies are used
    • Up to 3Mbps
  • Downstream
    • Higher frequencies are used
    • Between 27-56 Mbps
  • Note that communication speed is proportional to available bandwidth
downstream communication characteristics1
Downstream Communication Characteristics

Source: http://www.cable-modems.org/tutorial/08.htm

upstream communication characteristics1
Upstream Communication Characteristics

Source: http://www.cable-modems.org/tutorial/09.htm

osi iso reference model and cable modem communication1
OSI-ISO Reference Model and Cable Modem Communication

Source: http://www.cable-modems.org/tutorial/02.htm

sample dsl modem companies
Sample DSL Modem Companies
  • 3Com
  • CISCO Systems
  • Alcatel
sample cable modem1
Sample Cable Modem

Source: 3Com Modem

sample product demonstration1
Sample Product Demonstration
  • 3Com ADSL Modem Demonstration
    • http://www.3com.com/client/pcd/homeconnect/dsl/images/prod_sidenav.gif
    • Explore the purpose of the different status lights on the modem
    • Try this to see the product feature and rotate the modem to view the different sides of the modem
possible downside1
Possible Downside
  • Potential downsides to ADSL
advantages and disadvantages1
Advantages and Disadvantages
  • Advantages
    • Higher speeds compared to analog connections
    • The connection is always on
    • Possible assignment of static IP addresses
    • Existing POTS line can be used
  • Disadvantages
    • Higher costs compared to analog connections
    • May not be available at all locations
other dsl links
Other DSL Links
  • DSL Reports web site contains a good collection of selected links
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