1. Chapter 11
Voice and Data Delivery
Networks
Csc 113

2. Outline:
• The 56k Dial-Up Modem
• Digital Subsciber Line
• DSL basics
• DSL formats
• Cable Modems

3. The 56k Dial-Up Modem
• 33,600-bps modem
 was made available in 1995
 using standard telephone lines a modem would ever
achieve many experts believe this was the fastest
modem and this was based on two facts.
1. Telephone connection into a home is an analog-
modulated connection (using phase shift keying).
2. Telephone signal is transmitted with a certain signal
power level and a given amount of background
noise.

4. The 56k Dial-Up Modem
Did something in the telephone system change to
allow the faster transmission speed, or were the
industry experts wrong?

5. The 56k Dial-Up Modem
Did something in the telephone system change to
allow the faster transmission speed, or were the
industry experts wrong?
Digital Signaling
was introduced.

6. The 56k Dial-Up Modem
• 56,000-bps or 56k modem
 hybrid design, combining analog signaling and digital
signaling
 employs digital signaling instead of using analog
signaling
 Telephone system can send an 8-bit sample 8000 times
per second, which corresponds to 64 kbps.

7. The 56k Dial-Up Modem
If the telephone company can transmit 64-kbps,
does this mean that we users can receive a 64-kbps
downstream signal?

8. The 56k Dial-Up Modem
If the telephone company can transmit 64-kbps,
does this mean that we users can receive a 64-kbps
downstream signal?
The answer is NO.

9. The 56k Dial-Up Modem

10. The 56k Dial-Up Modem

11. The 56k Dial-Up Modem
• V.90 standard
 1st standard to appear that supported 56,000 bps dial-
up modems
• V.92 modem standard
 Introduced by ITU after V.90
 This standard is a slight improvement over the V.90 standard in
two respects.
1. the upstream link between the user and the telephone
company is capable of supporting connections up to 48 kbps
(as opposed to the 33,600 bps of the V.90 modem)
2. V.92 modem can place a data connection on hold should
someone call the user’s telephone number (call waiting)

12. Digital Subscriber Line
• Alternative ways to send data through the basic
telephone system
• Technology that allows existing twisted pair
telephone lines to transmit multimedia materials
and high-speed data.
• Transfer speeds can range from hundreds of
thousands of bits per second up to several million
bits per second.

13. DSL basics
• Transmission speed is an important issue.
• DSL is capable of a wide range of speeds.
• The transfer speed of a particular line depends on
one or more of the following factors -
 Carrier providing the service.
 Distance of your house from the central office of the
local telephone company.
 DSL service is either symmetric connection or an
asymmetric connection.
• DSL is an always-on connection.
• It uses a permanent circuit instead of a switched
circuit.

14. DSL basics
Type of connection in DSL Service
Symmetric connection
 is one in which the transfer speeds in both directions are
equal
Asymmetric connection
 has a faster downstream transmission speed than its
upstream speed

15. DSL basics
• Users are required 4 component to establish a DSL
connection
 DSLAM (Digital Subscriber Line Access Multiplexer)
 DSL splitter
 DSL modem
 DSL router

16. DSL basics
• DSLAM (Digital Subscriber Line Access
Multiplexer)
 The local telephone company (LEC) must install a special
router called a DSLAM (digital subscriber line access
multiplexer) within the telephone company’s central office.
• DSL splitter
 The local telephone company may also install a DSL
splitter on its premises, which combines or splits the
DSL circuits (the upstream and downstream channels)
with the standard telephone circuit of POTS.
 When no splitter is used to separate the DSL signal
from the POTS signal, then the service is called
splitterless DSL.

17. DSL basics
• DSL modem
 DSL modem is required to convert the DSL signals into
a form that the user workstation or network can
understand.
• DSL router
 DSLAM router at the telephone company’s central office
must be connected to an Internet service provider via a
high-speed line.

18. DSL basics

19. DSL formats
• DSL formats are in use today – referred to as xDSL
 Asymmetric digital subscriber line (ADSL)
 DSL Lite
 Very high data rate DSL2 (VDSL2)
 Rate-adaptive DSL (RADSL)

20. DSL formats
• Asymmetric digital subscriber line (ADSL)
 A popular format that transmits the downstream data at
a faster rate than the upstream rate.
• DSL Lite
 slower format compared to ADSL
 Also known as Universal DSL, G.Lite, and splitterless
DSL
• Very high data rate DSL2 (VDSL2)
 Very fast fast format (roughly 100 Mbps downstream
and upstream) over very short distances (less than 300
meters)

21. DSL formats
• Rate-adaptive DSL (RADSL)
 RADSL is a format in which the transfer rate can vary,
depending on noise levels within the telephone line’s
local loop

22. Cable Modems
• is a high-speed communications services that
allows high-speed access to wide area networks
such as the Internet via a cable television
connection.
• is a physical device that separates the computer
data from the cable television video signal, but
many people refer to the entire system as a cable
modem service.

23. Cable Modems

24. Cable Modems
• Most cable modems are external devices that
connect to the personal computer through a
common Ethernet network interface card, which is
either provided by the cable company or purchased
at most stores that sell computer equipment
• The connection is typically asymmetric.

25. Cable Modems

26. Cable Modems
• Advantage
 Cable modems provide high-spee connections to the
Internet and the demand for them is growing rapidly.
• Disadvantage
 As traffic on Ethernet-based local area networks
increases, there is a decrease in overall throughput.