Multiplexing,LAN Cabling,Routers,Core and Distribution Networks

Network Design & Technologies(Unit-1)
Dr.M.Rajendiran
Dept. of Computer Science and Engineering
Panimalar Engineering College

Network Design & Technologies(Unit-1)
Multiplexing
Shared Media Networks
Connectionless & Connection oriented
Quality of Service
LAN Cabling Technologies
Core Networks and Distribution Networks
2

The Concept of Multiplexing
 In telecommunications and computer networks, multiplexing is a method by
which multiple analog or digital signals are combined into one signal over a
shared medium. (or)
 Multiplexing is a popular networking technique that integrates multiple analog
and digital signals into a signal transmitted over a shared medium.
 Multiplexers and de-multiplexers are used to convert multiple signals into one
signal. This term is also known as muxing.
Ex:
 Phone calls are a good example of multiplexing in telecommunications.
 That is, more than one phone call is transmitted over a single medium.
3

The Concept of Multiplexing
 Multiplexing to refer to the
combination of information streams
from multiple sources for
transmission over a shared medium
 Multiplexor is a mechanism that
implements the concept
 Demultiplexing to refer to the
separation of a combination back into
separate information streams
 Demultiplexor to refer to a
mechanism that implements the
concept
 Figure illustrates the concept
 each sender communicates with a
single receiver
 all pairs share a single
transmission medium
 multiplexor combines information
from the senders for transmission
in such a way that the
demultiplexor can separate the
information for receivers.
 *
4

Multiplexing in networksMainpurposeis?
Sharingthemedium
5

The Basic Types of Multiplexing
 There are four basic approaches to multiplexing that each
have a set of variations and implementations
 Frequency Division Multiplexing (FDM)
 Wavelength Division Multiplexing (WDM)
 Time Division Multiplexing (TDM)
 Code Division Multiplexing (CDM)
 TDM and FDM are widely used
 WDM is a form of FDM used for optical fiber
 CDM is a mathematical approach used in cell phone
mechanisms
6

Code Division Multiplexing (CDM)
 Code-division multiple access is a channel access method used by various
radio communication technologies.
 CDMA is an example of multiple access, where several transmitters can
send information simultaneously over a single communication channel.
1.CDM used in parts of the cellular telephone system and for some satellite
communication
 The specific version of CDM used in cell phones is known as Code
Division Multi-Access (CDMA)
2.CDM does not rely on physical properties
 such as frequency or time
3.CDM relies on an interesting mathematical idea
 values from orthogonal vector spaces can be combined and separated
without interference
4.Each sender is assigned a unique binary code Ci
 that is known as a chip sequence
 chip sequences are selected to be orthogonal vectors
 (i.e., the dot product of any two chip sequences is zero)
7

Code Division Multiplexing
5.At any point in time, each sender has a value to transmit, Vi
 The senders each multiply Ci x Vi and transmit the results
6.The senders transmit at the same time
 and the values are added together
7.To extract value Vi, a receiver multiplies the sum by Ci
8.Consider an example
 to keep the example easy to understand, use a chip sequence that is
only two bits long and data values that are four bits long
 think of the chip sequence as a vector
9.Figure 1 lists the values
8

 The first step consists of converting the binary values into
vectors that use -1 to represent 0:
 If we think of the resulting values as a sequence of signal
strengths to be transmitted at the same time
 the resulting signal will be the sum of the two signals
9

 A receiver treats the sequence as a vector
 computes the product of the vector and the chip sequence
 treats the result as a sequence, and converts the result to binary by
interpreting positive values as binary 1 and negative values as 0
 Thus, receiver number 1 computes:
 Interpreting the result as a sequence produces: (2 -2 2 -2)
 which becomes the binary value: (1 0 1 0)
 note that 1010 is the correct value of V1
 receiver 2 will extract V2 from the same transmission
10
C1
Received data
Code division multiple access (CDMA) is a channel access
method utilized by various radio communication technologies.

