1. Modems: An Introduction The middlemen between the computer and the telephone system Convert analog data suitable for transmission over a phone line to digital data suitable for a computer (modulator/demodulator) Can be either an external device or an internal device that is installed in an expansion slot inside a computer A phone line connects to a modem or telephone using either an RJ-11 or older RJ-12 connector www.powerpointpresentationon.blogspot.com

2. Modem Types Telephone modem Optical Modem (Optical fiber) Cable modem DSL Modem etc

3. Modems Modulator Demodulator Transmitted Data Transmitted Modulated Data Received DataReceived Modulated Data Modem RS232, Ethernet etc. RS232, Ethernet, etc Phone Line, cable, optical fiber etc. Phone Modem, Cable Modem, DSL Modem etc. PC at home Remote PC, or Internet hub M DM D

4. What is a Cable Modem & how does it work? A Cable Modem is a digital modem that uses a coaxial cable connection for the data transmission. coaxial cable This data connection is received by a cable modem that decodes the signal into your PC. http://www.cable-modems.org/tutorial/01.htm http://www.cable-modems.org/tutorial/02.htm MORE INFO...

5. What is a Cable Modem? A device for high speed data access via a CATV network Source: CableLabs

6. Who Makes Cable Modems? Bay Networks -- LANcity Motorola Zenith General Instruments Hewlett-Packard Scientific Atlanta Phasecom

7. Who Doesn’t Make Cable Modems? Intel o Announced, then backed out in 1996 DEC o Resold LANcity modems in 1995, left business soon thereafter

8. Cable Modem Application

9. Typical Cable System with Internet Access Cable System Head End High-speed Internet Backbone Link Fiber Optic Links to Neighbor- hoods Conventional Copper Co-ax Cable to Homes

10. Possible Cable Modem Configuration: Multiple Computers in the Home Cable Modem PC with Ethernet Card

11. A Typical Cable Modem... …Connects 1 single host computer o Though some can connect dozens of hosts Has its own IP address o Though some share an IP address with the single connected host Operates at speeds from 1 megabit / second to 10 megabits / second o Though some claim up to 30 megabits / sec Is bidirectional o Though some use “telco return”

12. How Fast is a Cable Modem? Variable Bit Rate: Bandwidth on Demand Asymmetric Configuration o Downstream Transmission  Frequency Range: 50-860 MHz  Transmission Speed: up to 36 Mbps (3~10 Mbps realistic) o Upstream Transmission  Frequency Range: 5-42 MHz  Transmission Speed: up to 10 Mbps (200 Kbps ~ 2 Mbps realistic)

13. How secure is a Cable Modem? Cable connections are not 100% secure in any instance like many other connections on the Internet. Even though most cable providers block ports 137-139, cable modems are likely to be generated in any case where a user has file and print sharing turned on, or possibly other services like SMTP (Simple mail transfer protocol), Web Servers and Telnet services. A general rule is to keep passwords long and turn off any service that you don't absolutely need running. A firewall type application should be used to keep a network as secure as possible.

14. Who makes Cable Modems & what are some Cable Modem Service Providers? There are many cable modem brands, and some of the most common ones are from Com21, Motorola, Bay Networks, RCA, Cisco, Toshiba, 3Com, and Terayon. There are several popular cable modem providers. A few of them are: @Home available at http://www.Home.Com, Mediaone Express available at http://www.MediaoneExpress.com, and Road Runner, a service by Time Warner available at http://www.RR.Com.http://www.Home.Comhttp://www.MediaoneExpress.com http://www.RR.Com

15. 10/4/2009 Cable Modem Service On the Internet--Speed Kills Now, low-speed open access by telephone Soon, hi-speed closed access by cable modem

16. Cable Modems Will Have “Gatekeeper” Market Power Highest Speed Lowest Cost Fastest to Market

17. Modem Selection Criteria Digital or analog signals Asynchronous or synchronous Speed Distance Type of line Cost Use compatible modems for both end

