Matakuliah : H0122 / Dasar Telekomunikasi
Tahun
: 2008
Sistem Broadband
Pertemuan 13
Learning Outcomes
Mahasiswa dapat menyebutkan sistem akses broadband
yang telah digunakan.
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Outline Materi
• X-DSL
• Modem Kabel
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Broadband
• The need broadband system is due to the user demand for speed on
the order of Mbps for internet access and other applications.
• The bandwidth of the basic POTS analog is limited.
• High Speed means Megabits at least in one direction, always on for
continuous connection to the outside world and bidirectional.
• High speed from the home as well as to the home.
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Access Choices
• Many different approaches
– Twisted pair (xDSL)
– Hybrid fiber-coax cable (cable modem)
– Fixed wireless
– Satellite (two-way)
– Fiber to the home or curb (Gigabit Ethernet)
– Power line
– Digital terrestrial
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Access Choices
GigE Fiber
MDU
High-rise multidwelling units
Cable modem
Communication
Network
Homes
Individual
single units
Twisted pair DSL
Satellite
Farm
Isolated
single units
Determining Factors:
•
•
•
•
•
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Population density
Existing infrastructure (e.g., twisted pair, cable, fiber)
Government policies
Competitive and regulatory dynamics
Technology evolution
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Digital Subscriber Line
• Digital Subscriber Line (DSL) technology is one of the most
supporting high-speed digital communication over the existing local
loops. DSL provides high speed access over local loops.
• The various types of DSL are called xDSL family = {A,S,H,V}DSL
• Twisted Pair cables used for local loops has a bandwidth of 1.1MHz
Telephone companies limit the bandwidth to 4KHz using filters
(sufficient for voice communication), to allow multiplexing of large
number of voice channels
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Types of xDSL
• SDSL
: Symmetrical DSL, the bandwidth partitioning
is symmetrical, suitable for businesses
• ADSL : Asymmetric Digital Subscriber Line
• HDSL : High-bit-rate DSL (repeaterless E1)
• RADSL : Rate Adaptive DSL for noisy lines
• VDSL : Very-high-speed DSL upstream 50-56 Mbps,
coaxial, fiber-optic, or TP for higher rates over short
distances (300-1800m)
• G.Lite : Slower version of ADSL eliminating
need for POTS Splitter (filter) at customer. Provides up to
1.5 Mbps down, 128 Kbps up
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ADSL
• Asymmetric
– Asymmetry in upstream and downstream connection, higher
bandwidth downstream (to subscriber), lower bandwidth
upstream (to Internet)
• Frequency division multiplexing
– Lowest 25kHz for voice (POTS)
– Use echo cancellation or FDM to give two bands
– Use FDM within bands
• The existing local loops can handle bandwidths up to 1.1 MHz. Range
5.5km
• ADSL is a link between subscriber and network and uses currently
installed twisted pair cable
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ADSL
• ADSL is an adaptive technology. The system uses a data rate
based on the condition of the local loop line.
• Factors like the distance between the residence and switching
office, line quality, and signaling used affect the data rate
• ADSL tests the condition and the bandwidth availability before
deciding on a data rate
• ADSL is an asymmetric communication technology designed for
residential users; it is not suitable for businesses.
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Channel Configuration
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System Configuration
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Cable TV Network
• The cable TV network is a video service provider, it
can be used to provide high-speed access to the
Internet.
• Communication in the traditional cable TV network
is unidirectional.
• Communication in an HFC cable TV network can be
bidirectional.
• Downstream data are modulated using the 64-QAM
modulation technique.
• The theoretical downstream data rate is 30 Mbps.
• Upstream data are modulated using the QPSK
modulation technique.
• The theoretical upstream data rate is 12 Mbps.
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Hybrid fiber-coaxial (HFC)
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Cable Modem Configuration
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Cable Modem Operations
• Downstream
– Cable scheduler delivers data in small packets
– If more than one subscriber active, each gets fraction of
downstream capacity (may get 500kbps to 1.5Mbps)
– Also used to allocate upstream time slots to subscribers
• Upstream
– User requests timeslots on shared upstream channel (dedicated
slots for this).
– Headend scheduler sends back assignment of future tme slots to
subscriber.
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Summary
• Telah dipelajari XDSL.
• Telah dipelajari Modem Kabel.
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