Dense Wavelength Division Multiplexing(DWDM)
 Dense wavelength division multiplexing (DWDM) is a fiber-optic
transmission technique that employs light wavelengths to transmit data
parallel-by-bit or serial-by-character.
Limitations of Wavelength Division Multiplexing
 Inefficient usage of full capacity of the optical fiber
 Capability of carrying signals efficiently over short distances only
 Improvements in optical fibers and narrowband lasers
 Birth of Dense WDM (DWDM)
11

Evolution of DWDM
 .
12
16+ channels
100~200 GHz spacing
64+ channels
25~50 GHz spacing
2~8 channels
200~400 GHz spacing
2 channels
1310nm, 1550nm

How is DWDM better?
O-E-O required
Protocol & Bit Rate independence
Increased overall capacity at much lower cost
Current fiber plant investment can be optimized by a factor of at
least 32
Transparency
Physical layer architecture supports both TDM and data formats
such as ATM, Gigabit Ethernet, etc.
Scalability
Utilize abundance of dark fibers in metropolitan areas and
enterprise networks
13

Basic Components & Operation
Transmitting Side
 Lasers with precise stable wavelengths
 Optical Multiplexers
On the Link
 Optical fiber
 Optical amplifiers
Receiving Side
 Photo detectors
 Optical Demultiplexers
Optical add/drop multiplexers
15

Optical Amplifier
 Eliminates O-E-O conversions
 More effective than electronic repeaters
 Isolator prevents reflection
 Light at 980nm or 1480nm is injected via the pump laser
 Gains ~ 30dB; Output Power ~ 17dB
16

Dense WDM
 Dense wavelength division multiplexing (DWDM) refers originally to
optical signals multiplexed within the 1550 nm band.
 The capabilities (and cost) of Erbium Doped Fiber Amplifiers (EDFAs),
which are effective for wavelengths between approximately 1525–1565
nm or 1570–1610nm.
 EDFAs were originally developed to replace SONET/SDH optical-
electrical-optical (OEO) regenerators.
 EDFAs can amplify any optical signal in their operating range, regardless
of the modulated bit rate.
 EDFA has enough pump energy available to it, it can amplify as many
optical signals as can be multiplexed into its amplification band.
 EDFAs therefore allow a single-channel optical link to be upgraded in bit
rate by replacing only equipment at the ends of the link.
17

Dense WDM
 Dense wavelength division multiplexing (DWDM) is a technology that puts
data from different sources together on an optical fiber, with each signal
carried at the same time on its own separate light wavelength.
 Using DWDM, up to 80 (and theoretically more) separate wavelengths or
channels of data can be multiplexed into a light stream transmitted on a
single optical fiber.
A basic DWDM system contains several main components:
1. A DWDM terminal multiplexer.
2. An intermediate line repeater
3. An intermediate optical terminal, or optical add-drop multiplexer
4. A DWDM terminal demultiplexer.
5. Optical Supervisory Channel (OSC).
18

Dense WDM
1. A DWDM terminal multiplexer:
 The terminal multiplexer contains a wavelength-converting transponder for
each data signal, an optical multiplexer and an optical amplifier (EDFA).
 Each wavelength-converting transponder receives an optical data signal from
the client-layer, such as synchronous optical networking [SONET /SDH] or
another type of data signal, converts this signal into the electrical domain and
re-transmits the signal at a specific wavelength using a 1,550 nm band laser.
 These data signals are then combined together into a multi-wavelength optical
signal using an optical multiplexer, for transmission over a single fiber.
 The terminal multiplexer may or may not also include a local transmit EDFA for
power amplification of the multi-wavelength optical signal.
 In the mid-1990s DWDM systems contained 4 or 8 wavelength-converting
transponders.
 Commercial systems capable of carrying 128 signals were available.
19

Dense WDM
2.An intermediate line repeater
 This repeater is placed approximately every 80–100 km to compensate
for the loss of optical power as the signal travels along the fiber.
 The "multi-wavelength optical signal" is amplified by an EDFA, which
usually consists of several amplifier stages.
3.An intermediate optical terminal, or optical add-drop multiplexer
 This is a remote amplification site that amplifies the multi-wavelength
signal that may have traversed up to 140 km or more.
 Optical diagnostics and telemetry are often extracted or inserted at
such a site, to allow for localization of any fiber breaks or signal
impairments.
 Several signals out of the multi-wavelength optical signal may be
removed and dropped locally.
20

