Short Preamble necessary?

[mmatulevich]

Just a question as to whether or not my wireless lan needs to have this enabled or not on the lwapp controllers. It currently is and wanted to disable it during my next IOS upgrade if possible. We have a strong vocera deployment which is working decent at the moment, and although it is disabled on the badges I wanted to eliminate anything that may cause problems. Thanks for input

[Rob Huffman]

Hi Michael,

I would leave this setting "as is". Have a look;

The radio preamble, which is sometimes called a header, is a section of data at the head of a packet that contains information that wireless devices need when sending and receiving packets. You can set the radio preambles to long or short.

Short A short preamble improves throughput performance and is enabled by default. Cisco Aironet Wireless LAN Client Adapters support short preambles. Early models of Cisco Aironet's Wireless LAN Adapter (PC4800 and PC4800A) require long preambles. However, some wireless devices, such as SpectraLink NetLink phones, require long preambles. In such cases, unchecking short preamble enables long preamble to achieve interoperability with Spectralink Netlink phones. Refer to Using the GUI to Enable Long Preambles for information on how to disable short preamble.

Long A long preamble ensures compatibility between the access point and all early models of Cisco Aironet Wireless LAN Adapters (PC4800 and PC4800A). If these client devices do not associate to your access points, you should use short preambles.

From this good doc;

http://www.cisco.com/en/US/products/ps6366/products_qanda_item09186a008064a991.shtml

Hope this helps!

Rob

[scottmac]

Good Link Rob (as usual), Thanks!

I think I also read somewhere about a relationship between preamble length and 802.11b(uses either) versus 802.11g(needs short)... probably the same as the legacy/newer stuff explanation.

I've been meaning to dig it out of the books, but the swamp has been especially full of alligators lately ...

Thanks Again

Scott

[csco11044906]

Scott, i agree with you. 

When short Preamble is enabled, the 802.11 g clients do not send RTS /CTS packets. 

Though it improves performance but it disrupts 802.11b clients traffic. 

Wireless - 802.11b/g/n -- SHORT Preamble (check box enable / disable) 

This setting is by default enabled now a days and i used it for 7920 phones as well to avoid call quality issues (one of several points to take care) 

:-)

Sumit. 

[rnigam]

It is generally recommended to use long preamble in legacy devices while short preamble when you are using either cisco gear or CCX compatible clients.

[Rob Huffman]

Hey Scott,

Thanks so much :) It's great to have you back posting your usual excellent answers here! I had a good chuckle yesterday when I read about you accessing your corporate deployment from the Diner down the street. Too true!

Thanks again,

Rob