In a bus topology the computers are connected in a line

Graphics Files

DatabaseFiles

Spreadsheets

Word ProcessingDocuments

A server can hold data in a central place for better control over the information and for more efficient sharing

In a star topology the computers are all connected by cables to a central point

TRUE MESH

HYBRID MESH

Hub

Hub

Hub

HubHub

The Hybrid star network has several centralstar network points linked in a star.

In a ring topologycomputers are connected in a

circle

1 3 10 30 100 300

Frequency in hertz(cycles per second)

3 10 30 100 300

1

Kilohertz

Hertz

3 10 30 100 300

Megahertz

1

3 10 30 100 300

Gigahertz

1

3 10 30 100 300

Gigahertz

1

Audio Frequency

Power and telephone

Radio waves

Microwaves

infrared

Extremely low frequency (ELF)

Voice frequency (VF)

Very low frequency (VLF)

Low Frequency(LF)

Medium frequency (MF)

High frequency (HF)

Very high frequency (VHF)

Ultra high frequency (UHF)

Super high frequency (SHF)

Extremely high frequency (EHF)

Submillimeter waves

Far infrared

Intermediate infrared

Near infrared

Contd….

The electromagnetic spectrum

1

10

100

1

10

100

1

10

100

1

10

OV

kev

Mev

Gev

Ultra violet

X-rays

Gamma rays

Vacuum ultraviolet

Near ultraviolet

Soft-x-rays

Hard x-rays

Soft gamma rays

Hard gamma rays

Secondarycosmic rays(gamma raysproduced by cosmic rays)

Photonenergyin hertzvolts (ev)

Terrestrial Microwave connecting two buildings

Computer motherboard

Parallel data flows fromthe computer to the network adapter card

Serial data flows from the network adapter card onto

the network

Networkadapter card

Network interface adapter

Peer communication

Information flow

Network medium

Layer 7

Layer 6

Layer 5

Layer 4

Layer 3

Layer 2

Layer 1

Application

Presentation

Session

Transport

Network

Data link

Physical

Application

Presentation

Session

Transport

Network

Data link

Physical

DOS MACINTOSHPeer communication between two computers

7

6

5

4

3

2

1

Layer 7

Layer 6

Layer 5

Layer 4

Layer 3

Layer 2

Layer 1

Application

Presentation

Session

Transport

Network

Data link

Physical

Application

Presentation

Session

Transport

Network

Data link

Physical

UNIX MACINTOSHA message sent from one peer layer to another

7

6

5

4

3

2

1

Original data

Original data

Original data

Original data

Original data

Original data

Original data

Hp

Ht

Hs

Hn

Hd

Original data

Original data

Original data

Original data

Original data

Original data

Original data

Hp

Ht

Hs

Hn

Hd

Application

Presentation

Session

Transport

Network

Data link

Physical

DOS Macintosh

Hp -Presentation headerHt =Transport headerHs =Session headerHn =Network headerHd =Data Link header

The OSI model and headers

Application

Presentation

Session

Transport

Network

Data link

Physical

Messages&Packets

H1

H2

H3

H4

H5

Packets

Packets

Datagrams, segments&packets

Datagrams&packets

Frames&packets

Bits&packets

Common data package names

4. Transport layer

3. Network layer

2. Data link layer

1. Physical layer

3. Network layer

2. Data linklayer

2. Data linklayer

1. Physicallayer

1. Physical layer

4. Transport layer

3. Network layer

2. Data link layer

1. Physical layer

End-to-end transport connection

The transport layer provides end-to-end communication with integrity and performance guarantees

Router

5. Session layer

3. Network layer

2. Data link layer

1. Physical layer

3. Network layer

2. Data linklayer

2. Data linklayer

1. Physicallayer

1. Physical layer

4. Session layer

3. Network layer

2. Data link layer

1. Physical layer

The session layer provides for dialog between application programs

Router

4. Transport layer 4. Transport layer

Dialog betweenapplication programs

6. Presentation layer

3. Network layer

2. Data link layer

1. Physical layer

3. Network layer

2. Data linklayer

2. Data linklayer

1. Physicallayer

1. Physical layer

6.Presentation layer

3. Network layer

2. Data link layer

1. Physical layer

The presentation layer provides data conversion between different systems

Router

4. Transport layer 4. Transport layer

5. Session layer 5. Session layer

Data conversion betweendifferent systems

Twisted Pair Co-axial

RouterSubnet

LAN

Host

Relation between hosts and the subnet

Destination addresses Source address Data

Bytes 2 2 1 1 12 12

Packet type

Transport control

Packet length

Checksum

A Novell NetWare IPX packet

Air/silica boundary

Silica

Air

1 2 3

1 2 3

(a) (b)

Total internalReflection

Light source

(a) Three examples of light ray from inside a silica fiber impingingon the air/silica boundary at different angles.

(b) Light trapped by total internal reflection

ICI SDU

IDU

ICI SDU

SAP

Layer N+1

Interface

Layer N

SDU

N-PDUHeader

Layer N entitiesexchange N-PDUsin their layer Nprotocol

SAP = Service Access PointIDU = Interface Data UnitSDU = Service Data UnitPDU = Protocol Data UnitICI = Interface Control Information

Relation between layers at an interface