Dense WDM
4.A DWDM terminal demultiplexer
 At the remote site, the terminal de-multiplexer consisting of an optical
de-multiplexer.
 One or more wavelength-converting transponders separates the multi-
wavelength optical signal back into individual data signals and outputs
them on separate fibers for client-layer systems.
 This de-multiplexing was performed entirely passively
 De-multiplexed signals are usually sent to O/E/O output transponders.
 The output transponder has been integrated into that of input
transponder.
 Most commercial systems support bi-directional interfaces on both
internal side and external side. Transponders may also perform
forward error correction (FEC) via digital wrapper technology.
21

Dense WDM
5. Optical Supervisory Channel (OSC).
 This is data channel which uses an additional wavelength
usually outside the EDFA amplification band.
 The OSC carries information about the multi-wavelength optical
signal as well as remote conditions at the optical terminal or
EDFA site.
 It is also normally used for remote software upgrades and User
Network Management information.
 It is the multi-wavelength analogue to SONET's DCC.
 The OSC should utilize an OC-3 signal structure have opted to
use 100 megabit Ethernet
22

Orthogonal Frequency Division Multiplexing (OFDM)
 Orthogonal Frequency-Division Multiplexing
(OFDM) is a method of digital signal
modulation in which a single data stream is
split across several separate narrowband
channels at different frequencies to reduce
interference and crosstalk.
 System bandwidth is divided into a set of
parallel overlapping, yet orthogonal sub-
bands independent to each other
 Data is first split into independent streams,
which modulate different sub-carriers
 Then are multiplexed to create OFDM
signal
 OFDM is a special case of FDM
 Significantly improves spectral efficiency
 Avoid the need for steep band pass filters
 Avoids the need of a bank of oscillators,
since can be implanted digitally.
 *
23

 OFDM is a technique, method or
scheme for digital multi-carrier
modulation using many closely
spaced subcarriers - a previously
modulated signal modulated into
another signal of higher frequency and
bandwidth.
 Each of these subcarriers contains
numbers of parallel data streams or
channels and is modulated
conventionally at a low symbol rate.
 These are groups of bits of data
related to gross bit rate, which is
expressed in bits/second.
 This term is also known as coded
OFDM (COFDM) and Discrete Multi-
Tone modulation (DMT), used for
both wireless and physical
communication mediums.
24

 The term "orthogonal” is actually an
adjective describing two things acting
independently or in an uncorrelated
manner.
 Any two signals of an OFDM-based product
operating without dependence on one
another.
 OFDM is used for wideband digital
communication, which is commonly used
for digital television and audio broadcasting
(radio) as well as broadband Internet
access and wireless networking.
 OFDM is very similar to FDM (frequency
division multiplexing) but with technology
purposely emphasizing the minimization of
crosstalk or signal interference from other
nearby signal carrying communication
mediums.
 OFDM uses many narrow band signals as
opposed to a signal modulated at a high
symbol rate and a large bandwidth.
 *
25

 *
 *
26

ADVANTAGES
 Permits densely packed & overlapping sub-carriers
 Offers spectrally efficient transmission scheme
 Can be digitally implemented using, fast & efficient signal processing
 Permits flexible use of spectrum
 Supports different modulation schemes based on channel conditions
 Almost completely avoids the need for an equalizer
27

Shared Media Networks
 A local area network (LAN) that
shares its total available bandwidth
with all transmitting stations.
 Ethernet is the primary example,
although Token Ring and FDDI
networks were earlier examples.
 In the past, when shared media
LANs ran out of capacity to serve
their users effectively, they were
upgraded by replacing the network
hubs with switches.
 *
28

Shared media networks
 Need arbitration to decide who gets to
talk
 Arbitration can be centralized or
distributed
 Centralized not used much for networks
 Special arbiter device (or must elect
arbiter)
 Good performance if arbiter far away?
Nah.
 Distributed arbitration
 Check if media already used (carrier
sensing)
 If media not used now, start sending
Check if another also sending (collision
detection)
 If collision, wait for a while and retry
 “For a while” is random (otherwise
collisions repeat forever)
 Exponential back-off to avoid wasting
bandwidth on collisions
 *
29

