Introduction

• INFORMATION IS MOVED FROM Tx & Rx

• THE SPEED AT WHICH THE INFORMATION IS MOVED BETWEEN Tx & Rx IS SET BY ITS “BIT RATE” ON THE CHANNEL

Channels

Tx Rx CHANNEL

TRANSMITTER RECEIVER

• CHANNELS ARE PHYSICAL AND CAN EITHER BE

(BUT NOT LIMITED TO)– COPPER

– FIBRE

– WIRELESS

• ALSO KNOWN AS THE “TRANSMISSION MEDIUM”

Channels II

Bit Rate 1

• 1,000 bit/s = 1 kbit/s (one kilobit or one thousand bits per second)

• 1,000,000 bit/s = 1 Mbit/s (one megabit or one million bits per second)

• 1,000,000,000 bit/s = 1 Gbit/s (one gigabit or one billion bits per second)

• SECTION OF TEXT: “THIS IS A TEST ”– TEXT CONTAINS 14 CHARACTERS

– ASSUME 8 BITS PER CHARACTER

– TOTAL 112 BITS OF INFORMATION

Bit Rate 2

TransmissionSystem

Bit Rate Time Taken

Telex50 bits/sec 2.3 seconds

56k Modem 56 kbits/sec 2 milliseconds

Primary rate ISDN 2 Mbits/sec 57 microseconds

FDDI 100 Mbits/sec 1.1 microseconds

Gigabit network 1 Gbits/sec 114 nanoseconds

COMPARISON OF BIT RATE AND TRANSMISSION TIME

• IMAGE FROM NASA: SURFACE OF MARS

– PICTURE CONTAINS 1080 x 602 PIXELS, AT 8 BITS PER PIXEL THERE IS 5.2 Mbits OF INFORMATION IN THE PICTURE

Bit Rate 3

TransmissionSystem

Bit Rate Time Taken

Telex50 bits/sec

104,025 seconds(about 29 hours)

56k Modem 56 kbits/sec 92.8 seconds

Primary rate ISDN 2 Mbits/sec 2.6 seconds

FDDI 100 Mbits/sec 52 milliseconds

Gigabit network 1 Gbits/sec 5.2 milliseconds

COMPARISON OF BIT RATE AND TRANSMISSION TIME

Bit Rate 4

• Audio (MP3)– 32 kbit/s — MW (AM) quality – 96 kbit/s — FM quality – 128–160 kbit/s — Standard Bitrate quality; difference can sometimes be

obvious (e.g. bass quality) – 192 kbit/s — DAB (Digital Audio Broadcasting) quality. Quickly becoming the

new 'standard' bitrate for MP3 music; difference can be heard by few people. – 224–320 kbit/s — Near CD Quality. Sound is near indistinguishable from

most CDs.

• Other audio– 800 bit/s — minimum necessary for recognizable speech (using special-

purpose FS-1015 speech codecs) – 8 kbit/s — telephone quality (using speech codecs) – 500 kbit/s–1 Mbit/s — lossless audio as used in formats such as FLAC,

WavPack or Monkey's Audio – 1411 kbit/s — PCM sound format of Compact Disc Digital Audio

Bit Rate 5

• Video (MPEG2)– 16 kbit/s — videophone quality (minimum necessary for a consumer-

acceptable "talking head" picture) – 128 – 384 kbit/s — business-oriented videoconferencing system

quality – 1 Mbit/s — VHS quality – 5 Mbit/s — DVD quality – 15 Mbit/s — HDTV quality – 36 Mbit/s — HD DVD quality – 54 Mbit/s — Blu-ray Disc quality

• THERE ARE LIMITS ON BIT RATE

• ALL CHANNELS HAVE AN UPPER LIMIT ON BIT RATE

• THE LIMIT IS SET BY THE SO CALLED CHANNEL

BANDWIDTH

• BANDWIDTH IS MEASURED IN MHz & GHz

– MEGAHERTZ & GIGAHERTZ (MILLIONS & BILLIONS OF

HERTZ)

• IN GENERAL THE LARGER THE BANDWIDTH THE GREATER

THE INFORMATION CARRYING CAPACITY IN Bits/sec

Bandwidth

• A NETWORK CONSISTS OF A COLLECTION OF NODES AND CHANNELS

• A NODE CAN CAN BE ANY NUMBER OF THINGS, FOR EXAMPLE

– COMPUTER– PRINTER– SCANNER– BACKUP DRIVE– SECURITY CAMERA– SENSORS

What is a Network?

• TOPOLOGY DETERMINES THE WAY IN WHICH NODES AND

CHANNELS ARE INTERCONNECTED

• AN ANALOGY WOULD BE THAT OF A RAIL NETWORK

• STATIONS (NODES) ARE CONNECTED TOGETHER BY RAIL

TRACK (CHANNEL)

What is Topology?

Network Topologies

Point to Point

Network Topologies

Bus

Network Topologies

Ring

Network Topologies

Star

HUB

Network Topologies

• PHYSICAL STAR– RING CONFIGURATION

– STAR TOPOLOGY

Network Topologies

• COLLAPSED BACKBONE– SIMILAR TO STAR

Network Topologies

Shared Bandwidth network

Network Topologies

Switched Bandwidth network

Network Topologies

ETHERNET

• Ethernet is the most popular LAN standard in the world with over 1 Billion installed nodes (1Billion nodes - IET Computing & Control Engineering | February/March 2007)

• The original Ethernet came out around 1979 at 10 Mbps, and that’s where it stayed for more than 10 years

• Ethernet runs over co-axial cable or twisted pair copper wires and provides a 10 Mbps to share between all users

Ethernet

• Users were finding the 10 Mbps performance of Ethernet too slow. This bandwidth crunch is the result of three technological changes:

– the increased speed of computer processors– the increased number of users on networks – new bandwidth-intensive applications on networks

To Slow

• ETHERNET– 2/5 BASE T 10Mbps

• THIN/THICK COAX ETHERNET

– 10 BASE T 10Mbps • ORIGINAL TWISTED PAIR ETHERNET

– 100 BASE T 100Mbps • FAST ETHERNET

– 1000 BASE T 1000Mbps• GIGABIT ETHERNET

Ethernet Types

• 802.3 1985 – 10Mbps THICK & THIN ETHERNET

• 802.3u 1995 – 100Mbps FAST ETHERNET

• 802.3z 1998 – 1000Mbps GIGABIT ETHERNET (FIBRE)

• 802.3ab 1999 – 1000Mbps GIGABIT ETHERNET (COPPER)

Ethernet History

• PROTOCOL– CSMA/CD

• PHYSICAL MEDIUM– COAX

– TWISTED PAIR

– MULTIMODE FIBRE

– SINGLEMODE FIBRE

Ethernet

CSMA/CD

START TRANSMITTING

LISTEN FORCOLLISION

CONTINUE TRANSMITTING

BACK OF FORRANDOM PERIOD

COLLISIONNO

YES

CARRIER SENSEMULTIPLE ACCESSWITH COLLISIONDETECT

Ethernet Over Copper

• THIN/THICK COAX– OBSOLETE 2/5BASET

• CAT 3– OLD INSTALLATIONS 10BASET

• CAT 4– CAT5 MADE CAT4 OBSOLETE

• CAT 5– IN MAJORITY OF INSTALLATIONS