Cisco Cisco Catalyst 6500 Series 7600 Series Wireless Services Module (WiSM) Weißbuch
Wireless LAN Design Guide for High Density
Client Environments in Higher Education
33 © 2011 Cisco and/or its affiliates. All rights reserved.
Note that for Room A the scale of the swept spectrogram in the lower left corner of the display had the red level set to -39 dBm
and in Room B it was adjusted to -50 dBm. Signals were quite a bit hotter in Room A. Room A had fewer channels and the APs
were further from the client; this in turn caused the clients to increase their power. The combination of the increased power and
fewer channels in roughly the same space caused more noise and faster deterioration of the overall available spectrum.
and in Room B it was adjusted to -50 dBm. Signals were quite a bit hotter in Room A. Room A had fewer channels and the APs
were further from the client; this in turn caused the clients to increase their power. The combination of the increased power and
fewer channels in roughly the same space caused more noise and faster deterioration of the overall available spectrum.
In high-density WLAN design, more APs and less power mean higher spectral efficiency. Higher spectral efficiency encourages
higher speeds and requires less airtime for the same relative load and less airtime dedicated to recovery and retransmissions or
overhead.
higher speeds and requires less airtime for the same relative load and less airtime dedicated to recovery and retransmissions or
overhead.
The closer that the APs and clients can be to one another, the higher the spectral efficiency will be. If the APs and clients must
be operated at a distance due to architectural requirements, use of directional antennas will improve the cell isolation, and
reduce the power required for Tx in both directions.
be operated at a distance due to architectural requirements, use of directional antennas will improve the cell isolation, and
reduce the power required for Tx in both directions.
The foremost failure in most high-density designs is not enough APs or channels. The secondary reason for failure in most
high-density designs is poor channel isolation; too many APs and channels in the space
high-density designs is poor channel isolation; too many APs and channels in the space
Cisco Unified Wireless Network Best Practices
The following sections cover some of the basic design decisions that should be considered and why they are important. It is
understood that not all of these recommendations will be possible in a legacy design. These points are highly recommended
for the support of a high-density WLAN design. The market and the technology continue to evolve rapidly, and these
recommendations will also continue to evolve.
understood that not all of these recommendations will be possible in a legacy design. These points are highly recommended
for the support of a high-density WLAN design. The market and the technology continue to evolve rapidly, and these
recommendations will also continue to evolve.
Information in this section is not intended to replace the recommended design guides for campus and WLAN deployments
referenced elsewhere within this document. This is a partial list of considerations that pertain specifically to high-density
design considerations. Local Cisco sales teams or Cisco partners are the best resource for questions concerning the goals and
requirements of a particular WLAN design.
referenced elsewhere within this document. This is a partial list of considerations that pertain specifically to high-density
design considerations. Local Cisco sales teams or Cisco partners are the best resource for questions concerning the goals and
requirements of a particular WLAN design.
Pre-Deployment Site Inspection and Validation
Prior to deploying a WLAN, the site should be evaluated based on the following:
RF Interference
• The site may have pre-existing WLANs as part of the same RF network
• There may be nearby WLANs that are not part of the existing RF network
• There may be nearby sources of microwaves and/or surveillance cameras or other forms of non Wi-Fi interference
• There will most likely be Bluetooth
• The WCS and the WLAN controller provide accurate reporting on CCI conditions
• Cisco CleanAir provides in-depth interference analysis and monitoring 7×24
• There may be nearby WLANs that are not part of the existing RF network
• There may be nearby sources of microwaves and/or surveillance cameras or other forms of non Wi-Fi interference
• There will most likely be Bluetooth
• The WCS and the WLAN controller provide accurate reporting on CCI conditions
• Cisco CleanAir provides in-depth interference analysis and monitoring 7×24