Transcript Residential Area Networks

Network Technology
CSE3020
Week 11
Network Technology CSE3020 - 2006
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Residential Area Networks
 PSTN: Using an existing telephone line with a modem
to provide a data communication between a computer in
the residential area and a WAN server.
 ISDN: Same as PSTN but the data communication is a
digital one.
 ADSL: Using existing telephone lines, but with a pair
of special devices at the computer and the server.
 Cable modem: Using part of the CATV bandwidth to
provide data service.
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Public Switched Telephone
Network (PSTN)
The Internet
server
PSTN
home
56kbps
• PSTN provides dedicated communication link between
the computer and the server.
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Integrated Switched Digital
Network (ISDN)
The Internet
server
PSTN
home
n*64kbps
• ISDN (Integrated Service Digital Network) provides dedicated
end-to-end digital communication link between the computer and
the server.
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ISDN
• ISDN is intended to be a worldwide public telecom network to
replace existing PSTN.
• Narrowband ISDN: First generation specification (contributed
to Frame relay).
• Broadband ISDN: Second generation specification (contributed
to ATM) and supports very high data rate.
• Based on a set of channels at a single interface.
• B channel (64 kbps): principal channel used for circuit
switching, packet switching and leased lines.
• D channel: used for control signaling and carry some data.
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Principles of ISDN
• Support of voice and non-voice applications using a limited set of
standardized facilities.
• Support for switched and non-switched applications.
• Reliance on 64-kbps connections.
• Intelligence in the network.
• Layered protocol architecture.
• Variety of configurations.
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ISDN Features
Digital pipes to
other networks and
services
Customer ISDN
interface
...
ISDN
Subscriber loop
with ISDN channel
structure
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LAN
Circuit
switching
network
...
PBX
Packet
switching
network
Other
networks
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ISDN Architecture
Subscriber premises
TE
NT
Digital
subscriber loop
ISDN
CO
user-network
signaling
user-user
signaling
NT: Network Termination
TE: Terminal Equipment
Subscriber premises
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ISDN Architecture
• A common physical interface to provide DTE-DCE connection.
• Same interface for telephone, computer terminal, video
terminal, digital PBX and LAN.
• One or two twisted pairs for a basic full-duplex digital
communication link.
• Standards:
- Issued by ITU-T, called I-series recommendations.
- Standardization of services offered to users.
- Standardization of user-network interfaces.
- Standardization of ISDN capabilities.
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ISDN Channels
• B channel: 64 kbps.
- basic user channel to carry digital data, PCM-encoded digital
voice and a mixture of lower-rate traffic.
- Connections: Circuit switched, Packet switched, Frame
mode and Semipermanent.
• D channel: 16 or 64 kbps.
- Carries signaling information to control circuit switched
calls on B channels.
- Used for packet switching or low speed data when no
signaling information.
• H channel: 384 (H0), 1536 (H11) and 1920 (H12) kbps.
- User information at higher bit rates.
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ISDN Channels
Basic Rate
Interface (BRI)
B = 64kbps
B = 64kbps
Basic
D = 64kbps
Primary Rate
Interface (PRI)
B = 64kbps
…
…
Primary
2B+D
= 192kbps
B = 64kbps
D = 64kbps
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23B+D
=1.536Mbps
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ISDN Channels
H0 channel = 384 kbps
H11 channel = 1536 kbps
H12 channel = 1920 kbps
• PRI H0:
> 3H0+D or 4H0 = 1.544 Mbps
> 5H0+D = 2.048 Mbps
• PRI H1:
> One H11 in 1.536 Mbps
> One H12 +D 2.048 Mbps
• PRI for Mixture of B and H0:
> 0 or 1 D and any combination of B and H0
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ISDN Devices
• NT1 – Network Termination Type 1: A device that
connects 4-wire ISDN subscriber wiring to the
conventional 2-wire local loop facility
• NT2 – A device that directs traffic to an from
different subscriber devices and NT1. NT2 performs
switching.
• TE1 – Terminal Equipment 1: A device that is compatible
with the ISDN network
• TE2 – A device that is not compatible with ISDN and
requires a Terminal Adapter
• TA – Terminal Adapter: A device that is used to
connect ISDN BRI connections to existing interfaces
eg RS-232
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ISDN Reference Points
T
S
TE1
NT2
customer
premises
switching
equipment
ISDN
terminal
equipment
non-ISDN
terminal
equipment
NT1
subscriber
line
terminator
S
R
TE2
U
TA
terminal
adaptor
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ISDN Reference Points
• R – References the connection between a non-ISDNcompatible device (TE2) and a Terminal Adapter (TA),
such as an RS-232 serial interface
• S – References the points that connect into the
customer switching device (NT2)
• T – References the outbound connection from NT2 to
ISDN network or NT1
• U – References the connection between the NT1 and
the ISDN network provide the Telco
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ISDN Protocol Stack
Application
End-toend user
Session signaling
Transport
Presentation
Network
Data Link
Physical
Q.931
X.25
LAPD
X.25
I.465/V.120 LAPB
I.430 basic or I.431 Primary
Control
signaling
Packet Circuit
Semi
Packet
switched
permanent switched
D Channel
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B and H
Channel
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Asymmetric Digital Subscriber Line (ADSL)
• Modem technology designed to provide high-speed digital data
transmission over ordinary telephone wire.
