SHEKHAR HMP Assistant Professor, Wireless Networking Laboratory, Department of Computer Science

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SHEKHAR HMPAssistant Professor,Wireless
Networking Laboratory,Department of Computer
Science Engineering,M S Ramaiah Institute of
Technology,Bangalore, INDIAshekharhmp_at_msrit.edu
HIGH SPEED DIGITAL ACCESS AND CONNECTING DEVICES
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CDMA

• Transmission from different stations occupy
  entire frequency band at the same time.
• Transmissions are separated by using different
  codes for producing signals from stations.
• The receiver uses these codes to recover the
  signal from the desired station.

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CDMA

• User information is transmitted at R bps.
• Each user bit is transformed into G bits by
  multiplying user bit value (1 or -1) by G chip
  values (sequence of 1 and -1).
• Chip values is a unique binary pseudorandom
  sequence.
• The result is modulated and transmitted.
• G is called spreading factor and is selected such
  that it occupies entire frequency band.

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CDMA Contd.
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CDMA Contd.

• Ex. Suppose transmitter wants to transmits 1,
  then it is multiplied by chip sequence c1, c2,
  cG (each taking either 1 or -1). At the
  receiver, the received signal is correlated with
  know chip sequence. i.e.
• c1.c1 c2.c2 cG.CG G.
• If correlated with any other chip sequence the
  result would be zero or close to zero.

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CDMA Contd.
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CDMA Contd.
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CDMA Contd.

• Orthogonal sequences to eliminate interference
  between channels.
• Orthogonal spreading using Walsh functions.

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CDMA Contd.
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CDMA Contd.
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CDMA Contd.
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CDMA Contd.
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CDMA Contd.
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CDMA Contd.

• Let a (a1, a2, , an) and b (b1, b2, , bn)
  be the two spreading sequences. The two sequences
  are orthogonal is their dot product is zero.
• a b ? ajbj a1b1 a2b2 anbn 0
• Since spreading sequence consists of 1s and -1s,
• a a ? ajaj a1a1 a2a2 anan 0
• and
• b b ? bjbj b1b1 b2b2 bnbn 0

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CDMA Contd.

• If binary 0 is transmitted in a channel and a
  binary 1 in b channel, then signal in a channel
  is a (a1, a2, , an) and in b channel is b
  (b1, b2, , bn).
• The aggregate signal is r (r1, r2, rn) (-a1
  b1, -a2 b2, , -an bn) -a b.
• To recover the a channel, the receiver multiplies
  the jith received chip rj by aj and then
  integrates, or adds, the terms over all j.

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CDMA Contd.

• ? ajrj a1r1 a2r2 anrn a r a (-a
  b) -a a a b -n 0 -n
• To recover the b channel, the receiver multiplies
  the jith received chip rj by bj and then
  integrates, or adds, the terms over all j.
• ? bjrj b1r1 b2r2 bnrn b r b (-a
  b) -b a b b 0 n n

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CDMA Contd.
Walsh-Hadamard matrix provides orthogonal
spreading sequences of length n 2m.
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Applications

• Cellular Networks
• AMPS - FDMA
• IS-54, IS-136 TDMA
• GSM hybrid TDMA/FDMA
• CDMA

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AGENDA

• Digital Subscriber Line Technology
• Cable Modems
• Connecting devices
• Repeaters
• Hubs
• Bridges
• Switches
• Routers

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DSL

• Dial-up Connection for Internet access
• Analog modems have limited data rate, 56 Kbps.
• Digital Subscriber Line Technology provides high
  speed access to the Internet over existing local
  loops.
• DSL Technologies (xDSL) ADSL, VDSL, HDSL, and
  SDSL

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DSL Contd.

• ADSL (Asymmetric DSL)
• Downstream bit rate 500 Kbps to 8Mbps, Upstream
  bit rate 64 Kbps to 1Mbps
• Designed for residential users and is not
  suitable for businesses.
• Uses existing local loops

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DSL Contd.
DSLAM Digital Subscriber Line Access Multiplexer
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DSL Contd.

• Local loop twisted pair, theoretical 1.1MHz
• Filters limits the bandwidth to 4 KHz.
• Data rate is not fixed
• Affected by distance, size of cable, signaling
  used, etc.

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DSL Contd.
Bandwidth versus distance over category 3 UTP for
DSL
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DSL Contd.

• Modulation technique
• Discrete Multitone Technique (DMT)
• QAM FDM
• The bandwidth of 1.104 MHz is divided into 256
  channels.
• Each channel uses a bandwidth of 4.312 KHz.

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DSL Contd.
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DSL-Contd.

