COMMUNICATION TECHNOLOGY

by

Shashi BhushanSchool of Computer and Information Sciences

Communication Technologies

• ATM

• FDDI

• Fast Ethernet

• WAP, GSM

ATM

• Analyse the type of connection to be made.

• Analyse the type of data to be transmitted and knowing its traffic profile.

ATM

• Reserve a virtual path for the data to allow

• Splitting the data into small packets which have minimum overhead

Type of Connection

• Dependent upon type of data

• Computer data requires a reliable connection

Traffic Profile of Data

• Computer data tends to create bursts of traffic

• Real time data requires constant traffic

ATM

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

1 2 3 4 5 6 7 8 9 10 11

Example Traffic Profile for speech signal

ATM

0

0.2

0.4

0.6

0.8

1

1.21 3 5 7 9

11

13

15

17

19

21

23

25

27

29

Example Traffic Profile for computer-type data

ATM

Integrate real-time data (such as voice and video signals) and non-real-time data (such as computer data).

Objective of ATM

• Connection should be free of errors for computer type data

• Real time data are more tolerant to errors any losses of small part the data

Objective of ATM

• For real time data, constant sampling rate and low propagation delay required

Real Time Sampling

The basic principle in analog to digital conversion involves:

• Sampling Theory

• Pulse Code Modulation (PCM)

Sampling Theory

If a signal is to be reconstructed as the original signal, it must be sampled at a rate defined by the Nyquist Criterion.

Ts

Sampling

The Sampling Process

Sampling Theory

The sampling rate must be twice the highest frequency of the signal.

Sampling Theory

Type of Data Frequency Range (Bandwidth)

Sampling Rate

Speech (Telephone Channel)

4 khz 8000 time per second (8kz every 125 s)

Hi-fi quality audio

20 khz 40000 times per second

Video Signal 6 mhz 12mhz (or once every 83.3ns)

PCM

Once analog signals have been sampled for their amplitude, they can be converted into a digital format using PCM. The digital form is then transmitted over the transmission media.

Technology used in Transmitting Digital Signals

• PCM-TDM

• ISDN (Integrated Services Digital Network)

ATM Vs ISDN & PCM-TDM

ISDN & PCM-TDM uses a synchronous transfer mode (STM) technique where a connection is made between two devices by circuit switching.

The main problems with this type of transmission are:

• Fixed time slots, no matter whether data is being transmitted or not

ATM Vs ISDN & PCM-TDM

• Not possible to service high burst rate by allocating either time slots or switched circuits when all of the other time slots are full, or because switched circuits are being used.

ATM Vs ISDN & PCM-TDM

ATM

ATM overcomes these problems by–

• Splitting the data up into small length packets, known as cells

• Statistical multiplexing

ISDN

ISDN uses transmission bit rate of 64 kbps. This is the same as digitized speech signal rate.

ISDN

Digitized speech signal rate = 8

Sampling rate bits used for sampling

= 8 khz 8 bits = 64 kbps

ISDN

Computer type data can be transmitted using 64 kbps rate or can be split to transmit over several 64 kbps channels.

ISDN Channels

ISDN uses channels to identify the data rate, each based on the 64 kbps provisions.

ISDN Channels

CHANNEL DESCRIPTION

B 64 kbps

D • 16 kbps signalling for channel B (ISDN)

• 64 kbps signalling for channel B (B-ISDN)

ISDN Channels

H0 384 kbps (6 64 kbps) for B-ISDN

H11 1.536 mbps (26 64 kbps) for B-ISDN

H12 1.920 mbps (30 64 kbps) for B-ISDN

Ethernet

• Most commonly used LAN

• Based on IEEE 802.3 standard

• Requires other protocols such as TCP/IP to allow nodes to communicate

Ethernet

• Ethernet networks are easy to plan and cheap to install

• Well proven technology, which is fairly robust and reliable

• Simple to add and delete computers on the network

Ethernet

Drawback

• Not deterministic

• Does not cope with heavy traffic

Bit Rate

• 10 kbps – In its standard form

• 100 kbps – Fast Ethernet

• 1 gbps – Fast Ethernet

Ethernet

• Use of coaxial, fiber optic or twisted-pair cable

• Use of bus-type network topology where all nodes share a common bus

• Use of CSMA/CD

Ethernet Types

The six main types of standard Ethernet are:

• Standard or thick-wire, Ethernet (10BASE5)

• Thinnet or thin wire (10BASE2)

• Twisted pair Ethernet (10BASE-T)

Ethernet Types

• Optical Fiber Ethernet (10BASE-FL)

• Fast Ethernet

• Gigabit Ethernet

10BASE5 Parameters

• Data rate – 10Mbps

• Max. Segment Length – 500m

• Max. nodes on a segment – 100

• Max. number of repeaters – 2

10BASE5 Parameters

• Max. nodes per Network – 1024

• Min. node spacing – 2.5m