Switched networks
 A fully switched network is a computer
network which uses only network
switches rather than Ethernet hubs on
Ethernet networks.
[1] The switches allow for a dedicated
connection to each workstation.
 A switch allows for many conversations to
occur simultaneously.
 Before switches existed data could only
be transmitted in one direction at a time,
this was called half-duplex.
 By using a switch the network is able to
maintain full-duplex Ethernet and makes it
collision free.
[2] This means that data can now be
transmitted in both directions at the same
time.
 Fully switched networks employ either
twisted-pair or fiber-optic cabling, both of
which use separate conductors for
sending and receiving data.
30

Switched networks
[3] In this type of environment, Ethernet nodes can forgo the collision
detection process and transmit at will, since they are the only potential
devices that can access the medium.
 This means that a fully switched network is a collision-free environment.
 The core function of a switch is to allow each workstation to communicate
only with the switch instead of with each other.
 This means that data can be sent from workstation to switch and from
switch to workstation simultaneously.
 The core purpose of a switch is to decongest network flow to the
workstations so that the connections can transmit more effectively
receiving transmissions that were only specific to their network address.
Example:
If your network speed is 5 Mbit/s, then each workstation is able to
simultaneously transfer data at 5 Mbit/s.
31

End-to-end semantics – Connection oriented and connectionless protocol
Connection-Oriented Protocol
 In a connection-oriented protocol, a logical
connection should first be established
between the two nodes.
 After all frames that are somehow related to
each other are transmitted, the logical
connection is terminated.
 In this type of communication, the frames
are numbered and sent in order.
 If they are not received in order, the receiver
needs to wait until all frames belonging to
the same set are received and then deliver
them in order to the network layer.
 Connection-oriented protocols are rare in
wired LANs, but we can see them in some
point-to-point protocols, some wireless
LANs, and some WANs.
32

Connectionless Protocol
 In a connectionless protocol, frames are
sent from one node to the next without any
relationship between the frames.
 Each frame is independent.
 The term connectionless here does not
mean that there is no physical connection
(transmission medium) between the nodes.
 It means that there is no connection
between frames.
 The frames are not numbered and there is
no sense of ordering.
 Most of the data-link protocols for LANs are
connectionless protocols.
 Connection-less service is analogous to the
postal system.
33
 It uses packet switching for transmission of
data.
 The Internet Protocol (IP), and the User
Datagram Protocol (UDP) provides
connection-less service.

The points given below explains the difference
between connection oriented and connection-less
services:
1. There is a requirement for prior connection for
communication in connection-oriented services, in
contrast, it is not needed in connection-less
services.
2. Reliability is more in connection-oriented as
compared to connectionless services.
3. Traffic congestion is greater in connection-less
services whereas its occurrence is rare in
connection-oriented services.
4. In connection-oriented services order of packets
received at the destination is same as sent from
the source. On the contrary, order might change in
connection-less services.
5. All packets follow the same path in connection-
oriented services while packets follow a random
path to reach the destination in connectionless
services.
6. Connection-oriented service is appropriate for long
and steady communication whereas connection-
less service is fit for bursty transmission.
34
7. In connection-oriented services sender and
receiver are synchronized with each other
while it is not the case of connection-less
services.
8. Connection-oriented services uses circuit
switching on the other hand packet
switching is used in connection-less
services.
9. Bandwidth requirement is higher in
Connection-oriented services whereas its
low in connection-less services.

Wireless Scenarios
 Wireless networks operate using radio
frequency (RF) technology.
 Frequency within the electromagnetic spectrum
associated with radio wave propagation.
 When an RF current is supplied to an antenna,
an electromagnetic field is created that then is
able to propagate through space.
 The cornerstone of a wireless network is a
device known as an access point (AP).
 The access point is to broadcast a wireless
signal that computers can detect and "tune"
into.
 Since wireless networks are usually connected
to wired ones.
 To connect to an access point and join a
wireless network, computers must be equipped
with wireless network adapters.
 These are often built right into the computer.
35
The common wireless technology
standards include the following:
802.11b: The first widely used wireless
networking technology, known as 802.11b
(more commonly called Wi-Fi)
802.11g: In 2003, a follow-on version
called 802.11g appeared offering greater
performance (that is, speed and range).
802.11n: Another improved standard called
802.11n is currently under development.

