CCNA (routing and switching)

module 1 – Chapter 4A : Network Access

I broke this chapter into two (Physical layer {4A} then Data Link {4B})

 

To support our communication, the OSI model divides the functions of a data network into layers.

on the sending device

Data link : prepares data for transmission and controls how that data  accesses physical media

Physical layer: controls how the data is transmitted onto the physical media by encoding frames into binary bits

 

Receiving end

 

Physical layer :passes frame to the data link layer for processing

Data link: protocols that govern how to format a frame for use with different media

 

Types of connections on physical

all end devices  and wireless access points

network Interface cards (nic)

THE PURPOSE OF THE PHYSICAL LAYER

  • the idea is to get frame from data link and encode it as a series of signals

Process that data undergoes from source to destination node

 

  • data segmented by transport layer
  • placed into packets by network layer
  • encapsulated into frames by data link
  • physical layer encodes frames and creates electric,optical or radio wave signals bits
  • signals sent on the the media (fiber, utp,or coaxial cable for example) one at a time

 

  • Destination node physical  layer retrieves the individual signal from media and restores them to their bit representation. it also passes the bits up to the data link layer as a complete frame.

PHYSICAL LAYER MEDIA

  • copper cable
  • fibre -optic cable
  • wireless

 

chap4-1

 

physical layer standards

  1.  ISO
  2. IEEE
  3. EIA/ TIA
  4. ANSI
  5. ITU-T

functions of the physical layer

  • physical components : these are the electronic h/w devices and media
  • Encoding : method of converting a stream of data bits
  • Signalling : the generating of electrical optical 1’s and 0’s
  • Bandwidth : the capacity of a a medium to carry data, example is the chat belowchap4-2

Throughput : the measure of the transfer of bits across the media over a given period of time.  factors that influence it the amount of traffic ,type of traffic and latency (LATENCY – the amount of time ,to include delays for data to travel from one given point to another)

Characteristics of Copper Cabling

  • inexpensive
  • easy to install
  • resistance ti electrical current
  • limited by distance
  • signal interferenace

Interference of copper cabling

  1. EMI ( Electromagnetic Interference) and (radio Frequency Interference )

these can corrupt data signals being carried via copper cables

potential sources of EMI and RFi are flourescent lights

2. Crosstalk

caused by electric and magnetic fields of a signal on a wire to the one which is adjacent to the wire.

chap4-3

Copper Media

  • UTPchap4-4
  • STP (shielded)chap4-5
  • COAXIAL CABLEchap4-6

UTP cabling standards

1 Cat 3

used for voice communication

for phone lines

2. CAT 5 and 5E

for data transmission

cat 5 = 100 MBps

cat 5e =1000 MBps

 

3. CAT 6

data transmission

it has got separators to make data travel fast

1000MBps to 10 GBps

UTP CONNECTORS

chap4-7

chap4-8

 

Types of termination of cables

chap4-9

 

FIBRE – OPTIC

its good for long distance

less alternnation and complete immune to EMI and RFI

bits encoded as light impulses.

it is used in four types of industries

  •  Enterprise network
  • Fibre to the home
  • Long Haul networks
  • Subamarine Cable networks

 

Types of Fiber media

Single -Mode Fiber

  • small core
  • uses expensive laser technology
  • suitable for long distances
  • used with campus backbones for distance (different campuses)
  1. Multi mode

– uses led emitter to send light pulses.

– popular in LANS

– low cost LED

-up to 500 mchap4-10

 

Fibre Optic  Connectors

  • ST connectors
  • SC connectors
  • LC connectors
  • Duplex multimode LC connectors

chap4-11

Three common types of Fiber Optic Termination errors

  1. Misalignment
  2. End Gap
  3. End finish – this might be dirt on the end/tip of the fibre cable

The device below helps you to check if you have spliced the cable correctly as it shows you the power levels of the link

chap4-12

 

FIBRE VS UTP CABLE

chap4 14.PNG

 

WIRELESS MEDIA

Properties of wireless media

  • Electromagnetic signals that represent the binary digits
  • Uses radio and microwave frequency

 

 

AREAS OF CONCERN

  • Coverage area: work well in open environment but affected by physical setting like trees buildings
  • Intereferance : affected by microwave ovens
  • Security : an open network can be accessed
  • Shared medium : operate in hald duplex

 

Wireless  Standards

  • WiFi
  • Bluetooth
  • Wimax

 

 

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