18. Cable Modem Standards IEEE 802.14 (in May 1994) MCNS/DOCSIS (USA mainly, in January 1996) Multimedia Cable Network System (MCNS) Data Over Cable Service Interface Specification DVB/DAVIC (Europe mainly) European Digital Video Broadcast (DVB)/ Digital Audio Visual Council (DAVIC), EuroDOCSIS

19. Cable Modem

20. External Modem

21. Internal Modem

22. Relative Speed Comparisons Cable modems run up to 10 megabits / sec ISDN = 128 kilobits / sec Dialup modem = 28.8 kbps (or 33.6 or 56)

23. ADSL Asymmetric digital Subscriber Line:- ADSL is the current demanding of the phone companies for delivering advanced digital Services. It offers the promise of high Speed transmission.

24. Cable Modems vs. ADSL There is one major advantage that ADSL has over cable modems. Cable modems use a shared networking technology where all the cable modems share a single pipe to the Internet. This pipe speed will fluctuate depending on the number of subscribers on the network. When ADSL is used, the pipe to the Internet is solely "yours", and is not shared along the way to a central office. This allows for a more consistent speed, and this speed does not typically fluctuate like cable modem networks. MORE INFO... http://www.whatis.com/adsl.htm

25. Telephone Modems Telephone modems employ all three of the modulation techniques: o FSK o PSK o QAM Because of the limitations of voice-grade telephone lines, these modems are restricted to a bandwidth of about 3 kHz The trend in modem design has been towards more sophisticated modulation schemes to achieve the maximum bit rate with available bandwidth

26. FSK Modems The first telephone modems used FSK and this technique is still used in specialized applications such as the transmission of call-display information from the central computer to subscriber telephones

27. PSK Modems When faster data rates are needed than available with PSK, phase modulation is often used Most DPSK (delta phase-shift keying) systems use a four- phase system called quadrature phase-shift keying (QPSK) The bit rate is twice the baud rate and is referred to as a dibit system The Bell 212A modem is an example of this type of modulation, capable of data rates up to 1200 bits per second

28. QAM Modems Quadrature Amplitude Modulation (QAM) modems are capable of operating at several different speeds, depending upon the quality of the connection Modem speeds using the ITU V.34 standard are capable of 33.6 kb/s, full duplex V.34 modems monitor line conditions and select the appropriate speeds for a given noise level

29. 56K Modems The V.90 standards allow data transmissions up to a theoretical limit of 56 kb/s, but because of FCC requirements, the maximum allowable is 54 kb/s V.90 modems appear to exceed the Shannon Limit However, the higher rate is available only in the downstream direction and a maximum of 33.6 kb/s is available in the upstream direction Upper limits vary greatly according to line noise, distance from a telephone substation, and availability of digital connections throughout the phone system

30. Competition for Cable Modems

31. Faster Modems 33.6K modem is about 16% faster than 28.8 56K modem would be about twice as fast o …whenever it’s real Even fast modems are only a fraction of speed of Ethernet o Factor of several hundred o Only in theory! o Ethernet is shared

32. Faster Metropolitan Links: ISDN An old digital technology Provides about 128 kilobits / second Costs about $30 to $70 per month Rapidly being overshadowed by newer schemes

33. Faster Metropolitan Links: ADSL Moving 1.5 to 6.1 megabits/second Over existing copper phone wires Requires improvements to parts of phone network Asymmetric: megabits to user, only kilobits from user o URLs are small o Web pages are big o Don’t install a Web server on your ADSL link

34. Marketing Advantage (Why choose D-Link) Digital Home Completeness World-wide sales service Real-world experienced support team Excellent R&D, manufacture, quality control team

35. Pricing Typically starts at ~ $30 / month o Probably slow speed o 1 IP address o No Web server allowed Perhaps $70 per month for 1 IP address and 10 megabit service Perhaps $300 to $1000 per month for multiple IP addresses serving a business Some systems charge fees if you exceed monthly bandwidth quota