Wireless Scenarios
Applications of Wireless
Communication.
It involve security systems, television
remote control, Wi-Fi, Cell phones,
wireless power transfer, computer
interface devices and various
wireless communication based
projects.
Quality of service (QoS) for wireless.
QOS is an important topic because it
can lead, if misunderstood, to many
structural mistakes in wireless
networks deployments and poor
quality when QoS-dependent devices
are added.
37
QoS can be implemented in three
different ways:
1.Best effort, this is basically “no
implementation”
2.Integrated services (IntServ), also
called “hard” QoS
3.Differentiated services (DiffServ),
the most common method

End-to-End Solution (E2ES)
 An end-to-end solution (E2ES) is a term that
means that the provider of an application
program, software and system will supply all
the software as well as hardware
requirements of the customer such that no
other vendor is involved to meet the needs.
 E2ES includes installation, integration, and
setup.
 End-to-end solutions provide implementation
while being attentive to smart and efficient
ways of setting up a business.
 The systems are set up ensuring minimum
costs, incorporating the best material and
producing the best infrastructure according
to the demand of business.
 End-to-end solution greatly reduces hassle,
costs, resources and time.
38
 *
 Project managers often prefer to use end-to-end
solution services to keep pace with ever-
changing infrastructure and business needs.
 A project is handled by only one vendor, working
from beginning to completion, without the direct
involvement of any other third party.

Network level solutions
If the goal of security is to prevent the
unauthorised discovery of information
or use of resources, then one way of
meeting this goal is to prevent intruders
being able to read or access the
protected information.
If the intruder cannot copy the
communication data, then they cannot
read it.
So the first level of security is to
implement network level solutions to
prevent the traffic being visible to
potential miscreants.
39
*

LAN Cabling Topologies – Ethernet switches
 Switches operate at the Date Link
Layer(L2) of the OSI model. It can
interpret address information.
 Switches resemble bridges and can be
considered as multi-port bridges.
 By having multi-ports, can better use
limited bandwidth and prove more cost-
effective than bridge.
 Switches divide a network into several
isolated channels.
 Packets sending from 1 channel will not
go to another if not specify.
 Each channel has its own capacity and
need not be shared with other
channels.
40
 *

LAN Cabling Topologies – Ethernet switches
Advantages
1. Switches divide a network into several
isolated channels.
2. Reduce the possibility of collision.
3. Collision only occurs when two devices
try to get access to one channel.
4. It can be solved by buffering one of them
for later access.
5. Each channel has own network capacity.
6. Suitable for real-time e.g. Video
conferencing.
Limitations
1. Buffers to accommodate bursts of traffic,
can become overwhelmed by heavy
traffic.
2. Device cannot detect collision when
buffer full
41
 CSMA/CD scheme will not work
because of data channels are isolated.
 Some higher level protocols do not
detect error
eg:UDP

LAN Cabling Topologies – L3 switches
1. Layer 3 switches use network or IP
addresses that identify locations on the
network.
2. They read network addresses more closely
than Layer 2 switches.
3. They identify network locations as well as the
physical device.
4. A location can be a LAN workstation, a
location in a computer memory or even a
different packet of data travelling through a
network.
5. Switches operating at Layer 3 are smarter
than Layer 2 devices and incorporate routing
functions to actively calculate the best way to
send a packet to the destination.
6. But although they are smarter, they may not
be as fast as their algorithms, fabric and
processor do not support high speeds.
42
Figure : Layer 2 & Layer 3 in OSI model.

LAN Cabling Topologies – Routers
1. Router is a device that forwards the data
packets to parts of a computer network.
2. Routers are physical devices that join
multiple network together.
3. Routers operate at the physical, data link and
network layer in OSI model.
4. Routers consists of combination of the
hardware and software.
5. A router normally connect LANs and WANs in
the internet.
6. A router has a routing table that is used for
making decisions about the route.
7. Routers connect dissimilar network together
and have access to information from
physical, data link and network layer.
8. The key feature of a router is to determine
the shortest path to destination.
43
 Router uses or more routing algorithms to
calculate the best path through an
internetwork.

