Specifications

Another thing to consider when determining VLAN and ESS is whether or not multicast traffic
will be supported. While you can have multiple VLANs per ESSID it is not recommended as a
1-to-1 mapping VLAN to ESSID is required to support multicast traffic (e.g. push to talk voice,
streaming multicast video).
AP Density
We should be aware of how much APs overlap (i.e. the number of APs that can hear each
other). This can be determined by the number of neighbors shown in the wireless radio GUI
display. Note that in the past – particularly with AP200s and Vcell (Shared BSSID) we were
advised to be cognizant of how much AP overlap. With AP300 and Vport (Per Station BSSID)
overlap is a less of a concern but neighbor count should still be considered. If there are more
than 35 neighbors, consider channel layering. Which layering model you choose will depend
on the application requirements.
A good rule of thumb when determining the optimal AP density is that each and every
station, no matter where it is throughout the network, will be able to hear from 2 or 3 APs.
Signal Strength
The recommendation is for data only networks minimum signal strength of -70dbm
everywhere. For networks that will support voice and or multicast video we recommend
-65dbm or greater everywhere.
SNR
Another important metrics to consider when building a wireless network is the signal to noise
ratio (SNR).
The recommended SNR for data only networks is 20 or greater. For networks that will support
voice and/or video a SNR of 25 or greater is recommended.
Virtual Port
Virtual Port (Vport) is a new technique for virtualization of the WLAN. Virtual Port virtualizes
the BSS much like Virtual Cell (VCell) does however with Vport, the BSS that each client
associates to is unique to the client as opposed to Vcell where all clients associate to a
common BSS (for a given channel and ESS).
With Vport the clients unique BSS follows them as they travel around the network. Since the
client always sees a single BSS they never re-authenticate or re-associate as they get handed
off from AP to AP. This has profound implication for many applications, in particular RTP (real
time protocol) based apps such as VoIP and streaming video. There are many other
BPG_11n_v1.0 | Page 10
MERU BEST PRACTICES GUIDE | 11n Design, Implementation and Optimization