• Link between subscriber and a network (local exchange).
– Local loop.
• Uses currently installed twisted pair cable.
– Can carry broader spectrum (1 MHz or more).
• Asymmetric.
– Greater capacity downstream than upstream.
• Frequency division multiplexing (FDM).
– Lowest 25kHz for voice
• Plain old telephone service (POTS)
– Use echo cancellation or FDM to give two bands.
• Range of up to 5.5km.
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Asymmetric Digital Subscriber Line (ADSL)
Home
ATU-C
ATU-R
16-640kbps
POTS
PCM
PSTN
1.544M-6Mbps
server
The Internet
ATU: ADSL Transmission Unit
POTS: Plain Old Telephone Service
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ADSL: Frequency Spectrum
Downstream with
echo cancellation
Upstream
Downstream without
echo cancellation
POTS
frequency
1MHz
For PCM
For ADSL
Bandwidth of the telephone line
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ADSL Family
 ADSL-1: 1.544Mbps downstream + 16kbps full-duplex
control channel
 ADSL-2: 3.152Mbps downstream + 64kbps full-duplex
control channel
 ADSL-3: 6.312Mbps downstream + 64kbps full-duplex
control channel
These standards do not promise a certain data rate. The actual
data rate depends on the quality of the local loop, generally,
the distance between the two transceivers.
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ADSL: Modulation
• Carrierless Amplitude and Phase (CAP):
Uses a pair of analog signals to encode the inphase and the out-of-phase carriers of the
symbols. Used in ADSL-1.
• Discrete Multitone (DMT):
Similar to FDM, a channel is divided to several
subchannels. Each subchannel carries QAM
signals. Used in ADSL-3.
• These modulations do not promise a certain data rate.
The actual data rate depends on the quality of the local
loop, generally, the distance between the two
transceivers.
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Discrete Multitone (DMT)
• Multiple carrier signals at different frequencies (or
subchannels) carrying some bits on each channel.
• 4 kHz subchannels.
• Send test signal and use subchannels with better signal
to noise ratio.
• 256 downstream subchannels at 4 kHz (60kbps).
– Possible up to 15.36 Mbps.
– Impairments bring this down from 1.5 Mbps to 9 Mbps.
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DMT Transmitter
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xDSL
• High-speed digital transmission of the subscriber line.
• High data rate Digital Subscriber Line (HDSL):
– More cost-effective means of delivering a T1 data rate (1.544
Mbps).
– Up to 2 Mbps over two twisted pair lines within a bandwidth
of 196 kHz.
– Range of about 3.7 km.
• Single line Digital Subscriber Line (SDSL):
– HDSL is not suitable for residential subscribers because of
two twisted pair.
– SDSL provides same service as HDSL but over a single
twisted- pair line.
• Very high data rate Digital Subscriber Line (VDSL):
– Similar to ADSL but at a much higher data rate.
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The following slides are for Interest Only
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Community Antenna TV (CATV)
CATV
Trunk splitter
Head-End Coax
…
Coax
Residential area
• Distribute broadcast television (and radio) programs.
• Based entirely on coaxial cable.
• TV programs are multiplexed using FDM.
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CATV Bandwidth Usage
Control
Video Channels
Unused
52MHz
550MHz
frequency
750MHz
Delivered Bandwidth
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Hybrid Fiber Coax (HFC)
CATV
Head-End
RF Amplifiers
fiber
server
Fiber Node
…
coax
The
Internet
Residential area
•
•
•
HFC provides a relatively high data rate for users.
The use of existing infrastructure leads to a cheap solution (even
cheaper than ADSL) for high data rate access to the Internet
from residential areas.
The cable is to be shared by all users. The data rate per user may
drop during peak hours.
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HFC Characteristics
• Stations share the same coax.
• Downstream: broadcast (Up to 50Mbps).
• Upstream: a medium access control protocol (Up to 10.24Mbps).
• Number of stations: 200
• The coax may span over 10km (long signal propagation time).
• The coax provides full duplex communications (Upstream and
downstream channels are separated).
• There is an active device in Fiber Node, it may be used as a
central controller.
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HFC: Upstream/Downstream
2MHz (UP)
5
65
8MHz (DOWN)
850
Freq
(MHz)
• Downstream channel is a broadcasting channels. Transmitted
signals are received by all cable modems. Cable modems ignore
transmissions not addressing to them by checking MAC
addresses.
• Upstream channel is shared by all users. A MAC protocol is
required for channel assignment.
• A transceiver may not be able to detect a collision.
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HFC Pros and Cons
 It provides a relatively high data rate for users.
 The use of existing infrastructure leads to a cheap
solution (even cheaper than ADSL) for high data rate
access to the Internet from residential areas.
 The cable is to be shared by all users. The data rate per
user may drop during peak hours.
 Only available in areas that have cable installed.
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Required Reading
• W. Stallings, “Data and Computer Communications
(6th edition),” Prentice-Hall, 2000.
>> Chapter 8.4, 8.5, Appendix A
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