LAN Cabling Topologies – Firewalls
1. In computing, a firewall is a network security
system that monitors and controls incoming
and outgoing network traffic based on
predetermined security rules.
2. A firewall typically establishes a barrier
between a trusted internal network and
untrusted external network, such as the
Internet.
3. Firewalls are often categorized as either
network firewalls or host-based firewalls.
4. Network firewalls filter traffic between two
or more networks and run on network
hardware.
5. Host-based firewalls run on host
computers and control network traffic in
and out of those machines.
44
Figure : An illustration of where a firewall would
be located in a network
1.First generation: packet filters
 The firewall shows its settings for incoming
and outgoing traffic.
 The first network firewall is called a packet
filter.
 Packet filters look at network addresses
and ports of packets to determine if they
must be allowed, dropped, or rejected.

LAN Cabling Topologies – Firewalls
2.Second generation: "stateful" filters
1. Second-generation firewalls perform the
work of their first-generation
predecessors but operate up to layer 4
(transport layer) of the OSI model.
2. This is achieved by retaining packets until
enough information is available to make a
judgment about its state known as stateful
packet inspection.
3.Third generation: application layer
1. The key benefit of application layer filtering
is that it can "understand" certain
applications and protocols (such as File
Transfer Protocol (FTP), Domain Name
System (DNS), or Hypertext Transfer
Protocol (HTTP)).
45
Figure : An illustration of where a firewall would
be located in a network
 This is useful as it is able to detect if an
unwanted application or service is
attempting to bypass the firewall using a
protocol on an allowed port, or detect if a
protocol is being abused in any harmful
way.

Remote Access Technologies & Devices - Modem
 The term modem is a composite word that
refers to the two functional entities that make
up the device: a signal modulator and a
signal demodulator.
 A modulator creates a bandpass analog
signal from binary data.
 A demodulator recovers the binary data from
the modulated signal.
 Modem stands for modulator/demodulator.
 Figure shows the relationship of modems to
a communications link.
 The computer on the left sends a digital
signal to the modulator portion of the
modem.
 The data are sent as an analog signal on the
telephone lines.
46
 *
 The modem on the right receives the
analog signal, demodulates it through its
demodulator, and delivers data to the
computer on the right.
 The communication can be bidirectional,
which means the computer on the right
can simultaneously send data to the
computer on the left, using the same
modulation/demodulation processes.

56K modems
 Traditional modems have a data rate
limitation of 33.6 kbps. However, modern
modems with a bit rate of 56,000 bps are
available, these are called 56K modems.
 These modems may be used only if one
party is using digital signaling.
 They are asymmetric in that the
downloading rate, is a maximum of 56
kbps, while the uploading rate can be a
maximum of 33.6 kbps. (Figure).
47
 In uploading, the analog signal must still be
sampled at the switching station.
 In this direction, quantization noise is
introduced into the signal, which reduces
the SNR ratio and limits the rate to 33.6
kbps.
 However, there is no sampling in the
downloading. The signal is not affected by
quantization noise.
 The maximum data rate in the uploading
direction is still 33.6 kbps, but the data rate
in the downloading direction is now 56
kbps.

56K modems
Example:
 The telephone companies sample 8000
times per second with 8 bits per
sample.
 One of the bits in each sample is used
for control purposes, which means
each sample is 7 bits.
 The rate is therefore 8000 × 7, or
56,000 bps or 56 kbps.
48
*

Digital Subscriber Line (DSL)
 Telephone companies developed another
technology, DSL, to provide higher-speed
access to the Internet.
 Digital subscriber line (DSL) technology is
one of the most promising for supporting
high-speed digital communication over
the existing telephone.
 DSL technology is a set of technologies,
each differing in the first letter (ADSL,
VDSL, HDSL, and SDSL).
 The set is often referred to as xDSL,
where x can be replaced by A, V, H, or S.
 The first technology in the set is
asymmetric DSL (ADSL).
49
 ADSL, like a 56K modem, provides
higher speed in the downstream
direction than in the upstream
direction.
 That is the reason it is called
asymmetric.
 The designers of ADSL specifically
divided the available bandwidth of the
local loop unevenly for the residential
customer.
 The service is not suitable for
business customers who need a large
bandwidth in both directions.
Types:
1.ADSL
2.ADSL Lite
3.HDSL
4.VDSL

