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ENWLSD 300-425 Exam Prep Notes

Applying Wireless Design Requirements

  1. Defining AP coverage – The main goal of the Wi-Fi design to bring the network to the users.
  2. Considering Receive Sensitivity – AP Tx power is a major factor in determining the usable range of its signal. Every client device has a receiver that has a sensitivity level or threshold that divides the intelligible, useful signals from unintelligible devices.
  1. A commonly used cell boundary is 67dBm
  2. Considering SNR = SNR must be greater than the noise floor by a decent amount so that it can be received and interpreted correctly.
  3. SNR also determines the cell boundary.
  4. Further AP cell considerations
    1. DRS (Dynamic Rate Shifting) – Clients/AP can lower the data rate when data is not acknowledged at the same rate it was sent.
  5. DTPC – Dynamic Transmit Power Control is a Cisco Proprietary method that AP use to advertise their own tx power so that compatible clients can adjust their tx power levels accordingly. Clients must support Cisco Compatible Extensions (CCX) for participating in this. Cisco recommends DTPC to be turned ON, by default it is ON.
  6. Expanding coverage with additional AP – Need Tx power adjustments if capacity requirements need to be met for a design – Repeat channel layout can be used to work with co-channel interference issues.
  7. Designing a Wireless Network for Data
    1. Disable low data rates if legacy devices are not used.
    2. Clients will try to use higher rates if RF conditions support it.
    3. Even though disabling lower data rates does reduce the usable cell size, the cell boundary will not move enough to interfere with the design constraints.
  8. Designing a Wireless Network for High Density
    1. Distribute users multiple  AP and channels.
    2. AP cell size needs to be reduced to cater to more users. This can be done by adjusting the Tx power and using an appropriate antenna for the AP.
    3. Leverage DTPC to automatically influence the tx power.
    4. Use DFS channels to leverage the 5GHz band in dense environments.
    5. Use FRA (Flexible Radio Assignment) – aka software-defined radios in AP running dual radios to switch 2.4GHz channel to 5GHz when sensing more 5GHz client density.
  9. Designing a Wireless Network for Voice/Video
    1. Need to carefully use DRS (Dynamic Rate Shifting) to mitigate user disruptions
    2. Follow appropriate QoS consideration to mark and prioritise user traffic.
    3. Use 802.11r, k and v that streamline roaming and authentication.
    4. Consider using DFS only is radar activity is not detected in the location.
  10. Designing a Wireless Network for Location
    1. RTLS can be used to track assets, rogue devices, also to location wireless clients within a building or a campus.
    2. AP should be positioned such that multiple AP can receive a signal from a device to be located, a minimum of 3 AP should be able to receive a client’s signal while four or more AP are preferred.
    3. The derive a fairly accurate location, multiple AP must receive the client device or tag at RSSI above -75dBm.
    4. In a multi-floor building, AP should be staggered and not kept in straight lines.

Physical and Logical Requirements

  1. Physical Infrastructure Requirements
    1. POE and POE+
      1. POE is widely used technology that provides power to the AP over a twisted pair of Ethernet cable.
      2. PSE is mostly a POE injector or POE capable switch
      3. PDs (powered device) – Access Points, POS machines etc.
      4. IEEE 802.3af (POE) 15.4W PSE 12.95W PD IEEE 802.3at (POE+) 25.5W PSE 30W PD
    2. UPOE and UPOE+
      1. Cisco has developed extended POE capabilities
      2. Universal POE is capable of delivering 60W per port and UPOE+ up to 90W
      3. UPOE and UPOE+ are Cisco proprietary
      4. In 2018, IEEE standard 803.3bt as a standard to deliver up to 90W sometimes referred to as POE++
    3. MultiGigabit – Cisco AP can deliver speeds of 2.5Gbps, 5/10Gbps on existing cables. Cisco 3800/4800 and Catalyst 9100 AP support mGig technology.
    4. Ceiling and Mounting AP – Above/Below ceiling brackets.
    5. Grounding and securing AP – not always required for indoor AP, may be required to external AP requiring earthing/grounding connections.
  1. Logical Infrastructure Requirements
    1. CAPWAP flow
      1. CAPWAP Control Channel – uses UDP port 5246
      2. CAPWAP Data Channel -uses UDP port 5247
    2. AAA and DHCP services logical path
      1. CAPWAP uses controllers management interface t o communicate with AAA servers as well as other services.
    3. Licensing Overview
      1. Permanent Licenses
      2. Adding AP count licenses
      3. Evaluation Licenses
    4. Smart Licensing – uses centralised pool to license AP as and when required.
    5. Catalyst 9800 controllers require mandatory smart licensing

