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INTRODUCTION TO HIGH SPEED NETWORKING
TECHNOLOGY
PREPARED BY:
v.c.dandwani
TOPICS
 5.1 CABLE MODEM SYSTEM
 5.2 DIGITAL SUBSCRIBER LINE
TECHNOLOGY:HDSL AND ADSL
 5.3 FAST ETHERNET
 5.4 GIGABIT ETHERNET
 5.5 FDDI AND CDDI
5.1 CABLE MODEM SYSTEM
 CABLE MODEM BASICS:
 A Cable Modem is a digital modem that uses a coaxial cable
connection for the data transmission.
 This data connection is received by a cable modem that decodes the
signal into your PC.
 Cable TV (CATV) Network serves as the Internet Service Provider
(ISP)
 Cable Modem modulates/transmits and demodulates/receives
to/from a CATV channel.
 Downstream: data received at the modem is communicated to one
or more PCs on a LAN via Ethernet, USB, PCI Bus, etc.
 Upstream: data requests from the PC are transmitted through the
modem to the CATV network via coaxial cable, phone line or
wireless.
 CATV data service interfaces to the Internet via Cable Modem
Transmission System (CMTS )
5.1 CABLE MODEM SYSTEM
Coaxial cable bands
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.
5.1 CABLE MODEM SYSTEM
 Cable Modem Network Overview:
 Headend: DOCSIS-certified CMTS (Cable Modem Transmission System)
 One Headend supports @ 2000 Cable Modem Users on a single TV
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Channel
 CMTS interfaces the CATV network to the Internet
CMTS output channel combined with TV video signals
CATV Network to Subscriber via coaxial cable
One-to-Two splitter: One signal to Set Top Box (STB), other to Cable
Modem
Cable Modem
 One Modem can support up to 16 users in a local-area network
PC/Ethernet Card
 Cable Modem connected to PC via Ethernet, USB, PCI Bus, etc
DOCSIS – Data over Cable Service Interface Specifications
 Defined by the Multimedia Cable Network System Partners
(MCNS)
 This defines all the protocols necessary to transport data
from a CMTS to CM.
 Cable Modem Architecture
 Transmit/Upstream
 QPSK/QAM Modulator performs:
QPSK/QAM-16 modulation
 Reed-Solomon Encoding
 D/A Conversion
 Up-conversion to the selected
frequency/channel
 Receive/Downstream
 RF Tuner
 Converts TV Channel to a fixed
lower frequency (6-40MHz)
 QAM Demodulator performs:
 A/D conversion
 QAM-64/256 demodulation
 MPEG frame synchronization
 Error Correction (Reed-Solomon)
 MAC - Media Access Control
 Implemented partially in hardware
and software
 Data and Control Logic
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MAC layer provides general
requirements for many cable
modems subscribers to share a
single upstream data channel for
transmission.
Defines collision detection and
retransmission.
Communication layer between
Cable Modem and CMTS.
5.1 CABLE MODEM SYSTEM
 Cable Modem Technology
 It Modulates and Demodulates signals.
 Cable modems can be part modem,
part tuner, part
encryption/decryption device, part bridge, part router, part network
interface card, part SNMP agent, and part Ethernet hub.
 Typically, a cable modem sends and receives data in two slightly
different fashions.
 In the downstream direction
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The digital data is modulated and then placed on a typical 6 MHz
television channel, somewhere between 50 MHz and 750 MHz.
64 QAM is the preferred downstream modulation technique,
offering up to 27 Mbps per 6 MHz channel.
This signal can be placed in a 6 MHz channel adjacent to TV
signals on either side without disturbing the cable television video
signals.
 In the upstream direction
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the upstream (also known as the reverse path) is transmitted between
5 and 42 MHz.
This tends to be a noisy environment, with RF interference and
impulse noise. Additionally, interference is easily introduced in the
home, due to loose connectors or poor cabling.
Since cable networks are tree and branch networks, all this noise gets
added together as the signals travel upstream, combining and
increasing.
Due to this problem, most manufacturers use QPSK or a similar
modulation scheme in the upstream direction, because QPSK is more
robust scheme than higher order modulation techniques in a noisy
environment
The drawback is that QPSK is "slower" than QAM.
