In this webinar, we started the discussion about essential concept of multiplexed communication which is applied on wired and wireless communication. we then carried on with CSMA/CD, how wireless communication works, CSMA/CA, and wireless configuration on mikrotik. The recording is available on youtube (GLC Networks Channel): https://www.youtube.com/channel/UCI611_IIkQC0rsLWIFIx_yg

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Wireless CSMA with
GLC webinar, 7 september 2017
Achmad Mardiansyah
achmad@glcnetworks.com
GLC Networks, Indonesia
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Agenda
● Introduction
● Wireless CSMA
● Mikrotik wireless
● Demo
● Q & A
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What is GLC?
● Garda Lintas Cakrawala (www.glcnetworks.com)
● An Indonesian company
● Located in Bandung
● Areas: Training, IT Consulting
● Mikrotik Certified Training Partner/Consultant/Distributor
● Ubiquiti Certified Trainer/Consultant
● RedHat Certified Trainer
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About GLC webinar?
● First webinar: january 1, 2010 (title:
tahun baru bersama solaris - new
year with solaris OS)
● As a sharing event with various
topics: linux, networking, wireless,
database, programming, etc
● Regular schedule: every 2 weeks
● Irregular schedule: as needed
● Checking schedule:
http://www.glcnetworks.com/main/sc
hedule
● You are invited to be a presenter
○ No need to be an expert
○ This is a forum for sharing: knowledge,
experiences, information
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Trainer Introduction
● Name: Achmad Mardiansyah
● Base: bandung, Indonesia
● Linux user (since 1999), Mikrotik user (since 2007),
ubnt user (since 2011)
● Certified Trainer (Mikrotik, Ubiquiti, Redhat)
● Certified Consultant
● Work: Telco engineer, Sysadmin, PHP programmer,
and Lecturer
● Personal website: http://achmadjournal.com
● More info:
http://au.linkedin.com/in/achmadmardiansyah
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Please introduce yourself
● Your name
● Your company/university?
● Your networking experience?
● Your mikrotik experience?
● Your expectation from this course?
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Wireless CSMA
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Multiplexing (MUX)
● Method by which multiple analog or digital signals are combined into one
signal over a shared medium
● Advantage:
○ Can save money -> one shared media is used by many users
○ Increase media utilisation
● Disadvantage
○ No dedicated link for customer
○ Can lead to contention race
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CSMA/CD
● A Multiplexing technique where users communicate each other using shared
media
● CSMA/CD: Carrier Sense Multiple Access / Collision Detection:
○ Host sense the medium before sending
○ If medium is silent, then send
○ If some host send at the same time, collision happens. Then each host will retry at random
time
● Used on ethernet technology
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802.11 (wifi) communication
● Stations connect to Access Point (AP) -> infrastructure mode
● AP uses a frequency and broadcast SSID on that frequency
● The same frequency is used by all stations to receive (rx) and transmit (tx) ->
shared media
● As a consequence, only one host can send at a time -> half-duplex
● All stations should be able to listen each other
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CSMA/CA
● Multiplexing technique for wireless access (wifi)
● CSMA/CA: Carrier Sense Multiple Access / Collision Avoidance
○ Station cannot sense the medium while transmit (unlike ethernet which can detect collision
while transmit)
○ Therefore the appropriate term is Collision Avoidance (not collision detection)
○ So each station must carefully listen the channel before sending data
○ Unlike ethernet and similar to TCP -> every time a station successfully receive frame, it will
send ACK to medium. -> this means medium is empty
○ After hearing an ACK on medium, each station that want to send data will wait for a random
time before sending data.
○ When the random time is reached, the station will listen the medium again, and if its empty, it
sends the data
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CSMA/CA (picture)
● Unlike ethernet, wifi has no collision detection ability
● Unlike ethernet, similar to TCP: station will send ACK to medium whenever
successfully received
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From wififorbeginners

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Hidden node problem
● Ideally, stations should be able to hear each other
● If not -> hidden node problem -> which can lead to many collisions
● Example:
○ A and C cannot hear each other
○ Each always thinks the medium is free
○ this lead to collision -> corrupted frame
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From researchgate

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Hidden node solution
● RTS-CTS technique (this is not activated by default)
○ Adding a permission mechanism before sending data
○ Before send, station always send RTS (Request To Send) to AP
○ If it is approved, AP will send CTS (Clear To Send) to stations
● TDMA (Time Division Multiple Access)
○ Each station will be given a timeslot to send / receive
○ No permission mechanism like RTS-CTS above
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From sustr.sk
From Freakquency
From ubnt.com

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Wireless on mikrotik
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Wireless setting (standard)
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Wireless setting (rts-cts)
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Wireless setting (nv2 - tdma)
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Interested?
Just come to our
training...
Special price for webinar
attendees…
http://www.glcnetworks.c
om/main/schedule
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End of slides
● Thank you for your attention
● Please submit your feedback: http://bit.ly/glcfeedback
● Like our facebook page: “GLC networks”
● Slide: http://www.slideshare.net/r41nbuw
● Recording: https://www.youtube.com/channel/UCI611_IIkQC0rsLWIFIx_yg
● Stay tune with our schedule
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