CCNA 2 - Capitulo 12.3.2

CCNA 2 - Capitulo 12.3.2

1. WIRELESS NETWORK

   • WLAN OPERATION
     • CARRIER SENSE MULTIPLE ACCESS WITH COLLISON AVOIDANCE (CSMA / CA)
       • WLAN
         • HALF DUPLEX
           • ONLY CLIENT CAN TRANSMIT OR RECEIVE AT ANY GIVEN MOMENT
         • SHARED MEDIA CONFIGURATION
           • WIRELESS CLIENTS CAN TRANSMIT AND RECEIV SAME RADIO CHANNEL
       • METHOD TO DETERMINE HOW AND WHEN TO SEND ON THE NETWORK
       • HOW TO WORK ?
         • 1️⃣ CARRIER SENSE (LISTEN TO THE CHANNEL)
           • DEVICE CHECKS IF THE MEDIUM IS IDLE
           • “CARRIER” = WIRELESS CHANNEL
           • NO TRANSMISSION DETECTED → PROCEED
           • CHANNEL BUSY → WAIT
         • 2️⃣QUEST TO SEND (RTS)
           • OPTIONAL BUT IMPORTANT IN BUSY NETWORKS
           • CLIENT ASKS AP FOR PERMISSION TO TRANSMIT
         • 3️⃣ CLEAR TO SEND (CTS)
           • AP GRANTS PERMISSION
             • AP INFORMS OTHER DEVICES TO REMAIN SILENT
           • RESERVES THE MEDIUM TEMPORARILY
         • 4️⃣ BACKOFF MECHANISM (IF NO CTS)
           • O CTS RECEIVED → ASSUME CONTENTION
           • PREVENTS SIMULTANEOUS RETRIES
           • DON'T RECEIVED CLEAR TO SEND ?
             • CLIENT WAITS A RANDOM BACKOFF TIME
               • CLIENT WAITS A RANDOM BACKOFF TIME
         • 5️⃣ DATA TRANSMISSION
           • CLIENT SENDS FRAMES AFTER CTS
             • MEDIUM CONSIDERED RESERVED
         • 6️⃣ ACKNOWLEDGMENT (ACK)
           • EVERY FRAME MUST BE ACKNOWLEDGED
           • NO ACK → COLLISION ASSUMED
           • CLIENT RETRANSMITS
           • BACKOFF APPLIED AGAIN
     • DISCOVERY MODE
       • PASSIVE MODE
         • AP ADVERTISES PERIODICALLY SENDING BROADCAST BEACON CONTAINING
           • SSIID
           • STANDARDS
           • SECURITY SETTINGS
         • PRIMARY PURPOSE OF THE BEACON ?
           • ALLOW CLIENTS LEARN WHICH
             • NETWORK AND APs ARE AVAILABLE IN A GIVEN AREA
         • EX : WIZ CORPORATIVA
       • ACTIVE MODE
         • WIRELESS CLIENTS
           • MUST KNOW THE NAME SSID
           • CLIENT INITIATES WITH INITIATES
             • A PROBE REQUEST WITH
               • SSID NAME
               • STANDARDS SUPPORTED
               • SECURITY SETTINGS
           • EX : WIZ TV (HIDDEN)
         • AP OR WIRELESS ROUTER
           • DO NOT ADVERTISE , SENDS BROADCAST BEACONS FRAMES
     • WIRELESS CLIENT AND AP ASSOCIATION
       • THEY MUST FIRST ASSOCIATE WITH AN AP OR WIRELESS TO COMUMUNICATE OVER A NETWORK
       • THREE STAGE PROCESS
         • 1.DISCOVER A WIRELESS AP
         • 2.AUTHENTICATE WITH AP
         • 3.ASSOCIATE WITH AP
       • TO HAVE A SUCCESSFUL ASSOCIATE - CLIENT AND AP MUST AGREE PARAMETERS
         • SSID
           • NAME APPEARS IN THE LIST OF AVAILABLE WIRELESS NETWORK
           • LARGER ORGANIZATION THAT MULTIPLE VLAN
             • EACH SSID IS MAPPEAD TO ON VLAN
           • SEVERAL APs CAN BE SHARE A COMMON SSID
         • PASSWORD
           • REQUIRED TO AUTHENTICATE
         • NETWORK MODE
           • STANDARS TO THE 802.11 A / B / G / N / C/ AD
         • SECURITY MODE
           • WEP , WPA OR WPA2
         • CHANNEL SETTINGS
           • FREQUENCY BANDS USED TO TRANSMIT WIRELESS DATA
           • MANUALLY OR AUTOMATICALLY