 Cable Modem Service Providers
 Cisco Systems, Com21, General Instrument, Motorola, Nortel
Networks, Phasecom, Samsung, Terayon, Toshiba, Zenith, Bay
Networks, RCA, 3Com.
5.1 CABLE MODEM SYSTEM
How fast is a Cable Modem
Cable modems are up to 10-20Mbps downloads. Typical downloads are over
300Kbps, or close to 600Kbps, but the speed of the cable modem depends on a few
things. First it depends on how many users are on the system since the cable
technology is a "shared" bandwidth. Too many users using too much throughput can
drain this “shared” technology.
 The second factor to cable modem speed is a limit on the cable modem itself. Some
cable providers will limit the upload or download speed on the cable modem, and this
could affect your connection speed.
 Cable Modems vs. ADSL
There is one major advantage that ADSL has over cable modems. Cable
modems use a shared networking technology where all the cable modems
share a single pipe to the Internet. This pipe speed will fluctuate depending
on the number of subscribers on the network.
When ADSL is used, the pipe to the Internet is solely "yours", and is not
shared along the way to a central office. This allows for a more consistent
speed, and this speed does not typically fluctuate like cable modem networks.
5.2 DIGITAL SUBSCRIBER LINE(DSL)
TECHNOLOGY
ADSL(Asymmetric DSL)
ADSL is an asymmetric communication technology designed for residential
users; it is not suitable for businesses.
It is like a 56k modem, provides higher speed(bit rate) in the downstream
direction(from the internet to resident) than in the upstream direction(from
resident to internet).this is the reason it is called asymmetric.
It divides the available bandwidth of the local loop unevenly for the
residential customer. This service is not suitable for business customers who
need a large BW in both direction.
The existing local loops can handle bandwidths up to 1.1 MHz.
Twisted pair local loop is capable of handling BW up to 1.1 MHz, but filters
at end of telephone company has local loop terminates limits BW of 4KHz.If
filter removed entire 1.1MHz is available for data and voice communication.
LOCAL LOOP
 In telephony, the local loop (also referred to as a subscriber
line) is the physical link or circuit that connects from the
customer premises to the edge of the carrier or
telecommunications service provider's network.
 Traditionally, the local loop was wireline in nature from
customer to central office, specifically in the form of an
electrical circuit (i.e. loop) provisioned as a single twisted pair
in support of voice communications.
 A local loop may be provisioned to support data
communications applications, or combined voice and data.
 ADSL is an adaptive technology. The system uses a
data rate based on the condition of the local loop line.
Theoretical BW of local loop is fixed. factors such as the
distance between residence and switching office, the size of the
cable, the signaling used, and so on affect the BW.
The designers must aware of this problem and used an adaptive
technology that tests condition and BW availability of the line
before settling on data rate.
DMT(discrete multitone technique)
Modulation technique used for ADSL is DMT.and it combines
QAM and FDM.
Each system can decide on its BW division. Typically an
available BW of 1.1MHz is divided into 256 channels. Each
channel uses a BW of 4.312kHz,as shown in figure.
DMT
DMT
 voice: channel 0 is reserved for voice communication.
 idle: channel 1 to 5 are not used and provide a gap between voice
and data communication.
 upstream data and control: channel 6 to 30(25 channels) are used.
One channel is for control and 24 are for data transfer. If there are
24 channels, each using 4 kHz with QAM modulation, we have
24*4000*15,or 1.44 Mbps BW,in upstream direction.datarates
normally below 550 kbps because some of the carriers deleted at
frequencies where the noise level is large. So some channels may
be unused.
 downstream data and control: channel 31 to 255(225 channels).1
for control and 224 are for data. If there are 224 channels, we can
achieve up to 224*4000*15,or13.4Mbps.but data rate normally
below 8 Mbps because some of the carriers deleted at frequencies
where the noise level is large. So some channels may be unused.
