CS-09 – Data Communications and Networks

 

 

AGENDA (Session 3)

 

 

Quiz

 

Novell Netware

 

SMDS

 

X.25

 

Frame Relay

 

B-ISDN, ATM

 

Physical Layer

 

Nyquist, Shannon Theorem

 

Transmission Media

                                     

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Quiz

 

 

1. Layer Protocol Mean

a)     Direct Communication Between two layers on a host side.

b)     Direct Peer to Peer Communication.

c)     Virtual Communication between peer entities.

d)     Group of all protocols of any layer.

 

2. Packetisation Increases Transmission Efficiency.         TRUE/FALSE

 

3. Compared to old days of data-networking the error-rate is reduced in today’s communication systems. Why?

a)     Better Physical Mediums have now been discovered.

b)     Man has learnt to reduce cosmic noise.

c)     We have faster computers available now.

d)     Bulk of the communication is now satellite based.

 

4. ‘ICI’ stands for

a)     Interface Control Information

b)     Information Control & Interchange

c)     Interchange of Control Information

d)     Internet Control Information

 

5. Which one of the following is not true about a connectionless service.

a)     They are also called datagram services.

b)     It is an online connectivity system.

c)     Packets of same message can take different routes.

d)     It does have a model with acknowledgement.

 

6. In OSI model transport layer handles

a)     Data-Frame Acknowledgement

b)     Bit Transfer

c)     Packet Routing

d)     Packetisation and Packet Assembly

 

7. Software/Hardware residing on routers in a Sub-net shall generally implement

a)     Data-link Layer

b)     Network Layer

c)     Physical Layer

d)     All the above

 

8. HTTP is _____________ layer protocol on TCP/IP model

a)     Transport

b)     Internet

c)     Application

d)     Host-to-Network

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Example Networks and Services: Novell Netware

·        Provided Mainframe to PC network Downsizing

·        Implement Client-Server Model

·        Based on XNS (Xerox Network System)

 

Layers

 

 

 

 

 

 

 

 

 


SAP = Service Advertising Protocol

NCP = Network Core Protocol

SPX

IPX

 

 

IPX Packet

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


SMDS – Switched MultiMegabit Data Services

 

·        Interconnected LANs.

·        Uses Switches instead dual bus in case of DQDB

·        Less costly than a fully Connected LAN

 

Separate LANs
 
 

 

 

 

 

 

 

 

 

 

 


Fully Connected requires n(n-1)/2 Lines

SMDS requires n Lines

 

SMDS Frame

 

 

 

 

 

 

 


·        Broadcast is allowed.

·        Payload can contain ethernet or token-ring packets.

·        Allows bursty traffic.

 

 

 

 

 

 

 

 

X.25 Network

 

·        Developed By CCITT in 1970.

·        Physical layer x.21 (least used).

·        Data-Link – Deals with errors (Many Variations)

·        Network Layer – Allows Virtual Circuits to send 128 byte packet.

·        Works at 64Kbps

·        Connection Oriented.

·        Switched or Permanent Virtual Circuits (SVC & PVC)

·        Terminal connected by Using PAD (Packet Assembler-Dissassembler) equipment.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


Frame Relay

 

 

·       Bare-bone connection oriented service.

·       Provides Virtual Leased Lines.

·       Offers Permanent Virtual Circuits.

·       Frame of upto 1600 Byte Data.

·       Multicasting with 10 bit address.

·       Speed in the order of 1.5 Mbps.

·       Basic Services

o     Start/End Frame Detection

o     Transmission Error Detection

·       Acknowledgement and Flow Control Missing.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Broadband ISDN - ATM

 

·       Vision of converting the entire analog Telephone System to digital one.

·       Video-on-demand, CD-Quality Music, High Speed Data Transport were expected services.

·       ATM (Asynchronous Transfer Mode) is the underlying technology.

·       Fixed Size Small Packets (53 Bytes) called CELLS.

 

 

 

 


·       Digital Cell Switching Technology is used as against analog Circuit Switching Technology.

