TEL 355: Communication and Information Systems in Organizations

1
TEL 355 Communication and Information Systems in
Organizations

• Asymmetric Digital
• Subscriber Line (ADSL)
• Professor John F. Clark

2
Modem Basics

• Short for Modulate/Demodulate
• Converts digital signals to analog for
  transmission over the phone network
• Converts analog signals back to digital for
  reception by another computer
• All modems use compression to achieve higher line
  speeds and error checking to examine packets and
  request retransmission

3
Definition of ADSL

• Modem technology that converts existing 2X phone
  lines into access paths for high-speed
  communications
• Its asymmetric downstream speeds are faster
  than upstream speeds
• Increases dial-up line speeds by 1000-fold
• Can transmit up to 24 Mbps one way

4
Asymmetric Digital Subscriber Line

• An evolving high-speed transmission technology
  developed by Telcordia
• Developed with video-on-demand as goal
• Is now ANSI standard T1.413, ITU standard
  
  
  
  
  G.992.1 (8 Mbits/s) and G.992.2 (ADSL Lite)
• ILECs seek to extend the life of network
• Several billion miles of 2X in the local loop
• With ADSL, is valuable in convergence scenario
• CLECs are interested in competing with ILECs

5
Asymmetric Digital Subscriber Line

• Does not really refer to a line, but to a pair of
  modems one on each end creates a digital
  subscriber line
• ADSL can provide up to
• 1.5 Mbps downstream on 2X lines to 18,000 ft.
• 6.1 Mbps downstream on 2X lines to 12,000 ft.
• 8 Mbps downstream on 2X lines to 6600 ft.
• Simultaneous analog telephone service is not an
  option POTS is supplied in the C channel of the
  DSL line

6
T1 and E1

• Early 60s Bell Labs digitized voice into a 64
  kbps stream and multiplexed 24 elements in a
  channel resulting in 1.544 Mbps, or DS1/T1
• European systems modified the approach and
  multiplexed 30 elements for a line rate of 2.048
  Mbps, or E1
• Not suitable for residences because they require
  new wire installations and frequent repeaters and
  corrupt adjacent 2X pairs

7
High Data-Rate (HDSL)

• The most mature of the xDSL technologies
• An improved method of transmitting T1/E1 over 2X
  lines
• Four-wire method uses less bandwidth and does not
  require repeaters
• Advance modulation techniques transmits 1.544
  Mbps up to 12,000 feet
• Supplies approx. 70 of T1 service in U.S.

8
Symmetrical DSL (SDSL)

• Single line version of HDSL often all that are
  available, also known as HDSL2
• Transmits up to 2.3 Mbps over single 2X both ways
  up to about 10,000 feet
• Supports POTS and T1/E1 simultaneously
• At the same distance, ADSL is capable of
  transmitting over 6 Mbps
• Aimed at the corporate user with high bandwidth
  needs upstream and downstream

9
Asymmetric (ADSL)

• Specifically designed for the home user or small
  business customer
• Asymmetric channels allow greater data rates and
  longer line lengths
• Transmits two separate data streams
• much more bandwidth devoted to the downstream
  channel
• best option for most online multimedia
  video-on-demand, audio streaming, LAN access

10
The Market for xDSL Modems

• The first 14.4 kbps modem cost 14,400!
• Fortunately those days are over, but xDSL market
  maturity will follow the same plan
• Consumers will be less interested in standards
  and become more interested in ease of
  installation and use, plug and play features,
  small size and power requirements, and best
  speeds over 2X

11
ATM vs. IP 10/100baseT

• The great debate whats the best network
  interface for the PC?
• Is it Asynchronous Transfer Mode (ATM) protocol
  or the IP-based 10/100baseT Ethernet protocol?
• The two are actually similar and are often used
  in conjunction with one another the differences
  lie in the software and hardware
• This is done deal nowadays who won?

12
IP Advantages

• 10/100baseT is essentially self-learning
• Inexpensive Ethernet cards are common
• 10/100baseT is a bigtime industry standard
• LAN networks are everywhere connection is
  ubiquitous and expertise abounds (sort of)
• PC software and OS drivers are all equipped to
  deal with it

13
ATM Advantages

• Streaming video support is a proven factor
• Mixing of services such as video, telephony data
  is much easier
• Traffic speeds conform to standard telephony
  transport rates (marginal reason)
• New PC software and drivers will work with ATM
  (or not it depends)
• An idea whose time never came

14
ATM vs. IP 10/100baseT

• Both usually connect to ATM backbones
• At the moment, IP is winning Internet use
  rules, equipment is available and inexpensive
• But ATM may still be a factor standards for
  most services are complete
• Another but it will be very hard to overcome
  installed base of cheap IP, especially as IP
  telephony standards evolve

15
The Future?

• Standards werent an issue with early modem
  development, but they are in xDSL
• ATM vs. IP 10/100baseT (IP is the clear winner)
• Cellular Array Processor (CAP) vs. Discrete
  Multitone (DMT seems to be winning)
• Remember, Betamax had better quality picture, but
  VHS won the market

16
Local Prices Verizon 9/2000

• DSL Bronze Plus 768k down and 128k up your
  average service at 32.50
• DSL Silver Service 384k up and down for added
  oomph in transmission at 53.00
• DSL Gold Service 768k up and down for
  webhosting at 68.00
• DSL Platinum Service 1.5 Mbps down and 768k up
  at 95.00 Multiuser at 215.00

17
Local Prices Verizon 9/2001

• DSL Bronze Plus 768k down and 128k up
• your average service at 49.95 per month
• DSL Enhanced Bronze Plus 1.5 Mb down and 128k up
• For telecommuters at 59.95 per month
• DSL Silver Service 384k up and down
• for gamers and conferencers at 69.95 per
• DSL Silver Plus 1.5 Mb down and 384k up
• Professional model for offices at 79.95

18
Local Prices ATT 5/2007

• FastAccess DSL Lite 256 Kbps down and 128 Kbps
  up
• Free modem and 24.95 a month
• FastAccess DSL Ultra 1.5 Mbps down and 256 Kbps
  up
• Free modem, 75 cash back and 32.95 a month
• FastAccess DSL Xtreme 3 Mbps down and 384 Kbps
  up
• Free modem, 75 cash back and 37.95 a month
• FastAccess DSL Xtreme 6.0 6 Mbps down and 512
  Kbps up
• Free modem, 75 cash back and 42.95 a month