ADSL modem
HDSL
 HDSL (High-speed Digital Subscriber Line) is a relatively
early XDSL family development.
 a broader application: the use of echo suppression, adaptive
filtering and high-speed digital processing technology, using
2B1Q coding, using two pairs of twisted-pair data two-way
symmetrical
transmission,
transmission
rate
2048Kbps/1544Kbps (E1/T1), each of the telephone line
transmission rate 1168Kbit / s, use 24AWG (American Wire
Gauge American cable regulations) twisted pair (equivalent to
0.51mm) when the transmission distance up to 3.4KM, can
provide E1/T1 interface and V.35 standard interface.
ETHERNET
 The original Ethernet was created in 1976 at Xerox’s Palo Alto
Research Center (PARC). Since then, it has gone through four
generations.
5.3 FAST ETHERNET
 Fast Ethernet was designed to compete with LAN protocols
such as FDDI or Fiber Channel. IEEE created Fast Ethernet
under the name 802.3u. Fast Ethernet is backward-compatible
with Standard Ethernet, but it can transmit data 10 times faster
at a rate of 100 Mbps.
 GOALS OF FAST ETHERNET:
 Upgrade the data rate to 100 Mbps
 Make it compatible with standard Ethernet
 Keep the same 48-bit address
 Keep the same frame format
Topics discussed in this section:
MAC Sublayer
Physical Layer
MAC SUBLAYER
 A main consideration in the evolution of Ethernet from 10 to 100 Mbps was
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to keep the MAC sub layer untouched.
It is done to drop the bus topology and keep only star topology.
for the star topology ,there are two choices, as we saw before: half duplex
and full duplex.
In half duplex approach, the stations are connected via hub: while in full
duplex approach, the connection is made via a switch with buffers at each
port.
Auto negotiation(negotiation-give and take, discussion)
A new feature of fast Ethernet.
It allows a station or a hub a range of capabilities.
It allows incomplete devices to connect to one another. For e.g. a device
with maximum capacity of 10 mbps can communicate with a device
with 100 Mbps capacity.
To allow one device to have multiple capabilities.
Allow station to check a hub’s capabilities.
PHYSICAL LAYER
IMPLEMENTATION
ENCODING
Manchester encoding needs a 200 Mbaud BW for a data rate of
100 Mbps,which makes it unsuitable for a medium such as twisted
pair cable. So fast Ethernet designers make alternative
encoding/decoding scheme. So there are 3 different encoding
schemes.
5.3GIGABIT ETHERNET
 The need for an even higher data rate resulted in the design of
the Gigabit Ethernet protocol (1000 Mbps). The IEEE
committee calls the standard 802.3z.
 GOALS:
 Upgrade the data rate to 1Gbps.
 Make it compatible with standard or fast ethernet.
 Use the same 48-bit address.
 Use same frame format.
 To support auto negotiation as defined In fast ethernet.
 TOPIC DISCUSSED:
 MAC Sublayer
 Physical Layer
MAC SUBLAYER
To achieve 1Gbps data rate, was no longer possible. so it has two distinctive
approaches for medium access: half duplex and full duplex.
Almost all implementations of gigabit Ethernet follow full-duplex approach.
FULL DUPLEX MODE:
There is a central switch connected to all computers or other switches. Here
each switch has buffers for each input port in which data are stored until they
are trasmitted.so no collisions CSMA/CD is not used.
HALF DUPLEX MODE:
It can also use this mode. But it is rarely used. Here switch can be replaced
by hub, which acts as common cable in which collision might occur.so this
approach use CSMA/CD.
Three methods have been defined.
 Traditional:
 Here minimum length of frame is used(512bits).because the length of bit is
1/100 shorter in gigabit Ethernet than in 10Mbps ethernet,so slot time for
gigabit is 512bits*1/1000micro sec,0.512micro sec.Reduced slot time means
collision is detected 100 times earlier.
 Carrier Extension: to allow for longer network, we increase minimum
frame length. This approach defines the minimum length of a frame as 512
bytes(4096 bits).
 Minimum length is 8 times longer. This method forces a station to add extension
bit(padding) to any frame that is less than 4096 bits. So max length can be
increased 8 times to a length of 200m.
 Frame bursting: carrier extension is very inefficient if we have series of
short frames to send; each frame carries redundant data.
 To improve efficiency, frame bursting was used.
