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 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.


  • copper cable
  • fibre -optic cable
  • wireless




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.


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





Types of termination of cables




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


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 14.PNG



Properties of wireless media

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




  • 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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