Using Existing Local Loops
 ADSL uses the existing telephone lines
(local loop).
 But how does ADSL reach a data rate that
was never achieved with traditional
modems?
 The answer is that the twisted-pair cable
used in telephone lines is actually capable of
handling bandwidths up to 1.1 MHz.
50
 But the filter installed at the end office of the
telephone company where each local loop
terminates limits the bandwidth to 4 kHz
(sufficient for voice communication).
 If the filter is removed, however, the entire 1.1
MHz is available for data and voice
communications.
 An available bandwidth of 1.104 MHz is
divided into a voice channel, an upstream
channel, and a downstream channel, as
shown in Figure.

Using Existing Local Loops
 ADSL allows the subscriber to use the voice
channel and the data channel at the same
time.
 The rate for the upstream can reach
1.44-Mbps. However, the data rate is
normally below 500 kbps because of the
high-level noise in this channel.
51
 The downstream data rate can reach 13.4
Mbps. However, the data rate is normally
below 8 Mbps because of noise in this
channel.
 The telephone company in this case
serves as the ISP, so services such as e-
mail or Internet access are provided by the
telephone company itself.

ADSL Lite
 A new version of of ADSL technology called
ADSL Lite.
 It is available for these subscribers. This
technology allows an ADSL Lite modem to
be plugged directly into a telephone jack and
connected to the computer.
 ADSL Lite uses 256 Discrete Multitone
Technique(DMT) with 8-bit modulation.
 It can provide a maximum downstream data
rate of 1.5Mbps and an upstream data rate
of 512Kbps
HDSL(High-bit-rate Digital Subscriber Line)
 HDSL was designed as an alternative to the
T-1 line(i.e.1.55Mbps).
 The length of a T-1 line to 3200ft.
 A repeater is used for long distance.
52
 HDSL uses 2B1Q encoding, which is less
susceptible to attenuation.
 A date rate of 1.544Kbps can be achieved
up to 12,000ft.
 HDSL uses two twister pairs for full-duplex
transmission.
SDSL(Symmetric Digital Subscriber Line)
 The SDSL is a one twisted-pair version of
HDSL.
 It provides full-duplex symmetric
communication supporting up to 768 kbps.
 SDSL provides symmetric communication,
can be consider an alternative to ADSL.
 These feature meets the needs of most
residential subscribers.
 It is not suitable for business that send and
received data in large volumes in both
directions.

VDSL(Very high-bit-rate Digital
Subscriber Line)
 The VDSL an alternative approach that is
similar to ADSL, uses coaxial, fiber-optis or
twised-pair cable for short distances.
 This modulated technique is DMT.
 The upstream rate is 55Mbps and
downstream rate is 25 to 55 Mbps.
 Support 3000 to 10000ft.
 Figure 9.10 Discrete multitone technique
53
 1.SLIP is obsolete and has been replaced by
PPP in most applications.
 2.PPP can auto-configure settings while SLIP
cannot.
 3.PPP provides error detection and recovery
while SLIP doesn’t.
 4.SLIP has very minimal overhead compared
to PPP.
 *

Serial Line Internet Protocol(SLIP)
 The Serial Line Internet Protocol (also SLIP) is an encapsulation of the
Internet Protocol designed to work over serial ports and modem
connections.
 On personal computers, SLIP has been largely replaced by the Point-to-
Point Protocol (PPP), which is better engineered, has more features and
does not require its IP address configuration to be set before it is
established.
 On microcontrollers, however, SLIP is still the preferred way of
encapsulating IP packets due to its very small overhead.
54

 It is a means of sending Internet Protocol datagrams over a serial link.
 It can be used by two systems to communicate via a direct cable connection or
modem link.
 The initial purpose of this protocol was to connect Sun workstation to the Internet over
a dial-up line using modem.
DISADVANTAGES
 IP addresses must be preconfigured
No dynamic assignment
 No protocol (type) field
Only defined to transport IP packets
 No Frame Check Sequence (FCS)
Higher layers must care!
But higher layers just use checksums (CRC would be better)
 Inconstant overhead
Depends on data pattern.
55