• Channel 0 Voice
• Channel 1-5 not used
• Channel 6-30 (25 channels) upstream data and
  control one channel is used for control 24
  channels, each using 4 KHz with QAM (15 bits/baud
  ) provides 24 x 4000 x 15 1.44 Mbps
  bandwidth.
• Channel 31-255 (225 channels) downstream data
  and control one channel is used for control 224
  channels, each using 4 KHz with QAM (15 bits/baud
  ) provides 24 x 4000 x 15 13.4 Mbps
  bandwidth.

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DSL Contd.
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DSL Contd.

• SDSL (Symmetric DSL)
• equal bandwidth for up and down streams
• HDSL (High-bit-rate DSL)
• An alternative to T-1 line
• Use 2B1Q encoding, 2 Mbps dual-way up to 3.6 km
• 2 twisted-pair wires to achieve full duplex

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DSL Contd.

• VDSL (Very-high-bit-rate)
• Use coax, fiber-optic, or twisted-pair for short
  distance
• DMT with up to 50-50 Mbps downstream and 1.5-2.5
  Mbps upstream

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CABLE MODEM

• Traditional Cable Networks
• unidirectional

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CABLE MODEM Contd.

• Hybrid fiber-coaxial network
• bidirectional

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CABLE MODEM - Contd.

• Coaxial cable, 5 to 750 MHz.
• A TV channel occupies 6MHz

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CABLE MODEM - Contd.

• 54 to 550 MHz video band, 80 channels
• 550 to 750 MHz downstream data band divided in
  to 6 MHz channels QAM-64 or QAM-256 QAM-64
  (6bits /baud), 2 bit for FEC and 5 bits for data,
  1 Hz for each baud, 5bits/Hz x 6 MHz 30 Mbps
  (theoretical), standard specifies only 27 Mbps.
• 5 to 42 MHz upstream data band divided in to 6
  MHz channels, lower frequencies are susceptible
  to noise and interference, QAM not suitable, uses
  QPSK, 2 bits each baud, 2bits/Hz x 6 MHz12 Mbps

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CABLE MODEM Contd.

• Both upstream and downstream bands are shared by
  different users.

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CABLE MODEM

• Cable Modem

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CABLE MODEM

• Cable Modem Transmission System (CMTS)

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CABLE MODEM

• A data transmission scheme Data Over Cable
  System Interface Specification (DOCSIS)
• Upstream protocol
• CMTS advertises itself with allocated up and down
  channels
• CM starts ranging, estimating distance to CMTS
• CM asks CMTS for an IP address
• CM and CMTS exchanges messages for security
  matters
• CM sends a unique ID to CMTS

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CABLE MODEM

• Downstream protocol
• No contention, CMTS just sends the packet with
  address of destinations CM

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REPEATER

• Allows the connection of network segments
• Extends the network beyond the maximum length of
  a single segment
• Functions at the Physical Layer of the OSI model
• Connects segments of the same network, even if
  they use different media

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REPEATER

• Has three basic functions
• Receives a signal which it cleans up
• Re-times the signal to avoid collisions
• Transmits the signal on to the next segment
• No traffic filtering

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HUB

• A multi-port repeater is known as a Hub
• Functions in a similar manner to a Repeater
• A central point of a star topology
• Allows the multiple connection of devices
• Can be more than a basic Hub providing
  additional services (Managed Hubs, Switched Hubs,
  Intelligent Hubs)
• Works at the Physical Layer of the OSI model

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HUB

• Passes data no matter which device it is
  addressed to
• This feature adds to congestion
• No filtering of traffic, collision, not
  scalability

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BRIDGE

• Like a Repeater or Hub it connects segments
• Works at Data Layer not Physical
• Uses MAC (Medium Access Control) address to make
  decisions
• Acts as a filter, by determining whether or not
  to forward a packet on to another segment
• Builds a Bridging Table, keeps track of devices
  on each segment
• Filters packets, does not forward them, by
  examining their MAC address

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BRIDGE

• It forwards packets whose destination address is
  on a different segment from its own
• It divides a network in to multiple collision
  domains so reducing the number of collisions

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SWITCH

• A multiport Bridge, functioning at the Data Link
  Layer
• Each port of the bridge decides whether to
  forward data packets to the attached network
• Keeps track of the MAC addresses of all attached
  devices (just like a bridge)
• Acts like a Hub, but filters like a Bridge
• Each port on a Switch
• is a collision domain

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ROUTER

• Works at Network Layer in an intelligent manner
• Can connect different network segments, if they
  are in the same building or even on the opposite
  side of the globe
• Work in LAN, MAN and WAN environments
• Allows access to resources by selecting the best
  path
• Can interconnect different networks
• Ethernet with Token Ring
• Changes packet size and format to match the
  requirements of the destination network

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LAN DEVICES