 Here instead of adding a extension to each frame, multiple frames are sent.
PHYSICAL LAYER
Physical layer in gigabit ethernet is more complicated than in
standard or fast ethernet.
IMPLEMENTATION
ENCODING
8B/10B=8 Binary,10 binary. Group of 8bit of data is substituted by 10-bit code. provide
greater error detection capability than 4B/5B.
4D/PAM5=it is a multilevel scheme.(four dimensional five-level pulse amplitude
modulation)
4D means data is sent over four wires at same time.it uses five voltage levels,-2,-1,0,1
and 2.
SUMMARY
5.5 FDDI(fiber distributed data
interface)
 Fiber Distributed Data Interface (FDDI) is a set of ANSI protocols
for sending digital data over fiber optic cable with transmission
distances of up to 1.2 miles (2 kilometres).
 FDDI networks are token-passing (similar to IEEE 802.5 Token
Ring protocol) and dual-ring networks, and support data rates of up
to 100 Mbps.
 FDDI networks are typically used as backbones technology because
of its support for high bandwidth and great distance.
 FDDI uses dual-ring architecture with traffic on each ring flowing in
opposite directions (called counter-rotating). The dual rings consist
of a primary and a secondary ring. During normal operation, the
primary ring is used for data transmission, and the secondary ring
remains idle. The primary purpose of the dual rings is to provide
superior reliability and robustness.
FDDI specifies the physical and media-access portions of the OSI reference model.
FDDI is not actually a single specification, but it is a collection of four separate
specifications, each with a specific function. Combined, these specifications have the
capability to provide high-speed connectivity between upper-layer protocols such as
TCP/IP and media such as fiber-optic cabling.
 FDDI's four specifications are ,
(1)the Media Access Control (MAC)
(2) Physical Layer Protocol (PHY)
(3) Physical-Medium Dependent (PMD)
(4) Station Management (SMT)
 The MAC specification defines how the medium is accessed, including frame
format, token handling, addressing, algorithms for calculating cyclic redundancy
check (CRC) value, and error-recovery mechanisms.
 The PHY specification defines data encoding/decoding procedures, clocking
requirements, and framing, among other functions.
 The PMD specification defines the characteristics of the transmission medium,
including fiber-optic links, power levels, bit-error rates, optical components, and
connectors.
 The SMT specification defines FDDI station configuration, ring configuration, and
ring control features, including station insertion and removal, initialization, fault
isolation and recovery, scheduling, and statistics collection.
FDDI FRAME FORMAT
 Preamble---A unique sequence that prepares each station for an upcoming frame.
 Start Delimiter---Indicates the beginning of a frame by employing a signaling
pattern that differentiates it from the rest of the frame.
 Frame Control---Indicates the size of the address fields and whether the frame
contains asynchronous or synchronous data, among other control information.
 Destination Address---Contains a unicast (singular), multicast (group), or broadcast
(every station) address. As with Ethernet and Token Ring addresses, FDDI
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destination addresses are 6 bytes long.
Source Address---Identifies the single station that sent the frame. As with Ethernet
and Token Ring addresses, FDDI source addresses are 6 bytes long.
Data---Contains either information destined for an upper-layer protocol or control
information.
Frame Check Sequence (FCS)---Filed by the source station with a calculated cyclic
redundancy check value dependent on frame contents (as with Token Ring and
Ethernet). The destination address recalculates the value to determine whether the
frame was damaged in transit. If so, the frame is discarded.
End Delimiter---Contains unique symbols, which cannot be data symbols, that
indicate the end of the frame.
Frame Status---Allows the source station to determine whether an error occurred and
whether the frame was recognized and copied by a receiving station.
5.5 CDDI(copper distributed data
interface)
 Copper Distributed Data Interface (CDDI), a version of FDDI using twisted
pair cables, provides data rates of 100 Mbps.
 It uses dual-ring architecture to provide redundancy.
 CDDI supports distances of about(328 feet) 100 meters from desktop to
concentrator.
 The CDDI standard is officially named as the Twisted-Pair Physical MediumDependent (TP-PMD) standard. It is also referred to as the Twisted-Pair
Distributed Data Interface (TP-DDI).