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Network Operations & administration CS 4592
Lecture 10
Instructor: Ibrahim Tariq
5.2
5-2 ANALOG AND DIGITAL
Analog-to-analog conversion is the representation of analog information by an analog signal. One may ask why we need to modulate an analog signal; it is already analog. Modulation is needed if the medium is bandpass in nature or if only a bandpass channel is available to us.
Amplitude ModulationFrequency ModulationPhase Modulation
Topics discussed in this section:
5.3
Types of analog-to-analog modulation
5.4
Amplitude modulation
5
Amplitude Modulation
5.6
The total bandwidth required for AM can be determined
from the bandwidth of the audio signal: BAM = 2B.
Note
5.7
AM band allocation
5.8
The total bandwidth required for FM can be determined from the bandwidth
of the audio signal: BFM = 2(1 + β)B.
Note
5.9
Frequency modulation
10
Frequency Modulation
5.11
FM band allocation
5.12
Phase modulation
13
Phase Modulation
Packet Switching Vs Circuit Switching
Packet-switched and circuit-switched networks use two different technologies for sending messages and data from one point to another.
Each have their advantages and disadvantages depending on what you are trying to do.
Packet Switching
• In packet-based networks, the message gets broken into small data packets.
• These packets seek out the most efficient route to travel as circuits become available.
• Each packet may go a different route from the others.
Packet Switching
• Each packet is sent with a ‘header address’ for final destination
• The header address describes the sequence so that the packets are put back into the correct order.
• One packet contains details of how many packets should be arriving.
• If a packet fails to arrive, the recipient computer sends a message back to the computer asking for the missing packet to be resent.
Packet Switching
Difference between circuit switching and packet switching: – Packet Switching• Message is broken up into segments (packets). • Each packet carries the identification of the intended
recipient, data used to assist in data correction and the position of the packet in the sequence. • Each packet is treated individually by the switching
centre and may be sent to the destination by a totally different route to all the others.
Packet Switching
Packet Switching– Advantages:• Security• Bandwidth used to full potential• Devices of different speeds can communicate• Not affected by line failure (rediverts signal)• Availability – do not have to wait for a direct
connection to become available• During a crisis or disaster, when the public
telephone network might stop working, e-mails and texts can still be sent via packet switching
Packet Switching
Disadvantages• Under heavy use there can be a delay• Data packets can get lost or become
corrupted• Protocols are needed for a reliable transfer• Not so good for some types data streams
e.g real-time video streams can lose frames due to the way packets arrive out of sequence.
Circuit Switching
• Circuit switching was designed in 1878 in order to send telephone calls down a dedicated channel.
• This channel remained open and in use throughout the whole call and could not be used by any other data or phone calls.
Circuit Switching
• There are three phases in circuit switching:– Establish– Transfer– Disconnect
• The telephone message is sent in one go, it is not broken up. The message arrives in the same order that it was originally sent.
Circuit Switching
• In modern circuit-switched networks, electronic signals pass through several switches before a connection is established.
• During a call, no other network traffic can use those switches.
• The resources remain dedicated to the circuit during the entire data transfer and the entire message follows the same path.
• Circuit switching can be analogue or digital
Circuit Switching
• With the expanded use of the Internet for voice and video, analysts predict a gradual shift away from circuit-switched networks.
• A circuit-switched network is excellent for data that needs a constant link from end-to-end. For example real-time video.
Circuit Switching• Circuit Switching
– Advantages:• Circuit is dedicated to the call – no
interference, no sharing• Guaranteed the full bandwidth for the
duration of the call• Guaranteed Quality of Service
Circuit Switching
Disadvantages:• Inefficient – the equipment may be unused
for a lot of the call, if no data is being sent, the dedicated line still remains open• Takes a relatively long time to set up the
circuit• During a crisis or disaster, the network may
become unstable or unavailable.• It was primarily developed for voice traffic
rather than data traffic.
9.26
9-1 TELEPHONE NETWORK
Telephone networks use circuit switching. The telephone network had its beginnings in the late 1800s. The entire network, which is referred to as the plain old telephone system (POTS), was originally an analog system using analog signals to transmit voice.
9.27
A telephone system
Endoffices
Local loop
Trunk
Tandemoffices Regional offices
Trunk
• • •
9.28
The tasks of data transfer and signaling are separated in modern telephone networks: data transfer is done by one
network, signaling by another.
Note
9.29
Data transfer and signaling networks
9.30
Layers in SS7
9.31
DIAL-UP MODEMS
Traditional telephone lines can carry frequencies between 300 and 3300 Hz, giving them a bandwidth of 3000 Hz. All this range is used for transmitting voice, where a great deal of interference and distortion can be accepted without loss of intelligibility.
9.32
Telephone line bandwidth
9.33
Modemstands for modulator/demodulator.
Note
9.34
Modulation/demodulation
9.35
Figure 9.8 The V.32 and V.32bis constellation and bandwidth
9.36
Figure 9.9 Uploading and downloading in 56K modems
9.37
9-3 DIGITAL SUBSCRIBER LINE
After traditional modems reached their peak data rate, 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 local loops.
ADSLADSL LiteHDSLSDSLVDSL
Topics discussed in this section:
9.38
ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses.
Note
9.39
ADSL is an adaptive technology. The system uses a data ratebased on the condition of
the local loop line.
Note
9.40
Discrete multitone technique
9.41
Figure 9.11 Bandwidth division in ADSL
9.42
ADSL modem
9.43
DSLAM
9.44
Summary of DSL technologies