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Network Operations & administration CS 4592 Lecture 10

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1 Network Operations & administration CS 4592 Lecture 10
Instructor: Ibrahim Tariq 1.#

2 Topics discussed in this section:
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. Topics discussed in this section: Amplitude Modulation Frequency Modulation Phase Modulation

3 Types of analog-to-analog modulation

4 Amplitude modulation

5 Amplitude Modulation

6 Note from the bandwidth of the audio signal: BAM = 2B.
The total bandwidth required for AM can be determined from the bandwidth of the audio signal: BAM = 2B.

7 AM band allocation

8 Note The total bandwidth required for FM can be determined from the bandwidth of the audio signal: BFM = 2(1 + β)B.

9 Frequency modulation

10 Frequency Modulation

11 FM band allocation

12 Phase modulation

13 Phase Modulation

14 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.

15 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.

16 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.

17 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.

18 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, s and texts can still be sent via packet switching

19 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.

20 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.

21 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.

22 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

23 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.

24 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

25 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.

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.

27 A telephone system

28 Note The tasks of data transfer and signaling are separated in modern telephone networks: data transfer is done by one network, signaling by another.

29 Data transfer and signaling networks

30 Layers in SS7

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.

32 Telephone line bandwidth

33 stands for modulator/demodulator.
Note Modem stands for modulator/demodulator.

34 Modulation/demodulation

35 Figure 9.8 The V.32 and V.32bis constellation and bandwidth

36 Figure 9.9 Uploading and downloading in 56K modems

37 Topics discussed in this section:
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. Topics discussed in this section: ADSL ADSL Lite HDSL SDSL VDSL

38 Note ADSL is an asymmetric communication technology designed for residential users; it is not suitable for businesses.

39 Note ADSL is an adaptive technology. The system uses a data rate
based on the condition of the local loop line.

40 Discrete multitone technique

41 Figure 9.11 Bandwidth division in ADSL

42 ADSL modem


44 Summary of DSL technologies

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