Post on 23-Dec-2015
CHAPTER CHAPTER
ModemsModems
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• 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
END OF CHAPTER END OF CHAPTER INTRODUCTIONINTRODUCTION
MODULE
Modem Functional Considerations
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
• ITU standard– Universal standard– Currently in use
• Bell standard– Earlier low speed modem standard– No more in use
Standards in Modem Communication
• Modulation standard• Data compression standard• Error correction Standard
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
Data Compression Standards in Modem
• MNP 5• ITU V.42 bis
Error Correction Standard
• MNP 2-4
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
• 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
Software Intel Micro Modem
Intel Machine Code
Hayes AT Command
Modem Features
• Auto-dial• Auto-answer• Reverse calling• All the above features are standard
in today’s Modems
END OF MODULEEND OF MODULE
MODULE
Internal, External and Portable 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
Source: Black Box
External Modems
Source: Black Box
External Modem Ports and Connection
To Com2Port
To PhoneJack RJ 11
Connection
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
Source: Black Box
Multi-Purpose PC Cards
Source: Black Box
END OF MODULEEND OF MODULE
MODULE
A Modem Profile
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
• 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
• Operation– 2 wire dial-up
• Interface– RS-232C
• Connectors– 1 DB25 female– 2 RJ11 female
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• MNP 2-4 and 10
– Error correction
• MNP 5 – Data compression
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
• 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
• Fax details– 14.4 Kbps speed– Class 1 and 2 fax software support– Works with class 3 fax machines
END OF MODULEEND OF MODULE
MODULE
Modem Software Installation
Module Objectives
• Demonstrate the step-by-step installation of a modem in the Windows 95 operating system
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
Demonstration of Modem Software Installation
Accessing Modem Installation Icon Through
Control Panel
Start Settings
Control Panel Modems
Modem Icon in Control Panel
Double Click
Select the Modem
Selecting the Modem
Load the driver from the diskIf the modem is not found in the List.
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”
Selecting the Port
Finishing the Installation
Installed
Modem
1
2
3
Modem General Properti
esIncrease
the speed to the
maximum.
1
2
3
Connection
Properties
1
2
3 4
Port Settings
1
2
Advanced Connection Settings
1 2
3
4
Dialing Propertie
s1
2
3
END OF MODULEEND OF MODULE
MODULE
A Practical Asynchronous/Synchronous
Modem
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/Synchronou
s 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/Synchronou
s 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
Mainframe
Front EndProcessor
ClusterController
Terminal
SynchronousModem
Leased Line
END OF MODULEEND OF MODULE
MODULE
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
• 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
• Cedric Walravens’ web site is a good source of information on 56K /V.90 modems and communication
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
• 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)
ComputerModem with
BondingCapability
Phone Lines
Bonding of two phone lines can provide atotal bandwidth of 112K bps.
END OF MODULEEND OF MODULE
MODULE
Fiber-Optics Connection
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
• 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
Fiber Optic Line Driver
Some Fiber-optic Connections :Fiber Modems
Host
Fiber Line Drivers Terminal
2.5 miles
RS 232
Fiber-optic Line Drivers
T1
Building 1 Building 2
Fiber-optic Line Driver
Router,Bridge.(Support Videoconferencing)
Practical Fiber Optics Connection
END OF MODULEEND OF MODULE
MODULE
Null Modems and Short-Haul Modems
Null Modem
• Use for connecting two computers together – Communicate through their
respective serial ports
• Digital signals are not modulated
Null Modem
Send Send
Receive Receive
Comp 1 Comp 2
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
Comp 1 Comp 2Cable 1 Cable 2
Comp 1 Null Modem Cable Comp 2
Past
Present
Other Ways to Connect Two Computers (Network)
Comp 1
RJ 45Cross-over Cable
Comp 2
NIC
Other Ways to Connect Two Computers (Network)
Comp 1 Comp 2
Infrared Connection
Infrared Port Device
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
• 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 Modem
Asynchronous.Host
Short-Haul ModemRack
UNIX Computer
SHM Term.
SHMSHM Term.
SHM Term.
SHM Term.
Practical Implementation
Source: Black Box
In Summary
• Traditional modems– Perform modulation
• Nontraditional modems– Do not perform any modulation
END OF MODULEEND OF MODULE
MODULE
Cable Modems
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)
Cable Modem
Computer
Coaxial Cable
UTP (Cat 3 – 5)
NIC
Sharing Single IP Address with Multiple Computers
(10base2)
1
1
•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.
Source: Tim Higgins Site
2
Sharing Single IP Address with Multiple Computers
(10baseT)
1
1
•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.
Source: Tim Higgins Site
2
Two Computers Sharing One IP without a Hub
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.
Source: Tim Higgins Site2
1
2
3
Computer
Cable Modem LAN Connection (Multiple IP
Addresses)
Cable Modem Hub
Coaxial Cable
NICComputer
NICComputer
NIC
UTP (Cat 3 – 5)Crossover Cable?
UTP (Cat 3 – 5)
Cable Modem Customer Connections
Customer Customer Customer
Cable Service
Provider
CM CM CM
CMTS
CM: Cable ModemCMTS: Cable Modem Termination System
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
• 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
• 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
• 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
• www.cablemodemdatacom.com– Extensive information with good
graphics
Modulation and Demodulation Frequencies
Source: http://www.cable-modems.org/tutorial/01.htm
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
• 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
Source: http://www.cable-modems.org/tutorial/08.htm
Upstream Communication Characteristics
Source: http://www.cable-modems.org/tutorial/09.htm
OSI-ISO Reference Model and Cable Modem
Communication
Source: http://www.cable-modems.org/tutorial/02.htm
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 Cable
Modem
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
• Potential downsides to the cable modem are discussed in this ZDnet article
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
FAQs
• A collection of 100 FAQs from cable-modems.org– Includes FAQs for DSL as well
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
END OF MODULEEND OF MODULE
MODULE
DSL Modems
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
Source: xDSL Technology Web Site
Another xDSL Line Drop
Soource: XDSL
Typical DSL Modem Connection
(Single IP Address)
DSL Modem
Computer
POTS line
UTP (Cat 3 – 5)
NIC
10/100 Mbps(*Cat 5 is recommended)
Sharing Single IP Address with Multiple Computers
(10base2)
Sharing Single IP with Multiple Computers
(10baseT)
Source: xDSL
Sharing Single IP with Two Computers without a Hub
DSL Modem LAN Connection
(Multiple IP Addresses)
Source: xDSL
Source: DSL Reports
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
Source: ADSL Tutorial from adsl.com
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
• Internal Modems– Installed into a PC’s modem
• External Modems– An external box connected to the
computer’s NIC
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
• 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 Frequencies
Source: http://www.cable-modems.org/tutorial/01.htm
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
Source: http://www.cable-modems.org/tutorial/08.htm
Upstream Communication Characteristics
Source: http://www.cable-modems.org/tutorial/09.htm
OSI-ISO Reference Model and Cable Modem
Communication
Source: http://www.cable-modems.org/tutorial/02.htm
Sample DSL Modem Companies
• 3Com• CISCO Systems• Alcatel
Sample Cable
Modem Source: 3Com Modem
Sample Product Specifications
Source: 3Com
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 Downside
• Potential downsides to ADSL
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
• DSL Reports web site contains a good collection of selected links
END OF MODULE END OF MODULE
END OF CHAPTER END OF CHAPTER