Transcript Chapter 4. Signals

Chapter 9 Using Telephone and Cable
Networks for Data Transmission
1.
2.
3.
4.
5.
Spring 2007
Telephone Network
Dial-up Modems
Digital Subscriber Line
Cable TV Networks
Cable TV for Data Transfer
Data Communications, Kwangwoon University
8-1
Telephone Companies: Brief History
• Before 1984
– Almost all services are provided by AT&T Bell System
– In 1984, AT&T was broken into
• AT&T long Lines
• 23 BOCs(Bell Operating Companies)
• BOCs are grouped together to several RBOCs
• Between 1984 and 1996
– Divided into more than 200 LATAs (Local Access Transport Areas)
• After 1996
– Any companies can provide any services
Spring 2007
Data Communications, Kwangwoon University
8-2
A Telephone System
Spring 2007
Data Communications, Kwangwoon University
8-3
LATAs
• A LATA can be a small or large metropolitan area
• Intra-LATA services are provided by local
exchange carriers
– ILEC (Incumbent Local Exchange Carriers)
– CLEC (Competitive Local Exchange Carriers)
• Inter-LATA services are handled by IXCs (InterExchange Carriers)
– Called long-distance companies
Spring 2007
Data Communications, Kwangwoon University
8-4
Switching Offices in a LATA
Spring 2007
Data Communications, Kwangwoon University
8-5
POP (Point of Presence)
Spring 2007
Data Communications, Kwangwoon University
8-6
Signaling
• In-band signaling : the same circuit used for both signaling
and voice communication
• Out-of-band signaling
• The task of data transfer and signaling are separated in
modern telephone network
• Signaling system are required to
–
–
–
–
–
Providing dial tone, ring tone, and busy tone
Transferring telephone numbers between offices
Maintaining and monitoring the call
Keeping billing information
Maintaining and monitoring the status of the telephone network
equipment
– Providing other functions such as caller ID, voice mail, and so on
Spring 2007
Data Communications, Kwangwoon University
8-7
Data Transfer and Signaling Networks
Spring 2007
Data Communications, Kwangwoon University
8-8
Layers in SS7(Signaling System 7)
Spring 2007
Data Communications, Kwangwoon University
8-9
Telephone Network Services
• Analog services
– Analog switched services
• Dial-up service
• 800 service, 900 service
• WATS (wide-area telephone service)
– Analog leased service: called a dedicated line
• Digital service
– Switched/56 service
– Digital data service: digital leased line
Spring 2007
Data Communications, Kwangwoon University
8-10
Dial-Up Modems
• Data signals require a higher degree of accuracy to ensure integrity
Spring 2007
Data Communications, Kwangwoon University
8-11
Modem
• Modem stands for modulator/demodulator
Spring 2007
Data Communications, Kwangwoon University
8-12
Modem Standards
• V-series standards by ITU-T
– V.32 : Trellis-coded modulation: 32-QAM (4 data bits
and a redundant bit for error detection)  9,600 bps
– V.32bis : 128-QAM (7 bits/baud with 1 bit for error
control)  14,400 bps
– V.34bis : 28,800 bps with a 960-point constellation and
33,600bps with a 1664-point constellation
– V.90: Upload: 33.6 kbps, download: 56 kbps
– V.92: Upload: 48 kbps, download: 56 kbps
Spring 2007
Data Communications, Kwangwoon University
8-13
V.32 and V.32bis
Spring 2007
Data Communications, Kwangwoon University
8-14
V.90: 56K Modem
• Traditional modems
have a data rate
limitation of 33.6 kbps
by Shannon capacity
• Uploading : 33.6 kbps
• Downloading: 56 kbps
– 8000 samples x 7 bit
– 1 bit for control
Spring 2007
Data Communications, Kwangwoon University
8-15
ADSL
• Asymmetrical Digital Subscriber Line
• ADSL is an asymmetric communication
technology designed for residential users; it is not
suitable for businesses
• The existing local loop can handle bandwidths up
to 1.1 MHz
• ADSL is an adaptive technology. The system uses
a data rate based on the condition of the local loop
line.
Spring 2007
Data Communications, Kwangwoon University
8-16
DMT (Discrete Multitone Technique)
Spring 2007
Data Communications, Kwangwoon University
8-17
Bandwidth Division in ADSL
• There is no set way that the bandwidth is divided
• Upstream
– 24 channels x 4 kHz x 15 bits/Hz = 1.44 Mbps
• Downstream
– 224 channels x 4 kHz x 15 bits/Hz = 13.4 Mbps
Spring 2007
Data Communications, Kwangwoon University
8-18
DSL: Actual Bit Rate
• Because of the high signal/noise ratio
• Upstream
– Normally below 500 kbps
• Downstream
– Normally below 8 Mbps
Spring 2007
Data Communications, Kwangwoon University
8-19
Customer Site: ADSL Modem
Spring 2007
Data Communications, Kwangwoon University
8-20
Telco Site: DSLAM
• Digital subscriber line access multiplexer
Spring 2007
Data Communications, Kwangwoon University
8-21
Other DSL Technologies: xDSL
• HDSL (High-bit-rate DSL)
– Designed as an alternative to the T-1 line (AMI encoding)
– 2B1Q encoding used for less susceptible to attenuation
– Up to a distance 12,000 ft without repeaters
– Two twisted pairs for full-duplex transmission
• SDSL (Symmetric DSL)
– One twisted pair version of HDSL
– 768 kbps in each direction, symmetric communication
– Send and receive data in large volumes in both directions
• VDSL (Very-high-bit-rate DSL): Alternative approach to ADSL
– Coaxial, fiber-optic, or twisted-pair cable for short distances
– Uses DMT with 25-55 Mbps (downstream) and 3.2 Mbps
(upstream)
Spring 2007
Data Communications, Kwangwoon University
8-22
Summary of DSL Technologies
Spring 2007
Data Communications, Kwangwoon University
8-23
Traditional Cable TV Network
• Started to distribute video signals to locations with poor or
no reception in the late 1940s: Unidirectional
• It was called Community Antenna TV
Spring 2007
Data Communications, Kwangwoon University
8-24
HFC (Hybrid Fiber Coaxial) Network
• RCH (Regional Cable Head) feeds the distribution hubs
• Fiber node splits the signal to each coaxial cable
• Communication in an HFC network can be bidirectional
Spring 2007
Data Communications, Kwangwoon University
8-25
Coaxial Cable Bands
• Video band: 6 MHz per TV channel
• Downstream data band: 64-QAM (or possibly 256-QAM)
– Theoretical rate is 30 Mbps (6 MHz/sec x 5 bits/Hz)
• Upstream data band: QPSK
– Theoretical rate is 12 Mbps (6 MHz/sec x 2 bits/Hz)
• Both upstream and down stream bands are shared by the subscribers
Spring 2007
Data Communications, Kwangwoon University
8-26
CM (Cable Modem)
Spring 2007
Data Communications, Kwangwoon University
8-27
CMTS (Cable Modem Transmission System)
Spring 2007
Data Communications, Kwangwoon University
8-28
Data Transmission Schemes: DOCSIS
• Standard for data transmission over a HFC
network by Multimedia Cable Network System
(MCNS)
– Data Over Cable System Interface Specification
(DOCSIS) : defines all the protocols to transport data
from CMTS to a CM
Spring 2007
Data Communications, Kwangwoon University
8-29