Computer NetworksISO – OSI Physical Layer Devices

Presentation By : Md. Shahid Khan

Headed By : Jani Sir

ISO-OSI ModelInternational Standards Organization - Open Systems Interconnection

The concept of a seven-layer model was provided by the work of Charles Bachman, Honeywell Information Services.

OSI is not a protocol but a model for understanding and designing a network architecture that is flexible and robust.

“Open” means the concepts are non propriety , can be used by anyone.

Layered ApproachAPPLICATION

PRESENTATION

SESSION

TRANSPORT

NETWORK

DATA LINK

PHYSICAL

Please

Do

Not

Tell

Secrets

Passwords

Anytime

All

People

Seem

To

Need

Data

Processing

Functions Of LayersTo allow access to network resources.

To translate , encrypt and compress data.

To establish , manage and terminate sessions.

To provide reliable end-to-end message delivery.

To move packets from source to destination.

To organize bits into frames.

To transmit bits over a medium and provide electrical specs.

Physical Layer (PHY)

The physical layer consists of the basic networking hardware transmission technologies of a network.

It is a fundamental layer underlying the logical data structures of the higher level functions in a network.

Due to the plethora of available hardware technologies with widely varying characteristics, this is perhaps the most complex layer in the OSI architecture.

Functions of Physical Layer

Bit RepresentationTransmission RatePhysical CharacteristicsSynchronizeTransmission modePhysical Topology

Physical Layer DevicesCablesConnectorsRepeatersPassive HubSimple Active HubTransmittersMultiplexersReceiversTransceiversCouplers

Cables

•802.3 cabling10 Base 510 Base 210 Base -T10 Base -F

ConnectorsUTP Connector

• RJ45

Coaxial Cable Connector• BNC• BNC-T• BNC Terminator

Fiber Optic Cable Connector• SC Connector• ST Connector• MT-RJ

Standard RJ45• Ethernet physical layer device.

• A standard 8P8C (often called RJ45) connector used most commonly on cat5 cable, one of the types of cabling used in Ethernet networks

• Standard IEEE 802.3 (2002 onwards)• Physical media Coaxial cable, twisted pair, optical fiber• Network topology Point-to-point, star, bus• Major variants 10BASE-T, 10BASE2,100BASE-TX ,100BASE-T• Maximum distance 100 metres over twisted pair, up to 100

km over optical fibre.• The Ethernet physical layer is the physical layer component of the

Ethernet family of computer network standards.

Interconnecting LANs

Q: Why not just one big LAN?

Limited amount of supportable traffic: on single LAN, all stations must share bandwidth

limited length: 802.3 (Ethernet) specifies maximum cable length

large “collision domain” (can collide with many stations)

limited number of stations: 802.5 (token ring) have token passing delays at each station

Repeaters

Why to need - Attenuation : Length of cable used influence the quality of communication.

Repeaters repeat signals– Clean and boost digital transmission.

Repeaters only work with the physical signal– Cannot reformat, resize, or manipulate the data.

Regenerates the original bit pattern

Creates exact duplicate of incoming data by identifying it amidst the noise.

Repeater connects two segments of same LAN.

Cannot connect two LAN’s of different protocols.

Hubs

It is simply a multiport repeater.

• Passive Hubs• Active Hubs• Intelligent Hubs

References

Data CommunicationWikipediaGoogle ImagesLecture Notes

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