Controller Based WLANs

What is the difference between short and long preamble?

Aruba Employee

Product and Software: This article applies to ArubaOS 3.x and later.

The preamble, that is, the Physical Layer Convergence Protocol (PLCP) consists of two parts:

•       Sync
•       Start of Frame Delimiter (SFD)

This allows the receiver to synchronize itself with the transmitter.

Long preamble is mostly used by legacy systems and has a sync of 128 bits where as short preamble has sync of 56 bits. SFD in both cases remains same at 16 bits.

Short preamble was primarily introduced for efficiency. All 802.11g devices must be able to transmit and receive long preamble. But support of short preamble is optional for 802.11b devices.

Short preamble is enabled by default but disabled per SSID.

CLI:

(wlsw2h) (SSID Profile "default") #no short-preamble

WebUI:

To modify this option, follow these steps:

1)  Navigate to Configuration > Wireless > AP Configuration > Edit Group.

2)  Expand Wireless LAN > Virtual AP > Group Name.

3)  Click the name of the SSID and click the Advanced tab on right side of screen.

Here you can check or uncheck the short preamble option as shown.

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‎07-10-2014 01:06 PM
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