Data Format of SLIP
 The data format of SLIP is:
 A special END character marks the end of data.
56

Point-to-Point Protocol (PPP)
 PPP was devised by IETF (Internet Engineering Task Force) to create a
data link protocol for point-to-point lines that can solve all the problems of
SLIP.
 It is the most commonly used data link protocol.
 It is used to connect the home PC to the ISP server.
Benefits of PPP
 PPP defines the format of the frame to be exchanged between the
devices.
 It defines Link Control Protocol (LCP) for:
Establishing the link between two devices.
Maintaining this established link.
Configuring this link.
Terminating this link after the transfer.
57

Point-to-Point Protocol (PPP)
It provides error detection.
Unlike SLIP, that supports only IP, it supports multiple protocols.
It supports dynamic allocation of IP address.
It provides authentication.
It provides NCP (Network Control Protocol), that supports variety
of network layer protocol.
Such as Assignment and management of IP addresses and
Compression and authentication
58

PPP Frame Format
 Frame format of PPP is similar to HDLC frame:
 Flag Field: It marks the beginning and end of the PPP frame. Flag byte
is 01111110.
 Address Field: This field is of 1 byte and is always 11111111. This
address is the broadcast address i.e. all stations accept this frame.
 Control Field: It is also of 1 byte. It uses the format of U-Frame in
HDLC. The value is always 00000011 to show that the frame does not
contain any sequence number and there is no flow control or error
control.
 Protocol Field: This field specifies the kind of protocol of the data in the
information field.
59

PPP Frame Format
Frame format of PPP is similar to HDLC frame:
Information Field: Its length is variable. It carries user data or
other information.
FCS Field: It stands for Frame Check Sequence. It contains
checksum. It is either 2 bytes or 4 bytes.
60

Core Network
 The core network was the central part of a telecommunications network
that provided various services to customers who were connected by the
access network.
 One of the main functions was to route telephone calls across the PSTN.
 Typically the term referred to the high capacity communication facilities
that connect primary nodes.
 A core network provided paths for the exchange of information between
different sub-networks.
 Core networks usually had a mesh topology that provided any-to-any
connections among devices on the network.
 Many main service providers would have their own core/backbone
networks that are interconnected.
 Some large enterprises have their own core/backbone network, which
are typically connected to the public networks.
61

Core Network
Core networks typically provided the following functionality:
 Aggregation: The highest level of aggregation in a service provider
network. The next level in the hierarchy under the core nodes is the
distribution networks and then the edge networks.
 Customer-premises equipment (CPE) do not normally connect to the
core networks of a large service provider.
 Authentication: The function to decide whether the user requesting a
service from the telecom network is authorized to do so within this
network or not.
 Call Control/Switching: call control or switching functionality decides
the future course of call based on the call signalling processing.
E.g. switching functionality may decide based on the "called number" that
the call be routed towards a subscriber within this operator's network or
with number portability more prevalent to another operator's network.
62

Core Network
Core networks typically provided the following functionality:
 Charging: This functionality handles the collation and processing of
charging data generated by various network nodes.
 Two common types of charging mechanisms found in present-day
networks are prepaid charging and postpaid charging.
Ex.Automatic Message Accounting
 Service Invocation: Core network performs the task of service
invocation for its subscribers. Service invocation may happen based on
some explicit action (e.g. call transfer) by user or implicitly (call waiting).
 Its important to note however that service "execution" may or may not be
a core network functionality as third party network/nodes may take part in
actual service execution.
 Gateways: Gateways shall be present in the core network to access
other networks. Gateway functionality is dependent on the type of
network it interfaces with.
63

Distributed Network
A distributed network is a type of
computer network that is spread
over different networks.
This provides a single data
communication network, which
can be managed jointly or
separately by each network.
Besides shared communication
within the network, a distributed
network often also distributes
processing.
64
 *
Figure:The typical hierarchical design model is
broken up in to three networks:
Access, Distribution and Core.

Multiplexing,LAN Cabling,Routers,Core and Distribution Networks

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