Conducting an Offsite & Onsite Site Survey

  1. AP radio signals are expressed in dBm.
  2. Common obstacles
  3. Note that the above is for general reference only, they can change depending on the area/country requirements.
  4. Common deployment models.
    1. Enterprise office
      1. Increase in devices
      2. Increase in mobility needs
      3. Roaming requirements
      4. Voice/Video/Location analytics
    2. Healthcare
      1. Environments with X-ray/Imaging/Lab areas.
      2. Legacy or older devices.
      3. Interference expected from lab equipment like ECG etc.
      4. Aesthetics requirements
    3. Hospitality and Hotels
      1. Dense environments
      2. Captive portal/guest handling
      3. Aesthetic requirements
    4. Education
      1. Dense environments
      2. BYOD device catering
    5. Retail
      1. Legacy devices
      2. Neighbouring location wifi interferences
      3. PCI specific regulations
    6. Warehouse
      1. Directional antenna due to shelving
      2. Secure AP in enclosures depending on the environment
  5. Design with regulations in mind
    1. FCC
    2. ETSI
    3. Telec
  6. EIRP = Tx Power (dBm) + antenna gain (dBi) – cable loss (dB)
  7. FCC Regulations
Band (Domain)Rules
2.4GHz (FCC)36 dBm (4W) EIRP (P2MP), with 30 dBm (1 W) Tx / 6 dBi, 1:1 ratio. 36 dBm (4 W) EIRP (P2P) with 30 dBm (1 W) Tx / 6 dBi, 3:1 ratio.
U-NII-1 (FCC)Outdoors: Max EIRP 36 dBm (4 W). Indoors: Max Tx 17 dBm (50 mW), 6 dBi.
U-NII-2A (FCC)Max EIRP 30 dBm (1 W), max Tx 24 dBm ( 250 mW).
U-NII-2B (FCC)Not allowed for unlicensed use.
U-NII-2C (FCC)Max EIRP 30 dBm (1 W), max Tx 24 dBm (250 mW). DFS required.
U-NII-3 (FCC)Max EIRP 30 dBm (1 W), max Tx 24 dBm ( 250 mW).
2.4GHz (ETSI)Max EIRP 20 dBm (100 mW), max Tx 17 dBm ( 50 mW) on 3 dBi. 1:1 rule.
Band 1 (ETSI), Sub-band 1 (U-NII-1)Max EIRP 23 dBm (200 mW).
Band 1 (ETSI), Sub-band 2 (U-NII-2A)Max EIRP 23 dBm (200 mW) with TPC. Max EIRP 20 dBm, (100 mW) without TPC. DFS required.
Band 2 (ETSI) (U-NII-2C)Max EIRP 30 dBm (1 W) with DFS and TPC. Max EIRP 27 dBm (500 mW) with DFS and no TPC. Max EIRP 20 dBm (100 mW) without TPC and DFS.
Band 3 (ETSI) (U-NII-3)Under discussion. Not allowed for Wi-Fi yet. Target 14 dBm (25 mW).
  1. Conducting an Offsite Site Survey (Predictive Design)
  • Choosing the Right survey
    • Blueprint study
    • Predictive survey
  • Multiple types of onsite survey
    • Walkthrough
    • Layer 1 site survey
    • Layer 2 site survey
    • Post-deployment site survey

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