·       Can handle Constant or variable speed traffic.

·       Can Handle TV data as broadcast is allowed.

·       Connection Oriented.

·       155.52 Basic rate (Compatible to SONET).

·       4x155.52 = 622.08 usual ATM rate.

·       Model designed is independent of Transmission Medium.

·       Three basic Layers – (Physical , ATM and ATM adaptation Layers)

·       Different functionality of these layers conceptualised to give rise to a 3 Dimensional Layer Model.

 

 

 

 

 

 

 

 

Physical Layer

 

·       Signal Energy reduces while transferring across a physical medium.

·       This reduction has relation with frequency of signal.

·       Each Signal (taken as a periodic function) can be assumed as composed of components of various frequencies.

·       Components can be mathematically derived by Fourier Analysis.

 

 

 

 

 

 

·       Time required to transmit is related to Signal Encoding and signal speed.

·       Number of times signal changes value/second = Baud Rate.

·       No. of Bits transferred per second = Bit rate

·       Bit Rate = Baud Rate (for digital 0 & 1 Transfer)

 

 

 

 

 

 

 

Maximum rate of Data Transfer

 

Nyquist’s Theorem

 

·        Considers noiseless channel.

 

Maximum Data Rate = 2 H Log2 V Bits/Sec

 

H = Bandwidth

V = No. Of discrete Levels

 

e.g.

4000 Hz with 0&1 levels would require 8000 bits/sec sampling to reproduce the signal for a noiseless channel environment.

 

 

Shannon’s Theorem

 

·        Considers channels with Signal and Noise both components.

 

Maximum no. of bits/sec =  H Log2 (1+S/N)

 

S/N = Signal to Noise Ratio

 

10 log10 S/N is the commonly used expression for this ratio that is expressed in decibels (dB).

 

10 dB = Ratio is 10

20 dB = Ratio is 100

30 dB = Ratio is 1000

 

e.g.

3000 Hz channel with 30dB S/N can not transmit more than 30,000 bits/sec. Practical Limit of Telephone line cable comes to around 34 Kbps.

 

 

Transmission Media

 

Magnetic Media

·                   Capable of Transferring Bulk Data at low cost.

·                   May be considered in certain cases

 

Twisted Pair

·                   Twisting is done for noise cancellation.

·                   CAT 3 and CAT 5 cables differ in number of twists/unit length.

·                   Possible to transfer multimegabits to few kilometer order.

·                   Analog as well as digital transmission done.

 

Baseband Coaxial

·                   Central Copper core with Shielding Braid.

·                   50 ohm and 75 Ohm Impedance cables are commonly used.

·                   Data rates of 1-2 Gbps possible for 1 Km cable. Longer Cable usable with reduced rate.

 

Broadband Coaxial

·                   Broadband=Analog Transmission wider than 4Khz

·                   Standard Cable TV technology used for Data Transmission.

·                   300 Mhz Channel . Can run upto 100 Km order

·                   Each 6 Mhz TV Channel is good for Analog TV+1.4Mbps CD Music + 3 Mbps Data simultaneously.

·                   Signal Repeaters (Amplifiers) are required.

·                   Dual Cable/ Single Cable (Uses different Frequency Bands) Broadband systems due to unidirectional property of repeaters.

 

Fibre

·                   Uses Total Internal Property of Glass Media.

·                   Theoretical Bandwidth 50,000 Gbps. Practical 1 Gbps due to electrical to light conversion speed.

·                   Multimode fibre = allows different rays travelling together (50 Micron Dia) Single Mode = Allow 1 ray at a time (8-10 Micron Dia).

·                   Multimode = 1-2 Km, Single Mode = 30 Km  (Without Repeaters)

 

Wireless

·                   Uses Electromagnetic Waves of different types.

·                  Radio Waves (104 to 108 Hz)

·                  MicroWave (108 to 1012 Hz)

·                  InfraRed (1012 to 1014 Hz)

·                  Visible Light